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In Reply to: Re: building keyboard speakers - driver question posted by Paul C. on December 3, 2005 at 01:28:42:
"other CTS/Motorola drivers should use a 22 Ohm resistor across the input terminals of the driver."Not all... the 1.8 khz drivers (1142a, 1165a, the 2x6 horns) all have a built in series 22 ohm resistor. The 3.5 khz piezos don't. A 20 - 22 ohm resistor can be placed in series with the small piezos or the 1188 with no affect on sound. The purpose of this is to provide some amp protection at very high frequencies. Since the piezos look like a small capacitor to the amp, some amps can occilate at high (ultrasonic) frequencies. Usually a 10 ohm resistor and tiny inductor (sometime a few wraps of wire around the resistor and soldered to each resistor lead) is in the output of the amp to do this.
"I'm guessing that the 8-Ohm parallel resistor is intended to create an impedance?"Exactly! Or you could use 16 ohms and treat it as such. I usually use an 8 ohm resistor, and then it can be used in conjunction with an L-Pad. This L-pad and all comes after the simple capacitor crossover.
Again, as far as the 1188, almost impossible to find these days. I found one price of $48, but you can buy the very fine Eminence PSD2002 for about $1 more. So, it just does not make since to build a speaker for which, in a year or so, you will not be able to replace any components.
I am sorry to see the CTS Powerline piezos no longer in production. They really worked well, and held up well. The 1188 was an especially good driver.
But the market is flooded with 75 cent copies. Unfortunately, these cheap copies just don't sound as good.
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- Re: building keyboard speakers - driver question - Paul C. 13:51:02 12/04/05 (0)
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