Seeking feedback on room acoustic treatment and measurements

[Krakadon]

HI. Let me start by saying I'm a noob on this board so I hope I'm doing things correctly. Please feel free to let me know if not.

I have been a guitar player and hobbyist producer for years, but I really want to be able to produce broadcast quality results of the songs I make for me and others, I guess we can say clients, in my own project studio. At long last, I have some really good, for me anyway, equipment built around a MBP, a UA Apollo with a couple of quad satellites, and a UA 4-710d. I also have a quite decent (I think) monitoring set-up with a Drawmer MC3.1, Adam AX7s, Yamaha HS5s, Avantone Mixcubes, and a KRK 10S v2 sub (which I only use for spot checks or blowing the doors off). I run my speakers full range and the sub has a dedicated channel from the Drawmer. I have the cross-over set to 60Hz. What I am seeking now is the most accurate monitoring I can achieve within my constraints.

I rented a small duplex and have a 13'10"x13'10"x8'9" room with a hard floor (all of the details are in the subsequent slides). Clearly there are limitations with this small, somewhat cubic room. Also, as a renter, I can't make any structural changes. I spent a long time researching and planning the acoustic treatment, and ran the plans by some folks who said they looked good. I spent about $2,500, and a huge number of hours, designing, constructing and installing the treatment. When I took the REW measurements, I was quite bummed at the results.  I’m seeking feedback on the design and results and any recommendations for improvements. Thanks in advance to anyone that can help me out.

I posted 700px wide versions of slides that describe this whole thing. I will share a link to full res slides, selected full res pics and the REW measurements.

[Krakadon]

Link to REW measurements & high res slides & selected pics. I apologize if this link is considered too long. I don't know how else to do this.

https://drive.google.com/drive/folders/ ... sp=sharing

[Soundman2020]

Hi Dave, and Welcome!

OK, well... ummm... what I'm going to say here is probably not going to make you very happy, but I'm guessing that you came here looking for the truth, however harsh it might be, so that you can turn your room into a usable mixing environment. Even if it means doing a whole lot of stuff all over again.

On that basis, let's get started! (I'm hoping you'll take this in the spirit it is given: to help get you on track, NOT to criticize or make you feel bad!)

First point: Layout. The room is small, and square, and the layout is very wrong. You've been mislead into setting up your room badly. But it can be fixed. More on that later.

Second: Clutter. We've got to do something to get that room clean and usable. You do not need all those speakers, espeically in such a small room. They interact with each other, even when not turned on. Choose your best set, and stick with that. Personally, I'd go with the A7X's plus the KRK 10S. Yes it is nice to have extra speakers to "check the mix" on, but you don't have the luxury of that in your small, square room with limited treatment options. Set up your other speakers in a different room, such as your living room, bedroom, etc. and take your mixes there, to see how that sounds. Yes I know that big studios often do have several sets of speakers and engineers love to play around and switch between them to get a better feeling of the mix. But those rooms are also two or three times the size of yours, with massive treatment.

Third: Your REW tests are not valid. There's some big problem with the way the tests were run, and I'm suspecting that you had the ceiling fan on when you did those tests. My advice: lose the fan completely! Get out a screwdriver, and physically take off the blades. You absolutely cannot have that monster hanging above your head and hope to get a decent mix. And most certainly you can never use it while mixing! So get rid of it. Yes, it's a rented room, so you can't take out the entire thing, but you can take off the blades and store them, then put them back on when you leave. Also disconnect the switch, or if you don't know how to do that safely, get an electrician to do it. When you leave, reconnect the switch.

You also had your REW data set to 1/3 octave smoothing, which tells you nothing at all about the room: use 1/48 when you are looking at the low end, 1/24 for the mid range, and maybe go up to 1/12 when looking at the high end.

But even so, I suspect that there's something inherently wrong with the way you did the testing. A while ago I wrote up a thread on how to do the tests correct. You can find that here: http://www.johnlsayers.com/phpBB2/viewt ... =3&t=21122 . Don't do that yet! First you need to fix other things. But do read it over to make sure you have everything you need to do it right.

Fourth: Treatment. Yes you have put a lot of treatment in the room, but some of it is not right, and some of it is making matters worse, not better. To start with, you are way short on bass trapping: It's a small room, so it needs major bass trapping. Yes, you do have some, but I'm sorry to have to tell you this: it's no use. Once again, you have unfortunately been mislead.

Two things that will have to go are the beautiful diffusers on the rear wall, and the extremely dense bass traps in the corners. I'm sure you put a lot of money, time and effort into all of that, but it's not doing what you want it to do.

First, QRD diffusers (a.k.a. "skyline" diffusers) are based on numeric sequences. Your room is too small to be able to use numeric-based diffusers. They can only be used in larger rooms. All numeric based diffusers produce temporal lobing, frequency lobing, and lelvel lobing, close up. What that means is that they create patterns of sound waves that are more intense in some directions, and less intense in other directions that are only slightly different. As you move around in front of them, close up, you get areas where the timing (phase), intensity (volume), and frequency are not scattered evenly. There's a certain distance that you need be away from the face of the diffuser in order to hear a smoothly diffuse sound field, once the irregular patterns have evened out better. That distance is at least ten feet, regardless of the diffuser tuning, and can be greater than ten feet if the diffuser is tuned low. Yours is. Your room is too small to be able to get your head far enough away from the diffuser, and the poor guy sitting on the client couch is toast! He can never get any kind of diffuse field, since his ears are just inches from the diffuser.

Here's what it actually looks like, if you could see the sound waves:

QRD-Diffusion-lobing--pattern-graph-SML-ENH.PNG

So the diffusers have to go. Sorry.

Next up, you said that you built your bass traps with "8 lb Roxul". I'm assuming you mean "8 lb per cubic foot"? If so that is way, way, WAY too dense! You stand no chance at all of successfully absorbing deep bass frequencies with such massively dense insulation. Once again, you have been mislead. This is an area where lots of people make wrong assumptions, so don't feel bad about it. It's natural to think that "big heavy waves need big heavy absorption", but that's actually very wrong. Like many things in acoustics, what "seems" right, or intuitive, is often plain wrong. In reality, what you actually need to absorb deep bass, is light-weight insulation. Around 3 lb per cubic foot if you are using mineral wool, or around 2 lb per cubic foot ("PCF") if you are using fiberglass. The stuff you have will work reasonably well for high frequencies, but not for lows.

In fact, the parameter that you should be looking at is not even density. What really matters is the rather obscure parameter called "Gas Flow Resistivity", which is measured in the even more obscure units of "MKS rayls", which can alps be stated in terms of PaS/m2 (pascal seconds per meter squared). That's what sound waves actually care about, not the density. It's the measure of acoustic impedance, and what you need is material that has a Gas Flow Resistivity of around 5,000 to 15,000 rayls. The problem is that most manufacturers of insulation don't bother measuring that parameter, since it means nothing for the main purpose of the product, which is thermal insulation. So it's hard to find that number for most products. But fortunately, there is a roughly linear relationship between GFR and density, ... but it's different for each type of material. One relationship for mineral wool, and other for polyester, another for fiberglass, yet another for cellulose, etc.

Here's a graph that shows the approximate relationship for two common types of insulation, and the useful regions for each type of insulation:

gas-flow-resistivity-vs-density-graph-CLPD.png

It's in German, but fiberglass is on the left, and mineral wool is on the right. It's also in Metric units, but two useful points of reference: 2 PCF is 32 kg/m3, and 3 PCF is 48 kg/m3. Your stuff (8 PCF) works out to 128 kg/m3, so it would be way, way off to the right, far beyond the end of this graph, and way, way below the useful region...

So, unfortunately, your bass traps are useless, because they are made with the wrong density of mineral wool: it's nearly three times as dense as what it should be.

Also, there's no need to put MLV inside a bass trap, unless you specifically design it as a tuned membrane trap. MLV does have it's uses in acoustics, and membrane traps is one of them, but they are hard to tune in the first place, and the only deal with one frequency, even if you do get it tuned right. Yes, I'm familiar with the concept of "limp mass", and I've seen the same web pages that you found promoting this type of trap as the best thing ever, since the universe began, but in reality, that isn't true.

And the "diffusion plate" on the front of your traps might be OK, but probably not since they are covered with fabric!

Next, your poly-cylindrical diffusers on the side walls have to go. Yes, polys are useful devices, when used correctly, but those aren't. Sorry.

OK, so now that I've ripped your room to shreds, let me help you put it back together again, the way it should be.

Start by taking everything out of the room, except for the desk, chair, and A7X speakers, on their stands.

First, you need to set up your room geometry correctly, starting with the mix position. Right now, you have your head in the worst possible location in the room: right at the geometric center! That's the location of every single first order modal axial null, and every single second order modal axial peak. All of them are right there, in the middle of the room. And in a square room, that's big, bad news. You have to get your head out of there.

The theoretical best location for your head (or more accurately, for your ears), is 38% of the distance between the front wall and the back wall. However, I find that it's a bit better a few points forward of there in most cases, so aiming to get your ears at about 35% of the room depth is a good option. In your case, that implies that you set up your chair so that your ears are 58" from the front wall.

Next, your speakers CANNOT be on the desk, nor over it. That produces major comb filtering problems, as well as early sound from various sources.

Also, the room is small so the speakers CANNOT be at any distance from the front wall that would put the SBIR artifacts in a bad place in the spectrum. The room is not big enough to be able to get them far enough away to force the SBIR issues down below the bottom of the spectrum, so your only other option is to force them up high enough into the low mids that they can actually be treated. Therefore, the speakers MUST go tight up against the front wall, except for a gap of 4" where you will insert a single panel of 4" OC-703. That setup drives the lowest SBIR dips well up into the low mids, and OC-703 is really good at absorbing low mids...

Also, it's important to have your speakers located at distances from the side walls that will avoid bad stuff: in your case, I'd recommend that you place each speaker 49" from it's side wall, which implies that they will be 68" apart. Careful! I am NOT talking about the top, bottom, or side of your speaker cabinets! I'm talking about the acoustic axis of your speaker. Check with the manufacturer to found out where that is on the box. You need to know that point, because that's where the sound spears to come from, so that's the point you use for all measurements related to speaker positioning.

The speakers must be placed such that the acoustic axis is 50" above the floor.

Right, so now you have your speakers and head in the right location, but not yet the right angle. So that's the next item.

Get out a mic stand, and set it up very carefully, absolutely vertical, on the center line of the room, at a point about 18" behind where your ears will be. In other words, 58+18=76 inches from the front wall. That's your aim point. You want to orient your speakers such that each acoustic axis is pointing exactly at that mic stand. You can do this by taping a laser pointer to the top of each speaker, directly above the acoustic axis, and make sure it is shining out exactly perpendicular to the front face of the speaker. Carefully rotate both speakers on their own vertical axis, until the two laser pointers are hitting the same spot on the mic stand. Double check that the speaker axes are still the correct distances from the side walls and front wall, and that the rear corner of each speaker is just touching the OC-703 panel between it and the wall. It's a bit of a juggling match, but do take care to get it accurate.

Now follow the instructions in that link above, and do the initial set of three REW tests with NOTHING in the room except the speakers, chair, desk and DAW. That's your "empty room" test, and it will tell me what you are dealing with, acoustically. It will show up all the terrible ugliness of the room, so that I can help you treat it properly.

You might be wondering if my advice is any better than the other "advice" you already found on the internet, that has led you into the bad situation where you are. You are probably wondering: "Who the hell is this guy to tell me to tear my room apart and re-do it?" And also: "How can I know if I can trust his advice?". Excellent questions! And very smart. All I can do to help you with that, is to show you how my rooms usually turn out, then you be the judge of how good my advice is. So here's one that' I'm rather happy with, that includes comments by the studio owner, as well as a set of REW tests that we did on his room after I finished tuning it. http://www.johnlsayers.com/phpBB2/viewt ... =2&t=20471 Scroll through that thread, look at the REW graphs, and compare them to yours. That's what studio owners have achieved when following my advice.

I don't want to mislead you into thinking that your room will end up as good as the one you see there: It won't. Your room is too small to be able to achieve those results, his speakers are soffit mounted, the entire room is completely designed around the RFZ concept, and we spent months tweaking and tuning every last bit of that room, to the highest precision. So I won't promise you ruler-flat response in your place, but I CAN promise you that it will be a hell of a lot better than it is now!

So if you are up to it, and you really do want your room to be as good as it can be, then the above is my suggestion of how to start down the long path to achieve that.

You don't have to follow my advice, of course! The choice is yours. On the other hand, look at where the advice you found in other places has gotten you...


- Stuart -

[Krakadon]

Hi Stuart.

Thanks very much for such a prompt and thoughtful response. I really appreciate it.

Wow. As you can imagine, I’m reeling right now. I wish I knew about this forum and that I could get consultation with a professional acoustician before I started planning this room. I have some questions and comments to get clarification before I go down this road.

Re: Your critique:
I don’t confuse analysis with criticism. While I am in fact deeply hurt right now, that’s not your fault. Physics is physics. It’s not the doc’s fault when he tells you you’ve got cancer, but maybe he can help cure you!

Re: Keep the A7Xs and KRK 10S:
When you say keep the 10S, you mean running the A7X’s through it (as opposed to running another output from the Apollo for example)? I wasn’t sure if that was affecting the performance of the Adams. One of the main reasons I bought the Drawmer MC3.1 is so I can have an independent, controllable subwoofer output and keep my Adams “pristine”. It was like a fear and doubt thing. Also, would you have it on all the time? How would you set the crossover and level? I’m sure some of this falls into the camp of we’ll cross that bridge when we come to it.

Re: The REW measurements I did:
You know what? I think I did forget to turn off the fan before doing the test. Lame! Taking off the fan blades is a brilliant idea, I can’t believe I didn’t think of that. It does get very hot in the summer and cold in the winter. There is no central air and the air-conditioner/heater is in another room and it gets hot in the summer and cold in the winter. I guess I can use a floor fan from the other room (and turn it off and close the door as much as I can tolerate while mixing)? I read your SOP on the REW measurements very carefully and tried to follow it as closely as possible (in fact I downloaded it and filed it with the manual to be sure I could reference it in the future). I did, however, use a Behringer ECM8000 and Radio Shack SPL meter. Is that a deal breaker?

Re: The REW graph smoothing (i.e. 1/3 on full range and 1/24 on low end vs. 1/24 on mid-range and 1/48 on low end)
Since I posted the REW data I didn’t think this mattered. I have read different things about smoothing. But honestly your recommendation is more consistent with my intuition. More detail seems better.

Re: The bass traps:
Yes, 8 lb per cubic foot. I have read that low density material is better but most often read “the only thing effective in low frequencies is mass” and high density is better. I assume this means I can reuse the frames and change out the packing? They are 6” so I assume this is still suitable, yes? I have read many times about the limp mass membrane effectiveness, but yes, I have also read that the traps need to be tuned. The diffusion plate isn’t really designed. I just noticed in my previous room that when I added a lot of trapping it got so dead.

Re: Speaker Placement
Actually, my ears are 58” from the front wall. I did plan and get that right (based on the 1/3-2/3 generic recommendation you find). In practice that means I’m well in front of the fan which is in the center of the room. But I can get closer to the front wall if I eliminate the gap between the front wall and front wall broadband absorption as you recommend. I spoke with Adam and they said the acoustic center (in their parlance, they won't say "acoustic axis") is between the tweeter and woofer and that they couldn’t be more precise than that (basically they said it was proprietary). In practice that means they are about 1” too low. Once I have the speakers configured in the recommended way, I’m well in front of the sweet spot (i.e. point of the equilateral triangle). Is that ok?

Re: New REW measurements in empty room:
By three initial tests, you mean A7X left, then right, then stereo? I assume I should set all of the switches flat, yes? Also, what about the sub?

In closing:
I don’t doubt your capability at all. That room is awesome. Actually, after studying it carefully, it is astonishing. I have never seen anything like it. Clearly that level of design and treatment is out of my budget but I’m sure my room can be improved a lot. This is a lot to take in and obviously your recommendations constitute a huge effort and lots of emotional and physical energy (plus money I'm sure). This will take some time, but I want good results so I’ll see what I can do… When I have the new REW measurements, should I reply to this thread or PM you or what?

Thanks again. I really appreciate.

[Krakadon]

Oh, one other comment. When I built all of this it was with the idea that it was modular so I could move it to my future room(s). As much as is practical, I'd still like to be able to do this. I understand a "future room" is purely speculative but I do envision at least one, possibly two moves in the next few years. I sold my wife the idea that I was "getting what I need" with these expenditures. (As if any musician or studio owner is ever "done" spending money, ha ha).

[Soundman2020]

As you can imagine, I’m reeling right now.

I kinda expected that might happen!

I wish I knew about this forum and that I could get consultation with a professional acoustician before I started planning this room.

Don't feel too bad about it. The internet is a wonderful thing, but it's also full of a lot of junk, masquerading as truth. Especially in the world of sound and acoustics.... there's a lot of snake-oil dealers out there, that want to sell you their magical products that can't possibly work (such as fantastically expensive power cables made from amazingly exotic materials that nobody ever heard of... don't get me started... or the "acoustic foam by mail" people... AAARGH!!!), and there's also a lot of myth, legend, and plain old ignorance out there, all fighting for your attention. And then there's a couple of places like this forum that actually do have good, solid, scientific info. Few and far between, and not so easy to find... So spread the word!

It’s not the doc’s fault when he tells you you’ve got cancer, but maybe he can help cure you!

I pretty sure we can cure you! Your studio's cancer is not terminal, and there's good hope for the patient. Drastic surgery is needed, but we do expect that he'll live, and can live a long and productive life afterwards... It might hurt a bit, and recovery can take a while, but the prognosis is good...

When you say keep the 10S, you mean running the A7X’s through it (as opposed to running another output from the Apollo for example)?

Right. In general, it's good to keep your signal path as clean as possible, with as few things as feasible affecting the signal. So let the sub do the cross-over for you, unless you have a much higher quality crossover. Also keep the configuration as standard as possible, so it always sounds the same. One day you'll remember that advice if you don't take it... right after you do an amazing job of mixing an astounding track, with beautiful deep bass... then notice that you forgot to turn on the sub while you were mixing!... and when you do, the bass smothers you under a pile of mud....

I'm not a huge fan of having multiple sets of speakers in a room, with multiple ways of interconnecting them. I learned this many years ago, when I used to install high-end video post production suites. A very wise technical manager was one of my customers, and when I tried to sell him on the idea of having an extra video monitor in his machine room, of a different brand than what he had. He dumped that idea, saying: "If you have three different monitors in the rack, it's impossible to get them to show the exact same colors. And your clients will look at all of them, then decide that they want their commercial to have the reds from monitor 1, the green from monitor 2, the saturation from monitor three, and the contrast from monitor 4... and expect you to deliver! ... and be very unhappy when they watch their commercial on their cheap TV at home, and it looks nothing like any of that. If there's only one monitor in the rack, then that's all they see: no other choices. And they'll be quite happy." The same applies to audio. If you have three different speakers in the room, your client will want his mix to have the deep bass from set "A", the crystalline highs from set "B", the mid-range clarity and definition pf set "C"... and when he listens to the mix in his car, he'll be very disappointed because it wont sound like any of those! But give him just one set of speakers, one option, make it sound good on those, and he'll be happy when it also sounds good in his car, even if it sounds different.

Of course, that's just my opinion, and there's a large number of engineers out there that don't agree: they want sixteen dozen pairs of monitors spread around very possible nook and cranny, and an entire NASA inspired control rig to handle them all, so that they can blow you away with umpteen thousand different combinations that all sound amazing but totally different.... but I never got the point of that! Why? What's the purpose? Which "sound" will you actually put into your mix? Which of those will it sound like in your car? On ear buds? The radio? The club? Your living room? TV? I never figured out the purpose of that.

My philosophy is to have the entire room tuned to peak perfection for one set of speakers, so that you hear only the truth. The whole truth. Nothing but the truth. That allows you to make the mix decisions you need to make, and to produce mixes that translate perfectly to all other systems. Yes, it will sound different on other systems, but it will still sound good! If you can make it sound good on a system that is telling you the absolute truth, then it will also sound good on systems that lie. but if you try to mix on a system that lies, you'll never succeed. You might make your mix sound fantastic on that lying system, but it won't translate. If you play the mix elsewhere, it will sound terrible...

Anyway, excuse the rant, but I prefer to design rooms that do just one single thing, very, very well. One set of speakers tuned to perfection, and if the room is big enough, maybe just maybe, a second set of lousy speakers in a lousy location, just to check the way it will sound to most people on their typical consumer systems in typical rooms.

I wasn’t sure if that was affecting the performance of the Adams.

Yes, it will, but very little. The room itself is doing far, far more damage to your sound than the sub ever could.

One of the main reasons I bought the Drawmer MC3.1 is so I can have an independent, controllable subwoofer output and keep my Adams “pristine”.

You can do that if you want, so you can see how the mix sounds WITHOUT a sub, but you should normally track and mix with the sub on, and crossed-over perfectly. That should be your normal, standard, set-up, which you only change to check how your mix will sound on non-optimized gear.

Also, would you have it on all the time?

Absolutely! After you have found the correct location, orientation, and configuration for the sub, such that the entire system produces the smoothest, tightest bass, that's the way you should operate all the time.

How would you set the crossover and level?

That's part of the final tuning process, if you really do want to go down that path to get your room tuned to perfection. But probably around 80 Hz is usually a good place to start. The A7X is still reasonably decent at 80 Hz, not struggling too much, and the KRK 10S is good up to 80 and beyond, so that's a good spot to start at. Set the sub level to whatever gives you the correct bass response, and the flattest spectrum. I do offer a service for tweaking the tuning of your room as far as it can go, if you'd like to do that. PM me if you are interested. Or we can just walk through the basics here on the forum, then you can carry on tweaking on your own.

I think I did forget to turn off the fan before doing the test. Lame!

I'm pretty sure you must have! There's some huge, ugly "chopping" going on all over your REW data, making ir practically useless. There's nothing I can see with that there. Sort of like trying to see the fish on the far side of an aquarium filled with mud, instead of water....

it gets hot in the summer and cold in the winter.

Consider installing a ductless mini-split HVAC system. They are no cheap, but are within range of most project studios. Get a quite one, and it will not only keep you cool and warm as needed, but will also control the humidity in the room, which is a must anyway.

I did, however, use a Behringer ECM8000 and Radio Shack SPL meter. Is that a deal breaker?

The RS meter is probably OK. The ECM8000 might be OK, but I'm wondering if some of that garbage in your readings is coming from the mic, not the room. When those things fail, it's the low end that goes wonky. After you get the fan disconnected, the room silent, and your calibration process done right, let's have a look at the new data, to see if the mic is any good.

Since I posted the REW data I didn’t think this mattered.

It doesn't matter in the sense that it does not change the data: it just changes your view of the data. But with 1/3 smoothing, you can't see any real detail.

But honestly your recommendation is more consistent with my intuition. More detail seems better.

Right! Especially in the low end. Even smoothing 1/24 can hide modal issues with the room, or phase cancellations. You wont be able to see stuff that you can definitely hear with more than 1/48 for the lows. But 1/48 in the high end is pointless, as all you'll see is hash all over the place, that isn't really there, and most certainly isn't audible. 1/6 is a good approximation of human hearing resolution in the high end. But way too much for the lows.

I have read that low density material is better but most often read “the only thing effective in low frequencies is mass”

You are confusing isolation with treatment! Yes, for isolating a room, you need mass. Huge amounts of mass. Your walls must be massively heavy, and dense. But treatment is very different. It's an entirely different aspect of acoustics. The stuff you use to isolate a room is lousy for treating it, and the stuff you use for treating a room is lousy for isolating it. Exact opposites.

I assume this means I can reuse the frames and change out the packing? They are 6” so I assume this is still suitable, yes?

Weelllll.... not so much. Bass traps need to be BIG. 6" is not big: it's tiny. Think of this: the wavelength of an 80 Hz tone is about 14 feet. That's typical tuning for a kick drum. The wavelength for 35 Hz (the bottom end of a 6 string bass), is about 32 feet. So 6" ain't gonna do much for those guys! To control bass, you need BIG traps.

There's a type of trap called the "superchunk" that is very effective down to quite low frequencies. You build it by cutting up panels of OC-703 into large triangles that measure at least 24" on the sides, and preferably 36". You stack those triangles in the corners of your room, from floor to ceiling, like this:

superchunks-04 - SML.ENH.jpg

superchunks-01 -ENH.SML.jpg

If your room shape does not allow that in all vertical corners, just do the best to get as close as possible.

And there are also horizontal corners in rooms...

superchunks-08-vertical-and-horizontal1 - Copy.jpg

Corners are the best possible place for bass traps, since all room modes terminate in corners. Small rooms need a lot of bass trapping, so do all the corners you can.

I have read many times about the limp mass membrane effectiveness, but yes, I have also read that the traps need to be tuned.

Right. And a tuned trap can only handle one specific bass frequency, whereas a Superchunk deals with all of them at once, and takes up the same amount of space...

I just noticed in my previous room that when I added a lot of trapping it got so dead.

Right, but that's only because you didn't compensate! Large bass traps don't trap only bass: they trap EVERYTHING. But the mids and highs don't need trapping. So you have to design the traps such that they reflect mids and highs back into the room, selectively, in a controlled manner, and only allow them to suck up the bass.

But I can get closer to the front wall if I eliminate the gap between the front wall and front wall broadband absorption as you recommend.

If you are at 58", that's fine. We can tweak the exact spot later, but for starting, that's fine. What's far more important is to get the speakers tight up against the front wall, such that the SBIR artifacts at are at a place in the spectrum where we can actually deal with them. With the speakers away from the front wall, the SBIR is too low, and can't be treated with anything reasonable. Certainly nothing that could fit in your room....

I spoke with Adam and they said the acoustic center (in their parlance, they won't say "acoustic axis") is between the tweeter and woofer and that they couldn’t be more precise than that (basically they said it was proprietary).

That's pretty dumb of them! It's a key parameter for correct speaker set-up! Take a look at other manufactures, such as Genelec, Barefoot, and K&H; They put out publications that show the exact location of the acoustic axis for all of their speakers, because it is important!

Such as this one:

genelec-acoustic-axis-locator-page-1.jpg

That's just page 1 of the Genelec document that shows the location, accurate to the millimeter, for every single speaker they ever made.

My guess is that the guy you spoke to at Adam doesn't have a clue, didn't know where to find the info, and couldn't be bothered to help you anyway. That's actually not unusual with Adam. Their documentation sucks, and they aren't very helpful. That's a pity, because they make excellent speakers. But they never have figured out how to do marketing, or customer support. Next time you are in the market to buy speakers, take a look at Eve Audio: Very similar concepts, fantastic speakers, and great support. Some of the top guys at Adam got frustrated years ago, left, and started their own company, called Eve Audio. ("Adam and Eve", get it? Eve was built out of the bones from Adam? Sigh!!! Slick... ) I've had much better response from Eve, as compered to Adam. When I designed Studio Three, the chief engineer at Eve Audio was kind enough to help me personally with info I needed for that specific room. Great guy, and great speakers. And thanks to his help, I achieved those rather nice results, with Eve speakers.

So anyway, since Adam doesn't want to help one of their customers with important information, we'll guesstimate intelligently. Or cheat! I've used the A7X in several studios, so I already have a model with my best guess:

EQUIPMENT--SPEAKER--Adam_A7X-S03.jpg

Once I have the speakers configured in the recommended way, I’m well in front of the sweet spot (i.e. point of the equilateral triangle). Is that ok?

Ahhh yes, the famous "equilateral triangle"! Yet another myth... Even though you see it all over the place, it's actually not drawn correctly in the majority of cases. Think about this: If you have the acoustic axes done the way those diagrams show, then they meet in the middle of your head. Right? Which would be fine if you have your ears surgically transplanted onto your eyeballs! Because the axes are pointing at your EYES like that, not your ears!

In reality, the focus point for the speakers should be at a spot about 18 inches behind your head, which means that the axes are now pointing at the tips of your ear lobes, where they should be. But that also implies that hte triangle is no longer equilateral! It's now squished up a bit. And that is absolutely fine! There is no logical reason why the distance between the speakers should be exactly the same as the distance between each speaker and your ear. Yes, the two "speaker to ear" distances must be the same, but there's no need for those to be the same as the "speaker to speaker" distance.

By three initial tests, you mean A7X left, then right, then stereo? I assume I should set all of the switches flat, yes? Also, what about the sub?

Yes, yes, and yes!

Actually, if you are using a sub, you need to do a set of 7 tests for the initial baseline:

S--
L--
R--
LS-
RS-
LR-
LRS

You don't need to do that every time, but for the initial baseline it's important to have as much data as possible.

That room is awesome. Actually, after studying it carefully, it is astonishing. I have never seen anything like it

Thank you for the kind words! It took a long tome to do it, but it worked out well. Feel free to give Rod a call (the studio owner) and ask about the process, and the outcome.

This will take some time, but I want good results so I’ll see what I can do…

When I have the new REW measurements, should I reply to this thread or PM you or what?

That depends on which way you want to go here! If you just want basic help and don't mind waiting a lot between replies, then the forum is fine. If you want more detailed tuning and need it done quicker, in great detail, then maybe paid consulting is what you need.

But either way, once you have the initial tests, post them here on the forum anyway, so everyone who is interested can take a look, then you can post more results later, during the process and after, to show what you accomplished.

When I built all of this it was with the idea that it was modular so I could move it to my future room(s). As much as is practical, I'd still like to be able to do this.

No problem. Superchunks are pretty modular, for example: just triangles of 703 stacked up, with plastic in front, and fabric on a light frame. It can be more complex than that if you want to optimize, but it can still be modular, and portable.



- Stuart -

[Krakadon]

Hi Stuart. It will be quite some time before I can take the baseline measurements. It will take me days to remove everything and do the test. But I did follow your advice to butt the front wall absorbers against the wall and placed the speakers as you said. The center image is amazingly improved, full, detailed and has that psychoacoustic effect type feel where the sounds is "thrown". It's like you can reach out and touch it, but "it" isn't near the speakers, "it" is behind the video monitor. Very cool man, thanks!

[Soundman2020]

I did follow your advice to butt the front wall absorbers against the wall and placed the speakers as you said. The center image is amazingly improved, full, detailed and has that psychoacoustic effect type feel where the sounds is "thrown". It's like you can reach out and touch it, but "it" isn't near the speakers, "it" is behind the video monitor. Very cool man, thanks!

So you now have a proper "phantom center"! That's good. It means that your speakers are set up roughly correctly in a decent location in the room. It's called the "phantom center" because for things that are panned dead center in the mix, it sounds like they are coming directly out of a non-existent speak in the center of the front wall. If you close your eyes and don't look, you could swear that there are no speakers out to the sides, and there's just none single speaker up front, in the middle. Then you open your eyes, and there is no speaker! Just the phantom appearance of something that isn't really there. So since you are already getting that, and the room isn't even treated properly yet, this bodes well for a good outcome.

By the way, if you really want to have a good set of REW data, do a set of tests right now, before you take out the existing treatment, so you can then see what your treatment was actually doing (by comparing it with the "empty room" test later), and then also see how much improvement you get at the end of the process, by comparing it with the final set of tests. It would be good to do that now anyway, to check that things are working out with REW when you have the fan off, and after re-calibrating.

- Stuart -

[casaestudio]

Krakadon, just read your post and thought I’d stop to cheer.

I’m sure you’ll eventually get there. Enjoy the ride!!!

[Krakadon]

UPDATE:

Completed:
• Repositioned broadband absorbers on front wall to be tight against wall
• Placed studio monitors per Soundman2020’s suggestion (i.e. 4” from back wall, 49” from sidewalls, acoustic axis placed at 50” height)
• Removed diffusion array from back wall
• Removed headboard from broadband absorber above former diffusion array position
• Replaced 3” 8 lb./ft^3 Roxul with 4” OC703 in rear wall broadband absorber and moved it down behind the sweetspot, just above sofa flush against wall
• Since I can’t put superchunk bass traps in left rear corner, I reused the two old bass traps in that location, removed diffusion grates and 6” of 8 lb/ft^3 and replaced with 8” of OC703. Still need to remove limp mass membranes on those two. Also plan to fit some OC703 scraps behind traps
• Took quick set of REW measurements (w/o sub)

Planned:
• Remove limp mass membranes from rear traps and add additional OC703 to fit gap
• Remove existing bass traps from front corners and replace with floor to ceiling superchunk traps
• Remove polysorbers
• Install some amount of superchunk bass traps in the wall/ceiling corners
• Upgrade RadioShack SPL meter and Behringer ECM8000 calibration mic
• Retest room
• Remove everything from room and do baseline characterization (this will take several days and take my studio off-line so I don’t know when I can get to this. All of the other stuff I can do in the margins so to speak).
• Solicit input for revisions

Questions:
• When I build superchunk traps, do I put a layer of plastic or craft paper over the insulation below the fabric to reflect some mid/high frequencies? I have read this in some places. Often, I have seen wood slats placed on the outside of the superchunks, i.e. facing into the room, presumably for some diffusion or reflection of mid/high frequencies back towards the mix position, yes?

[Soundman2020]

I'd need to see the actual REW data file, but from the little that is visible on those graphs, it looks quite reasonable.

• When I build superchunk traps, do I put a layer of plastic or craft paper over the insulation below the fabric to reflect some mid/high frequencies? I have read this in some places. Often, I have seen wood slats placed on the outside of the superchunks, i.e. facing into the room, presumably for some diffusion or reflection of mid/high frequencies back towards the mix position, yes?

Yes, probably, but that's part of the tuning process. That plastic acts like a "foil", acoustically, and there are equations for predicting what type of plastic you'll need (thickness), and how much coverage (percentage of total frontal area of the bass trap that needs covering). You might also need slats on the front, for the same reason, and also for the other, rather more practical reason: prevent people and objects from bumping into the fabric, and damaging it...

- Stuart -

[Krakadon]

I'd need to see the actual REW data file, but from the little that is visible on those graphs, it looks quite reasonable.

I added that to google drive. Here is the link:

https://drive.google.com/drive/folders/ ... sp=sharing

[Krakadon]

UPDATE 171102

Completed:
• Removed ceiling fan blades.
• Removed polysorbers from sidewall/ceiling corners flanking sweet spot.
• Reworked front corner bass traps. Removed diffusion grates, limp mass membranes and 6” of 8 lb./ft^3 and replaced with 8” of OC703. Once I complete the Superchunk bass traps, I’ll relocated all six of the reworked 8” bass traps to the ceiling/wall corners. Also, since I have a ton of 8 lb. Roxul and some OC703 scraps, I shredded them into fluff (<2 lb./ft^2) and mixed them 1:1 then put them into small garbage bag “cells” which I tacked behind the front corner traps. Putting them into cells prevents them from settling to the bottom which increases density and unbalances the trap. Depending on the feedback I get, I plan to put them behind the 8” traps when I put them up on the wall/ceiling corners.
• Took new REW measurements and uploaded to Google Drive (link below). These measurements I think are of decent quality. Also, I took all seven measurements (-L,-R,-LR,-S,-SL,-SR,-SLR).
• The results are a definite improvement but there is still are nulls at 100Hz, 3-6kHz and 13kHz.
• Regarding the high frequency nulls, I tried to move things around and put up some hard board and plywood here and there just to see if I could improve them but I didn’t really so I’m not sure what do to there.
• Regarding the sub, no matter where I placed it or set the crossover the results weren’t very good. It increased the reach towards 20Hz but exaggerated the null at 100Hz and also cut out a huge chunk all the way down to 60Hz. It seems there is no point using it until I add more trapping except to check the kick on EDM or whatever.

https://drive.google.com/drive/folders/ ... sp=sharing

Planned:
• Remove limp mass membranes from rear traps and add additional OC703 to fit gap.
• Build floor to ceiling Superchunk traps in front corners. Someone suggested putting peg board on the front as a possibility. I’m thinking of taking some hardboard and drilling out holes in some type of pattern and putting in on the front of the Superchunks in the front corners.
• Move 6 reworked old bass traps to ceiling/wall corners.
• Build 2 additional framed 8” OC703 traps for back corner behind door where I can’t fit Superchunks.
• Upgrade RadioShack SPL meter and Behringer ECM8000 calibration mic.
• Retest room.
• Remove everything from room and do baseline characterization (this will take several days and take my studio off-line so I don’t know when I can get to this. All of the other stuff I can do in the margins so to speak).
• Solicit input for revisions.

[Krakadon]

Completed:
• Reworked all six old bass traps. They are now 2’x4’x8” OC703 and have been relocated to wall/ceiling corners. Behind each trap is two plastic bags of <2 lb./ft^3 of 1:1 Roxul/OC703 fluff.
• Built and installed floor to ceiling Superchunk bass traps in front corners (24”x24”x36”). Put a lattice of vertical slats in front of traps (1.5”, equidistant, 70% coverage). I did this with cheap furring strip, but I like the way it looks and would love to upgrade to a premium finish appearance board, such as select pine from Home Depot, assuming it doesn’t get shredded by the acousticians of course.
• Built and installed a large columnar bass trap in left rear corner where a Superchunk can’t fit. It is 2’ wide, 8’9” tall and has 12 inches of OC703. Also has lattice in front like Superchunks.
• Built and installed 46”x52”x3” Roxul 8 lb./ft^3 broadband absorber trap to cover the brick fireplace. Finished with vertical slats (1.5”, equidistant, 70% coverage).
• Relocated 2’x’4’2” OC703 broadband absorber that was in front of fireplace to hang in front of rear wall broadband absorber increasing the depth to 6” in the area behind the sweet spot.
• Took new REW measurement.
• Updated slides.

https://drive.google.com/drive/folders/ ... sp=sharing

Planned:
• Upgrade RadioShack SPL meter and Behringer ECM8000 calibration mic.
• Remove everything from room and do baseline characterization (this will take several days and take my studio off-line so I don’t know when I can get to this. All of the other stuff I can do in the margins so to speak, maybe over holidays).
• ??? – Not sure where to go from here. It is disappointing to see how little $450 of additional OC703 impacts the room response. There are a couple of spots where I can add some panels (~2’ superchunks in wall ceiling corner above door and fireplace, 2’x4’x6” panel across floor wall corner on left side of room). Other than that, I can add a ton more treatment on the back wall and maybe add more treatment to the ceiling.
• Solicit input – OK I’M OFFICIALLY SOLICITING INPUT. WHERE DO I GO FROM HERE?

[Krakadon]

Here is my latest update. I'm not sure how much more I will do until I replace my KRK 10S (planning to buy an Adam Sub10) and measurement mic. Hopefully over the holidays I can find time to empty the room for baseline characterization. How much I do now depends on the feedback I get from people. I am pleased things are moving in a positive direction but there is still a lot of room for improvement...

UPDATE 171118

Completed:
• Repositioned subwoofer (after testing many positions) to optimize low end response
• Repositioned sidewall broadband absorbers to get into reflection zone
• Added equidistant 1.5” vertical slats (70% coverage) set 1.25” from face of rear broadband absorber on each side which is not in reflection zone
• Added 2’x4’x3/16” wood panels (horizontal orientation) with equidistant 2.5”d circles (70% coverage) to the face of the top corner treatments on the side walls and rear wall
• Added 2’x4’x3/16” wood panel (vertical orientation) with equidistant 2.5”d circles (70% coverage) to the face of the top corner treatments on front wall (they curve up over the top of the ceiling cloud)
• Took new REW measurement.
• Updated slides.

https://drive.google.com/drive/folders/ ... sp=sharing

Planned:
• Upgrade RadioShack SPL meter and Behringer ECM8000 calibration mic
• Replace KRK 10S sub with Adam Sub10
• Remove everything from room and do baseline characterization (this will take several days and take my studio off-line so I don’t know when I can get to this. All of the other stuff I can do in the margins so to speak, maybe over holidays).
• Solicit input