| Thomas Jouanjean wrote on Mon, 06 December 2010 13:03 |
Just a quickie here: your diffusion system isn't standard in the sense that it's more based on "time spread edge diffraction" from the panels rather than "standard" diffusion, for lack of a better way to describe it?
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Yes, well-spotted, in fact, we originally based our "diffuser" design on a slat absorber!
but we used Schroeder's numbers sequence in order to calculate the depth of the slats.
In the end, as you can see, visually, it still looks more like a diffuser than a slat absorber.
Functionally, a slat-absorber means, that in addition to diffusion and/or time spread edge diffraction we have Helmholtz's Resonator here, with channel depths which vary with Schroeder's number sequence.
Time spread edge diffraction is a good name, even very good, but one must not forget that in addition to the presence of a resonator cavity in every well in a standard QRD diffuser with fins, one (rear) side is closed and the other open (front), in our case we also have a resonator cavity (with air mass), only here its open on both sides.
Also we have used such 'diffusers' in a different studio, as described in the paper, placing them horizontally oriented ABOVE the speakers in some sort of "soft" soffit mounting [there are nothing to reflect from this diffusers]. Therefore, we did not excessively amplify the bass, due to the transition from full space to half space radiation, but resolved the speakers' edge diffraction using the method you correctly described as 'time spread edge diffraction', while at the same time we did not increase low frequency response much, just enough to the client's liking. Because, besides a few dB gained, better definition was obtained (diffraction from one box edge was transformed into many diffractions which were time temporally and spatially shifted, and thus reducing their negative impact, in my opinion, (if you can’t “kill” diffraction, separate it into many parts, and make it random in space and time
in other words ).
You can see this on image below (this is second control room described in white paper, aesthetically unfinished yet, but fully functional):
| Thomas Jouanjean wrote on Mon, 06 December 2010 13:03 |
Hence it seems for perpendicular coincidence the amount of absorption is really pretty high, from the "absorptive wells", while still maintaining some small amount of this diffused "edge diffraction".
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Unfortunately we did not have the sound intensity probe system to measure the acoustic impedance 'in situ'.
However, subjective impressions indicated that listeners did not have the impression of a real classic diffuser behavior, rather more, much more noticeably more detail, which would otherwise not have been able to have been heard in a classically treated room... also treated room sounds bigger than physically is (this is a known diffuser phenomenon)
We had no problems in just calming low bass in the first studio; the ceiling was high and the room was fairly long, there was a space to prevent and reduce reflected low-frequency energy in the room.
However, we wanted to go a step further and bring back the nice reflections to the listener, we knew that it could be done with diffusers, but the sheer quantity of classical diffusers would badly spoil the absorption of low-frequencies, because they can't let air flow through
'Diffusers on ALL surfaces' was a condition that we set for ourselves because of surround monitoring, and we didn't want to give in to the frequent compromise that the rear speakers are less important than the front ones ...
However, when you begin to draw the positions of the diffusers in an ordinary room (for five speakers), and where all of the diffusers should be placed using the principle of mirrors, you soon realise that there you need all surfaces to be diffuse ... which is logical in some sense; if surround is a speaker system ... surround will be the reflections, won't it?
We feel that before everything, a small space for any kind of serious combination, and one for a client who desires the 'best', must have:
1. Low end settled/calmed as best as possible
2. Mid range which has diffusion and absorption, and for:
3. High frequency diffusion mainly homogeneous across all surfaces of the room, insofar as is possible.
| Thomas Jouanjean wrote on Mon, 06 December 2010 13:03 |
For other angles it seems that this "time spread edge diffraction" (diffusion) plays a more important role in the MF and HF in parallel to absorption, while for LF, absorption kicks in when the waves become surfacic?
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Yes!
The idea was to integrate more
homogeneous and
frequency dependent treatment on all surfaces, with the exception of the floor, in a small space. This meant that:
1. 'Diffusers' must be able to allow air to pass through freely (a condition for smooth absorption of low frequencies).
2. 'Diffusion' was initiated from 1kHz because of the 'three wave length' distance from the listener rule (Meaning, it can get lower in larger rooms).
| Thomas Jouanjean wrote on Mon, 06 December 2010 13:03 |
Good stuff
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Thank you Thomas
Best regards,
Boggy
Author
Topic: Acoustical Design of Control Room for Stereo and Multichannel Production — A Novel Approach (Read 50108 times)