Confused on room design and the inclusion of sound treatments

2471 Views 8 Replies 3 Participants Last post by SierraMikeBravo, Dec 10, 2009

uncle

Discussion Starter · Dec 4, 2009 (Edited)

I've been working on designing a home theater space that also doubles as a critical 2 channel listening space. This room would be incorporated into a basement, but the design is open to really any size and shape options.

Because the size and shape of the room is completely open, I'm trying to determine what is the best acoustical shaped room. Up to this point I've determined that a 'golden trapezoid' shaped room with a tapered high ceiling is a good place to start.

I've been using various room calculators to determine the approximate size, and have several different room dimensions, all around the 18ft wide, 28ft long, and 9ft high area.

My problem is after the size and shape of the room is selected.

I don't want a room that plastered with hanging sound panels so I'm trying to create some interior room designs that will serve as the room sound treatments. For example: stone work that would act as diffusors, wood trimmed panelled walls containing absorbers, baffled ceiling panels acting as reflectors or absorbers, etc....

The problem in creating such a design is determining what type of sound treatment material belongs in which location:huh:. There are different schools of thought on this. Some say absorbers should be used on the speaker wall, first order reflection points, ceiling, etc... and as you work past the 'one seat of excellence' the absorbers change to diffusors. Others say that in 2 channel listening situations the need to create a large sound field is important and therefore using diffusors on the speaker wall, first order reflection points and ceiling points is important.:dontknow: (BTW - when I say first order reflections I just mean the reflection points between the speakers and the first listener - not all first order reflection points).

I've studied expensive listening rooms and theaters alike trying to find a common theme, but without luck. There are 2 channel rooms with either diffusors or aborbers, and there are home theaters with either or both in the various locations.

I see problems with both. If absorbers are added at the aforementioned locations, this would add to deadening the room and closing in the sound field. If I add diffusors wouldn't that spray sound around? That would create a larger sound field but wouldn't that hurt your imaging?

If anyone could advise me on what type of treatment should go in which location I'd greatly appreciate it. Once I know and understand this I can continue to create the interior design to naturally incorporate the proper sound control items.

I do understand I'm attempting to serve two masters by incorporating a 2 channel listening area within my home theater. But there has to be a happy medium. I do enjoy the one seat of excellence for my music enjoyment. If you design a room with great music listening properties that can't hurt your movie watching experience can it? When you're watching a movie you want to be surrounded by the sound and have all the depth and height which puts you there in the movie, but you're not listening to the audio in a critical manner. If it's doing it's job you can hear the dialog and experience the action but that's not your only focus, there's the picture as well.

Where as when you're listening to a music CD you also want to be there, but sound shouldn't be coming from around and behind you. Unless otherwise recorded, the CD was recorded in 2 channel stereo and that's how it was to be heard and experienced. The musicians are suppose to be seated in various locations in front of you performing and you should be able to tell where the piano is, the drums, where the vocalist is, etc... There should be an intelligible height and depth to each and every instrument.

Again, any advice would be appreciated:help:.

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bpape

· #2 · Dec 5, 2009

And there's the rub. You're trying to do 2 completely different things in the same room. You'll not get an optimal for both. It will be a compromise. You simply have to decide which way to lean. There are certainly some shared elements in both - and other things that will help one without harming the other.

There is no one right answer for exactly where a room needs to be treated and how. There are multiple ways to go, and multiple preferences. The overall goals are:

- Have the decay time in the proper range across the spectrum
- Minimize harmful reflections
- Maintain a smooth frequency response
- Provide a good 3 dimensional image in the front.

In addition, for HT:
- Provide both a diffuse yet identifiable soundstage in the rear
- Maintain good screen lock
- Deal with an averaging of frequency response over multiple seats and potentially multiple rows
- Compromise potential optimal 2 channel imaging for proper viewing angles of multiple rows depending on screen size.

... and a hundred other things.

As for how to not make it LOOK like there are a lot of treatments, there are a lot of ways to do it. All depends on your visual preference.

Bryan

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uncle

Discussion Starter · #3 · Dec 6, 2009

Ok, so let me better explain what this room would look like so you can advise further.

2 rows of seats, 1st row with 3 seats (center seat being the throne - all seats located approximately 3/8ths to 1/2 the rooms length), the 2nd row would have 4 seats (with spacers between some of the seats), and at the rear I was going to have a raised bar ledge with bar stools. There would be some space between the back of the bar stools and the rear of the theater.

The height would also vary. The ceiling will likely be straight, and as you enter the theater from the rear, you would walk down the riser stairs to the 1st row - which would have a ceiling height of 9-10ft, upper most rear level would be 8ft.

Now, hopefully you have a mental picture of the room and the seating arrangement. What if i wanted to LEAN towards 2 channel acoustics for the throne in the 1st row. Can this area be enhanced without ruining the acoustics for the 2nd and 3rd row during movie watching? The center channel and surround speakers would be throughout the room and would be positioned for home theater. They would only be on during a movie. The 2 front towers should still be able to convey the auditory information without sounding either muddy or terribly unfocused.

I understand there will be a compromise - I can live with that. Anything is better than nothing - and I can't build 2 rooms.

"There is no one right answer for exactly where a room needs to be treated and how. There are multiple ways to go, and multiple preferences. The overall goals are:

- Have the decay time in the proper range across the spectrum
- Minimize harmful reflections
- Maintain a smooth frequency response
- Provide a good 3 dimensional image in the front"

I take it you're saying that it's hard to predict without the room already built and seeing how it sounds? Then there's personal preference? Are there some good rules of thumb that most experts agree on regarding 2 channel audio sound treatment?

"In addition, for HT:
- Provide both a diffuse yet identifiable soundstage in the rear" - yes, this is needed

"- Maintain good screen lock" - yes this too

"- Deal with an averaging of frequency response over multiple seats and potentially multiple rows" - yes i agree

"- Compromise potential optimal 2 channel imaging for proper viewing angles of multiple rows depending on screen size." - screen will be no smaller than 109, likely around the 120 dia size, and all the seats will be within 10-15 degrees from center so viewing angle won't be an issue

"As for how to not make it LOOK like there are a lot of treatments, there are a lot of ways to do it. All depends on your visual preference." Could you please either provide me with some examples or direct me to some images so I can wrap my head around it. I first need to determine what type of sound treatment goes where, so I can then visualize what needed in the given areas.

Brent

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bpape

· #4 · Dec 7, 2009

OK. So basically what we do is make sure the rear wall still helps with bass control but doesn't kill the highs. We lean toward a little less absorption on the side walls for a little more 2 channel life at the expense of pinpoint focus during multi-channel for the other rows.

Front wall is 100% dead. Front corner bass control. All front treatment can be hidden behind a false wall. Speakers can also be behind if using an AT fabric for the walls and just framing.

For bass control around the room, you can do what appears to be Wainscotting but over a 3.5" cavity. You can vary what's behind and in front of it in terms of thickness and density to achieve different tunings but the same flush surface visible. Cavity depth and front panel mass determine the tuning. These will only be good for about 2 octaves each and are not as efficient as 'soft' absorbers but can be tuned lower with less depth at the cost of efficiency and needing more of them.

For the tops, the easiest way is to just use all cloth walls and hide the treatments behind them. That gives a nice clean look and allows us to do whatever we want without concern for the visual component of the arrangement.

Behind the cloth, you can use a combination of absorbers and thinner diffusion products. more absorbers in the front, difusion in the rear.

Bryan

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uncle

Discussion Starter · #5 · Dec 7, 2009

NOW THAT'S WHAT I'M TALKING ABOUT. AWESOME!!!!!

The speakers will be exposed and approximately 5 feet from the front wall, so no need for a false wall. I was already thinking of angling the front corners of the room. Can I frame in my corner base traps as part of the walls? so the front of my room has 5 walls instead of 3.

I had already been mauling around the wainscotting idea before, it's nice to see I wasn't crazy. The face of wainscotting, what material could you suggest that would vary in thickness and density but still look uniform. Or is the face just a thin mask over the entire 3.5" cavity. How transparent does this material have to be to allow base waves to pass through and into the sound treatment material?

Now when you're talking about the top of the walls and using a combination of absorbers and thin diffusers - is there going to be a section of the wall that has both absorbers and diffusers? When combining two different sound treatment products within the same space, how do you know which should go where - or does it matter overall for that one section. You want to absorb some sound but not everything so that's why you put in a diffuser.

Can shaping the front and rear walls help acoustically? I was thinking either convex, concave, or tapered as apposed to just a flat wall. As it sits now there's going to be a minimum of 5 walls in the front, tapered side walls, and a sunken floor - the only surface that's typical so far is the ceiling, but that's going to have a soffit system and might have a baffle system as well. If shaping the front and rear walls would adversely affect the sound then I'd leave them flat. But if it wouldn't matter or might even improve the sound characteristics I'd like to do it. What do you think?

This is great, thanks for letting me pick your brain.

Brent

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bpape

· #6 · Dec 7, 2009

I'd frame the room square and build corner absorbers covered with cloth at the angles. Front wall will be all cloth anyway. Use black to get better video contrast.

For the Wainscott, you're looking at a combination of 1/8", 1/4", 3/8" materials for different sections. Thicker (more massive) = lower tuning.

PLEASE to not do any radiusing in the room, ESPECIALLY concave shapes. Those are absolutely the worst thing you can do for room acoustics. It's basically a lens that focuses everything.

Tapering the rear wall will muck up surround imaging and 2 channel 'feel' by having a ton more reflections heading to one side than the other.

Bryan

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uncle

Discussion Starter · #7 · Dec 7, 2009

Sorry, my error for not describing in accurately. By tapering I mean tapered to the center of that wall. Concave but with a sharp seam in the middle instead of rounded. Now - listening to what you're saying about concave shapes - that idea is out the window. good to know.

Can you tell me why some elaborate 2 channel rooms have a big convex shape in the middle of the front wall, and smaller ones at the first order reflection points between the speakers and the listener? I thought this would have something to do with diffusion and imaging - but those are two opposing terms so I really don't know why they do that.

Brent

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bpape

· #8 · Dec 7, 2009

No problem - though that's almost as bad. It's still focusing things somewhat and creating another corner for things to build up.

Convex is not nearly as bad as concave. The convex in the front is a Rives thing. I'm not really sold on it personally.

The idea behind a convex shape is to scatter things evenly in space. On the front wall, according to their theory, it also helps with boundary issues.

Bryan

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SierraMikeBravo

· #9 · Dec 10, 2009

Greetings,

In addition to scattering and acting as diffusors (which work better in the back in my opinion), this type of design works very well in absorption of low frequencies. It is the depth of the radius that makes these work so well. You can actually tune these to absorb much lower frequencies than standard tri-traps, but you need to know which frequencies you are trying to target. As with anything in the low frequency range, you can do more harm than good unless you know what you are doing. The other part of the secret to their effectiveness is that they must be physically attached to the wall so that they resonate with the rest of the room. However, I would not incorporate these unless you have a clear understanding of how these type of absorbers work. :reading:

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