How to connect piezo speakers to an amplifier

[Audioguru]

The spec's tor the Kemo Piezo tweeters have no details:
1) Distance for dB output.
2) Peak-to-peak voltage for dB output.
3) What frequency (probably a frequency that produces the highest loudness).
Piezo transducers have their dB loudness rated at a distance of only 10cm.
Tweeter loudspeakers have their loudness rated at a distance of 1m (100cm) and a voltage of 2.83V RMS which would make 1W into 8 ohms.

 

[ChrisO]

Hello
Received also those two:

https://www.kemo-electronic.de/en/Car/Speaker/L003-Piezo-tweeter-approx-8-Ohm-50-mm.php
In fact they are not Kemo made, see photo. They are known as TLX-1e,
but the company producing them doesn't exist ;-)
I tried them on this thing I recently bought:
https://www.hifiberry.com/docs/data-sheets/datasheet-amp2/
powered at 19V.
Those TLX-1e were louder than all the other Kemo tweeters I tried so far.
Asking myself what would be the best method to drive them. They praise themselves 150W. The HiFiBerry can do max 30W per channel.
And I have difficulties to sort out all those Watts when it comes to piezo tweeters.

 

[Audioguru]

The new piezo tweeters have a transformer that is 8 ohms but the HifiBerry amplifier produces 30W when it has additional cooling into 4 ohms per channel when the distortion is high (but you do not care about distortion). The power into 8 ohms will be half (15W RMS per channel) with a 18V supply at high distortion.
105dB at 1W/1m, 108dB at 2W/1m, 111dB at 4W/1m, 105dB at 8W/2m, 108dB at 16W/2m and 102dB at 16W/4m.
It might be loud enough but I think the HiFiBerry is made for music and does not have additional cooling needed for a continuous tone so you need a circuit to pulse the tone on and off.

If you use one tweeter for each amplifier channel then the random phasing produced by various distances from the listeners will add 3dB or completely cancel the sound. Maybe you can use a circuit to warble the frequency of the sound.

 

[ChrisO]

That means, the HiFiBerry is not strong enough for those tweeters, right? Should I mount a cooler on the TAS5756M chip?
What do you mean by: "you need a circuit to pulse the tone on and off"?
I could generate a sin wave sound with some small gaps of "silence", would this help?
I experiment using self generated sound composed of .25 sec 16kHz followed by .25 sec 17kHz, in other words it alternates 16 & 17 kHz every .25 sec.

If I use one tweeter for each amplifier channel and both are mounted close to each other, the distance difference to the listener would be negligible, no?
English is a foreign language for me, couldn't find sufficient translation. What do you mean by "warble"?

Last question ;-) Wouldn't be better for my purpose such an amplifier: https://www.banggood.com/502C-HIFI-...tml?rmmds=myorder&ID=6278570&cur_warehouse=CN ?
Thank you.

 

[Audioguru]

Kemo and Le Son do not say the maximum allowed power of the tweeter. V Automotive Line shows 150W when a 15 ohm attenuating resistor feeds 51W to the tweeter, is 51W the maximum allowed power?

The TAS5756 chip has its cooling metal tab on its bottom so it cannot have a heatsink in top, it uses the copper on the pcb for cooling its 15W per channel into 8 ohms. If you use a 30W amplifier instead then the loudness will be only +3dB more which is only a little louder. 10 times the power sounds twice as loud.
The Banggood amplifier uses the TAS3116D2 chip which has its metal tab in top for a heatsink to be attached when its power is more than 15W into 8 ohms per channel (or up to 50W per channel into 4 ohms) when its supply voltage is higher than your 19V. The TAS5756 and the TAS3118D2 are basically the same chip. The very cheap Banggood amplifier does not have a proper heatsink, AliExpress and probably ebay sell the same cheap Chinese amplifier.

The IC runs cooler when the sound is pulsed on and off with a pulsing circuit. The cooling occurs during the gaps of silence.

Warbling the tone slides its frequency up and down then there is less effect of phase change caused by different distance from each tweeter to the listener from cancelling the sound,

Yes, when two tweeters are close together they are about 50mm apart. At 16.5kHz the wavelength is 21mm so of a listener is to one side only a little then the more distance from the far tweeter causes its phase to cancel sound the near tweeter.
Warbling the tone will not work because you need to slide the frequency up to where it cannot be heard and down to where anybody can near it. Instead you should alternately alternately the two tweeters. 18kHz to the left tweeter while the right tweeter is in a pause. Then 18kHz to the right tweeter when the left tweeter is in a pause.

The Pest Kids might like it and invite all their friends to come and hear it.

 

[ChrisO]

The more I read your writings the more confused I am and have the impression it doesn't make any sense what I'm trying to achieve.
Thanks anyway.

 

[Audioguru]

1) The HiFiBerry amplifier is made to produce 15W into 8 ohms at high distortion when its power supply is 18V.
2) Banggood wrongly says TAS3116 but also says the correct TPA3116 for their amplifier IC. The same amplifier sold by Amazon shows that it must be mechanically assembled and has a proper heatsink in top of the TPA3116 amplifier IC that produces 26W at high distortion into 8 ohms when the power supply is 19V.
3) The tweeters all have inaccurate power ratings and loudness levels.
4) Tweeters mounted beside each other have phase problems that adds or cancels their sounds.
5) Your system will need to be located very close to the kids for them to hear it because its loudness in not high.

 

[ChrisO]

2) I don't buy on Amazon and Aliexpress' recent shippings (due to Corona virus?) are just ridiculous.
4) I guess the best is to use just one but a loud one. As for the loudness:
5) Recently our house alarm system needed some service. At the end of all the work, the technician made a sirene test which is located inside on the ground floor of the house. We were in the basement, the only one "person" ignoring the sound was our 19-year old 100% deaf cat sleeping there. The loudness was terrific. 115dB told me the service man, IIRC. It's not hard to find such a siren used for all kinds o alarms: house, car, "personal alarm", but so hard to find a speaker with such a loudness. Why?

 

[Audioguru]

In Canada, a "siren" sweeps its frequency up and down in a speaker. Its speaker is a tweeter that can also play music.
But a smoke or CO alarm produces a single frequency beeeep and is in a tuned enclosure causing it to be VERY loud at its tuned frequency. Usually a piezo beeper has an oscillator inside that drives it only at its loudest frequency and is powered with DC.

The Kemo piezo tweeters are made for cars where the car owner makes as much noise as he can then turns down the windows so everybody can hear how foolish he is.

Most people buy many sound systems that play music at home and in their car. The speakers do not need to be extremely loud, they need to sound clear and produce a wide range of frequencies then they are not efficient. But hardly anybody needs a very loud siren or alarm and they do not need to sound clear or play a wide range of frequencies so they are VERY loud.

 

[miker123]

In Canada, a "siren" sweeps its frequency up and down in a speaker. Its speaker is a tweeter that can also play music.
But a smoke or CO alarm produces a single frequency beeeep and is in a tuned enclosure causing it to be VERY loud at its tuned frequency. Usually a piezo beeper has an oscillator inside that drives it only at its loudest frequency and is powered with DC.

The Kemo piezo tweeters are made for cars where the car owner makes as much noise as he can then turns down the windows so everybody can hear how foolish he is.

Most people buy many sound systems that play music at home and in their car. The speakers do not need to be extremely loud, they need to sound clear and produce a wide range of frequencies then they are not efficient. But hardly anybody needs a very loud siren or alarm and they do not need to sound clear or play a wide range of frequencies so they are VERY loud.

Howdy. I've been following this conversation and have been working on a similar project for the same reason. I'm new to this stuff, so please bear with me. I got the above Amp2 & a Raspberry Pi 4 and have been getting some momentum with the project, but hitting a few snags. I hope I'm not in over my head, but any guidance would be appreciated.

I've mostly been testing that above-mentioned https://www.amazon.com/gp/product/B07DRQPKG9/ref=ppx_yo_dt_b_asin_title_o05_s01?ie=UTF8&psc=1 piezo tweeter.

The crux of my initial problem has to do with testing decibels (sound pressure level - whatever the correct terminology) and frequency. I can download clean sine wav files from https://www.wavtones.com/functiongenerator.php or generate wav files from sox.

I'm in my early 60's in age and have had my share of loud music, so I wouldn't trust my ears AT ALL for these 17500 HZ being tested, THOUGH I DO HEAR A HIGH PITCHED TONE FROM THE TWEETER. I thought that I adequately guarded against clipping, but am not sure. I would have hoped that a successful sine wav of this 17500 HZ caliber would be something INAUDIBLE to myself to be deemed a success, but who knows - I never went to an ear doctor and could be blessed with good ears. If I had youngsters around (other than the ones tormenting me), I'd ask them. I have a https://www.amazon.com/gp/product/B00ECCZWWI/ref=ppx_yo_dt_b_asin_title_o09_s00?ie=UTF8&psc=1 sound meter, which supposedly reveals results ranging from 85 - 90 decibels, but its top frequency response is rated at 8 kHz (Frequency response: 31.5Hz ~ 8KHz ), so it be beats me why it would be registering a 17500 hz wav coming from that piezo tweeter. (The meter is A-weighted decibels; I know they also have C-weighted and Z-weighted). If the meter's limit is 8000 HZ, I don't get why it's showing 850-90 HZ. So I'm really confused as to what to trust in the way of decibel meters and human ears at this 17500 HZ frequency as far as how loud it really is.

Then as far as frequency, audacity analysis says a tested wav file is about 17500 HZ, as does the sox-generated spectrogram confirms and agrees. Could the Rasp Pi volume too high or software be distorting the wav? Also the sox command, "sox /path-to-file/17500.wav -n stat" says that the "rough frequency" of this 17500.wav is 13306. Any idea what "rough frequency" is?

So I'm looking for guidance on how to trust loudness and frequency measurements for this project. Any help would be greatly appreciated.

 

[Audioguru]

The piezo tweeter and the sound level meter are VERY cheap with poor quality. I think maybe your amplifier or even maybe your ears are clipping and producing a frequency of may half or 1/3rd the 17.5kHz you are playing. The sound level is extremely high.

 

[miker123]

That was very useful guidance, well taken. I just did a controlled experiment in which I downloaded 17400 HZ with -2dBFS from https://www.wavtones.com/functiongenerator.php (sox was used to make a 60 second loop from the 5 second download).
I played it both on desktop computer speakers (supposedly rated for this [?]) as well on the Rasp Pi, but now upgraded the piezo tweeter to https://www.amazon.com/gp/product/B07FY2YVK3/ref=ppx_yo_dt_b_asin_title_o02_s00?ie=UTF8&psc=1 which is that https://www.kemo-electronic.de/en/Car/Speaker/L003-Piezo-tweeter-approx-8-Ohm-50-mm.php TLX-1e you and ChrisO were discussing above - the one with the transformer. I have heat sinks and a cooling fan & gaps of silence could be used to accomodate cooling.

That cheap meter shows that 17400HZ_-2dBFS-1minute.wav at about 55 db at 1 meter from a desktop computer speaker, while it showed almost about the same on ChrisO's TLX-1e connected to a Rasp Pi /Amp2. I then measured using with the iPhone app, SLA Lite. The iPhone sound level app showed about 80 db at 1 meter away in both systems. In both systems, this clean 17400HZ_-2dBFS-1minute.wav was barely audible to my old ears in both systems. When I put my ear right up to the speaker, I can hear a slight high pitched tone and a faint hiss. But if it's 80db at 1 meter, would that not be as profoundly loud as a vacuum cleaner in its lower frequency audible equivalent? In other words, now I have something that is faintly audible to myself, but may be blairing loud to ears that aren't as old as my ears. But both systems get similar sound meter readings, but they both say 55 db on the cheap sound meter, while both saying about 80 db on the IPhone Sound Level app (which might not be professional grade, but at least the IPhone has some pretty decent audio hardware).

Can you recommend an affordable sound meter for these high frequencies so that I'm not shooting in the dark?

Also, let's say that 80 db were accurate. My next hurdle would be to get that up to a good loud 95 db. My understanding of these complicated voltage/decibels algorithms is that changing the Rasp Pi / Amp 2 power supply from 18 volts to 24 volts would only add a couple of decibels. Do you have any ideas as to how I could boost the loudness to the required 95 db without clipping/distorting the clean 17400HZ_-2dBFS.wav file?

 

[Audioguru]

+10dB needs 10 times the amplifier power and sounds twice as loud. +3dB is double the amplifier power and sounds only a little louder.
Adding +15dB will cause an explosion.

Amazon sells cheap junk made by a company that nobody knows about.
The Amazon tweeter has Absolutely No Detailed Audio Spec's.
A real audio speaker says how much its output deviates, maybe +3dB and -3dB but this one could be +30dB and -30dB.
A real audio speaker says how much power it is fed at what frequency at what distance for its output level.
Here are the detailed spec's for a half-decent sounding tweeter:

 

[miker123]

I tried to give my self a quick education of some of these stats, but regret that it would take me weeks to be sufficiently versed. Please forgive me if this shows. It was a lot to absorb.

I found a Dayton Audio alternative tweeter, the AN25F-4, https://www.daytonaudio.com/images/resources/275-114--an25f-4-soft-dome-car-tweeter-spec-sheet.pdf The frequency response chart seemed better suited for this loud 17 - 18 kHz unusual application. It would have to be compatible with the amp specs at https://www.hifiberry.com/docs/data-sheets/datasheet-amp2/ (There would be a 4 ohm scenario and an 8 ohm scenario). I was planning on using mono running in one channel. Here's where it gets tricky... 10 AWG wire would allow this 4 ohm tweeter to be placed at the necessary given 100 feet away from the amp, but it seems that it may be more like 120 feet, so I'm not sure how that would be addressed. I'm considering a pair of these Dayton AN25F-4's connected in series such that so that 8 ohm load could use 10 or 12 AWG wire at 120+ feet away. But wouldn't that be at the expense of power getting to the second (further away) tweeter? I would simply point the second tweeter 180 degrees away toward a garden to protect vegetables from animals. Or maybe there's some other way I could accomodate a cable run to a single 4 ohm tweeter should the distance be greater than 100 feet?

Do I need just a capacitor, just a crossover or both? If using two tweeters in series, rather than the preferred single tweeter, would a single capacitor and/or crossover suffice for both tweeters? Is this capacitor compatible?.. https://www.parts-express.com/dayton-audio-dmpc-68-68uf-250v-polypropylene-capacitor--027-424
Which https://daytonaudio.com/category/35/crossovers crossover would you recommend for this? (I read something about using a 12db/octave crossover).

I appreciate the guidance. I may not catch on to the advice right away, but am trying my hardest to wrap my head around an adequate understanding. It may take a little longer to catch on, but I do learn in time.

 

[Audioguru]

Tweeters are designed to produce audio that has only occasional full power bursts. You will probably burn out the tweeters by driving them with a full power tone continuously. The same for an amplifier.

A tweeter uses a capacitor as a crossover to block low frequency sounds that will destroy it. Your wrong calculation of 68uF will destroy a tweeter if the amplifier plays music or voices. Your high frequency tone does not produce a low frequency so a capacitor or crossover circuit is not needed.

You need a beeper, not a tweeter. A beeper is loud when driven by low power because it is in a resonant housing. The resonance increases its output sound tremendously.

 

[miker123]

I understand and have accepted what you're saying. I'm still challenged in the field of such electronics, but this is what I came up with thus far.

has a very easy-to-understand video that my simpleton mind could put together quite simply. The video is accompanied by a parts list through either of two companies and there are some silly comments about the video.

If I could adapt those instructions, but replace that Youtube's "5V Electric Magnetic Active Buzzer" with the proper beeper OR buzzer OR transducer OR whatever, then apply it to that circuit, instead of that "5V Electric Magnetic Active Buzzer" (if that's possible), then I might stand a chance.

I found this APC Company https://www.americanpiezo.com/standard-products/buzzers.html which looks like it has some useful resources. It describes relevant mounting options for audible sound transucers. If I can find somebody helpful and knowledgeable at this APC Company, what might I describe to them that I need for this?

(I don't kid myself into thinking that this will be as easy as replacing that buzzer in that youtube video with the proper APC Company part, but if I CAN, then I'd be delighted.)

What might I describe to APC if I want to use that youtube video concept?

 

[Audioguru]

The video you found was made by a science student who copied this simple circuit.
There is no schematic but the breadboard shows an ordinary 555 astable oscillator. I think the "DC buzzer" is actually an AC piezo transducer (speaker) not a buzzer. A piezo buzzer has an oscillator inside it. The transducer has one frequency that it is the loudest since it has a strong resonance at that frequency. A proper piezo buzzer will beep with only a battery and the 555 circuit is not needed. It automatically beeps at its loudest frequency.

I do not know if you want the beeper to make kids laugh at it or to make mosquitoes laugh at it. The beeper will not scare either one away.

 

[miker123]

Let me make sure I understand the scenario you're suggesting for the intended use.

- Are you suggesting something that has its own built-in electronics, such as a built-in oscillator?
- Does the one you suggest need anything (and if so, what?) other than a battery to make sound?
- Does the type you suggest have one frequency that it's the loudest at?

 

[Audioguru]

A piezo beeper has a transistor inside it. It makes a continuous beeeep at its resonant frequency when DC is applied.
A piezo transducer is a speaker that produces sounds when fed an AC signal like from the 555 IC in the video. They also have a resonant frequency.

The beepers are indicators that are not very loud, 85dB is loud but only at a distance of 10cm which is only 4 inches.

 

[miker123]

Then beepers are ruled out as being not quite loud enough, which I guess leaves a piezo transducer as the viable option. I need to track down a piezo transducer with the right specs.

Given a transducer with the required loudness and frequency specs, I'm confused as to whether the unit I want to track down would be of the type that has its own built in electronics, as opposed to one of the type that needs to be fed its optimal frequency.