In Reply to: Room Treatment Question posted by Juan on November 09, 1999 at 23:31:28:
1. Most any speaker will benefit from some room mode damping, and the corner is the best place to put such damping, as that will affect ALL the room modes the most, but especially the deepest (lowest frequency) MODES more than the higher frequncy modes. It is the lowest frequency modes which need the most damping anyway, so as to reduce the deleterious effects of the room. Corner placed bass traps of the resistive type, ala ASC or my own DIY bass traps, will not reduce actual bass output in the room as such, but will tend to damp the room modes much more, and allow clean development of the speakers bass.2. No, this would not be very good to treat the entire room with absorbing materials, as the sound would end up way too bassy and dull.
You have the basic idea right, treat the primary reflection points with a reasonably thick layer of absorbing materials, but after that, you ned to consider that killing the rest of the room only in the highs and uper mids would make the room sound very bassy and dull. See my DIY Acoustics Treatment note at my web site:
http://members.xoom.com/Jon_Risch/a1.htm
for information on home-made treatments AND placement and use.3. An equal thickness of foam and fiberglass has the edge going to the fiberglass, as it tends to have a superior avoidance of HF reflectance at oblique angles, and a slightly better absorption of bass frequencies. As the 8" fiberglass is twice as thick as the 4" foam, it would absorb to a frequency over twice as low.
As for mounting, ALL typical full range absorbing materials absorb better when spaced away from the wall, and the more, the better. There is a minimum spacing that is typically used for almost ALL published measurements, and that is 2". Sometimes the spacing is 4" for the measured and published data, but as many as 6" to 8" of spacing will improve the LF absorption even more.
I suspect that the other poster is correct, in that the foam is too flimsy to support itself, and therefore would be more conveniently instaled onto the wall, other wise a frame would be required.
If you make the room as absorbing as posible in the hihgs and mids, then I think you would be terribly dissappointed with the final sound.
Sometimes, those who construct a basic treatment package, as per my note (two bass traps, and 2-4 wall panels), find themselves uncomfortable with the room acoustics at first, as they have become accustomed to the wall reflections and the sound seems lifeless and dry to them. It is only after they hae lived with it awhile, that they realize just how colored the sound was, and how the room was imposing it's signature over every piece of music played. Once they start hearing the superior imaging, and the more nearly flat system frequency response, they begin to appreciate the sound they are getting, and begin to recognize the same reflection problems in other's room's.
The secret to getting a good tonal balance is to make the spot absorption at the reflection points wideband, that is, don't just absorb the highs and mids, but get down as low as you can. This assures that the bass energy of the relection is not allowed to continue on, while the highs and mids are absorbed almost completely.
The most common mistake people make when attempting to acoustically treat a room is to use too much absorbing material that is too thin, creating a room that has little bass absorption, and almost all the highs and a lot of the upper mids completely absorbed. The end result is a room that lets the bass modes continue to resonate, and the bass portion of the reflections continue on, but kills all the highs, and the classic dull, overly dead room that seems bass heavy is born.
Even after using wideband wall panels, the room modes are still present, and need some attention. This is where the bass traps come into play. They help to tame the room's tendency toward boom and tubbyness, without killing the speakers bass output.
Jon Risch
You can not post to an archived thread.