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Mikes And The Mechanics

Straight to the source, Jon Lewin quizzes Sennheiser technicians on what goes where.


Jon Lewin took a plane to talk technical with the engineers of Sennheiser. He asked them questions. They showed him microphones.

So why was I sent to Germany? Well, it wasn't as a punishment. Sennheiser and their UK distributors Hayden Laboratories flew a motley of journalists out to their factory near Hanover for two days to show us a variety of new products, and generally demonstrate to the music press what their firm and making microphones is all about.

Probably the most popular piece of Sennheiser in the UK is the HD414, the high quality budget open headphones. However, on the continent, they are equally well-known for their vocal microphones — metallic objects with snappy titles like MD421 and MKE2. These have a good reputation in many professional fields: TV and radio as well as popular music.

Sennheiser use basically three types of microphone for their musicians' models: dynamic, condenser, and electret condenser... er... remember physics lessons?

Dynamic microphones contain a small diaphragm, attached to a wire coil; when you bellow into the mike, this diaphragm and coil arrangement moves around. By a fortunate freak of engineering, the diaphragm is suspended between the poles of a magnet, which means that its movement generates an electrical current.

Condenser microphones work on a different principle. Condenser mikes contain two metal plates, one fixed, the other movable (by your shouting); these plates are then charged by running a voltage across them. As they move closer together/further apart, the voltage changes — hence the signal that goes off to be amplified. Running that charge across the plates means that condenser microphones need an external power source, as well as extra amplification for the tiny output signal.

Unless they're electret condensers. With these mikes, the electrical charge is permanently 'fixed' (in much the same way that metallic objects can be magnetised) into a plate. Back-electret condenser mikes have the charge in the fixed back-plate. Electret mikes don't need phantom powering, but they do still require a pre-amp.

Phew. Now back to Germany. The team of hacks was introduced to the charming and handsome Dr Sennheiser, son of the founder, Professor Sennheiser. Herr Doktor introduced us to his new products, chief amongst which was the MKH 40P8. This cardioid (heart-shaped field of response) directional mike is Sennheiser's response to the increasing demands of digital recording, with an "extremely low inherent noise level" (it's quiet), and "very good tolerance of sound pressure levels up to 142dB" (it won't distort even if you blow something up in front of it).

The MKH 40 was put through a comparative test with a Neumann U87, and an AKG C414. We donned headphones and listened to the microphones working in turn at very high volume; as the room was reasonably quiet, it was possible to pick up even the slightest shufflings of feet and rustling of clothing over the background noise produced by the mike and amplification. Each mike had its own particular sound, but the most obvious difference between them was that the Sennheiser had a significantly lower level of background hiss coming from the mike itself. An interesting test.

A further point that the demonstrators made on paper (it's difficult to prove without an oscilloscope) was that the MKH 40 actually has very few tonal characteristics of its own. Of the popular studio vocal microphones, nearly all have an uneven response across the frequency range — some enhance the middle frequencies (around 5kHz), while nearly all emphasise the high end (15kHz and upwards). Sennheiser's comparative statistics show that the MKH 40 does neither, being an almost completely transparent mike, which colours the sound significantly less than its competitors. There's a slight and gradual increase in response at the higher frequencies, but far less than in the others.

Yes. Or no. I can't argue with the figures, but there is a point to be made in favour of older microphones with a less linear response. Mikes like the Neumann U87 are popular with engineers and producers precisely because they colour the sound, warming up vocals without recourse to EQ. Such a 'perfect' piece of equipment as the MKH 40 might actually mean more work for the engineer.

Still, there are plenty of other applications for microphones outside of recording vocals on pop records, as our tour around the Sennheiserfactories demonstrated. We imagined how many mike modules there were in all the telephones in Germany. Then we admired the machines putting the mikes together, smiled to the girls soldering the teeny-weeny bits in place, nodded at the enormous drums of headphone cable, and went back to the demo room for a play with Sennheiser's VHF wireless transmission systems (available '87), as fitted into their test guitar — look, no wires at all.

A further demonstration involved the tiny (inbetween little toenail and large bogey) sized MKE2 lapel mike. This omni-directional back-electret condenser mike is barely wider than its own lead, and yet it manages a frequency response of 40Hz-20kHz. Should you ever require a tiny microphone that can be (a) banged on a table-top; (b) held in a lighter flame; or (c) thrust into a glass of Perrier, then this is the one for you. It survived all these tests admirably, though the immersion left some water in the diaphragm — apparently curable by a quick baking. At last, the mike for stuntmen.

Time for one last chat with Dr Sennheiser, who denies any possibility of a cheapo range of products under their name, and also seemed very dubious about the possible development of digital microphones. Then we all got given press packs, and umbrellas (umbrellas?), and it was off to the "typically continental restaurant [for] German beer in Bavarian ambience".

Our thanks to Hayden and Sennheiser for such a pleasant trip, and also for helping me realise the inherent problems in dealing with good quality microphones...

The major difficulty is shown by the MKH 40: unless it's broken, you can't hear it working.

This makes it difficult to pass any qualitative judgement in the short term. Only through workbench tests and long-term use can a microphone truly demonstrate its character.

At the moment, the microphone market is a bewildering jungle (pardon my metaphor). Brand identification isn't helped by the manufacturers' obtuse liking for unmemorable serial numbers — MKHs, PVMs, WM-Ss. While I realise that the more technically-minded amongst us revel in the ability to recognise reams of otherwise meaningless initials, it's about time that a little logic was applied to the marketing of microphones. Giving such slim and insubstantial objects names might seem a flippant suggestion, but it would be the first step towards giving them individual character.

The user needs to know what job their microphone is best suited to. He/she needs to know the basic differences between the individual models in particular lines, and their limitations. The information is readily available in the manufacturers' spec sheets, but rarely is it stated explicitly. Tell us what we need to know.


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Making Music - Copyright: Track Record Publishing Ltd, Nexus Media Ltd.

 

Making Music - Jan 1987

Topic:

Microphones


Feature by Jon Lewin

Previous article in this issue:

> Technically Speaking

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> Sampling A Vintage


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