John Sayers' Recording Studio Design Forum Archive

Well, I'm back at it after 2 months of family obligations. I've got version 6 going on the speaker soffit design. Been drawing in places like ER waiting rooms, etc...
Here is the revamped framing for the right soffit. More-robust framing and the two plywood "shelves" are shown. The absorber assembly attaches to the lower shelf (also shown). I have been woriking with drawing in the bass trap hangers above and below the speaker. I came up with two versions so far, trying to get as much height, width and quantity in that space and, at the same time, allow ventilation for the speaker. Here is version A withing the framing: ... and again, with frame removed for visibility. Gray is Roxul and the panels are 3/4" Homosote with 1" 703. I couldn't find a way to get a "fan shape" within the geometry of the soffit. The hangers would overlap in the back and be too far apart in the front. Going straight out like this seems to allow the most hangers. The last one on the right is perhaps useless, though, since it is so shallow (only 4 7/8"). Maybe fill that area with Roxul?: Here is version B. I tried angling the panels to the right. Again, there is that skinny space left over with a narrow leftover hanger! I don't think it bought me anything! : Now for ventilation... I have a triangle opening on the lower shelf behind & under the speaker that is about 77 square inches to allow the air path from the lower trap area up through the upper trap area. I have a couple of bird's-eye views here to show what it looks like looking straight down (Top "shelf" hidden for visibility): The 2nd view has one of the hangers removed so you can see the path down past the shelf into the lower area. The panels are 1" apart in the drawing.
Here is the current complete right assembly, showing the gray grills, one on top and one on the bottom. The opening on the top grill is 64.5 sq. inches and can easily be made larger. The bottom grill is 693 sq. inches: I really could use some comments on the best layout of the bass traps and on the ventilation scheme. Should I sacrifice some depth of the middle two hangers to allow for more air or will that suffice?
As always, very thankful for your valuable inputs!
-Ron

Well, I'm back at it after 2 months of family obligations. I've got version 6 going on the speaker soffit design. Been drawing in places like ER waiting rooms, etc...

I hope things are alright on the family front dude!

Here is the revamped framing for the right soffit. More-robust framing and the two plywood "shelves" are shown. The absorber assembly attaches to the lower shelf (also shown).

Here is version A withing the framing:

This one is better for sure.

the panels are 3/4" Homosote with 1" 703.

You might be better off using 1/2" Homasote. This would allow for more insulation which would be more beneficial. If the Homasote is too expensive, you could use 2" insulation with it as well... or a combination.

I really could use some comments on the best layout of the bass traps and on the ventilation scheme.

I'd put a divider type panel above your speaker that would connect your left and right vertical studs. It will strengthen the assembly and also allow you to easily fill the speaker area with loose insulation. You'll just have to cut your ventilation hole in it like you did the bottom divider.

Should I sacrifice some depth of the middle two hangers to allow for more air or will that suffice?

There isn't too much heat to move. I believe you have more than enough space!

Greg

Thanks for your input, Greg! I'm beginning to think that the design for the speaker soffits (Right and Left) are almost build-ready! Of course, I will have to design the area BETWEEN the left and right - above and below the window before I get going.

I hope things are alright on the family front dude!

Thanks. My 91-year-old dad is near the point of going into assisted care. He's been in the hospital 5 times in the last two months. Since I'm the sibling that lives 2 miles away, I'm on the front lines. Being widowed myself and working 11 1/2 hour days, it is a challenge, not to mention putting time on the studio too.

You might be better off using 1/2" Homasote. This would allow for more insulation which would be more beneficial. If the Homasote is too expensive, you could use 2" insulation with it as well... or a combination.

Not sure what you mean here by 2" insulation. Can you clarify? I realized after drawing it that I probably should have done 1/2" homasote. I'm trying to find out the difference between "homasote" (if I can find some) and "sound board" (half the price). I've used sound board in the past, but it had an odor. I learned that they changed how it is manufactured now, containing no formaldehyde. It had an odor before, but not now. I also noticed 2'x4' ceiling tile that looked similar and is near the size I need for the soffit area. I want to find some specs on these items and compare before spending a lot on something that may not be much better. I supposed DENSITY is what I'm looking for?

This one is better for sure.

Yes (speaking of version "A"), my opinion too. I'm thinking about taking that skinny last hanger on the right out and "fanning" out the rest of them on the front end, perhaps making some of the pieces a little longer? Do you think that would help or take away from the effectiveness?
Thanks again!
-Ron

Any feedback on my questions?

Hi Ron,

Sorry I didn't get back to you. Thanks for the nudge!

Not sure what you mean here by 2" insulation. Can you clarify?

In this picture, you can see some of my hangers on the right. They are 1/2" thick Homasote with 2" thick insulation screwed to either side.

I supposed DENSITY is what I'm looking for?

Homasote serves several purposes. Mainly, it is quite strong but not very rigid. Also, it actually has decent acoustic absorption characteristics. So, I wouldn't say you're only looking for a product with a similar density.

I'm thinking about taking that skinny last hanger on the right out and "fanning" out the rest of them on the front end, perhaps making some of the pieces a little longer? Do you think that would help or take away from the effectiveness?

Basically, get your cavity as packed full of hangers as you can without them being close enough to risk touching one another. Also, the bigger they are, the better they will work. So, juggle what you have and try to fulfill those needs the best that you can. You're doing great!

Greg

Thanks Greg! I'll tweak the panels and start drawing the mirrored images for the left speaker. Then I can go to work on the middle section above/below the window.

Homasote serves several purposes. Mainly, it is quite strong but not very rigid. Also, it actually has decent acoustic absorption characteristics. So, I wouldn't say you're only looking for a product with a similar density.

Do you know anything about those 2' x 4' lay-in ceiling tiles? Would they be comparable to Homasote? They would be a pretty-good size for my speaker sections if they would work acoustically. I'm trying to understand if there is some tangible difference between "sound board", homasote and ceiling tile materials. It would be good to find some spec sheets, if I knew what specs I'm looking for.

Do you know anything about those 2' x 4' lay-in ceiling tiles? Would they be comparable to Homasote?

I know there are several types out there. Some are even just 703 type fiberglass! Some are drywall-like. So, it is impossible to say whether they would work.

I'm trying to understand if there is some tangible difference between "sound board", homasote and ceiling tile materials.

Try to find some pictures, videos or data sheets for your products and hopefully you can make an informed decision. I wish I had an answer for you other than use Homasote if it's available in your area.

It would be good to find some spec sheets, if I knew what specs I'm looking for.

Find something that specs similar to Homasote acoustically and in density. You also don't want something that is going to deteriorate or vibrate your anchoring screws (the ones holding your insulation on with fender washers) out over time. None of us want to be tearing into our walls to fix hangers, ever!

Greg

Thank you, Greg. I will do my research I thought someone else had surely been through this before and didn't want to re-invent the wheel. That can be interpreted as "I'm lazy, just tell me what I need to know". Of course NONE of us are like THAT! ...... Right???

Hi Guys, most Soffit Mount Designs I have seen used only light fibre, suspended against sagging here and there by wires or shelves.
It's been a while but any hanger designs I have seen, e.g. Newell, were vast and involved that 'lobster pot' effect caused by angling the big sheets.
As yet I haven't seen anything to suggest they perform better than simple fibre, perhaps with 'membrane' layers to act in a membrane fashion, or a gradient of densities.
I have seen Eric write of similar doubts.
I am of course interested in the idea, given that several successful and trusted by me Acousticians use them.
What am I missing?

Hangers work like waveguides, mainly. There are several acoustic processes going on at once in a set of hangers, but the main one is that they act as waveguides, redirecting the path of the wavefront along the surface of the actual panels, where it meats with the porous absorption and is attenuated, as well as being further absorbed when it finally hits the wall behind the hangers. The reflected wave then encounters the panels once again, but this time somewhat normal to the panels, so it pretty much hits a partly solid wall again, being further absorbed, and the part that is transmitted the goes on to encounter additional panels on its wya back out into the room. There is also some panel resonance if you get lucky, or at least bending wave absorption in the panels, and possibly also some resonance between adjacent panels, but those are minor effects when compared to the waveguide effect. And of course, there's also the large impedance mismatches that the wave encounters at several point along its path through the hangers.

So there's lots going on in there, which is why they are so effective, when done properly. The core needs to be fairly solid, but not too massive, and also act as a damper somewhat, which is why Homasote works so well here. Cork is another option. Thick cardboard too. Somewhere in between a lip membrane and a rigid plate seems to work best. The insulation also needs to be fairly low density, as it must act on low frequencies, and the wave also "sees" it at grazing angles initially, but then also closer to normal after the wall bounce. The hangers need to be kept from touching each other, so the don't interfere with the panel resonance or bending wave resonance, so they are hung loosely, and spaced sufficiently to allow all of the above to happen. Spaced too close, and the impedance mismatch at the front is too high, so it just acts like a bunch of porous absorption, not like a waveguide. Spaced too far apart, and the reverse is true: it acts more like a bunch of empty air with porous absorbers in it, not like a waveguide. Angles are important too. It seems that an angle of about 40° to the wavefront works best. I ave no idea why: I haven't gone that far into theory. Just far enough to get why they work so well.

- Stuart -

Thanks Stuart. With LF traps one inevitably ends up back at the same question. Which works best?
Eric tested and replaced them.
http://forum.studiotips.com/viewtopic.php?t=820

But Eric also expresses puzzlement as to why they work so well.

Perhaps he is just being respectful and maybe other peoples implementations work better than the Eastlake ones he (and subsequently they) abandoned.

I have read about them, and my abiding impression is just questions. What is a waveguide? I get it with tweeters but hardly at LF.
Looking at Newell implementations I can see the Wave front being redirected a bit. Reguided perhaps, but it depends how you look at it. Overall the Wave still hits the back wall with just a momentary nuisance detour. Perhaps that is effective by removing some energy?

I'm thinking about taking that skinny last hanger on the right out and "fanning" out the rest of them on the front end, perhaps making some of the pieces a little longer? Do you think that would help or take away from the effectiveness?

Front end, meaning the side facing me at the front of the speaker. Stuart, would you like to weigh in on that? Do I have it right or am fanning it out backwards?
I'm going to redraw, showing 1/2" Homasote and ejither 1.5" or 2" fiberglass on the panels.

Guit-picker wrote:

I'm thinking about taking that skinny last hanger on the right out and "fanning" out the rest of them on the front end, perhaps making some of the pieces a little longer? Do you think that would help or take away from the effectiveness?

Front end, meaning the side facing me at the front of the speaker. Stuart, would you like to weigh in on that? Do I have it right or am fanning it out backwards?

By "fanning them out", I assume you mean that each hanger would go at a slightly different angle to the room? For that space, there's probably not much in it, between fanning them out and leaving them straight. I don't think you'll be able to angle them very much, so it would probably be better to not remove that last one: I'd say that "more is merrier" here. If you have to take one out to fan them, then you are losing all that surface area....

I'm going to redraw, showing 1/2" Homasote and ejither 1.5" or 2" fiberglass on the panels.

Yup! Time for an update in your model / pictures! So we can see where you are right now...


- Stuart -

Thanks Stuart. I'm off for TWELVE WHOLE DAYS for Christmas/New Years and hope to have a new drawing to post.
Merry Christmas and a Happy New Year to all of you forum friends!
So very thankful for your help!
-Ron

Merry Christmas to you as well!

- Stuart -