Let's consider a 0.5 uF capacitor in series with a piezo tweeter of capacitance 0.5 uF.
At any frequency this would form a potential divider where the two reactances are equal in magnitude.
The applied voltage would therefore divide equally between capacitor and piezo, resulting in an attenuation of 6 dB.
Or am I missing something?
1) That we are talking 1.5uF (suggested by you and accepted by the OP) so attenuation will be about 2.5dB
Detectable, but nothing to write home about.
2) more to the point: such attenuation will be flat/uniform across the Audio band, so it will somewhat lower level but not correct any shrillness, no ugly peaks removal.
While using an RC highpass, crossover frequency can be chosen to attenuate typical 3-4kHz peak while leaving higher frequencies unaffected.
What the OP is asking for.
Detectable, but nothing to write home about.
2) more to the point: such attenuation will be flat/uniform across the Audio band, so it will somewhat lower level but not correct any shrillness, no ugly peaks removal.
While using an RC highpass, crossover frequency can be chosen to attenuate typical 3-4kHz peak while leaving higher frequencies unaffected.
What the OP is asking for.
2.5dB is fine. Clearly audible & satisfies the brief - take the edge off.
Where I'm a little confused: the higher frequencies are required to circumvent: 1.5uF in capacitors, a 1 ohm resistor, & an inductor of whatever value corresponds to 2.7kHz @ 8ohms.
-3dB perhaps?
You appear to be running the piezo off the 2nd order LC filter designed for the original Eltax moving coil tweeter, but with its 4.7 uF capacitor now converted to 1.5 uF.
The statement "2.7 kHz @ 8 ohms" would not apply in this new configuration, but only to an 8 ohm moving coil tweeter and a 4.7 uF capacitor.
However, I can say that the modified LC crossover will provide very little attenuation of the piezo and your -3 dB may not be wide of the mark.
For best results, one would dismantle the HF section of the LC filter and connect the piezo directly to the speaker input terminals via the RC circuit in post #3.
You should try it one day, provided your piezos don't get blown at your garden party on Sunday! 🤓
The statement "2.7 kHz @ 8 ohms" would not apply in this new configuration, but only to an 8 ohm moving coil tweeter and a 4.7 uF capacitor.
However, I can say that the modified LC crossover will provide very little attenuation of the piezo and your -3 dB may not be wide of the mark.
For best results, one would dismantle the HF section of the LC filter and connect the piezo directly to the speaker input terminals via the RC circuit in post #3.
You should try it one day, provided your piezos don't get blown at your garden party on Sunday! 🤓
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P.S. If you also want attenuation while using the RC circuit then add a small value capacitor as in the following description.
Looking from the amp, first a 1.5 uF or 2.2 uF series crossover cap, then the 22 ohm shunt from hot to ground, then a series cap of about 0.15 uF for 6 dB attenuation.
Smaller than 0.15 uF will give even more attenuation.
Looking from the amp, first a 1.5 uF or 2.2 uF series crossover cap, then the 22 ohm shunt from hot to ground, then a series cap of about 0.15 uF for 6 dB attenuation.
Smaller than 0.15 uF will give even more attenuation.
It's fine - the edge is off! I note: when I 'normalise' mp3 tracks, 3dB is a lot. Although there may be other issues, perhaps with the body of these piezos.
I did a piezo project a little while back: https://www.diyaudio.com/community/threads/trying-to-get-the-best-out-of-cheapo-piezos.409639/
Mostly I was measuring and trying to make a good crossover.
I did have some cheap physical mods, however.
I can't tell how yours is built up, so dunno if these tips will help you... Good luck!
Mostly I was measuring and trying to make a good crossover.
I did have some cheap physical mods, however.
- (disassemble piezo) add modge podge to the diaphragm
- (disassemble piezo) add poly fluff behind diaphragm, around piezo element
- make sure acoustic seal is good around various parts of the piezo assembly
- damp the body of the horn with putty or butyl rubber
I can't tell how yours is built up, so dunno if these tips will help you... Good luck!
It was interesting. A strange phenomenon. At reasonable output levels the speakers sounded surprisingly good. When we cranked it up the piezos began to dominate. I suspect the inductor on the woofer may be contributing to the problem. At high volume it seems to be all bass & treble will very little mids.
Considering that neither the woofer nor the tweeter are original to the ported box, one would expect to do some fettling to achieve the best possible result.
I know where I would start! (Hint: See post #26) 😉
Ha-ha! For the record - there will be no 22ohm resistors any time soon!
An equation that proves interesting . . .
Simple first order: 6 ohm woofer, 30 ohm tweeter, 5k crossover point - what value capacitor?
I really can't understand why you started this thread. 😕
"Any quick & dirty tips?" you asked, and that's exactly what you got.
Earlier you said that the piezo's impedance is 30 ohms @ 5 kHz. I assume you read that in its specs.
The piezo is a capacitor and its capacitive reactance (Xc) in ohms is large at low frequencies and small at high frequencies
So technically, a piezo does not require a crossover circuit as it performs a self filtering action, opposing the low frequencies more than the high.
However, a piezo may still receive sufficient voltage at low frequencies from a powerful amp to overload it and produce distortion.
This eventuality is ruled out by using an RC circuit as has been described to you in this thread by folks who know what they are talking about.
Here endeth my final lesson! You can lead a horse to water, but...
I hear you. You guys are providing an ideal solution to a problem. Me - not so much. I'm playing with leftover parts. I perhaps should have asked "Can I improve the sound of these speakers using only these components."
Ironically, I've re-created a school disco sound. Remember when the Mobile DJ had 2 x 12" Fanes + 2 Piezos crammed into a box way too small? These speakers are taking me back.
Ironically, I've re-created a school disco sound. Remember when the Mobile DJ had 2 x 12" Fanes + 2 Piezos crammed into a box way too small? These speakers are taking me back.
Then the answer would have been a simple "No"! 😉
P.S. My fab sounding 70s Mobile Disco set up included 4 sizeable 2 x 12" Fane/Goodmans cabinets and 2 x 120 W of valve amplification.
Crucially, there were no piezos involved! High frequencies were reproduced by Goodmans Hifax 750P dynamic horns with integral filters.
Happy days!
If your DJ had stereo you may well be younger than me! It started with 120w mono then Citronic revolutionised the market with 100w + 100w stereo console with Garrard decks.
Happy Days.
btw - they do sound different. Female vocal, Aretha, Whitney et all sound a little more compressed.
Happy Days.
btw - they do sound different. Female vocal, Aretha, Whitney et all sound a little more compressed.
My Mobile Disco predated Citronic's dominance of the scene. I operated with a very effective mono mixer which I'd proudly built myself.
A stereo mixer would have granted me full stereo capability. However I deemed stereo sound to be unnecessary since the 70s punters, busy concentrating on their dance moves, wouldn't notice the difference! Over the decade I can't recall anyone commenting on the fact that my Disco wasn't in stereo!
A stereo mixer would have granted me full stereo capability. However I deemed stereo sound to be unnecessary since the 70s punters, busy concentrating on their dance moves, wouldn't notice the difference! Over the decade I can't recall anyone commenting on the fact that my Disco wasn't in stereo!