Listening room project - alternative absorber

Hey, jesper and welcome.  First know that I'm not a construction guru.  The idea that concerns me regarding your concept is that I hear you want to turn your "inner room" into an absorbent surface.  I feel certain that approach is not at all conventional. 

Noise isolation and acoustic treatment are related but separate.  I say that you should first follow standard isolation procedures while planning for extra volume/surface area for treatment.  In other words, don't make your inner wall absorbent but make a big enough space so you can make another inner false absorbent wall.  In that sense, you'll be making three layers: two for isolation and one for aesthetics and acoustic function. 

Thanks.

Usually when we talk about a room within a room, we are talking about isolation. Now in your case, if in fact you are not interested in isolation, it might work if I understand correctly.

So lets say you start with an empty rectangular room. Ok. Now you build a wood 2x4 frame inside the room in front of all 4 walls. Build the new frames 4" from the existing walls. Space the studs 24" so fiberglass can fit between. You can use 8" thick fiberglass. Instead of drywall to finish the walls, staple grille cloth or burlap on the walls. You now have all 4 walls completely sound absorbing. If you want to completely treat the ceiling, you can use a drop ceiling frame system and put fiberglass above the frame too.

I forgot about corner traps for more bass absorption so let's go back and frame across the corners and fill the extra space with fiberglass (super chunks). The front of the corners have paper or plastic for improved bass absorption.

Is this what you have in mind? What I have laid out here is basically a pseudo anechoic chamber with almost all surfaces absorbing (except the floor). Will this work? Well, it will be pretty dead at mid and high frequencies. You will still have low freq room mode peaks and nulls but they will be reduced too.

Rock,

Appriciate your responds

I don’t intend to treat the entire surface of the walls and ceiling.

Not sure how to explain it. I’ll build the room walls like normal - Wooden frame, isolation and drywall on both sides. But where the absorbers should be hanging (eg. early reflections) I want to integrate them into the wall. See illustration:

There will be a lot space adjacent to room and there’s no problem letting the sound through to here – if there’s something to gain doing it this way.

Or will it be preferable to stick to ‘normal’ tuned absorbers?


Jesper

First I suggest you please forget about "Tuned Absorbers" If you read all Ethan's info, he explains.

Thanks for posting the illustration, it helps a lot and I have questions:

My first question is, what is the entire scope of this project? Seems like you have a big space and are subdividing it and have some other purpose for the remaining space. Some of the following questions relate to some "yet unknown to us" details.

Where is the "outside or existing wall in relation to your "new" wall? If it's about 1 foot away, fill your space behind the grill cloth with 6" to 12" of fiberglass. If it's really farther, your opening is like a window and the sound just goes out and very little reflects back in the room.

Why do you have drywall on the back of your new wall? Is it for cosmetic reasons for the adjoining room you're creating? If so, fine, but you don't need it for your listening room.

For that matter, why do you want drywall or any hard reflective surface on the front at all? In most rooms, it's there already and we can't tear it off or we need it for isolation but if those are not issues for you, drywall just reflects the sound around, if you don't want that much absorption, why not use diffusors instead?

Thant's all for now.

Cheers,
Rock

Thanks for all your help guys

Answer to your questions:

Scope of the project is to end up with a listening room for Music (playback), no recording, mixing, live etc. Living room like, but with acoustics prioritised.
That’s why I’m thinking cometics as well, so I’m not going to end up with a room looking like a recording studio – if possible
 

Here’s illustration of the rooms and the adjoining space - not scale.

Dry wall on both sides is for cosmetics- and practical reasons. Then it’ll be possible to mount shelf, lamps etc.


I know that this way the traps can’t be tuned, but my idea was that in this way the trap(s) will be effective through most of the frequency range - but I don’t know. And, maybe it’s not to be preferred at all compare to tuned traps. - of course I need some tuned ones on the wall that interacts with the outer wall.

- I’ll keep in mind the loosely packed insulation –

Jesper

As you say small rooms need absorption at all freq, and that's wy I thought my approach might be an idea - Wouldn't it be a good broadband absorber (maybe also bass trap) when the sound is let through these 'traps' out of the room?
BTW room size will be approx 23 x 17 feet