Piezo Tweeter Power Ratings

Thanks, Nick ... I've been in the industy for nearly 38 years (sometimes it scares me when I think about it ), and there's always something new to learn. If I stop learning, well I've probably stopped breathing

Kind regards ...

You've been in this industry for 38 years? Judging from your apparent youth (see avatar), my guess is you started slinging electrons as a toddler! (Not to worry: Carl Frederich Gauss balanced his father's books at age six.)

At any rate, I tested several tweeters using a sine-wave signal. My test setup consisted of a 50-ohm resistor in series with the tweeter, and I measured the voltage across the tweeter and the current through the resistor, noting the phase shift between them. As you know, power computations in AC circuits aren't as straightforward as with DC circuits if the circuit contains reactance. I computed the power consumed by the tweeter as follows:

P = V_rms·I_rms·cos θ,

where θ is the phase shift between the voltage and current.

My power amp is rated at 2080 watts into a 4-ohm load and is flat out to 50 kHz. I didn't run the amp at this power level, of course! But I did need a constant-voltage source with a very low output impedance.

Judging from what I measured, the tweeters consumed 619 mW average with 23.0 V_rms at the tweeter terminals. SPL at 1 meter was 118 dB, avg, with a 4.72 kHz input signal at which they produced the loudest sound. Their performance at 27 kHz - at which they are shown as producing an SPL (@ 1W @ 1m) around 100 dB (!!!) - is positively dismal. As my test mic is pretty flat out to 32 kHz, I know the mic wasn't the cause of this apparent lack of performance.

These tweeters are advertised as having a 'sensitivity' of 94 dB at 1 W input at 1 meter. (One watt consumed by what load? Again they don't say.) Nor do they state at what frequency this sensitivity figure is determined. If it's 1 kHz, they're not going to get 94 dB out of these no matter how hard they pray. Piezo tweeters perform best above their self-resonant frequency which, for these, is around 2.65 kHz.

My general impression is that loudspeaker specs seem to consist largely of smoke and mirrors. Is that the general consensus around here as well?

At any rate, thanks to all of you for your help. Especially yours, DCad. Hope to hear from you guys again!

Kindest Regards,

TV

Thanks for your comment's but age is age, regardless of appearances (you all are SO LUCKY not to see the just-out-of-bed-in-the-morning-in-front-of-the-bathroom-mirror photos ) ... I'm 56, so yes, I did start a little earlier than some.

Regarding tweeters and specs and such, the manufacturer should have published a frequency response to you, and hopefully it wasn't with too much smoothing, and they should have published the process of measuring beyond the basics of "1W-1M". High frequencies don't 'couple' well with the air, so how it is 'loaded' (phasing plugs, horns, wave-guides, etc.) is extremely important. I can't really tell you much here, but HOW the tweeter diaphragm is mounted is very critical. If you are planning to operate at a discrete frequency, it gets easier because you can specifically load the diaphragm to actually have gain at that point.

Also, it's pretty important to only use a HF device of any kind well above the Fs frequency. At least one octave higher if using a 12dB/octave crossover. At resonance, the mechanical stress is high, and you will experience mechanical failures (and a lot more distortion).

When you can, let me know your application ... sounds like fun .

Kind regards ...

"When you can, let me know your application ... sounds like fun."

Hi DCaD:

I'm using the tweeters in a linear phased array. In the pix below, the T-handles on the back of the array are mechanical phase adjustments that allow me to experiment with beam steering and divergence. Except for the PVC pipe, the array is made entirely from scrap-yard materials which I machined. (The cross-piece in each T-handle, for instance, is made from a section of a stainless-steel rung out of a junked commercial refrigerator.) I'm interested in the 17 to 25 kHz range because the shorter wavelengths reduce both the beam divergence and the distance I must move the phase-adjustment screws - a real PITA after awhile. I'd use DIY electronic phase adjustments, but I can't afford the parts at this time.

<I'll upload the pix in a later post. CR4's servers just seem to hang when I try to submit the pix. They don't even acknowledge the request.>

Kind regards,

TV

Still unable to upload images to CR4.

The best coupling between the tweeter and air is an exponential horn, and not the sections of pipe you see in the pix. The pipe is useful, however, because the acoustic impedance mismatch causes reflections which allow me to measure the speed of sound via the transit time of a 'click' out to the end of the tube and back to the tweeter, which acts like a microphone.

No problem getting to your site and seeing your pics. Just buried lately in visitors and little time to do other 'fun' things. (actually, very little is blocked, but much is 'viewed', so sometimes the speed is slow.

I hope to write more later on your device ... feel free to remind me if necessary ... sometimes I 'forget' when my work gets too deep.

If you like, you can also find me at dennis@sonavox.com ...

Talk more later ...

______________Dennis