Audio and Room Acoustics (Building a Listening Room)

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Audio and Room Acoustics (Building a Listening Room)

Postby jadis » Wed Jul 14, 2004 11:01 am

In the letters to the editor wherein my letter to HP was published, I wrote primarily to thank them for the great article one of their writers wrote about room acoustics and its great effects to our sound.

Back in '84, I had Bose901 S3. ( I guess jjm will tell me who he is now since he must be pleased with this newsbit. ) I put them in a squarish room about 16' x 16'. The sound was not a bit close to what I heard in the showroom where I bought the speakers (locally). I remembered reading in Audio magazine about someone putting eggtrays on his ceiling to 'tune' his room and to diffuse the reflected sound. I sent
my guy to the palenge to buy 200 pesos worth of eggtrays. I think he came home with a jeep full of eggtrays. I had them thumbtacks-ed to the ceiling and, boy oh boy, my jaw dropped at how solid and how
pure my sound became. I recall that it even sounded good while I was OUT of the room listening through the door!!! That was the beginning of my quest for proper room treatment.

I then read about the LEDE concept in Audio mag. Live end Dead end. At around '86, me and my very technically oriented audio buddy set out to actually follow the LEDE to the hilt. Based on specs of the
article, we constructed wooden frames that looked like Planar speakers and stuffed the front side with fiberglass wool from top to bottom with plywood as backing. Then we covered it with cloth. These panels were supposed to be placed behind the speakers. I did only on panel, but my friend made his acc. to the real specs, meaning it has to be 3 panels folded by hinge to resemble a phone booth. (without a door)

In my single panel, I was surprised to hear that my soundfield has deepened. Highs became less harsh and mid was very focused and solid. My friend reported even more dramatic effects with his 3 piece panels on EACH Spica TC50. I visited him am was utterly dumbfounded beyond belief that despite have all three sides surrounded by flat panels of fiberglass (leaving only the front side open for direct speaker sound to travel to us), his sound actually has a solid CENTERFILL! I was like the sound from the speakers PIERCED through the panels and created a holographic image in the center. Being a technical guy, he explained that it is bec our ears, listening to direct sound, translates that to our brain, and we 'see' the center imaging bec our brain told us what was really recorded in the musical source, that there was a center image in the recording, barring the physical barriers that were set up. The phone booth panels (as we love to call them ) ultimately
got sold to Lito Gelano whose wife was not all that happy to have them planted in the main living room where he used it to demo his gear. The idea of the panels was to create a dead end at the speaker are and the live end at our listening chair area. Not bad, but ugly.

After that, I moved to another house, and transported all my equipment to the living room of this house. Marble floor, cement walls, and nothing else. Remembering my sound from the old treated room, my sound became like ten cents. In short, trash. I was too unhappy I decided to build a new room on top of my
garage. Once finished, I treated the walls with cork initially, and the sound was bad, like I was inside a drum with someone banging on it. I invited Mang Dima who brought along my good friend, Eric Dimson, an organist and pianist who would become habitual visitors to my top- of-the-garage room. Eric made great suggestions as to what to do. I changed the cork to acoustic boards and immediately the harsh
echo disappeared. Eric suggested putting slats on the side walls to diffuse the sound even more, and I did; and the sound again, improved further. BTW, the room was 'small' about 13' x 16'. Hence the necessity
to treat the room since the sound waves would be travelling at faster velocities. At this point I came across Tube Traps. And after reading from Stereophile how it was made and what it was made of, another
friend of mine ventured into making them via our ingenious craftsmen. The traps were to be put in corners, preferably at the speaker end, where the sound pressure velocity would be highest. It has to be killed, to prevent bass nodes from clouding our sound. In the end, both of us
loved what the traps did, reducing bass boom and producing a more balanced sound from top to bottom. The sound here was warm and I enjoyed it. Speakers then were Thiel 3.5 and I had ARC D115, and SP10MKII with my present analog system. The year was about 1987.

The house had to be demolished, torn to the ground to build a new one in 1990. 3 years of limbo. But by the time my house was done, I had what I have now, in the pictures I posted. 17' x 23' room with a 10' light dome ceiling sprayed with acoustic fiber from the UK. I installed wooden slats all around the wall after that
spray. And built my own little RPG diffuser to put behind my listening chair. I made corner traps, stuffed with fiberglass and one round tube trap for the center image to be more solid. Also made 6 pcs of Room
Tube ( our friends love to dissect one pc and build it locally to be cheaper), and floor entirely rugged. And when I owned the gargantuan 800s, I had to make Bass Tunes to lessen the boom. All worked well,
and that is what I have now. My room is tuned to produce a warm sound that is tailored to my listening bias. And I prefer a wide open soundstage that is deep, hence my placement is a 'pull-out' from the
back wall, something I learned from Mang Dima and Eric. And as as final piece, I should mention that I was very impressed with Eric's room, with JBL 250s pulled in midway into the room, the sound was incredible, realistic and life-like that creates a sense of an eerie 'you- are-there' feeling...I learned from the guy, and I'm glad Mang Dima brought me there. And, umm, the last thing I have to say is, Eric's is the first audiophile I know, or maybe ever, to put his turntable INSIDE his bathroom to prevent room reverberation from affecting his analogue system. What dedication. OF course in those days, we did not have turntables with good isolation like we have now, but still, that proves that the quest for good sound is infinite.
Last edited by jadis on Wed Jul 14, 2004 7:32 pm, edited 1 time in total.
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Postby qguy » Wed Jul 14, 2004 11:34 am

Jadis,

will the phone booth treatment work for smallish rooms with bookshelf speakers, 9 x 15 room concrete walls and wooden floor ?

whats the effect if a sub is behind the panel ?

Would it also work if it was designed like a divider spanning the whole wall behind the speakers

how high / thick is the panel ?

thanks...

This should not be difficult to make...problem na lang is where to store those panels when not in use......hmm under the sofa ...heheheh
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Postby jadis » Wed Jul 14, 2004 1:23 pm

qguy,

I feel that with such small size room, the speaker area would be too overcrowded
with the phone booth panels. What is more probable to work would be what I did, a flat
panel behind the speakers to absorb the back waves. The height of the panels would
be about 2 feet higher than your speaker top height. The width would be about twice
the size of your speaker width, and the thickness is about an inches or 1.5 inches of
fiberglass flat sheet. When wrapped with khaki cloth, the panels really would look like
magnepans.

I think that entire panels at the full back wall is not a good idea. With the pair of
movable panels behind each speakers, you can adjust the distance between it and the
speakers, like tuning. And I do not believe the sub will have any problems with these
panels. In those days, I don't store it, just left it standing there behind my speakers.
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Postby qguy » Wed Jul 14, 2004 1:51 pm

Thanks

also what would be a good initial distance of the panel from the wall and from panel to the back of the loudspeakers ?

Fibreglass sheets..is this the same material as those commonlu used to cover ceilings in most offices ?
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Postby jadis » Wed Jul 14, 2004 2:07 pm

qguy,

to be safe, start from one meter to speaker or more and another meter or more to
back wall. you can play with it. that's the beauty about it. and yes, that is the stuff, only,
tell them you dont want the one with aluminum foil backing, just plain fiberglass, and,
be careful, they are itchy stuff, use long gloves.
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Postby qguy » Wed Jul 14, 2004 2:25 pm

thanks...I try foam first since I have a pair of foam that is about 5 feet high and 3 feet wide...
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Postby jadis » Wed Jul 14, 2004 2:32 pm

qguy,

I had tried foam and it has very minimal absorpsion value. Unless it is moulded like
the Sonex Wedge type to diffuse. As flat entity, it has little value.
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Postby highlander » Wed Jul 14, 2004 2:38 pm

Jadis,
I'm interested on the tube traps. Can you share the plans?
How about the slats on the walls, any specific dimensions?
I will be moving to a new place where the walls will be concrete
so I need to treat the room.

Thanks
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Postby jadis » Wed Jul 14, 2004 2:55 pm

highlander,

There was an issue of Stereophile that talks about it's make and size. It's too long
for me to remember the details. My slats are like 2 x 3 inches and they are like 5 to six
inches apart.
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Postby highlander » Wed Jul 14, 2004 4:16 pm

Are your traps similar to these?

http://www.teresaudio.com/haven/traps/traps.html
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Postby jadis » Wed Jul 14, 2004 4:21 pm

highlander,

Yes. You got it. A great resource for all. Fiberglass is the yellowish material. And
that is the same material used in RoomTunes and BassTunes.
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Postby highlander » Wed Jul 14, 2004 4:24 pm

Are your traps similar to these?

http://www.teresaudio.com/haven/traps/traps.html
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Postby jadis » Wed Jul 14, 2004 4:31 pm

highlander wrote:Are your traps similar to these?

http://www.teresaudio.com/haven/traps/traps.html



double post? :)

Yes, that is it.
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Postby highlander » Wed Jul 14, 2004 4:32 pm

Sorry, double posted....
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Postby highlander » Wed Jul 14, 2004 4:37 pm

The article only mentioned about the diameter of the tube relating to frequency. How about the length - is it also critical?
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Postby jadis » Wed Jul 14, 2004 5:02 pm

highlander,


imo, it should be taller than your speakers. the originals maybe like 6 feet tall
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Scientific Acoustic Design

Postby noctilux » Wed Jul 14, 2004 7:24 pm

The first line of defense in a good sounding room is having the right dimensions. The following is the basic ratios used formulated by designers to end up with the right dimensions (HxWxL):

Sepmeyer:
1x1.14x1.39
1x1.28x1.54
1x1.60x2.33
Louden:
1x1.4x1.9
1x1.3x1.9
1x1.5x2.5
Volkman
1x1.5x2.5
Boner
1x1.26x1.59

These ratios of Height vs. Width vs. Length is related to the way the dimensions of the room magnify a certain frequency. If you are lucky enough to have a room to be within these ratios, it means that a certain frequency or axial modes will not be bunched up. Bunched up axial modes let's say in the 280 hz range may indeed pose a boom in the upper bass area. As an example, a length of 19.5ft will have a resonance of 29.1hz. Multiples of this frequency can be mapped to get the axial modes of your room. It's going to be difficult to explain further without going into even more jargon but as a baseline, you can use the ratios above to find out if your room makes the grade.
Cheers
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Postby jadis » Wed Jul 14, 2004 7:35 pm

noctilux,

great info, noct. keep them coming....
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Postby quarterback » Wed Jul 14, 2004 11:03 pm

Jadis,

I previously owned a pair of Maggie MG1.5 (am not to sure about the model na) and I based the design oy my diffuser on the said speaker. The DIY diffuser shown here is 2' x 5' x 1" thick medium density accoustic board wrapped in abaca fibers. The frames are made of narra planks. Am no audiophile so am not sure the placement is correct nor it really made any difference.

http://www.pbase.com/image/31337190
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Re: Scientific Acoustic Design

Postby Jon Agner » Thu Jul 15, 2004 10:59 am

noctilux wrote:The first line of defense in a good sounding room is having the right dimensions. The following is the basic ratios used formulated by designers to end up with the right dimensions (HxWxL):

Sepmeyer:
1x1.14x1.39
1x1.28x1.54
1x1.60x2.33
Louden:
1x1.4x1.9
1x1.3x1.9
1x1.5x2.5
Volkman
1x1.5x2.5
Boner
1x1.26x1.59

These ratios of Height vs. Width vs. Length is related to the way the dimensions of the room magnify a certain frequency. If you are lucky enough to have a room to be within these ratios, it means that a certain frequency or axial modes will not be bunched up. Bunched up axial modes let's say in the 280 hz range may indeed pose a boom in the upper bass area. As an example, a length of 19.5ft will have a resonance of 29.1hz. Multiples of this frequency can be mapped to get the axial modes of your room. It's going to be difficult to explain further without going into even more jargon but as a baseline, you can use the ratios above to find out if your room makes the grade.
Cheers
Noct


Noct,

like you said, great if the room dimension is similar to the one above, and if you only have a chair, amp & speakers inside the room. However, most of us here do have to contend with using the living room or bedroom as the listening area, so other factors (i.e. furniture, plants,displays) come into play.

So, the next question would be: considering these factors, how would one provide treatment to a room that will have a minimal effect on freq. & axial modes but at the same time can also pass the WAF? :)

Mr. Jadis,

Thank you for enlightening us on room acoustics... As one AES member had said (after visiting the audio fair) " Room acoustics is the other 50% of a good listening environment"

Cheers. :)
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