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hi alli'm building a pair (for stereo amplification)of musical instrument speakers for my keyboards for gigging out. i'm looking at the coaxial eminence beta12cx - one in each box. my question is, eminence recommends their psd2002 compression driver, however would the cts ksn1142 piezo driver work in its place? it would save cost on drivers and crossovers. do you guys think that this is an acceptable woofer for a keyboard speaker or should i consider the delta 12A woofers instead. i'm mostly playing parties and clubs with a rock band but not exceedingly loud. my ears are not ringing at the end of the night so i guess that's a good sign. since i'm building two boxes i'm trying to keep the cost down. thanks in advance for any advice. i was also looking at the selenium 12pw5 woofers as an alternative to the eminence woofers - any opinions on these drivers?
bob
Follow Ups:
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.
"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.
If you can locate a CTS/Motorola KSN 1188, think about using that. You really should cross-over under 2,000 Hz, and you can do so with this driver (as low as 800 Hz, but a bit higher is probably better, perhaps 1500 hz). If you use it, be sure to use an 8 Ohm power resistor across the terminals of the driver, and calculate your crossover component(s) based on 8 Ohms. You may not have to pad this driver, but if you do, that's pretty easy. This driver has a 1.5 mfd capacitance (the others are much lower). If you use a 1.5 mfd cap AFTER the crossover network (probably a simple capacitor before the driver and resistor across the terminals) this will pad the driver by 6 dB, for example. Use quality high voltage film caps and audio grade power resistors for the best result. BTW, other CTS/Motorola drivers should use a 22 Ohm resistor across the input terminals of the driver.Mike Klasco, who helped design this driver, had an article in Speaker Builder some years ago about this very application with the same speaker and horn driver.
DMW- By any chance, do you recall which issue/year of Speaker Builder Magazine contained the Mike Klasco article involving the KSN 1188? I inherited an old pair of Motorola KSN 1188 Powerline drivers and I would like to see some good design ideas for them. Thanks!
If you'll send me your e-mail address, I'll send you the pages via e-mail.I don't know if you know who John Risch is, but I take anything he tells me to the bank, so to speak. The Speaker Builder article tells about the capacitance value of this driver - 1.5 mfd. Most piezos have much smaller values of capacitance. John Risch told me to use an 8 Ohm power resistor across the terminals of that driver, due to the capacitance of this driver. Others piezos should use values of about 16 to 22 mfd, depending on the drivers. Calculate your crossover accordingly. Wayne Parham, another guy whose advice I take, says to not design multi-pole crossovers for piezos that include inductors, unless you are trying to attract birds (ha!). I can also send you a file, in a Word format, with his suggestions for designs. Just remember, this 1188 is a bit different animal than the others.
DMW- Thanks for responding! Unfortunately, I didn't get to see the X-over for this old driver in the original cabinet. I'm guessing that the 8-Ohm parallel resistor is intended to create an impedance? Apart from that, I'm thinking about a cap in series for an 800Hz roloff? I did find a CTS download concerning piezos in general, but it didn't include any specifics for the KSN1188A. Here's my e-mail address: CuppaJoeF8@aol.com
DMW- OK, upon review of the CTS piezo download, it does say something about using a 1.2mF cap in series with 800Hz drivers (no specific model given), but says nothing about an 8-Ohm value parallel resistor in conjunction with that particular cap. More info, but no closer to an answer!
I just sent you six e-mails with crossover design information for piezo horns and drivers.
DMW- Your thoughtfulness is VERY much appreciated, and if I can ever dig up any info for you, let me know! Your straight jacket must truly have the most...um...shiny things on it! Thanks again. -MB
Save money and hassle as well by ditching the stereo set up. Just go with a single cabinet. I would also switch to a 15" coaxial for better low end response. Makes playing that left hand stuff a lot more gratifiying. Eminence discontinued their 15" but I've seen folks on ebay selling off the last of the stock. B&C makes some very nice coaxial drivers, and Assitance Audio out in the Salt Lake City area carries some made by BMS, also very nice.Best regards,
John Halliburton
Stick with the 2002. The off-axis response of the 12cx demands a crossover no higher than 2 kHz, and piezos don't sound good below 3.5 kHz or so. There's also the matter of sensitivity, and the piezo runs a good 10dB less than the 2002. Piezos work fine above 3.5 kHz, and have adequate sensitivity if you use enough of them, but this is one application where a piezo is the wrong choice.
The Delta 12a is a guitar driver, and shouldn't be used in a full range application.
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