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PostPosted: Tue Feb 26, 2013 5:22 pm 
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1) i would go with the semi-rigid insulation and cloth.
2) if you can tap off the output air from the iso box and flow it up around the speakers while keeping those boxes sealed, you're better off.
3) you need framing to hold the speaker box nice and solid. the speakers are decoupled from the box and not touching the face plate (but you ultimately seal around that). the boxes should (assuming you're ducting them) be sealed all around.
4) blue - loose insulation, green - hangers or loose insulation behind slats or other absorption/diffusion
5) you can do slats and hangers but if you don't seal the slats, they are not operating as Helmholtz resonators. you might make a slat box in the center section and make the lower and upper sections loose insulation for absorption.
6) i'd pick one side or the other below the stereo speakers for the sub and use your crossover/etc as needed to time align and set the actual x-over etc.
7) 10 degrees is pretty much maximum. so even though the 300's are "softer" than say ADAM or horns, you might try an experiment to set the speaker on a (crudely made lumber) stand (which matches the proposed height) to test the angles and see how you feel about them sitting @ 7 and @ 10.

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PostPosted: Tue Feb 26, 2013 11:01 pm 
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That is great, Glenn! I think I am almost there to start with the full design. Only these questions left at htis point:

gullfo wrote:
2) if you can tap off the output air from the iso box and flow it up around the speakers while keeping those boxes sealed, you're better off.
3) you need framing to hold the speaker box nice and solid. the speakers are decoupled from the box and not touching the face plate (but you ultimately seal around that). the boxes should (assuming you're ducting them) be sealed all around.


I wasn't sure, if the hot air from the speakers would cause a problem for the speakers. But it is the most elegant solution for sure, so I will go with it! Regarding the speaker boxes: sylomer has to compress by 20% to act decoupling. If the speaker would just stand on four pieces of sylomer, I would simply determine the right amount, adding piece by piece or calculating it from the weight of the speaker. If I understand you correctly, you say I need rubber from all sides connected to the speaker box. How would I find out the right amount for that? And is the setup right, as I shown here?

Attachment:
Adam Box.jpg


Quote:
4) blue - loose insulation, green - hangers or loose insulation behind slats or other absorption/diffusion
5) you can do slats and hangers but if you don't seal the slats, they are not operating as Helmholtz resonators. you might make a slat box in the center section and make the lower and upper sections loose insulation for absorption.

Ok, what I still don't get: What exactly is the advantage of hangars compared to just loose insulation? And: Sealed box with hangars inside = Helmholtz-resonator? But as far as i know, such a Helmholtz reonator is only meaningful, if tuned to the room. As the factor of that tuning is mainly the capacity of the sealed space and the size of the opening, I guess I cannot just use any kind of size, that is left under the center speaker. Actually, I planned another Iso-box for power cleaners (furman) and other rack equipment that does not need regular access. But I might fit that stuff into the other iso boxes, if there is a significant advantage having a bass trap in the middle section.
And what do you mean by sealing the slats? I thought the slats would be attached to a plywood surface? Regarding slats I found many different posts and opinions here. Is there something like a slat-thread? ;-)
I'm afraid I couldn't find the one that meets your advices.

Quote:
6) i'd pick one side or the other below the stereo speakers for the sub and use your crossover/etc as needed to time align and set the actual x-over etc.

Time align? By that you mean delay to compensate for the difference of distance (which is unavoidable, as I see it)? The crossover of the sub itself doesn't have a delay feature. Or am I getting something wrong here?

Quote:
7) 10 degrees is pretty much maximum. so even though the 300's are "softer" than say ADAM or horns, you might try an experiment to set the speaker on a (crudely made lumber) stand (which matches the proposed height) to test the angles and see how you feel about them sitting @ 7 and @ 10.

This is something I cannot do, as I just want to build the soffit with a look in the nearer future, where I am quite sure I will buy the o300s. At the moment I cannot afford them together with all building costs. So, what would be better: finding a way to plan that ahead now, or just leave the o300s and tilting out of the build and modify it later? I think, I will be able to afford the o300s end of the year or first quartal of 2014.


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PostPosted: Wed Feb 27, 2013 1:23 am 
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And: Sealed box with hangars inside = Helmholtz-resonator?
No. Hangers are one thing, and sealed Helmholtz resonators are another thing. Two different principles of physics. Helmholtz resonators need to be sealed (except for the neck, of course!), in order to operate, since the interior is a fixed-volume resonant cavity. If it is not sealed, then it won't work. Slot walls are Helmholtz resonators, so if you do slot walls as part of the design, then the slot walls must be sealed. However, if you do hangers, then the box does not need to be sealed, but you can still seal it if you want! As long as you leave a large opening at the bottom, of the front panel. I think John recommends about 12" (30 cm).

There isn't much published literature on how hangers work, but the empirical evidence is that the do work very, very well. It seems that they act somewhat as damped waveguides, leading the waves down a path with lots of absorption on the sides and at the end. It seems like orientation, size and spacing are important, but not critical. Maybe John or Glenn can provide more detailed info on the theory of operation.

Quote:
But as far as i know, such a Helmholtz reonator is only meaningful, if tuned to the room.
Not necessarily. Slot walls act more like broadband absorbers than individual tuned resonators, if the perforated areas is greater than about 10% to 15%. They don't need to be tuned to individual frequencies, but rather tuned generally in the range of interest, which is often the low mids and mids.

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As the factor of that tuning is mainly the capacity of the sealed space and the size of the opening, I guess I cannot just use any kind of size, that is left under the center speaker.
For hangers, the cavity is large enough and the opening is large enough that this is not a problem. The tuning is so far off that it won't matter.

Quote:
And what do you mean by sealing the slats? I thought the slats would be attached to a plywood surface? Regarding slats I found many different posts and opinions here.
"Slat resonators" and "slot resonators" are exactly the same thing, viewed from different points of view. They are made of wooden slats with slots between them, so if you want to call them by either of the two names, that is fine. They are Helmholtz devices: the air in the slot is the "slug", the slot is the "neck", and the air space behind is the resonant cavity. If you put slats on a plywood surface, then you have no resonant cavity! So that would not work. The slats MUST be over a sealed air space. You tune these by adjusting the size and thickness of the slats, and the size of the gap (the "slot"), and the depth of the air cavity. There are equations for tuning them, but as I mentioned before, if the percentage perforation is fairly high, then the set of slats acts a single broadband device. If the percentage perforation is low (less than about 10%), then they act more like a set of individually tuned devices.

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Time align? By that you mean delay to compensate for the difference of distance (which is unavoidable, as I see it)?
Exactly. Whenever you have speakers that are at different distances form your head, you need to adjust the timing by delaying the signal for the ones that are closes to your head, so that all the waves arrive in-phase at your ears.

Quote:
The crossover of the sub itself doesn't have a delay feature.
Usually they don't, but many external crossovers do have time delay adjustments, and so do most speaker management systems.


On the speaker soffit venting issue: Another forum member is working on that in his build right now, and came up with this idea, that you might find interesting:

viewtopic.php?f=2&t=14814&start=186




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PostPosted: Wed Feb 27, 2013 10:45 pm 
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Thank you Stuart! That made some things clear.

However, I am still struggling with the whole concept of the soffit mount. Before I make the final design, I would really appreciate it, if you guys could help me figuring out these things:

Attachment:
Draufsicht 2.jpg


1) Overview:
So, basically I have two sections behind the slot wall, that need to be sealed from the rest of the constuction from the inside. There I put the hangers inside. Then I have two iso boxes (possibly a third one in the center section). These are connected with the speaker boxes above via ducting and let the air out of the soffit mount close to ceiling level. The remaining cavity can be filled with loose mineral wool, acting as an additional LF absorber.

Attachment:
stereo section - seite.jpg


2) The stereo sections (as also the center section, if I decide to put a third Iso-box there)

Here I have the iso box and the speaker boxes connected via ducting and one exhaust port close to the ceiling. They are all sealed from the rest of the cavity, right?
Do I also seal that remaining cavity to the studio air, as I attach the front plates? Or should I rather create another area, where more air can pass inside the cavity? Obviously, the tiny gap between the soffit face and the speakers themselves already leave a little air through. I am just not sure, if I should rather increase that or not ... if I decide to only build no third iso box in the center section, I could obviously put an additonal cloth-only-part on the bottom and maybe even some more slots up to the speaker section. But if I need the third iso box: where would I reate more room for air to pass to the cavity not to close to the speaker I guess)?

Attachment:
slot resonator with hangars (seite).jpg


3) The side wings with slot resonators

On this wall I just attach the slots to the frame construction, right? Other wise the air wouldn't flow into the sealed cavity behind and there would be no absorption. Usually, those slot resonators are built with a smaller cavity behind and just loose insulation, as I looked up in many posts here. However, if I understand Glenn correctly, I would gain something with hangars instead of loose insulation. And according to stuart, I would not "tune" the size of the cavity to a specific frequency, but rather as a broad band device, so ...

- did I choose the right size for that cavity to be sealed (the green area in the overview picture)?
- how exactly would I seal this? I thought of attaching MDF panels to the frame and sealing the edges with silicon.
- can I just screw the slots to the frame?
- about the slots: which material would be preferable and how thick? there seem to be different sizes of slots, that are following a sequence, like 10cm, 7 cm, 3 cm, ... what is the criterium to choose these sizes and also the gaps in between?
- can/should there the clothing between the pillars of the frame and the slots? after all there is mineral wool behind them and I am not sure if there is a health risk due to respirable dust ...
- about the hangars: can I use the bulletin board stuff (12mm) I described in my last post for the core? how thick and how dense should the attached mineral wool be? would the alignment in the overview picture be good? Would I make these hangers just as large as the height of the cavity allows?


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PostPosted: Thu Feb 28, 2013 1:08 am 
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Quote:
These are connected with the speaker boxes above via ducting and let the air out of the soffit mount close to ceiling level.
I would not do it that way. The air arriving at the O300 is going to be way hot already, so it won't be cooling them at all. It will have already cooled the PC's and the P22's, so it will be too warm to be useful. In fact, depending on your PC's, the air will probably already be too warm when it arrives at the P22's. I would figure out a separate supply duct to take cool air to each speaker. You might still be able to have the exhaust "chimneys" joining at some point, for only one final outlet.

Quote:
Usually, those slot resonators are built with a smaller cavity behind and just loose insulation, as I looked up in many posts here. However, if I understand Glenn correctly, I would gain something with hangars instead of loose insulation. And according to stuart, I would not "tune" the size of the cavity to a specific frequency, but rather as a broad band device, so ...
What we are both saying is that you should have a sealed slat "box" at the front, just a few inches deep, then the hangers behind that, in their own separate space, that has a large entry port at the bottom, below the lowest slat, about 12" high. You could even take your cooling air feeds for the speakers from inside the hanger section, sideways. The slat box could probably even be a removable "module" that you could take out to gain access to the hanger area, and therefore to all the connections and cooling ducts for the PC's and speakers (just a suggestion).

Quote:
- did I choose the right size for that cavity to be sealed (the green area in the overview picture)?
That looks like the right size for the hanger area, but much too deep for the slot wall. Generally, you only want a few inches of cavity depth behind the slats. If you have several feet of cavity depth, then the slat and slot sizes become rather strange in order to tune them to useful frequencies. Play around with the equation for figuring out slot resonator frequencies, and you'll see that the cavity generally is just a few inches deep.

Quote:
- can I just screw the slots to the frame?
Yes. Screws or nails is fine.

Quote:
- about the slots: which material would be preferable and how thick? there seem to be different sizes of slots, that are following a sequence, like 10cm, 7 cm, 3 cm, ... what is the criterium to choose these sizes and also the gaps in between?
Use ordinary wood slats. They could be cut from a sheet of MDF or plywood, for example, or you could use real wood, if you prefer natural grain. You choose the gaps and slat dimensions and air cavity depth by using the equations for slot resonators, and the needs of your room. If you need mostly low mid absorption, then tune the entire wall to low mids. If you need high absorption, then tune to high mids. If you need general mid-range absorption, then tune it broadly. Etc. After you analyze the acoustic response of the finished room, then you can decide on what range you need to tune the slot walls to.

Quote:
- can/should there the clothing between the pillars of the frame and the slots? after all there is mineral wool behind them and I am not sure if there is a health risk due to respirable dust ...
YEs, you do need thin cloth right behind the slats, for both visual and acoustic reasons. Visual, so you can't see the ugly insulation between the slots, and acoustic, to keep the insulation from fouling the slots.

About the health hazard issue, you might find this thread interesting:
http://www.gearslutz.com/board/bass-tra ... eview.html

Quote:
- about the hangars: can I use the bulletin board stuff (12mm) I described in my last post for the core?
That should be OK, as long as it is low density and sort of "soft" to the touch. John recommends a product called "homasote".

Quote:
how thick and how dense should the attached mineral wool be?
For mineral wool, about 50 kg/m3 would be good, or maybe a bit less. One to two inches thickness should be good.

Quote:
Would I make these hangers just as large as the height of the cavity allows?
Yes, but they must be free to move: There must be enough space around each hanger so that it can swing freely a little bit each way, without touching anything else (another hanger, framing, cables, etc.)


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PostPosted: Thu Feb 28, 2013 1:33 am 
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Alright! Now I get the slot design! Thank you very much, Stuart!

Regarding the cooling, Glenn suggsted this, if I didn't missunderstand him:
Quote:
2) Where should I get the cooling air for the speakers? I am not sure, if it has to originate from directly under the speakers or if it may also come from the side panels of the construction?

Quote:
2) if you can tap off the output air from the iso box and flow it up around the speakers while keeping those boxes sealed, you're better off.

So, you would rather take the air from inside the soffit?

Hopefully, I will present the complete design for the soffit mount tomorrow. Hope you will chime in again and tell me, what's wrong with it then! ;-)


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PostPosted: Thu Feb 28, 2013 4:22 am 
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Quote:
So, you would rather take the air from inside the soffit?
That really depends on how hot the air is coming out of your PC ventilation. I design machine rooms for video post production facilities, and the air coming out the back of those computer is often really warm, especially if there are several hard disk, lots of RAM, extra interface boards and video boards. I'm not sure what your computers are like, but I would get a digital thermometer and test the temperature of the air coming out the back of the fans, when you have had the system on for several hours and are using it heavily. Let us know what the temperature is. Measure for a long time (several minutes), with the system running heavy processing and disk access, to make sure you get an accurate reading.

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PostPosted: Thu Feb 28, 2013 7:20 am 
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Soundman2020 wrote:
Quote:
So, you would rather take the air from inside the soffit?
That really depends on how hot the air is coming out of your PC ventilation. I design machine rooms for video post production facilities, and the air coming out the back of those computer is often really warm, especially if there are several hard disk, lots of RAM, extra interface boards and video boards. I'm not sure what your computers are like, but I would get a digital thermometer and test the temperature of the air coming out the back of the fans, when you have had the system on for several hours and are using it heavily. Let us know what the temperature is. Measure for a long time (several minutes), with the system running heavy processing and disk access, to make sure you get an accurate reading.

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Thank you, but ... no! I will not even care to measure it! :-) My Computers (at least the mac pro) is stuffed with cards and gets very hot, because I do intensive stuff (steaming lots of samples rom disk) with all computers.
And you say you design rooms for post pro professionally? Then I will trust, this is not a good idea. I had planned it to do differently, anyway. Just didn't know, I could use the air from within the soffit, which makes things even simpler!
So, could i just leave a big gap under the box of the Adam P22a and an leave the rest as in the picture? If the speakers get hot, the hot air goes up and sucks fresh air from beneath in to provide circulations. if that would work, it's even simpler than combining it with the iso boxes. I just have to lead the PC-air up in a separate pipe. Bueno! Muchas gracias! :-)


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PostPosted: Sun Mar 10, 2013 1:05 am 
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Ok, while figuring out the design of my ceiling, I would like to plan ahead for the soffit construction. I think I will leave it with the monitors I have now and modify the contruction later, when I have gained some experience working in that environment and have the budget to buy new monitors to try some thing out before building.
So, now the time has come to really dig deep into decoupling:
There seem to be (at least) two general methods on that matter. In John's Schematics the box of the speaker seem to be fixed to the same framing the bezel is fixed to. On that matter John said something about "building the construction very rigid" (sorry, I can't find the exact quote anymore). Some people seem to use neoprene, sylomer or other rubber material in a way to decouple the speaker from its box, just like I did in my last picture here. My question, would that kind of decoupling be enough or would it still be required to fix the speaker boxes to a separate framing, like in the following thread?
viewtopic.php?f=12&t=718
Some people build blocks or pillars of concrete as speaker stands within the soffits. Obvioulsy, I cannot do that, because of the PC-iso-boxes in my construction. So, I would be left with building a complete new frame (maybe something like a table fixed to the floor) to have a monitor stand completely decoupled for the soffit face framing, right?


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PostPosted: Sun Mar 10, 2013 1:55 am 
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There are several ways of building a soffit, but the two that make the most sense (which are the two you see here on the forum), are roughly as follows:

1) Build the thing so heavy and rigid that it cannot move, such that the speaker is unable to transmit any vibration to the front panel. In this case, the speaker is held rigidly in a tight-fitting wooden box, which in turn is rigidly attached to massive framing. Sometimes this one has a variation, where the actual baffle (front panel of the soffit) is on a separate frame from the speaker mount itself, and there is a small gap around the speaker, where it pokes through the baffle.

2) Totally decouple the speaker from the mounting. In this case the front panel is still rigid and massive, held very firmly in place, but the speaker is decoupled from the framing by some method, usually with resilient rubber mounts. Here too there must be a small gap between the baffle and the actual speaker.

In both cases there are variations, as seen in many build threads here on the forum. For example, the "brick pillar" stand for the speakers that you mention is an interesting alternative, but isn't always possible, and does mean that there is no space below for John's "hanger bass trap" design.

Quote:
So, I would be left with building a complete new frame (maybe something like a table fixed to the floor) to have a monitor stand completely decoupled for the soffit face framing, right?
You could do that, or you could use Barefoot's method of building a rigid shelf attached to the walls. As long as the speaker mount is very rigid and solid, it does not really matter how you achieve that. Personally, I like the concept of building the entire soffit as a single rigid unit, then decoupling the speaker itself from that with resilient mounts.

Quote:
Some people seem to use neoprene, sylomer or other rubber material in a way to decouple the speaker from its box, just like I did in my last picture here. My question, would that kind of decoupling be enough
As long as you calculate or empirically determine the correct deflection of the rubber for your speakers, then yes, you can get good decoupling like that.



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PostPosted: Mon Apr 15, 2013 8:22 pm 
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Meanwhile, a friend (an artist) has 8 huge 21mm thick plywood boards left from a finished project. He could give them to me for free and I was thinking about the great savings I could make that way ...
However, Glen suggested 25mm thick ones for the soffit front, so I am missing 4mm here. As thicker cannot be worse in this case, i was thinking of glueing and/or screwing two boards together, hence, getting 42mm thick ones ... As I assume, this situation is pretty similar to 2 gypsum layers of 11mm thickness not having equal resonance behavior as one 22mm board, I was thinking, if there is a way to make this work.


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PostPosted: Thu Apr 18, 2013 9:00 pm 
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you could go with doubling it - 1 layer to be the bit that holds the framing and speaker box together (rough finish) and the second is a final bezel which is nicely finished.

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PostPosted: Thu Apr 18, 2013 9:23 pm 
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Ok! I'll see, if I can integrate this idea to my design. However, that means, there is no problem with the plywood of 21mm having worse resonance than a 25mm one? As I understand, the final bezel may not touch the speaker, therefore, the rough layer may not touch the final bezel as well. Could you clarify that a little?
By the way: I probably won't go with a separate decoupled frame/stand for the speaker box, but rather with a framing as rigid, as I can get it and decouple of the monitors by sylomer. Separate stand for the speaker seems to be to complicated in my case. In that case: Would I have to put sylomer, where the monitor touches the inner bezel?


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PostPosted: Mon Apr 22, 2013 10:38 pm 
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the speaker box would attach to the rough finish plywood, by speaker box i mean the box within the soffit where you mount the speaker, not the speaker itself. between the frame and rough plywood and speaker box, damping via insulation etc the soffit should have very little in the way of resonance, never mind "bad" ones... the finished face would be separated from the speaker itself by (say) 3mm (or less) and then you would caulk that gap. while the 25mm MDF is nice, if you have 21mm plywood, and take your time building this you should be fine. measure twice, cut once... design first, then build...


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PostPosted: Tue Aug 13, 2013 3:28 am 
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Being in the last stage of my design, as you would think, some doubts arise:

1) What has to be sealed "airtight" in the soffit front:
If you look at the picture "Draufsicht 2.jpg" from the top of this page - what has to be sealed airtight?
What I think must be sealed:
- the iso-boxes except for their air in and air out port
- the speaker boxes (sealed around the edges of the speaker front as last step)
- the slat walls (except for the gaps between the slats)
What I am not sure about:
- the complete soffit face! Do the acoustical benefits of flush mounting only work, when the entire face plates are sealed to the back? Or is it ok to just place the face plates neatly next to each other with minimal gaps between each other. I don't understand that so far.
- the green area with hangars. Obviously, there has to be a huge air port at the bottom. But does it have to be sealed from the rest of the volume behind the soffit front? Or can it share the air with the loose insulation in the brownish area?

2) The soffit front surface:

Glenn, who helped me a great deal, brought me to changing the concept from drywall at the soffit front to 25mm plywood with insulation and cloth cover. However, I really doubt, the 3 - 5 cm of insulation come close to the "hard, and reflective front", that is necessary for the soffit front (especially surrounding the monitors I cannot see how that would be good sound wise and also building wise). I have not found an easy but nice looking way to attach insulation and cloth to the plywood boards, that have to be screwed to the frame work afterwards. That's why I want to go with a plain wooden surface for the area surrounding the speakers. Under the L and R speaker there is the glass door for the iso boxes , so the small rest of that area will be wooden surface as well, which leaves the area under the center speaker and over L+ R for an absorbing cloth on insulation area.
Also, I am looking into using this kind of 3D wood decor for the wooden areas on the front (maybe plain wood surrounding the speakers about 100 mm:
Attachment:
wodewa.jpg

They have an irregular relief structure (ranging from 8-22 mm), therefor provide HF diffusion, a little MF absorbing and - something that is a factor as well IMO - I like the looks of it! ;-)
I have seen some designs, where a similar front in stone is used. I know the sonic result is not very much predictable. Maybe, this is some of those things I want to do for a nice look. This is what I imagine right now:
Attachment:
soffit front.png

What do you thing about that? 3D wood as a diffusing front a good/bad idea? I will have hangars under the center an behind the slat wall. Is that enough bass trapping in the front for now?

3) Is there any reason for not using hangars, but rather loose insulation between L, R and C part (the orange area in the last birds view)? Also: Does orientation of the hangars make any difference? I might get some big hangars behind the center speaker maybe one between L and C and R an C. I am not sure how those hangars compare to loose insulation, but there is a ton of space there, because the Iso-boxes needed room. In other words: How are hangars effective regarding orientation and stacking multiple hangars next to each other vs. just a huge single unit alone.


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