Questions on practical room treatments

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Questions on practical room treatments

Postby desmo » Wed May 16, 2007 2:40 pm

I don't have a dedicated music room so I have to make do with my sala. I get good sound with my setup but would like to optimize the room to push for what's possible.

1. What effect would a carpet have?

2. Would putting some damping material on the ceiling help?

3. I have vertical plastic blinds on 2 big windows, will changing these to curtains help?

4. On stand alone diffuser panels, I asked these questions (to solidtubes)on another thread. I'm thinking of trying them out but their science eludes me.

a) What if speakers don't have backwards firing ports, won't that render the panels placed behind them useless? (Added: How will the panels prevent the reflections happening in front of the speakers when they are placed behind the speaker?).

b) The sound coming from the drivers reach the ears first before the reflected sound right? I think you mentioned earlier that our brain will register only the first sound it hears and ignore the ones that closely follow (the reflections) so why the need to get rid of the reflections?
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Postby troporobo » Wed May 16, 2007 7:19 pm

1) positive in reducing HF reflections

2) sure, same as carpet on floor

3) absolutely, probably greater effect on HF reflections, especially if windows are at first reflection points, need to be fairly heavy though (if you can breathe through fabric it is transparent to HF)

4) sound waves are omnidirectional. Your hearing filters out later reflections to a degree but does still perceive them. Panels are effective especially at first reflection points (see my system thread for an example of small wall mounted versions - i was amazed just how much a small panel can make a bid difference)

None of these treatments will affect LF - that requires mass
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Re: Questions on practical room treatments

Postby Jon Agner » Wed May 16, 2007 8:48 pm

desmo wrote:4. On stand alone diffuser panels, I asked these questions (to solidtubes)on another thread. I'm thinking of trying them out but their science eludes me.

a) What if speakers don't have backwards firing ports, won't that render the panels placed behind them useless? (Added: How will the panels prevent the reflections happening in front of the speakers when they are placed behind the speaker?).

b) The sound coming from the drivers reach the ears first before the reflected sound right? I think you mentioned earlier that our brain will register only the first sound it hears and ignore the ones that closely follow (the reflections) so why the need to get rid of the reflections?


desmo,

since tropo's comments on questions 1, 2 and 3 are sufficient enough, I'll try my best to comment on 4 a) and b)

a) true, the panels would be more useful for rear firing ports and woofers. But the panels are also there to arrest the reflected waves that travel behind the speakers.

b) While the law of the first wave front is correct, there is also such as effect called comb filtering- wherein reflected waves interact with the direct waves, thus altering the signal that the ears perceive.

Hope this helps
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Postby JackD201 » Wed May 16, 2007 8:49 pm

Whew! Madami at mabusisi ito Desmo!

First things first para we're all on the same page.

1. Every material absorbs sound to some extent. There are two widely used methods for classyfying them.

a. NRC - Noise Reduction Coefficient w/c measures 4 frequencies
b. Absorption Coefficient w/c measures 5 frequencies

2. Every material allows sound to pass through even as they convert the energy to heat. This is called the Sound Transmission Rating or ST Rating. Siyempre if the rating is ST=0 then nothing passes ;)

3. What a material does not absorb it reflects.

4. It can either reflect it in one direction or not. In a few directions it is deemed diffracted. When it is scattered in many it is deemed diffused.

5. All items in a room have these qualities.

6. The art is in combining materials and using shapes to acheive SPECIFIC noise reduction for SPECIFIC frequencies.

7. SPECIFIC? Yup every room is unique as is the systems in them. After proper measurement these offensive peaks or nulls can be dealt with. True acousticians will measure a room first. Manny O. does this, Willy does this, Mike Pedero does this, Dar Quintos does this, Jigs does this, Joel Yabut does this, Ferdie Ludo does this. Some of them build, others choose from an array of available products. fld sends the measurements to ASC and ASC will build the required treatments.

8. They can be dealt with in three ways.

a. Passive Correction - using anything under the sun to absorb, or redirect offensive sound waves.

b. Active Correction - using equalizers

c. A combination of both

Notice that I did not say flat response is the goal. For professional purposes yes, for home it is a matter of taste.


Oki Doki! Installment muna tayo.

Question Number 1 : Carpet

Here is a table of Coefficients for carpets of different types

Image

As you will notice te thicker the carpet and if they have backing carpets absorb more of the lower frequencies. The immediate effect is to help in ameliorating high frequency reflections from the floor. Note that it does not do much for the midrange and practically nothing for bass.
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Postby Jon Agner » Wed May 16, 2007 9:03 pm

Jack,

That is what I was trying to point out in the other thread. Details and how to's :wink: :D
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Postby desmo » Wed May 16, 2007 9:07 pm

Am appreciating this, I'm sure others as well. Keep 'em coming sirs. :)
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Postby JackD201 » Wed May 16, 2007 9:37 pm

Question 2: Damping material on the ceiling

Again this would depend on what you are after. Sound shrill or sharp? Damping would do it. Strong first reflection but don't want your room to sound dead? Diffusers would be the way to go. Some fixes like tiles or skyline diffusers are easy enough to get. Custom diffusers hung from the ceilings are called "Clouds". These can be very cool looking. One installation had one in the shape of a piano. Way cool! I like clouds because their adjustability allows you to aim the reflection away from the listening position and onto a secondary surface where the now weakend waves are further diminished by any of the methods already mentioned.

A warning. Many DIY panels use ordinary fabrics. Being around lots of cords and electricity and owing to the fact that these free standing or wall mounted panels are highly flammable. Fire resistant fabrics should be insisted upon. Guilford of Maine offers a wide variety of colors, weaves and thread densities. Vinyl based materials similar to those used for Futura roll up blinds are what I use for my Bass Cylinders. Sorry I don't make these commercially nor do I intend to because i don't have the testing equipment to see if I did them right. I just guinea pig myself :lol: To sell an untested product would be fraudulent in an infomercial kinda way. Dontcha think? :lol:

Question 3: Blinds to Curtains

Again here great care must be taken. Fabric is expensive and so is the labor for getting curtains made. I've seen installations where curtains used were so heavy that the sound became thick and there was little air left. They can certainly help but done improperly they can also cause harm.

Question 4:


a) Ports are tuned to extend bass response and so as far as bass is concerned they are "almost" useless. 125Hz ACs for fabric covered panels with rock wool stuffing from the likes of Purdue (an architectural acoustic supplier) will be in the range of 0.20 to 0.45. Note rockwool is far more absorbent than pressed fiberglass in this range. If your speaker's return route however is between about 2 to 5 feet sufficiently broadband panels will help imaging. If you already have your speakers way into the room and you are listening nearfield within 6 feet. they are still usefull. This time however throw that 10ms thing out the window because this time they help shorten reverberation times for the frequencies they handle.

b) The sound coming from the drivers reach the ears first before the reflected sound right? I think you mentioned earlier that our brain will register only the first sound it hears and ignore the ones that closely follow (the reflections) so why the need to get rid of the reflections?

Lets clear up some bad science here. There is a tiny window in which the average person will not be able to tell what is direct and what is reflected. This "After 10ms" stuff is bandied about by people who probably tried to study but didn't finish the lesson. In actually it isn't even 10ms it is app 9.98ms. Well close enough :lol:

The scientific occurence popularly known as the Haas effect states that reflections that occur between 10ms and 40ms is what matters. Beyond 40ms all is hunky dory again because now the brain can tell it is a reflection. This is a GOOD thing because if you can tell you can do something about it. Personally I would prefer to redirect the first reflection first, diffract it and absorb what's left. This brings a randomized wave pattern with much diminished energy. As visitors to the lair can attest we get phantom images far beyond the side walls and not just beyond the outside of the speakers. This was done with angled walls fitted with 1"x1" slats spaced and then have ASC wall panels mounted at two intersection points each side.
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