On 2/15/2017 9:13 AM, Scott Dorsey wrote:
In article , Paul wrote:
In contrast, you can listen anywhere in front of the Yammies, and
although they may sound bright, and have tons of "presence", they never
get HARSH like the piezos!
Okay, you saw that 4kc peak on the piezos. Now, assuming you're using a
12dB/octave filter, if you crossed over at 8kc then the peak would only be
12dB down. You'd probably want to cross over at 16kc in order to really
control the problem, or use a sharper filter. Which kind of makes it useless.
You'd think maybe you could use a Zobel network like you would with an
electrodynamic tweeter to control the peak, but really nobody has ever been
able to make that work well. It might not be minimum phase.
http://www.wavecor.com/html/zobel_networks.html
So when the cap becomes low impedance at higher frequencies,
it essentially adds a shunt resistor to a dynamic speaker's voice coil
inductance, attenuating the higher frequencies I assume.
But maybe this wouldn't work on piezos since they look capacitive?
It MIGHT be possible to use an acoustic network in order to deal with the
problem, but it's hard to do that and not screw up the pattern.
In the 1980s some grad student built a PA speaker system using a horizontal
array of piezo tweeters and phase-shift networks, which somehow wound up in
the EE department auditorium at gatech, probably because nobody else wanted
them. They had oversized Motorola drivers with the worst of the ugliness
around 1kc, and they were crossed over around 5kc using a conventional
midrange driver. Even though the plot wasn't so horrible, there was still
severe harshness due to the nonlinearities.
Now... Jon Dhalquist with the DQ-10 actually did use a piezo tweeter and
did actually get some benefit from it. But he was crossing them over at
18 KHz or so and using them only as a supertweeter in order to add a little
more air.
--scott
So it appears piezos are only acceptable in the high fidelity
world from 10kHz and above?
Non-linearities implies clipping and odd order harmonic generation.
What is it about the physics of the piezos that would cause such
distortion below 10kHz?
It appears piezo tweeters are everywhere! Obviously because they
are cheaper to manufacture. MP3s and earbuds are also widely used
by the public at large, but MP3s never made the high end unlistenable!