Building non parallel walls to combat standing waves

[childejc]

Construction has started on my Media Room, and within the next few weeks (or possibly days) I will need to confirm the position of the interior block wall behind the seating position.

I know low frequency standing waves can be a problem, and that they are caused by sound bouncing between parallel walls. I have read that irregular shaped rooms can help. By how much would I need to angle the rear wall away from being parallel to the front wall to get a significant improvement? Would 5 degrees (which aesthetically would not be too significant) be enough?

More radically, should I consider creating a V shape behind the seating position? This would give the added benefit of a bit more space for the desk in my office?

Any thoughts/advice greatly appreciated as I really don't want to make the wrong decision if I can help it.

Thanks

 

[Trollslayer]

I'd be more concerned about the 24cm cavity and the thin wall with speakers against it.
BTW, what ventilation does the equipment room have?

 

[childejc]

Re the 24cm cavity behind the stud wall, that is to enable me to install in-wall speakers behind the micro perforated screen. I was intending to fill the cavity with some kind of insulating material, and put soundproofing material on the single skin brick/block wall behind the speakers. Do you foresee some problems with this approach?

An alternative I am considering is to forget the stud wall. Part of that wall (the one behind the screen) already exists in the current building, and is a double skin with a cavity as it is an exterior wall. I could retain the second skin on the wall and simply fit the speakers into the cavity in the wall, then fix the screen in front of the speakers. Would this be a better solution?

Re ventilation, to be honest, I’m not yet sure. My drawings show an arched door with a curtain, but I am moving towards a solid door (for security) but with a ventilation grille. Would that work?

 

[Isco 3]

You will only need 10cm of depth for in wall speakers. Unless you are fitting the Artcoustics speakers that sit on the wall, and you need to make a deeper cavity. You must gently fill all cavity with insulation to avoid airborne transmission.

It is impossible to predict the room modes in such a complex shape room. Especially when you have partition walls and a few doors. You will have to build and then measure.

You might be better off putting some absorptive panels on the back, and when you've measured the room, build some resonant absorbers to lower the modal amplitudes. Membrane absorbers can look quite flat and rest on a wall. Not difficult to model, just need some tunning.

It is a nice room you have there. It might be handy to calculate if the speakers that you are planning on buying can reach reference levels at your seating position. Triad speakers will do the trick nicely.

 

[childejc]

Thanks for the advice. My biggest problem right now is that I don't really know what I want. Up to now I had been aiming for a kind of stealth home cinema, with everything as hidden as possible. However that can be expensive and inflexible. Given the main use of this room will be for home cinema, I am now moving to a simpler design. This will allow me to make use of my existing quad lite 5.1 system and still be able to painlessly upgrade it at some point in the future.

In the meantime getting the structure of the room and its acoustics right is my main priority. I am considering getting a very large print for the rear wall (about 3m x 1m panorama picture). Would I be able to hide the absorptive panels you mention behind the picture, or would the picture reduce their effectiveness?

Any thoughts on my original suggestion of making the rear wall non-parallel to the front wall? Given I have the opportunity, it would be a shame to miss the chance, if it will actually deliver some benefit.

Thanks

 

[Isco 3]

I do not have a mathematical equation in hand to say "yes, 7.5 degrees and you are done". If somebody can do that, it would be nice.
Giving an angle to your back wall, will get you a different result, but who can tell you exactly what?
You will always have to deal with room modes in a small space. Angling your wall does not mean you will not have to build resonant aborbers. All room-ratios publications I came accross were reffering to rectangular rooms, because they could model it.

If you want to angle your wall, you can. Knowing what room modes your room is going to have is hard, especially yours.
You can do some 'ray tracing' though, and see where reflections are coming from.