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I am currently considering room treatment options and have a number of questions I was hoping others could answer.1. Is bass absorption required for my Ariel Transmission line speakers? I know that transmission line speakers "energize" the room, would corner absorbtion eliminate too much bass?
2. I am considering complete mid and treble treatment with Auralex foam products. I am considering the 4" wedge sheets on the walls and ceiling in the hotspots (primary reflection points) and 1" or 2" (help with thickness please) foam panels on the rest of the walls and ceiling. Would this be an effective setup?
3. How does the performance of Auralex foam (4" for the sake of argument) compare to the DIY 8" fiberglass discussed here in the past. I know that the foam is supposed to be flush mounted (per the Auralex web site), and the DIY panels are supposed to be at least 4" away from walls. Any assistance here would be appreciated.
My goal is to create as absorbative a room as possible for mid and treble, and work on base control if it is needed or reccomended.
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
John, you sure now how to explain these things so that they sound logical. I thank you for your reply, however, I have a few new questions to ask now:1. Considering that my listening room is not 56 feet across, and I don't sit 56 feet from my speaker, I should never have to worry about having to deal with extreamly low frequency waves. With this in mind, would DIY panels of your design utilizing 8 inch fiberglass (along with 4" minimum gap from walls) go low enough to cover the bass possible in my room of size 14' x 13' x 9'?
2. I am open to the tube trap design, but have to admit to being quite skeptical of the mechanics of the device. Are the traps only able to absorb wavelengths up to the diameter of the trap?, or do the traps absorb wavelengths longer than the diameter?
3. Ok, lets consider a hypothetical situation where I could produce a treatment device capable of absorbing all the pressure of all frequencies. From what I have read about the mechanics and theory of stereo reproduction, it seems that the ideal enviroment would be no room at all. The ideal enviroment would be the listener floating in space with no reclection points at all. Our hypothetical panels if placed on all surfaces of a room would create this ideal listening room, would it not? If this is the case, why am I reading posts about striking a balance between a live and a dead room. Isn't the ideal an absolute dead room? In my situation, I have limited esthetic constraints, and am striving for audio purity, not simply MY SUBJECTIVE compromise of what sounds best. I also don't care if a conversation can be carried on in the room or not.
If listeners want to here a spacious sound from the music that they listen to, shouldn't that spacousness come from the recording, and not from the reflections and diffusion of the sound in the listening room? How could the sound possibley sound too "dry"? What does that mean anyway? That does not make sence, I don't think that headphones sound "dry", and they operate on a minimal reflection principle.
1. Ever hear deep bass in a car? Bass waves will develop in even small rooms, it is just thatthe ROOM MODES of the smaller room will intrude more than those of a larger room. Hence, the smaller room will SEEM to be limited to it's lowest mode, but this is a subjective thing, and not the actuallity. The DIY 8" thick panels will avoid the worst of the "absorb the highs, but not the bass" syndrome.2. The traps work on a resistive principle, and will absorb down to their VOLUME and resistive limits. Placed in a corner, a 11"-12" diameter trap will provide absorption down to all but the lowest modes in a very large room. In a smaller room, such as yours, they WILL tend to damp all the possible modes efferctively.
3. I hae tried listening to the "perfect" loudspeaker in an anechoic chamber. On special recordings, such as binarual recording made fro headphone use, it can sound uncannmily real. On all other recordings, ones which have been recorded to sound good in a "typical" room, one that has some reflections, they sounded overly derad and artificial.
In rooms that have been over treated, the same thing occurs, only their is NOT benefit of the linear absorption of all frequencies, and the sound becomes quite boomy and bass heavy.
Without special speakers (true omni with full power response art ALL frequencies, not just the lows), and special recordings made to take advantage of this envirionment, you would be quite dissappointed.
My treatment recommendations have been tested, and are tried and true to good sound reproduction. It would be very hard to go wrong if you follow them to the letter. For those who wan tthe most accurate sound reproduction using typical modern recordings, classical included, use ofthe FULL recommended treatment regime will result in a highly accurate and pleasing sound.
Jon Risch
As mentioned by me in the past, including in my system profile (maybe nobody cares), there is company out there who makes great corner traps and other absorbtive panels at about half the price of ASC products, and they look a thousand times better as well. The company is Kinetics Noise Control out of Dublin, OH. Their phone is (614)889-0480, fax (614)889-0540. They will tell you who their closest dealer is, and none is nearby, you may be able to talk them into selling direct. I now have four of their corner traps. Each is shaped in a semi-pyramidal fashion, about five feet long and tapering down to a point. They are about thirty inches wide at the base and shaped such that the base forms a triangle also with the wall corner behind it. They are constructed with a dense yellow foam and fiberglass-like composite and covered with cloth in a choice of colors. When hung with the base up and point down, you can easily stuff polyester fill at the top and down behing the panel to modify the amount of absorption. I paid about $160 per trap through a dealer who doesn't discount much. In my previous home my listening room was the corner of very large great room with a cathedral ceiling, attached open kitchen, and overlooking loft. One KNC trap placed in a corner did wonders to solidify imaging and get rid of bass bloat. My new home has a much smaller, conventional rectangular living room- listening room (until the wife lets me use the 20x20 family room). Four corner units eliminated all booming and bloat and as a bonus, look cool as hell. If you can get them, and don't care to spend many angst ridden hours hoping you don't botch your home-brew project, they are highly recommended.
1. Your ear should tell you if you need bass traps. If the bass is boomy or has peaks then bass traps are called for. Also, you can simply walk around the room with your ear near the wall and hear if the bass energy builds up at any point. Stand back near the corners of the room and listen for build up of bass energy. But, have you first tried moving your speakers around to be sure that you're not exciting some room modes? You need to do this first becasue the first reflection points will change based on the location of your speakers. Check out the sugestions on the Cardas website for a starting point on how to place your speakers.2 and 3. The Auralex products appear not to be very good absorbers based on the absorption data which is presented on the auralex web site (see the page labeled NRC testing data). Firstly, they are not very dense (0.3 lbs/cu ft) and this is refelcted in the NRC data that is presented. Mounted on a wall the 2-inch panel does not provide significant absorption below about 500 Hz and the 4 -inch panel quits at about 300 Hz. Jon's DIY panels absorb to well below 200 Hz, a claim that I have verified using the ETF room acoustic program with my system.
All absorbers benefit from being moved out from the wall. Spacing a 1-inch panel 3 inches from the wall gives it the absorbance of a 2-inch panel placed directly on the wall. I suspect that Auralex suggests mounting their panels on the wall because the foam is not stiff enough to stand up on it's own. If you decide to go with the auralex and mount it on the wall use only the 4-inch stuff. Of course many find the appearance of the auralex stuff more to their liking than the larger DIY panels, but performance is the price to be paid.
For a fairly complete discussion of this, you might consider getting a copy of the Master Handbook of Acoustics-it fairly easy reading and will leave you with a good appreciation for what you need to accomplish.
I've also found a company, Acoustical Soutions, in Virginia which makes wall panels from glass fiber board which are reasonably priced and seem to be very good based on their NRC data. By the way for those of you building Jon's DIY panels, this company also sells the Guilford fabric that is used to cover the commercial panels. It's 19.50 per yard. Also, for those who are using decorator burlap and wish to fireproof it there is a company called Flameseal (http://www.flameseal.com) in Texas which makes a spray-on product to fireproof fabrics, its 30.00 per gallon. Good luck.
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