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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: Phase Response Effects. . . what? posted by Schlep on January 28, 2016 at 07:55:28:
Well, first of all, there is the electrical phase response of a speaker and the *acoustic* phase response of a speaker.
An LR2 crossover imparts a 180 degree phase shift, which is why the tweeter is connected in reverse polarity. This crossover has non-constant group delay, which means it's not "transient accurate" or what some call "time coherent" or, a bit of a misnomer, phase-coherent.
And LR4 crossover imparts a 360 phase shift, which is how all drivers can be connected with the same relative polarity. So, this crossover design may be phase-coherent but it's not time-coherent aka not transient accurate.
The only crossover that is inherently time-coherent is a proper 1st order acoustic (not electric) design. Putting a single cap on the tweeter does not a 1st order acoustic crossover make. Much equalization needs to be done to get to the correct acoustic "target" response. Often, these speakers are less sensitive that a typical speaker because only "cuts" can be made with passive crossovers, rather than cuts and boosts as is the case with active crossovers.
There are some other crossovers (special ones) that can yield transient accurate (time coherent) response:
- Subtractive delay
- Filler Driver (originally by B&O)
- in DSP-based crossovers with "phase correction" algorithm
I've used the DSP based approach with an emulated 4th order LR crossover c/w phase correction and can obtain the transient response from measurements, comparing the 'before' and 'after' results. This technology does work, but there are some costs. First off, in the DSP realm it requires a time delay since you can't move the delayed part of the spectrum forward in time, but you can move the "relatively forward" parts of the spectrum BACK in time with a special kind of delay. They call it "forward/reverse processing" in that you pre-mangle the group delay so that when the speaker "re-mangles" it, the phase distortion is removed.
Neat stuff.
Cheers,
Presto
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Follow Ups
- RE: Phase Response Effects. . . what? - Presto 12:03:32 01/28/16 (0)
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