The No.1 Website for Pro Audio
 Search This Thread  Search This Forum  Search Reviews  Search Gear Database  Search Gear for sale  Search Gearslutz Go Advanced
eigenmodes calculator Reverb & Delay Plugins
Old 12th September 2011
  #31
Lives for gear
ok, i thought diffusors were capable of extending 1 octave below and above their designed frequency. seems i confused typical 1d versus air transparent 1d.

so from a lamens point of view, you have designed your room to fullfill a min 20-30db attenuation rather than a theoretical isd termination for frequencies below 1khz.

just on your room. i really do like it. you've managed to combine the aesthetics and the functional into one very mature package. nice work!
Old 12th September 2011
  #32
Lives for gear
 
boggy's Avatar
Quote:
Originally Posted by gouge View Post
ok, i thought diffusors were capable of extending 1 octave below and above their designed frequency. seems i confused typical 1d versus air transparent 1d.
Highest working frequency of QRD diffuser is defined with well width. (~8kHz in my case)
Lowest working frequency is defined with well depth. (~1kHz in my case)
Air transparent construction is similar to QRD, but wells are spaced:
1. to enable air circulation to second layer of acoustic treatment,
2. to lower reflection coefficient (needed because required RT60 in finished room)
3. to give some amplitude grating component in diffusion, which original QRD didn't have..
Quote:
Originally Posted by gouge View Post
so from a lamens point of view, you have designed your room to fullfill a min 20-30db attenuation rather than a theoretical isd termination for frequencies below 1khz.
Yes, if you talk about ETC graphs, which I attached here: https://www.gearslutz.com/board/7015786-post45.html, and inspiration for this came from George's Massenburg Blackbird Studio C design, then we introduce wtih MyRoom a definitive balance between diffusion and absorption, that already exist in Blackbird, but in rooms which may be a much smaller, using conventional absorption and air transparent diffusion instead of only diffusion (like in Blackbird).

Both MyRoom principle and Massenburg design don't need an ISD gap like LEDE and RFZ. Approach is much different... I think, mostly because one of requirements for these control rooms, was also a surround sound monitoring, where you can't have strong forward backward assymmetry (like in N-E, LEDE, RFZ), which is absolutely needed for an ISD gap, this means that ISD gap principle isn't compatible with surround monitoring without favoring front speakers.

Even if most designers try to put surround speakers in any existing design principle, Blackbird studio is a first surround compatibile acoustic design (AFAIK!) for control rooms, and because this we used it for idea how to treat a smaller room for surround monitoring... after that we found that room is excellent for stereo monitoring too... etc..

N-E design don't have an ISD gap too, BTW

And yes, ISD gap is specific to LEDE and RFZ designs, but it's not a basic control room requirement... people can live happily (and can have excellent mixes too) without an ISD gap.

Also, as I already wrote, but it's not bad to write again... ETC measurements may be misleading in fully diffuse rooms, probably because nature of analysis and averaging of reflections which arrive to one single measurement microphone.

If you look only to ETC measurement results, you may get a wrong conclusion that this rooms are anechoic (because measurement results are too similar to anechoic rooms)... but this rooms aren't anechoic at all... when you listen/mix music in it.

RT60 measurements are much better to get an information if room is too dead or not too dead... I don't have measurement results of RT60 for Blackbird studio C, but I publish RT60 measurements in our AES paper (most of it you can find in MyRoom Design white paper), of rooms designed following MyRoom principle, and limits which are recommended by AES/EBU/ITU organisations is satisfied (room reverberation is in recommended limits in other words)
Quote:
Originally Posted by gouge View Post
just on your room. i really do like it. you've managed to combine the aesthetics and the functional into one very mature package. nice work!
Thank you!
Old 12th September 2011
  #33
Lives for gear
 
Jens Eklund's Avatar
Quote:
Originally Posted by boggy View Post
RT60 measurements are much better to get an information if room is too dead or not too dead... I don't have measurement results of RT60 for Blackbird studio C, but I publish RT60 measurements in our AES paper (most of it you can find in MyRoom Design white paper), of rooms designed following MyRoom principle, and limits which are recommended by AES/EBU/ITU organisations is satisfied (room reverberation is in recommended limits in other words)

Thank you!
You cannot apply RT60 or any calculation, that assumes a completely diffused field, to a small room. Even if stuffed full of diffusers, the sound field is not going to be completely diffuse. This is why you never see RT60 numbers of studios designed by acousticians. Perhaps a rough estimation of "decay rate/time" using the slope of the Schroeder integral long after it has settled in order to avoid the effect of any sparse reflections and/or the drastic drop in energy level after the direct sound.
Old 12th September 2011
  #34
Lives for gear
 
boggy's Avatar
Quote:
Originally Posted by Jens Eklund View Post
You cannot apply RT60 or any calculation, that assumes a completely diffused field, to a small room. Even if stuffed full of diffusers, the sound field is not going to be completely diffuse. .....
Formula for Schroeder frequency in cavities (rooms, actually) give us a info from which frequency and above, sound field can be diffuse:

fSch = 2000*sqrt(T60/V)

Even in small rooms, diffuse field can exist above fSch, and it is really enough to check if room reverberation satisfy recommended nominal value and proposed limits.
Below this frequency we have dominant room modes in room, and it's already recommended to treat it with absorption as best as is possible...

Example:
In our design in RES Media, fSch=140Hz, and in Pressed Lizard fSch=164Hz. Following Schroeder's formula, measured RT60 values are valid above this frequencies. Values of calculated fSch's are below 200Hz, from which it is recommended for RT60 to have defined nominal value and to be constant with frequency, something like this:
Quote:
Originally Posted by EBU Technical Review
The nominal reverberation time (Tm ) for the 1/3-octave bands from 200 Hz to 4 kHz is found as follows:
Tm = 0.25*(Roomvolume/Ref.volume(100))^(1/3)
(bolded by me)

You can see this in any of papers listed below:
1. "Multichannel surround sound systems and operations", AES Technical Council, Document AESTD1001.1.01-10, New York.
2. “Methods for the subjective assessment of small impairments in audio systems including multichannel sound systems”, ITU-R Recommendation BS.1116 (rev. 1), ITU, Geneva, 1997.
3. W. Hoeg, L. Christensen, R. Walker, “Subjective assessment of audio quality– the means and methods within the EBU”, EBU Technical Review Winter 1997, pp. 40-43.
4. "Listening conditions for the assessment of sound programme material: monophonic and two–channel stereophonic", EBU Tech. 3276 – 2nd edition May 1998, European Broadcasting Union, Geneva, Switzerland

Also, in MyRoom design, I define requirements for lowest allowed working frequency for diffusers, that is limited with maximum distance from diffuser, and this is already well above calculated Schroeder frequency, then diffusion sound field can exist in room above defined lowest diffusion frequency for sure. To be clear, we already successfully complete subjective tests long ago, and differences with or without diffusers are easily noticeable, but theoretical conclusion is also good.

Measuring room reverberation is one of ways of room analysis, not a target, instead of this, main target in studio acoustics is human ears and brain. I use RT60 measurements for characterisation of already finished room, because I really can't "measure" human subjective impressions (which will be the best), and because there are international/european organisation's papers that recommend this.

I know, In bigger rooms situation is much better, but people usually don't have money for it today, so we cannot close our eyes in front of small rooms...
Old 12th September 2011
  #35
Gear Guru
Words

Quote:
You cannot apply RT60 or any calculation, that assumes a completely diffused field, to a small room. Even if stuffed full of diffusers, the sound field is not going to be completely diffuse. This is why you never see RT60 numbers of studios designed by acousticians. Perhaps a rough estimation of "decay rate/time" using the slope of the Schroeder integral long after it has settled in order to avoid the effect of any sparse reflections and/or the drastic drop in energy level after the direct sound.
Primarily, I agree. I would like to see technical language used more carefully. However one cannot insist on it heh
Also, how many of our rooms have a 60dB S/N ratio?
Even in the case of REW where Room Decay is considered and treated very carefully, we still see the Lingua Franca T60 used.
John's real world version is Topt. Reverb estimation adjusted to take account of lack of proper diffusion- a word I would like to see restricted to diffusors and spaces where diffusion is actually happening.
Personally, and I of course wish to recruit others for my world domination bid, I use the following substitute terms.

Room Decay.
38% Start postion.
Scattering.

DD
Old 12th September 2011
  #36
Lives for gear
 
Jens Eklund's Avatar
Quote:
Originally Posted by boggy View Post
Formula for Schroeder frequency in cavities (rooms, actually) give us a info from which frequency and above, sound field can be diffuse:

fSch = 2000*sqrt(T60/V)

Even in small rooms, diffuse field can exist above fSch, and it is really enough to check if room reverberation satisfy recommended nominal value and proposed limits.
Below this frequency we have dominant room modes in room, and it's already recommended to treat it with absorption as best as is possible...

Example:
In our design in RES Media, fSch=140Hz, and in Pressed Lizard fSch=164Hz. Following Schroeder's formula, measured RT60 values are valid above this frequencies. Values of calculated fSch's are below 200Hz, from which it is recommended for RT60 to have defined nominal value and to be constant with frequency, something like this:
(bolded by me)

You can see this in any of papers listed below:
1. "Multichannel surround sound systems and operations", AES Technical Council, Document AESTD1001.1.01-10, New York.
2. “Methods for the subjective assessment of small impairments in audio systems including multichannel sound systems”, ITU-R Recommendation BS.1116 (rev. 1), ITU, Geneva, 1997.
3. W. Hoeg, L. Christensen, R. Walker, “Subjective assessment of audio quality– the means and methods within the EBU”, EBU Technical Review Winter 1997, pp. 40-43.
4. "Listening conditions for the assessment of sound programme material: monophonic and two–channel stereophonic", EBU Tech. 3276 – 2nd edition May 1998, European Broadcasting Union, Geneva, Switzerland

Also, in MyRoom design, I define requirements for lowest allowed working frequency for diffusers, that is limited with maximum distance from diffuser, and this is already well above calculated Schroeder frequency, then diffusion sound field can exist in room above defined lowest diffusion frequency for sure. To be clear, we already successfully complete subjective tests long ago, and differences with or without diffusers are easily noticeable, but theoretical conclusion is also good.

Measuring room reverberation is one of ways of room analysis, not a target, instead of this, main target in studio acoustics is human ears and brain. I use RT60 measurements for characterisation of already finished room, because I really can't "measure" human subjective impressions (which will be the best), and because there are international/european organisation's papers that recommend this.

I know, In bigger rooms situation is much better, but people usually don't have money for it today, so we cannot close our eyes in front of small rooms...
"... in small rooms, there is no Dc, no well-mixed sound field, hence, no reverberation but merely a series of early reflected energy, the measurement of RT60 becomes meaningless in such environments."

Sound system engineering - Google Böcker

Old 12th September 2011
  #37
Lives for gear
 
SörenHjalmarsson's Avatar
 

Quote:
Originally Posted by DanDan View Post
Primarily, I agree. I would like to see technical language used more carefully.
Agreed!

Quote:
Personally, and I of course wish to recruit others for my world domination bid, I use the following substitute terms.

Room Decay.
38% Start postion.
Scattering.

DD
You left out the Anechoic Zone©? I'm hurt DD, truly hurt... heh
Old 13th September 2011
  #38
Lives for gear
also don't forget alphism, it's a new architectural movement i coined....

now just need to tell the world!
Old 13th September 2011
  #39
Lives for gear
 
boggy's Avatar
Quote:
Originally Posted by Jens Eklund View Post
"... in small rooms, there is no Dc, no well-mixed sound field, hence, no reverberation but merely a series of early reflected energy, the measurement of RT60 becomes meaningless in such environments."

Sound system engineering - Google Böcker

Yes, but this is only one (interesting) opinion about room measurements, published in the book, and still not an international/european recommendation.
Even I have some (different) point of views too , most of people has, but only a couple of it become international/european recommendation.
Old 13th September 2011
  #40
Lives for gear
 
Jens Eklund's Avatar
Quote:
Originally Posted by boggy View Post
Yes, but this is only one (interesting) opinion about room measurements, published in the book, and still not an international/european recommendation.
Are you saying that the un-usefulness of RT60 calculation in small rooms is an ”opinion”?


I don’t see how this is a “debate” except maybe in forums:
http://www.hometheatershack.com/forums/home-audio-acoustics/12027-appropriate-replacement-rt60s-sas.html
Post Reply

Welcome to the Gearslutz Pro Audio Community!

Registration benefits include:
  • The ability to reply to and create new discussions
  • Access to members-only giveaways & competitions
  • Interact with VIP industry experts in our guest Q&As
  • Access to members-only sub forum discussions
  • Access to members-only Chat Room
  • Get INSTANT ACCESS to the world's best private pro audio Classifieds for only USD $20/year
  • Promote your eBay auctions and Reverb.com listings for free
  • Remove this message!
You need an account to post a reply. Create a username and password below and an account will be created and your post entered.


 
 
Slide to join now Processing…
Thread Tools
Search this Thread
Search this Thread:

Advanced Search
Forum Jump
Forum Jump