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The Amperite P.G. is a 1937 American dynamic microphone, made in New York.

In the thirties, all dynamic microphones were omni directional, all around sensitive. For P.A. use this usually caused problems: the dreaded "howling" was common, sometimes even well before the sound was loud enough to be heard by the audience. For that reason it was always important to place the speakers away from the microphone.
Therefore, many companies tried to solve this problem.
One of the first attempts to do this was made by Amperite, with this "Pressure Gradient" (the word "Gradient" means small difference).

Today, all directional microphones are pressure gradients, but as far as I know this is the first microphone to be identified as such.

Pressure transducers (omnis) have a diaphragm where sound reaches the front only. Pressure Gradient transducers are "open" on both sides of the membrane. Because it takes a little longer for the sound to reach the rear, there is a small phase difference and that also gives a pressure difference.
The larger the pressure difference, the greater the diaphragm movement and because the angle of the sound reaching the diaphragm influences the pressure difference, the gradient microphone is directionally sensitive.

Amperite named the recording pattern of the P.G. ' elipsoid', the first truly cardioid (directional) would be presented by Shure two years later: their model 55.

This did not alter the fact that in 1937 many were very happy with the Amperite P.G., it was also important that the size of this microphone was small: 7.5 cm long and 11 cm high. Artists were therefore clearly visible to the audience behind this microphone, while their faces often disappeared completely with the large ribbon microphones.

It did not matter that the microphones were not very lightweight, with their 615 grams: they were always placed on a microphone stand. The P.G. was produced until at least 1952.

These and many more types feature in my book Witnesses of Words.. More information about that can be found at

wow cover

Amperite PG
elipsoid pattern

Top: the modern styled P.G. dynamic

Middle: the elipsoid pattern & optional baffle

Below: the sound, and adverts for the P.G.

Listen to the sound of the Amperite P.G.H. (high Z version)

amperite PG ad
PG Dynamic