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In Reply to: RE: Why not 10HZ or higher? posted by Chip647 on May 02, 2015 at 06:03:27
apart from the fact that it can be measured, can anyone give some good reasons why absolute sub-100hz phase accuracy is vital?
dave
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Hi Dave:
the use of the terms "absolute" and "vital" is perhaps a bit too stringent and probably "unobtanium" in practice.
If instead of vital we used the term "important"...
I'll throw out a few quick thoughts on the subject as I understand it...
or as I perceive the question being asked...
Steve O below mentions one consideration where concern over phase behavior is important... namely, if your using feedback.
The other thing phase behavior does is provides the designer with some benchmarks or "indicators of performance"...
something must cause phase anomalies... if so, we might want to know how, why, where and when. depending on the severity of the phase misbehavior it might be wise to try to ameliorate it.
Poor phase behavior can result in higher intermodulation distortion (so it is not only a "bass" problem but the intermodulating of two different signals creates new (i.e., distorted) signals.
Poor phase behavior will also show up in square wave tests. the import of square waves is it tells you something about the signal and it's effects ten times greater than the fundamental--- i.e., the harmonics.
Poor phase response also tells us something about the power handling (delivery) capabilities of an amplifier.
I would not think anyone would want to say that phase behavior is unimportant. It it has any importance then we might want to consider how it can be addressed.
And, again, in my opinion--- it's not a wholly black and white issue--- not that we have to have "absolute" phase integrity--- but the total lack of phase integrity is an issue that would impact performance in my opinion.
MSL
Builder of MagneQuest & Peerless transformers since 1989
Glad somebody finally asked the question. IMO phase shift at bass frequencies is a benign as bass distortion ... it takes a lot of it to be heard.
Anyone who has played with Subs will know just how much the phase angle can be varied with little ill effect other than to change the response at different frequencies depending on room resonance and speaker placement.
Naz
my experience is the opposite, I've found dialing in the phase of a sub especially critical to the soundstage.
This wasn't my point. Sorry, should have better explained.
In the context of rolling off at say 2-3 Hz vs 10-20 Hz the phase angle change is only 20 degrees or so at say 50 Hz and less as frequency in increased.
One would need to vary Sub phase by 90 degrees or so to be audible and this assumes a good sub with steep rolloff that doesn't leak into mid bass and mids too much.
Naz
I know. I think some of it has to do with the amps measurements as part of a Lab rating. I have never been able to identify the sonic impact, but engineers will beat you about the head and neck that it is a critical consideration.
Maybe the "engineers" concern themselves with managing LF phase shift because they're attempting to attain unconditional subsonic stability in a global feedback amp.
Personally, I don't mind not listening to 10Hz signals. Rolling off an amp at 40hz can also solve subsonic issues.
I agree . Brickwall filters at 40 and 18Khz suit me fine, but that is extra circuitry in the signal path.
Also have you seen the phase shift
caused by the woofer's inductance?
I sometimes think we are making more
of the situation than is valid.
DanL
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