Olde tymey mics

[N0SYA]

I often see a cylinder underneath the mic head on "studio" desk/podium mics from the 30s and 40s. They routinely appear to be around a foot or more long and 4 to 6 inches in dia. What porpoise, other than supporting the mic, did these serve?

[K8ERV]

I don't know, but possibly a tube pre-amp?

TOM K8ERV Montrose Colo

[KL7AJ]

Many of them had tube preamps.....and these were not NUVISTORS, but probably more like the jugs you had in Atwater Kent radios!

[W9GB]

Microphone pre-amplifier (using vacuum tubes) OR
phantom power supply for microphone (depending on microphone element type).

In the era you mentioned (1930s, 1940s), a carbon microphone element
(like those mfg. by Western Electric for telephones) would require DC power.

The RCA ribbon microphones were used in broadcasting and music.
http://www.coutant.org/ribbons.html
Today, these RCA originals are highly prized $$$

Stephen Sank, son of RCA engineer / designer repairs and
produces new versions (under cloud brand name)
http://proaudioheaven.com/fr_home.cfm

[WB2WIK]

The tubing can house a preamp for sure, but they also alter the microphone response.

A microphone is a "tuned system," much like a speaker or an antenna. While an antenna is unlikely to cover more than a few octaves, mikes and speakers do that. Everything about the structure and its housing impacts that.

Now they can be computer modeled, but the old mikes weren't, they were designed empirically based on lots of experimentation.

[N0SYA]

Should have known the mics might have been amplified, durrrrr! I was guessing it was what wik said, some kind of forgotten 30s magic mic resonance/tuning chamber.

[AC0OB]

Since the ribbon output was low impedance, the base or lower part of the mike often contained the audio transfomer to convert the low impedance to the amplifier input impedance of about 600 ohms.

Some audiophiles use this transformer in reverse for ribbon mikes:
http://www.jensen-transformers.com/datashts/10k611m.pdf

Phil

[AC0OB]

or this one:
http://www.jensen-transformers.com/datashts/115ke60.pdf

Phil

[KW6LA]

Since the ribbon output was low impedance, the base or lower part of the mike often contained the audio transfomer to convert the low impedance to the amplifier input impedance of about 600 ohms.

Some audiophiles use this transformer in reverse for ribbon mikes:
http://www.jensen-transformers.com/datashts/10k611m.pdf

Phil

You have it right the Ribbon Mics ( RCA 77 & 44 BX ) have a large transformer in the base.

[AC0OB]

The newer ribbon mikes use neodymium magnets (for higher output) and either FET or tube amps for amplification of signals to feed the mixer amp.

Phil