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Speaker Asylum General speaker questions for audio and home theater. |
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Speaker Asylum General speaker questions for audio and home theater. |
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In Reply to: RE: Phase Response Effects. . . what? posted by RoyJ on January 29, 2016 at 18:39:41:
Roy,How have you been?
Yes, it's really hard to try and explain the concept of group delay in laymans terms. It's really a derivative, a rate of change thing. The big deal is that if the group delay is non-constant, the original signal is not preserved. It actually sounds amazingly good despite that that poor waveform looks like!
A true first order *acoustic* design has constant group delay. A capacitor thrown on a tweeter is a 1st order crossover, BUT as you know this does not a 1st order ACOUSTIC design make. It's simply a first order ELECTRIC crossover. Obviously, 4th order LR acoustic targets are going to be far far easier to hit because of the rapid roll-off rate. And, you enjoy quite high power handling even with band-limited drivers and you don't need a tweeter with special power handling considerations and ultra-low Fs.
There are only two ways to go about it really: 1st order acoustic design or some form of trickery, and by trickery I mean passive methods like subtractive delay or "filler drivers" or DSP-based trickery like FIR filters or phase-corrected IIR filters. I've worked with the latter and really it was a lot of fun to be able to compare the pre and post correction impulse response.
A few big myths about group delay.
1. You can "fix" group delay and obtain time/phase coherence by flipping a driver's polarity, as in the case of the 2nd order LR crossover.
2. You can "fix" group delay and obtain time/phase coherence by ONLY time-aligning the drivers using a simple delay.
3. LR4 is time/phase coherent because all drivers are in phase electrically.The last one is where people don't get that although the LR4 is in phase at all frequencies due to the 360 degree phase shift, the group delay is actually worse that 2nd and 3rd order designs. Yep, even with it's inverted mid-range a properly executed BW3 design will have better pulse response than an LR4.
Cheers,
Presto
Edits: 01/30/16
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Follow Ups
- Oh, Hi Roy! It's been a long time! :) - Presto 13:37:07 01/30/16 (0)
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