Thought i would start this discussion on the different tyope of elements that can be used in a harp mic. My first one [ one so far ] i used an old rotary telephone element. Rather large at 2" round but does have that old victrola sound. I bought some new smaller ones [ 1 1/8" round ] from a surplus electronics site i found on the net. These are alot newer the the rotary phone ones. I`m thinking i can make the housing smaller which will be alot better in holding the mic itself.
In theory any old speaker can be used as an element correct?
It can, I've done it a couple of times. Used the speakers from an old set of big headphones. It worked but it isn't very good, I also had some luck using a piezo disc suspended in a diaphragm of cling film. Worked surprisingly well.
I was given an ebook the other day of electrical circuits and there was a circuit diagram to make any miniature speaker into a microphone element. I'll have a look and post up when I find it.
Just messing around the other day I took a 3 inch speaker and hooked it up to an old instrument cable I had lying around.
I plugged that into one of my homemade amps... It worked... Just not very loud. I really had to almost yell to hear anything at all and that was louder than my typical busking set up and thus, pointless.
I have a few Shure SM57's laying around and I looked at the elements in those and the diaphragm is a clear plastic, not the black paper material used in most speakers. I think the clear plastic requires less force into the microphone to drive. At work I found an old government rotary dial phone and checked the microphone in there and it is also a clear plastic driver.