Audiophile coaxial drivers????

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Soundminded

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Coaxial and triaxial speakers were a popular trend during the 1950s but they seem to have died out. AR3 probably put a nail in their coffin since it was not a design of that type and very highly regarded in its day. The West Coast challenger, the JBL 3 way bookshelf system was also not coax or triax. The rationale for this seemed to have been forgotten in the time aligned phase coherent marketing fad during the 1970s since one criteria for two drivers being phase coherent at the listener is that they not only have the same group delay but that their sound originate from the same point in space. But even so, with the group delay for tweeters typically shorter than for woofers and the tweeter mounted closer to the listener than the woofer, only a delay line could achieve true phase coherence and then only on axis. Digital delay and biamplification to the rescue. It is now possible to build phase coherent multiway speakers, at least they'll be that way listened to on axis.

That's the good news if you're into that. The bad news is as far as I can tell there is no actual advantage to such a design. To test whether it is even audible would require the speaker to be switched from a phase coherent mode to a phase incoherent mode which can be done with switching between corrected and uncorrected delays. But why spoil the fun for those who sell or build these types of speakers by investigating what is fact and what isn't.
 
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phase_accurate

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Joined 2002
To me it doesn't matter whether tests show the audibility of group-delay distortion or not (do we test the right things at all ?). I build my speakers that way simply because I know how to do it !
From the scientific point-of-view one can say that an information channel with group-delay distortion has a lower information capacity than one without group delay distortion (everything else being equal).

Regards

Charles
 
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Soundminded

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Joined 2008
Even if the drivers are in perfect time synchrony, they will still form interference patterns if they are not coincident in space. It's like throwing two rocks in a still pond and they land at exactly the same time but in different places. The ripples from each will form interference patterns with ripples from the other. to prevent this they must land in the same place a the same time. This BTW this is a classic example in standard wave mechanics theory. The same thing happens with light too.
 
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doug20

Member
Joined 2009
Soundminded said:
Coaxial and triaxial speakers were a popular trend during the 1950s but they seem to have died out. AR3 probably put a nail in their coffin since it was not a design of that type and very highly regarded in its day. The West Coast challenger, the JBL 3 way bookshelf system was also not coax or triax. The rationale for this seemed to have been forgotten in the time aligned phase coherent marketing fad during the 1970s since one criteria for two drivers being phase coherent at the listener is that they not only have the same group delay but that their sound originate from the same point in space. But even so, with the group delay for tweeters typically shorter than for woofers and the tweeter mounted closer to the listener than the woofer, only a delay line could achieve true phase coherence and then only on axis. Digital delay and biamplification to the rescue. It is now possible to build phase coherent multiway speakers, at least they'll be that way listened to on axis.

That's the good news if you're into that. The bad news is as far as I can tell there is no actual advantage to such a design. To test whether it is even audible would require the speaker to be switched from a phase coherent mode to a phase incoherent mode which can be done with switching between corrected and uncorrected delays. But why spoil the fun for those who sell or build these types of speakers by investigating what is fact and what isn't.
Click to expand...


Danley's latest designs have a 5" Coax in them (some impressive stuff in those new designs, I think Danley gets it!!). Mark Seaton's Catalyst and sparks designs have Coax drivers in them. Tannoy Designs have coax in them, so do Kef so Im confused why you posted they "died out" but I guess they did...I never followed what happend 30 years ago? Phase coherence was never a fad either (IMO), phase coherence in the critical voicing 400Hz to 5KHz range just sounds better from all my experience. Now we just need to find the best driver (horn or whatever) that handles that range the best for our individual applications.
 
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phase_accurate

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Joined 2002
Edit: The text below is refering to post #24


Agreed. But this will not be very extreme since the wave propagation "incoincidence" is smaller than the maximum mechanical path-difference. Apart from that it is only relevant around the crossover frequency (OK this is a little simplified since it doesn't pay attention to the fact that each driver interferes with itself as well). And time accuracy is only really relevant on the listening axis BTW.

Furthermore why critisise something for not being perfect in a specific discipline whereas all other principles are even worse !

BTW I don't use a coaxial primarily because of time-accuracy but because of the VERY important parameter of symmetrical and even directivity pattern - I can make almost any principle transient-"perfect". The advantage of the coax is of course that the tweeter is delayed against the woofer. It is easier to further delay the woofer electronically than delaying a tweeter.

Regards

Charles
 
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Soundminded

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Joined 2008
To produce a phase coherent audio wave, a coaxial driver will need to have a delay of several milliseconds applied to the signal fed to the tweeter. The precise time delay for a particular pair or trio can only be determined with careful measurement. Non coaxial or triaxial driven multi-way systems can never be phase coherent. This is a consequence of standard wave mechanics analysis.
 
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talaerts

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Joined 2005
Soundminded said:
To produce a phase coherent audio wave, a coaxial driver will need to have a delay of several milliseconds applied to the signal fed to the tweeter. The precise time delay for a particular pair or trio can only be determined with careful measurement. Non coaxial or triaxial driven multi-way systems can never be phase coherent. This is a consequence of standard wave mechanics analysis.
Click to expand...

I thought that placement of the tweeter in a coaxial speaker would be chosen to be phase coherent when used with the recommended filter slopes.
Does anyone have better insights?
 
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phase_accurate

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Joined 2002
I would definitley NOT bet on that.

Keep in mind that there are coaxials with the tweeter in front (like the typical car coaxials), with the tweeter on practically the same plane as the woofer voice-coil (many Hifi coaxials) and with the tweeter at the back , using the pole-piece as waveguide (many P.A. drivers and some Hifi drivers). You cannot easily time-align all of these principles with passive crossover for instance - the easiest is the P.A. style driver type.

Regards

Charles
 
Adam Bernau

Adam Bernau

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Joined 2010
Well, i think that this is impossible within a coaxial driver. Theoretically the tweeter should be recessed so the woofer is a bit closer to the listener. But when we recess the tweeter IN the woofer, the woofer membrane is creating some sort of a horn that becomes a "mouth" of the tweeter. Then it is not anymore the tweeter only, but the air mass in the "horn". Also the ideal shape of the horn mouth is unfortunatelly not the same as ideal shape of a woofer membrane..
 
Adam Bernau

Adam Bernau

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Joined 2010
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