little speaker, big noise!

Discussion in 'The Projects Forum' started by Macabra, Sep 29, 2008.

  1. Macabra

    Thread Starter Active Member

    May 31, 2008
    hello all,

    i'm working on a little gadget that through a speaker outputs "emergency" or something speech type alarm. I've got a little audio kit from radioshack which is basically as loud as the typical recordable things they put in stuffed animals or in toys. I'm wondering if any of you know of a way to actually make this really loud that it will be heard from inside a vehicle with doors and windows closed.

    I've done research and found the LM386 which is an audio amplifier. I've connected it to a 8ohm speaker with a gain of 200 and although loud, it just not enough. Any of you fellas know of another chip I could use? I seem to only bump into this LM386. I also need this speaker to be relatively small so it would fit into a box of some sort so I can't have a large speaker.

    Much thank yous
  2. hgmjr

    Retired Moderator

    Jan 28, 2005
    If you have some flexibility as to the size of speaker you are permitted to use, you could move up to as large a speaker as possible and then mounted it properly so that its sound pressure output is better matched to the area into which the sound is being directed. This is typically managed by mounting it so that the output pressure wave is not able to find a short path from the front of the speaker to the back of the speaker and thus cancel much of the output sound level. A good speaker enclosure can make all the difference in the output sound level from all but the cheapest of speakers.

  3. S_lannan

    Active Member

    Jun 20, 2007
    why not just get a 12v siren

    no need for an audio amp, ear piercingly loud and small.
  4. Audioguru


    Dec 20, 2007
    A little LM386 IC produces only 0.4W into an 8 ohm speaker.
    A car radio amplifier IC produces about 2.2W into an 8 ohm speaker.
    A bridged car radio amplier IC 14W into a 4 ohm speaker.

    If you want more volume than a littlw LM386 then use a real audio power amplifier IC.
  5. -Excalibur-


    Jul 20, 2008
    You could try a TDA2822M, since it can accept 12V. Since you only want loud noise, look for a 4Ω speaker if possible in such small sizes, and look for one that has a resonant frequency near or at the main frequency(s) of the output sound (and in the sensitive human hearing range of 300 - 3000Hz). Obviously audio quality (fidelity) is not really important here, but an enclosure which has a resonance of the speaker and output sound will increase further your loudness.

    Typically 56mm, 44mm and 27mm speakers are used in most toys (though they are 8Ω usually), most have "horrible" resonant frequencies which you can use to increase loudness. Eliminate any bass from your output to avoid distortion from the amp and speaker.

    Or you could just get one of those sirens like S_lannan said. (Although you did want a speech alarm.)

  6. Macabra

    Thread Starter Active Member

    May 31, 2008
    thank you for all your suggestions! :) I will look into those IC chips mentioned above and yeah, I agree that the enclosure makes the difference as well! lucky me that I'm using 4ohm speaker =D