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Simple Low Frequency Sound Generator

Discussion in 'Audio' started by Clemson2019, Feb 19, 2018.

  1. Clemson2019

    Clemson2019

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    Feb 19, 2018
    Hey hope everyone is well.

    I’m trying to build a small frequency generator that outputs through a 10W speaker. I need it to output exactly 128 Hz. I’ve done a bit of research, and from my understanding I need an oscillator. What is the most simple way to build this on a breadboard? Where should I look for schematics? I’m pretty new to this all.

    Thanks!
     
  2. Kabelsalat

    Kabelsalat

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    Jul 5, 2011
    Hi.

    You'll ned both an oscillator and amplifier for this task. Do you have other criterias then just the frequencies ?
     
    Last edited by a moderator: Feb 19, 2018
  3. Clemson2019

    Clemson2019

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    Feb 19, 2018
    All I need is to output 128 Hz from a small 10 watt speaker.
     
  4. kellys_eye

    kellys_eye

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    128Hz is readily derived from a standard crystal of 32.768kHz (i.e. a 'watch' crystal) using binary dividers.
    Then feed the resultant 128Hz to a simple audio amplifier - add a filter to 'smooth' the squarewave if you feel it needs it.

    Here's a simple oscillator/divider with a 2Hz output but you need only tap off a different output pin on the 4060 device (get the datasheet for the CD4060 to see which pin number you need to use for 128Hz)

    clock-crystal-4060B-time-base-circuit.jpg
     
    Last edited: Feb 19, 2018
  5. BobK

    BobK

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    You don't specify a waveform. Different ones will sound quite different.

    Bob
     
  6. Clemson2019

    Clemson2019

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    Feb 19, 2018
    Sinusoid Waveform
     
  7. hevans1944

    hevans1944 Hop - AC8NS

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    Then, if you use the binary divider approach from a 32.768 kHz crystal-controlled oscillator, you will need to follow that with either a narrow band-pass filter tuned to 128 Hz, or a low-pass filter that attenuates the higher frequency harmonic content of the square waves. Either way, ten watts of 128 Hz sinusoidal audio will be very disturbing to hear from any reasonably efficient loudspeaker with a properly ducted enclosure.

    Can you tell us what you are actually trying to DO before we waste anymore time on this? Maybe an electromagnetically-driven tuning fork would be a better solution to your problem. Direct, accurate, sinusoidal sound production and no waveform filtering required. Loudness will depend on the size of the tuning fork and how its vibrations are coupled to the surrounding air, but these can fill a lecture hall with sound when properly designed. Outdoor amphitheaters, not so much.
     
  8. 73's de Edd

    73's de Edd

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    Aug 21, 2015
    Sir Clemson2019 . . . . .

    So . . . . .you need yourselfs a C3 note . . . .then.
    I would be using a dedicated tone generator as my choice, rather than some purified square wave . . . .or better yet . . .a triangle wave generation and then trying to clean it up with multi filtering.

    Here is a free listening site, should you want to pull up that frequency and then initially hear the pure sine, then the slight voicing of its triangular waveform variance and then, the final raspiness and harsh sounds of a square or sawtooth waveform.

    Aside . . . .
    I guess that I am losing it as my aural capabilities now only encroach 40~-----13Khz . . . . .

    http://onlinetonegenerator.com/

    No extra charge . . . . here is one that I use its constantly adjustable frequency for testing speaker and enclosure resonances .

    http://www.szynalski.com/tone-generator/


    73's de Edd
    .....
     
    Last edited: Feb 20, 2018
    BobK, hevans1944 and darren adcock like this.
  9. Clemson2019

    Clemson2019

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    Feb 19, 2018
    The end product in mind is to have a small 3-4 in. diameter speaker that will produce a constant 128 Hz frequency that operates on a disposable battery. The current prototype is a 3 watt speaker that is plugged into a device with a 3.5mm jack. I have to run a frequency audio generator on my computer to get the 128Hz output to the speaker. The basis of this project is to make it independent of the headphone jack and the computer and have it in a compact form to be placed in a device.
     
  10. BobK

    BobK

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    That was fun.

    On my iPhone, sitting in a crowded MacDonald’s, I can’t hear the 128 sine wave until I put the speaker right ip to my ear. The square wave is quite audible though.

    Bob
     
  11. AnalogKid

    AnalogKid

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    Jun 10, 2015
    Driving a speaker rated to handle 10 watts, and producing 10 watts of electrical energy are two very different things. What is the final result for? How loud does it have to be?

    Four AA batteries have a total energy of around 17 watt-hours, but not all of that is available and electronic circuits are not 100% efficient. You probably would not be able to get 10 W-h out of a set, so the system would make 10 watts of electrical power for less than one hour.

    Do you really need a 10 W sine wave? In a normal room, that's *very* loud.

    ak
     
    hevans1944 likes this.
  12. Audioguru

    Audioguru

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    Most small 3-4 in. diameter speakers are 8 ohms. 10W into 8 ohms is 9V RMS which is 25.6V peak-to-peak. An amplifier can produce it when its power supply is about 28.5V and its current is about 0.6A. Not a disposable battery.
    A bridged amplifier needs a 14.4V at 1.2A supply to produce 10W into 8 ohms.
     
  13. hevans1944

    hevans1944 Hop - AC8NS

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    Welcome to Electronics Point, @Clemson2019.

    So, are the responders here at EP left to produce a 128 Hz sinusoidal oscillator that drives a three or four inch diameter speaker with ten watts of power delivered from a disposable battery? And are you coming to this forum for help because you (1) don't know the simplest way to build this on a breadboard, (2) have no idea what schematic to use, and (3) are pretty new to all of this? That's okay. Some of us here live for the opportunity to help you, no matter how long it takes to squeeze out the information of WTF you are trying to actually DO. For example,do you expect this thing to repel biting insects? Terrorize mice? Annoy neighbors? Help you tune your guitar?

    If all you have done so far is to attach a 3.5mm phone plug to a small prototype speaker and try to drive that from the headphone jack on your personal computer, are you expecting to actually build something, or do you expect us to do all that work for you? What is your contribution to your project?

    Perhaps the inductance of the speaker voice coil can be part of a power-oscillator resonant circuit? Maybe mounting the speaker in a resonant enclosure tuned to 128 Hz will help produce a sinusoidal audio wave in air? Perhaps you can run the contraption from a set of D-sized alkaline dry cells?

    Maybe drive the speaker directly with a class D mosfet power amplifier sampling a 128 Hz sine wave at ten kilohertz or so? As @Audioguru noted, about thirty volts at 0.6 amps would do the trick. So, twenty 1.5 V D-size alkaline cells would do just fine and enrich the coffers of Eveready and/or Duracell immensely if you run it at full blast for awhile...
     
  14. Clemson2019

    Clemson2019

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    Feb 19, 2018
    Everyone, I apologize for my vagueness. I have signed an NDA for the project I am working on so I this is why I have been limited on the info about it. It is a medical device. The current prototype sends 128 Hz frequency to the head of the individual using the product. The 128 Hz resonates well in the skull and this is why the frequency is used. The problem currently is that a 3 watt speaker is being used in conjunction with a headphone jack to produce the frequency is not loud enough. That is why I was trying to increase the wattage. Probably not the solution I was looking for. I need it louder, and I need it to run off of a battery instead of receiving power and signal from a headphone jack. I hope this is descriptive enough. Excuse my noviceness.
     
  15. Clemson2019

    Clemson2019

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    Feb 19, 2018
    Also, going back to the power draw. How loud could I get it off of a 9V battery? The device is handheld so 24 AA batteries would be unrealistic for the design. I'm guessing that the max voltage that my phone is outputting to the headphone jack is around 2V? Is that why the 3W speaker isn't outputting that many decibels from the frequency?
     
    Last edited: Feb 21, 2018
  16. duke37

    duke37

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    To shift more air you will need bigger speakers.
    A better solution would be to alter the coupling between speaker and skull. A direct physical connection would be much better.
     
    hevans1944 likes this.
  17. Hopup

    Hopup

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    I agree with duke, if you are not trying to alter brainwaves using binaural, isochronic or monaural means and it is only for skull resonance then direct connection is obviously much better way to do it.
     
  18. hevans1944

    hevans1944 Hop - AC8NS

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    Jun 21, 2012
    A hand-held medical device, huh? Monaural rather than binaural? Here is a website to get this forum's participants started on the fascinating subject of brainwave entrainment, which is not necessarily what the OP is actually working on. So please don't hijack this thread to go off on that tangent... yet.

    I agree with @duke37:
    A large headset with cushioned ear pads will couple sound to the skull much better than any loudspeaker separated by air from the patient. It will probably be necessary to use ear-plugs to prevent damage to the inner ear structures, while providing sufficient sound intensity to couple to the interior of the skull.

    Anyone who has attended a rock-music concert is familiar with body cavity resonances. To fully experience this requires a LOT of audio power, but that is generally not a problem with public performances. I think it will be a huge problem creating head cavity resonance effects with a small, hand-held, loudspeaker. And it will be an even bigger problem to sustainably power it from either disposable or rechargeable batteries.

    Not very loud and not for very long. But you need to experiment! Purchase a cheap transistor radio that operates from a 9 V battery and has a small 3" speaker. Buy or rent a modulated RF signal generator and play a 127 Hz tone through the radio. How loud is it? If you hold the radio up against the side of your head, over one ear and press really hard, with the volume cranked up to maximum, it will probably be painfully loud. But that's hardly a scientific measurement. You need a sound pressure level (SPL) meter to perform meaningful tests. And a reproducible environment.
     
  19. Clemson2019

    Clemson2019

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    Feb 19, 2018
    Thanks so much for all the info. I will definitely invest in a SPL meter. So if currently it’s pressed against the skull, but is not loud enough, is the agreed solution to just use a larger speaker with more voltage? I’m not sure what the current decibal level is, but at max volume from my phone, the 3W speaker isn’t outputting enough do do anything. Is this just because my phone can only output so much to the 3.5mm jack? Is my limiting factor the output from my phone or the 3W speaker?
     
  20. Clemson2019

    Clemson2019

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    Feb 19, 2018
    I will also add that the speaker is making direct contact with the forehead, so using sealed ear couples isn’t an option for this project.
     
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