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Help the newbie

by midwest_medic
Tags: audio, electro, mechanical, piezo, vibration
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Oct6-09, 09:14 PM
P: 9
Hello, I am trying to figure out if I can replace the audio speaker from a pair of "cheap" ear bud speakers from a mp3 player with a piezo so that when the music is playing there is produced a vibration instead of an audio signal? Is this possible? would the small battery used in a small ipod shuffle-like mp3 player be enough to "cause" vibrations? I have an autistic son who I believe will benefit from the stimulation of the vibrations across the skin at the boney aspect of the mastoid bone (boney part of the skull that is just behind the ear). This is a trial and error experiment. He constantly is making noises. It appears that he needs more stimulation but we need to differentiate between the stimulation of hearing and speach. Thanks for any replies.
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Oct7-09, 01:39 PM
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Danger's Avatar
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That's an interesting concept.
As for the technical side...
Speakers already produce vibrations; that's how they work. The air (or other material) around them is caused to vibrate, and those vibrations are sound. Bone-conduction speakers, as might be used in covert communications, simply bypass the air and impinge directly upon the body. The brain still interprets the stimulus as sound.
I don't know much about this, so don't take my word for it, but I suspect that you would have to have your transducers produce an inaudible frequency in order to achieve your desired result. Best that you wait for an expert in something like biomechanics to respond.
Oct7-09, 02:17 PM
P: 9
thanks for the reply. I understand how sound waves are transmitted by vibration through the air. What I am trying to discover is 1. What is the mv output from an ipod 2.5mm jack to the earbuds? 2. Is it enough to "activate" a piezo (which will produce a greater/different type of vibration)? 3. If it is not enough voltage or amperage, how much would I need? and 4. How would I calculate it in order to purchase the correct piezo or step up the size of the ipod to produce a higher output?

Oct7-09, 02:20 PM
P: 9
Help the newbie

Oh and I forgot. I have seen the bone conduction headphones that are sold. they are rather "bulky" and would also draw much attention. I am trying to conceive a way to achieve the desired effect while still maintaining some "invisibility" which will help him by not attracting negative attention. Thanks.
Oct7-09, 03:50 PM
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The ones that I have found, e.g.

Look pretty fashionable and not bulky at all. To be honest, these are the first that I've heard of these headphones and they seem pretty cool. I might have to try some out myself.

I digress. I would guess that you could check the voltage on your jack just by using a multimeter. You might need to hook some sort of leads to the leads...paperclip maybe? If that fails, you could possibly get a male-to-male adapter to get easier access.
Oct7-09, 04:02 PM
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There are a few problems to overcome. I assume you intend for the bass parts of the music to be used to create the vibrations.

The audio jack on a typical handheld mp3 player will probably not be able to provide enough power to produce strong vibrations. The battery in the player can provide plenty of power, though -- you just won't be able to get it directly through the headphone amplifier.

You could probably use an external driving transistor, powered directly from the handheld's battery, to accomplish your goal.

- Warren
Oct7-09, 04:53 PM
P: 9
Ok, I have found that the output from the 2.5 - 3.5 mm audio jack is 60mv. Very tiny. I was thinking piezo because of size and unsure of the power requirements. My interest was not directed at the bass only. Knowing that there are limitations of the human ear, I wanted to just use a vibration, of sorts. I thought about the mp3 player as a source due to the idea of possibly creating different files of different frequencies. Use many and eliminate the ones that appear to be not useful. If the output from the player is too small to drive a piezo, any ideas on how to increase the output. I am not sure of how I would use an external driving transistor. Thanks
Oct7-09, 04:57 PM
P: 9
Btw, is there any way to post this in any other areas? The more responses the merrier.
Oct7-09, 06:02 PM
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There are amplifiers (battery operated) that you can purchase that might be of interest.

Just curious if you did anything with the pager/cellphone buzzer idea?
Oct7-09, 06:08 PM
P: 9
No to the pager/cellphone idea because I could not come up with a "timing" circuit so that it was not always on.

Thanks for the amazon hit. Will go there now.
Oct8-09, 01:42 AM
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Quote Quote by midwest_medic View Post
Btw, is there any way to post this in any other areas? The more responses the merrier.
No. Mentors and Admins can move the thread if it looks like another sub-forum may give extra help, but no multiposting please.

60mV is tiny. How did you measure that?

The bone conduction headphones posted by minger look to be a great solution, especially if teamed with the amplifier posted by dlgoff. Will that work?
Oct8-09, 08:02 AM
P: 9
I went to Radioshack and had them look up the spec's on their mp3 players.

As for the bone conduction headphones, yes, they do look promising. And thanks for the amplifier posting from dlgoff.
Oct11-09, 06:33 AM
P: 825
I would be surprised if the audio jack will only produce 60mv. The specs for the line level of consumer audio are around .3V And I agree that you need an amplifier for noticeable vibrations. A piezo crystal by itself would run on any voltage, you just won't feel it.

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