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So the main purpose of a supertweeter (any tweeter working at 7 kHz or above is a supertweeter) is to improve the sensation of spaciousness - to "open up" the soundstage. This works hand-in-hand with the narrowing directivity of the T= 0.707 LeCleac'h horn and the 1.4" throat size of the large-format driver. Unlike a small-format horn which aims at reaching 15 kHz or above, this horn gives up the top octave in return for another octave at the bottom of the range. The diaphragm of a large-format driver is twice as large as a small-format driver, and that's the tradeoff.
You wouldn't expect a 15" bass driver to behave in the same way as a 7" midbass; they cover different frequency ranges, and have different power-handling characteristics. Similarly, the large and small-format drivers do different tasks.
We further concur regarding the narrowing directivity in the top octave, but that would appear to be less a function of whether the driver is large vs. small format than the size of the exit/throat diameter. We've clearly demonstrated that suitably designed large (4" diaphragm) and medium (3" diaphragm) format drivers can play to/through 20 kHz; the 3" JBL 2435HPL is pistonic out to 18 kHz. As with these larger diaphragm drivers, however, the small format (1.75" diaphragm) BMS 4555 cannot hold a wide dispersion pattern in the top octave with this 1.5" throat, either:
I'd suggest R/S measurements in the top octave may not be particularly reliable, but if you perceive them as having too much "sizzle" or "air," then, yes, you can dial down the VHF with an L-pad. That's not going to alter the rising response up there, if it's real, but you may be able to strike a more pleasing balance....
Footnote: If you review my research on JBL Screen Array, I believe you'll see that a similar on-axis peak in the top octave is a response characteristic of speakers designed for deployment behind a perforated screen. Again, if "real," that would not be a mistake on QSC's part:
OK I read this thread and as much of the AK thread as I could without meltdown and I am goign to build a set of SR's but I have some questions.
Do the SR or SP Compacts sound much different?
Are these ported? I did not see anything about that?
Should the baffle be moved forward or cut back with a router? more for looks for me, will it hurt? Which way is better?
Should the woofer hole be rounded over since the woofer is back mounted?
Zilch, do you sell a circuit board for the crossover? seeems like the least we can do for all the work you have done. Thanks!!
I am going to use these with a subwoofer, one of the BMF horns.
Mike
Are these ported? I did not see anything about that?
They are ported. I'm running at ~32 Hz tuning, but consensus among others running the numbers here seems to indicate somewhat higher would be better when used with sub(s). Finalize your cabinet volume, and we can nail that down.
Should the woofer hole be rounded over since the woofer is back mounted?
The improvement in performance is measurably minor, but I believe it confers a major aesthetic benefit. Though I haven't tried it yet, it appears that with the QSC waveguide recessed flush with the baffle face, the woofer roundover (3/4") might incorporate the waveguide flange at the center, as well. All of this is using the stock baffle and woofer location that comes with the cab kit. If you make your own baffle, there are other options, but I would not increase the center distance between woofer and waveguide by much, as that will degrade the vertical polar performance.
Zilch, do you sell a circuit board for the crossover? seeems like the least we can do for all the work you have done. Thanks!!
Yes, I stock a PC board for the original generic EconoWave crossover design, which may be suitably adapted for use with most of the more refined custom crossovers in this thread. SR adds an external notch filter, R4/C4/L3, and SR Compact, two external notch filters. They are $10 apiece postpaid in the USA; PM me for the PayPal address....
More proof diffraction off of the baffle edge affects both woofers and tweeters. In this case, the woofer especially. (Move those KDT baffles forward guys.) The directivity is getting so progressive and smooth throughout the frequency range... what remains to be done?
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