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Ultrasonic speaker or ??

Discussion in 'Electronic Projects Design/Ideas/Reviews' started by MrDEB, Apr 12, 2010.

  1. MrDEB

    MrDEB Active Member

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    Open for suggestions. I am willing to try anything
     
  2. audioguru

    audioguru Well-Known Member Most Helpful Member

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    Here is an extremely simple poor quality (it has high distortion) amplifier using only 3 transistors. Its output is only 1.6W into 8 ohms.

    A TDA7240A bridged amplifier IC will have an output of 5.5W into 8 ohms.
     

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  3. MrDEB

    MrDEB Active Member

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    Not real concerned with distortion? as the deer don't need hi-fi
    will look into availibility of tda7240a
     
  4. dave

    Dave New Member

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  5. audioguru

    audioguru Well-Known Member Most Helpful Member

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    Repeat: The voltage swing is so low that the loudness will be very low. Where is the stepup transformer that you will steal from a school's gym?

    Will you sneak up to a deer then give a BEEP at a distance of 1m or less? Then it will be scared and run away.
    At a distance the piezo tweeter with only 5.5W into 8 ohms will sound like a little mosquito. The deer won't care.
     
  6. MrDEB

    MrDEB Active Member

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    I am currently running a phezio tweeter off of a 555 and it is about as loud as a loud burp, maybe louder but not much. One needs to remember that deer can hear up to a mile away so their hearing is a whole bunch better than any human.
    Besides going down the highway I don't want the 2-8 khz very loud but wouldn't hurt the piezo tweeters to be loud as a human can't hear above 15khz very well.
    Maybe just addiong an amp that is big wattage for lots of decibles??
     
  7. audioguru

    audioguru Well-Known Member Most Helpful Member

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    The loudness of a piezo tweeter is determined by the voltage swing, not power.
    A 1.6 ohm speaker or paralleled speakers take a lot of current which needs a lot of power from a certain voltage. But a piezo tweeter is not a low resistance like a speaker so its loudness is determined by the power of an amplifier into 8 ohms which is a fairly low power and fairly low voltage swing from a 12V battery.
    You need more voltage to make it louder. A transformer will stepup the voltage.
     
  8. MrDEB

    MrDEB Active Member

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    If I connect as per my one transistor then the tweeter receives 12-14volts
     
  9. audioguru

    audioguru Well-Known Member Most Helpful Member

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    With only one transistor and no wasteful resistors then the piezo tweeter does not receive a signal. The 8 ohm speaker does not receive a signal if it has a coupling capacitor. It might burn up or be damaged by the DC through it if it has no coupling capacitor.
     
  10. MrDEB

    MrDEB Active Member

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    different circuit direction ?

    the one transistor appears to work but for how long?
    found this curious circuit in one of the EVIL GENIUS books
    it is supposed to have 2 - 555s connected together to creat a varing square wave. My plan is a PIC but the output is where I am thinking of going with?
    The book suggests using 4 - Piezo tweeters with 2- 1MH inductors and 2- 4.7 ohm 3W resistors per piezo.
     

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  11. MrDEB

    MrDEB Active Member

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    Circuit theory as described in book = the square wave is fed into the transducer in series with the parallel combination of the 2 - 1 MH resonating coils (L1 & L2)
    the resonant action between the inherent capacity of the transducer, .01/1kv capacitor and the inductance now produce a sinusoidal-shaped wave peaking around 25khz, dependent on the input square wave frequency.
    Hopefully Audio or ? can make some sense of this circuit as the inductors are labled in the parts list as 1mh inductors (6080) 2 used per transducer (2 - 120 ohm 5w resistors per transducer as well.
    the L3 inductor is made of 2 - Hitaachi 30.48 E CORES AND MATING BOBBIN
    wonder what inductor coils to purchase? just 1mh coils for L1 & L2?
     
  12. audioguru

    audioguru Well-Known Member Most Helpful Member

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    Before you wanted a variable frequency and now you have a resonant circuit of only one frequency.
    Since your piezo tweeters are cheap and no-name-brand without a datasheet then you don't know their capacitance unless you measure it.
    Calculate the value and purchase suitable coils after you measure the capacitance of the piezo tweeters.
     
  13. MrDEB

    MrDEB Active Member

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    Using the posted circuit, Can't I just input a variable frequency?
    cycle randomly from 2khz to 8khz and throw in a few 15khz to 20 khz frequencies?
    this is all new to me.
    If I can't due to inductor design then will stick to the amp you posted.
    My goal is a random frequency of two different frequency spans 2-8khz and 15-20khz.
    If I do it randomly and using one or two tweeters. Did some reading that stated that putting piezo tweeters in parallel increases the spl db by 3db per piezo element without increasing the amp load.
    also looking at better tweeters
    SOUND AROUND ELECTRONICS TW125 7 x 3 150 Watts Piezo Horn Tweeter
    MCM Audio Select Piezo Horn Tweeter | 53-800 (53800) | MCM Audio Select
     
  14. audioguru

    audioguru Well-Known Member Most Helpful Member

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    If you use coils to resonate a piezo tweeter then it will have a peak at one frequency. That frequency might not be at a sound peak of the tweeter.
    Doubling the number of tweeters or doubling the effective power increases the sound by 3dB which is slightly louder. Of course the amp then has double the load but a piezo tweeter is not much of a load anyway.
    I think that no-name-brand piezo tweeters without a datasheet are absolutely useless. The second one you linked looks like the one I have heard. It sounds like a whistle.
     
  15. MrDEB

    MrDEB Active Member

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    After re reading the posts concerning this subject, perhaps is there a method to create a large voltage swing but at the desired frequencies?
    I borrowed a unit that supposed to deter rats, dogs deer etc (it has a knob that selects what you want to deter)
    I took it apart and from what I can tell it's a 556 connected to a piezo via a couple of transistors and an inductor that has 4 leads coming from it. Thinking that maybe just go with two seperate sound producing elements (an 8ohm speaker and a piezo tweeter( one of the last two I posted links to)
    the 8 ohm speaker for 2 - 8 khz frequencies and the piezo for the 15-20khz frequencies. Thinking that if I use an inductor then perhaps a circuit to vary the resonant frequency of the inductor?
    in the book I purchased it has similar where a 3 pos dip switch is used to produce 3 different frequencies (25khz, 16khz and 12khz all using two 1mh inductors.
    will post schematic as soon as I get one drawen up.
     
  16. MrDEB

    MrDEB Active Member

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    selectable resonat inductor

    here is the schematic of the selectable resonant inductor.
    L3 is supposed to be two separate 1mh inductors.
    the zener clips any overshoots across Q1(50v 1 watt)
    I need to find out what inductor to use for other frequencies?? if this is the best way to achieve large voltage swings?
     

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  17. audioguru

    audioguru Well-Known Member Most Helpful Member

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    Try it and maybe the deer will run towards you or run away.
     
  18. MrDEB

    MrDEB Active Member

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    question is how to determine what the resonant frequency of an inductor?
    a formula might help or ?
    And am I correct in assuming that an inductor will creat or assist in making the large voltage swings I am after?
     
  19. audioguru

    audioguru Well-Known Member Most Helpful Member

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    An inductor plus a capacitor makes a resonant circuit. The piezo tweeter is a capacitor. Its datasheet says its value.

    One time I had a 230VAC fan and by tuning it to 60Hz with a series capacitor I got it to run with about 180VAC when the supply was only 115VAC.
     
  20. MrDEB

    MrDEB Active Member

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  21. mneary

    mneary New Member

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    Tell me you actually believe the author who says you get "400 watts equivalent" (whatever that is) from nine 'D' cells?

    Your math teacher should be ashamed.
     

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