• The move to the new server is done. There are some software and database maintenance updates in process. This has us passing the hat around to help out. We appreciate any donations. Seriously, even a dollar helps. The payment page may be found here - https://www.audiokarma.org/support.html

Why don't more designers use a coaxial tweeter arrangement?

89grand

89grand

Addicted Member
Banned
I guess I never thought much about it, except in car speakers, until I got the DCM TW3's, but there seems to be something to the point source type arrangement over having the tweeters in a different location than the woofers. I find the TW3 to sound noticeably better than my TW1's, although there are other contributing factors, the speakers sound better with a single source location for the whole frequency spectrum. Even in a 3 way, if one used a small neo tweeter, they could coaxial mount it over a midrange, or do like some Kef's and mount it in the dust cap area.

It appears to be a good design, yet it's hardly ever used. Maybe someone can shed some light on the pro's and con's of coaxial/point source setups that I'm not aware of.
 
Register to hide this ad
It causes no end of problems. The extremely complicated engineering of the current generation of KEF drivers are good evidence of that.

If you mount it out flush with the baffle, it works pretty well, but you get quirks from the woofer firing into it, and the time alignment is way off so the whole point source idea doesn't work out anyway.

If you mount it around the top of the woofer VC where a dust cap would be, the woofer starts acting a bit like a poor waveguide/horn (and a moving one), and that causes some issues.

So, you can put a waveguide/horn on it to deal with that a bit (and also move it back into the pole piece if you like), but now you're got that in the way of the woofer.

Anyway, maybe the strongest point against doing it is that a well designed small 2-way arrangement can actually act more like a point source than any coax I'm aware of. You'll still want more bass, but coax speakers already have that problem to the same extent.
 
I've enjoyed the TF 400 speakers that I have with that arrangement. I lucked into a pair of Altec 604E duplex drivers this spring and can't wait to find the time to build an iteration of Billforts cabs this summer. They oughta be the shizzle from all accounts that I've read.:yes:
 
Maybe DCM dealt with reflection issues of a coaxial arrangement and what not with this felt stuff. The design seems to work pretty well, but I don't understand exactly what they were doing, and why they did what they did.

attachment.php
 
Very interesting arrangement there, 89. From all that I've read about DCM they had some pretty innovative ideas. The transmission line in the LF and the coaxial set up makes my TF 400s sound way better than they have any right to.
 
Heh, I'm not gonna make a fool of myself by trying to guess what the before/after is on that, but that's another clear indication that it's problematic, right? I'm not on any kind of anti-coax campaign here, just trying to answer the question of why it's not more common. I'm actually planning to mess with a couple pretty soon.
 
Pandovski said:
One word:
Tannoy
Click to expand...
That's really more like restating the original question - why not 30 words? Because I said already ;). Tannoy uses sort of compromised but time aligned (guessing on that but they should be and look like it) little horn things in their home stuff (yes I know they sound pretty good), a weird partial waveguide in their live sound stuff, and normal 2-ways for their studio monitors.
 
Wait... I just noticed Tannoy calls their dual concentric lineup 90° constant directivity now? Are there measurements available confirming that they are anywhere close to that? That would be news to me, and pretty cool.
 
Time delay and phase distortion exist in coaxial designs.
The listener is hearing the tweeter first.
 
sm19422 said:
Time delay and phase distortion exist in coaxial designs.
Click to expand...
Yes, and worse things. Like I said, a really good tiny 2-way is a more effective path to a psuedo point source, at least short of really complicated stuff like synergy horns.
sm19422 said:
The listener is hearing the tweeter first.
Click to expand...
Not necessarily, and in any competent design where that's true, they are hearing the higher frequencies sooner than the lower ones, but they hear the woofer and the tweeter at the same time at the crossover point where they are making the same (part of the) sound. Well, okay if it's the kind where the tweeter is way out in front of the woofer, it's probably gonna be an aligned phase rotation of some sort at crossover point, 0.25-0.5ms or so, much like the average 2-way.
 
Last edited:
I wonder if there is anything in the owners manual that may shed some light on what they were doing. They do claim the crossover was time aligned.

I have the owners manual in pdf, but I don't know how to attach it, it says it's too big.

I'll figure it out and post it once I do.
 
Few basics. http://www.tnt-audio.com/casse/tannoy-concentric_e.html


There are several inherent virtues of the dual concentric design. The most obvious being the true point source emanation of sound waves which ensures a phase coherency not attainable by other means.
In conventional multi driver systems, the sound is emanating from different physical planes and positions, making off axis response rather variable. This is complicated by the cossover distributing different parts of the same sound to different physical drivers, which cannot help but to destroy the cohesiveness of the wavefront received at the listening position.
Imagine for example the sound of a viola playing a single musical line, reproduced via a typical two driver loudspeaker system. Part of the sound, including many of the fundamental frequencies, will be handled by the bass/mid driver and part of the sound will be handled by the tweeter.
The problem is, even the lower frequency fundamentals will have harmonics way above the range of the bass/mid driver, which are passed to the tweeter. You therefore have spectral elements of the same note being reproduced by two very different drivers and reaching your ears at different points in time due to the different position of the drivers. This destroys absolute phase coherency and produces different effects at different axial positions.

With a true point source design there are little or no time and phase differences between harmonics either side of the crossover region.
Furthermore, there tends to be a more accurate balance between the fundamentals and harmonics, not only on axis, but even off axis, where many do a great deal of their listening. With the Tannoy dual concentric drivers there is a tight physical integration of the high and low frequency drivers, leading to a coherent and linear phase response. This in turn means that a simpler crossover can be used, providing even greater sonic benefits.
It has long been understood that complex crossovers which attempt to provide phase alignment and other elements of control, invariably have negative effects upon sound transparency.
Click to expand...

TannoyCutAway.JPG
 
Are you talking about Tannoy or DCM? That DCM can't possibly be time aligned unless they put allpass delay on the tweeter, but even then it would only be when you were directly in front of it.
 
sm19422 said:
The listener is hearing the tweeter first.
Click to expand...

I'm having some difficulty grasping why the tweeter mounted in front of the woofer would do this, but having it on the same plane (the baffle) but above or below the woofer wouldn't.:scratch2:
 
The biggest strength of dual concentric tannoys is perfect time alignment, zero phase shifts, simple crossovers (first or second order) and unlike other dual concentric there is a perfect physical integration of the HF and LF driver. The LF driver cone compliments the HF compression driver as a horn and is specially shaped (not a straight conical cross section).

They are perfect, expensive to make, patented and historically owned and recognized as Tannoy's work of art. No other manufacturer has even come close to be as good as the Tannoy dual concentric. They have been making them since the 50s.
 
Pandovski said:
The biggest strength of dual concentric tannoys is perfect time alignment, zero phase shifts
Click to expand...
It's a very cool driver, but we know that isn't true. If it were, measurements of Tannoys reproducing stunning square waves would be all over the place. It should be able to get pretty close on one axis if they made it a priority, though. The biggest question with a Tannoy (particularly the modern ones which are apparently claimed to be constant directivity), is what happens as you move off-axis?
 
89grand said:
I'm having some difficulty grasping why the tweeter mounted in front of the woofer would do this, but having it on the same plane (the baffle) but above or below the woofer wouldn't.:scratch2:
Click to expand...
It would. The point would be that you haven't solved the problem (moved any closer to a point source) with that arrangement.
 
You must log in or register to reply here.
Back
Top Bottom