Re: Ribbon Microphones

On Mon, 28 Aug 2006 14:58:41 -0700, Bob Cain
<arcane@xxxxxxxxxxxxxxxxx> wrote:

<mostly snipped, 'cause ya already read and saved it>

Beautiful; thanks as always.

I do have two (closely related) unresolved issues though. The first is
that this ideal model is based on a diaphragm that appears massless
forever. It assumes that the diaphragm can always respond to the
instantaneous pressure differential across itself.

The assumption is good for most of its passband, but not forever.

Just as we would like for a flat frequency response to pressure. Thus
the ribbon response to pressure is inherently flat over the band in
which it is mass controled and that certainly includes the higher
frequencies. The effect of higher ribbon mass is just to reduce the
sensitivity of the mic.

The second is the possibility of misunderstanding from the use
of the words "mass controlled". Its plainest meaning is that
we're operating above fundamental resonance, but many other
meanings are often implied.

When this came up last summer, some posters had conflated the
term to mean that the diaphragm somehow "lagged behind" instantaneous
pressure differential in the passband.


Anywho, a freely suspended diaphragm in moving air has its own
upper limit of response to differential pressure because of its
mass. Otherwise, the models predict some ringing around the
geometrical region, then response (plus 6dB) forever.

Much thanks, as always,

Chris Hornbeck
"History consists of truths which in the end turn into lies,
while myth consists of lies which finally turn into truths."
- Jean Cocteau
.

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