Category Archives: Vintage sound gathering equipment

MB – UNITRA TONSIL MDO 23 (Circa 1975-80s)

Between 1973 and ‘75 German microphone manufacturer MB Electronic (today known as MBHO) designed a range of quality microphones that were licensed to Polish state owned electronics company UNITRA TONSIL.

Back in May 2020 I wrote a post about the UNITRA Tonsil MCU-53, an excellent cardioid condenser. Now, (from the same stable) here is the MDO 23, a slender, omnidirectional, studio dynamic.

MB UNITRA TONSIL MDO 23

So What is it Good For ?

The thing I have always liked about omnidirectional dynamic microphones is the absence of proximity effect coupled with the ability to handle high SPLs. This makes them perfect for close-micing loud guitar amps without having to mess around EQing unwanted boominess caused by proximity effect. I have often used a Sennheiser MD21 on rock ’n’ roll theatre shows for this purpose.

Omni dynamics also make excellent speech mics and are very often used in TV and radio for interviews. Once again the absence of proximity effect is useful, allowing a good deal of freedom of movement without significantly affecting the frequency response.

Picking up sound from 360 degrees, Omnis are also just the job when it comes to capturing ‘atmosphere’.

CLICK HERE to hear a range of sound sources recorded with the MB UNITRA TONSIL MDO 23

Technical Specifications

MB UNITRA TONSIL MDO-23
MB UNITRA TONSIL MDO-23

Frequency Response graph

MB UNITRA TONSIL MDO-23  FREQUENCY RESPONSE GRAPH
MB UNITRA TONSIL MDO-23  Grill

Standard 3 pin small Tuchel  connector

MB UNITRA TONSIL MDO-23  Tuchel Connector

Conclusion

Having scoured the internet for information about this microphone I have come to the conclusion that it is somewhat rare! Apart from a couple of photographs, the tech spec and frequency response graph pictured above were pretty much all I could find. Sadly, it would appear that company records of this period have long since vanished in the mists of time.

In common with the MCU-53 I wrote about previously, this microphone has been generously sent to me by a friend in Poland, Adam Wilma. It is a serious quality professional microphone with a myriad of uses, and a very welcome addition to the Polish section of my collection. So thanks once again Adam!

Martin Mitchell Polish Microphone Collection

UNITRA Tonsil MCU-53

Acel GM-17B

MB UNITRA Tonsil MDO-23

The Capac BIN-AURAL (1936- c1960) ‘The accurate and simple equipment for testing the internal condition of mechanism “by sound” .

Although we are all familiar with the medical stethoscope used by doctors to listen to the internal condition of the patient’s heart and lungs etc., few will be familiar with the use of stethoscopes in other industries.

In 1936 British engineer Charles Edward Noel-Storr, Managing Director at Capac Co. Ltd in London, came up with an interesting variation on the stethoscopes that were available at the time.                                            

 The Capac BIN-AURAL 

Capac BIN-AURAL oak case
Who can resist a gorgeous oak case?
Capac BIN-AURAL in its oak case
WOW!
Capac BIN-AURAL in oak case with tray removed.

Capac Company’s BIN-AURAL was somewhat similar in appearance to a medical stethoscope and was used to detect faults and assess the condition of a variety of mechanical devices and structures.

Capac BIN-AURAL with single tectoscope.

The long probe called a tectoscope can be put in contact with the outside part of a machine/engine/structure and the sound from inside is transmitted back to the earpieces via a metal diaphragm. In this way the skilled mechanic can identify specific problems. Virtually no sound is picked up from outside, making it perfect for isolating faults in noisy environments such as factories and machine shops.

The Author. Listening to car engine using Capac BIN-AURAL with single tectoscope.

So what made the Capac BIN-AURAL different to its competitors?

Apart from the single tectoscope illustrated above the user could also employ a second tectoscope. This enables the operator to listen to the mechanism from 2 different points simultaneously.

Capac BIN-AURAL with two tectoscopes.

A further option is also available in the form of the Tectophone.

The tectophone (illustrated below) is a small exponential horn which is screwed on to the diaphragm. This can be used to listen in close proximity to the outside of a mechanism in the particular location where faults are suspected. It can also be used in conjunction with a tectoscope to listen to the outside and inside simultaneously or to compare.

Capac BIN-AURAL with tectophone and tectoscope.

For a detailed explanation of the uses of the Capac BIN-AURAL I have reproduced below the original manual that came in the box.

01 CAPAC BIN-AURAL Manual Cover
02 CAPAC BIN-AURAL Manual Page 1
03 CAPAC BIN-AURAL Manual Page 2
04 CAPAC BIN-AURAL Manual Page 3
04 CAPAC BIN-AURAL Manual Back Page

CONCLUSION

In the build up to World War 2 aero engine makers such as Armstrong Siddeley Motor Limited, Bristol Aeroplane Company Limited, D. Napier & Son Limited and many other British engineering companies adopted the Capac BIN-AURAL as an effective diagnostic tool. With the aid of the BIN-AURAL, a mechanic could pinpoint the source of a sound, or listen to that sound from 2 different perspectives.

P.S. Whilst the Capac BIN-AURAL is not itself a microphone, a microphone can be easily attached, making it a great tool for gathering unusual sounds from inside engines and machines and other structures.

Capac BIN-AURAL with Sennheiser MKE2. Insert into tubing.
Capac BIN-AURAL with Sennheiser MKE2. Insert into tubing. Closeup.

The following ‘collage’ recording of bits of my car engine has been made with a Sennheiser MKE2 inserted into the rubber tubing which connects to the tectoscopes.

CLICK HERE to listen