Monday 27 November 2017

Apple and Biscuit Microphone for Acoustics Laboratories - the STC 4034

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The STC 4034 is a vintage high sensitivity, stable and robust moving coil dynamic microphone, frequently used with Brüel and Kjær test instruments to accurately measure sound levels and frequency response in acoustic laboratory work. These particular 4034Bs saw good service in a telephone transducer development lab, right until the mid seventies. Even though the design is from 1935!

Based on the STC 4021, the STC 4034B used specially selected 4021 internals (higher precision engineering tolerances), to ensure a stable and repeatable frequency response, together with improved sensitivity and lower distortion.

On the left, a section of an STC 4021, identical internally to the 4034.
On the right, the STC 4034 showing the exponential horn replacing the Romanow acoustic screen, detail below  -

Instead of the "biscuit" (the omnidirectional Romanow acoustic screen), an exponential acoustic horn is fitted, the tube of which extends some 14cm from the body. The extension uses (I think) the STC 4001 B acoustic baffle. The horn enables sound measurement to be taken at precise positions, for instance, inside the ear-canal of an artificial ear to enable accurate measurement of telephone transmitter transducers.

Modern artificial ear measurement
of a mobile phone

Here's more information about the STC 4021, around which the 4034 is based. -

The "Apple & Biscuit" microphone, the STC 4021, gained widespread professional use soon after its introduction in 1935. It quickly became a design classic. It's still a highly sought after vintage microphone for studio work, because of the omni-directional reception with flat frequency response, ruggedness and warm sound. They maintain their value, and they look good!

Also known as the -

Apple & Biscuit
Ball & Biscuit
Western Electric 630A
Dalek eye-stalk!

Martin Mitchel has produced an excellent video concerning the 4021 (below), and his blog post on the microphone is here

Romanow acoustic screenpatent GB436508 here

The following pages are from chapter 6, Studio Microphones, in the BBC Engineering Training Manual, Microphones -

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"Hodges emitted a scream the like of which
I hadn't heard since his scrotum was burned off
during my experiment with fluorine gas last year."

The Exotic Experimentation of Ernest Glitch,
Victorian Science with a Smile

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Unrelated to this post, below is an example of
eclectic science esoterica 

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WARNING - Many subjects outlined within this site are extremely dangerous and are provided here for information only. Please don`t experiment with high voltages or chemicals unless you are fully conversant with safe laboratory practices. No liability will be accepted for death, injury or damage arising from experimentation using any information or materials supplied.