Cheap PA speakers distorting - advice?

[Doc Rock]

Got a pair of cheap PA monitors with a 10" speaker and a piezo horn. There is kind of a buzzy distortion that sounds like something loose in the cab, but nothings loose. This happens at fairly low volume. I think it might be the piezos distorting. I've read several discussions online about this problem, and some seem to think the problem is related to one of several issues - 1. piezos are mostly cheap junk, 2. if the piezo is not in a separate area from the woofer, rattling can be induced by sound pressure from the woofer, 3. piezos are by nature "distortion detectors", and will accentuate any distortion coming from the amp. I'd ideally like to keep the piezos in there but make them sound good.

Any advice?

 

[Naptown Rob]

A good sounding piezo is an extremely rare animal. I think Motorola made one.

You say they're cheap PA monitors ? I wouldn't expect much from them new, & they've probably been beat pretty good....

 

[markshan]

First, since with piezos there is no crossover, I would pull the leads from the woofer and see if the piezo distorts by itself. Try to narrow it down.

 

[Dan ʕ•ᴥ•ʔ]

Piezos don't "have" to have a crossover, but are buzzy/tizzy without them. You can add a non-inductive 8 ohm resistor across the piezo's leads and add a 8-ohm crossover at the right crossing frequency. A bit of money and hassle, but well worth the end result.
And yes, if cheap piezo drivers were used, you may want to consider upgrading them.

 

[Gang-Twanger]

A good sounding piezo is an extremely rare animal. I think Motorola made one.

You say they're cheap PA monitors ? I wouldn't expect much from them new, & they've probably been beat pretty good....

What he said.

What brand/model are they? That way we have an idea what kind of piezo horn you're talking about and maybe what you can put in there.

 

[fpitas]

Piezos don't "have" to have a crossover, but are buzzy/tizzy without them. You can add a non-inductive 8 ohm resistor across the piezo's leads and add a 8-ohm crossover at the right crossing frequency. A bit of money and hassle, but well worth the end result.
And yes, if cheap piezo drivers were used, you may want to consider upgrading them.

Yes, I agree. Martin Sound has the decent piezos:

http://www.martinsoundpro.com/product-category/speaker-parts/piezos/

Piezo tweeters also have a response peak about 4 - 5kHz that needs to be nulled down for hi-fi.

 

[Doc Rock]

Its a Kustom KPC10M. They're really pretty decent for the very low price. I had decided to try to upgrade them some, so I took one apart (easier said than done) and replaced the speaker with a better Celestion T1020. It does have some sort of crossover in there, but its hard to get to, so I don't know exactly what it is. It does have a couple of caps/resistors on a small board. I also added some Acoustistuff and put thick foam in the ports, as I planned to convert it to more of a sealed cab to improve accuracy. I modded one, then hooked them up to compare the modded to unmodded. The improvement, at least at low levels, was a little disappointing considering the effort, but the modded one does sound better. Unfortunately, they both have some distortion on the high end. I'll try another amp soon first, as getting them apart is not an easy task.

 

[Doc Rock]

I checked on the Martin Sound site - they "don't sell to the end user". How do the copies Parts Express sells compare?

 

[cablephil212]

I checked on the Martin Sound site - they "don't sell to the end user". How do the copies Parts Express sells compare?

If you're going to replace them, stick with the "GRS" brand. A very close copy of the CTS/Motorola design. After using others, the GRS sound the best.