Quick piezo tweeter question

[Bikeman]

Hi everyone.

I'm nearing completion of a project using peizo tweeters. The manufacturer recommends a series resistor to help protect the amp.

And yes, I know they should really have a proper crossover, but the project doesn't need to sound nice, the name of the game is cheap.

The question I have is: does in matter what side of the tweeter the series resistor is? I mean do I have to have it between the amp + and the tweeter +, or can I put it on the - side.
From what I can remember of AC, shouldn't really matter. But something tells me it just might.

Any ideas?

Mark

[sreten]

http://www.diyaudio.com/wiki/index.php?page=piezoXO

/sreten.

[Bikeman]

Thanks for the quick reply, Sreten

I'd actually read all that. I actually USED the search function.

This is just a piezo chucked in a bass guitar cab, I can't be bothered doing a proper crossover, as long as it doesn't blow the amp. I don't really care as it's a bit of an experiment.

But the info in the wiki doesn't seem to address the specific question of whether an inline resistor needs to be on the positive side, or if the negative side is ok.

I'd appreciate any help, I know it might seem like a strange question. It's just to do with the wiring layout, It'd be more convenient to put it on the negative side if it won't make any difference.

Thanks,
Mark

[geminni]

I believe that it is same, resistor on + or -. Looking from amps view it is series connection of one resistor and cap.

[Bikeman]

Thanks geminni,

Yeah, that makes sense to me. BUT... I just have this lingering feeling it might not be quite right.
Maybe it's because on every crossover I remember seeing, all the components were on the + side (from the amp's positive).

Be good to get a definitive answer, I'd rather not find out by sending the amp into oscillation or something


cheers.
Mark

[sreten]

Hi,

whilst it is traditional to draw crossovers all relative to the negative
rail, in reality it does not matter which way round you do it, either
rail can be used, or to confuse people, both at the same time.

The Wiki contains important information on controlling piezo nasties.
For a bass cab I think the piezo mid drivers + horn might work best.

http://www.wle-shop.co.uk/modules/sh...odcode=902.490



http://www.wle-shop.co.uk/modules/sh...odcode=902.388



130 x 385 x 155mm

/sreten.

[Bikeman]

Thanks again Sreten.

Yeah, I know they will sound a bit nasty, but I already had them. The plan is to make them switchable so I can add a bit more top end "sparkle".
Or not...

If my ears feel like they're gonna bleed, I'll do a bigger cut out and add a cheap compression driver with a wave guide or horn.

Like I said, it's a cheap experiment!
Here's a couple of progress shots.

Cheers,
Mark

[Bikeman]

And another.
Tweeters haven't been connected yet.
So far I'm very satisfied with the sounds it makes.

The neighbours probably aren't quite as thrilled.
Especially considering how badly I play!


Cheers,
Mark

[PigletsDad]

It definitely does not matter which side the resistor goes.

I would strongly suggest adding a basic crossover - the tweeter will sound much, much better if you keep the big bass notes away from it.

The crossover needs two very cheap parts, a capacitor and a resistor (you still want the other series resistor, so you will end with two in total).

Connect one end of the cap to an input terminal. The other end of the cap goes to the junction of the two resistors. The series resistor that you already have goes to one side of the tweeter. The extra crossover resistor goes from the junction to the other wide of the tweeter

If you use one of the midrange horn devices, I would suggest a 1uF cap (50V or bigger rating) and 100Ohm crossover resistor - this will roll-off anything below about 1.6kHz. If you are using one of the small round tweeters, make that 0.33uF (again 50V or bigger), which will roll off below 5kHz. Any old cap will do, except for a polarised electrolytic.

Parts should leave lots of change from a dollar.

[Bikeman]

Ok, Ok, I'll throw a basic crossover at it

Thanks guys.

Mark