Re: Mic Mods

[Mike Curtis <wd6ehr@xxxxxxxxxx>]

> 
> : Secondly, I can't see how the thickness of the shells makes one iota of 
> :difference. The mic element in the Astatics is mounted into the grill 
> :with a rubber gasket, and the element is directional. For the shell to 
> :make a difference, the sound waves would somehow have to leak through the 
> :gasket, bounce off the inside of the shell, leak through the gasket again, 
> :make a Magic U-Turn and head back into the element. In other words, these 
> 
> First the element WILL NOT block ALL the sound waves. Some will pass
> thru and they will reflect off of the back of the inside of your mic and
> back into the element. I feel that case thickness plays into your sound.
> Ever measure the thickness of a Green Bullet? A whole lot thicker shell than
> an Astatic. Why don't they sound better? Some people think they do, but it
> has alot to do with the element. The old elements are alot of the way an old
> mic sounds. But so is the size, shape, and yes, thickness of the case.

The JT-30 is considered to be omnidirectional, as is the Green Bullet.

All airborne vibration sensing microphones have diaphragms, and all 
diaphragms have two sides.  In the case of omnidirectional mics such as 
the Bullet and JT30, the enclosure prevents sound from getting to 
the backside of the mic, which would cause feedback and give a terribly 
ragged and wimpy sound in general.  To verify this, take your JT30/Bullet 
apart and play through the raw element.  You'll find that you can play 
through either the front or back of the element, and it will feed back 
like a stuck pig.

In the case of cardioid or other directional microphones, part of the 
sound is allowed to reach the rear of the diaphragm, phased in such a way 
as to cancel out sound coming from undesired directions.  "Cardioid" 
means "heart shaped", which is about the pattern of this mic.  There's a 
sharp null at the rear, and a broad polar response off the front.  When 
you cup it in your hands, it destroys this pattern, often causing feedback.

But we're talking about the JT30, an omnidirectional mic.  The back 
enclosure is sealed.  Because of the small air space, it raises the 
resonant frequency of the mic.  This is quite similar in operation to 
acoustic suspension, quite popular for small bookshelf speakers with 
great bass response (and VERY low efficiency!)  In the JT30, a thicker 
case would raise the resonant frequency of the back enclosure.  This of 
course will affect the timbre of the microphone.

Case thickness also affects overall weight, which also will affect the 
sound.  A heavier enclosure 1. vibrates less, and 2. resonates at a lower 
frequency.  A good example of weight vs sound is a woofer enclosure.  The 
best ones are quite heavy.

There's a lot more to life (and acoustics) than the simple answers :-)