For the 1188, you could put a 20 ohm 10 wt resistor in series with the 1188 driver. So, no matter how high the freq, there has to be at least 20 ohms present, right? The, in parallel with the 1188 and resistor, an 8 ohm non inductive resistor. So, now the whole thing looks like 8 ohms. So, come from the hot lead of the spkr's input terminal with a 25 uf cap (10 uf + 15 uf cap paralleled).

Thanks for the Boxplots! I'll check my home e-mail for them. Given the efficiency, it looks like I could go the cheap rout and use the PMY1555 and still get good result (assuming that Pyle's specs are correct). I don't need the high power handling capacity and I could use the money I saved on air-core inductors, polypropylene caps and good non-inductive resistors. There are not that many parts; I might as well use good stuff. I have used expensive wire in the past (when I got it free because I worked in a high-end stereo store) but good quality twisted pair 18 gauge solid core copper wire seems to work fine (as well or better) for me as long as I don't make it too long.

With regard to speakers, it amazes me what a better value pro gear seems to be. Its more rugged, presents easier loads, has lower distortion, is more linear, handles more power, is more efficient, has a wider bandwidth and is cheaper. When you spend more money for JBL, the specs are incredible (so is the sound). Actually, it was hearing some JBL speakers that first made me realize that I should be looking at pro speakers. I couldn't get over the clean dynamics.

Thanks,

Dave

Add a resistor in parallel, and the driver can be made to look like a current driven device to any outside components, such as a crossover cap. However, to keep costs and power dissipation down, 8 ohms is way too small of a value. The impedance of most piezo's is still quite high at 20KHz, so use a 22 ohm resistor, this makes any series crossover cap smaller and less expensive, and the resistor dissipates less energy. Use of an 8 ohm parallel resistor will also tend to lose you a little bit of output level.

For most piezos, use of a 22 ohm resistor, and a 4-4.7 uF cap will allow the response to be identical to what it was in stock form, but rolls off the lows at 6 dB/oct below 1 kHz or so. This actually increases the power handling of the piezo, as it is voltage limited. Exceed the voltage used to pole (polarize the piezo element during manufacture) the unit, and it will loose sensitivity, and eventually burn out. Most pro grade piezos will handle 35 volt transients, and 28 volts continuous, which are 150 watts and 100 watts into 8 ohms respectively.

Add in the cap and 22 ohm resistor, and the power handling could effectively be quadrupled, as the LF voltages are not imposed upon the unit, just the HF voltages.

Piezo's crossed over in this manner don't sound as harsh and spitty, and tend to be quite a bit more reliable. Many of the piezo units have a mild peak just before they roll off in the LF, so making the series cap a little smaller can actualy flatten response, and provide even more protection and smoother sound. For the smaller piezo units that cut off at 4-5 kHz, a series cap of 1.5 uF will do the trick, larger units that go down to 3 kHz can use a 2.2 uF, and the large compression driver units meant to be mounted on a horn need about 5 uF, as they do not peak, and any higher would lose the sloping LF output even more.

Attenuation, HF roll-off AND the crossing over can all be done at the same time. To attenuate, place a cap in between the piezo and the 22 ohm resistor that is shunting across the unit, then if HF roll-off is desired, use a series resistor in this location too. Then the series crossover cap should be in front of the 22 ohm shunt.

Looking from the amp, first the series crossover cap, say 4 uF, then the 22 ohm shunt from hot to ground, then a series cap of about 0.15 uF for 6 dB attenuation, and then a series resistor of about 30-50 ohms to tame the very top end, then the piezo itself.

I hope this will help shed some light on how to put a piezo to best use, and make them sound quite decent.

Jon Risch