Will painting an acoustic panel lower absorbency?

Rives...thanks for the comment.

The results from adding the panels have been very good. I started by completely covering the front and back walls with the 2" thick panels. I then installed panels 2" thick on the 4' tall knee walls along the left and right side of the room. Finally, I added 1" thick panels on the sloping ceilings along the left and right sides of the room. At that point is where I may begun hearing some of the effects of over damping, but the sound is much better now than ever before.

As I remove and cover the panels, I will be doing so in such a way that I can remove some panels, listen to the results, and see if the removal of a few of these panels will "brighten" the sound somewhat. Although my stereo sounds much better than ever, a little "less dead" would be better.

Jcambron: You probably need a combination of other acoustical devices, such as diffractors. You want to get a balance of absorption, so over damping won't work terribly well, which it sounds like you've discovered. You can actually tune (build) diffractors to certain frequencies, which is what we typically do in order to get a good balance in the room. These are not trivial things to figure out. The difficulty is the whole room works together and although it might seem that eliminating reflections with fiber board would get rid of some of the nasty reflections (it will), but at the expense of over damping the room. Our website has more on the subject, but does not go into diffractors. If you go to www.rivesaudio.com and go to the listening room. You can get to the listening room either by clicking on the tag line on the 1st page (not the intro page) or by clicking on "Issues" on the first page. It's a pretty basic tutorial section, and you may already know the information there, but hopefully it's helpful to you.

Rives, thanks for your additional comments. I will take your advice and visit your listening room to see what else you have there that might be helpful. I've always had a decent quality stereo and/or home theatre in my home, but this is my first high end system with a dedicated listening room.

As I listen to various recordings, the "dead" effect we've discussed is much more pronounced on some discs or LP's than it is on others. On many recordings, I don't notice the dead effect at all. It may be that the problem is more directly related to the source material than I first thought. I am going to clock a number of hours listening to my current set up before I start making changes. I want to have a good reference point as I go forward.

Many recordings are very bright and harsh. Particularly CDs that were recorded in the first several years of CD. A dead room might actually help these, so if your collection has a lot of early recorded CDs, the deading effect might be welcomed. There are a number of threads here on A-gon that discuss reference listening material. You might want to take a look at some of those suggestions and buy some (or you may already own) that you would enjoy as well as being able to use as reference listening material. What I find is important is to find a good variety (unless you only listen to one type of music). I generally use a vocal, large symphony, jazz, acoustical guitar, and solo piano. I enjoy listening to all types of music, but these are my favorite types and they work well for me to evaluate a system and room performance.

HI J:

Well, from a simple question about paint to general room acoustics.

Rives is a pro at this and has lots of hands on experience so my $.02 isn't much. But I think he is right on re asking about how much fiber board you want to put in the room and pointing out that it might be best to paint some of it. I would like to hear more from him on practical points of "how to." I'll throw a couple things out if nothing more than to get a response.

I agree with Rives re the over damping. I know some folks actually like the dead anechoic chamber sound but not me. Usually the rationale is that you are listening to direct sound but I just do not care for it.

A few point to consider.

-You will need additional devices to deal with the major low frequency resonances and even the mid frequencies. You can break down how sound acts in a room by frequency. Lower frequencies act like waves, higher like rays, and there is a middle section that is really neither and both. The size of your room determines the frequencies where these regions are. Your fiber panels will not do it all. The bottom line is that, like Rives said, you will want some additional devices in the room to control the frequencies that your fiber panels do not absorb. Stuff like the devices talked about in the Risch site Sean mentioned.

-There are ways to calculate all this (what your room reverberation time is, total absorption at different frequencies, ect.....) but I have not been that lucky with that approach. I use the calculations to get “ball park” figures and then experiment. I really recommend the book I quoted above (F Alton Everest “Master Handbook of Acoustics). It is really well written and a good $35 spent. It is a little work reading and has a lot of good info. On the other hand it is really clearly written and you do not have to be a physicist to take a lot away from it. It’s easier to read than it is to tear down fiber board!

Room calculations seem to have limitations because all speakers have different off-axis response and some “cohere” 6 feet from the speaker and some you need to sit 15 feet away, ect. Read the articles by Toole below and what Linkwitz has to say about a speaker's radiation pattern and room interaction. I tend to think of it as room/speaker interaction and every speaker (or at least each type of speaker)has it's own particular characteristics.

Also the furniture plays a big part as you can see from Rives excellent site. You can, however, fairly easily calculate the resonant frequencies that will dominate your room and tune traps for those as Rives pointed out.

My approach would be to get an idea about the additional traps / diffusers you might want and actually place some of those in the room before you line the whole thing with fiber board. This way you aren’t going to extremes in one frequency area before you even start in another. Just seems more balanced. Then start placing the fiber board. You can get a good idea about the traps needed and where the crucial areas typically are for placing the board from the Everest book or the Risch site.

Lots of work but the room is 50% of the sound. I hope you can take your time on the project because it’s worth it. You know how it takes some people many years to tweak a system to taste? I think it can take a lot of time to tweak a room too. Don't be in too much of a hurry and don't do things you can't undo w/o lots of work.

Anyway...that is all too much advise for not even knowing the dimensions of your room! Take it for what it's worth. Let us know how you do. If not in a post drop an e-mail. I like to learn form other's in this area.

If you are going through all the trouble of a dedicated room you might find these sources interesting.

Two of the best web sites on audio acoustics that I really found helpful.
Art Ludwig’s site. http://www.silcom.com/~aludwig/
Linkwitz Lab. http://www.linkwitzlab.com/rooms.htm

A few articles on line.

Two articles by William Dudleston:

http://groups.yahoo.com/group/Thunderstone_technical/files/Room%20Acoustics/Dudlestone%20-%20Acoustical%20Sense.pdf

http://groups.yahoo.com/group/Thunderstone_technical/files/Room%20Acoustics/Dudlestone%20-%20Stereo%20Effect.pdf

Two articles by Floyd Toole:
http://groups.yahoo.com/group/Thunderstone_technical/files/Room%20Acoustics/F%20Toole%20Room%20and%20Speaker%20Working%20Together.pdf

http://groups.yahoo.com/group/Thunderstone_technical/files/Room%20Acoustics/F%20Toole%20Maximising%20Loudspeaker%20Performance.pdf

Let us know how you come out!

Cheers,