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The Sennheiser MD 421
cardioid dynamic mic (1960)

Sennheiser MD421-U Shock mount

The MD 421 is a well-known Sennheiser microphone of proven reliability and per­form­ance for many years now. Because of its excellent quality it is being used for al­most all kinds of applications. The broadcasting stations use it for radio and TV field work, the musician prefers it for stage work as well as the recording amateur for home and outdoor recordings. The studio cardioid micro­phone MD 421 features a wide frequency response from 30 to 17,000 Hz. Its high sensitivity and slight increase in response towards high frequencies are responsible for its brilliant sound. Each microphone is custom cali­brated and delivered with its own per­form­ance chart which may be com­pared with the published standard per­form­ance plot printed in this leaflet. Each individual frequency plot has to fall within the published limits of the standard per­form­ance curve. The cardioid direction­al characteristic of the MD 421 with its front-to-back ratio of approximately 18 dB is an important feature making the microphone suitable for use in sound rein­forcement systems and all situations where it has to be used near loudspeakers. To prevent hum pickup by mag­netic stray fields the IVID 421 is fitted with a compensa­tion coil.

Individualized frequency sweep MD421 ii Sennheiser MD421-U technical specifications MD421SE

There are different types of MD 421, the main difference between them being the type of connector fitted. The models are:

Sennheiser MD421model variations

MD421 N
The MD 421 N is fitted with a three-pin plug according to DIN 41524 which is sym­metrically wired according to DIN 45594. This mic is fitted with a roll-off filter.

MD 421-2
The MD 421-2 is fitted with a large 3-pin Tuchel plug as pre­ferred by most European Broadcasting Authorities which is also wired symmetrically. The IVID 421-2 is a low-impedance microphone. A roll-off filter is not pro­vided with this model.

The MD 421-U is provided with a 3-pin Cannon plug (XLR). It is, as the other two models, a low-impedance mic which is symmetrically wired. A roll-off filter is provided. Two versions of the MD 421-U are available: MD 421-U-4 with adapter for ⅜-inch threads and MD 421-U-5 with adapter for ⅝-inch x 27G threads. The MD 421 N and the MD 421-2 are available in light grey heavy-duty finish. The models MD 421-U-4 and MD 421-U-5 feature a matt-black housing.

Directional Properties
The MD 421 has a cardioid directional characteristic which means that the maximum insensitivity to unwant­ed sound sources is at about 180°. The directional index of the MD 421 at 1000 Hz and 180° is at least 18 dB. This means that sound from the rear with a frequency of 1000 Hz produces an 18 dB lower signal as sound of the same intensity reaching the microphone from the front. As can be seen from the polar diagram, the MD 421 should therefore be spoken into directly from the front.

Adjusting the Roll-off Filter
When a directional microphone is spoken into from a close distance, the lower frequencies are over-empha­sized. If this effect is not desired it is possible to counteract or compensate for it by means of a roll-off filter. From the diagram showing the influence of the roll-off filter, it can be seen that in position M (music), the frequency response curve is not altered in any way. In position S (speech), however, the frequencies below 500 Hz are reduced by approximately 6 dB/octave. Be­tween the positions M and S, the frequency response can be altered in three defined steps. See Figures 4 and 5.

Listen to a comparison of the five Roll-off Filter positions.

Roll-off adjustments MD421 MD421 MD421 MD421 The 421U base The 421U case

Text and illustrations are from the Sennheiser Users Guide for the MD 421.


The two photos above were taken at
WYAY, Eagle 106.7, Atlanta in 1985.

MD421-U The MD 421-2

The MD 421-2 Tuchel connector.

Hinton Instruments offers Tuchel-to-XLR cables.
No compensation to me is received for providing this link.

MD 421 cover

Download the technical data sheet for this mic.


Download the instruction booklet for this mic.

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