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RE: Apogees and ethics - comments

Posted by josh358 on February 12, 2012 at 16:19:36:
Good about the Neo's, since the chance I'll have time to build a midrange ribbon is somewhere between nil and zip. :-)

I'd think that 250 Hz is a pretty ideal crossover point for the Tympanis. AFAIK, there still isn't anything that can beat Tympani midbass. Sure, you're going to get a bit of lateral smearing from the offset, but to my ears smearing is pretty minor at those frequencies. Of course, I haven't heard the Neo 10, but (besides their cost) I remain a bit suspicious of their beaming above 2 kHz. I think I'd rather compromise at 250 Hz than in the midrange.

(BTW, did you know that the Neo 10's use the force of the magnets to bow the perforated metal to accomodate the diaphragm? Just read the patent. They also have pleats on either side of the diaphragm to reduce stresses and improve damping. Also learned something about the failure mechanism of overdriven planars -- apparently, heat leads to differential expansion between the film and the foil, and when combined with large mechanical stresses, the diaphragm can wrinkle, delamination can occur, and conductors can break.)

One of the changes they made in the Tympani IVa was to give it a down-tilted response. I don't think there's a right or wrong here -- it seems that works recorded in a large hall need the downtilt, works recorded in a smaller space don't. But with so many recordings hyped in the highs, a downtilt can't hurt. I didn't know that Billie Holliday made any stereo recordings.

I have the same problem you do with my memories of speakers, though these days, it's more likely to be that amps back then were underpowered and colored. Forex, how much of the magical imagining I remember from the IRS V had to do with the speakers themselves, and how much to do with the big Conrad-Johnsons? And how much with the acoustics? I'll never know.

Not sure about how much of a gap you'd need. I looked up the formula for acoustic impedance of a slit, but realized I didn't know what SPL the ribbon could tolerate so didn't bother running the numbers. It depends not just on the width of the slit, but on the depth of the baffle, and by the time you'd plugged in all the numbers and figured out ribbon resonances and coupling you could have just tried it 20 times over.

BTW, I found a guy (Valvetude) who's running his homebrew 0.75" neo ribbons down to 200 Hz. He gets +/-0.125" excursion from them and says he can play them at deafening levels without distortion. Assuming you can get a sufficiently uniform field, I wonder what the practical limit on this is -- ribbon fatigue? The reason I wonder is that I assume narrower ribbons are less susceptible to torsion, and of course they also have lower mass, better dispersion, and more uniform field strength.