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In Reply to: building keyboard speakers - driver question posted by RBS on June 23, 2005 at 19:26:28:
I found this thread looking for something else via a search... but I have a lot of experience with the CTS/Motorola piezos and PA and MI speakers.The KSN1142a can still be found. This is the 1800 hz driver, and is of the Powerline series, which means it has a protection circuit. Martin Sound has these for about $16 each.
It is best to let a piezo do what is does, and design the rest of the speaker around it. Fit the woofer to the piezo, not the other way around.
You must use a crossover cap if you are going to pad. Place an 8 ohm resistor in parallel (across the terminals). Then treat it like any other 8 ohm driver. Use an L-pad with it, and a cap (6 db/oct) to feed it calculated for 1800 hz or higher.
I would just roll off the woofer at 1600 hz and nothing on the 1142. It will work quite well for you.
KSN-1188a's actually roll in about 650 hz (-3db at 650hz). Roll off your woofer at 650 hz. I am running mine with an active crossover dialed in to 800 hz. Presently I am running 4 1188's with my PA gear. 1188's work well with the 5"x15" plastic horn lens that are quite cheap now.
Though the 1142 is rated 92 db SPL, and the 1188 rated 93 db, they are actually about 4 db higher that this, around 96-97 db. Or at least they sound that way. I use them with woofers in the 96-97 db SPL range and they sound quite natural. Matched with 92 db woofer they do sound "harsh".
While most of my usage of CTS/Motorola piezos is with PA and Musical Inst speakers, they can work well for home stereo. I have a pair of speakers with Speakerlab 1008 woofers and KSN-1165a's that sound great. I have .75 mH inductors and zobels on the woofers, and a 11 uf (10 uf + 1 uf) crossover cap , L-pad, to the 1165's with an 8 ohm resistor across the terminals. I have to dial the L-pad down 4 db to make it match the 1008, which is rated 92 db.
The various no-name clones coming from who knows where do not sound as good as the real CTS/Motorola piezos, and lack the Powerline protection circuits. I just have not been satisfied, and no longer waste time trying to build anything with them.
All but a few sources of 1188's have dried up, they are just not to be found... well, I found a few, but they were priced as high as the Eminence PSD2002.
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Follow Ups
- Re: building keyboard speakers - driver question - Paul C. 01:28:42 12/03/05 (1)
- Re: building keyboard speakers - driver question - Paul C. 13:51:02 12/04/05 (0)
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