Room treatment in phases...where to start

08-01-13: Larryi
My dealer believes that the center of the front wall should be a hard reflective surface. This is consistent with a listening room a friend of my has which was designed by the acoustic firm Rives. The front of the room has a very large, curved, convex reflector made of wood. The corners of the room have bass traps built into them.

Thank you Larryi...I am going to give it another listen tonight with and without the pillows on the front wall. This feedback is very interesting. When I look at people's room setup, I usually see either some sort of diffusion like the curved surface you refer to or absorption panels. Now I am utterly confused on what to do. What I do know is that I need minimal treatments in my room. Unfortunately I cannot treat the first reflection points because there is a window on one side and a closet door on the other. Hmmm....what do to???

A clearer understanding of the room generated problems and frequency response characteristics should make selecting the correct solutions a lot easier

You need to establish what the problem is .. where it is occurring .. and how to defeat it correctly with either absorption or diffusion

The other thing that is critical to understand is called .... the “Schroeder Effect”

Basically your room has a Transition Point .. above this Transition Point all frequencies behave like RAYs or BEAMs of light launching from your drivers in a straight line until they come into contact with a surface and are reflected

Frequencies below your rooms Transition Point behave like pressurizing modes .. pressurizing the entire room .. imagine your room is a balloon and you blow in and out .. the balloon expands and contracts evenly in all directions

So above the room’s T/P frequencies will beam like Rays of light and must be “Absorbed” where they strike ... below the room’s T/P the room will be pressurized similar to the balloon example

It’s not as important to know the point where your room transitions .. but the fact that it does and frequencies behave differently above and below it and must be treated separately

The problem with the pressurization is certain areas of the room naturally boost the response and add extra energy ... this is Room Gain and not to be confused with Standing Waves

The points of highest pressurization are the 4 corners of the room and at the mid point of each wall .. if you want to reduce bass energy with a resistive bass trap you need to place it in the corners where the problem is occurring and at the mid point of the wall where the pressure is also the highest

That’s not to hard to understand .. above the T/P absorb at point of strike .. below the T/P absorb at the 4 corners and then any mid wall you can starting with the wall behind the speakers

The front of the room has a very large, curved, convex reflector made of wood.

I believe this is a diaphragm style Bass Trap meant to reduce the excessive energy at the mid point of the back wall

Lets start on the bottom as cleaning up the bass always improves the midrange .. so fix the bass first

In your room with the back opening into another area I would first put a basic 4 inch thick 2x4 foot Bass trap in each corner behind the speakers .. I would also add 1 or 2 more (side by side) Bass traps on the same back wall at the mid point spaced out 4 to 6 inches from the wall

What this does is dissipates some of the excess Bass energy that is created in the corners and wall mid points thus taming done the ringing

Next up the ladder and above the room’s T/P would be first reflections ... I understand you have issues with windows but she will never know if you toe the speakers in a bit ... this will not eliminate the first reflection problem but move the point where the RAYs hit the wall to a less offensive spot

Other issues to be treated are also all above the room’s T/P and behave like RAYs ...

Echo Slap or the sound bouncing between two parallel surfaces ... this could be your next move after the back wall .. place a 2 inch thick 2x4 bass trap directly to the sides of your speakers and against the side wall .. this will reduce the energy that is reflected off that part of the side wall and bounces back and forth between the the other wall causing ringing

Other room generated problems are comb filtering or the same frequency running by you ears numerous times due to being reflected and Long Decay Time (RT60s) where the note just lingers to long

Here’s one for Long Decay times and she’ll never see it coming ... install 6 or 8 inch curved crown molding around the ceiling’s perimeter .. energy travels along the ceiling and up the walls and meets at the point where they intersect .. here the excess energy is reflected back into the room again extending the note’s ringing ...the curved crown molding diffuses the reflection and tames down the Long Decay Times

Davehrab, thank you for taking the time to writeup such a thorough response! I truly appreciate it. Just to be clear, when you say "back wall" you are referring to the wall behind my speakers right?

Yes that is correct ... the wall behind the speakers is what I was referring to as the back wall ... that can be a confusing term

If you are handy and can make some nice frames it’s easy enough to get the 703 and 705 material or better yet and less expensive is Roxul which is what I made mine out of ... if you want to buy ready wear off the rack be aware the the quality varies quite a bit

Kits are usually disappointing and the bags I bought were a nightmare .. they're not even offered any more because the guy had so many problems

I think you have a much better handle on it now that you see the problems and where the occur