Help w/ beginner s room treatment

Felthove:
1. An absorber does just that, it absorbs sound. The newspaper things I described, Sonex panels are examples of absorbers. Diffusers do that, rather than absorb the sound they reflect it, but not uniformly like a flat wall would. An example would be the RPG diffuser panels. You can make diffusers with wood or other material, you just make small sqares or triangles that are varying heights. Diffusers are frequently used behind the listener to break up the sound, but still have some sound reflected to create ambiance.
2. The readings on the SPL meter are not correct. The meter either needs to be modified or you just add the correction values. The values are as follows:
10Hz +20.5
12.5Hz +16.5
16Hz +11.5
20Hz +7.5
25Hz +5
31.5Hz +3
40Hz +2.5
50Hz +1.5
63Hz +1.5
80Hz +1.5
100Hz +2
125Hz +0.5
160Hz -0.5
200Hz -0.5
250Hz +0.5
315Hz -0.5
400Hz 0
In order to correct the low frequency roll-off, you can do the following modifications to your meter. This will make the meter FAR more sensitive to low frequencies and allow measurements with very good accuracy to well below 20 Hz. Due to the increased sensitivity at very low frequencies, it is possible for low frequency "thumps" to slam the meter if using a very low SPL setting. In order to prevent meter movement damage, take precaution not to peg the meter off scale on a regular basis. If this is occuring regularly, you either need to move up to a higher SPL range on the meter or take more caution as to how your performing your tests. All of the following capacitors must be rated for AT LEAST 15 volts or so. Size does matter, so try to use the smallest package possible.C1 & C2 are changed from 1 uF to 10 uFC3 & C4 are changed from 1 uF to 47 uFC7* is changed from 10 uF to 220 uFC8 is changed from 100 uF to 470 uFC9 is changed from 22 uF to 220 uFC15 is changed from 100 uF 220 uFWhile all of the above parts are spec'd as microfarads, the following is in picofarads. Do not confuse the two values or the meter will not work very well at all. This last change helps minimize high frequency roll-off that is inherit in the stock microphoneC12 is changed from 33 pF to 12 pF.Please note that all of the above parts can be soldered directly in place of the originals EXCEPT C7. Due to its location, a "normal sized" 220 uF cap will be too big to allow the case to close correctly. In order to get around this, simply solder it on the "solder side" of the board instead of on the "parts side" of the board. Pay special attention to the POLARITY of ALL of the caps as you pull them out to replace them. For this reason, i recommend pulling and replacing the caps one at a time to minimize confusion. Once all of these mods are done, the meter is more than accurate enough for anything that a home audio enthusiast would ever need use of. If you really want to "get crazy", you can remove the factory installed mic and either remotely mount it on a "wand" or make use of a calibrated mic like those available from Old Colony.

Note: I need to give Sean credit for providing us A-goners with this valuable information the first time.

3. ASC is a company name: Acoustic Science Corporation I believe. They make tube traps and other room acoustic devices. WAF= Wife Acceptance Factor. This is very important to many of us in the real world.

Thanks to all for your responses (especially Abstract). I do, however, have a couple of clarifying questions:

1) what's the difference between and absorber and a diffuser (both in purpose and in the actual item one would use)

2) what does it mean to say that the Radio Shack SPL meter is "not linear" and that I need to make corrections?

3) What do ASC and WAF stand for?

Thanks again!

Thanks: Yes, the fibers would be a major problem if released into our household. If I build one, I will place it in a plastic bag and rough it up a little to see how well the batting performs.

Dekay--looks like Sean beat me to answering your question--and I agree with his comments. I have used fiberglass in a built in bass trap, and it works well. Since it's built in, I have less of a problem with fibers getting into the room.

Great posts everyone. You sound like quite a bit more than a beginner to me too. Something I have found to be beneficial is to put plants and trees in the corners of the room. This has high WAF too. Also, if you have a coffee table, try to cover it with some non-reflective material, or make it easily movable. Lastly, if it is practical for you, move your speakers out into the room for serious listening & mark their location. Moving your speakers out into the room can solve quite a few imaging and bass boom problems.

Fiberglass is about as good as it gets in terms of sound absorption unless you want to start spending big cash. Like anything else though, due to varying densities and overall thickness, the attenuation / absorption ratio may not be linear across the band. As such, ANY type of "sound panel" or "absorber" can create a tonal imbalance due to only working on a specific section in the audio spectrum.

The problem with fiberglass is that it is literally a fiber. As such, some people are afraid of the fibers "floating" into the room and imbedding in their lungs ( not to mention pets ). A simple "trick" that is mentioned in several of the "DIY" bass trap designs is to wrap the finished product in Polyester batting and then cover that in some type of coarse fabric. Most mention Burlap in that it is non-reflective, relatively cost effective and can be dyed easily to match an interior. The batting acts as a filter to the fiberglass and the covering material lends a professional look to the finished product. Covering the ends of the tube trap with some type of finished wood also looks quite nice.

For some good DIY projects ( acoustics, cables, tweaks, etc...) try checking out this site:

http://members.nbci.com/Jon_Risch/index.htm

Hope this helps some of you out while keeping a few bucks in your pocket. Sean
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Abstract: I have read some of the plans for DIY bass traps and had wondered if just using a ready made wire tube (such as those used to protect and train plants in gardens) would work if stuffed and then covered with fabric? I have not heard of using newspaper, but had thought of just stuffing it with wall/ceiling insulation (think that it may be fiberglass). Does paper work better for low frequencies?

Well, your not that much of a beginner to recognize the room's effect on the system. There are a few good books on this subject that can answer far more than anyone can in a post. One is Robert Harleys "Complete Guide to High End Audio" and the other (if you want to really get in depth) is Master Handbook of Acoustics.

Some of the issues are pretty easy to solve. The windows behind the speaker. The rear wall--because the couch will be very close to the rear wall you will need some absorber/difuser or you will hear that reflection and it will definitely muddy the sound--drapes are a good idea, heavy fabric that will absorb the sound. Sidewalls: I would also recommend first order reflections have either an absorber or diffuser. Floor: If it isn't carpeted I would recommend buying an area rug. This will take care of most high and mid frequency issues. That's pretty easy. Also, since you mentioned that this will be a family room--and let's face it, Sonex has never been in any Home and Garden magazine--you can build a frame for the Sonex and cover it with a lightly woven cotten or other fabric. You will get near the same results sonically and usually MUCH better results from your spouse.

Bass frequencies need to be addressed as well, but they are much harder to deal with. I don't know what speakers you are using, but based on your room dimensions (I don't know the ceiling height either), you are going to have some bass issues to deal with. You can buy computer programs that will tell you where the problems lie--but I recommend just measuring the actual results and then tackling the problem (if there is one). Get a Radioshack SPL and the corrections for it (it's not linear), but if you do a search on the forums you can find the correction. Use a test CD that will give you warble tones from 20Hz to 500Hz (higher is fine). Then plot the SPL at the listening position. If your problems aren't too bad (no more than +6dB at any frequency below 80Hz) you can probably make a good correction with bass traps or other similar devices. It's difficult to make large bass corrections with only acoustic treatment. Assuming you need bass treatments you have a couple of options. You can buy bass traps and ASC or others will help you based on the plot and the room as to what you need. If you like to experiment you can make your own bass trap with a frame about 3 feet high and large enough to fit newspaper in it (it has to be open on the sides). Fill it with newspaper and cover it with WAF certified fabric (see Better Homes and Gardens). You can start with 2 in the corners behind each speaker. Moving them will change the attenuation. Also the amount of newspaper will change the amount of absorption.

Good luck--happy listening.