SDAs and Acoustics

Did your room look like this?

A good thing to do with A/Bing, at least with my treatments and my room, is to pick some music with more than one vocalist and especially where on is much lower level and see how decipherable and separable they are. Like for example Chris Isaac Wicked Game or Peter Gabriel Mercy Street. That's a great test that isn't going to ever show up on any freq. resp. plot.

VR3 wrote: »

I find a panel behind me helps bass tremendously in my room

VR3,
Interesting.
How far behind you?

Do you listen with only one ear pointed at the cardboard fan shaped absorber or do you listen facing towards your speakers with both ears? I guess what I'm getting at is that I think you should face the mic towards the speakers not the cardboard, especially since it may be acting as more of a diffuser than an absorber.

Yep I get that. This might not relate perfectly to your own situation but in my office/listening room I have the speakers up on stands and pulled well into the room over 4 ft from the wall behind them which is half of an octagon, which is said to be a superior shape to a rectangle. Anyway, I never liked the way it sounded when I was in the equilateral sweet spot. The clarity was never there. If I listened off axis near a corner of the room everything was great. If I listened back at the wall as far away from speakers it was good too. In the sweet spot the clarity of vocals and airiness was lacking.

I realized that when I'm off axis and further back I am not getting hit so much with the reflections off of the wall which are out of phase and time delayed to the primary sound wave. Putting open cell foam on that wall has proven this and sweet spot is much better. I have a large piece of mattress foam around3ft x 6 ft taped (wide blue tape stapled to the foam) with a belly in it for air space and the spikey side facing the wall. That has proven the point because subtle vocal separation is so much better in the sweet spot now. It needs to be even thicker.

None of my room treatments are what you would call WAF friendly at all at this point but I can clean them up with more professional looking ones in the future. Work in process.

The boxes act as a diffuser as @Gardenstater suggested. That pic I posted was an architect example for a music hall I believe for USC. Basically a square room makes for the worst acoustics.

One thing you can be sure of is that it's doing a combination of reflecting and absorbing but mostly reflecting. If you look at NRC charts of sound absorption materials vs frequency, they always absorb much less at lower frequencies, especially for thin materials. Your cardboard probably is absorbing the most at high frequencies.

What is the shape of your flattened boxes? I thought you said it formed a fan shape, which is why I said it was probably acting mostly as a diffuser. It's like you're adding a small partial wall that is closer to your ears than the original wall and has angular features. When sound reflects it can exhibit constructive and destructive interferences to the original sound wave depending upon the location of the ear and the frequencies. Those sum up in a way for the ear that can interfere with clarity but they can make the sound seem louder or softer. You can't look at a spectral graph and see the distortion, only the resulting amplitude which is why I was recommending listening tests for specific songs.

You could also get a phase change when a small part of the sound goes from the harder acoustic impedance of the cardboard to the air spaces inside and back out into the room.

Just my current understanding. I'm still learning about acoustics and it is obviously pretty hard to nail down. Anyway, have fun experimenting.

http://hyperphysics.phy-astr.gsu.edu/hbase/Sound/reflec.html