Acoustical Treatments Master Thread - Page 260

I don't doubt it... However, I am waiting to take delivery of a CNC router this summer and it would be a piece of cake to fabricate them as long as I knew the hole spacing and size. Material cost would be just a few hundred dollars... but than again, you need the CNC machine too.

a good conversation going on regarding HT surrounds. this commentary by jhbrandt should be explored and discussed further.

his diagram:


discussion:
http://www.gearslutz.com/board/studi...chunks.html#23

Hole spacing and depth is proprietary and will likely not be divulged...not to mention copyright infringement. There is also more going on than meets the eye here as well regarding materials. Hate to be the party pooper, it is what it is, but I also support it since the amount of math, engineering and testing that went into designing such panels is quite extensive and expensive. They deserve to get out of it what they put into it IMHO.

i believe d'antonio and cox's AA&D had a fairly detailed section, but i haven't had it in front of me for some time and cannot confirm.
check your local library?

http://www.amazon.com/Acoustic-Absor...6878681&sr=1-1

Yes they do, but there a many things they don't divulge. Chris Karikakis and Sunhil Baritkahr also wrote a master's level text that hint at a few of the elements of Audyssey, but certainly the equational derivations and implementation are left up to the reader.

Except that A) its not copyright infringement. B) The materials used are posted on their website (16MM Class A rated MDF) and C) And if they happened to have patented it, like they did with the BAD panels, the information is in the public domain.

Yep, good catch! Don't know why I was thinking copyright. Getting old I guess. Best wishes!

From my read of the interesting thread, that diagram is explicitly not for home theaters, according to its designer.

correct - i didnt think that solution applied to the general crowd here (hence phrasing it for HT playback discussion). curious to thoughts?

OK, why would this design be good for creating mixes but not for playing them back in a home theater???

Jeff

Jeff,
Sent you a PM yesterday about an REW soundcard - Thanks in Advance for your input.
Now back to our regularly scheduled thread...

Jeff - Thanks Again!
Thread Hi-Jack is now concluded

It is apparently useful in emulating the diffuse character of a theater or dubbing stage. It would therefore help when doing mixes or predubs that will find their way to those larger rooms, so as to avoid surprising differences in aesthetics.

It was mentioned about adding some background noise to help mask low level details, again to help predict the theatrical result. Probably would be better to run the audio thru some room modeling software with impulse responses from a real theater, so as to get the room decay into the equation.

If you want to replicate the disadvantages of theatrical acoustics at home, there are lot of solutions available, from THX dipoles to cinema DSP.

I'm in the process of making panels. When choosing cloth for the covers, are there certain things to look for? For instance thickness of the fabric?

Acoustic transparency... either by specification of the fabric like some GOM fabric, or by the "breath test" where you blow on it and see if the air goes through relatively unimpeded.

With our Frequency Response Panel (FRP) system we are often asked this question and reply, in part, with the following information:

Fabric contenders will be similar to speaker grill cloth. Look for weights around 9-13oz. per linear yard and >65% polyester content. Primary use may say for panels and upholstered walls. Here are a few tests you can use to evaluate a custom fabric contender:
1. When holding the fabric in front of your eyes, you should be able to easily identify objects across the room.
2. When holding the fabric with a spread-fingered hand against your lips and blowing through it, you should be able to feel air passing by your fingers.
3. When pulling on the fabric, it should not exhibit any elasticity.

Fabrics can be acoustically verified via air-flow resistivity or impedance tube tests depending on the function of the cloth i.e.; covering a speaker or covering an acoustic panel.

For installation, understand values for rip, grab, sag and track hold. Fabrics will be tested for elasticity, retainer hold, tensile strength, tear strength, pattern alignments concerns, read-through concerns and light reflectivity concerns.

Understand that just because a fabric is porous enough to see through or pass air through, does not mean is is acoustically friendly. Every type of fabric absorbs and reflects energy uniquely. This noise reduction coefficient needs to be understood in order to control the sound quality of the room properly.

Not in agreement, I take it, with the thinking behind single dipoles for surrounds? Or have the mixes changed since then and now more direct radiated sound is more correct?

I will toss out there that I recently "discovered" my M&K's "Tripole" mode and that has made a big difference. In my case, more output from the monopole portion "goes over the head" of the near seat to the far seat, and correspondingly reduces the dipole component of the speaker's output (and the level of the surround at the near seat). Things are still peachy in the center seat with a touch more localizing of surround content, but now the surrounds are more enjoyable at the left and right seats as well.

Jeff

Mixes are still all over the place. A lot of older DVDs still contain the theatrical mix, which is too sibilant and will sound most correct with the old fashion THX surround recommendations (diffuse).

More and more home video releases are mixed for small rooms and direct radiating speakers all around.

I would not say the mixes have changed fundamentally, the surrounds still carry ambience, music and effects. And no, I never got on the dipole wagon. Tried them several times, but the inability to timbre match them with the fronts bothered me--I could not feel I was in one seamless space, but in a splicing of distinct front plus rear spaces.

Theaters have line arrays for very good reasons of audience coverage. But I'm not out to replicate theatrical sound in my home theater. I want to hear the soundtrack as cleanly and clearly as possible, in a single, seamless, contiguous space-time continuum. I find 7.1 works really well, direct radiators all around, for movies and also for music, which is the majority of my listening.


I like the idea of the Tripole. Wouldn't it be cool to have a surround processor that could feed the diffuse parts of the sound to the dipole drivers and the direct sounds to the monopole?

Hi Roger,

This touches on a subject that came up in the Audyssey thread. Some folks were complaining that with DSX processing they weren't hearing their surrounds as distinctively. In an earlier posting Chris K mentioned that DSX involves decorrelating the surrounds and I wondered if that was what the folks were reacting to. In today's movies, particularly action movies, there is a significant portion of direct sounds as well as diffuse sounds in the surrounds and if decorrelation is being applied ideally it should only be applied to the diffuse sounds. Is there a way to selectively decorrelate sounds? Does THX Adaptive Decorrelation do this?

Thanks.

Larry

EDIT:
I did a little Googling on THX Adaptive Decorrelation and found this in the Audio Dictionary, by White & Louie.


So this wasn't what I was looking for.

Getting back to Roger's remarks, are there existing signal processing technologies that permit isolating diffuse sounds from direct sounds in a soundtrack?

Interesting discussion tucked away in the Master acoustics thread...
When I bought my set-up Dec-2007 seemed most people were still recommending dipole surrounds, so I got mid-level Paradigm Monitor 9 speakers for my 7.1 set-up, with (4) of their ADP-390 for side and rear surrounds.
http://www.paradigm.com/products/par...series/adp-390


Now, my brother inlaw just outfitted his HT with Monitor Audio Gold series, and his surrounds are their GSFX surrounds, which have a dual mode configuration (dipole or monopole) so you can pick and choose.
They even state "The GSFX is ‘ambidextrous' meaning the speaker can be configured as right or left "handed" during installation (via front panel switch) so the polarity of the front speakers is in phase with the GSFX surrounds. "
You can see the switch on front face in this picture:
http://www.monitoraudiousa.com/produ...x/your-speaker


So, where I'm going with this is from Jan-2008 thru Feb-2011 I did not have any acoustic treatments, now I've added side/ceiling RFZ panels.
Nothing specifically on the rear portion, so I still have that similar ambiance from the dipole config, but I have to wonder if I'm "missing something"..

Seems like most of the dipole manuf should at least add a switch like Monitor Audio/others have done, and let the end user choose based on their preference and listening material.

I've toyed with the idea of replacing the rear ADP-390's on the back wall with the Paradigm Titan Monitor, keeping the side surrounds as ADP-390's.
Or.....re-wiring the rear ADP-390's so instead of the sides being out of phase and creating a null along their axis if both are in-phase then that would give more "forward" coverage, in effect like a monopole switch on the Monitor Audio GSFX's.....
yea, I should probably move this thought to one of the speaker forums or audio set-up theory forums....but it was brought up here and got my mind churning...

I'm not going to agree entirely with Roger, nor entirely disagree. Each has their place and proper application. Certainly monopoles can be made to work in a small room with a single (maybe two) listening positions. They aren't going to be timbre matched unless they are the same distance as the mains from all boundaries and at the same height. (The timbre, as heard in the listening position, will change with height on a monopole design.) Once you have a small room with, say, two rows of seats and three to four seats in each row, monopoles can easily create a bigger problem than they solve. Other than timbre, you now have a situation where those on the ends of the rows are overwhelmed with that nearest side surround ... in other words, ears are soooo close to their respective side surround speaker, that speaker will over power the rears and opposite side speakers.

In larger rooms, with multiple rows, a relatively respectable distance between the end seats and the walls and the luxury of surrounds for each row, now you can create something really stunning with an array of monopole surrounds.

In the end, saying one is better than the other without context is not entirely correct. That's, of course, my opinion. Take it, leave it, or roll your own.

While I do not know for sure, I suspect that such is part of Neo:X. Only because the creators of that have discussed the benefits of such processing in AES papers. I realize that cannot be taken as anything other than mere speculation at this point. With Onkyo's announcement, it might not be too long until we find out.

I hope everyone understood my post as expressing nothing more than my personal opinions and preferences.

Hi Dennis,

With regard to timbre matching surrounds to the front speakers, a long time ago I thought recalled that you stated that due to the fact that surrounds are positioned to the sides or rear of the listener, even if they were identical to the mains, that they could never completely match in timbre. I have I expressed this correctly?


Can you give us a rough idea of an acceptable distance between the end seats and the monopole surrounds?

Larry

For the record, there's a great thread here that deals exclusively with dipoles, bipoles, quadpoles, etc...

http://www.avsforum.com/avs-vb/showthread.php?t=874378

Not Dennis, but one could say that HRTFs heavily influence the spectral balance for each speaker position. No matter, human brains don't interpret that as a timber shift, but as a directional shift.

Anyway, the point I was making about timbre matching was aimed at what is coming out of the speakers. Identical speakers in a room that avoids degrading the responses is what I would qualify as timbre matched. And it is indeed achievable with monopoles (and judicious EQ and acoustic care) whereas with dipoles it simply is not.

It was Floyd E Toole that said that. See this thread:

Timbre matching a dubious feature?
http://www.avsforum.com/avs-vb/showt...8#post18467318

Thx, 10 pages of detailed discussion, with references linked...started July-2007 and going strong thru Oct-2010.
I subscribed (my way of bookmark), this way I can read and absorb it.
(love my iPhone for these pure readings)

Memories of SRS.

I don't want to leave the impression timbre isn't important; but, it is only one of "billions and billions" (to quote Carl Sagan) of combinations and permutations which need be considered when putting together a high performance (acoustic) space. When we consider the challenges of 6 to 8 seats in a small residential space, timbre matching surrounds will not necessarily be the biggest elephant in the room.

Larry, a doubling of the distance from the source will result (in round numbers) in a 6dB decrease in SPL. If you want to determine the SPL difference from surround speaker "A" between seats located at R1 and R2, here's a reasonable means to estimate that difference. SPL2 = SPL1 − 20 log10 (R2 / R1 ) With side surrounds you'd want the delta in SPL between the closest seat to the speaker to be not more than 3dBSPL higher than at the furthest seat from the speaker. You'd want to achieve the same with the rear surrounds and, of course, the front speakers as well. (Note ... you have to account for the radiation pattern of the speaker.) If you look at two rows of seating and a monopole speaker, from a timbre AND SPL perspective, you also need to recognize that one, if not both, rows will be off axis from the speaker. Since the distances (from side surrounds particularly) are much shorter than from the LCR's, listeners will be more off axis with respect to the side speakers than the front. More off axis equates to not only SPL differences but timbre as well.

Referring back to ITU specifications (and those configurations suggested by other sources), we generally see the ideal is that all speakers are equidistant from the (single) listening position. The impossibility of equidistant in most rooms was solved by receivers/pro-pros allowing you to set that distance in the speaker set-up menus. Or, did it really solve the problem? Not exactly. It solved a path, or phase, difference problem to a single seat. It certainly does not resolve a timbre difference in a room with multiple rows of multiple seats due to off axis response. How do you resolve that? Simple (maybe). You need to be careful of the off axis response characteristics of the speakers you select for *your* specific physical environment. The low hanging fruit may not be timbre.