Time alignment

[amirm]

Now that is funny. Design process is a constant battle between mutually exclusive goals. You have to ultimately choose priorities and make tradeoffs.

Normally any speaker crossover with a rolloff steeper than 6 dB per octave will warp phase and screw up time alignment. That's not a fatal flaw and most speaker designers accept this in return for the advantages of steeper slopes. There may be a high-tech solution with digital signal processing, but even in the digital realm you typically get the same phase warp as with analog crossovers. There is a software app called "phase arbitrator" designed to reverse the phase warping of a DSP crossover, and probably some other DSP tools with the same goal.

I was going to say "excellent first post" but this is an excellent post whether it is the first one or not .

Welcome to the forum.

 

[TJE]

Actually, there are plenty of passive filters that provide linear phase, but they are generally more complex and there are other trades, like slower roll-off, ripples in the pass and/or stop bands, etc.. Always compromises and trades...

I'm not a technical expert and should maybe put that in a signature, because my comments may sound definitive even when not strictly accurate. Don, maybe you're referring to the Bessel filter (link). It sounds like a good idea and is a solution available to speaker designers, but are there examples of speakers that have a perfect inpulse (like the Dunlavy speakers in the OP) with Bessel crossover filters?

 

[TJE]

I was going to say "excellent first post" but this is an excellent post whether it is the first one or not .

Welcome to the forum.

Thanks Amir. I've been lurking here for some time and felt the impulse to chime in.

 

[NorthStar]

-- In addition to John Dunlavy, Richard Vandersteen's loudspeaker designs are also worth exploring.

These two gentlemen are both into coherent phase, time aligment, low-order crossover slopes, ...

Are the compromises made into their designs compensating for other attributes requested by others?
And what about KEF with their coaxial drivers?
And speakers that are x-over-free?
And separate actice crossovers?
Flat panels, electrostatics?

* Welcome TJE! :b

 

[Gregadd]

Phase Coherent Crossovers Network by Nelson Pass
http://www.passdiy.com/pdf/phasecrx.pdf
http://www.google.com/patents?hl=en...ssovers&printsec=abstract#v=onepage&q&f=false

 

[DonH50]

I'm not a technical expert and should maybe put that in a signature, because my comments may sound definitive even when not strictly accurate. Don, maybe you're referring to the Bessel filter (link). It sounds like a good idea and is a solution available to speaker designers, but are there examples of speakers that have a perfect inpulse (like the Dunlavy speakers in the OP) with Bessel crossover filters?

Bessel is one of several (probably many; if I can think of several, a real filter expert can think of many ) filters that offer linear phase, which leads to constant group delay, which leads to good time response. We use a bunch of different filters in radar systems (and lidar, and sonar) and preserving time information is critical.

I have no idea what sort of crossovers various designers use; I have not researched them for ages. IME the speakers with the best time response are planers and line sources, e.g. electrostats, Magnepans, the new line sources, etc. Most use pretty simple crossovers. I think it is a lot more work to achieve time coherence when multiple drivers and higher-order crossovers are used.

Impulse, or step, response is but one parameter and I suspect most people (a) don't really understand it and (b) don't really care. In the real world I worry a lot more about what happens after the impulse; ringing and slow decay will muddy the sound, whilst it is not clear to me that having a perfect initial arrival matters all that much. That from a guy who has chosen speakers at least partly for their very good time response...

FWIWFM (probably not much!) - Don

 

[NorthStar]

-- If Time Alignment don't truly matter that much, why are some speaker's designers paying particular attention to it?

 

[Mark Seaton]

-- If Time Alignment don't truly matter that much, why are some speaker's designers paying particular attention to it?

I'd argue it's very hard to isolate and evaluate time domain issues without also having other dramatic effects on a real speaker, especially a passive one. For most cases you are changing off axis behavior significantly, along with out of band issues, making an isolation of the issue very tricky.

The way the issue should be evaluated is to take a wide band, waveform preserving design (ie full range driver or electrostat), and then use an active crossover in front of the amplifier to simulate different crossover types. In other words you feed the speaker the electrically summed output of a 1st order crossover vs. that of say a 4th order crossover. If the amplitude response is matched, the only remaining difference will be the group delay/phase response. Of course this is a very simplified comparison case where real speakers with separate elements can create other offsets and discontinuities due to physical separation of the drivers. Even if this particular case isn't audible, that still leaves the time misalignment vs. physical position or listening angle.

One interesting anecdote is that if you dig into some of the past room correction efforts, there were more than a few cases (I seem to recall one in particular from B&W) where they would find mixed results/preferences as to the benefit of the frequency response smoothing at the listening position, but correction of the time domain/group delay was suggested to be preferred. I don't pretend these cases are conclusive, but worth thinking about.

 

[DonH50]

IIRC, the B&W white paper addressed having clean pulse response, which was preferred over a flat freqeuncy response. That is sort of what I was trying to say in my earlier post. Technically, you can swap between time and frequency response, so if one is very good the other should be as well. You must look at phase in the frequency domain, however, and not just amplitude.

B&W did some really neat things, like the traveling laser interferometer show, back in the 80's. No idea if they still do that sort of thing...

 

[NorthStar]

-- Mark, and Don, are you familiar, or do you know Richard Hardesty from the Audio Perfectionist Journal?

He also used to write very interesting articles and review high-end audio products for Widescreen Review mag.
Now he's even more 'high-end' in his experience and knowledge everything audio related.

Perhaps Amir knows him.

___________________

I'll wait for your reply before embarking in this amazing audio's odyssey.
...And with various/different views from other audio experts, on this subject of Time Alignment.
...Loudspeaker's Phase Coherence. ...All the ins and outs, from the recording studios right to our loudspeaker's sound reproduction at home.

...Should be an excellent exploration/re-exploration. :b

 

[puroagave]

-- Mark, and Don, are you familiar, or do you know Richard Hardesty from the Audio Perfectionist Journal?

He also used to write and review for Widescreen Review mag.

Perhaps Amir knows him.

___________________

I'll wait for your reply before embarking in this amazing audio's odyssey.
...And with various/different views from other audio experts, on this subject of Time Alignment.
...Loudspeaker's Phase Coherence. ...All the ins and outs, from the recording studios right to our loudspeaker's sound reproduction at home.

...Should be an excellent exploration/re-exploration. :b

theres a name from the past. Richard was a partner at Havens and Hardesty, a high-end audio dealer in orange county - they folded sometime in the '90s. they were a huge proponent of time aligned speakers, vandersteen in particular.

 

[Steve williams]

I remember the store well

 

[DonH50]

Visited the store, recognize the name, but cannot put a face to it, sorry.

 

[microstrip]

-- Mark, and Don, are you familiar, or do you know Richard Hardesty from the Audio Perfectionist Journal?

He also used to write very interesting articles and review high-end audio products for Widescreen Review mag.
Now he's even more 'high-end' in his experience and knowledge everything audio related.

Perhaps Amir knows him.

___________________

I'll wait for your reply before embarking in this amazing audio's odyssey.
...And with various/different views from other audio experts, on this subject of Time Alignment.
...Loudspeaker's Phase Coherence. ...All the ins and outs, from the recording studios right to our loudspeaker's sound reproduction at home.

...Should be an excellent exploration/re-exploration. :b

Bob,

I have referred several times to his writings in my posts - his interviews with high-end designers for Audioperfectionist are very interesting. I found particular interest in Bill Low words about cables ...

You can find them at
http://www.auriclepublishing.com/page3.html

The one with Jim Thiel addresses time alignment.

 

[NorthStar]

theres a name from the past. Richard was a partner at Havens and Hardesty, a high-end audio dealer in orange county - they folded sometime in the '90s. they were a huge proponent of time aligned speakers, vandersteen in particular.

---- I guess that they must be very good friends because Richard Hardesty uses Richard Vandersteen's loudspeakers and subwoofers in his own home theater surround sound system (also acting as a high-end only 2-channel stereo sound system).

I like these two guys, a lot. ...Because they go to extreme dispositions and analyses in their audio pursuit and perfectionism.
John Dunlavy too, I loved very much so. ... R.I.P. John

Richard Hardesty is like a mentor to me; I learned a lot from him. And I kept several of his audio articles and reviews over the years.
And I also quoted him few times in the past.

 

[NorthStar]

Visited the store, recognize the name, but cannot put a face to it, sorry.

---- Google him. :b

 

[Mark Seaton]

Just remember there is a lot of audiophile folklore which is just as misguided as the many hypotheses of what makes for subjectively "fast bass" <I cringe even typing that phrase>. Regardless of how well intended those ideas were or how much they follow some simplified intuition, most have little basis in science, and fall into the realm of coincidence rather than causality.

 

[Mark Seaton]

IIRC, the B&W white paper addressed having clean pulse response, which was preferred over a flat freqeuncy response. That is sort of what I was trying to say in my earlier post. Technically, you can swap between time and frequency response, so if one is very good the other should be as well. You must look at phase in the frequency domain, however, and not just amplitude.

I agree, and understanding of our hearing also aligns with the importance of decay vs rise of a sound. As with most things, if you chase time perfection without regard for other obvious concerns, you end up with a more interesting story than end result.

At higher frequencies the minimum phase relationship of magnitude and phase no longer hold. As a simple example, any device with changing directivity will not be minimum phase. This of course tracks with the reality of different type crossovers all providing a flat on-axis sum, but very different phase and off axis responses.

There are a handful of approaches to achieve a constant group-delay result, and many more to minimize the shift. As one often overlooked example, a specifically overlapped 2nd order filter can achieve this, although direct comparing to a 1st order filter shows there's a lot more similarity than difference between these two examples.

 

[NorthStar]

Just remember there is a lot of audiophile folklore which is just as misguided as the many hypotheses of what makes for subjectively "fast bass" <I cringe even typing that phrase>. Regardless of how well intended those ideas were or how much they follow some simplified intuition, most have little basis in science, and fall into the realm of coincidence rather than causality.

---- Mark, there is nothing 'folklore' about Richard, Richard, and John.
These guys are true to their 'sport', audio perfection.

"Fast bass", from who? ...Accurate bass, and coherent bass (in phase with the full audio spectrum); ok then.
...Just like at a live Classical Chamber music concert/event. ..Or Jazz (small ensemble) venue.

And I'm glad that Mep (Mark) knows about the man (Richard Hardesty), as it will make my job easier.
By the way, that Audio Perfectionist Journal; you need a subscription, and it ain't cheap.
Plus, if you want to read his articles and reviews online from Widescreen Review; you need a subscription too.

But I got them all here in my home (from Widescreen).

The thing is this though: before I took my time to quote some of his great stuff, but people didn't get interested, or just simply didn't dig it.

This hobby of ours is a tightrope act; you need to be well balanced and coordinated (in sync) to get your message properly across. ...And speak the same language (verses) as your audience.

And we haven't even start yet. ...The experts should always take the lead IMO.
Well, Jeffrey started this thread, and you guys joined in; so all is good. :b

 

[Mark Seaton]

---- Mark, there is nothing 'folklore' about Richard, Richard, and John.
These guys are true to their 'sport', audio perfection.

That comment was made generally on the topic and not directed at yourself nor Dunlavy, etc. I've heard and measured the SC-VI's and was quite impressed with what was achieved. I also well remember Richard Hardesty's subwoofer comparisons and measurements from the late 90s I believe.