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post #181 of 376 Old 09-28-2011, 11:42 AM
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Originally Posted by noah katz View Post

Precious how?

2D diffusers will have a higher absorption coefficient by nature than 1Ds (more wells, more viscous losses, more 1/4wavelength resonations).

our ears are on the side of our heads - the lateral returns (eg in a 2ch stereo setup) are what's important to create envelopment. diffused returns from floor and ceiling are not as important. however, with a 2D diffuser you are now spreading the same finite energy in 2 planes (vertical + horizontal), vs 1 plane with 1D diffusers. why waste that energy to the floor and ceiling?

many people mistakenly assume that 2D diffusers are automatically better than 1D - but it really depends on the application, location, etc and how the user wants the energy to impede the listening position.


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How about something by the gallon that can be applied with a brush, like floor adhesive, or maybe latex paint thickened with a filler.

Ah, something I used last year - flexible wall texture.

sure. bear in mind im in a small living quarters in the city (no garage) and have limited tools, space, etc to work on such projects. so whatever works best for you with regards to work-flow. with regards to foam - make sure the caulk/adhesive is NON-SOLVENT!
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post #182 of 376 Old 09-28-2011, 11:54 AM
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Originally Posted by penngray View Post

localhost, what is the mininum board dimensions needed in room to make it effective? ie...2'x4' at the first reflection points in room??
I have a so much scrap wood that its just easier for me to use it up with something like this and its a good time to try it since Im slowing redoing my HT room.

there are some things you must keep in mind with regards to diffusers at first reflection points.

1st of all, there is a flat-plate frequency with schroeder diffusers where the diffuser will act like a flat wall (boundary) - as if the reflection point were not treated at all! secondly, effective HF cut-off of the diffuser is lowered as angle of incidence changes. so, if you have the diffuser on your side wall, and your speaker was pointed at it perpendicularly (0* angle of incidence, normal incidence) - then the designed HF cutoff is the same. however, since your speakers will be at the front of the room and the off-axis energy will be hitting the first reflection point at an (assumed) angle of 45*, this means that the HF cut-off of the diffuser is lowered. so there are additional constraints regarding diffusers that it is important to be aware of.

the depth of the diffuser dictates LF cut-off frequency, but the period width must be as large or larger than that wavelength to be seen by that wavelength. so tiny diffusers (1'x1' , or even 2'x2') may not have very wide bandwidths. remember, the object must be large in relation to wavelength to be seen and affected by it.

let's design a QRD in QRDude. now, i can make the DEPTH of the wells quite deep such that the diffuser has a lower design frequency. BUT, since the WIDTH (overall size) of the diffuser is SMALLER than that wavelength, it will not work as intended (larger wavelengths will diffract around the diffuser, instead of being 'seen' and diffused by the diffuser).



size (period width) of the diffuser is important as well, especially when diffusing lower frequencies (large wavelengths).
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post #183 of 376 Old 09-28-2011, 03:30 PM
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per N19 diffuser:

(1) 4'x8' x1" thick extruded polystyrene foam sheet ($14)

(1) 4'x8' x1/8" thick hardboard wood sheet (cut (19) 1"x48" strips for lining the well bottoms, and 48"x19" for the backing of the diffuser) - ($8)

probably going through $25 in caulk per unit...the baseboard is only 1/8" thick hardboard so i am using plenty of caulk between all wells and sealing as many edges as possible to make sure the unit is structurally sound. im pretty confident in handling...it's quite strong. the bulk of the weight of each unit is mostly due to caulk

then however much each will cost to paint. i live in a small studio-loft in the city, and no way am i tackling any paint job in my place. once i get the third completed ill start calling around to see if i can find a paint shop to have them painted with the proper tools...

No, not what it cost you, rather selling them to me!!
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post #184 of 376 Old 09-28-2011, 04:56 PM
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lol

too much time involved to sell away! there's a reason why QRD/PRDs are so damn expensive online....such a headache to make!
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post #185 of 376 Old 09-28-2011, 06:31 PM
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many people mistakenly assume that 2D diffusers are automatically better than 1D ...

I was one, thanks for straightening me out.

Noah
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post #186 of 376 Old 09-29-2011, 05:57 AM
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Let me try and ask my question again, differently.

What is the minimum size of the QRD Diffuser for a standard 15x25 room??

Im looking for a Square footage. Do you know what it is??

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post #187 of 376 Old 09-29-2011, 06:17 AM - Thread Starter
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Originally Posted by penngray View Post


This might be one of the easier CNC projects/flat pack options for EricH to source. We could have it made in 2'x4' sections (easier shipping).


If you guys can let me know exactly what you want, I'll contact the foam company again and get pricing. There have been a lot of different ideas in this thread, so I'm not sure which 2 are the best to go with.

I thought 1 foam and one CNC wood kit would be nice. I figured you guys would want one of those wood slat type set ups cut with a CNC machine?
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post #188 of 376 Old 09-29-2011, 02:56 PM
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Originally Posted by penngray View Post

What is the minimum size of the QRD Diffuser for a standard 15x25 room??

Im looking for a Square footage. Do you know what it is??

Penn, I'd say the answer is zero. Diffusers are not really required, though they can be desirable. Many Erskine rooms look to me like they don't even have space for fabric-covered diffusers, but that's because they are using architectural features such as extensive coffering to achieve a very similar result. As a guess I'd think the barest minimum in a domestic HT might be a 2'x2' diffuser on each side, but whether that's really desirable depends on a lot of details.

In my case I'm planning to use polys and expecting to have something like 100sf of diffusing surface in a ~18x10x8 room. That said, I also have ~80sf of absorption as well as faced bass absorbers. Of course in the future it's likely that I will decide to get jiggy and test some BAD panels in place of pure diffusion on the sides anyway.

On the styro diffuser discussion, if I were going to build styro stuff I'd come up with a DIY hot wire cutter something like on this gearslutz thread. Looks like the right tool for the job to me.
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post #189 of 376 Old 09-29-2011, 03:47 PM
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Penn, I'd say the answer is zero. Diffusers are not really required, though they can be desirable. Many Erskine rooms look to me like they don't even have space for fabric-covered diffusers, but that's because they are using architectural features such as extensive coffering to achieve a very similar result. As a guess I'd think the barest minimum in a domestic HT might be a 2'x2' diffuser on each side, but whether that's really desirable depends on a lot of details.

In my case I'm planning to use polys and expecting to have something like 100sf of diffusing surface in a ~18x10x8 room. That said, I also have ~80sf of absorption as well as faced bass absorbers. Of course in the future it's likely that I will decide to get jiggy and test some BAD panels in place of pure diffusion on the sides anyway.

On the styro diffuser discussion, if I were going to build styro stuff I'd come up with a DIY hot wire cutter something like on this gearslutz thread. Looks like the right tool for the job to me.

Thanks, I will say that for 5 years I enjoyed my custom HT room with only OC703 without issues and friends simply have that "WOW".

Of course being a DIYer who constantly builds a new speaker, I like adding something new even though it "might" not have any substantial improvements.

so my question is a simple one.....maybe I can re-word it again.

How big do I have to build one of these contraptions for it to make any difference??

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post #190 of 376 Old 09-29-2011, 06:54 PM
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Originally Posted by penngray View Post

Thanks, I will say that for 5 years I enjoyed my custom HT room with only OC703 without issues and friends simply have that "WOW".

Of course being a DIYer who constantly builds a new speaker, I like adding something new even though it "might" not have any substantial improvements.

so my question is a simple one.....maybe I can re-word it again.

How big do I have to build one of these contraptions for it to make any difference??

I agree, I love the heck out of my theatre just with modal control and basically early reflection absorber panels. But I'm still tweaking, because "good enough" isn't really good enough. If it were, I'd stop now and not bother with the diffusion or the infrasub among other things. It's already a "wow" situation for most people anyway, and even more importantly I love it.

There are a lot of factors in deciding how much area you want as diffusion, and it's probably OT. I suggest an offline dialogue; I will shoot you a PM.
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post #191 of 376 Old 09-29-2011, 07:22 PM
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I agree, I love the heck out of my theatre just with modal control and basically early reflection absorber panels. But I'm still tweaking, because "good enough" isn't really good enough. If it were, I'd stop now and not bother with the diffusion or the infrasub among other things. It's already a "wow" situation for most people anyway, and even more importantly I love it.



reminds me of Andreas' commentary in this thread;

http://www.gearslutz.com/board/studi...s-trigger.html

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The before/after is startling. To say the least. Feels like I've done the same sort of upgrade that I did when going from no treatment to well treated room.

Still got some tweaking to do to the response, but it's getting very close to the goal. I thought the room was 90% there in the first picture.. W R O N G. It was more like 50% there in terms of what it feels like listening to it..

who knows what the next stage brings
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post #192 of 376 Old 09-30-2011, 05:27 AM
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I agree, I love the heck out of my theatre just with modal control and basically early reflection absorber panels. But I'm still tweaking, because "good enough" isn't really good enough. If it were, I'd stop now and not bother with the diffusion or the infrasub among other things. It's already a "wow" situation for most people anyway, and even more importantly I love it.

There are a lot of factors in deciding how much area you want as diffusion, and it's probably OT. I suggest an offline dialogue; I will shoot you a PM.

I have been in some expensive rooms with all the incredible duffusion/absorption money can buy. I didnt get the "Oh my this is so much better" opinion but then again, JL113 type subs , High end Electrostatic speakers.or high end B&W speakers are not what I consider high end HT components so maybe it was the speaker choices and not the room which testing movies. I will say that music probably couldnt sound better.

Thanks for the PM, lots too read through when I have time. Even though this is another project I want to do its about 8th on the list. Still have to finish my current speaker design

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post #193 of 376 Old 09-30-2011, 11:11 AM
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There are a lot of factors in deciding how much area you want as diffusion, and it's probably OT. I suggest an offline dialogue; I will shoot you a PM.

Seems on point to me; please share!

Noah
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post #194 of 376 Old 09-30-2011, 03:48 PM
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Seems on point to me; please share!

OK, well there are a few details you would need to PM for but I'll post the bulk of it if you're interested.

Firstly, here are some comments I got from kevinzoe privately about the effects of diffusion in his music room, as while there are some things about diffuser use that could be done by measurement or calculation (such as using diffusers at early reflection points or to densify the late arriving field - see the ETC thread for those), much of their use will have to be guided by your goals and subjective assessments.That's almost embarrassing to say as I tend toward a fairly objectivist-heavy view. *shrug*

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* bare reflections on the side walls provided the best/most mid/high freq energy and aliveness quality but reduced some musical details
* absorption on the side wall 1st reflection points offered the best solution for hearing the most musical details but at the expense of a narrower sound stage and uneasy fealing that the volume had to be turned way up to make up for the lost mid/high freq energy.
* latteral diffusion in the horizontal dimension seemed to offer the best of reflective and absorption by preserving the mid/high freq energy levels and ability to hear the musical details, although just slight behind what the absorption offered for musical detail.

One area I will mention that is pretty easy to calculate is use of diffusers to control flutter echo. I've read that you have to treat at least 20% of a surface for that, and I don't think there would be a significant difference in that value regardless of what type of treatment was used. Also you want to keep the treatment on non-opposite surfaces (so 20% on one wall and 20% of the opposite wall in areas not directly opposed to the first 20%). This is actually one of the reasons behind the diffusion I am putting into my HT, though it is probably unnecessary (for that purpose) as the flutter echo isn't really audible at the listening position. I just want to make the room have a nice, comfortable, tuneful ambiance everywhere - though the same diffusers will also help to densify the late arriving field as well as providing my diffuse lateral late arrivals for envelopment.

So, to determine how much diffusion to deploy, it seems logical to me to start with what we want the diffusion to do. This is why I provided kevinzoe's comments, as they relate directly to what you want the diffusion for.

The main things that diffusion is supposed to do (in a listening environment) is give a sensation that the room is larger than it is (questionably necessary in HT since the surrounds are supposed to reproduce the spatial cues anyway) and to provide a sense of spacious envelopment (which I see as very desirable in an HT). The envelopment is said to mostly happen with lateral, late-arriving diffuse reflections -- so that is what we need to create.

Put more technically, you want early (20ms after direct) reflection control (-10dB in multichannel industry standards, -20dB or more for typical studio control room) verified (or created) using the impulse/ETC (check the thread on that for more information) for LCR. After that you want the reflections seen during the decay to be "dense" rather than "sparse". Also, you need enough energy to be available later on to cause the envelopment feeling. Additionally, if you run RPG's room optimizer software, it recommends absorption at first reflection points of LCR, and diffusion at all first reflection points of surrounds. That last part seems like a good start which is one of things leading me to the setup I'm working on (though front wall diffusers are not happening). Quick note, whenever I say reflection I mean from any surface including ceiling, front wall, floor if not carpeted, coffee table, whatever.

OK so now how do you translate that into a useful design for your theatre room? Well, you start with translating that time into distance and make a few estimates, plot lines in CAD, whatever. The trick is that sound moves about 1.1 ft per millisecond. So you can determine the time taken by the direct sound, and look at the path lengths from the mirror points and determine the difference to know whether or not they need to be controlled in some specific way.

If your room is wide enough to provide the 20ms gap between direct and reflection, then definitely throw diffusers at the lateral reflection points! And if you have front speakers with great dispersion characteristics you probably want to use diffusers on the sides regardless of delay.

Now at non-first-reflection points? This is where you get to play. Try diffusers to the sides of the listening positions above your absorber panels for sure. Remember you have 2D units as well as 1D units in two different orientations available as options. In RFZ studio control rooms, the object is to return a specific amount of diffuse energy laterally to the listeners right at 20ms, so they actually would use flat deflection panels to create paths that are direct+18ft to the listener including the lateral diffusers as the end of the path. I actually toyed with the idea of doing this in my theatre but decided it wasn't worth doing until I already had all my other acoustical issues worked out. But even if you're not trying to return a lot of energy right AT 20ms, you should be making sure there are some of those direct+18ft paths without too many bounces to make sure there is still enough energy in them to create an audible effect. The real trick here is energy management, and to do it you have to have energy to manage - which is why localhost refers to it as "precious". And remember that diffusers have absorption too!

So there are a lot of factors in determining exactly "how much" diffusion to put into a HT. It's not quite like needing a certain amount of absorption to reach a certain decay time. It encompasses factors like orientation in the room, speaker and listener positions, speaker directivity, current acoustic treatments. And even more PITA, personal preferences. What is your 2-channel/multichannel balance, or at least where would you like to bias your setup? Do you prefer "more accurate" or "more aliveness and expansion"? Are there other reasons you want the room to feel "more dead" or "more alive"?

Hopefully that explanation is a bit useful. It gets complicated quickly because you can't really talk about diffusion without talking about the overall acoustical environment, and you get into subjectives fairly quickly. I don't claim expert status nor to have a final answer, because everyone could have their own idea of how best to deploy diffusers - and many of them would be right (for them).
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post #195 of 376 Old 09-30-2011, 04:02 PM
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you want early (20ms after direct) reflection control

Im kind of confused because there isnt a room that has 20ms early reflections that I know of. The early reflections happen at 4 to 6 ms so Im confused what that 20ms means.

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post #196 of 376 Old 09-30-2011, 09:44 PM
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Im kind of confused because there isnt a room that has 20ms early reflections that I know of. The early reflections happen at 4 to 6 ms so Im confused what that 20ms means.

Sorry if that was unclear, I mean any sound arriving within (that is, in less than) 20ms after the direct sound. Certainly having reflections arrive at the listeners within this window will happen in a typical size HT.

However it'd be easy to make some early reflections at about 20ms... listening to speakers in the near field in a room about 44x44 (so walls are ~22 ft away) and you and speakers in the middle of it (and a fully absorptive floor and ceiling.... or let's just say I'm ignoring that for the moment). The early reflection time depends on the geometry of the room, location of listener, location of speakers. You can see that early reflections aren't generally a problem in a large space... in fact concert halls often include features to intentionally provide reflections at ~20ms to the audience. I am pretty sure the 20ms figure comes from early studies of better and worse-judged concert halls - I believe research done by Beranek. Talk about standing on the shoulders of giants.

This leads to why one can actually use deflector panels instead of absorption at first reflection points - you can save the energy by just redirecting it rather than absorbing it. And taking that idea a bit further you can make the path lengths whatever you want by intentionally firing the sound around the room so it takes longer before arriving at the listeners. There's actually a formalized audio control room model using the "deflect it rather than absorb it" idea called "controlled image design". Documents on it are free in the BBC research archives.

In my theatre, my initial plan (for creating a strong termination of the ISD gap... to stray into the ETC thread territory again a bit) was to put a diffuser on left and right above my early reflection absorbers, and in front of each to put a deflector panel. The deflector would block the near-side speaker from hitting the diffuser (thereby preventing early arrivals) while directing sound from the opposite-side speaker to the diffuser. For clarity, the left side speaker sound would hit the right side deflector and be deflected toward the left side diffuser (this aiming is easy to do with a hand mirror, laser pointer, and helper). Since my room is ~10ft wide, the sound going across the room twice plus the direct distance for a centered listener would approach the 20ms delay. Additionally, I figured it was advantageous that the late diffuse reflections would be on the same side as the speaker having originally emitted them. In such a scheme if the pulse isn't strong enough, you just add more deflector panels to get more energy onto the diffuser. One of the guys on GS uses a similar scheme with deflectors on the side walls to deflectors on the rear wall to diffusers on the sides. Anyway we'll see if I ever implement this, because if I like the sound with all the poly diffusers I am planning I probably won't bother with it.

As a side note, it's possible for sound to arrive before the direct sound if it's conducted through a solid object wherein the speed of sound is _higher_ than through the air. But this is definitely not the place for a long discussion of decoupling!

Yes, I'm mixing my 18's and 22's here. I'm sorry if this is confusing. The last post should have said "direct +22ft" I believe. I'm trying to demonstrate concepts more than get everything right here.
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post #197 of 376 Old 09-30-2011, 10:02 PM
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One thing that strikes me is that I'm totally neglecting "How weird do you want your room to look"? Diffusers probably typically have a low-ish WAF. At least they can be nicely finished if you like. Deflector panels probably have lower WAF if I had to guess. They could be painted or stain/polyurethane but it still might not go over very well to have these strange shapes sticking out of the walls. One option is to frame them out into sort-of sawtooth shapes, and one could let the wife do something artistic with the paint.

On this end, I already got approval from the artistic director for my poly plan.
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post #198 of 376 Old 10-01-2011, 01:56 PM
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in fact concert halls often include features to intentionally provide reflections at ~20ms to the audience. I am pretty sure the 20ms figure comes from early studies of better and worse-judged concert halls - I believe research done by Beranek. Talk about standing on the shoulders of giants.

and especially schroeder.

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This leads to why one can actually use deflector panels instead of absorption at first reflection points

caveat that the deflector is large with respect to wavelength of the specular energy

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- you can save the energy by just redirecting it rather than absorbing it. And taking that idea a bit further you can make the path lengths whatever you want by intentionally firing the sound around the room so it takes longer before arriving at the listeners. There's actually a formalized audio control room model using the "deflect it rather than absorb it" idea called "controlled image design". Documents on it are free in the BBC research archives.

one of the principal factors of the RFZ model
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post #199 of 376 Old 10-01-2011, 01:59 PM
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Originally Posted by penngray View Post

I have been in some expensive rooms with all the incredible duffusion/absorption money can buy. I didnt get the "Oh my this is so much better" opinion but then again,

design, placement, how the energy is made to be reintroduced to the listening position, etc are all critical factors.

just because someone has the funds to purchase enough diffusers to cover entire boundaries (which may 'look' impressive), doesn't mean it was designed appropriately with regards to the specular behavior of the energy and how it impedes the listening position.

how many times have you seen 'listening rooms' with whole boundaries covered in repeating diffusers with limited bandwidth - with no consideration factored in to how such arrays of diffusers behave in such a fashion?

look at the 3rd polar response here:



someone who doesn't know what they're doing but can afford a massive array of repeating diffusers will clearly have issues!
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post #200 of 376 Old 10-01-2011, 02:06 PM
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Originally Posted by aackthpt View Post

One area I will mention that is pretty easy to calculate is use of diffusers to control flutter echo. I've read that you have to treat at least 20% of a surface for that, and I don't think there would be a significant difference in that value regardless of what type of treatment was used. Also you want to keep the treatment on non-opposite surfaces (so 20% on one wall and 20% of the opposite wall in areas not directly opposed to the first 20%).

in a recording room, perhaps - but in a listening room, theater, etc - symmetry should be maintained.




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Put more technically, you want early (20ms after direct) reflection control (-10dB in multichannel industry standards, -20dB or more for typical studio control room)

for control room design, the ISD-gap must be larger than the ISD of the recording room. that's one of the sole functions, as you want to hear the recording room in its entirety without the control room masking its reflections earlier in time.

20ms is not set in stone regarding the haas interval.

attenuation requirement of early reflections is to get the energy below the detection threshold
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post #201 of 376 Old 10-01-2011, 02:44 PM
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Originally Posted by localhost127 View Post

in a recording room, perhaps - but in a listening room, theater, etc - symmetry should be maintained.

Symmetry need not be absolute in home theaters in certain places. Where the sound is not sent early to listeners it's unnecessary and for treating flutter echo with diffusers maintaining precise symmetry will cause you to use twice as many as necessary. Naturally symmetry is important in any area where sound may be directed to the listeners in an earlier time frame, but in areas where the reflections just contribute to the later decays strict symmetry is an overly limiting requirement. Of course there is a caveat with everything, here the caveat is that the diffusers can't be large features of the space, and you should maintain roughly equal area coverage on opposing surfaces.

I doubt diffusers would be used to improve flutter echo in most HTs anyway but in a general treatment of how to use diffusers it's worth mentioning.

Pretty much no real space maintains strict symmetry anyway. It's less of a rule and more of a guideline.
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post #202 of 376 Old 10-01-2011, 02:52 PM
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is flutter echo a worry if the energy doesn't impede the listening position?

i think it should be maintained ... example of treating flutter echo to the side-walls of the listening position. you could place an absorber on the left side and maintain bare wall on the right, which would cure the flutter echo, but now you have asymmetric treatment which could change the perceived sense at the listening position.
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post #203 of 376 Old 10-01-2011, 02:52 PM
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and especially schroeder.

Leo Beranek's book resulting from his concert hall research was published in 1954. It appears from his quick self-bio that Manfred Schroeder was not publishing acoustical research until the mid-60s. While Schroeder did work relating to the sound quality of lateral-arriving reflections, the original idea of the ISD gap had been realized by Beranek at least a decade earlier.
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post #204 of 376 Old 10-01-2011, 02:57 PM
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is flutter echo a worry if the energy doesn't impede the listening position?

As I noted earlier, no. But it depends what you mean by "a worry". Many people use their HT as a general social room, and in those situations the listening position might be anywhere. Or they may just be like me and want the acoustic to seem natural throughout the room, not just in the listening positions. Besides which, I think people should have as many tools in their pocket as possible.
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post #205 of 376 Old 10-01-2011, 03:05 PM
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Originally Posted by localhost127 View Post

i think it should be maintained ... example of treating flutter echo to the side-walls of the listening position. you could place an absorber on the left side and maintain bare wall on the right, which would cure the flutter echo, but now you have asymmetric treatment which could change the perceived sense at the listening position.

Right well it depends factors including proximity to the listening position - in areas closest to the listening position, or most defining of the acoustic at it, of course you want to maintain symmetry. And in most home theaters you will want to use absorption or BAD panels next to the listening position anyway for early reflection control anyway so in that area there probably is no flutter echo problem except up high in an HT with a higher ceiling. I'd guess it's mostly something you hear more in front of most HTs, which is where I get it in mine. And, yes, that isn't near any listening positions but I want it anyway.
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post #206 of 376 Old 10-01-2011, 03:47 PM
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Leo Beranek's book resulting from his concert hall research was published in 1954. It appears from his quick self-bio that Manfred Schroeder was not publishing acoustical research until the mid-60s. While Schroeder did work relating to the sound quality of lateral-arriving reflections, the original idea of the ISD gap had been realized by Beranek at least a decade earlier.

my comment was with regards to the topic of the study of concert halls.
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Im kind of confused because there isnt a room that has 20ms early reflections that I know of. The early reflections happen at 4 to 6 ms so Im confused what that 20ms means.

http://www.gearslutz.com/board/5294278-post264.html

http://www.gearslutz.com/board/5296309-post273.html
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Schroeder is overrated anyway. It's all about Joe Cool.
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post #209 of 376 Old 10-05-2011, 07:32 PM
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i've got 3 done.



should look much better once they're painted..

i think the plan is now, build 2 more for a total of 5x 1D N19 PRDs - with one of the new being an Inverse N19 PRD. (4x normal, 1x inverse)

using the barker code for modulation:
http://en.wikipedia.org/wiki/Barker_code

a length of 5 diffusers will require the following order: +1 +1 +1 −1 +1
where +1 is a normal diffuser and a -1 is the inverse diffuser.

then, i will use the 5 panels to build a nested fractal 1D N5 PRD

example of a nested diffuser:



PRD N5 design


^^each well in the N5 represents one of the N19 diffusers. purple being a 'normal N19' and the orange being the 'inverse N19'

the max depth of the N19s is 7.6"
and the max depth of the N5 nested will be 24-28"
which will extend the bandwidth below 300hz (lower limit of the specular region).

another example of a nested/diffractal
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post #210 of 376 Old 10-05-2011, 08:19 PM
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something like this:

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