John Sayers' Recording Studio Design Forum Archive

I don't have measurements of the empty room, but REW Room Sim is bang on.

REW Sim is good for what it is: a simulator. It makes a lot of assumptions about the room, the speakers, and the treatment, and produces theoretical predictions of what the frequency response would be if all the assumptions happen to be totally correct. Sometimes it matches reality quite well. Most of the time, it does not. It also only predicts frequency response, which is just a small part of overall room acoustics, and not even the most important part. It tells you nothing at all about issues in the time domain, nor reflections, nor diffusion, nor diffraction, nor phasing. Those are rather important shortcomings.

I use REW Sim sometimes in designing rooms to get a rough idea of what the response might be, and make some basic decisions about initial treatment, but I never use it as the sole tool for treating a room. Proper treatment can ONLY be determined from a correctly done acoustical analysis of the room once it is finished but before it is treated. That analysis can certainly be done using REW, which is a fantastic tool for doing that, but using the actual measurement tools in REW, not just the prediction tool.

I do have other measurements, however. Files are HERE

I only saw a few frequency response graphs there. They aren't very useful, because frequency is only one aspect of room acoustics, and not even the most important aspect, as I already mentioned above. Your graphs don't provide any useful information. I would need the actual MDAT files.

2. The old account was under the email dannycurtean@yahoo.com which I still have but I never use, thus the new name

I just forced the reactivation of that account, so you should get an e-mail about that, and be able to log in again. However, it is not possible for two accounts to use the same e-mail address.

"You're doing it all wrong" is not constructive what so ever - its just empty words dude. Let's get specific about what is in the wrong place, and why, and where it would be placed better, and why.

Actually, that's not true, and that's not going to happen.

Think of it this way: if you are sick, and go to your doctor, then he tells you that you have a "gastro bug" and need certain treatment, would you tell him that he was off base because he didn't explain all the micro-biology of your illness, the specific strain of the bacteria, the effect it has on your intestinal flora, the manner in which the medication he prescribed works on that specific bacteria, the chemical and biological processes involved, the details of why you should take it exactly that frequently, for exactly so many days, in exactly that dosage, etc.? Or would you just go out and buy the pills, and take them on schedule? Would knowing all the intricate details of the biochemical response make you better any sooner?

That's the issue here. I simply do not have time to explain every last reason behind every recommendation I make to forum members, who are getting a lot of valuable advice absolutely free of charge. When one of my paying customers asks for a detailed explanation of why I did what I did for his room, I'll be more than happy to spend the time with him going through it. But I will not do that for free, for forum members who are just curious, and don't need to know WHY something works in full theoretical detail: they just need to know THAT it works.

That said, occasionally I do have some spare time to do that, and some forum members "get lucky" if I happen to explain something in detail on their thread that will be useful to other people who find it later. But that doesn't happen all the time, for one basic reason: there's only one of me, and I simply do not have the time to be answering every single question posed by every one of the 20,000 members on this forum. I do my best, because I really enjoy helping out when I can, but I cannot possibly be on-line on the forum 24/7 as an automatic free acoustic consultation service.

4. I haven't seen a single piece of information that points to tweaking or improving anything. You're too busy saying "its all crap", which I know for a damn FACT it is not!

If you really did know that for a fact, you wouldn't be here asking for advice!

I do this for a living. Designing studios is what I do. I look at yours, and I see what is wrong, and I see how to fix it, and I can pretty much tell by looking how it will work out, of you do it right. Just like a doctor can look at you, ask a few questions, and pretty much know what the prolbem is.

Your place could be pretty darn good. Way better than what you are describing, and way better than what your graphs are showing.

Here's an example of a room I did a couple of years ago, so you can see what can be accomplished.

The RT-60 decay plot for the original untreated room:
Based on the dimensions and use of the room, the target RT60 time I calculated at the above time was 290ms. Here's the final plot of the completed room:


Here's the frequency response plot of the original untreated room, for the entire spectrum:


And the final plot, for the treated room:

Concentrating on only the low end of the spectrum, which is the most important part, here's the original frequency response, untreated:

And the final plot, treated:
And most important of all, of course, are the waterfall plots.

First, the untreated room, for the full spectrum:
And the treated room, full spectrum:
And the cherry on top: The plot for just the lowest part of the spectrum, untreated room:

And the final treated room: The customer wanted a 6 dB boost in the low end: he got it. He wanted some high frequency roll-off: he got it.

I'm not going to go into all the details of every last bit of treatment I designed for that room, or how I did each part, any more then your doctor would go into the intricacies of how the active components of the medication he prescribed actually work at the cellular level: it's not necessary to know that. My customer never asked, and I never told him (although I would have, if he had asked, since he was a paying customer). He simply asked what he needed to do, I told him, he did it, and he got the results.

It isnt wrong until you show me what IS right!

Yes, it is wrong, regardless of whether I show you what is wrong with it, or how to fix it. Wrong is wrong, regardless of your opinion of it. There's no relativism here: It's wrong because it is wrong, not because I say so, or because you don't understand it. It's just wrong, period.

The speakers are at 48 inch for the tweeter in the final design,

... which is wrong. For perfect accuracy, that should be 47 1/4" for the acoustic axis, not the tweeter. The acoustic axis is the point from which the sound appears to emanate. For most speakers, oriented correctly, it is not at the tweeter. It is usually close to the tweeter, but not at the tweeter.

The tuned diffuser is there to control any front to back reflections and deal with them.

Diffusers do not control reflections: they diffuse part of the reflections, within a controlled frequency range. In doing so, they cause massive phasing and timing artifacts that are manifested as lobing patterns that greatly alter many aspects of the sound, within a distance of roughly 5 to 7 times the wavelength of the low cut-off frequency, and scattering artifacts for another octave below that. That's why diffusers are not recommended for small rooms, since it is not possible to keep them far enough away from all critical listening positions. They are only suitable for large control rooms. There should be a distance of at least ten feet between any tuned diffuser and the mix position or client couch position, and if the wavelength makes it necessary, then the distance should be even greater. Yours are only 55" away from your face, and they are tuned plenty low enough that they should not be used in that room at all. There is no location where they can be sufficiently far away from your head.

There should also never by anything that substantially changes the spectral, phase, or timing characteristics of the sound field, in the front section of the room. Behind you, it is possible, but not in front of you. The reason is simple: you do not want ANYTHING that would change the direct sound coming from the speakers, between them and you, or even around them, where they could have a detrimental effect on the direct sound.

My advice would be to ditch the diffuser: even though it looks very nice, it is doing you no favors at all, and I'd bet good money that the artifacts will be glaringly evident in your MDAT file, (assuming you took the measurements correctly).

It's not a necessity, but I figured with the window there it may be a good idea as most people like diffusers front to back.

Yes, many people do "like" them, but they use them inappropriately, where they are not only not needed, but are actually doing detrimental things. Many people "like" putting small boxy NS10-style speakers on their meter bridges too, but it doesn't mean they will ever sound good there! Which is the reason why the expert engineers do it: so they purposely do not sound good! But there's an awful lot of studios and engineers around who do it because it "looks cool" and "the big studios do it so I must too", without having any idea why they are really there...

Just because you see something in photos of other studios does no mean that it makes sense for your studio. It does not even mean that it makes sense for the studio where you saw it! There's an awful lot of "Gee that looks great! I want one too!" among studio owners and sound engineers...

There's a lot of studios that have diffusers on the rear wall, just inches from the client's ears. Go figure! Move your head a fraction left or right while seated on that couch, and you can hear the artifacts, clearly. I never figured out why people would do that... Probably they saw a photo of a properly designed studio with a diffuser on the rear wall, but never noticed that the client couch was several feet away from it... They just thought it looked cool and "since the world class XYZ studio has one, I must need one too!" But failed to notice that their room was much smaller, with no way to separate the couch, and probably needed very different tuning on the diffuser anyway...

3. No they're not.

Sorry, but they are. They are too close to the corners, where they will trigger modes and cause bass-build up unnecessarily, they are too far away from the front wall, and are therefore causing comb filtering and mid-range lift, as well as SBIR issues in the low end, and they are angled incorrectly, since your ears are not on axis to the speakers. Off-axis response is never smooth, even for the best of speakers. On axis-response is usually pretty darn good, even for mediocre speakers. If you listen off-axis, you are NOT hearing what the speakers are trying to tell you: you are hearing a version that is distorted in both frequency and phase, and also in intensity. I try to never have the key listening positions more than about 10° off axis, max. That's not always possible, but it's a good goal to shoot for. (That said, there are also some good reasons why being perfectly on axis can also be a mistake...).

They certainly are not in the ideal place, of course, but this isn't changing, period! I made this clear in the OP.

Then I'll make something equally clear: unless you put them in the right place, oriented the right way, and with the right treatment around them, you will not ever get smooth response. Period. It's that simple. Either you can move them to where they should be, or you can give up on ever getting usable response. Speaker placement is critical.

Not because I'm a dick,

Neither am I: I'm just telling you the plain truth. Because the laws of physics and psycho-acoustics prevent anything else from happening. I didn't make those laws: all I can do is tell you how they work. Ignoring them won't make them go away.

but because I have constraints.

Then remove the constraints! If you want your acoustic response to work well (which it could in that room), then fix whatever is preventing you from doing it right.

And besides, I moved the speakers around front to back by as much as 3 feet and although different, there are only tradeoffs.

I'm not talking about simply moving them a bit front to back: all you would accomplish with that is to move the SBIR artifacts and comb filtering artifacts to different frequencies. I'm talking about the holistic approach: setting them up with correct geometric relationship to the room and the listening position, in all aspects at once, including treatment.

Hint: you CANNOT set up a room by ear. It would take you forever to try all the possible combinations, and human auditory memory does not last long enough to be able to compare them all intelligently anyway. Our brains only have the ability to accurately remember what another setup sounded like for a few seconds: hence the need for fast A-B switching when auditioning speakers. Human hearing also does not have the resolution to determine differences in level at each frequency accurately: it just "sounds wrong", but the ear and brain are not capable of calculating what the problem is. If you can't calculate it accurately, you can't fix it accurately.

The ONLY way to set up a room optimally, is by using acoustic prediction principles, and acoustic measurement tools (such as REW) that can accurately graph a number of different responses visually, for easy comparison.

and happen to also be bass traps which mounted right on the boundary surfaces of the room.

... which is the least effective place for them to be! The main purpose of bass traps is to damp room modes. All room modes terminate in corners. The most effective place for bass traps is the tri-corners of the room (where 3 surfaces meet), because that's where ALL modes terminate. The second most effective place is in the corners where 2 surfaces meet. And a distant third place is the surfaces themselves. And that assumes that the correct treatment is placed on the correct wall: it is pointless treating a 0.0.x axial mode on the side walls, for example. Zero effect.

There's quite allot of slap back in the room

... which is best treated by using a "checkerboard" approach. You still have opposing surfaces that are untreated, and opposing surfaces that are treated. Not a smart way to deal with flutter, slap-back, or similar issues.

5. Yeah, carpet on the floor - its staying.

That's a pity. It messes up your psycho-acoustic perception of the speaker locations, as well as your ability to determine directionality, so you'll never get an accurate sense of the real sound-stage, and never have an accurate stereo image. Carpet is pretty good at destroying spatial perception. So since you are determined to keep the carpet, you'll be sacrificing all of that.

Have you ever noticed that world-class control rooms practically never have carpet on the floors in the front half of the room? There's a reason for that. So as long as you are happy with your room never being able to provide the clues to your brain that it needs to correctly determine spatial locations, then that's fine: leave the carpet in. On the other hand, if you want your room to be the best it can be, do what the pros do, and take it out.

I built the first round for the room, trying to keep it minimal, and realized it wasn't cutting it.

Then something was wrong with the way the treatment was design, built, or located. The first round should show a major, marked difference. Subsequent rounds are just tweaks. If the first round didn't work, then there was something wrong with it. Adding more won't fix that.

They're being converted to MLV traps which should.

Membrane traps are notoriously hard to tune accurately, and have to be located at the pressure peak for the node in question. If that happens to be under your seat, what are you going to do? Once again, if the issue is a vertical axial mode, then putting a trap that is tuned for it on the rear wall is going to accomplish zilch: it would have to go on the ceiling pressure node, or the floor pressure node.

Why does it matter if I built them "cosmetically" as the commercial stuff?! Seriously?!

Yes, seriously. commercial treatment is designed very carefully for specific response. If you substitute anything, then it will not work the same way: the response will be different. If you did not use the exact same insulation, for example, then it will be tuned differently. I'm not worried about the cosmetic aspects: that's not what I was referring to. I was talking about building it the same, using the same materials, and the same finish. If they used 1" thick oak, and you used 5/8" MDF, then it won't work the same. If they used fluffy fiberglass with a GFR of 6,000 MKS rayls, and you used semi-rigid mineral wool with 60,000 MKS rayls, then the response will be very, very different. If they screwed and glued theirs together, but you only nailed yours, it won't work the same.

You cannot just look at some photos of an acoustic treatment device, build something that looks similar, and expect it to perform the same. Unless you know every spec of what they used, then your knock-off will not work the same as their original.

And yes, I wouldn't spend dozens of hours building shit without calculating what the hell I'm building. What kind of question is this?!

It's a perfectly solid, reasonable, and sound question for anyone who understands acoustics.

I was aware that a limp mass absorber can do that, but the alternative is......."crickets"

Well, you could probably build a bass trap using crickets if you wanted, but I doubt it would be very effective!

There are many alternatives. First, set up the room geometry to minimize SBIR, since it is practically impossible to fix with treatment. Second, test the room and place deep, thick broadband porous absorber traps at the most suitable location for each modal issue. Third, test the room again to see what worked, what didn't work, figure out why, and modify, remove, or add new treatment as needed.

Intended purpose of tube traps is as speaker stands,

Bad idea. Speakers stands need very large amounts of mass to be effective. Concrete blocks are often recommended, or sand-filled steel profiles. Tube traps have very little mass.

as diffusers on walls

Poly-cylindric traps need to be sized correctly for the wavelengths that are to be treated, and they need to be spaced correctly too. And positioned correctly. They need to go at the nodal points for the wave in question. There's no point at all in placing a poly at a modal null... It won't ever "see" the problem that it is suppose to treat.

And none of them are placed in the wrong place.

Sorry, but they are. that's evident from looking at the pics and the model.

but there is hardly a "wrong place" for a bass trap man!

Huh? You HAVE to be kidding! Bass traps treat room MODES. If you put one at the point where there is no mode, then it does NOTHING. That's just plain logic. if you place a velocity-based trap at a location in the room where the velocity component of the mode is zero, or close to zero, then you get zero effect. If you place a pressure-based device at a location in the room where the pressure component of the mode is zero, or close to zero, then you get zero effect. Modes are standing waves: they have peaks and nulls at specific locations in the room, and those do not change. You MUST place your device in the correct location for the mode you need to treat. If your number one issue is a first-order axial mode, then the absorption MUST go on the front or back wall. Putting it on the side walls or the ceiling would be pointless, because there are no nodes on the side walls or ceiling that are relate to x.0.0 modes. Correctly placing a bass trap of any kind is important, but if it is a tuned trap then it is imperative to place it at the peak pressure or velocity node for that specific mode. Any other location is pointless.

I don't know where you are getting your information from, but clearly it is not a valid source of sound acoustic knowledge.

All traps are tuned to 60Hz or 140 Hz

That's not what I asked: I asked HOW they were tuned, not what frequencies they were tuned to.

Also, how did you determine that you have modal issues at exactly 60 Hz and 140 Hz? Are you sure it isn't, for example, 57 Hz and 145 Hz? Or 63 Hz and 136 Hz? Are you aware that room modes are very narrow-band, just a couple of Hz wide, and that hitting them exactly with a tuned device is really, really hard to do? If you have a modal problem at 62 Hz, and your device is tuned to 55 Hz, it won't work. That's a huge difference: 13% difference. Two entire notes on the musical scale. If the mode really is at exactly 62 Hz, you'd need to ensure that your device is tuned to 62 Hz, +/- 1.2 Hz. If not, you won't hit it.

And that's assuming that the problem really is a mode: if it is an SBIR issue, then no tuned trap can ever fix it, since it is not related to standing waves or resonance of any kind; it is related only to phase, time and distance.

How did you determine that 60Hz and 140Hz are modal, not SBIR?

QRD 13 tuning.

That isn't tuning: that's the period number (prime sequence). That only tells you how many wells you have, not the tuning of the device. I was asking for the tuning: the tuned center frequency, the lower cut-off, the upper cut-off, and the scatter cut-off.

If it's overkill, what about it is.

Pretty much all of it. There's very little in there that is in the correct location, correctly tuned, correctly dimensioned, or even using the correct concept. It looks like a "let's throw in everything but the kitchen sink and hope something works" approach.

The reason why you put in one round and got no results is because you put the wrong things in the wrong place, with the room set up wrongly to start with.

You clearly had a reason to say everything you said, else you wouldn't have bothered.

Right. But I do not plan on trying to explain every last detail of every last recommendation I make: I just do not have the time for that. Just like your doctor telling you to take 21 pills of 50 mg, 3 times per day after meals for 7 days without question, you can either trust that I know what I'm talking about and do it, or you can ignore it and stay sick. I already spent far more time on you than I do with the vast majority of forum members, and I don't plan to spend any more. That's a whole bunch of rather expensive advice that you got for absolutely nothing. Free. Gratis. If you don't like it, don't take it. If you don't trust the doctor, don't take his pills. But don't pester him to explain the intricacies of biochemistry and pharmacological action, just to please your ego.

--

Listen to what Stuart has to say, I don't think being so aggressive and ignoring his advice is going to help though!

Matt knows what he is talking about. I've walked him through a number of REW tests until he got his bugs worked out, and now he is working on his treatment, based on what I saw in his REW data. He's not interested in understanding the particle velocities at the boundary faces of the bass traps, nor the minimum phase slope at the critical frequencies: he just wants to know what size trap to put where, and how to build it most effectively. He just wants the prescription and the results, not a master's thesis on how it works.

I'll take your advise and tear everything out, and try adding one section at a time.

That will work, but only if you get the geometry correct first. Until you locate, orient and angle your speakers and mix position correctly, there isn't much point in placing treatment correctly.

That said, my end goal, budgets and overall plan is to create "that" room ultimately -

Sorry if this comes over the wrong way, but to me it sounds like you have already decided what you want the room to look like, and to hell with the way it sounds! In other words, it seems to me from what you have said that aesthetics come first, and acoustics a distant second. If some acoustic issue forced a change in the appearance of the room, you'd rather live with the acoustic problem and keep the appearance. Maybe I'm wrong about that. but that's what it sounds like. When I design a room, I take the exact opposite approach: I design whatever is needed to make the room sound the best it can, then I figure out how to make all of that look nice, and work aesthetically, as a secondary goal. It's a studio, after all, so the primary goal is that it must sound good. A studio that looks good but sounds like crap, is not a studio at all: it's just an exercise in interior decoration.

We can get into measurements, and a bunch of largely useless data,

If you think the data from measurements is largely useless, then there's not much I can do to help you. In reality, the data from measurements is the key to understanding the room, and treating it right. In order to tune the room that I posted the data for above, I have 112 MDAT files that were created by the customer, totaling well over 2500 megabytes. Some of those files have 5, 10, 15 or more measurements in them. There's probably over 500 individual measurements in there, that we took to get the room right. In some cases he took a series of dozens of readings, moving the mic a specified number of inches in a specified direction from one reading to the next. It took several weeks. And every single test was pertinent. The customer wanted the room to be as good as we could possibly make it, so we went through the effort that was necessary to make it so.

The results speak for themselves.

And now we are about to do it all again, a couple of years later, because he decided to upgrade his speakers to something even better, which changes everything. So we'll be re-tuning his room for the new speakers in a couple of weeks. He doesn't mind spending the time and money to do that, because he has already seen that it works. And he doesn't give a damn about why there's a dip at the beginning of the impulse response graph, or why the perf-panel holes need to be spaced 3-7/16" apart and have a diameter of 5mm: he just does it, because he trusts the doc, because the doc already fixed his illness a couple of times before. He took the pills, got perfectly healthy again, and now wants another set of pills to fix him even better. He'll get it.

So I updated the SKP file, and did 3 photo-realistic renders for quick visual reference.

They look very pretty, and there's some great SKP skills there, obviously, but pretty renders and good modeling skills wont make the room sound good unless you first get the geometry correct.

2. Incorporate allot more diffusion on side walls – reason is simple!

The room is too small to be able to use diffusion. Bad idea. Don't

Those walls, although boundaries, are not best candidates for absorption.

Actually, they are great candidates for porous absorption, correctly placed and dimensioned.

I don’t like dead rooms,

Good, because control rooms should NEVER be dead. Nor should they be live. They should be neutral. The decay times should perfectly match the calculated times for that room volume. Not more, not less.

I only need flutter control there, so that’s why diffusers.

That's not correct. You need far more than flutter echo control on your side walls, and you do not need diffusers. Absorption works well for flutter echo too...

My biggest standing wave is a front to back axial node around 58 Hz. So the idea is that I get relatively broadband LF absorption in a non resonant panel which also “cuts the head and tail off of” the standing wave (1/4 wavelength rule).

Don't look know, but the 1/4 wavelength of 58 Hz is 4'10-1/2". You would have to make your traps nearly five feet thick, if you believe that is the way to do it...

So I get great SBIR control for rear of speakers,

I doubt it.... What SBIR frequency are we talking about here?

There may be little things here and there, but otherwise any objections?

My objection is that you are still going with the "Let's throw it all up in the air and hope something sticks to the ceiling" approach. That's not the right way to go about it. The correct way to go about it is to FIRST get the geometry correct, then measure, then place initial treatment, then measure, then place additional treatment, then measure, then place final tweaks treatment.

I know allot of this is based on theoretical research and ideas, and that’s not ideal but we must have some sort of goal, right? And this is mine, based on what I've learned to be sound (no pun intended) acoustic principles.

Sorry, but the acoustic principles that you are using are NOT sound. If they were, then it would have worked at the first try. ...

Im updating my profile now.

Yup, that was it.

Well, I get your tone and Ill say this "prove that I'm wrong".

You might want to take a look at Anton's thread: He gets it. He's getting it right. His studio will work. And he got even worse treatment than you did! But he figured out why, and corrected it. Now things are going great for him.

They could go well for you to...


- Stuart -

.......................give me like 24 hours to completely remove my jaw from the floor! I am BLOWN AWAY (good thing).

I'm still completely flabergated by that response - Im serious! That post made me realize EVERYTHING I did wrong with the room in one shot - that's one hellofa response! I don't even think a "thank you" would be anything short of an insult at this point, so I'll just shut the hell up and read that post 15 more times!

I don't even think a "thank you" would be anything short of an insult at this point, so I'll just shut the hell up and read that post 15 more times!

I just updated it it with some correction of spelling and grammar errors, and to clarify a couple of points that weren't clear (I originally wrote it at 4 AM, half a asleep, so my fingers weren't keeping up too well with my thoughts...) So you might want to add one extra, and make it 16 times...


- Stuart -

Firstly let me say a big THANK YOU for all the contributors which took time to smack some sense into me, and for those that had the patience to straiten me out. I don't like vague absolutes, and so I find it frustrating when they're presented. That said, I was then given ample explanation for many things and I truly do appreciate that. I am consulting with multiple sources and improving the design by measurement and time tested strategies of acoustics design - so this isn't just "seat of my pants", at best it is "seat of OUR pants"

I also took many queues from the previous posts, especially SoundMan's and incorporated them into this latest design package and renders. I am working with DanDan as well over email.

I actually have undergone some major revisions over the last couple of weeks. I ripped out all diffusers units out of the design and replaced them with angled slats on all broadband absorbers on side walls, and a few multi-function units like the scatter/absorber devices on side walls you see below to name just a few of many changes.

I've also tested going from 6" to 9" on the two "superchunk" style traps at the front corners of the room and am happy to report it is a nice increase in low end control audibly - allot tighter if I were to use adjectives. And so I'll be increasing all 6" Roxul corner traps and upgrading them to 9" of Roxul. Obviously the last 3 inch sheet can only be about 15" wide as opposed to the 24" of the front two stacked Roxul sheets because the back tapers off into a triangle, so there's less room back there. But considering that most of what was air, will be Roxul I'm sure it's an increase in the performance of the traps - In fact, I know, I heard it with just 4 units of 9" Roxul on front corners. I have some measurements but they're not direct comparisons as some major things have changed since previous measurements. The biggest of which, by far is placing the speakers relatively flat against the front wall - BOY that was a massive improvement! Nearly all the low mid buildup was gone, or at least supplemented by a huge, beautiful and controlled bump in the sub 80 Hz area - we're talking 10 dB here, which was lacking before!

So if nothing else but less SBIR and therefore less comb filtering and a huge bump in bass smoothed out the FR quite dramatically not just in the low end, but there are audible dividends in the high registers as well from this speaker placement move. Of course further micro tuning is required, but I really need to get those corner traps up at the wall /ceiling junctions.

Because I have to sand and finish the wood of the traps on the outside, Ill be taking all of them out of the room soon. When I do, I'll have the opportunity to do a whole slew of measurements in many different locations in the room to compare progress as units get installed. So I'll be monitoring progress and data gathering and so have put together a plan to consistently capture data with as few variables as possible but still practical. Ultimately if practical testing doesn't reveal increases or improvements, then the treatment is not good enough . That said, we still need consistency for comparative analysis so the test plan I have written up and will follow keeps both of those things in mind.


What has changed recently?

20 Degree Angled Slats on Broadband Absorbers - this is perhaps the biggest change in itself. I removed diffusers, but need the air and slats seemed the best way to go. Big thanks to DanDan for this suggestion.

Incorporate 8 units of Scatter, Poly Absorbers for control of the slap back in that area of the room. These will give me what I need and nothing more.

Increased the "cloud" density. Because of the 125" electronic projector screen at the top, I cannot do a very deep trap or cloud in front of the screen, but can do a 6" with air gap behind it, so I did that. Front 2 pieces are flush mounted, the rear 2 cloud pieces have a 4" air gap cause I have plenty of real-estate laterally back there.

Then we have the VPR metal sheet panel absorber at the back to help with the very low end and tame some of that length axial node I have. This is more conceptual and a "beta" idea that I think is a good idea to implement in that relatively available closet space back there. I figured the low end is relatively omni-directional, and having that large 2x2 meter VPR back there will help alleviate that low end pressure wave and attenuate it a bit before it inevitably comes back at my head, granted with allot less intensity because of that VPR. So this is an idea that I think will work great, although its more of an icing on the cake type thing, than a real heavy slammer.

For the rear we also have 6 TubeTraps which are 12" diameter. These help "offset" that closet cavity back there by allowing for a less angular or more flat rear wall acoustically. They help attenuate as broadband traps all the way down to about 70 Hz effectively, after which they become far less efficient. This is fine for me because I need these type of devices at the back as simple porous flat panels won't do enough for me back there. TubeTraps in their intrinsic design allow for great pressure control, and it is the ideal place for them in this situation. I also chose TubeTraps for antoher good reason, and that is "mobile vocal booth". I can take those rear traps and while recording, I can place them around the talent or source and tighten up the room as needed. So they're dual purpose, that's why I like the TubeTraps there.

Apart from other small things like foam on top shelf of the desk to increase that RFZ, speaker de-couplers under the Metronome's and moving the studio monitors as far back to the front wall as possible, it's all pretty similar. Also, there are more corner traps on the ceiling as well.

And last but not least are 2 pieces of 10x8 foot bamboo wood rugs which go over the carpet. I've been guided to do this by several people and it has to do with the overall imaging of the speakers. It is not as ideal as a full replacement of the carpet, but granted that this is not a property I own, I have to be creative about the solutions. And having real bamboo covering a large section of the carpet is more than a compromise in the right direction in my book.

I've undergone much scrutiny from the first posts, to these on various forums, which is fantastic cause it means allot of growth. I am happier with this design package than any other so far. It ticks all the boxes, fixes all my standing issues, gives me the kind of response I need and also importantly has the aesthetic appeal that I find important for myself, and my clients as well. Aesthetic are powerful and therefore they are important when running a business.

Although I am reaching the final stretches in the conceptual design before phase 2 of the build kicks off, I am by no means unwavering in this design. If you find any gross issues which I missed that could cause major problems, or you see improvements that could actually help please do chime in!

However I must say this, with measurements on my side, a relatively simple "armament" of acoustic devices and tried and tested methods of acoustics control the margin of error is relatively small because the devices used are all broadband type and relatively easy to build. Unlike MLV devices or tuned resonators which improperly used could actually worsen the situation, these largely porous design traps are the meat and potatoes of acoustics and therefore somewhat idiot proof.

There is of course the post build phase where the small tuning continues in which I may remove some panels, or modify them slightly here and there, lacquer them over, or not all depending on desired response - the way I see it is "Rome wasn't built in one day" so I don't expect perfection when what you see in the renders is done, but I do expect a damn impressive room and no major issues.

Sound like a plan?

Any progress on this? You never did send those MDAT files, so I couldn't offer any further advice, but it would still be good to see how it is turning out.


- Stuart -

Hi there! I just want to provide an update on what is going on right now. This week I am installing all the traps into their final positions, as they have all been completed, and "upgraded".

I converted or upgraded *all* corner traps to 12" pf Roxul as opposed to the initial 6". So now all corner traps are 12" deep of Roxul.

Today I am installing the 4 piece cloud, 2 of which are pegboard sealed back traps and 2 are 6" broadband Roxul absorbers overhead. I have had a single piece directly overhead for a week or so and I was amazed at the stereo field difference with it. I've also installed on the front wall, corner the 2 traps above mix position. Another updated is I have moved speakers and mix position to affect frequency response in absolutely dramatic ways! So for now I believe to have gotten the best of both worlds - I have an even better placement physically than before meaning more space, and the FR is quite good now! This has me 3 feet from the front wall, and the speakers right up against it. Speakers are on TubeTraps are touching the front wall.

Ill wait to provide MDAT files as soon as I finish mounting all the traps I have available to get an actual room response. It's been going in the right direction though, I can tell you that! I just hope that the cloud traps will suck up that low mid buildup that I still get just a tad.

So give me a few days, Ill get the old MDATs and clean them up, label them and get new measurements done for analysis.

I appreciate your help!

I've also updated the design over my period of silence - I wont go into details, but you can see them. Main difference is VPR's! I'm incorporating them in the area where there is the most pressure in the room, the head end (as ASC calls it). I have a good reason for this, but again, won't go into it now as they're not built yet. I am still sourcing parts.

I've installed some new traps and moved speakers and mix position around by a much as 3 feet, give or take and have gotten great results. Frequency response has smoothed out considerably from the beginnings of the project to today.

There's allot of information to discuss, but I'll spare you all. Basically you can take it that I am getting closer and closer to the renders which I have provided recently, so that should answer many of the practical questions for those who care to ask.

For the not so obvious things, I have the MDATs which show RELATIVELY a chronological progression of speaker, mix position, treatment placement and so on. Now unfortunately because of the fact that I do work in this room even now, levels werent precisely matched, and for the some of the measurements were not exactly in the same exact place for the mic front to back. All measurements that are similar had mic are "similar" placement, but some of the peaks and nulls you see are actually mainly due to mic/mix position - so keep that in mind. Some of those nulls disappearing are not so much the traps themselves, but rather positioning.

Also, the notes I've written were "quick notes" as basic ideas for me to keep track of what changed. So read between some of the missing lines. Also look at the dates, and keep in mind of the slight differences in measurement volumes.

Now I know, these are not perfect measurements, but given the amount of data and the provided caveats I think one can extract quite allot of info from these measurements and explanations, at least I hope. The latter measurements accounted for mic placement with a tape measure, so those are a bit more consistent. The room problems and the resolution of those problems should make themselves quite obvious with a bit of investigation - I hope this helps!

***Second Post - upload failed. So since its not working, Ill provide MDATs by means I have control over.

MDAT Here
https://onedrive.live.com/redir?resid=B ... ile%2cmdat

Sorry about the delay: hectic times. Lots going on.

Anyway, I downloaded your MDAT and looked at all your tests carefully, but unfortunately your data is not valid. You did not calibrate REW or run the tests correctly, and it seems like you are not even using a proper measurement mic, so there's only limited conclusions that can be drawn.

What mic did you use for those tests?

You should first calibrate REW correctly, with an proper, calibrated sound level meter, then use a good measurement mic to conduct the tests at a level of 85 dBC, not the 65 you were using. at 65 dBC, you won't be triggered many of the room modes. You also need to set REW to run the full audio spectrum and a bit extra, from 18 Hz to 22 kHz, instead of the 25 Hz to 8 kHz range that you used. You are missing an entire one and a half octaves from the top end, and nearly half an octave at the bottom end.

You also need to set up your speaker system correctly, or get a good sub: there's very little energy in your room below about 140 Hz, and it rolls of pretty steeply. Almost as if you had some type of filter applied, or used a mic that has very poor response in the low end.

That said, there's some clear things in the data: You have pretty heavy modal issues: 44 Hz, 74 Hz., 82 Hz, 94 Hz., 106 Hz, 118 Hz., 139 Hz, 155 Hz., 172 Hz, and several others stick out clearly. The do no't change much (some don't change at all) with your treatment, so clearly the treatment is not working. The room is a little on the dead side, and gets deader as you over-treat it later on. There's several strong early reflections going on, notably a really big one at around 3.9 ms, and two others around 11.9 ms and 25 ms. The overall decay is uneven, not smooth.

Overall, the room is over-treated in the mids and highs, but unevenly, and under-treated in the lows.

I would go back to my original suggestion: take out ALL of the treatment, put in ONLY the main speakers, the desk and the chair, with no other furniture or treatment, set up the room geometry correctly, and do an initial REW test like that. Post the results here, so we can see how the empty room is behaving, then we'll start treating it in a logical, planned, progressive, sequence, following what the data is saying, not what your imagination is saying.

But before doing that, you need to get a good measurement mic with flat response, and you need to calibrate REW correctly. Only then can you run the tests validly.


- Stuart -

Hi Soundman,

I use the DBX measurement mic - the one's they use for the Drive Rack. It's a ~$100 mic, going through a Neve 1073 preamp, with no HPF into an Apollo 8 interface.

Do you have any guides for repeatable measurements? The SPL suggestion makes sense. And I agree about the room being too dead at the wrong end.

But keep in mind that the ONLY LF treatment I have in the design doesn't exist yet, so there is NO LF treatment. There are 6 VPRs in the design which are proven devices in lowering decay times in LF and improving FR as well, and that's ultimately my goal.

But I am in a transaction currently which would allow me to purchase this property as my home. If that happens, I will tear out the room to the 2x4's themselves, and build not only a soundproof room, but also in-built acoustic devices all together. So that means a new design and having to re purpose allot of my removable absorbers, which sucks, but that's life.

Ill keep you guys updated on whether I get to own the property, and can find the money to literally build from a skeleton, or not. For now, we will see what will happen and that shall dictate my next move.

I use the DBX measurement mic - the one's they use for the Drive Rack.

That's actually a pretty good measurement mic, so that isn't the problem. The pre-amp should be pretty flat too, so it's a mystery where the low roll-off is coming from. Do your speakers have a low frequency "roll-off", "tilt" or "room correction setting"? If so, it might not be set correctly. As a quick test, set all controls on your speakers for flat response (no boost, no cut) and do one REW run like that, then set them back they way they wer (since you are probably accustomed to that sound at present. You'll have to re-train your ears for the room once it is completely treated correctly, but for now it's not worth doing that yet).

Is there something else in the signal path that could be rolling off the bass? Console? Sound card settings on your DAW?

Are you using a sub for those tests, or just the two main speakers?

What speakers are they (make, model)?

If you have a sub, did you try inverting the signal on it? Often flipping the phase inversion switch can have good consequences. If you have two subs, try all combinations: both 0°, both 180°, and each one flipped to 180° individually with the other set to 0°.

Do you have any guides for repeatable measurements?

I'll send you (PM) the setup instructions I give to my paying customers when we are about to start tuning their room, so you can follow those. Basically, you calibrate REW for your sound-card following the built-in manual, then you do the additional steps I outline in the notes, which is setting things up the the recognized "standard" calibration level of 86 dB and setting up the mic at the correct location, which is the middle of where your head will be while mixing, pointing directly ahead, and angled upwards 60°. Some acousticians say 90°, but I find that makes it too sensitive to the ceiling-floor axis, and not sensitive enough to artifacts coming off the desk and first reflections off the ceiling, so I prefer 60°.

You then carefully measure the exact location of the tip of the mic in the room, such that you can always get it back to that exact spot, within a few mm (1/4"). You need that precise location for repeatability of the tests, so you can validly compare graphs at different points in time. You might also need to measure in other locations, but you need to be able to get back to that one consistently, so use measurements points on the walls, floor and ceiling that won't be covered with treatment at some point, making it hard to measure. I often put gaffers-tape on the floor and mark the spot directly under the tip of the mic with a fine tip permanent marker, and use a plum-bob to position the mic tip directly above that point, then measure the height with a tape measure.

The SPL suggestion makes sense.

86 dBC is the level you want with all speakers running, and since REW uses coherent sound for its tests, you need to calibrate each speaker up at 80 dB if you are just using two mains, or 77 dB each if you are using two mains plus a sub, or 74 dB each if you have two mains plus 2 subs. Use full-spectrum pink noise to set the level of the mains, and HPF filtered pink noise to set up the sub levels. REW can play both types of calibration signal for that. (if you set up your individual speakers to the correctly level, then the combined level will automatically be correct too.

Do not adjust any settings between tests! And leave the room for each test: use the "Start Delay" setting in REW to give you time to get out.

But keep in mind that the ONLY LF treatment I have in the design doesn't exist yet, so there is NO LF treatment.

When I tune a room, I normally start with the bass trapping first, for three main reasons. 1) The bass junk in most rooms is so huge that it masks most of the mid-range issues. You need to get rid of that first, so you can at least see the mid range. 2) Bass trapping takes up a LOT of space, so it's best to get that in first, then fit the other treatment around it. 3) Bass trapping often does good things to the mid range and not-so-good things to the high end that you might need to compensate for.

So I start out with the room totally empty, fo my "baseline" REW tests, then add the basic bass trapping and do another REW test, to check that it worked and see how much more I will need. Then add a second round of bass trapping, check, rinse, repeat. When the low end is under control, I look at the highs to see how bad I made it, and either modify the bass traps to fix that, or add other treatment. Then I go for the mids, which are often the hardest to deal with.

There are 6 VPRs in the design which are proven devices in lowering decay times in LF and improving FR as well, and that's ultimately my goal.

Well, yes, VPR's can do that, but they don't necessarily smooth out things evenly. Your goal should be to meet ITU BS.1116-3 spec, or maybe EBU TECH-3276 specs. Those are the ones that are normally used for precision tuning of control rooms. It's not just about overall decay times, or overall frequency response.

But I am in a transaction currently which would allow me to purchase this property as my home.

Cool! That means you can start from scratch, and get the entire room properly designed as a control room. I would strongly suggest that you do it as a true RFZ style room, due to all the major benefits that can provide.

If you do it right, you can get excellent results. Remember that room whose graphs I showed a few posts back? The owner just replaced his old speakers with new Eve SC-407's, which we flush-mounted in custom-designed isolated soffits that I designed for him, then we spent a couple of weeks re-tuning his room. This is where we are right now:
That's smoothed 1/3 octave, as he wants to make sure it meets BS.1116-2. Full-spectrum frequency response is within +/- 1.7 dB of flat.

Low end waterfall:
That's the entire low end response, up to 500 Hz, un-smoothed graph. Flat and even decay times across the board.

And the spectrogram for the low end:
Also unsmoothed, also 20 Hz to 500 Hz.

That's not how the final tuning will be, as he wants to add his house curve to that, which is similar to the old B&K curve, but we went this route first as "proof of concept" that we can get it dead flat and as smooth as mill pond on a calm day. Perfectly flat response isn't nice on the ears, but that's what it looks like if you want it.

OK, so his room is bigger than yours, and was designed and treated from the start as a control room. You won't be able to get yours that flat, and neither should you try, but you can still get it much better than where it is now.

I wanted to show you that so you don't get discouraged! There is hope... Follow the procedure logically and carefully, starting with an empty room, and you can get it really good. Randomly trying things that you find on half a dozen different web forums and manufacturer websites, won't get you there. You need to ditch that approach, and just follow one simple procedure, slowly, step by step, testing at every step. If you note in the FR graph above, that result is for "test number 127-Y"... (and we aren't done yet...)


- Stuart

Testing Details:

As stated in my previous posts, the difference in the placement of the mic axially varies quite widely due to ignorance. This ultimately taught me about placement of not just speakers, but also mix position. So the latter treatments, about half way down are actually pretty consistent in mic position. Consequently, the mix position, speaker placement, mic placement and also many of the treatments moved around during these tests as that is the purpose of these measurements - to see how it improves with changes. Most of these I tried to clean out, and attempted to keep only major movements for historical reasons.

So these measurements unfortunately because of the revolving changes are not 1:1, but not that far apart either. I think that major, large wavelength issues will still do the same thing relatively speaking, so they are still at least valid if only abstract. Again, these are mainly for historical documentation for me to learn as changes are made, but again, the latter few are pretty much identical with the changes being in traps and so on, so the last third set is pretty valid with only exception being SPL varying a bit.

About the speakers:
My speakers are Focal Solo 6 BE LTD - FR of 30-40K

The speakers have shelving EQ on HI and LOW bands. I don't know where they start/cut off, but most of the measurements have the speakers at 0-0 meaning no boosts or cuts. The first few measurements had, from what I remember, a HPF on my Console which I didn't notice was engaged. I noticed this later, but only the first lets say 1/3rd of the measurements may potentially be hurt by this. By the latter set of measurements I know for a fact that apart from SPL matching, everything else was verified to be the same. However, I really think I re-did the measurements when I learned my blunder, so the LPF may or may not be valid anymore - I just don't remember! But again, the last third is accurate.

No sub, and no phase flip on either.

Nothing else in the path, again the HPF was potentially engaged for the first few, although I feel like I re-measured without.

I CAN however tell you that once the speakers were flush to the front wall, LF improved dramatically. And I also seem to need another +2dB boost on the back of the speakers to get a balanced LF audibly. However, as noted, the measurements were at 0-0.


Regarding your graphs:
Wow! I did not think that is possible! Looking at these measurements just completely blew my mind!

Granted, I get that it was probably ideal in dimension and a build and so forth, but still, that is impressive!

I'll send you (PM) the setup instructions I give to my paying customers when we are about to start tuning their room, so you can follow those.

Thank you - that's very generous and kind!

When I tune a room, I normally start with the bass trapping first

I do as well, but in this case different vendors and subsequently "path of least resistance" won out first in that parts and labor to build thick Roxul absorbers and QRD diffusers was lower, so they came first. The problem with VPR's is the specificity of the components. Allot of research was needed to understand exactly why and how VPR's function, which dictates the very specific ways in which they must be built - namely the plate thickness, but more importantly the adhesion to the Carruso ISO Bond and also which absorber material will work best given the complex eigenmodes of the resonating plate - the winner being CIB of course. Not only is the design incredibly specific, but materials are not exactly "down the street", where the treatments which have been completed thus far pretty much are! So that's why broadband absorbers and diffusers/scatter devices were built first.

I would strongly suggest that you do it as a true RFZ style room

In theory I know what that means, but it sounds like this is more of a philosophy of implementation that I need to really absorb. I'll start looking into the ideals of "true" RFZ room design and see what I can learn.

You mentioned "custom designed soffits" and I thought about this as my previous "proper" mix room from years back in Cali had these. The soffits were made with absorption at the back, concrete encasement for speakers, and hangars at the bottom from the top of my head. And I liked how that place sounded! I don't know if I want to do this same here though, cause I don't want to pigeon hole myself with my Focal's if I choose to augment, or replace these down the line.

What are your thoughts on these?

the mix position, speaker placement, mic placement and also many of the treatments moved around during these tests as that is the purpose of these measurements - to see how it improves with changes.

To a certain extent, yes. But there's a basic set of "rules" for getting things to the starting point, that saves you a lot of hassle. And time. From that initial position, you normally only need to check maybe a range of a +/- one foot forwards/backwards for the mix position, and maybe +/- 5% of the room width for speaker position. That's it. The rest all falls into place, pretty much automatically. It isn't necessary to "re-invent the wheel" by trying dozens of positions that won't work. It's unfortunate that you found the forum so late in the game! We could have saved you lots of trouble if you would have found us right at the start of your quest.

I think that major, large wavelength issues will still do the same thing relatively speaking, so they are still at least valid if only abstract.

Right, but once you start getting up through the mid range and into the highs, small position changes can make big measurement changes. And even for the low end, it's surprising how much difference a small move of the mic (or speaker) can have. For the same room above, we did a series of tests with the sub, sliding it in steps of 3 inches at a time. Sometimes we got rather interesting changes from one step to the next, and moved down to 1" steps. And that's for a sub that cuts off at about 100 Hz! Wavelength 135 inches...

We also did tests moving the mic all the way from the mix position to the back wall in 6" steps, to clearly identify which issues were SBIR, which were modal, and which were reflections. There's actually big differences in the low end between adjacent 6" locations.

My speakers are Focal Solo 6 BE

Nice! but the response I am seeing in those graphs is not the response I would expect from those speakers in that room.

I don't know where they start/cut off,

According to the manual, if you set that to -6, the low roll-off starts at about 1kHz and hits the -3 dB point at about 200 Hz.

I CAN however tell you that once the speakers were flush to the front wall, LF improved dramatically.

Yup. That's where speakers need to be in a small room like that. If they are moved away from the front wall then you start getting pretty serious SBIR issues. The bigger the gap, the lower it goes, and the larger the problem. You need to get it a couple of meters away before it goes off the bottom end... and that isn't possible in a small room. So the only place is tight up against the front wall, except for just enough separation to get the necessary absorption panel in there.

Wow! I did not think that is possible! Looking at these measurements just completely blew my mind!

Yup! Those are nice graphs, aren't they? Thanks for the kind words. Not everyone appreciates just how hard it is to do that.

This is the actual room:
That's the way it was before we replaced the speakers and started re-tuning. It's still a work in progress, but this is how it looks right now, with the Eve SC-407s in place:
It's a bit messy: Speaker surrounds not finished yet, etc. Should be done by next week, hopefully.

Granted, I get that it was probably ideal in dimension and a build and so forth, but still, that is impressive!

It's a reasonably big room, yes, and the best part of it is the height. That always makes it easier. But the shape is not that good. Unfortunately, I was only brought in once the basic shape had been built, with no possibility to change it, so I had to live with it. The room was intend to face the other way, bu that was not going to work at all, so I had to flip it around, which left me with a strangely angled back wall. A nice challenge!

So that's why broadband absorbers and diffusers/scatter devices were built first.

You probably don't want to hear this, but I'm not at all convinced that you need those "diffusers/scatter devices" in your room... I suspect that some of your problems are actually being caused by those things, not solved by them... Those are apt for much bigger rooms. Small rooms and QRD's do not play well together. That's not just myu opinion: it's the opinion of the guys who wrote the book on QRDs, and came up with the math that describes how they work, and how to design them. I suspect you'd get better results without those, or at lest without some of them.

In theory I know what that means, but it sounds like this is more of a philosophy of implementation that I need to really absorb.

The basic concept is not hard to follow: you angle the surfaces forward of the mix position such that all first reflections go past the head of the mix engineer by a wide margin, and end up at the back of the room to be absorbed (small rooms), or absorbed/diffused/scattered (larger rooms).

The room in the photo above is RFZ-based. Most of the rooms I design are.

he soffits were made with absorption at the back, concrete encasement for speakers, and hangars at the bottom from the top of my head.

That's one way of doing it, yes. I use a different approach, but the results are the same. Two main methods for doing it, that end up at the same finality.

And I liked how that place sounded!

I bet you did! To my way of thinking, its the best possible way of building a room, since it takes the speaker completely out of the room, acoustically speaking. So you get none of the artifacts from having the speaker in the room. That's a major plus. In addition you get a free LF boost (since the soffit baffle solves the power imbalance problem), and it looks cool as well.

I don't know if I want to do this same here though, cause I don't want to pigeon hole myself with my Focal's if I choose to augment, or replace these down the line. What are your thoughts on these?

For the room above, the owner originally had the Genelecs as his mains (now on stands behind the desk), but always planned to upgrade at some point. So I designed the original soffits with the speakers mounted in "trays" that can be unbolted and pulled out completely. I made the trays larger than the largest speaker he ever thought he'd use. That was three years ago. So when the time came to upgrade, I re-design the tray innards for the Eve's, and all he had to do was pop out the tray, modify the tray interior, and pop it back in again. In reality, he ended up building new trays to save time, and minimize downtown, so it became a "slide out, slide in" speaker swap.

I designed the trays in advance to make that possible, with a complex internal suspension mechanism, so the entire speaker actually "floats" inside the tray, and is fully decoupled from it. I'm not sure if he'll allow me to share the details of how I did that, since he was the one who paid for the design, but I'll ask.

Anyway, that's what I would do for your room too, if you wanted to soffit mount but aren't sure what speakers you might end up with.

An interesting aside: for those folks who say it is not possible to soffit mount rear-ported speakers, look at the pics! Those are Eve SC-407's which are rear ported, yet there they are, soffit mounted, and performing fantastically. The head designer at Eve Audio gave me some info that helped to do that: it actually wasn't that hard! So it can be done.

Soffit-mounting and RFZ style design sound daunting, and they do have their complexities, but with careful design and a bit of experience, the results are well worth the effort.


Another interesting aside: I have never even been inside that room personally! All of the design, treatment and tuning have been accomplished purely by "remote control", over the internet. (It's amazing what modern technology allows... )


- Stuart -

Firstly, I feel like I need to donate to this site, and I will ASAP. I am very thankful for your info, and it's hard to find level-headed, KNOWLEDGEABLE, no BS people which one can learn from - so thank you!

Now on to the other stuff. You've piqued my interest with a few of your claims, so let's go through some of them!

1. I agree about the Frequency Response of these speakers in this room. It was a "what the!" from day one! A bad "what the"!

2. So you're a proponent of absorption behind the speakers? Interesting! There seems to be so much contradictory information out there, allot of people explain, for good reason I think, that broadband absorption is pointless behind the speakers because even at 1/4 wavelength touching those SBIR frequencies is not possible with your standard broadband trap. I do however believe in proper "powerhouse" (diaphragmatic/pistonic or helmholz) absorber, that can actually absorb LF, being placed behind speakers, and it is why I have 2 VPRs in my initial design behind the speakers and 2 to the sides. I know this room enough through experimentation and measurement that I reason in having these VPR's back there would really help keep those modal issues and more importantly SBIR at bay.

And I think that the shear pressure behind the speakers, and to the sides as well would really excite the eigenmodes of the metal plate of the VPR's which would should theoretically make them work incredibly efficiently! They are pressure activated devices after all, and so they work in high pressure areas. So theoretically the problem frequencies would really light up the plate, and thus cause high absorption coefficients. I really love the explanation that ASC, makers of Tube Trap, put in their whitepaper when defining what I am experiencing - they call it "head end ringing", and I feel that is a phenomenally accurate description of the problem I have. The front part of the room rings like all get out without treatment, and as soon as one back's up in the room, it tames, with the exception of the "expected" LF buildup at the back. So I feel that after many moons of gray-hair generating frustration, that VPR's are a definite and proven solution for my so called "head end ringing". Of course this is just theory, but one I feel very strongly about due to experiential and empirical evidence that I have access to. YMMV

3. Regarding the diffusers, you already had convinced me way back to get rind of them up close, even though they are already built. The scatter devices are as a direct "knee jerk" reaction, if you will, of the "deadness" of the room. And FWIW, so were the QRD's, but because of the phase issues with diffusers I figured scattering is wiser?

This room has slapback and ringing like all get out, without absorption or diffusion! So having untreated parallel surfaces is really a bad idea in this room, much more than any room I've ever "treated" before honestly. For instance, with 3" of Roxul, I found that it is not enough to stop the ringing/slapback at those mid frequencies. The scattering devices, specifically those half cylindrical shape ones are really quite good from my experience at controlling the slapback! Because they absorb using Roxul with cut poly slats, covered by fabric and cylindrical wood micro poly's, which scatter/diffuse - they are pretty "invisible" sounding, if that makes sense, but more importantly they are really quite good at dealing with those paralel slap back on the side walls. They are away from my mix position though, so I doubt they are affecting anything at mix for the ranges they work in.

Like I said, they "sound invisible". For instance, an absorber "sounds" like a black hole, I think anyone can relate to that. A diffuser, generally, sounds like a bigger room. But these scattering devices sound like.....nothing. It's kind of like a half way point between a bigger room and a black hole, so I kind of like what they do. Because they dont just piss out the energy back into the room, the absorb a good part of it, and control the rest of it. I hope that makes sense! The benefit is that I get complete control of slapback (which is hard to do with flat absorbers, you need the really thick stuff covering huge parts of the wall), and I don't add to the problem of over absorption on the wrong end of the scale. But if I wind up building the room, honestly, I'll build all this stuff into the walls which may mean no scatter devices, or not! Who knows where that'll go, I am playing with concepts now.

4. I like your concept of "deflect and absorb at the back". This is what we did in the room in Cali. See pictures below of the room there. So theoretically speaking, you're not a fan of flat slatted wood panels over large absorption surfaces?

I see allot of conflicting info here as well, because there are guys from the likes of "Acoustic Fields" which argue that the decrease in SQF and thereby volume of the room of slanted wall builds is not as welcome when comparing to just treating the parallel walls appropriately - in other words the benefits are not huge, but the cost is pretty high regarding angled walls. And to some degree, obviously presuming that the absorption is at the correct "rates and levels" as he says (meaning frequency and coefficients) slanted walls are not all that big of a benefit - I kind of agree with that, because honestly it makes sense! I mean the way I reason it is, I am already in the lower end of the scale for room size. It's not a TINY room, but it's not a large room either, so lowering the SQF in this situation seems to be counter intuitive to some degree. The sound proofing effort will already do that with floated floors, ceilings and walls, so doing more would really start to hurt both size wise, but more importantly volume wise.

Your thoughts?

5. "Because it takes the speaker out of the room..." when I saw that I freaked out! Like WHAT!?

To me, a direct translation of that means "NO SBIR". Is that kind of.....right? Because holy flying squirrels batman! If we can resolve that, the modal issues of this room are a joke to get rid of. Even me, at my current knowledge level can relatively easily handle the rest of the modal issues in this room IF SBIR is largely eliminated! I feel I have currently, largely already dealt with the natural internal modes of the room with thick absorbers. Obviously the low end is the exception, and I feel that most of the LF problems are largely caused by this damned SBIR! I think that the SBIR in my room are causing huge oscilations in the walls themselves, which is a big reason for why that FR in my room looks so retarded!

Honestly the more I know about this property I am in, the more I am thinking that the biggest problems I have are caused by the walls actually ringing themselves, because it simply doesn't make sense otherwise. Meaning the drywall and studs are resonating because of piss poor build quality. Even though it is to code, I think that cavities in the walls, and the drywall and stud choice together are causing allot of these issues. Which is why I am more and more motivated to burn it down (proverbially speaking) and build it from studs! But if I build it up, the soffits are definitely an option, pretty much everything within reason is an option at that point.

I don't want to commit to anything yet, because I don't know if this transaction will go through, allowing me to own the home, and second I don't know if Ill be able to front the 10-15 grand out of pocket. I don't run a commercial studio, so I have basically no clientele for the audio division of my business yet, which means nothing but my own funds would finance this. It's basically a glorified home theater and office at this point, which I want to turn into a proper mix room simultaniously - thus the challenge! Buying a home, AND remodeling a room out of pocket in quick succession is pretty much out of the question of what I can support financially, obviously. So there are some logistical issues that have to be sorted well before I can commit to building it.

What is positive however, is I have close professional friends which would work for pennies on the dollar to help me build this from a construction perspective, so that lowers the cost drastically from what commercial prices and costs would dictate. Basically that means this situation is a give and take. It has positives and negatives, but it is reasonably realistic!

I am merely trying to upload this information so that once a move is made, the entire history and right turns of this project are documented for the help of others. So they can see where it started, and what it wound up being.

Standby, I'll let you guys know what is happening in the next 2 months. By end of June I should know confidently what can happen.

Firstly, I feel like I need to donate to this site, and I will ASAP.

John will certainly appreciate that! It costs him money to run the forum, and he gets no return on that, except donations. Last time we spoke about that, he mentioned that donations only cover a fraction of the running costs, so I can tell you for certain he'll appreciate your donation!

I am very thankful for your info, and it's hard to find level-headed, KNOWLEDGEABLE, no BS people which one can learn from - so thank you!

Thanks for the kind words!

1. I agree about the Frequency Response of these speakers in this room. It was a "what the!" from day one! A bad "what the"!

Yup. The good news: I think it can be fixed. It won't be perfect, but it can be a lot better than where it is.

2. So you're a proponent of absorption behind the speakers? Interesting! There seems to be so much contradictory information out there, allot of people explain, for good reason I think, that broadband absorption is pointless behind the speakers because even at 1/4 wavelength touching those SBIR frequencies is not possible with your standard broadband trap.

Weeeelll.... take what you read on the internet with a grain of salt! The 1/4" wavelength thing is part true, part myth. Yes, porous absorption is most effective if it happens to be 1/4" wavelength away from the wall for the frequency you are targeting, and 1/4 wave thick. True. However, that does NOT mean that it won't work anywhere else! At 1/8 wave it is still 70% effective, at 1/16 wave it is nearly 40% effective, and even at 1/64 wave you still get a usable effect (about 10%). Another "however": all of the above is for normally incident sound (sound hitting the front of the absorber at 90°). For all other angles of incidence, the sound wave "sees" an even thicker absorber, so it is more effective than for normal incidence. For random incidence, you can get some very effective absorption for thicknesses and positions that would surprise you. In reality, it turns out that for normally incident sound, porous absorption can be 7% thick (7% of the wavelength) and be effective. For random incidence, it only needs to be 3.5% thick to be effective. Which is why superchunk bass traps work so very well down to low frequencies, even though they are not that thick at all, compared to the wavelengths: most of the sound is not normally incident to a superchunk.

But we are not talking superchunks: we are talking absorbers behind speakers, just 10cm thick (4"). Here's the thing: 4" of suitable porous absorber against the wall actually has good effect down to about 120 Hz. (wavelength = 113", 3.5% = 4") for randomly incident sound, and about 240 Hz for normally incident sound (wavelength = 56", 7% = 4"). Since SBIR is normally incident, you'd think: "Darn! 240 Hz! That's too high. SBIR happens much lower!" ... well it would be too high, if the speakers were a long way away from the wall, and the SBIR was down low... But with the speaker tight up against the front wall, things are different! The cancellation frequency formula for SBIR is F=c/4dx. This is easier in metric, so: assume the front of the speaker is 35cm from the wall. Speed of sound is 343 m/s. So 343/(4x0.35)=245 Hz. Oh yeah! Now we are talking! So provided that you can get your speaker up really close to the front wall, which forces the SBIR null up into the low mids, then you actually can get a usable effect on SBIR with just 4" of suitable absorption. But for speakers that are more than a few inches away, it wont work.

As usual, there is some small truth in the Internet myths, but only partial, and only under the wrong circumstances. Yes, "they" are correct in saying "you can't treat SBIR with front wall absorption". But "they" are ignorantly assuming that the speaker is away from the wall. But when the speaker is close enough to the wall, you actually can have some useful effect on that. The closer you get it, the better you can treat it. Plus you have the added benefit that SBIR in the mid range is much less objectionable psycho-acoustically than SBIR in the low end.

I do however believe in proper "powerhouse" (diaphragmatic/pistonic or helmholz) absorber, that can actually absorb LF, being placed behind speakers,

I wouldn't do that in y room. All those are resonant traps, and resonant traps have a bad habit: they resonate! I have a serious religious objection to resonant things in the front part of the room, as they can "color" the direct sound from the speakers. To my way of thinking, the direct sound field from the speakers is almost sacred: Don't touch it! After it goes past your head, do whatever you want, but in front of you, keep it as pure and crystalline as you possibly can. That's why you'll see in most of my designs I only use absorption and reflection up front: Resonant stuff can happen from the ears backwards, but not forwards. (Usually! But not always)

And I think that the shear pressure behind the speakers, and to the sides as well would really excite the eigenmodes of the metal plate of the VPR's

Oh yes, definitely! And that will make them ring and ding and zing very nicely, along with your music... You'll have a resonant chorus going on up front!

I really love the explanation that ASC, makers of Tube Trap, put in their whitepaper when defining what I am experiencing - they call it "head end ringing",

Mmm hmm! yup. I like that phrase. It really does describe what happens! I'm just not so sure if the cure will stop the ringing, or cause even more of it...

The front part of the room rings like all get out without treatment,

Yup. It usually does. Which is why you need to damp that ringing, or deflect it away from you, not add even more ringing to it...

3. Regarding the diffusers, you already had convinced me way back to get rind of them up close, even though they are already built.

Great! Save them for the day when you build a live room. They can do unusual things in live rooms, and that's actually good! Just not in small control rooms.

The scatter devices are as a direct "knee jerk" reaction, if you will, of the "deadness" of the room. And FWIW, so were the QRD's, but because of the phase issues with diffusers I figured scattering is wiser?

Scattering causes phase changes...

This room has slapback and ringing like all get out, without absorption or diffusion!

Yup. Small rooms generally do.

So having untreated parallel surfaces is really a bad idea in this room,

Again, that's pretty much always the case with small untreated rooms.

For instance, with 3" of Roxul, I found that it is not enough to stop the ringing/slapback at those mid frequencies.

What density Roxul? Where did you locate the panels? How big?

4. I like your concept of "deflect and absorb at the back". This is what we did in the room in Cali. See pictures below of the room there.

I'm looking, but not seeing! ? No pics?

Also, do you mean "Cali" as in "California, USA", or "Cali" as in "Cali, Columbia, South America"?

So theoretically speaking, you're not a fan of flat slatted wood panels over large absorption surfaces?

Oh actually, I AM a fan of slats over absorption! Just not in the front of the room, Sides and rear? Great, Front? Nope. (For RFZ-style rooms, at least): I do use both tuned slat walls and un-tuned slats in many of my designs.

I see allot of conflicting info here as well, because there are guys from the likes of "Acoustic Fields" which argue that the decrease in SQF and thereby volume of the room of slanted wall builds is not as welcome when comparing to just treating the parallel walls appropriately -

Yup: Agreed. to kill flutter by angling walls, you need an aggregate angle of at least 12°. That takes up a lot of space. For control rooms, I tend to NOT angle the side walls (I keep the parallel), and only angle certain parts of the front wall, enough to get RFZ conditions.

in other words the benefits are not huge, but the cost is pretty high regarding angled walls.

Yep.

The sound proofing effort will already do that with floated floors,

Floated floors? Nope! no no no. Nope. Baaaad idea. Floating a floor property is complex, and expensive. Floating it "non-properly" will make things worse than not floating it. Far worse, in some cases. Its not easy to do, requires a huge amount of mass, and eats up your head room. And is NOT necessary at all in the vast majority of cases. Nope. Don't even think of doing that in your room.

so doing more would really start to hurt both size wise, but more importantly volume wise.

Volume is key. Try to maximize the total air volume in the room, and the height of the room (especially at the rear). Those are your two best friends. Anything that takes away height or volume should be examined very closely, to see if the benefits outweigh the lost volume.

5. "Because it takes the speaker out of the room..." when I saw that I freaked out! Like WHAT!?

To me, a direct translation of that means "NO SBIR". Is that kind of.....right?

Sort of. It eliminates SBIR with respect to the front wall, 100%, and with respect to the side walls very greatly, but you still have the rear wall effect, as well as some of the ceiling and floor effect.

What soffit mounting does do, is to kill all edge-diffraction artifacts, and all other artifacts associated with reflections form the front wall (early reflections, comb filtering, phasing, etc.), as well as to correct the power imbalance inherent to small speakers on stands, and a few other Really Good Things.

If we can resolve that, the modal issues of this room are a joke to get rid of.

Dont' confuse modal with SBIR! Two very different animals. Modes ring, SBIR does not. Soffit mounting is very useful for SBIR, but wont' do much for modes (except to avoid triggering some of them).

Meaning the drywall and studs are resonating because of piss poor build quality. Even though it is to code, I think that cavities in the walls, and the drywall and stud choice together are causing allot of these issues

Tell me more about those walls: how are they built? Layer by layer, including air layers, starting from the surface of the room that you see, and going outwards.... material, thickness, attachment, etc.

It's basically a glorified home theater and office at this point, which I want to turn into a proper mix room simultaniously - thus the challenge!

Yep! Control rooms and home theaters have rather different layouts, acoustically. Pretty hard to do both at once...

By end of June I should know confidently what can happen.

Hopefully, it will work out for you. And hopefully,you have a lot of musician friends who would love to cut their demo tracks in your room, and fork over a few greenbacks in compensation...


- Stuart -