Sennheiser LABOR W MD4 Noise-Cancelling Microphone.

Following on from my posts about the LABOR W MD7 and the MD21, here is another gem from the early years of Sennheiser.  Released in 1951, the MD4 is an unusual looking, handheld, noise-cancelling, dynamic microphone designed to suppress feedback and ambient noise.

Back view.

So How Does It Work?

The MD4 is side addressed. Sound can enter through the openings on either side of the capsule. When the user is speaking in close proximity to the front of the microphone their voice is strongly reproduced and very little sound is entering at the back of the diaphram. On the other hand, unwanted sound arriving at the microphone from further away, and in particular at the sides, will enter front and  back simultaneously. Bearing in mind that the back of the diaphragm is 180 degrees out of phase with the front, these sounds will be cancelled in varying degrees. This capsule design achieved a considerable degree of off-axis rejection, making it much less likely to pick up unwanted sound from PA loudspeakers or other sources.

Outside of the military and commercial aviation, the MD4 was the first purpose designed, dynamic, noise-cancelling microphone that I can think of, on sale for domestic use.

N.B. Sadly the original Grosse Tuchel connector has gone missing but at some point I will replace it. For now it works fine direct wired.

In a market previously dominated by feedback-prone omnis, the MD4 gained considerable popularity for use in public address and continued in production until 1973. Although initially intended for use with speech the MD4 also found favour as a vocal mic.

Here is the legendary Sonny Boy Williamson II pictured at a folk/blues festival in Germany in 1963. 

So what does it sound like? 

Here is a Voice Recording Demonstrating the Noise-Cancelling properties of the MD4

CLICK HERE to listen.

And now for something completely different ………….

Close-Mic’d Guitar Amp

CLICK HERE to listen.

N.B.   In the context of a live gig the noise-cancelling properties of the MD4 will provide considerable isolation from other performers.

Below is some technical information on the MD4 from the 1953 LABOR W catalogue.

English Translation 

Moving coil microphones

Moving coil microphones have two major advantages over other types of microphones:

• They are robust and insensitive to weather influences.
• Due to their low source resistance, they can be easily connected via lines of several 100 metres.

Moving coil microphone MD 2

Universally usable microphone for particularly rough operation. Well suited as a table microphone because of its elegant shape in combination with a table base. Frequency range 50-10,000 Hz. Sensitivity approx. 0.1 mV/ub at 200 . Dimensions: 54 Ø x 120mm. Table base available as an accessory.

Moving coil microphone MD 21

Thanks to a new design and modern production methods, we have succeeded in creating a high-quality universal microphone that, despite its low price, is top class. Frequency range 50-15,000 Hz. Sensitivity 0.20 mV. Dimensions: 120 x 46 x 46 mm. An elegant table base is available as an accessory.

Stand microphone MD 3   

Very popular as a stage microphone because of its barely visible input stage. The high-quality moving coil element housed in the base ensures high transmission quality. Frequency range 30-10,000 Hz. Sensitivity approx. 0.08 .V ub and 200 Ω. Spherical polar pattern. Dimensions: base 170 mm Ø, 60 mm high, tube 900-1 500 mm long.

Stand microphone MD 3 Studio

In a frequency range of 30 to 15,000 Hz, it has an effective treble boost from around 6,000 Hz. Externally, it can only be distinguished from the MD 3 by the form of the input stage.

MD 3 and MD 3 Studio are supplied with an attachable Plexiglass panel, which gives the microphones a slight directivity.

Probe measurement microphone MD 3 M

The extremely small sound absorption of only 8 mm Ø does not cause any distortions in the sound field. Therefore particularly suitable for many acoustic measurements. Frequency response 50-10,000 Hz + 2.5 db.

Moving coil microphones (page 2)

Table microphone MD 3 T

A particularly elegant table microphone for first-class transmission of speech and music. Base plate can be unscrewed and has a thread suitable for mounting on a photographic tripod. Balanced frequency range 50 -10,000 Hz. Sensitivity 0.08 mV/ub at 200 Ω. Omnidirectional polar pattern. Dimensions: ball 60 mm Ø, plate 70 mm Ø, projection 450 mm.

Hand microphone MD 4

The MD4 has proven to be excellent for all voice transmissions where there is a risk of acoustic feedback. Through particularly effective compensation, any sound coming from a greater distance is very strongly suppressed. The MD4 is therefore just as suitable for transmissions from very noisy rooms. Frequency range 50-10,000 Hz. Internal resistance 200Ω. Voltage emitted during normal discussion 4mV. Dimensions: case 60 mm Ø, length 180 mm, weight 380 g. – The MD4 is available with a talk switch and also in a switchable high-impedance version.

Hand microphone MD 42

Field of application like MD4; but is end addressed. Frequency range 200-10,000 Hz. Internal resistance 200Ω. Voltage emitted during normal discussion 2.5 mV. Dimensions 47mm Ø. Length 120 mm, weight approx. 135 g.

Moving coil microphone MD 5

Universally usable microphone in a favourable price range. Can be used as a hand, table or tripod microphone. Excellent reproduction, especially for voice transmission. Available in low and high resistance, with and without a switch. Sensitivity approx. 0.25 mV/ub or 7mV/ub. Dimensions: 86 x 65 x 52 mm.

Speech microphone MD 7

Particularly good speech intelligibility due to emphasis on high frequencies. Therefore recommended for announcement and dictation systems. The soft rubber housing makes the MD7 insensitive to rough use. Available in low-impedance and high-impedance versions. Dimensions: 76 x 48 x 48 mm.

Microphone Accessories

Tripods, flexible necks, table bases, cables, couplings in various designs available.

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Conclusion

Throughout the decade following the establishment of LABOR W in June 1945 Fritz Sennheiser and his colleagues at Laboratorium Wennebostal worked hard producing a range of innovative microphones for a variety of purposes, aimed at different sectors of the market. They offered microphones for the home, the office, the stage, journalism and TV and sound studios. As we can see from the catalogue above they demonstrated a remarkable degree of ingenuity, technical expertise and creativity. These are characteristics which distinguish the Sennheiser brand to this day.

Credits

Many thanks to my old school friend Alan Marchant for kindly donating this fascinating microphone. Alan is owner of The Vintage Wireless Co in Manchester at 174 Cross St, Sale M33 7AQ. His shop is an amazing Aladdin’s cave of ancient wirelesses, car radios, gramophones and phonographs. Well worth a visit!

Thanks also to Keith Thompson for sparing the time to record the tasty blues guitar clips.

And thanks to Hazel Hanson for the English translation of the LABOR W Catalogue.

Electro-Voice Rags To Riches. T45 Noise-Cancelling Microphone (1944)

In 1942 after America entered World War 2, the US military estimated that only 20% of radio communications in combat were successful. Failure in the other 80% was mainly due to the voice of the radio operator being drowned out by the surrounding cacophony of war. Like no other conflict before, success on the battlefield relied on communications. Spotting a gap in the market Al Khan and Ed Burrows, the owners of Electro-Voice, came up with a brilliantly simple, ingenious and cost effective solution to this problem.

Even in 1942 the single button carbon microphone was a piece of old fashioned tried and tested technology, having been in use in telephones since the tail end of the previous century. Although the audio quality of the T45 is little better than it’s telephonic predecessors it is extremely reliable and very robust. It also has a high output making it ideal for long distance communication. Even if the microphone gets wet you can simply dry it out (as per the instructions above) and it will carry on working! However, the really clever part of this design utilises 2 small holes of equal size on the front and back of the mic.

These allow the surrounding noise to enter the microphone on both sides of the diaphragm. The sound striking the back of the diaphragm is 180 degrees out of phase with the sound at the front. This causes a very impressive cancellation of the unwanted noise whilst the speaker’s voice, which is less than a 1/4 of an inch from the front opening, dominates the transmission.

In terms of manufacturing costs it would be hard to produce a cheaper microphone.  A carbon button is a very small tin of glorified coal dust (carbon granules) with a simple diaphragm attached.  A bit of wire and some lightweight plastic fittings and that is it! Pure genius !

After some initial military skepticism the product was thoroughly tested and a first order came through to Khan and Burrows  for 100,000 units! The T45 was soon taken up by all branches of America’s armed forces and  the success rate of combat communications rose to 90%.

Rags to Riches.

Prior to World War 2 Electro-Voice was a small struggling company, with 20 employees, manufacturing a handful of dynamic and velocity microphones per week. By the latter part of the war Electro-Voice had 500 employees working in 3 shifts  producing more than 2,000 T45 microphones a day! After WW2 it was also adopted by commercial aviation and remained in service for several decades.  The T45 was also used on the Mercury, Gemini and Skylab space missions.

Over the entire production run more than a million were produced placing the T45  among the highest selling microphones ever made.

During the war many small firms went out of business due to a shortage of manpower and materials, but for those involved in the war effort fortunes were to be made. In 1946 Electro-Voice moved into an impressive new factory at Buchanan Michigan where they continued to manufacture  innovative and exciting audio products  for the next 60 years.

 

Footnote 

Circuit for powering a carbon microphone.