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Old 13th October 2010, 01:32 AM   #11
CLS is offline CLS  Taiwan
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Quote:
Originally Posted by serenechaos View Post
I'm listening to a coaxial in a 160Hz Azura.
....
Hi,

Would you please share more?

I've been thinking of horn loaded coaxial (maybe 8~12" with 1" compression driver), but it seems there'd be directivity problems which are hard to resolved.

At the typical xover point of such assembly - around 1kHz, the sound from the treble unit is largely guided by the cone of mid-bass unit, which is mostly very wide conical. So I'd imagine the waveform of the outer edge would hit the horn wall (near the throat). The treble sound leaves the smaller horn and then meet another bigger one. The transition between the 2 are not smooth So I think a horn or WG for such driver should be very wide and shallow, thus it can minimize or eliminate this issue. (while the loading and directivity control of the midbass unit are another 2 stories.... )

That is in my thinking, though. I don't know how it behaves in reality, and whether it's a real problem or something very small which can be ignored.

Hmmm......
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Old 13th October 2010, 04:01 AM   #12
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hmm, where to start...
this was just thrown together days ago, just as a general check to see what it would sound like, and if it would be worth the work to do right.
also, it's just meant to be an "interm," then second system, until i get wooden Eleven Horns - lower midrange horn.... 140 Hertz Le Cleac'h... and
Eleven Horns - upper midrange horn.... 600 Hertz Le Cleac'h... ,
(hopefully will be in this weekend),
to use with compression drivers.

the azura has a more rapid expansion ( 0.8 T factor), so is shorter than an oris (~38" x 17" / 950mm x 450mm); doesn't sound as "dark."
however, the azura throat is for a 8" Lowther, i just made an adaptor and bolted the 10" Tannoys on...
i've made a fiberglass mold though, and intend to experiment w/ different materials (glass, carbon fiber, kevlar), make some for Phil's field coil Lowthers, and another pair cut back shorter, so the throat will be larger, and match up properly to the Tannoys.

actual directivity-- easy enough to ck/match in hornresp, but i haven't even simmed anything for these yet (just the compression driver system).
mid-treble x-over is ~1800 on the Tannoys;
one of the cool features is the shape of the compression driver to cone interface, and that the shape of the cone curves/flares, (isn't just conical).

the mid-bass horn sims +/- 1 dB from 70 - 350Hz, -3 is ~60 & 500Hz (a little to high, i just adjusted the angle for now, will try a choke to roll it off a little sooner).
that was the only thing that has appeared as a problem (by ear, not worth running measurements yet, i'm tearing it down tomorrow).
actually, i would say the mid-bass is the best part of this system, (actually, IMHO it's probably the second best mid-bass i've ever heard).

i really was suprised how well this sounds, with so little work, (just adjusting angles).
don't know if that helps, pm me if you want more details--
again, this doesn't even belong on this forum...
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Old 13th October 2010, 11:00 PM   #13
Ivo is offline Ivo  Netherlands
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Quote:
Originally Posted by CLS View Post
Hi,

Would you please share more?

I've been thinking of horn loaded coaxial (maybe 8~12" with 1" compression driver), but it seems there'd be directivity problems which are hard to resolved.

At the typical xover point of such assembly - around 1kHz, the sound from the treble unit is largely guided by the cone of mid-bass unit, which is mostly very wide conical. So I'd imagine the waveform of the outer edge would hit the horn wall (near the throat). The treble sound leaves the smaller horn and then meet another bigger one. The transition between the 2 are not smooth So I think a horn or WG for such driver should be very wide and shallow, thus it can minimize or eliminate this issue. (while the loading and directivity control of the midbass unit are another 2 stories.... )

That is in my thinking, though. I don't know how it behaves in reality, and whether it's a real problem or something very small which can be ignored.

Hmmm......
You raise interesting questions that I think about as well.

Different units have different directivity, so choosing a unit with a narrower dispersion would be step one.

Secondly, the larger the woofer, the shorter the horn. The effect is that the horn walls are further away from the main "lobe" of the tweeter's response, so less reflections.

Thirdly, the part that I am not certain of. In a simplified assumption, the woofer and tweeter should have the same response at the crossover frequency. In balance, in phase and also dispersion pattern. If that is the case, then the two should act together as a single driver. If the woofer's interaction with the horn at (or just below) the crossover frequency was not a problem, it also won't be for the tweeter at (or just above) the crossover frequency. Directivity will only increase above that frequency. In other words, the problem might not be that big anyway.
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Old 14th October 2010, 01:21 AM   #14
CLS is offline CLS  Taiwan
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Hi,

The 3rd point would be very difficult, I guess. For example, in Oris 150 (or Azura 160 might be similar in this regard), horn loading is effective up to 2kHz or so. If the xover point is set right at here or slightly higher, than the dispersion of the treble unit is mostly much wider than the midbass unit due to the source size.

According to the long Wave Guide thread by Geddes, the design guideline is controlling the directivity of the 1" CD to be exactly the same as the 12~15" midbass unit at and around the xover point which is near 800~900Hz range (that is about 90 degree).

So if the horn load for midbass is to be controlled under such frequency range, and also fulfill other needs (get out of the way of treble, and proper loading, directivity control of itself... ), that would be very difficult to design. Eventually, it might be an extremely wide and shallow one which is just like a slightly recessed baffle

Or, in the end, maybe this idea will inevitably evolve to the Unity horn concept. That'd be a special design coax with its treble unit extending to the entire horn, and the sound of midbass unit coming out through several passages around somewhere near the throat of treble unit.
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Old 16th October 2010, 12:23 PM   #15
Ivo is offline Ivo  Netherlands
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The Unity horn is fascinating and when properly done I bet it's very good. I won't be able to do it properly...

Good points about the mismatch in directivity. An option then would be a smaller woofer, to push the point of beaming higher. Again, there are coaxials with a horn tweeter with a smaller directivity. I haven't looked extensively now, but I saw coaxials with a 70 degree disperion and I know I have seen 60 degrees as well. I don't remember at which frequency dispersion is controlled like that, which may not be as low as the proposed crossover frequency.

I have read accounts of people using Altec coaxials in their VOTT cabinets, which are frontloaded and rear reflexloaded. I did wonder how they were getting away with that and assumed they had narrower dispersion patterns and, possibly, the benefits of a fully hornloaded pointsource outweighed the negative effects of reflections inside the horn.

It is always hard to draw lines of sanity or efficiency in our hypothetical DIY discussions and I think this is where my experience falls short. I would love to hear from someone who tried his Altec coaxial in his VOTT or related horn and tell us what his impressions were.

I hope to try something like this out some day, it would be nice to know at least what gives a better chance of succes, a laaaarge driver or a small driver.
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Old 16th October 2010, 01:33 PM   #16
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Originally Posted by Ivo View Post
...it would be nice to know at least what gives a better chance of succes, a laaaarge driver or a small driver.
I (by far), prefer compression drivers, in a five-way...
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Old 16th October 2010, 02:21 PM   #17
Ivo is offline Ivo  Netherlands
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Fair enough, but my curiosity is how a large Oris-style horn with a coaxial could be made to work. I have heard a number of conventional systems and a a good number of far out designs. When tastefully done, they can all get very close to each other. My personal experience with a multiway compression driver system was very, very positive (probably my favorite so far).
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Old 16th October 2010, 02:33 PM   #18
Sheldon is offline Sheldon  United States
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Quote:
Originally Posted by CLS View Post
Or, in the end, maybe this idea will inevitably evolve to the Unity horn concept. That'd be a special design coax with its treble unit extending to the entire horn, and the sound of midbass unit coming out through several passages around somewhere near the throat of treble unit.
This one has been used that way in Tom Danley's latest:
Overview

Sheldon
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Old 16th October 2010, 03:29 PM   #19
Ivo is offline Ivo  Netherlands
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Nice driver. Had seen the Danley product. I also see the triaxial drivers from BMS. They allow a lower crossover and perhaps that reduces the different dispersion problems enough?
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Old 16th October 2010, 03:29 PM   #20
Ivo is offline Ivo  Netherlands
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The big midrange horn might also get in the way, to be honest...
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