The AM Forum

I've  been noticing that the old el-cheapo dynamic  mic that I have been using as an on-air mic is giving me a strange sort of distortion. It's sounding muffled and moderately distorted, sort of like  a cheap stock CB mic going bad.  I usually run it into a  mic amp/mixer and then into my eq. No matter how I set my eq it just doesn't sound right. I can get  it sounding not so  bad but is never quite right and if I try to run it without and equalization it sounds downright yellowy.

So while I was playing around experimenting with different mics I picked up a little electret condenser element I had laying around, clipped a couple leads onto it along with a 9V battery as a  dc power source for the element ran it through a condenser (dc blocking and audio cooupling) ans plugged it into the mixer. I immediatly noticed the audio sounded much cleaner.  No audible distortion. It seemed to have a nice clean flat response and sounds pretty good even with no equalization. Note, I was monitoring the line audio coming out of the eq. I didn't put it on the air.

Leads me to two  questions:

1) As far as  the dynamic mic goes, do dynamic mic elements sometimes go bad with use or just  over time with age ?? Reason i ask is because I don't  remember that dynamic mic sounding this bad. Matter of fact in years gone by it sounded quite good and I prefered it to other mics that I had laying around here. Leads me to wonder if it is charachteristic of dynamic mics to sometimes just go bad or deteriorate ?

2) I have the body of an old mic laying around here. I was thinking of housing that electret condenser element inside of it and trying it out as a station mic and see how it sounds on the air. Has anyone else  done this with an inexpensive condenser element and how did it work out ?



 

John,
I've had dynamic mics go bad in much the same way you describe. I don't know what goes bad as I've never investigated with the exception of one time. I had a mic that went downright bad and it turned out that the magnet inside got loose and rubbed up against the voice coil.

Tom (JJ) turned me on condensor mics along time ago. I stuffed one into an old mic body and run it along with a dynamic mic into a mixer.  I run them at the same time.  The electret has a nice sound to it.  The dynamic mic has a nice sound too (warmer) as it has a different curve to it. When I run them simultaneously the sound is good.  I get the deep low punch and good dynamic range from the electret and the dynamic mic adds a touch of midrange that I like.

Maybe you used to think it sounded good, I have recently gone back through some old recordings that i made and the quality was terrible, but at the time i thought the mic sounded great.
could be your ear is getting better.
I find that you have to pay alot more for a dynamic to get one with good sound quality.
Condensers are dirt cheap and sound great, but also have a very large pickup area, i can hear this with my MX990 and AKG condensers.
Tom JJ has had great luck with the radio shack corndenser mic, I would try stuffing one of those into the old shell and see how it sounds.

Dynamic mics are little speakers.  The voice coil is moving in a magnetic gap with very little clearance.  My guess is that dynamic mic distortion is almost entirely due to the coil rubbing against the wall of the gap.  

What is the final straw here is the design gap dimensions, how poorly centered the diaphragm was to begin with when assembled, aging warp, high temperatures encountered, resting on side ?, dropped ?

One thing I 'd like to add about stuffing a condensor element into a mic body, I had to experment with different acoustic materials in the body that exhibited different acoustic qualities.  I tried fiberglass, foam rubber and an old piece of cotton tee shirt. Combination of tee shirt and foam rubber won the sound check.

I'd have to agree with that. Microphone bodies may have all sorts or resonances in order to provide better response / pattern  with a stock dynamic element. sticking a onli directional electet element infront of a tuned pipe may require a bit of fiddling.
 When I ve used electret inserts the best resonse has generally been with the thing dangling in mid air,
                                                                                                         Ian VK3KRI

I found a couple more condenser elements I happened to have laying around. I am going to try them as well to see if there is any noticeable difference from 1 element to the next. Also, interesting points about the placement of the element in a mic body.  I'll have to experiment and see what happens.  I'll ley y'all know how it goes.

With the element and mic body I used I suspended the element in a piece of foam.  I didn't roll it up and stuff it in.  I cut a hole for the element and sized the foam to the opening of the mic body so it was lightly suspended.  Behind that piece of foam is an additional piece but more compacted inside the mic body.  Behind the foam are loose pieces of cotton tee shirt.  Different densities seemed to make the difference of whether the mic would sound hollow or ring.  Eventually after enough trial and error I arrived at what I thought sounded natural.

Thanks. Much appreciatged.  I'll keep this in mind as I assemble my condenser element into the mic body.