Audio and Room Acoustics (Building a Listening Room)

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Postby zach » Thu Jul 15, 2004 11:08 am

ey jon w/c aes member was that?
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Postby Jon Agner » Thu Jul 15, 2004 11:22 am

zach wrote:ey jon w/c aes member was that?


Zach,

Sorry, I forgot, :( but he was there during the audio fair. I happen to talk to him while waiting for an elevator.
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Postby qguy » Thu Jul 15, 2004 11:34 am

Guys...I mean Jadis..hehehe

I have a pair of 12 inch subs, one is in the right corner of the front wall and one is dead spot in the center of the front wall... front wall is the wall infront of the listener...I have great bass everywhere except where I am seated which is about 10 feet away from the subs and 5-7 feet from the back wall...any ideas what to do ?...BTW...I cant move the subs so treatment like panels would be the only way to go..or can equalizers help ?

would panels behind the listener help ?

ok cge na nga...anyone can answer...hehehe
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Postby noctilux » Thu Jul 15, 2004 12:02 pm

[quote]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?


Jon,

These ratios for room dimensions are citical for closed rooms and usually used as empirical design data for control rooms and mastering rooms. In the residential environment, it may be rare that the same situation applies especially for living rooms which are adjacent or part of other living areas (i.e. dining, kitchen, staircase, foyer). Bigger open spaces are easier to control in terms of room dimension resonant frequency and related axial modes. The problem lies however in the focus of sound in terms of soundstaging and imaging due to asymmetrical layout of the speakers vs. the listening position vs. room boundaries.

The use of absorbers and diffusors against room boundaies lies the trick. Put these on first reflection points in your room. You can opt to keep the Live-end, Dead-end setup. Dead being the rear of your speakers, Live being behind your listening position. Diffusors are used for live-ends.

The best absorbers (next to people) that lie around the place are overstuffed sofas and lounge chairs and heavy drapes. Next move is to use 4 inch fiberglass stuffed panels which may be a problem in domestic spaces. Further control of soundwaves through diffusors is another tool to use. What Jadis may be using are the clones of the recording industry standard RPG diffusors. These are actually called quadratic residue diffusors used to breakup the reflection of sound on the live end of the room. My best bet for WAF for this are open bookshelves. Useful for both storage and sound diffusion. Stuff it with books, vinyl and cd's and you're ready to rock.

The real world situation in residential spaces is always the difficult part in sound control. That's why my listening room is stuffed with 15 years of all my junk, tames the listening environment pretty well. In your case, taming resonances is always easier with limited bandwidth mini monitors because the most difficult to control is actually the lower frequencies. That's why we wonder why smallish speakers sound better, it's quality vs quantity.

Guess what, sometimes you don't need any of this cr_p at all. I've heard set-ups in living rooms that sound good at first crack without too much fuzz, just regular residential furniture. I was lucky to get that sound in a secondary listening area in my house. must be good feng shui working...

rgds
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Postby noctilux » Thu Jul 15, 2004 12:40 pm

qguy wrote:Guys...I mean Jadis..hehehe

I have a pair of 12 inch subs, one is in the right corner of the front wall and one is dead spot in the center of the front wall... front wall is the wall infront of the listener...I have great bass everywhere except where I am seated which is about 10 feet away from the subs and 5-7 feet from the back wall...any ideas what to do ?...BTW...I cant move the subs so treatment like panels would be the only way to go..or can equalizers help ?

would panels behind the listener help ?

ok cge na nga...anyone can answer...hehehe


When you walk around the room and you feel you have great bass may mean you are at the locations where axial modes are strongest (aka bass boom)

Remember, human hearing is more sensitive in the mid bass area, 60hz-120hz. You may not really be hearing bass in the sub region but in the mid bass region. Stuff below 40hz are often synthesized electronic music, theatrical sound effects and of course the venerable 32ft pipe organ. You hardly hear stuff below 40 hz but you feel it psychoacoustically. This feeling gives you a feeling of the size of the instrument or music.

I think your problem lies in balancing the sound rather than streghtening it at your listening position. Bass is best controled by speaker positioning than room treatment. Keep your sub away from boundaries and behind your speakers to better balance your sound. Better yet, try using your speakers without them and slowly bring the volume up. Low frequency is the hardest to tame due to it's long wavelength. You may need either a humongous bass trap or an act of God. With room dimensions fixed, room treatment is only secondary, speaker positioning always primary concern.

Sorry guys to take up so much space. I may end up oversimplifying things and generalize too much. This may not be the right venue to explain things in greater detail.

rgds
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Postby jadis » Thu Jul 15, 2004 1:05 pm

qguy wrote:Guys...I mean Jadis..hehehe

I have a pair of 12 inch subs, one is in the right corner of the front wall and one is dead spot in the center of the front wall... front wall is the wall infront of the listener...I have great bass everywhere except where I am seated which is about 10 feet away from the subs and 5-7 feet from the back wall...any ideas what to do ?...BTW...I cant move the subs so treatment like panels would be the only way to go..or can equalizers help ?

would panels behind the listener help ?

ok cge na nga...anyone can answer...hehehe


sorry, qguy, I wouldn't be able to help bec Ive never used subs
in my listening room. I know it's a tough problem, and I hope someone
here would know more about this.
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Postby jadis » Thu Jul 15, 2004 1:14 pm

Low frequency is the hardest to tame due to it's long wavelength. You may need either a humongous bass trap or an act of God. With room dimensions fixed, room treatment is only secondary, speaker positioning always primary concern.

noct

That is exactly why I have not owned a sub in all these years.
I had Entecs in mind before, offered to me, but I declined to buy it.
It has earth shaking and chandelier shimmering qualities but I knew
I would not be able to intergrate it properly into the music. But
I have one for my video system in my bedroom. MK. 12" powered, it
rocks like hell, really, and I enjoy it. For some reasons, on DVD musicals
and concerts like Eagles on DTS, a sub is a must! And I do not even
have any sort of room treatment for my video room except for my
double layered curtains.
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Postby qguy » Thu Jul 15, 2004 1:38 pm

hmmmm

aint the B&W 800's a sub with satellites glued on top :twisted:

jadis wrote:
That is exactly why I have not owned a sub in all these years..
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Postby jadis » Thu Jul 15, 2004 3:28 pm

[quote="qguy"]hmmmm

aint the B&W 800's a sub with satellites glued on top :twisted:

[quote="jadis"]


qguy,

The one on top is a woofer, just like the one below, they are
identical and part of the mid and the hi's- meaning, they are connected
to a single crossover network inside which is driven by one amp. The idea,
it is said, is for the top woofer to cancel out the bass node at exactly the
frequency range that the lower woofer reproduces; that in turn, produces
a more uniform bass response without boom. By sub, my understanding
is that it is a separate woofer assembly that is either powered with internal
crossover and amp, like the Entec; or a woofer that has no internal
crossover nor amp but has an EXTERNAL crossover and it needs
an external power amp. The 800s' woofers is neither. Or to be
more precise, the 800s are full range loudspeakers (one tweeter, one
midrange driver, and 2 woofers per side) and not a satellite/subwoofer
combo.(examples of the latter are the Celestion 600/6000 sat/ sub combo,
the Spica TC50 with whatever is the model for its sub ( I forgot), or
such independent 'mating' like ProAc Tablets with Entec Sub, Rogers LS7
with RH Labs ( once used by Mang Dima ), or the Martin Logan CLS
mated with the Celestion 6000 sub ( HP used to rave about this ).
Last edited by jadis on Thu Jul 15, 2004 6:29 pm, edited 1 time in total.
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Postby aero » Fri Jul 16, 2004 12:46 pm

Thanks, jadis, for sharing your experiences and in the process starting this interesting discussion on room treatment. This seems like a good area for DIY, e.g., the traps that you built and the diffusor (QRD, as pointed out by noctilux?). A Web site was posted earlier for the traps, and info can be found on the Internet as well for designing QRD diffusors (okay, alam kong redundant 'yan). If anyone's interested, some months back I came across a freely downloadable Excel spreadsheet as an aid for designing QRDs (1D and 2D), it's in Spanish but there's very little text (and if you want I can help you with that). With the measurements churned out by the program, should be no trouble for anyone handy with a saw or with access to a neighborhood karpintero.
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Postby jadis » Fri Jul 16, 2004 6:57 pm

aero,

thnx too for joining in...keep your inputs coming.
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Postby dogears » Sat Jul 17, 2004 7:48 am

Cool story :D
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Postby noctilux » Sat Jul 17, 2004 10:48 pm

aero wrote:Thanks, jadis, for sharing your experiences and in the process starting this interesting discussion on room treatment. This seems like a good area for DIY, e.g., the traps that you built and the diffusor (QRD, as pointed out by noctilux?). A Web site was posted earlier for the traps, and info can be found on the Internet as well for designing QRD diffusors (okay, alam kong redundant 'yan). If anyone's interested, some months back I came across a freely downloadable Excel spreadsheet as an aid for designing QRDs (1D and 2D), it's in Spanish but there's very little text (and if you want I can help you with that). With the measurements churned out by the program, should be no trouble for anyone handy with a saw or with access to a neighborhood karpintero.


Hi Aero!
That's a great resource. The QRD is actually expalined well by F. Alton Everest in his Acoustics Manual, highly recommended reading. That book I got from Audio Advisor some ten years ago. You gould try getting this used at Amazon maybe at around 12USD. I think I got mine, softbound, for amybe 30usd then. Come to think of it, where did I put that book...
To correct myself, upon inspection of Jadis' room, what he had used on the walls were not QRD's but slats to break wall creep and diffuse sound. These were defacto wall treatment in theatres/moviehouses then.
rgds
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Postby jadis » Sun Jul 18, 2004 5:38 pm

noctilux, aero,


I think what you refer to as QRD, we would call it RPG at that time. It was a patented
US product, and one of our guys, a doctor, got some specs and copied it. This is what
I put behind my listening chair, RPG. The three sides of the room are the ones with slats.

Image
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Postby noctilux » Sun Jul 18, 2004 7:59 pm

jadis wrote:noctilux, aero,


I think what you refer to as QRD, we would call it RPG at that time. It was a patented
US product, and one of our guys, a doctor, got some specs and copied it. This is what
I put behind my listening chair, RPG. The three sides of the room are the ones with slats.

Image


Jadis,
Oh, there they are. Sorry, I didn't know you had the diffusors at the back. That's the best place to use them really.
Not to defy you (pardon the pun), RPG is more of the company that makes the QRD, meaning Quadratic Residue Diffusor (or Diffuser). A lot more can be seen here:
http://www.rpginc.com/products/qrd734/index.htm

These actually come in avariety of forms the simplest being the 734 which a lot of the guys in Manila have knocked off, including myself. It's pretty simple to copy. One of these days, I will have to post this for everyone to have access to. I don't think it's patented since everyone can actually get the quadratic sequence and build his own version.
rgds
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Postby zach » Sun Jul 18, 2004 9:29 pm

its also knwn as a schroeder diffuser. you also need some space between the back of your head and the diffuser for it to be effective. i believe it should also the cover the wall from left to right. i believe the older diffusors are about 4inches deep. the newer ones are 8inches deep. fiberglass is also put inside the cavities. :)
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Postby jadis » Sun Jul 18, 2004 11:40 pm

noctilux,zach,

thnx for the inputs. right, we called them the RPG Diffusors then because of the company.
we never got hold of the real product name. everyone was wild copying and building
these things then....
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Postby highlander » Tue Jul 20, 2004 6:28 pm

Jadis,
While surfing the web, I came accross this interesting site on Bass Trap Resonance Absorbers. Comments please....

http://web.archive.org/web/200008161452 ... mTubes.asp
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Postby jadis » Tue Jul 20, 2004 7:00 pm

highlander,


..very interesting, though I would not know what these thick toilet papers would
sound as opposed to real fiberglass wool...but if we have them here, why not ?
i think we don't have yata.
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Postby noctilux » Wed Jul 21, 2004 3:55 pm

highlander wrote:Jadis,
While surfing the web, I came accross this interesting site on Bass Trap Resonance Absorbers. Comments please....

http://web.archive.org/web/200008161452 ... mTubes.asp


Again, a great resource, Mr. Highlander.
These are actually Helmholtz resonators (a bit of a mouthful). A bit of trivia which I remember i got from my dear departed Acoustics professor: Bottles ranging in sizes where actually embedded in walls of huge churches to act as helmholz resonators in the medieval ages.

If you blow against the hole in the bottle, you will get the resonant frequency of that size/shape. This will be the bottle/tube trapping frequency you can expect. This means trapping a bass boom will be quite a humongous bottle

rgds
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