Third Try is the Charm? Finalizing design..

OK - So, I originally tried to get help with laying out my space.. and John drew me up an amazing design to get started. That's here: Then, I posted some pictures of the space with more detail-oriented questions. That's here: Lastly, I thought I was getting close and realized the entire room was 180o backwards. That's here:. Now - I think I've finally got it right!! Opinions? Thoughts? Comments? I think I have a pretty good idea about HVAC - will update this thread when I add that detail into sketchup. I'm also trying to figure out how exactly to add mass to my subfloor (I have Georgia-Pacific wood I-beams, not regular 2x joists) because of the 'i-beam' shape.. more on that later. Attached below are the latest sketchup file (zipped) and a couple of images.

To me, it looks like you have some unnecessary walls between your air lock and your control room/booth.

The 'wall' at the 45o angle is the speaker soffit - so no 'mass' per se.. I was trying to make sure there were 2 leaves at every location. If you grab the sketchup file - there's a couple of layers you can make visible that show where drywall goes. Thanks!

Anyone else care to comment?

Well, I see quite a few issues there: 1. When I turn on the layer called "controlroomdrywall", which I imagine is intended to be the inner leaf, it shows drywall on the soffits. Soffits are not part of the inner leaf. 2. The same layer also shows drywall on the face of the rear bass traps, where it does not belong, and nothing on the actual inner leaf frame at the back, where it does belong. Bass trap would probably work better if they were inside the room, instead of outside it, in the MSM air gap. 3. You have a quadruple-leaf system between the live room and the outside world, through the sound lock. 4. There are several sections of framing that don't seem to be doing anything useful 5. The front section of your CR ceiling slopes up at an angle of nearly 18 degrees. That seems rather steep. Is there a reason for that? I've seen recommendations for an angle in the range 10 to 15, and most designs here seem to have settled on 12 degrees, or thereabouts. 6. Your soffit walls are at different heights, two different widths, and set at two different angles. The speaker axes therefore do not intersect at the same height, not do they intersect on the central axes of the room (axes of symmetry), and the speakers are not at the corners of an equilateral triangle. That makes it really hard to figure out where your listening position is, but as near as I can tell it seems to be at about 45% of the room depth, which seems pretty close to 50%. Those are the biggies I noticed at first glance and wimple measurements. What ratio is your room based on? I couldn't figure it out. - Stuart -

1. When I turn on the layer called "controlroomdrywall", which I imagine is intended to be the inner leaf, it shows drywall on the soffits. Soffits are not part of the inner leaf.

Stuart, I undestand soffits are not part of the inner leaf, but how come in bassman's build, it appears as if he used drywall on the soffit wall? viewtopic.php?f=2&t=10533&start=60 - right under "itchy mcsuffnpuff" I have seen this elsewhere, and am quite curious to know the reason on it (not?) creating a triple leaf.

Stuart, I undestand soffits are not part of the inner leaf, but how come in bassman's build, it appears as if he used drywall on the soffit wall?

Well, you need mass on your soffit panel. Lots of it. Drywall is reasonably good as mass(!! :) ) MDF, HDF, concrete, steel plate, lead sheet, etc. are also good for soffit panels. The denser the better. The soffit panel is doing its best to pretend that it is an infinite baffle, so the more mass you can put into it, the better. Occasionally you see folks here proudly show of their soffit walls that are just speakers stuck in the middle of a huge pink fluffy bass trap, with only acoustic cloth over it: that won't work! I have no idea what it will do, but I do know that it most certainly will NOT be an infinite baffle, which is the entire purpose of a soffit. So why is it not a third leaf? Personally, I think it is! I would imagine that, to a certain extent a soffit actually IS a third leaf, just like a panel absorber is a third leaf, to a certain extent. But consider the following: 1. It does not fill up the entire wall: Worst case, it only covers maybe a quarter of the wall, left to right, and maybe half or so vertically. Maybe more. But never the entire wall. 2. It is not over a sealed cavity. You don't want your soffit to be sealed! Yeah, it certainly is true that you can still have a third leaf without it being sealed, but see (1) above: The soffit panel isn't very big compared to the entire wall, so the effect is not that great Theoretically, if you hold a large book (such as an atlas) close to the wall, you create a third leaf, but obviously the effect is minimal. (OK, soffits are bigger than atlases, but you get the point.) 3. The soffit is not in front of the speaker: it IS the speaker! I'm still trying to think this one through, but it seems to me that waves on the soffit panel are traveling across its surface, spreading out like ripples on a pond, and are not hitting it head-on, as they would if the same panel were at the back of the room. That must make a difference. Of course, it still gets hit with sound coming back from other places in the room, but that will hopefully already be several dB down, and it never gets hit with direct sound from the speaker. Like I say, I'm trying to check this and see if I'm on the right track here, but I'm not having much success. It just seems logical. But take that with a pinch of salt: Lots of stuff that seems logical in acoustics, actually isn't logical at all! :) I'm hoping one of the acoustic experts here can either confirm this, or shoot me down in glorious technicolor flames, and make me feel like a dunce.... 4. Other minor stuff: the soffit is angled steeply (at least 30 degrees, maybe more) to the second leaf, not parallel to it, so I reckon that must have some effect too. Maybe you could say that it will be a "broadband" third leaf, if there is such a thing! Also, it is massive, and held rigidly in place. So my take is that the third-leaf effect is going to be small, at best, and that the big advantages to be gained by soffit mounting strongly outweigh the third-leaf disadvantages. Anyway, that's my line of reasoning: It actually is a third leaf, but the effect is minimal. Of course, I might be totally wrong on that! It wouldn't be the first time.... - Stuart -

Wow, thanks for the input Stuart, that clears some stuff up for me, let me know if you find anything else out in your continuing adventure into the acoustic infinity.

Soundman2020 wrote:

Well, I see quite a few issues there: 1. When I turn on the layer called "controlroomdrywall", which I imagine is intended to be the inner leaf, it shows drywall on the soffits. Soffits are not part of the inner leaf.

Sorry about the naming convention and lack of a color key - the tan color is drywall, the maroon color is acoustic treatment of one sort or another (soffits, slatwall, bass traps in rear).

2. The same layer also shows drywall on the face of the rear bass traps, where it does not belong, and nothing on the actual inner leaf frame at the back, where it does belong. Bass trap would probably work better if they were inside the room, instead of outside it, in the MSM air gap.

see above

3. You have a quadruple-leaf system between the live room and the outside world, through the sound lock.

This was the reason for the thread I started a while back about the distance between leaves and when the third leaf becomes far enough away to not be a leaf anymore, which you helped me out with. viewtopic.php?f=2&t=11521 That small hallway isn't really going to be an airlock, per se - the doors that lead to the mechanical room and the rest of the house will NOT be heavy sealed doors, only the doors leading into the 2 studio rooms. I figured that there was enough space in there to not act like a 3 or 4 leaf wall. [edit] if you're referring to the section around the soffit/corner of the control room - I see what I did wrong when drawing it.. will fix it[edit]

4. There are several sections of framing that don't seem to be doing anything useful

probably - which is why I need extra eyes on it! Which sections, specifically (I suspect around the front of the CR - that was my attempt at keeping everything at 2 leaves while still making the soffits in there)

5. The front section of your CR ceiling slopes up at an angle of nearly 18 degrees. That seems rather steep. Is there a reason for that? I've seen recommendations for an angle in the range 10 to 15, and most designs here seem to have settled on 12 degrees, or thereabouts.

Mostly because I have to start it down around 6' at the low point, and want to get it up out of the way to allow for the door.. I can play with angles, but I think if I go much shallower - I won't be able to get a door in there without cutting off a bunch of the drum room.

6. Your soffit walls are at different heights, two different widths, and set at two different angles. The speaker axes therefore do not intersect at the same height, not do they intersect on the central axes of the room (axes of symmetry), and the speakers are not at the corners of an equilateral triangle. That makes it really hard to figure out where your listening position is, but as near as I can tell it seems to be at about 45% of the room depth, which seems pretty close to 50%.

I think that's mostly because I suck at sketchup. I'll go back and try to clean it up a bit better, but I was shooting for the listening position around 40%, maybe a hair less (about 6.5' back from the front wall).

Those are the biggies I noticed at first glance and wimple measurements. What ratio is your room based on? I couldn't figure it out. - Stuart -

Ask John - this is just some minor modifications to his original drawing first posted here: viewtopic.php?f=1&t=7057 I just flipped it 180o to make the front of the room the end with the sloping ceiling (if you look at the pictures in my other thread, you'll see the ductwork that I'm working around - which is why the slope has to be on that end). Thanks!!! "-)

Sorry about the naming convention and lack of a color key - the tan color is drywall, the maroon color is acoustic treatment of one sort or another (soffits, slatwall, bass traps in rear).

I don't think it is just an issue of naming: I turned on all of your layers, and if the stuff on the soffits is acoustic not inner leaf, then I can't see any inner leaf at all! Did you forget to put it in? It should be on the inner leaf frame behind the soffits, and also on the inner leaf frame behind the bass traps at the rear.

That small hallway isn't really going to be an airlock, per se - the doors that lead to the mechanical room and the rest of the house will NOT be heavy sealed doors, only the doors leading into the 2 studio rooms. I figured that there was enough space in there to not act like a 3 or 4 leaf wall.

Ahhh! I think I recall that discussion, from a while back! It still might be an idea to get the drywall off the outside of the studs on the wall from your live room into your sound lock, as that really is not doing anything good for you, and would at least take you from a 4-leaf to a 3-leaf.

Which sections, specifically (I suspect around the front of the CR - that was my attempt at keeping everything at 2 leaves while still making the soffits in there)

Yup, that's it. But don't take out the frame yet! Now that you clarified your color code, I think that frame should have drywall on it, and be your inner leaf. Your soffit panels do not really count as a "leaf", and they should not be part of the inner leaf. - Stuart -

Well - the soffit angle/listening position issue has been cleared up.. I can sit where I want. I spent about an hour on the phone with the designer of my monitors, and he said in no uncertain terms 'do NOT soffit-mount those speakers! They weren't designed for it, and it'll kill their low-end response.' So, that clears up at least one issue.. the front of the room can just be bass-trapping of my choice. I'm in the process of really cleaning up the drawings... stay tuned.

What kind of monitors are they again???

They weren't designed for it, and it'll kill their low-end response.'

Huh? That's kind of hard to figure! Soffit mounting should theoretically give you a large BOOST in the low end, not a REDUCTION! Soffits act as infinite baffles, which forces the speaker to radiate into half-space, so there should be a 6 dB boost in the low end, not a drop. I'm wondering what design of speaker could reverse that, and why... What make and model of speakers do you have? - Stuart -

I know that I mentioned to my Sweetwater guy that I would be soffit mounting my monitors and he tried to talk me out of it. I think people don't understand the benefit, and most likely think it's a poor idea. A little more research needs to go in their end in order to be able to argue the concept of soffit mounting nearfield monitors.

Picking up a set of Truth Audio TA-1Ps.. from the guy who designed them. Truth Audio is sadly defunct due to the death of one owner, and a couple of hurricanes (they were on the Florida panhandle)... great monitors, just weren't around very long. The guy who designed them lives near me and is going to part with one of his sets.. I figure since he designed them (and REALLY knows speaker design) that he would understand soffiting (he does). I'll be speaking with him again shortly - maybe I misunderstood the low-end comment and why he recommends NOT soffit-mounting the speakers. Will report back.

I'll be speaking with him again shortly - maybe I misunderstood the low-end comment and why he recommends NOT soffit-mounting the speakers.

Whatever the technical explanation is, I would like to understand it. If there is some type of speaker design that can destroy low end response by soffit mounting, then that might be applicable to other designs, too. So I'd like to understand the reasoning and the theory behind that. Could you ask him to give you an explanation? It sounds very interesting, and is something that we all should be aware of, if there is a potential issue that destroys the low end from soffit mounting. If you can't soffit mount them, then you obviously also cannot put them anywhere even close to walls. So it looks like you'll need a major re-design of your studio front section, that will allow you to keep the speakers a couple of meters away from all the walls. Otherwise you will have all of the usual nasty issues associated with placing speakers too close to walls. Unless, of course, he is only talking about the speakers not having any built-in method for rolling off the bass to compensate for the soffit boost. If that's the case, then somewhere here on the forum there is a circuit design that you can build, that will do exactly that for you. It rolls of the bass response of speakers that do not have the ability to do it themselves. - Stuart -

The Truth Audio TA-1P box is rear ported.

Yeah - thanks for the info.. I picked up the Truths a few weeks ago, and they are definitely rear-ported. They're also freaking amazing monitors! It's really a shame that the company didn't survive.

The Truth Audio TA-1P box is rear ported.

Ahhh! Now THAT makes sense.

I may actually try to work with the guy who designed these - and build a set of mini mains for myself that are meant to be soffit mounted. This guy is seriously gifted in designing phase-coherent crossovers - I heard some more speakers that he designed when I was there at his place.. wow. that said, most mixes will be done on these Truth Audios... they're just amazing.