Using choke coils in SERIES with piezo tweeters?

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Cal Weldon

Cal Weldon

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#1
Many moons ago I used to take somewhere around a 1-5mH choke and run it in series with piezo tweeters. 5mH seems to ring a bell as the one that made a really noticeable difference, if I remember correctly.
Not sure if this old hat, or if anyone bothers with piezos anymore. But if you had or do, I found this a great way to cure that damn piezo sound harshness and give the tweeter a nice boost, yes BOOST at the upper end it needed. Now I'm not sure why I tried it in the first place as a choke doesn't seem like regular business when comes to running it in series with a tweeter .

Are there others who have done this? Am I too old and out of touch? I'm only forty something for gods sake, but I never hear about this. Was there something I was doing wrong there? Screwing with someones amp or worse their ears?

Disclaimer: Unfortunately budget constraints allowed me to become all too familiar with piezos.
Big ones, small ones, fat ones, skinny ones.

Cal 😕 :smash:
 
#2
Here is an Application Note on crossing over piezoes:
http://www.ctscorp.com/components/Datasheets/PIE_Speaker_Application_Note.pdf

No mention is made of chokes.

I have never tried what you said. However, if you have nothing else hooked up to that circuit, I would not recommend it. A piezo is basically a lossy capacitor, and running an inductor and a capacitor in series results in a resonance point where no impedance is present-hence burnt out amp.

Running an 8 ohm or even 20 ohm resistor across the piezo might make such an arrangement possible, I don't know. But hooking up a choke and piezo together in series soundls like not a good idea.
 
#3
A piezo is basically a lossy capacitor, and running an inductor and a capacitor in series results in a resonance point where no impedance is present-hence burnt out amp.
Click to expand...

It's possible that this resonance-point was responsible for the EQing Cal liked.
As far as the resonance goes: A piezo tweeter seems to be a very lossy capacitor and might therefore not present a too dangerous load in series with an inductor. To be really sure one has to perform measurements though.
I remember that some speakers a workmate once bought (at the end of the seventies) used a piezo tweeter with some circuitry that was also including an inductor.

Most users don't get the maximum performance out of their piezo tweeters anyway by simply paralleling them directly to the woofers. So I think there is quite some room for improvement.

Regards

Charles
 
#4
Hi Charles,

Thanks to you and kw for the responses. If it is not going to pose a problem to the amp then I think someone out there might want to do some tests and let us know. I always found those tweeters were really shrilly, even the one that had a deep throat [approx 5-6 inches overall depth] and about a 3X8 front face. This to me was the only piezo I got to use that sounded half decent.

So try the experiments with different coils and see what effects you can get out of it. I am simply not set up to do it but would be really interested in anyone who can. I'd like to compare the graphs of different coils vs. without. I always enjoyed the "improvement" this made.

Thanks to anyone ahead of time,

Cal
 
#8
Maybe a good idea would be to hook a choke in series with a piezo and a resistor of some 10 ohms, and do an impedance test.

Then run a choke in series with a piezo in series and a resistor of 5 ohms. Run an impedance test.

If that turns out okay, then go down to lower resistances and finally no resisitance at all. That way you don't risk a burnt out amp.

Just a suggestion.

By the way, Cal, did you find any success in looking for that online tone generator for the Mac?
 
#11
It sort of makes sense. What you have there is a 2nd order LPF, with likely a high Q. In other words it would be actually rolling off the high end, but a high Q filter has a resonant peak with a considerable amount of boost right before it rolls off. Just speculating, but perhaps the value of inductor you used set the roll off (& peak) freq fairly high (maybe 10-16 Khz range). I suppose to your ears that may have helped over ride or balance out against the nasty high Q peak in response that piezo's typically have around the 3.5 Khz range. I think something like a coil & resistor in parallel with the piezo & a cap in series with that might be a better approach though. It's really that very high peak at the 3.5 Khz range that's the main culprit for the piezo's obnoxious character. Crossing them over above about 6 Khz & I think they can be tolerable. I've always used a 15-20 ohm resistor in parallel with the piezo & a 1-2 uf cap in series but a steeper roll off below 6 Khz would help I believe.
 
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