rePhase, loudspeaker phase linearization, EQ and FIR filtering tool

[ra7]

No, haven't done the two separately. Well, I started with just the bass correction and things were sounding different, so I went for the full monty. Only after the full correction did I start switching between corrected and uncorrected.

Really need to test blind.

[CopperTop]

So I can now get ruler-flat phase from the driver's impulse response using my homebrew active crossover software, with a selectable degree of smoothing. But what is the rationale behind correcting the phase and not the amplitude? My best efforts with corrected phase-only seem to give me improvements(?) in the stereo image but (and I may be imagining this because I'm half-expecting it) I'm not convinced that it's not also producing some 'uneasiness' in my ears. Perhaps transients are less 'solid'.

If I correct the amplitude as rigorously as the phase, I'm not sure I like the sound as much as the uncorrected (it is testing measurement technique and microphone quality in a much more clearly audible way than phase alone). However, and again I may be imagining it, it does seem to get rid of the 'uneasiness'.

The definition of minimum phase says that phase and amplitude are inextricably linked. Does correcting one without the other mean that the system is no longer minimum phase and our ears detect this as unnatural? The phase is then effectively floating around arbitrarily compared to the amplitude, and vice versa with no way for the ear/brain to link the two together.

[pos]

What are your crossover points?
Are you doing the whole filtering with phase linear crossovers?

If you only correct the allpass of your acoustical crossovers (with the "filter linearizion" tab if you use IIR crossovers, and some additional phase EQ to get it right, as the acoustical slopes are never completely textbook) and let the rest untouched (the small variations along the passband and the bass rolloff) then you should end up with something similar to a minimum phase "perfect" fullrange driver response-wise (on axis...).
Then if you also correct the bass rolloff the system becomes non causal, as the (unavoidable) magnitude rolloff does not come together with its "natural" phase shift...
Same thing for all the small phase glitches that you might correct along the passband (and that you should maybe let alone, as well as the magnitudes ones, if you are not sure they are not artifacts of a particular measurement and are not repeatable along several measurement points).

I should really include minimum phase EQ in rePhase but I have been to busy (err lazy) to put any serious work on it lately...

[Barleywater]

Originally Posted by CopperTop

So I can now get ruler-flat phase from the driver's impulse response using my homebrew active crossover software, with a selectable degree of smoothing. But what is the rationale behind correcting the phase and not the amplitude? My best efforts with corrected phase-only seem to give me improvements(?) in the stereo image but (and I may be imagining this because I'm half-expecting it) I'm not convinced that it's not also producing some 'uneasiness' in my ears. Perhaps transients are less 'solid'.

If I correct the amplitude as rigorously as the phase, I'm not sure I like the sound as much as the uncorrected (it is testing measurement technique and microphone quality in a much more clearly audible way than phase alone). However, and again I may be imagining it, it does seem to get rid of the 'uneasiness'.

The definition of minimum phase says that phase and amplitude are inextricably linked. Does correcting one without the other mean that the system is no longer minimum phase and our ears detect this as unnatural? The phase is then effectively floating around arbitrarily compared to the amplitude, and vice versa with no way for the ear/brain to link the two together.

Have you applied these techniques to small full range setup?

Information transmission line with periodic IR is correctable. Desired property is output matching input for all in band frequencies both in amplitude and phase. Passage of in band signal representing minimum phase IR is then perfect.

[kgrlee]

Originally Posted by CopperTop

The definition of minimum phase says that phase and amplitude are inextricably linked. Does correcting one without the other mean that the system is no longer minimum phase and our ears detect this as unnatural? The phase is then effectively floating around arbitrarily compared to the amplitude, and vice versa with no way for the ear/brain to link the two together.

Yes. This truly evil.

[john k...]

The vast majority of multiway speaker systems are not minimum phase to start with. Equalizing such systems to have perfect band pass response using minimum phase equalization will therefore not correct phase. So whether you use MP EQ or nonMP eq in such cases makes little difference. If MP Eq is used the amplitude correction will also impose phase corrections. If you use amplitude only corrections the phase will remain unaltered. The two approaches with yield different system phase but in neither case with the EQ'ed system be MP.

[pos]

Originally Posted by kgrlee

Yes. This truly evil.

Yes but in case of a multiway loudspeaker only linear phase crossovers can give a minimum phase system (summed responses)

[john k...]

Originally Posted by pos

Yes but in case of a multiway loudspeaker only linear phase crossovers can give a minimum phase system (summed responses)

There are lots of non-linear phase crossovers that sum to minimum phase systems. Examples are, of course, 1st order crossovers, the B&O filler drivers approach, there is a class of 2nd order crossovers, and the family of subtractive crossovers. We don't see many of them implimented because they don't always have the best polar response.

[pos]

Fair enough John, so remove the "only" in my previous post

Using phase minimum EQ in the driver passband (and around) and then using linear phase (or linearized) complementary crossovers looks like a good practical way to obtain a minimal phase system from a multiway loudspeakers.
Of course it is not always easy to get the phase right in the passband with only minimum phase EQ, as it requires lots of EQ well outside of the passband, down low (Linkwitz transform).

[john k...]

Originally Posted by pos

Using phase minimum EQ in the driver passband (and around) and then using linear phase (or linearized) complementary crossovers looks like a good practical way to obtain a minimal phase system from a multiway loudspeakers.
Of course it is not always easy to get the phase right in the passband with only minimum phase EQ, as it requires lots of EQ well outside of the passband, down low (Linkwitz transform).

Yes, that is one pretty good approach. That is the UE approach, but actually extending the MP well into the stop bands. But there is an advantage to using minimum phase filters (or targets) and then using phase linearizion to eliminate GD associated with the low frequency cut off of the system. That is that the individual pass bands with have causal response. Thus, there will be no pre-ringing in the individual pass bands which may become audible off axis. I've never been able to hear the pre-ringing, though I can measure it. Other claim it is very audible.