Can I fix a room decay of 1500ms?

Bjorn

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Oct 12, 2010
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We were talking about below 100 Hz solutions. And there, peaks in general are minimum phase. And regardless, if you get a DSP solution (and some automated ones) you can easily toggle them on and off to hear the difference. If it sounds worse, undo the change. Indeed it is pretty educational to learn such effects rather than go by graphs and technical terms.
It can be minimum phase.
In general, "time domain" correctness is more there to please the eye than the ear. :)
Wow! No pun intended, but if that's general statement on the time domain in the room it's very wrong and you must have misunderstood something. That would imply that decades of psychoacoustic researchers were a waste.
 

amirm

Banned
Apr 2, 2010
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Wow! No pun intended, but if that's general statement on the time domain in the room it's very wrong and you must have misunderstood something. That would imply that decades of psychoacoustic researchers were a waste.
Misunderstood something? That happens to me all the time so that would be no surprise on this occasion. :D

I don't know about decades of research into this field but do have two references counter to audibility of phase distortion in rooms using loudspeakers:

1. Peer reviewed paper in J. of AES, On the Audibility of Midrange Phase Distortion in Audio Systems: http://www.aes.org/e-lib/browse.cfm?elib=3824



2. Measuring Audible Effects of Time Delays in Listening Rooms: http://www.aes.org/e-lib/browse.cfm?elib=11750

A circuit consisting of cascaded first-order all-pace sections was constructed
Fig. 11. Two channels each use IS cascaded opamp sections to achieve a delay
of nearly 8700 degrees over the audio bend with taps at intermediate delays.
Approximately 7 ms of delay at low frequencies is also produced. The circuit
centers about 630 Hz the geometric center of the audio range. Although this
circuit does not represent all possible time delay and phase shift
characteristics it is felt that the amounts and rates of change off these
characteristics are worse than what ts encountered in high quality equipment.

No one to date has been able to detect the presence of this circuit in
hundreds of sensitive double-blind tests on speech or music program material
with peripheral equipment including time coherent speakers and headphones.

A change in sound can be detected using a narrow pulses a test signal by a
slight TEE-OOM sound, Even this clue disappears however below a mere 1,000 or
so degrees. The inescapable conclusion is that frequency response is what we
hear when phase shift, time dispersion and Frequency response are all occurring
simultaneously."


If you have something like this I can read, I appreciate the reference. Otherwise, I am signing off from the thread. :)
 

Scion

New Member
Jul 7, 2016
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Mostly London
We were talking about below 100 Hz solutions. And there, peaks in general are minimum phase. And regardless, if you get a DSP solution (and some automated ones) you can easily toggle them on and off to hear the difference. If it sounds worse, undo the change. Indeed it is pretty educational to learn such effects rather than go by graphs and technical terms.

In general, "time domain" correctness is more there to please the eye than the ear. :)

Are we talking about the same thing i.e., is "time domain correctness" the same thing as the long decay time in my room; because I'm hearing a boomy, slow decay on all the bass below 110Hz?

On the ASC website there is a paper by Art Noxon, Room Acoustics and Low Frequency Damping (published at 81st AEs Convention 1986) that I found interesting. In the conclusion, he writes " It is the Q not the EQ that distinguishes the listening room from the standard room." As I understand it, DSP is intended to fix the response curve. If I understand the thrust of his paper, he argues that the way to reduce Q and RT60 to a target level is by a calculated amount of absorption. In my waterfall graph, the RT60 at 55 Hz (dropping from 105dB to 45dB)takes 1500ms. This is the dominant axial mode (front to back) at 27Hz and is repeated at 54Hz, 81Hz, etc. This is clearer in the response graph.

So, will lowering the peaks, say at 55Hz, with DSP also reducing the decay and ringing? I rather hope so as I may not have to buy as many Tube Traps....:)
 

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Bjorn

VIP/Donor
Oct 12, 2010
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128
993
Norway
The frequency response is a derivative of the time domain. So to say that the time domain doesn't matter is like saying the earth is flat. He couldn't be more mistaken. Every knowledgeably acoustician works primarily with the time domain in the room. The frequency response will follow.

Your waterfall graph shows several audible resonances in the room. Something that's only dealt properly with physical treatment. However, the treatment needs to be effective. That implies both a high coefficient from the acoustic product and correct placement.
 

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