Acoustic Panels

[rlyach]

Well, I finally gave up trying to compensate for the fact that my system is on a dresser, and less than 1 foot from the wall. When I play the music a little louder, I get distortion from the wall. I can't move the speakers any further out and I like to listen a little louder sometimes. I finally placed a 1" piece of foam behind each speaker and that helped tremendously. I finally broke out my miter box and router table and built a pair of acoustic panels to put behind the system. I am using 2" stone wool and acoustically transparent cloth from ATS acoustics. Here are the boxes. I am waiting for the insulation and cloth so I can finish the project.

 

[Follow the white rabbit]

Hi, I personally made good experiences with stone and glasswool with a wooden bracing for stopping the sound to grow...!
chris

 

[Doc B]

I will suggest that everyone interested in acoustic treatment check out the cotton material manufactured by Bonded Logic. It is made from shredded t-shirts and blue jeans. The "acoustical" version is monopolized by one company and commands what I feel are inordinately high prices - because I used to buy the stuff wholesale. But the thermal insulation Bonded Logic makes is essentially the same stuff and can be had at green building supply stores. The material doesn't fill your skin with itchy glass fibers and it actually works better at low frequencies.

 

[rlyach]

Doc,

I wish I had done a little more research before I ordered my insulation. Here is the table of acoustic properties of different materials. The recycled cotton is a little better than the Roxul AFB that I ordered. Oh well. The next time I need to build panels I will rethink the insulation choice.

Randy

 

[4krow]

One of the biggest payoffs for me has been with acoustic treatment/management. Glad that you will benefit too. Opens up the soundstage and depth, etc etc. as you already know.

 

[drewh1]

i second that - I have had great luck with absorption panels. I now use them on front and back walls. I would put them at an angle to speakers on side walls too. I just don't have the room for it in my small living room.  Room treatment is definitely the best bang for the buck in this racket - unless you invest in shiny pebbles   

 

[VoltSecond]

Can the back panel be tuned for a bass absorber?

Is there are way to fire proof the cotton batting?

 

[4krow]

i second that - I have had great luck with absorption panels. I now use them on front and back walls. I would put them at an angle to speakers on side walls too. I just don't have the room for it in my small living room.  Room treatment is definitely the best bang for the buck in this racket - unless you invest in shiny pebbles   

You have shiny peebles? Wow, I only have Tibetian singing bowls arranged in a heart shape on the floor of my living room. It pleases the gods. But seriously, panels are great because they can easily be moved around to determine best placement. I once used a large, heavy quilt behind my speakers and the effect was dramatic. Then I tried it behind my listening position,,,equally dramatic. In the end I preferred it behind my speakers.

 

[rlyach]

VoltSecond,

First, the cotton batts are class A fire retardant. Other insulation is also fire retardant. Using panels to control bass requires different panels and insulation. From what I have read, bass traps are physically larger and many work best in corners. The best bass absorbers are at least 4" thick. If you look at the table in the previous post, 4" Corning 703 gives the best bass absorption. The 2" panels I am building only offer about half the low frequency absorption, but I also need to reduce some mid frequencies. I plan on putting these panels directly behind and on the wall beside the speakers. I experimented with 1" foam and it made such an improvement that I decided to build the panels.

 

[4krow]

Randy,

  You are probably familiar with the side wall reflection waves being able to be visually detected by placing a mirror at a point along the side wall where you can see your speakers from your listening position. This indicates the 'bouncing point' if you will, of the sound waves coming from the speakers and arriving as an unwanted wave at your listening position. Absorbers are most effective at those reflective points. And as I recall bass control devices work best, as you stated, in corners where the bass is concentrated. I look forward to your reported progress in this effort.

 

[rlyach]

4krow,

My situation is very non-standard. I do not have a dedicated listening room. I have placed my system in my bedroom in a corner on a dresser. I know this is not optimal but that is where I have it. The side panel is actually in the corner to get any reflected waves off the back that then are reflected off the side. I don't have room for a full corner trap so this is the best I could do. I tested the setup with 1 inch foam and the sound was much better. Additionally, there are window treatments that help to deaden the reflections off the wall, and the ceiling is vaulted. As you can see, I am limited in what I can do but I think you can see from the picture where I plan on putting the panels. If there is something else I could do I would appreciate any feedback.

 

[4krow]

Randy,

  Your ability to recreate the bedroom as a diagram is very helpful. Let me just say this, experimentation is an incredible tool. What seems odd may well work. I have had bedroom systems too, and they are a challenge. As I recall, lower volume helps disassociate some of the acoustic problems encountered in typical rooms. And if possible, near field listening is helpful. No doubt, you are a thinker, so try brainstorming ideas. You may well be surprised with the results

 

[rlyach]

I finally finished the panels. The sound improvement was very noticeable. The sound-stage is more defined. It is also more consistent over all listen levels. This is a very inexpensive improvement and very easy to build. Notice the pilot light under the 12AT7  .

 

[manis]

Kudos, that looks very very nice!

 

[drewh1]

Yep room treatment is awesome.  I have always wanted to build a diffuser.

http://www.flickr.com/photos/39812136@N08/3711143217/

Maybe my next project - You can make them out of styrofoam and so they can be pretty light.  Maybe my next project.

 

[manis]

Yep room treatment is awesome.  I have always wanted to build a diffuser.

http://www.flickr.com/photos/39812136@N08/3711143217/

Maybe my next project - You can make them out of styrofoam and so they can be pretty light.  Maybe my next project.

Those definitely have a lower WAF, though.

 

[drewh1]

well, I am single and so do whatever I want - there are tradeoffs to that though!

Actually some of the diffusers look pretty artistic IMO, they can be done in wood and look quite nice.

 

[rlyach]

I have some data to report using the panels. The first thing I noticed was that the sound was much tighter. The second thing I discovered was that the system seemed louder. This was very subjective so I got out my R/S sound pressure meter. I tried two different songs, both had a large dynamic range. I tried both slow and fast readings. Without the panels I barely got 86db peaks. With the panels hung and nothing else changed I got 91db. I am not an expert in acoustics but is it possible that the sound coming out the back of the ported speakers, being 180 degrees out of phase with the front, is reflecting off the wall and canceling some of the sound in the room? This explanation sounds sketchy to me, but the wavelengths in question range from 267 inches at  50Hz to 0.7 inches at 20KHz. The speakers are 8 inches from the wall, which is 1673Hz. I can almost convince myself that frequencies up to about 5KHz or 6KHz will experience some destructive interference from the wall. In any even, I can't argue with the measurements. Plus, the sound is much, much better. I love this amp and the Orcas.

 

[Paul Birkeland]

You could gather some evidence to support or refute your hypothesis by tightly plugging the ports with a cork made of rubber or cork, then remeasuring.

I like your approach to this: listen, measure, postulate.  Far too often we have lots of postulation, debatable listening, and no measurements, lol.

 

[4krow]

Randy,

  I am glad that you use your head in these matters. Sometimes, I find myself stabbing in the dark. Strangely, it works more often than it should, but not very scientific.