Blown tweeters?

[impactwrench]

I picked up an old Kustom 1-15P monitor speaker to use for live shows with the PA. It has an 8 ohm woofer, I believe a Rola (285 code). I think Im reading the date code as 44th week of 76 (speaker). It has 2 tweeters, but no crossover. There is a resistor on the back of the tweeters. I plugged in a bass amp and it sounds pretty good at low volumes. Hopefully our drummer can hear my bass better than through the EV monitors we use now.

How do I check if the tweeters are operating? Can I just put the multimeter across the terminals?

[will33]

No crossover and a resistor says they're piezo tweeters. Your meter would tell you if the resistor's good but not neccesarily the tweeters. Easiest thing is to crank the treble on your amp and put an ear up there, should hear a slight hiss. If still in doubt play something high through them like popping a G string, should hear them working then if they're good. If not, hey they're only a couple bucks and don't need a crossover.

[impactwrench]

I think they are both blown. I turned down all EQ but the treble and still only heard sound out of the woofer. I'll try to post pics later today, but any idea what to get? We are using this for a monitor for the drummer to hear me better. Not sure it needs tweeters for that but for a couple bucks it probably cant hurt.

Just from memory they look very similar to this tweeter
http://www.adelcom.net/MOTOROLA_ksn1005b.htm

I see a knockoff type at Parts Express for $1.80 each, and 20ohm 20watt resistors for $.75 each. Is this what I need?
http://www.parts-express.com/pe/psho...70-011&scqty=2


Should I replace both tweeters or just one? Not sure why it would have 2...

[craig.p]

Unless your usual tone is super-sizzly, I can't see piezos doing anything for a PA monitor doing BG duty besides adding unnecessary parts count and complexity. Your typical BG frequency range runs way below where those little screamers begin to kick in. But if you just feel like fiddling, I don't really see anything wrong with your plans. I might up the resistor wattage by 50%. I also might make the 20 ohms 100, but it depends on how loud you want those things to run. (On the other hand, like I said, there's not much in a typical BG feed to wake them up in the first place, so maybe that resistance value is fine the way it is.)

[impactwrench]

Let me clarify a bit. The monitor will be used as a monitor, with the possibility of guitar and vox going into it also. It will be replacing a 3 way EV with a blown mid speaker, and I hope will provide a little more thump for the drummer to hear me. It's angled 45* instead of standing on end like the EV.

I think I will probably change the tweeters, but dont need a ton of sizzle, since theres no way to attenuate it anyway. Will the higher the resistor I use, the less sizzle? I'm not sure how strong the pa power amp is, and this may be daisy chained off another monitor, but a 30 watt resistor should be fine?

[will33]

A 4ohm, 10 watt resistor is pretty standard for piezo's, it's more to protect the amp than the tweeter. You could also install a DPDT switch on the cab so you could run none/half/or all the tweeters....more tweets running = more sizzle.

[craig.p]

Ok, now I see what you're doing. Yeah, increasing the resistor value will drop the tweeter volume and make them far less piercing. Some people like to run piezos WFO, some people like to resistor-limit them. It's all personal taste. In general I tend to super-size resistor wattages but like Will says there's probably no need here, so I'll withdraw my recommendation for 30-watters. BTW, some of those piezos have resistors already inside them, as I recall, but it's been years since I've used piezos and I don't remember which ones have them and which don't. I recall them being (or appearing to be) way under-rated power-wise, and so I wonder how many piezo tweeters get replaced whose only problem is a burnt out internal resistor.

[impactwrench]

Originally Posted by will33

A 4ohm, 10 watt resistor is pretty standard for piezo's, it's more to protect the amp than the tweeter. You could also install a DPDT switch on the cab so you could run none/half/or all the tweeters....more tweets running = more sizzle.

Im not looking to complicate it too much, just maybe add a little top end.

I wonder if I could reuse the resistors from the current piezos, if they still measure up? I think they say 8 ohms. Ill pull them out before I order anything.

[impactwrench]

OK I think I'm going to go with the Piezos from parts express. What resistor should I get then? It will be run with a crown power amp, not sure of the wattage. I really want to protect the amp since its not mine. So should I look at a higher wattage resistor?

The highest wattage I see is about 20W, and the resistance can be anywhere from 20-100 ohms.

http://www.parts-express.com/wizards...TOKEN=22985527

[impactwrench]

The stock resistors are 50ohm 5 watt. I think Ill go with 20 watt 40 ohm. Do I just solder them across the terminals then?

The stock piezos have 2 sets of terminal with about 8 lugs to solder it looks like.

DANG! The piezos at parts express need a 3 1/16" cutout. Mine are 2 1/2".
The other dimensions seem the same, its 3 5/16" square. I thought these piezos came in a standard size...

[impactwrench]

I ended up ordering those horns anyway, and the new resistors. the new resistors were about 2x as long as the old ones, so I couldnt really use them. I unsoldered the old ones and put them on the new piezos. Since the holes I was installing into were too small , the piezos wouldnt sit flush. It probably would have been fine, but I just took the back part of the piezos off and put it on the old plastic "horn" part and it fit right on. Now both piezos work. All I used out of the new stuff is the back part of the piezos! Oh well, $10 spent and now my cab has all the hiss I can stand