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Room Treatment: Diffusion


SWL

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16 hours ago, SWL said:

Yeah, I like to think that if it ain't broke don't fix it......but I usually experiment anyway.
 

 

… the last spot, perhap's…. (for experimental purposes) replace the clock above the TV with one panel... but I wager that you might not have a handful of panel's at your fingertip's for the moment... so this idea come's into motion.... for a poly semispherical diffuser, as seen in PWK's dope from hope articles.. which could entail using a picture frame hung backwards (for testing purposes) with the panel held into place, in the routered picture channel frame....  just an idea....

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… the last spot, perhap's…. (for experimental purposes) replace the clock above the TV with one panel... but I wager that you might not have a handful of panel's at your fingertip's for the moment... so this idea come's into motion.... for a poly semispherical diffuser, as seen in PWK's dope from hope articles.. which could entail using a picture frame hung backwards (for testing purposes) with the panel held into place, in the routered picture channel frame....  just an idea....
Yeah, I think that is the very last spot in the room that hasn't had any room treatment yet LOL.

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Turning those panels above/behind the speakers really has me baffled. It sounds kinda like.....in a way....the speakers are out of phase. In a good way....I think. It's different and not what I'm used to hearing. Not a major change in sound but DEFINITELY a change in sound.

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I had to change it back. I wanted to leave it for at least a day but it was like bass was being robbed and the 'out of phase' thing just wasn't jiving with my ear holes.

Maybe it was more 'right' but I just couldn't get used to it.....or didn't want to. Actually, as I sit here and type it does sound more right this way with them scattering vertically. Yeah, definitely more right. Definitely. More right. Yes. That's my final decision......and I'm sticking to it. [emoji39]

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This just blows me away how much better my 222c sounds now after dialing in my room's acoustics. I just ordered another quad of EL84's and a buddy is meeting me this weekend with some more NOS tubes. Rollin, Rollin, Rollin...keep those tubes a Rollin. By this weekend I'll have three more quads of power tubes to check out. I'm a tube man again. Dig it.

Not only my tube amp but I brought my Marantz 1200b up from out of the basement system and it had SO much more clarity than before the treatments. It sounded like a new amp.

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If you get a chance to run an upsweep in your room using REW and a calibrated microphone, you might take a look at what is occurring with your "early decay time" curve and the other T20 and T30 curves.  I think that if you ran another sweep without treatments in the room, you'd see a great deal of change in these curves, especially the EDT curve:

 

705228d1537707719-rt60-listening-chris-l

 

In the plot above, the cyan (blue-green) EDT curve shows a distinctive downward trend away from the other curves.  I've found this is one characteristic of my measurements that diverges sharply from non-treated rooms, and corresponds to greatly increased clarity in the room, without a corresponding loss of spaciousness or ambience since the longer delayed reflections are not significantly affected by the front-of-room absorption.  Note that my listening room is 40 feet deep, so I really don't need any treatments on the rear wall, or any more than 3-4 feet from the loudspeakers. 

 

Chris

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Thanks Chris. Last winter I finally broke down and bought a mic. I ended up not needing it with my Mini-Dsp 2x4 HD (subs only) but I do intend to do what you said with REW. Probably this winter when things slow down. I'm still a little intimidated by that whole process but am anxious to SEE what's really going on in my room. In the meantime, my ears are quite content I must say.

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I should add that after implementing the horn loaded subs and using the Mini-dsp to tame them.....I simply used my SPL meter to check all seating locations and for the first time ever in this room, the output at each location was so close it wasn't even funny. My bass is so smooth throughout the room I can't believe it. Subs play at 35hz and down.

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One more plot that a lot of people use that have direct radiating loudspeakers is the filtered impulse response (filtered IR) with the so-called "Schroeder Integral" above the impulse response.  Ostensibly, you should have margin between the IR curve and the Schroeder Integral curve in order to maximize clarity for the room.

 

557959192_ChrisAsListeningRoomwithSchroederIntegralFilteredIRplot.thumb.jpg.71386576723db32232a8e5ea2481d483.jpg

 

If the impulse response tail goes above or even near the Schroeder curve, then it tells you where to put your diffusors/absorbers (distance from the loudspeakers--path length--in milliseconds). 

 

Chris

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This link may help someone with working with diffusion panels. Simple explanations of some of the concepts of how distance and placement and amount of diffusion effects the sounds we hear.

http://arqen.com/sound-diffusers/faq/?awt_l=809_W&awt_m=3vamGTydekOvzB9&utm_source=diffusersdiy-list&utm_medium=email&utm_term=reflex&utm_campaign=DiffusersDIY-followup#modulations

 

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8 hours ago, Schu said:

I think he's conceded absorption on the front wall was counter productive.

Diffusion will have a similar effect on nearfield reflections (related to EDT) as does absorption. 

 

EDT isn't really reverberation time, as the REW help facility points out.

 

Chris

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From your link, above ( arqen.com/acoustics-101/room-setup-acoustic-treatment/#diffusion):

 

Quote

If accuracy is not your sole concern, a diffuse sound field can add a lively, musical quality to your room. This is often desired in hi-fi listening rooms and home theaters.

To achieve this, you can start by covering 20 percent of the total wall and ceiling surface area with broadband absorption (Ideally over 4 inches thick. 2 inches is an absolute minimum). Then, cover 20 to 30 percent of the wall and ceiling surface area with scattering or diffusive materials.

You can then run acoustic measurements to test the decay times in your room, and tweak the absorption / diffusion coverage as needed.

 

This is good advice in my experience for smaller listening rooms with short reflection delay times.  The comment on accuracy caught my attention--it's often forgotten that adding significant amounts of "second room" delayed reflections (the first room being the original recording venue) is not really acoustic accuracy, but rather added to every recording without it actually being in the recording.

 

The second highlighted quote is also important--measuring and adjusting the overall decay times for the longer delayed reflections (also called reverberation times).  Early decay times (EDT) are not perceived in the same manner as longer delayed reflections.

 

In my listening room, I have nowhere near 20% absorption--more like 10% or less--but the dimensions of the room are conducive to longer reflection delays from the back of the room (40 feet depth) which allows for retaining longer T20 or T30 reverberation times without having to add significant amounts of diffusion to break up the reflections.  The room itself is not strictly rectangular but has architectural features: a bay window expansion at the left rear, built-in expanding angled walls/cabinets along a right rear wall, under stair closet intrusion at mid point on the right, and cabinets and entryways at the rear wall which also serve to break up the longer delayed acoustic waves into a more broadband diffuse field from returning reflections.

 

Chris

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The thing that makes this challenging is that some configurations of diffusion and absorption I can hear directly.......I mean plain as day. Then on the other hand there are configurations that are heard much more indirectly but are no doubt influencing how the sound is making it's way to my ears.

This has really made me realize....in my room.....how too much broadband absorption has a 'padded' sound to it and I believe I was living with that for years. It has an artificial quality to it where I've found that the diffusion injects a genuine quality to the sound because it kinda sorts things out. More clarity and focus in the midrange and in return a cleaner bass.

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I'd say the main thing that has been throwing me off is not only the locations of the absorption or diffusion panels but how the QRD diffusion panels are mounted as far as scattering vertically vs horizontally. This is as I mentioned earlier an example of hearing the difference in sound indirectly. It has a weird effect on the sound....usually when they scatter vertically in my room....but not always.

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