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Pulsar Developments Ltd - Piezo Tweeter Application Note
Found this site with everything I need to figure out these piezo's. It will take a few reads to comprehend. I just hope these ones I bought from Radio Shack back in the '70's are the real Motorola ones, nothing is labeled on them at all.
A piezo looks like a cap to the amplifier. Using a resistor in parallel is a very good idea for the amp and also for designing your crossover. Just put an 8 ohm resistor across the collective terminals of your bunch of piezos. Then choose a cap to fit. Buy a few values, like 2.2, 1.5, 0.68 and smaller. The Dayton brand are cheap and good. With those values you can tune by ear.
Thinkin 'bout the piezos. If you use 6 or 8 per side (yes?) then you might try to spread them into 2 groups either side of the Altec horn center line. The idea being that the horn will be a narrow beam at at the high frequencies, so you don't need extra there. Spread the highs around a little to the edges of the horn. Might give a more uniform dispersion of the top end.
A hare-brained idea, but it wouldn't be hard to try!
Playing with 8 per side so far.Quote:
Originally Posted by Panomaniac
Maybe increasing to 12 when I get to it.
Hanging (literally) off either side of stacked 828-G cabs, set back to be ~aligned with the 288 MF VC.
Might be a bit better than the pseudo 'coaxial-y' mounted CP-09, which works well enough, but primarily when at a greater distance.
I'd offer commentary on the wiring of the piezo's, but the jury is still out.
My XO is a custom mess.
What I did find, is 2 banks (series) of 4 ea (paralell) in order to knock down the output a bit.
Realistically though, I don't think I am getting any thing above 17k, but that may be happening ahead of the Altecs in the signal chain, or just my hearing.
To boot, I don't think the piezo cap is limiting fc as much as desired, or as shown in the motorolla pizeo sheet I have somewhere.
Thanks for the update.
Let's see if I have this figured out right. If these tweeters are 94 dB SPL (Sound Pressure Level) 2.83V Input @ 1Meter sensitive, and doubling speakers in parallel raises sensitivity 3 db, and in series doubles power capacity (100wrms), those 8 Piezos should be 100 db with 200 watt power handling? How does that relate to altec’s rating of 1 watt at 4 feet? Would just four in parallel be ok?
At $22 each, those Motorola/CTS are kind of expensive to buy 16 of them.
CTS / Motorola KSN-1001 Recessed Mount Piezo Electric Super Horn Tweeter</font>
I’m not too clear on the resister for each Piezo and how they all would wire up with an L-pad.
$22 for a piezo? Ouch! Even if they are (maybe) the real Motorola version.