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Room treatment...


Schu

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Generally you need both, but many rooms have a fair amount of diffraction built-in, in the form of bookcases, CD/DVD storage shelves, other loudspeakers, bay window openings, equipment racks, chairs, tables, etc.

 

One answer to your question involves "where" relative to the location of the loudspeakers and walls.  Usually more absorption is needed in the near field of the loudspeakers, and more diffraction is needed on side walls and ceiling in moderate and small rooms to break up strong reflections.

 

Diffraction is much more difficult to do well down to low enough frequencies.  Absorption is needed in the area around your loudspeakers to reduce early reflections, but it is possible to also use diffraction panels to deal with early reflections, albeit much, much more difficult to do effectively.

 

Chris

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Hmmm... still trying to get a handle on this whole thing.

If I do the clap test, the room seems fairly in need of help but I only have three walls and the echo comes from the area where there is no wall that opens into the kitchen because the left side is covered in curtains and the back wall is covered in thick carpet.

Ill have to do a drawing.

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I'm in the same boat now.  Moved some furniture to better the stage as Chris A. had suggested.  After moving the furniture the stage sounded much better.  I definitely notice an 'echo' in my room though.  Mainly, just a 2 channel setup.  I will be trying some absorption panels behind the mains and to the sides of each.  I'm expecting that it will smooth the sounds and soften the first wave reflections.  I read about a mirror technique to identify where the panels should be.  With my little setup it's pretty obvious where they should go.

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@Schu @Chris A  So here's a 'cheapo' test that I did tonight.  I was waltzing by a downstairs bedroom and noticed a coupled of rolled up memory foam mattress pads from my girls beds.  They are the size of a single mattress as we bumped them to fulls recently.  Anyway, my little brain started churning.  The pads are about 1 1/2" thick and pretty dense. 

 

I rolled them out on their sides from just behind the rear of each main, curving through the corner, out to the sides, extending past the front of the mains.  On their sides the pads were just taller than my cabinets from the floor up.  Played a couple of jazz, musical tunes, and what a difference.

 

The sound was warmer, cleaner, and more 'there'.  Less distractions in the music.  I pulled them down and listened to the same tracks and again a definite difference could be heard, but the wrong way.  Honestly, I wanted to put them back up but I know the wife wouldn't go for the pristine painter's tape/mattress pad install.

 

So, I suppose in my room some absorption panels are the way to go.  Each room is different obviously, but for me it's a place to start.  All I do know is I'm ordering some soon.

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Many people are using panels filled with rock wool for absorption, with good results.

The ones that want to do it properly are using acoustic measurements.

 

For example, a man moved into a new apartment in a modernist building.  Flat concrete bare walls everywhere. A friend come by to help with acoustic measurements and calculation. It appeared that the wall behind the speakers needed absorption. Rock wool behind some nicely painted perforated plaster panels were used. Then the ceiling was done in a way of suspended second ceiling. On top of that second ceiling rock wool was also used. They installed a customized set of lighting in that ceiling to look nice. And final touch was a few refraction panels on the side walls. Now the room still have that contemporary look and is well acoustical treated.

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I don't know many details, but I recall being told (paraphrased) "you want to kill any first reflections within "X" milliseconds and after that you want to diffuse, diffuse diffuse, and.....diffuse some more"

 

His point was most people over absorb

 

My wife however, will tell you that I don't absorb anything she says... :huh:

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The cool thing about the Tubetrap is that it is diffusion as well as absorption.  There is a diffusion panel on one side of the tube that you can turn in whatever direction you wish.  

I feel I am getting the most bang for buck from the single 16" tubetrap I have center stage  between my speakers.  I can slide it forward or back and to focus the sound stage as I like.  Cool stuff!   I'd like to have a few more but they are expensive even for the cheaper dealer version.  I'd maybe consider cheaper bass traps for the corners and maybe reserve the Tube traps for the front and rear center as well as side reflection points to save the budget.  If money was no object my room would be pretty full of those cylinders although not quite as full as ASC might seem to encourage.  Get fat enough ones!    It takes the isoThermal 16's or bigger to absorb low enough.  The regular 16" version only goes down to 55hz.  

There is way more science to this stuff than I know!  Every room is different and the results desired are different for each listener as well.  

 

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I've just discovered how expensive this stuff is to implement... I mean to treat a moderate sized room is going to be well over 1000$.

 

Somehow, that seems ridiculous...

 

I've got a lot of wall space that can not be touched because it doubles as a liv8ng room where living takes place and art hangs on the walls.

 

I can see need ceiling treatment though.

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13 minutes ago, Schu said:

I've just discovered how expensive this stuff is to implement... I mean to treat a moderate sized room is going to be well over 1000$.

 

Somehow, that seems ridiculous...

 

I've got a lot of wall space that can not be touched because it doubles as a liv8ng room where living takes place and art hangs on the walls.

 

I can see need ceiling treatment though.

 

Yeah, I saw that as well as far the prefab ones go.  There were some nice features on some of them, such as adding your own artwork to them, but for the cost it's not worth it to me.  In looking at some DIY panels, using the Rockwool material as Chris A had suggested, I figure that I could build the 4 panels I want for right around $100.

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Room treatments are tough. Here are few random notes: 

 

I'd recommend you identify a specific issue before trying to solve the 'problem'.

 

As a rule of thumb: A very good room will have about 20% of all surfaces covered with broad band absorption and 20% of all surfaces with broadband diffusion -- plus bass traps in corners. and by all surfaces, I mean walls, floor and ceiling.

 

Treating only a small area of a room is kind of like throwing a bucket of water on a house fire. Try opening a window and seeing if there is a difference -- a window is a perfect absorber; as any sound that hits it does not reflect back into the room. My point being that, the small relative surface area likely does very little to the overall sound in your listening space... 

 

Be careful when using thin absorption. You can reduce a specific high frequency reflections that accentuate other frequency -- either positively or negatively.

 

 

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It's funny you mention Windows, when I have mine open, sound seems to suffer... the best sound I get is at night with everything closed and all curtains drawn. I have been looking at thick acoustic curtains also. One wall is fully curtained front to back and both areas behind main L and R are also curtained. While I currently use only lined curtains, and they seem to do pretty good, I would like to get thick theater curtains.

 

When I do a clap test.... clearly the echo is coming from the right side of the room. It opens into the kitchen and a long hall way that leads into the front of the house.  That hall is an echo generator, not sure if anything can be done about that and it may not matter because we're not talking milliseconds.

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10 hours ago, Coytee said:

I don't know many details, but I recall being told (paraphrased) "you want to kill any first reflections within "X" milliseconds and after that you want to diffuse, diffuse diffuse, and.....diffuse some more"

 

His point was most people over absorb

Well one man's poison is another's cure.  "X" is about equal to 2.5 to 5 microseconds--or feet in terms of distance--in my experience using directional loudspeakers.  Loudspeakers with collapsing polar midrange horns (i.e., Heritage) will require more treatments.

 

In my particular case, I've found that I like a live room relative to typical acoustically dead home theater rooms.  That means that I apply only as much absorption as needed to the front of the room to control early reflections.  My shoebox-shaped room needs surprisingly little due to its length and internal shape--which makes the room feel quite large, i.e., longer time delays from the back of the room add to the sense of depth without resorting to other "tricks" like high output impedance amplifiers or dipole loudspeakers spaced away from the front wall to provide tight "reverb".

 

Diffusion comes from a CD rack on the right, masonry across the front, front corner bass traps, a partially absorptive equipment rack on the left and two large surround loudspeakers astride the main listening chairs.  This is actually a fair amount of diffusion with only the flat 9' ceiling untreated providing spaciousness reflections from the front of the room.

 

Absorption comes from heavy curtains on the left covering a large box bay window a foot in depth, carpet across the area in front of the chairs, and Sonofiber pads placed across the front wall, on the side walls adjacent to the K-402 horn mouth exit planes, and on the Jub bass bin fronts.

 

If you're dealing with irregular sized or multiple rooms conjoined into a larger space, your particular treatment needs will likely differ greatly with diffusion, absorption, and reflective surfaces needing specific attention to dial in the needed diffuse reflections and control side and ceiling reflections as well as back wall reflections that may arrive too early or at too great a lateral angle from the room front (i.e., too many side reflections). 

 

Canted ceilings provide the most challenging conditions from the reports of those "blessed" with them in their listening rooms.  Typically, these require nearly 100% absorption coverage in the canted portions to control reflections toward seated listeners.

 

Chris

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^Ty good sir...

 

@Chris A my room does indeed slant upwards from the main speaker wall to the back wall... starting at 9'+ and slanting upward to maybe 15'+. Most of the echo comes from down that hall during a clap test. Ive never listened in a completely dead room, but it does sound like an interesting idea.

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3 hours ago, Schu said:

^Ty good sir...

 

@Chris A my room does indeed slant upwards from the main speaker wall to the back wall... starting at 9'+ and slanting upward to maybe 15'+. Most of the echo comes from down that hall during a clap test. Ive never listened in a completely dead room, but it does sound like an interesting idea.

 

 

I'm curious Schu.  I presume the picture you posted is to the side of the listening area.  The curiosity is this, if you put a mic in that hall I wonder what your results would be?  Maybe putting the mic in a few places in the kitchen area and the hall could help to paint a picture as to what treatments you may need?  I don't know if this would mean anything at all.  I would think though that any significant reverb/reflection would show as a signal in those areas.  To me, if you deadened those reflections your listening area could be improved with timing and clarity.  My two cents, or one cent, anyway.  Poke holes in this thought as necessary.

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16 hours ago, Schu said:

Most of the echo comes from down that hall during a clap test.

Then that's your area of focus, it would seem.  Perhaps tapestries or a quilt on a wall in the hall to absorb some of those reflections.  I assume that the hall has a hard floor--no carpet?

 

16 hours ago, Schu said:

my room does indeed slant upwards from the main speaker wall to the back wall... starting at 9'+ and slanting upward to maybe 15'+.

That in itself shouldn't be an issue, but it will put more first reflections (the strongest type of reflections) on the back of the room. 

 

I had a room like that in my prior abode where I was using Magnepan MG-IIIa's, and the ceiling height reached almost 20'.  It didn't seem to strongly affect the imaging of the speakers when they were stationed 6 feet away from the low ceiling portion of the room.  I tried the Magnepans in another room with high flat ceilings and couldn't discern any real differences.  The high ceiling itself is good, because it delays the reflections outside of the so-called "Haas zone" (more than 20-25 ms delay time arrivals).

 

16 hours ago, Schu said:

Ive never listened in a completely dead room, but it does sound like an interesting idea.

I listened to a Jub (K-402/K-69 then a K-510/K-69) inside the Hope anechoic chamber.  I don't really want to do that again.  The effect was fairly disorienting to balance/equilibrium, although it wasn't as bad with the speaker playing as when there was no sound at all.  It was very easy to hear the frequencies of polar spilling around the K-402 and the K-510 horns as you walked around to the back of the speaker.  It was like visualizing the 3-D field of the loudspeaker (a synesthesia-like experience) in front of you: overall it was a weird experience. 

 

They could probably put that sort of thing in a fun house at a Midway to thrill the teenagers...:blink:  It was also very stuffy--like crawling through an attic covered in rock wool...:emotion-41:

 

Chris

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