15kHz Sound Generator

Thread Starter

Ringolds Jargans

Joined Feb 7, 2018
5
Hello,

I am working on the following private project and I would like to get some advice on my thinking about it. Unfortunately, the things I am trying to make does not fall in my area of expertise, thus some help is needed :)

Objective: Sound generator @ 15kHz frequency.
My thinking: Since I only need one specific frequency I was thinking it would be simple to use a piezo buzzer. However, I have had hard time finding a piezo buzzer that would actually work for this frequency. Maybe someone could suggest something?
OR
Maybe I am going about this completely the wrong way? If you had to design a generator for this specific frequency how would you do it? :)

Some additional notes: the sound generated can be dirty, meaning that as long as i hit the 15kHz I don't really care much if there are unwanted frequencies present.

Any advice is welcome to get me started thinking in the right direction.

/R
 

Alec_t

Joined Sep 17, 2013
14,408
Welcome to AAC!
Any decent hi-fi amplifier ought to be able to generate the frequency at a reasonable level, but what output level do you actually need? Would a tweeter be a suitable transducer?
 

wayneh

Joined Sep 9, 2010
17,504
Thanks! :)
I am looking to get at least 90dB.
That shouldn't be any problem for a good loudspeaker, particularly one with decent tweeters, driven by any mediocre amplifier. Just use a free tone generator app to generate the 15kHz signal.

FWIW, that frequency is not audible to most people, depending on age. Your device may make a good teenager repellant. Perhaps you already know that.
 

Thread Starter

Ringolds Jargans

Joined Feb 7, 2018
5
Haha, there is no doubt that it will be annoying, but that's not the point :D
Hmm... thanks for the answers. Maybe I was overthinking it a little bit, but yeah. Don't really have much (or any) experience with audio...

I'm thinking if i could make it W/O MCU. so basically have an IC that would generate PWM at 15kHz, then have an amplifier and a speaker?

Would this work for the speaker: https://www.mouser.ch/ProductDetail...TkJYgZlQcSVWQ9puBTGvySwe/y3j1HgUwbactgYQmdg== ?
 

wayneh

Joined Sep 9, 2010
17,504
I'm thinking if i could make it W/O MCU. so basically have an IC that would generate PWM at 15kHz, then have an amplifier and a speaker?
I recommend a sine wave. A square wave has a lot of higher frequency information. That might all get filtered out by the amplifier or ignored by the speaker if it cannot reproduce it, and be no problem at all. But sending a whole bunch of energy at say 30-50kHz to the speaker may not be something the designers anticipated. Amps are so good these days that some can reach up to 100kHz.
 

MrChips

Joined Oct 2, 2009
31,079
Use a 555-timer circuit set for 15kHz. Tap off the signal from the timing capacitor. Use a simple RC low-pass filter with cut-off frequency of 20kHz.
Use audio amplifier, output to high frequency tweeter with a 3.3μF non-polar capacitor in series.
 

Colin55

Joined Aug 27, 2015
519
A 555 is only good for 100mA. 3u3 at 15kHz is 3 ohms A tweeter is 8R 11R is going to blow up the chip.
How do expect to get 90dB out of a tweeter ???
 

MrChips

Joined Oct 2, 2009
31,079
A 555 is only good for 100mA. 3u3 at 15kHz is 3 ohms A tweeter is 8R 11R is going to blow up the chip.
How do expect to get 90dB out of a tweeter ???
Standard LM555 is good to drive 200mA. You missed the part about "audio amplifier".

For a simple solution, use the LM555 to drive a power transistor to an LC circuit to the tweeter, all running from 12V.
I don't know about the 90dB part. TS will have to do the math.
 

Colin55

Joined Aug 27, 2015
519
Obviously you have never used a 555. Go and put one in a circuit and drive it at 15kHz and feel it before you post irrelevant information.
 

Colin55

Joined Aug 27, 2015
519
A standard LM555 will drive 200mA @ 500kHz.

(Obviously I have never used a 555 and don't know what I am talking about)

That's right. .
 

AnalogKid

Joined Aug 1, 2013
11,199
How accurate does the 15 kHz have to be? If 5% is ok, here's my vote:

555 operating at 15 kHz, symmetrical square wave circuit with pin 3 driving the timing resistor.
Rt = R1 + R2 = 2.7K fixed + 500 ohm pot = 3.03K near the pot midpoint.
Ct = 0.01 uF.

Pick off the timing capacitor voltage to reduce the energy in the harmonic field.
Coupling capacitor Cc = 1 uF

LM383 or equivalent audio amplifier.

5 W tweeter

ak
 
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