Finishing my new room..

Whew.. where to begin.. I'm a huge fan of Martin Pilchner's control rooms and wanted to experiment with replicating his inner shell design in a space I'll be working out of for the next couple years. I built this modular so it splits up into 4' wide sections. The walls I built follow the floor plan of his downtown music studio B room in NYC, but at a 70% scale and open at the rear where it utilizes the existing room for a rear wall. Obviously, isolation wasn't a priority in this endeavour. I didn't want to add the cost of fully enclosing it in the rear and making the low end harder to treat. The smaller scale seemed a good match for the fact I was to use nearfields instead of big mains. I've always liked nearfields in small rooms. The only concrete nearby is the slab under the hardwood flooring. As a result, whatever sound leaves the room doesn't get reflected back by any significant amount. The walls in the new room are just a single layer of 5/8 with exposed studs on the outside. The angles (as used in MP's design) - Rear sections angle out 5°, then in 8°, then the Typical 30° for speaker walls. This made sense to me since angled walls are less ideal for small spaces. So fairly moderate angles and the room is widest around the listening position. The ceiling slopes down at 16° starting from the middle of the room and the rear is flat. My first priorities to figure out right now are as follows.. -Would I be a fool to not go ahead and flush mount my monitors (Focal Twin) in this room? It would bring my mix position that much closer to the front wall away from the 38% mark. Maybe this is alright though? The room also gets narrower the more forward I go. I *could* reverse the drywall to the outside of the studs for that middle section to give me more trapping space. The room length is also less relevant with the rear being partly open. Lightweight construction and a window on the exterior wall makes for no reflection interference. Tested that already. -Should I be thinking about reversing the drywall at all? If it was important enough I could do that with the middle section which seems the spot to do it. I could do the walls or walls and ceiling in that section to get me more trapping width. -Should I get rid of my ceiling slope? In hindsight it may have been better not to slope the ceiling with this room height. Maybe it'll work well with the monitors flush mounted though? If I really need to I can raise up the front 2 sections getting rid of the slope. The internal ceiling height is 8' 6 1/2" at it's highest. This leaves about 1/8" of space from the existing room's ceiling. Here's where I'm at now plus a scale version of the floor plan as well as a 3d sketchup of the build:

I think I'm going to go ahead with flush mounting the monitors. The front end geometry is ideal for this after all, right? Still not sure if I should get rid of the ceiling slope to give me more room for LF trapping & air gap. I'd probably do a big front soffit across the top of the front wall combined with an angled cloud. It's an obvious hassle to raise up that section and flatten it out then drywall the gap, but if it's worth it I'd do it. How should I construct the speaker boxes for this size of monitor (Focal Twins)? 1" thick MDF? 3/4" MDF? How tight should the fit be around the top, bottom, & sides? (in rear I'll design for amp venting) Should I put anything between the speaker cabinets and the interior of the boxes as a lining? Neoprene around all sides or at least the speaker's bottom?

I can't really advise on the design concept... I don't truly know enough about it... just thinking about it though, I'd expect that you'd be able to have good control over the higher frequencies, but I'd be a little more concerned with the low end of the spectrum. What happens to low frequencies in that space, with the back open like that? I'd kinda guess (and that's all it is) that you'd need to be more careful than usual to have plenty of low frequency aborption, and that what the picture shows wouldn't be enough. I'm partial to the inside out wall/ceiling design that has been discussed on this site. It just makes so much sense that I'm a complete convert... that's what'd get my vote. As re: thickness, I'd use the 1 inch if you can, but at minimum the 3/4. I'd also advocate the flush mount, which you've already decided on.... I don't think you'd have to do anything all that different from the soffit mounts described already on the site... i definitely wouldn't take a shortcut though and just have them open on the back side, because that back side is going to be radiating into your larger room which is open to your control area, and I'd be concerned about impacting the sound in your listening area... especially on the low end. Re the ceiling slope... how do your ray tracings look with or without the slope?

Johnnie wrote:

What happens to low frequencies in that space, with the back open like that? I'd kinda guess (and that's all it is) that you'd need to be more careful than usual to have plenty of low frequency aborption, and that what the picture shows wouldn't be enough.

Yes it's nowhere near the finished acoustic treatment, but that needs to be customized according to what the room needs after monitors & listening position are set. If by "open back" you mean the way the rear opens into another room, that greatly alleviates the LF issues that would be otherwise present from the length mode.

Re the ceiling slope... how do your ray tracings look with or without the slope?

With a good cloud there the ray tracings are somewhat redundant either way. I'll probably go ahead with the flush mounts then experiment with raising the sloped section to whatever point gets me to the best sweet spot with the room modes. I thought Stuart might have a strong opinion there but I guess the only way to know is to test it. I do regret not thinking of the inside out method til afterwards. Though doing it on the front end does conflict with some flush mount fundamentals. I'm tempted to do the middle wall sections though. I have to get the ball rolling again here so I'll go pick up the mdf and look for some neoprene tomorrow to get the boxes done. Still undecided on the stands under the boxes. People usually frame it with lumber but this does go against the emphasis on heavy denser bases under monitors. It seems to me that the requirements of stands should hold just as true here.

ahh.. I thought that was a picture of a theoretical design! Sorry, didn't realize that it was of the work already done. I definitely see how that'd impact the longways room mode, but at the same time, given that sound would function kinda like water, your overall experience would be impacted by the total room and not by just the enclosed area wouldn't it? That'd mean things like a significant increase in the total number of corners, such as wall-ceiling/wall-floor joins which would bump up the low end wouldn't it... or is the dbl level low enough by the time it gets round all the corners and back to the sweet spot, to not have much impact? (I'm asking, not advising... I consider myself a student of this stuff, not a pro)

Wow! Looks like I missed this thread for some reason! :oops: Sorry about that! Oh well, better late than never, I guess! :)

I'm a huge fan of Martin Pilchner's control rooms and wanted to experiment with replicating his inner shell design in a space I'll be working out of for the next couple years.

That's fine, but as Johnnie already pointed out indirectly, the inner-shell is only part of the entire acoustic system that makes up your studio. The inner-leaf and outer-leaf work together in many aspects, but in your case you don't really have an outer leaf, so from that' point of view it is hard to predict what the results will be.

Obviously, isolation wasn't a priority in this endeavour. I didn't want to add the cost of fully enclosing it in the rear and making the low end harder to treat.

Putting the rear wall in will not necessarily make it more difficult to treat bass: The bass response of the room does NOT depend solely on the rear wall. It depends on the overall modal response, which is defined by all of the walls. By "removing" the rear wall, all that you accomplish is making it much harder to predict the response! In essence, you eliminate the one single axial mode associated with that wall, as well as some of the tangential modes and some of the oblique modes, but the rest are all still there, and especially so for low frequencies, which are not directional anyway. So you haven't actually helped yourself much by not building the back wall in the best possible position to give you a good ratio. In fact, the back wall is not even really removed at all: it is only displaced to the location of the next hard, solid, rigid surface, which is the wall of the room. Plus, you now have the situation where the bass is no longer fully contained within the walls, and some of it is now present on the OTHER side of your inner leaf walls, which should never happen.

but at a 70% scale

That is also a problem: While scaling a room up or down does not change the ratio, it still changes the acoustic response of the room, and since 70% is not a musical ratio, if the original design was based on music theory, then the scaled version no longer follows that. There is also the issue that comb filtering now occurs at different locations on the spectrum, since the speakers are now at different distances from the side walls, floor and ceiling, so that too has changed. In other words, even though you might have started with a room that sounded great, by scaling it it might not sound so great any more, since the acoustic response is now very different from what it was in the original room, even though the angles and ratios are still the same. Also, even though the original room might have been RFZ, that does not mean that the scaled version is also RFZ... smaller rooms generally need larger angles on the side walls and ceiling to accomplish that, than large rooms do.

The only concrete nearby is the slab under the hardwood flooring.

Is there any air gap between the slab and the hardwood flooring?

As a result, whatever sound leaves the room doesn't get reflected back by any significant amount.

Well, not really. Your inner-shell is located within an existing room, which most certainly is returning some of the sound. And since the room is an open shell (not sealed, since there is no rear wall), that reflected sound is certainly interacting with the sound retained by the room. The only way that you could have a situation where no sound comes back, is by building the room on top of a fifty foot pole, with nothing around it any any direction for a hundred feet or so. So the issue isn't whether or not sound is coming back, but rather "How much is coming back?", and "At what frequencies?". Also, 5/8" drywall is pretty good at reflecting the entire spectrum: better at some frequencies, worse at others. So the room is actually keeping in a rather large percentage of the sound: If you do a REW test, I'll be you'll be surprised at just how much is staying inside! :)

The angles (as used in MP's design) - Rear sections angle out 5°, then in 8°, then the Typical 30° for speaker walls.

That isn't enough for either flutter-echo control, nor for RFZ. Sorry. Flutter echo needs at least 6° per side (total of 12°), and RFZ for that size room is going to need something more like 15°. Also, the hard reflective surfaces of a room should never narrow down again towards the rear: that creates a compression effect, which is basically an impedance mismatch at the rear of the room, causing reflections back to the front. The room can stay the same width beyond the mix position, or it can get wider, but not narrower. Of course, there can be treatment at the rear of the room that makes it appear narrower, but the actual acoustic boundary of the room should not do that.

This made sense to me since angled walls are less ideal for small spaces.

Actually, the opposite is true: smaller rooms need larger angles, not smaller angles. You can get away with smaller angles if the room is large enough, and very large rooms need no angles at all, but the smaller a room is, the larger the angles need to be to create the RFZ. The same applies to bass trapping: the smaller a room is, the more trapping it needs. I don't see any bass trapping at all in your room.

The ceiling slopes down at 16° starting from the middle of the room and the rear is flat.

That sounds about right, assuming that it slopes down towards the front. That's what the photo seems to show, so it looks like you are fine there.

@Stuart - Seems it's mostly you helping around here these days. I can't begin to express the respect & appreciation for how much time you devote to helping people and how thorough you are in so many replies I've read. You do a great service my friend

:oops: :oops: :oops: Thank you very much! It's good to get feedback like that! It really makes it worthwhile to know that folks appreciate my help.

-Would I be a fool to not go ahead and flush mount my monitors (Focal Twin) in this room?

Nope! Not a fool at all. In fact, it would make yo a genius! :) Those are front-ported speakers, and they have the necessary baffle step correction controls on the rear, so they will sound incredible when soffit mounted.

It would bring my mix position that much closer to the front wall away from the 38% mark.

Not necessarily: the speakers need to be offset from the soffit center-line to reduce artifacts, so if you offset yours "outwards", then you should still be OK. And if that still won't give you a good location in the room, then you can always change the angle of the soffits: 30° is ideal, but there's nothing wrong with 28°, or 25°, or 33°, or even 40°. You can safely go down to about 20° (and up to about 45°) if you really have to. Yes, it changes the sound stage a bit, but also makes the sweet spot wider, and the differences are not a huge deal. Also, many engineers do prefer to be a bit closer to the front wall than 38%, as it just "sounds better". So I wouldn't worry about it too much.

I *could* reverse the drywall to the outside of the studs for that middle section to give me more trapping space.

That is known as "inside-out construction", and is a very good idea. It's not really "trapping" space that increases, though, but rather general space for acoustic treatment.

The room length is also less relevant with the rear being partly open.

Mmm.... debatable! See comments abvoe...

Lightweight construction and a window on the exterior wall makes for no reflection interference.

Windows are actually very good at reflecting sound.... :)

-Should I get rid of my ceiling slope? In hindsight it may have been better not to slope the ceiling with this room height.

That depends on what studio design concept you are trying to achieve. If you want a true RFZ design, then yes, you do need to slope the front section of the ceiling, ESPECIALLY if the ceiling is very low anyway.

The internal ceiling height is 8' 6 1/2" at it's highest. This leaves about 1/8" of space from the existing room's ceiling.

only 1/8" of AIR GAP? Or of gap between the FRAME of your shell and the existing ceiling? There's a big difference, acoustically...

I think I'm going to go ahead with flush mounting the monitors. The front end geometry is ideal for this after all, right?

Right! Or very close. You should figure out the geometry on paper or in SketchUp first, to be sure that you have it correct.

Still not sure if I should get rid of the ceiling slope to give me more room for LF trapping & air gap.

You say you are not interested in isolation at all, and indeed you left the entire back end of the room open so you don't have ANY isolation at this point. Therefore the air gap is a moot point: it has no real meaning. And bass trapping can be accomplished inside the lower section of the soffit, if you use John's design for soffits. So you don't need to flatten out the ceiling, especially considering that it is already probably about the correct angle for RFZ, at a rough guess.

How should I construct the speaker boxes for this size of monitor (Focal Twins)? 1" thick MDF? 3/4" MDF?

It's not just the speaker boxes that you need to worry about: it is the entire soffit design. All the parts work together as a system, so the complete soffit needs to be designed properly.

How tight should the fit be around the top, bottom, & sides? (in rear I'll design for amp venting)

That depends on which of the two main soffit design concepts you want to go with... :)

Should I put anything between the speaker cabinets and the interior of the boxes as a lining? Neoprene around all sides or at least the speaker's bottom?

same as above: that also depends on which design concept you want to follow for the soffits. And if you do go with the decoupled design, then you have to carefully calculate the dimensions of the rubber to put around the speaker, based on its characteristics and on the weight of the speaker itself.

I'd be a little more concerned with the low end of the spectrum. What happens to low frequencies in that space, with the back open like that? I'd kinda guess (and that's all it is) that you'd need to be more careful than usual to have plenty of low frequency aborption, and that what the picture shows wouldn't be enough.

Right! :thu:

I'm partial to the inside out wall/ceiling design that has been discussed on this site. It just makes so much sense that I'm a complete convert... that's what'd get my vote.

Me too! :)

If by "open back" you mean the way the rear opens into another room, that greatly alleviates the LF issues that would be otherwise present from the length mode.

Wellll.... like I said above, it eliminates only one or two of the dozens or hundreds of modes that will be causing you problems. And even them, the main axial mode is not really gone at all! It will still be there partially, due to the reflection off the impedance mismatch where the rear walls of the shell suddenly end into the much large space of the surrounding room (very much like the reflection you get at the open end of an impedance tube), and there will also be a secondary reflection from the more distant hard boundary surface of the surrounding room. So it is not "gone": it is just moved to different frequencies that are no longer easy to predict. And it is just one of many modes that affect your bass response.

With a good cloud there the ray tracings are somewhat redundant either way.

Not really! A cloud only absorbs a small fraction of the wave, at best, so it is still very relevant.

I'll probably go ahead with the flush mounts then experiment with raising the sloped section to whatever point gets me to the best sweet spot with the room modes.

It would be much better to do the exercise in SketchUp first: It's a lot easier to try 20 different positions and angles in SketchUp than it is to tear down and re-build your ceiling twenty times! :shock: :)

I thought Stuart might have a strong opinion

:yahoo: 8) :lol: Yup!

Though doing it on the front end does conflict with some flush mount fundamentals.

Well... yes and no. For the center section, there's no conflict: many people make that absorptive anyway. But for the actual infinite baffles, that does present a problem. However! the front baffle is NOT the actual shell of your studio, as Johnnie already pointed out. The shell continues behind the speaker, to make a sort of triangular shaped cavity that the speaker sits in. The lower section of that can be turned into a bass trap.

and look for some neoprene tomorrow to get the boxes done.

Neoprene is OK, if you can get it soft enough: you'll probably need something like 50 durometer, or maybe even 30. But I would suggest switching to Sorbothane, which is much better for decoupling speakers.

Still undecided on the stands under the boxes. People usually frame it with lumber but this does go against the emphasis on heavy denser bases under monitors. It seems to me that the requirements of stands should hold just as true here.

Here too, that depends on the basic design concept you want to use for the soffits: Fully rigid, or fully decoupled.

but at the same time, given that sound would function kinda like water, your overall experience would be impacted by the total room and not by just the enclosed area wouldn't it?

Correct.

or is the dbl level low enough by the time it gets round all the corners and back to the sweet spot, to not have much impact?

Not really: there will only be a few dB of loss by the time the sound reaches the back edge of the side panels, and at that point there is a major impedance mis-match which will reflect part of the wave back again, with inverted phase. This is just like an impedance tube, or an HVAC silencer box, or a tweeter without a horn: any time there is a sudden drastic change in cross section, the wave is partially reflected and phase inverted. ---- I would suggest that, before you do anything at all, you should first run a full REW test on your room, exactly as it is, and post the resulting MDAT file here, so we can analyze it and see how your room is behaving right now. Based on that, you can decide which way to go and what to do. - Stuart -

Soundman2020 wrote:

Wow! Looks like I missed this thread for some reason! :oops: Sorry about that! Oh well, better late than never, I guess! :)

Heh.. Yes I'm surprised you didn't see this til now Stuart! There's good fun to be had here :)

Johnnie wrote:

I definitely see how that'd impact the longways room mode, but at the same time, given that sound would function kinda like water, your overall experience would be impacted by the total room and not by just the enclosed area wouldn't it? That'd mean things like a significant increase in the total number of corners, such as wall-ceiling/wall-floor joins which would bump up the low end wouldn't it..

Well, sound is directional (varying by freq) and also prone to taking the path of least resistance. If you look at that floor plan you can see the sound is primarily being projected into that rear opening.. which leads to a small guest bedroom occupied mostly by a big bed, and another doorway to a bathroom which is what's located on the other side of the studio's rear wall. The bed absorbs the majority of the low end that arrives into that room but I'll be building a floor to ceiling movable trap for the remainder. It's pretty good without that though. If my room didn't taper in at the rear I'd definitely be sending more sound to the outer area rather than the guest bedroom & bathroom. I'm sure a lot of people would look at that and scoff at the idea of it providing any amount of isolation, but if you walk out to the window of the outer room there is a huge attenuation of sound.

or is the dbl level low enough by the time it gets round all the corners and back to the sweet spot, to not have much impact? (I'm asking, not advising... I consider myself a student of this stuff, not a pro)

To put it one way, I placed a full bag of rock wool in the space behind my speaker and the result was less than placing a single slab in a non-critical location of the inner shell. The SPL's are really low in that window area and there just isn't any amount of mass strong enough to reflect back a significant amount of low end (the only freqs that make it there).

Is there any air gap between the slab and the hardwood flooring?

No gap.

That isn't enough for either flutter-echo control, nor for RFZ. Sorry. Flutter echo needs at least 6° per side (total of 12°), and RFZ for that size room is going to need something more like 15°.

I meant per wall. So 16° total on the middle side walls. This was to match the 16° ceiling which begins sloping down at the midpoint of the room in tandem with the wall splay. The W&H actually hit Sepmeyer ratio 1. The length did too, but I lengthened the room an extra 6" by pushing it forwards (it floats on carpet runners). Stuart is correct in just how much is contained by 5/8" gypsum walls that are properly decoupled from the existing room. After the tests I ran, I concluded that I can safely forget about treating the outer room and focus on what's going on inside the studio.

Putting the rear wall in will not necessarily make it more difficult to treat bass: The bass response of the room does NOT depend solely on the rear wall

If the room didn't have those openings at the rear the rear wall would be MUCH more of an issue. Huge difference. My last room was like this and it was my saving grace. Check this out... this is where I got to with my LAST room and a few pics of the broadband rock wool treatments I used to get there: Can you imagine getting this kind of low end in a room this small? H= 8' 11", W= 8' 7", L= 9' 10" All I had for trapping at the rear of this room was a 2x4 panel and a loveseat! SO much REW testing and adjusting to get there though. The tri traps weren't cutting it so I switched to square soffit style for twice the results. 6" Thick panel along front wall and straddle. 3" thick cloud.

Continuing on...

the hard reflective surfaces of a room should never narrow down again towards the rear: that creates a compression effect, which is basically an impedance mismatch at the rear of the room, causing reflections back to the front. The room can stay the same width beyond the mix position, or it can get wider, but not narrower. Of course, there can be treatment at the rear of the room that makes it appear narrower, but the actual acoustic boundary of the room should not do that.

This is actually a favorite method of Martin Pilchner, a really highly acclaimed (and my favorite) designer. Two well known rooms he did recently with this geometry are deadmau5's new room as well as the B room at http://www.downtownmusicstudios.com/about. That facility is amazing and subject of a few awards & magazine features. Here's a couple pics of one of them being built: The speaker mounts are a double layer which could possibly have a decoupling layer of MLV or Sorbothane between them. Those are BIG monitors though! Novawall stretch fabric wall covers the whole room. I have no idea, but they may have a layer of rigid insulation under the fabric. This is something that does happen on flush mounted front ends of in some rooms to assist in the acoustics for the nearfields. Unlike mine, the ceiling is flat in both those rooms.

The internal ceiling height is 8' 6 1/2" at it's highest. This leaves about 1/8" of space from the existing room's ceiling.

only 1/8" of AIR GAP? Or of gap between the FRAME of your shell and the existing ceiling? There's a big difference, acoustically...

That's 1/8" of space from the big room's ceiling to the top of the studio's framing at it's high section (the flat section at the rear).

I'll probably go ahead with the flush mounts then experiment with raising the sloped section to whatever point gets me to the best sweet spot with the room modes.

It would be much better to do the exercise in SketchUp first: It's a lot easier to try 20 different positions and angles in SketchUp than it is to tear down and re-build your ceiling twenty times!

[/quote]Sketchup doesn't help me with predicting what the low end will be doing in there though. Well, perhaps in the hands of someone who can calculate with all those angles! The low end is the tougher part and my first priority. Don't forget, I attached the sketchup model in my first post. The raytraces seem good to me though. I've only started placing some rock wool slabs in places for preliminary testing to get an idea what I'm up against and assist in getting the monitors placed. Once that's done I can build the treatments needed. First order of business is getting the flush mounts figured out & built which need to get done in the next 2 days. Here's the current Mdat taken at different steps to give you a feel for how the room is responding thus far: http://www9.zippyshare.com/v/73178228/file.html

Well, sound is directional (varying by freq) and also prone to taking the path of least resistance. If you look at that floor plan you can see the sound is primarily being projected into that rear opening..

Yup, but you are forgetting that a lot of it (especially low frequencies) is still being reflected back due to the drastic impedance mismatch where the wall ends. It's the exact same principles as an open-ended impedance tube.

If my room didn't taper in at the rear I'd definitely be sending more sound to the outer area

Actually, you'd be sending LESS sound out the back if it didn't taper, and less still if it flared... :) You really should look into what happens when sound waves leave a restricted tube and hit an unrestricted space beyond that. This is why most musical instruments and speakers have flared horns: to better match the impedance of the sound moving in the tube, to the free air outside. You have a REVERSE flare at the rear of your room, which INCREASES the impedance mismatch, meaning that MORE sound is reflected back into the room, with the phase inverted.

I'm sure a lot of people would look at that and scoff at the idea of it providing any amount of isolation, but if you walk out to the window of the outer room there is a huge attenuation of sound.

I think you are attributing the quietness to the wrong effect. It is quieter in the outer room because a lot of sound is being reflected back into the room by the impedance mismatch... :)

The SPL's are really low in that window area and there just isn't any amount of mass strong enough to reflect back a significant amount of low end

Ummmmm.... once again, you are attributing the observed effect to the wrong cause. Drywall provides very significant reflection down to very low frequencies. Take a look at mass law for the surface density of 5/8" drywall... the Mass Law equation is: TL = 20 log (F * M) - 47 dB where: F is the frequency (Hz), M is the mass per unit area (kg/m²) The surface density of 5/8" drywall is around 12 kg/m2, so at 150 Hz a single sheet of drywall provides about 18 dB of isolation. That's not insignificant. So it is reflecting back or absorbing at least 18 dB at 150 Hz., and probably a bit more due to the mass and rigidity of the studs. In reality, it's more like 20 dB coming back from a single sheet of drywall at 150 Hz.

The W&H actually hit Sepmeyer ratio 1.

Not with that shape it didn't! Ratios are only applicable to rectangular rooms with six sides and parallel walls. That's a ten-sided room with no two surfaces parallel, so simple and simple calculators are not applicable. You can only use ratios to predict room modal response if there are three sets of parallel walls (the ceiling and floor are considered as "walls" here). As soon as you put an angle on one of those, or add an extra wall, then ratios are not longer an accurate indicator of room response. You can see that clearly on your own graphs.

If the room didn't have those openings at the rear the rear wall would be MUCH more of an issue. Huge difference.

That's not what your REW data is saying... :)

This is actually a favorite method of Martin Pilchner, a really highly acclaimed (and my favorite) designer.

Tom Hidley was a highly acclaimed designer in his day. Considered by many to be the best in the world, and still greatly admired even today, for the ground-breaking work he did. He too built rooms with compression shapes to them.... for a while, then later abandoned that design, when he started understanding how it was affecting the room response. He did compression ceilings, but the effect is the same with compression walls.

The speaker mounts are a double layer which could possibly have a decoupling layer of MLV or Sorbothane between them

That's another common myth: MLV is really lousy at decoupling. It is heavy, vinyl, and not very resilient at all. Sorbothane, on the other hand, is great. Some swear by it, saying there simply is no better material available today for decoupling. MLV is in no way comparable to Sorbothane, unfortunately, despite the hype put out by the manufacturers. The data doesn't lie.

Novawall stretch fabric wall covers the whole room. I have no idea, but they may have a layer of rigid insulation under the fabric.

Yup. That's pretty much a given, in order to get decent time-domain and frequency-domain response out of a room that size. The laws of physics are pretty simple and pretty clear about how much absorption a room with a given volume needs in order to attain a given decay. It doesn't matter too much what the room shape is: decay time is mostly a function of overall dimensions, volume, and boundary surfaces.

This is something that does happen on flush mounted front ends of in some rooms to assist in the acoustics for the nearfields.

Well, you can use fabric as a decorative cover on soffits, right on top of the heavy, massive, rigid infinite baffle, but if there is absorption behind it then it is not a true flush mount, and does not follow the same principles, or produce the same effects. That may or may not be a good thing (you can design rooms that way), but you can no longer call it a true soffit mount, or a true flush mount, simply because it isn't.

Here's the current Mdat taken at different steps to give you a feel for how the room is responding thus far:

Cool! I'm downloading it right now... - Stuart -

Here's the current Mdat taken at different steps to give you a feel for how the room is responding thus far:

First comments on the MDAT file: 1) You are doing the tests at a level that is way too low. Either that, or REW is not calibrated correctly. But whatever the cause, that needs to be fixed or your test results are not valid for absolute measurements. REW is showing that you did those tests at an average level of about 63 dB. The standard level is 85 dB for both speakers on, or 82 dB for each individual speaker. If you don't have at least 80 dB average, then there isn't enough headroom to get accurate decay values before hitting the noise floor. At very low levels, there also might not be enough energy present to fully excite all of the modes, so the resulting modal analysis is not telling the truth about the room. 2) There is no calibration file for the mic (although there is one for the sound card), so the results are not valid. Depending on what mic you are using, you can either download the file from the manufacturer's web site, or send your mic out to get it calibrated by a company that does that. 3) You don't say which speaker was used to do that testing, or where the mic was positioned. 4) One of the measurements has a curious comment on it: "flatten LF eq". Please don't tell me you are trying to use EQ to fix room acoustic problems? :shock: That doesn't work. (Once again, despite the hype spread by manufacturers of some speakers and some "room correction" devices / software). IF you are using some type of EQ this early in the treatment, then that needs to come out right now and you need to re-do the measurements. EQ can be used as a last resort, right at the end, to help smooth some of the few remaining details (provided that you are aware of the sever drawbacks and artifacts), but it should NEVER be used until all the acoustic treatment options have been exhausted. OK, so maybe I'm over-reacting and all that you did was to adjust the baffle-step correction controls on the speakers themselves. If that's all it was, then please excuse the above rant! I'm just not a big fan at all of using EQ to try to fix problems that it simply cannot fix. (Having said that, the change to the response before and after that "flatten LF eq" step is not what you'd expect from adjusting baffle step response...) As soon as I have some free time, I'll do a more detailed analysis, but those are the initial red flags. - Stuart -

... more on the REW tests. The biggest single issue is the huge mode at about 55 Hz. that is undoubtedly your 0,1,0 mode, associated with the room width (theoretically it should be at 56.5 Hz, but the room walls are angled so that explains the difference). To treat that in a normal rectangular room, you would put bass traps in the front and rear vertical corners, but you don't have rear corners, and the front is being used for full-length soffits, so the only options open to you are the wall/ceiling an wall/floor corners on the side walls. They will have to be pretty massive to damp that mode: it's pretty wild. Or you could switch your soffits to John's design, and put bass trapping in the lower section. Then there's the 1,0,1 mode at 82 Hz. (theoretically 84.2 Hz), which strangely enough involves the rear wall behind the sofa, even though you insist that there is nothing happening at that rear wall... :) Then there's the "little sister" of that same mode: the 2,0,1 mode, at 116 Hz. That also involves the rear wall, which is why you aren't seeing much change in it as you have treated the room so far. Then there's the other big one at about 139 Hz, which could be either the 3,0,0 mode at 137.5 Hz, or the 1,2,1 oblique at 140.9 Hz. But I'm very inclined to go with the 3,0,0 mode, since obliques are not usually that big, and I can't see any reason why an oblique would even be there, with that shaped room. It is also not changing much with the treatment so far: another good reason to suspect 3,0,0. So if that is your 3,0,0 mode, then that is also directly associated with the rear wall that you insist is not involved... :) Finally, there's the overall decay: It's around 180 ms and has hardly changed at all, despite all the treatment. And the area where it has changed least is in the low end: It started out at around 510ms, and is now down to about 450ms. That won't change until you start putting in some serious bass trapping. However, you are going to need to do some interesting tricks to accomplish that, as you also need to put some low-level reverberant field back in the room. Right now, it is too dead overall: The ITDG is fairly well defined, but the level after that is too low. It's almost like an old LEDE room, which you certainly don't want! One question: What is the distance from the tweeter cone of the speaker, going straight back to the point where the side walls end at the rear? It seems to be about 8'? - Stuart -

Soundman2020 wrote:

If you look at that floor plan you can see the sound is primarily being projected into that rear opening..

Yup, but you are forgetting that a lot of it (especially low frequencies) is still being reflected back due to the drastic impedance mismatch where the wall ends.

I'm not sure I follow there. To put it simply, if those rear doorways were not there, the rear of my studio would have a significantly higher SPL and require more than just broadband trapping. The doorways alleviate the pressure at the rear of the room as a matter of physical fact.

If my room didn't taper in at the rear I'd definitely be sending more sound to the outer area

Actually, you'd be sending LESS sound out the back if it didn't taper, and less still if it flared... :) This is why most musical instruments and speakers have flared horns.. You have a REVERSE flare at the rear of your room, which INCREASES the impedance mismatch, meaning that MORE sound is reflected back into the room, with the phase inverted.

Your second sentence here appears opposite to the first! In the first you're saying if it was flared I'd be sending less out, but go on to say the taper is containing more sound within the room (which is correct and what I said). If you walk into that rear room it's just like walking further into a room, whereas going out the rear right wall exit provides an immediate and significant attenuation once you're on the other side of the wall.

I'm sure a lot of people would look at that and scoff at the idea of it providing any amount of isolation, but if you walk out to the window of the outer room there is a huge attenuation of sound.

I think you are attributing the quietness to the wrong effect. It is quieter in the outer room because a lot of sound is being reflected back into the room

I don't want to get into semantics, but the important thing is the studio shell is attenuating the sound transmission to the larger outer room and it's not loud at the window.. and nothing going on in that outer room or window area is causing any measurable significant impact to the sound inside the room. No matter where I place absorption in that outer room.

The SPL's are really low in that window area and there just isn't any amount of mass strong enough to reflect back a significant amount of low end

Ummmmm.... once again, you are attributing the observed effect to the wrong cause. Drywall provides very significant reflection down to very low frequencies.

Like I said, I placed 8 slabs of rock wool there and tested to confirm this. The 5/8" drywall of my studio shell is greatly reducing transmission through the front wall plus making it that much harder for what filters through it to bounce off the front window wall and pass back through the drywall to affect anything at the listening position. If there was concrete there then it'd be a bit different. But right now, the greatest mass is the 5/8" drywall of my shell. What LF breeches the front wall of the studio is greatly attenuated and does not get reflected back into the room by anything in the window area.

If the room didn't have those openings at the rear the rear wall would be MUCH more of an issue. Huge difference.

That's not what your REW data is saying...

You saw what I achieved in my previous room despite the bad dimensions right? This would have been impossible otherwise. It makes a HUGE difference when a room has such rear openings leading to extra space and absorptive objects. REW confirmed that any treatment I make in that rear room trap cavity is effective at a small fraction of what you get placing the slabs in the front end and has been ineffective at reducing the null in the 90hz region which is the worst issue currently.

This is actually a favorite method of Martin Pilchner, a really highly acclaimed (and my favorite) designer.

Tom Hidley was a highly acclaimed designer in his day. He too built rooms with compression shapes to them.... for a while, then later abandoned that design, when he started understanding how it was affecting the room response. He did compression ceilings, but the effect is the same with compression walls.

Sure, but it's not the 80s anymore. We're talking about a design which is being currently used by a world renowned designer who's been designing rooms and teaching acoustic design in universities for the past 30 yrs. It's safe to say he understands the effects of the angles he's implementing 100%. There is absolutely a difference between compression that begins at the front of the room vs compression that begins behind the mix position. In my case, we're talking about a 4' section of wall that tapers in 5° per side. Regardless of front angles, I've never seen him use more than a 5° angle per side on the rear section and never with a compressed ceiling above. Still, with the room built and more pressing matters to think about, it's a waste of time to dwell much on things like this or the rear doorways.

MLV is really lousy at decoupling. It is heavy, vinyl, and not very resilient at all. Sorbothane, on the other hand, is great. Some swear by it, saying there simply is no better material available today for decoupling. MLV is in no way comparable to Sorbothane

True. And the best way to implement sorbothane is to consult the company with your details to tailor the correct thickness, durometer, & strip orientation.

Soundman2020 wrote:

1) You are doing the tests at a level that is way too low. Either that, or REW is not calibrated correctly. But whatever the cause, that needs to be fixed or your test results are not valid for absolute measurements.

Absolutely. A quick glance at the signal vs noise floor should clear that up ;) I never had a need for absolute dB levels so my levels aren't accurately calibrated for that. I do my measurements around 85-90dB though. The current set are about 85. Any louder would be unnecessary at this (rough early) stage especially. When I'm narrowing in I usually do around 90dB but it's not good for right now when I'm doing a lot of late night sweeps. I've got a ways to go before I get to that stage though as my monitors aren't even mounted yet.

2) There is no calibration file for the mic (although there is one for the sound card), so the results are not valid.

Dayton EMM-6. I realized halfway through that the calibration file wasn't loaded so I disregarded it for continuity. I'm in rough early stages and it makes very little difference to the low end so it's fine for what I've been doing so far. I'll add it when I'm doing the flush mounts.

3) You don't say which speaker was used to do that testing, or where the mic was positioned.

That set's all stereo, which is all that's needed for now since I don't even have the monitors in yet. Monitor & listening position need to get taken care of before anything else. The mic position distance is listed in places where it was changed. For consistency I measure from the green light on the speaker.

Please don't tell me you are trying to use EQ to fix room acoustic problems?

Of course. That was the LF EQ on rear of the speaker since I had it at +3dB in my previous room. The new room will be much more efficient for LF response and I'll be reducing that further for flush mount compensation. Anyhow, the current issue at hand needing to be figured out is the flush mounts for the monitors. I'm really eager to get this moving forwards!

Alright.... The all important flush mounts! Adding mass and reinforcing the speaker boxes before any decoupling just makes sense to me. I'm thinking to build a tight fitting (the kind you can't remove without unscrewing) MDF box supported by concrete blocks. No contact point with the front wall and I can also add an extra layer of 5/8" gypsum to the backside of the speaker walls (notice the missing center stud in the pic - I left it wide open to accommodate later flush mount framing and wall reinforcement). How does that sound? I don't think that stand mass alone is enough though.. so what about (load matched) sorbothane hemispheres between the MDF boxes and the concrete blocks? That seems like a rock solid plan that would also be fully decoupled. I'm curious to hear your thoughts here though! The sorbothane will be a 5 day delay so I'd want to order them asap. 30 duro is best but I'd either need to go with three big 2" dia, 1" thick hemispheres or around seven 1.5" dia, 3/4" thick hemispheres. IIRC, the 1" thick sorbothane has a resonant freq of 10hz.