Experience with CTS Mid/Tweeter Piezoelectric Driver

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Do any of you have experience using the CTS KSN1188A Mid/Tweeter Horn Driver in a PA Cabinet? I'm experiencing failures with this driver and wonder if others have also struggled with this.

I am not using any resistor with this driver, would adding a 20 ohm resistor help improve the life?
diyAudio Moderator Emeritus
Joined 2001
I sent away for a whole slew of papers on piezo speakers from Motorola years ago, but the 1188 was not among them.

CTS is located at the same place as Motorola Piezoelectrics are, a factory in Albuquerque. When I talked to the people there years ago, they said that they were changing to CTS the next week. So CTS is really the Motorola people who poplarized the piezoelectrics, which I think is good.

I do not have the flyer for the 1188, but all the Motorola, (CTS) horns have an impedance curve that dips from 75 ohms at 10K Hz to 40 ohms at 20 K Hz. So a 20 ohm resistor should not hurt it much.

In piezo speakers, a resistor acts the same way a capacitor does in resisitive circuits.

The purpose of the 20 ohm resistor is to prevent oscillation at high frequencies. I do not know the frequency of oscillation, but if it is over 20 K Hz, you will never hear it. So your piezoelectrics could possibly be oscillating themselves into oblivion and you'll never know it.

The fact that Motorola mentions a 20 ohm resistor says something.

One thing-since this is a midrange, not a high range horn, the impedance might be different at 20 K Hz. So if the 20 ohm resistor seems to cut the highs, try a 15 ohm, then a 10. Your impedance might possibly be lower at 20 K Hz with this horn.

You can download a large and informative "application note"-actually a lengthy booklet all about piezoelectric speakers-at this link:
diyAudio Moderator Emeritus
Joined 2001
Here is a thought for a quick and easy test to see if the 20 ohm resistor is the way to go.

Download a free NCH tone generator here:

Make sure you set the generator for sine waves.

Click or write in tones at 16 K Hz or so. Some people cannot hear any higher-or even that high. Make sure whichever tone you choose is audible to you.

Hook your sound card to any amp. Run the tone through the piezo horn with the resistor-and without.

Do this at LOW volume.

If the 20 ohm resistor does not audibly cut your highest highs, use it. If it does, use a slightly lower value resistor-they are certainly cheap.

Good luck.
Andy G

The poor old piezo gets another bad rap !!!

I wish the manufacturers did not say "can be used without a crossover" !!!
This statement has led to nearly all the bad press that piezos get.

The 1188 is actually a VERY good driver, and with a simple x-o can do some very good music, smooth, clean , precise etc etc

If you go to my web site, bottom right of index page is a link showing a simple x-o for use with most piezo drivers.

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