"Keith G" wrote in message
...

I'm tempted (that is to say planning) to add a 'multi-pattern tube mic' to
my collection and, until just now, was mystified as to how a mic like this
one:

http://cgi.ebay.co.uk/ws/eBayISAPI.d...MEWA:IT&ih=005

...could provide the various patterns (with in-between settings, it
appears) simply by fiddling with the power supply??

Without looking I'll guess that this is a condenser mic with a number of
capsules.

By varying the polarizing voltage to the various capsules, their output can
be varied. The different patterns result from how their outputs sum up.


Anyway, a bit of Googling has cleared this up (to a point) with
information like this...

http://www.tvtechnology.com/pages/s.0071/t.433.html

http://www.tonmeister.ca/main/textbook/node469.html


Now the questions a Is there any downside?

There are two common ways to make mics with different pickup patterns.

One is to use a single capsule that has the desired pickup pattern because
of its acoustical properties.

The other is to use multiple capsules, and add the outputs of the capsules
in different ways.

The results of using these two different approaches are not always
identically the same.

Are there any reasons to avoid these 'dual/variable capsule' arrangements?
(Especially at the the lower price point of these cheerfully cheep chinky
chappies, or is it like everything else from the Land Of The Noodle - if
the basic principle is sound, one takes one's chances, sucks it and
sees...??)

Now we compare and contrast using two half-priced parts or one full-price
part. All other things being equal, the one full-price part will perform
better. However the better may be too subtle to appreciate.

The alternative is to stick to a straightforward cardioid design like this
one:

http://cgi.ebay.co.uk/ws/eBayISAPI.d...MEWA:IT&ih=005


Suggestions/caveats welcome....

Bag the tubes.

If you don't know what you are doing, stick with known quantities. That
means there is something to be said for a known brand with a track record of
sorts like Studio Projects, versus a relatively unknown brand like "Golden
Age Project".