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Old 22nd August 2012, 02:23 AM   #7811
Pano is offline Pano  United States
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I understand the search for the super tweeter as I'm going thru the same thing with my Altec 288 drivers on the 1005 horns. Also coming in at about 7 KHz.

Been meaning to pull the trigger on a pair of Faital Pro HF-100 drivers with matching horns. Not too pricey at $50 each for horns and drivers - or $200 a pair all told. Funny that the horn costs as much as the driver. I've held one of the drivers in my hand (cute) and it seems well made, but not yet heard it.
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Old 22nd August 2012, 02:55 AM   #7812
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Default 10db of efficiency and headroom...

Quote:
Originally Posted by Lynn Olson View Post
The super-high-efficiency ribbons like the top-of-the-line RAAL Lazy Ribbon are an excellent match
And there we were worring about saving $100 on the GPA bass driver....

But when you're looking at almost 10db of sensitivity over the Ariel and 10db or more in headroom while maintaining the quality of sound one might expect that the parts cost would grow similarly.
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Old 22nd August 2012, 05:12 AM   #7813
DeonC is offline DeonC  South Africa
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Hi Lynn

Have you tried the Fostex alnico supertweeters? Seeing as the rest of the speaker is alnico, this could be a good match sonically. I have heard a lot of good things about the alnico Fostexes, so your input would be greatly appreciated.

Thanks,
Deon
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Old 22nd August 2012, 07:10 AM   #7814
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Quote:
Originally Posted by Pano View Post
I understand the search for the super tweeter as I'm going thru the same thing with my Altec 288 drivers on the 1005 horns. Also coming in at about 7 KHz.

Been meaning to pull the trigger on a pair of Faital Pro HF-100 drivers with matching horns. Not too pricey at $50 each for horns and drivers - or $200 a pair all told. Funny that the horn costs as much as the driver. I've held one of the drivers in my hand (cute) and it seems well made, but not yet heard it.
If you go with either of Lynn's recommended compression drivers, and listen to them I am very confident you will be impressed with how good tney are
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Old 22nd August 2012, 08:03 AM   #7815
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One of the primary goals for the large-format horn was the lowest possible diffraction, along with respecting the maximum-length limitations mentioned in the Newell and Holland book. As the project developed and Bjorn Kolbrek developed custom simulations of diaphragm loading vs frequency, another goal became constant (resistive) diaphragm loading over the working frequency range, without the severe peaks and dips of more traditional horns. This is when a T ratio of 0.707 emerged as one of the flattest diaphragm-loading profiles, with other profiles (including Tractrix) having somewhat rougher diaphragm-loading characteristics.

Following the Newell and Holland guidelines, uniform diaphragm loading, and the lowest possible diffraction, became the primary design goals, with other parameters falling by the wayside. That's the same set of priorities as N&H; they explicitly state that if other parameters are sought, such as constant directivity, then time response and acoustic flatness will suffer. The conventional techniques for creating constant directivity involve the intentional use of diffraction in the throat, which degrades time response and flatness.

Flatness (due to changes in diaphragm loading vs frequency) can be restored in the crossover, but once diffraction has happened (anywhere in the horn), the reflections cannot be cancelled by electrical means. There are FIR digital techniques for reflection cancellation, but the reflections unfortunately vary with emission angle, making the on-axis correction wrong for off-axis emissions.

My feeling is that diffraction is undesirable in any loudspeaker, since the resulting time errors are not correctable, even in principle. (What is right at one point in space is wrong everywhere else. The only exception would be a truly omnidirectional radiator with identical time response in all directions. Let me know when you find one.)

Following the N&H guidelines, directivity is allowed to simply be what it is. A side effect of time optimization is lack of sharp sidelobes (in the spatial domain), so the polar pattern has soft edges, like a direct radiator. In spatial terms, it sounds like a direct radiator, not like a horn, but in terms of dynamics, it sounds like a horn - a very powerful horn, since the large-format diaphragm has twice the area of a small-format driver, and the horn has 90~100% horn loading over the working bandwidth.

The debate over directivity is where I part company with my contemporaries. I put about 70~80% weighting of the direct sound, and look at the rest in terms of total power into a sphere, instead of what happens 30 degrees off-axis. That's because the first three reflections are off the floor, the back wall, and the side wall. Only the floor reflection is anywhere close to 30 degrees off-axis, while the rear and side-wall reflections are much further off-axis. The next ten to twenty reflections are also mostly very far off-axis.

When you consider the spectral response of the first three to twenty reflections, what matters is total power into a sphere, not the frontal radiation pattern. As for the first-arrival direct response, you can't be in several places at once. You only have two ears, a few inches apart. What matters is the direct sound arriving at each ear and the summation of the total power into the room, with a heavy weighting towards the first-arrival sound.

This is why I consider the absence of unwanted sidelobes important. This isn't a PA speaker, where audience coverage is the primary consideration. This is a speaker intended for high-quality listening in a domestic living room with domestic furnishing (no floor absorbers, no walls covered in damping or quadratic residue diffusors). If there are narrow sidelobes (characteristic of high-Q controlled-directivity designs), there's a good chance one of these might reflect from a sidewall, degrading stereo image quality. Better to have a soft-rolloff polar pattern, which is exactly what these horns do. The "edges" of the polar pattern are much softer than any other horn I've heard to date.

The caution with horn supertweeters is that using a conventional horn, particularly a constant-directivity type, results in a very different presentation than the AH425. That's what I heard when I auditioned commercial supertweeters with integral horn assemblies; the supertweeter said "look at me, I'm a horn!" while the AH425 said, "well, I'm a big electrostat, and I don't sound anything like you!"

I'd guess that a horn supertweeter is OK provided the horn is a small LeCleac'h with the same T ratio of 0.707, possibly as high as 0.8. Otherwise, it won't match spatially or tonally.

At this point you might think "How on Earth does a ribbon integrate with the AH425 and the large-format compression driver?" Very well, really, despite the huge difference in polar pattern. What's similar, though, is the time response. The AH425 has near-electrostat time response, with very fast decay characteristics, and the supertweeter needs to be as good or better - preferably much better.

If the time response is worse, I can say from experience it really draws attention to itself, and not in a good way. The ear is very sensitive to the time response imprint that a given driver imparts to the sound, and drivers with chaotic decay characteristics draw attention to themselves.

All three drivers (LF, HF, SHF) have very good decay characteristics (compared to the other drivers with similar efficiencies). They were selected for these characteristics, and share them with the drivers selected for the Ariel. Which is why the new system sounds like a (very) big Ariel.

So if you want to roll-your-own supertweeter, be my guest. Measure the decay of the time response and see how it compares to the competitors. The ones with the quickest, cleanest decay will probably be the best match for the AH425 and the Altec/GPA 416B in a resistive-vent cabinet.

Last edited by Lynn Olson; 22nd August 2012 at 08:26 AM.
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Old 22nd August 2012, 03:08 PM   #7816
soongsc is offline soongsc  Taiwan
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Lynn,
What set of parameters do you think make the compression driver driven horns more dynamic than direct radiating drivers?
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Old 22nd August 2012, 04:08 PM   #7817
Pano is offline Pano  United States
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Quote:
Originally Posted by Melon Head View Post
If you go with either of Lynn's recommended compression drivers...
Can you help me out? I can't find the reference. Thanks!
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Old 22nd August 2012, 07:34 PM   #7818
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Quote:
Originally Posted by Pano View Post
Can you help me out? I can't find the reference. Thanks!
Pano

I'm keeping track of this in case I decide to build. Here's the info:

The large-format compression driver is either a
  • Radian 745Neo (Neodymium magnet, 16 ohms) or
  • Altec/GPA 288 (Alnico magnet, 16 ohms)
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Old 22nd August 2012, 07:38 PM   #7819
Pano is offline Pano  United States
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Thanks Charlie. I thought Melon meant compression drivers for super tweeters, that's what I've had a hard time finding.

FWIW, I run a pair of Altec 288 (16 ohm) and also have a pair of older Radian large format drivers. Love 'em! Altec 416A are my woofers.
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Old 22nd August 2012, 09:57 PM   #7820
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You will be very impresed with the Radian 745Neo in the horn from Azura horns or even if you want to start with a cheap constant directivity wave guide first before upgrading to the more expensive wave guide.
I think once you have heard it you will be very satisfied
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