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Hands On: Large Diaphragm Microphones


High-quality large diaphragm mics are used in the recording of many a hit — David Mellor explains why they are worth their weight in gold.

L to R: AKG C414, Beyer MC740, Neumann U87, Sanken CU41.


Do you have some money in your pocket? OK, go down to your local record store and buy one of the current top 10 chart singles on CD. Better still, buy them all and think of it as an investment (And keep this article to show to your income tax inspector!). Before you listen to your new singles collection you need to be in the right frame of mind. Firstly remember that, whatever you think of the musical styles involved, these are currently some of the most successful recordings around. More people chose to buy these particular recordings last week than any others that are available. It follows therefore, that there must be something about these recordings that is right. Now that you're ready, listen to the quality of the recording of each CD and make comparisons with your own recordings. Does your work match up?

If you can honestly say that the standard of your engineering matches that on the 10 most popular recordings then either you are one of Sound On Sound's top professional readers or you are one of the great undiscovered (as yet) geniuses of our time. A more likely scenario is that you can hear a difference in the recordings, but you can't quite figure out what actually makes that difference. The good news is that anyone who reaches the stage of recognising deficiencies in their own recordings is well on the way towards being a good engineer.

It would be very easy to put down any lack of professionalism to your equipment and say that the mixer isn't good enough or the multitrack isn't up to scratch. In fact, the sound quality achievable on modern semi-professional equipment is very close to that obtainable in a pro studio. Indeed, if you had a Soundcraft Spirit mixer or equivalent matched with an Alesis ADAT or Tascam DA88 mixing onto DAT, then you would be hard pressed to measure any technical difference between your setup and the best studios with the biggest mixing consoles. The differences must be elsewhere.

As you already know that this Hands On is about microphones, then it's pretty obvious that I am going to suggest that you acquire a better quality microphone for your work. But how good — and how expensive — does the mic have to be? What makes the difference between a good mic and an average one? And precisely what benefit does a better quality mic have on the recording? Let's find out...

HOW GOOD IS GOOD?



Modern mics are very good — there's no doubt about that, only about what precisely the word 'good' means. If I had to start again from scratch and select a microphone kit I would be looking in the catalogues of the major mic manufacturers — AKG, Beyer, Bruel and Kjaer, Electrovoice, Neumann, Sanken, Schoeps, Sennheiser and Shure, among others.

I would select a number of Shure SM57s or SM58s at a relatively low price, safe in the knowledge that these have been standard rock 'n' roll mics for years, and I'll use these when I want the dynamic mic sound. I'll also select a couple of medium price capacitor mics, such as the AKG C460 series or Neumann KM100 series, because they are always useful to have around. But, most importantly, I would also buy at least one very high quality microphone for vocals, which might be a Neumann U87, AKG C414 or Beyer MC740.

The first two of these have been around for donkey's years in their various incarnations and are to be found in just about every serious sound recording and broadcasting establishment in the world. The Beyer MC740 is a bit more recent, but it's a high quality mic in the same style. These aren't the only high quality mics, and other contenders for the studio dollar include the AKG 'Tube', Neumann TLM170 and U47. And how much can you pay for one of these mics? Unfortunately we are talking about nearly a grand, or more, but believe me it will be money well spent.

Besides the U87, C414 and MC740, I have also chosen to illustrate this article with the Sanken CU41 — one of the most expensive microphones available, and one that's fairly well-known in the industry. A shiny new Sanken CU41 will cost £2360 (including VAT, excluding haggling). I suppose I also should mention that in my view the main use of one of these is as half of a stereo pair. Try not to think about the cost!

WHY SPEND SO MUCH?



So why spend all this money on a microphone, or microphones, when you can spend much less and still get a flat frequency response and a crisp clear sound? The answer is that some mics have that certain 'something' that make them special. It's very difficult to say what it is, but once you have compared one of these mics against an 'ordinary' £300-400 model then you'll know what the difference is.

This difference is most marked when you are recording in stereo with two mics for overall pickup, and also when you are recording vocals, which brings me back to my first point: with relatively few exceptions you will find that most commercially successful recordings are made using these very high quality mics for the vocals. It makes the difference between a product that will stay on the shelf and a product that people in their thousands will buy. Yes really!

NEUMANN U87



Way back in the mists of time, the engineers at Neumann decided to make a mic that would beat the best then currently available. As was the style at the time, it would have a fairly large diaphragm, and it would operate with those new-fangled transistors which were just beginning to oust valves as the active circuit device of choice. Add to that powering from a 48V phantom power supply — at a time when it was still quite common for mics to use inconvenient dedicated mains power supplies — and the option of an internal 22.5V battery and you had what was considered in those days a very desirable mic.

The strange thing is that the Neumann U87, now reincarnated as the U87 Ai, is still a very desirable mic after all these years. I find it very surprising that as technology makes such tangible improvements in every other field of sound recording equipment, that the old mic designs, tweaked for lower noise and higher SPLs, are still subjectively among the best.

Like the AKG C414 and Beyer MC740, the Neumann U87 is a multi-pattern mic with a double diaphragm. The outputs of the two diaphragms are combined within the mic to give omnidirectional, cardioid or figure-of-eight patterns. I'd be willing to bet, however, that most U87s are left set to cardioid for at least 364 days of the year.

Compared to modern compact microphones the U87 is big and bulky, which is partially the result of the large diaphragm. Once upon a time, diaphragms had to be large to capture enough sound energy to produce a reasonable signal to noise ratio at the output. In fact, even now you would expect a large diaphragm mic to have a better noise performance. The problem the engineers had with the large diaphragm, of this mic and similar ones, was that the mass of the diaphragm created a resonant frequency which was within the audible range. If you look at the frequency Response chart of the Neumann U87 Ai you will see a peak at around 10kHz which is probably produced as a result of this resonance. The engineers had a problem with this, because it didn't look right on paper, so they started designing small diaphragm mics which measured better but somehow didn't have the same sound that people liked, and still like.

Microphones generally don't have much in the way of controls. I imagine that one day they will have LCD readouts and up/down nudge buttons like the rest of the equipment we have to deal with. They will probably also come dedicated software running on a Mac or Atari to optimise the mic's performance for your particular task. Anyway, for now we only have to deal with three switches on the U87, which I would say is about the right number.



"Old mics never go away, and in fact if they go the way of valve models like the Neumann U67 and AKG C12 the mics described here will increase in value as they age."


On the front (you can always identify the front of a mic by the maker's badge — Lenny Kravitz obviously couldn't on his 'Are You Gonna Go My Way?' video!) is the pattern switch selecting omni, cardioid, or figure-of-eight. Around the back are switches to set a 10dB attenuation and a low frequency roll-off.

But why should you need these facilities on the mic when you can more easily adjust gain and EQ from the console? The answer to this question is that a capacitor mic consists of two parts — the capsule which picks up the sound, and the amplifier which makes the signal strong enough to travel down more than a hundred metres of cable if necessary. The capabilities on the amplifier are limited by the maximum of 48V available from the power supply, so with an exceptionally strong sound source, such as a close miked drum, you would risk clipping the amplifier, causing distortion. Also, it's quite possible to get high levels of low frequencies finding their way into the mic and these are again best disposed of at source. The attenuator is only single stage with a fixed 10dB cut. You would probably still need to make sure that Pavarotti stands well back from the mic.

As well as vocals, the U87 is also widely used for orchestral miking, not so much as an overall stereo pair, but as individual section mics. Having spent a lot of money on your U87, you might not want to put it within 10 metres of a drummer, but in fact the U87 has often been used for close miking the kit. It's a bit bulky for the job perhaps, but if you have a drummer who is willing to shift his kit around a bit the U87 will give a nice solid drum sound.

AKG C414



It must be frustrating for microphone designers when they are full of ideas for brand new microphone designs, but all the customers want is improved versions of the mics they know and love. Like the Neumann U87, the AKG C414 has been in the catalogue for a long long time and is a very popular microphone. Once again, this is a multi-pattern mic with a double diaphragm. One characteristic of multi-pattern mics is that you don't point them lengthways at the sound source, they are positioned sideways on so that the sound strikes the diaphragm squarely. This doesn't cause any problem to sound engineers, since even if you have never met one of these mics before you can hear that the sound is wrong and reposition it accordingly. I have, however, met musicians who thought that the mic position was wrong and 'helpfully' adjusted it themselves. Like the U87, the C414 has the maker's name and logo at the front so you know which way round the mic goes.

The AKG C414 currently comes in two versions, the C414B-ULS (can you imagine any sound engineer saying, "Pass me the AKG C414B hyphen ULS please", to his assistant?) and the C414B-TL. The ULS version is the standard model, and like most other professional mics it has an output transformer to drive an interference-cancelling balanced line. Although transformers are useful devices, they need to be large to work perfectly at high levels of low frequency. The maximum sound pressure level (SPL) spec for the ULS is 140dB SPL at 1kHz and 134dB SPL at other frequencies between 30Hz and 20kHz. With the TL model, which has a transformerless output stage, the maximum level is 140dB SPL at all frequencies between 30Hz and 20kHz, which is obviously a significant improvement. 140dB SPL is, by the way, very loud.

The AKG C414B-ULS and TL have the same combination of switches as the Neumann U87, but here they are a bit smaller and fiddlier. The 414 has four polar patterns: cardioid, hypercardioid, omnidirectional and figure-of-eight. The attenuation switch offers -10dB and -20dB (raising the maximum level to 160dB SPL!), and the filter gives roll off frequencies of 75Hz and 150Hz.

BEYER MC740



The Beyer MC740, or MC740 N (C) to give it its full title, is a relative newcomer compared to the U87 and C414. Obviously Beyer wanted to get a slice of the prestigious large-diaphragm action, and a very good job they have made of it too. Just to go one better, the MC740 offers five polar patterns, adding a wide cardioid to the usual four. Although this might seem like overkill for vocals (do you know any vocalists with a wide cardioid mouth?), changing the polar pattern in all three mics subtly changes the bass response and the overall 'warmth' of the mic.

Some engineers, for instance, use cardioid for lead vocals and omni for backing vocals, so-the lead stands out from the crowd just that little bit, even before making adjustments on the faders. Should you not fancy the idea of running into the studio to change the polar pattern yourself, or diverting your assistant from coffee making duties, you can buy the MC740 N (C/5) version of the mic, which operates from the MSG 740 power supply unit offering remote control over the mic's pattern. The MC740 has switches for 10dB attenuation and low frequency cut, similar to the Neumann U87.

SANKEN CU41



Strange as it may seem, some microphones are not made in Austria and Germany. The Sanken CU41 comes from the land of the rising synthesizer and is one of the most expensive mics on the market — the list price is around £2360. Introduced in 1983, the CU41 is already well established and the price is, in terms of what you get for your money, quite justifiable. So what, you may ask, do you get from this mic that you don't get at half the price from a Neumann U87, AKG C414 or Beyer MC740?

You'll know as soon as you pick up this mic that you are handling a precision instrument. I would say that it oozes quality like an expensive Swiss watch if it wasn't for the fact that the comparison would be better made the other way round. Exceptional build quality aside, what this microphone has that others don't is an extra diaphragm. One diaphragm handles low frequencies and the other smaller diaphragm handles the highs — a bit like a loudspeaker in reverse where you find a large woofer and a tiny tweeter, linked together via a frequency dividing network, or crossover.

In most microphones the response has been optimised for on-axis pickup, which usually means in effect that the frequency response at angles other than 90° to the mic's 'line of fire' is rather less than flat, sometimes markedly so. The response of the CU41 is practically flat from 125Hz to 12.5kHz from the front all the way round the side as far as 120° — a remarkable achievement which gives the CU41 a incredibly solid sound. This comes into its own when you use two CU41s (and to hell with the expense!) as a stereo pair. As part of its 'no-compromise' design, the Sanken CU41 is cardioid only, with no attenuator and no filter. It is quite sensitive to mechanical noise — Sanken recommend using the S-41 shock absorbing stand adaptor.

USING QUALITY MICS



When you have achieved the status of having one of these very expensive quality microphones in your studio, the first rule of operation is 'don't drop it'. In all seriousness, these mics are quite robust but they will repay care and consideration with two decades or more of operation. Old mics never go away, and in fact if they go the way of valve models like the Neumann U67 and AKG C12 the mics described here will increase in value as they age.

Once the mic is mounted firmly on its stand, probably the first thing to do is discard any thoughts of using the slip-on foam windshield which you may have acquired with the mic. As far as I can see, the only advantage they offer is that they keep spit out of the mic, and they might have some attraction for people who prefer a muffled sound. All of these mics are sensitive to popping, however, and you will need to take action to prevent 'p' and 'b' sounds creating undesirable low frequency peaks on your recording. It is currently fashionable to use a stocking-on-a-coathanger pop filter in front of the mic, and although the home made version can look crude it certainly works. It also has the additional advantage that it keeps the vocalist at a fixed distance from the mic.

All three manufacturers have such pop screens in their catalogues — at rather more than the £0.00 that home made ones cost. Neumann's PS20 and AKG's PF20 (the similarity in the names is entirely coincidental) can be stand mounted, and are probably more versatile then Beyer's clip-on PS740. If you can't afford a name brand pop screen — and let's face it, you've probably broken the bank already — then you could use the alternative technique of placing the microphone so that the diaphragm points at the mouth, but not in the direct line of fire of the breath. To do this you really need to have the mic above the level of the mouth and you should tell the vocalist not to sing directly at it.

I hope this has been interesting reading for you, but you may be thinking that at list prices approaching or exceeding the thousand pound mark all this is rather academic. The good news is that these mics are available from hire companies at rates that put them well within the scope of anyone who is serious about recording and wants to get the best result possible, particularly on the all-important vocals.

Hire companies are unfortunately mostly based in London, but commercial studios worthy of the name have at least one high quality mic, and you could consider taking your project into a studio to do the vocals, as long as they use the same tape format as you. I strongly recommend exploring the world of high quality mics — It really will make a big difference to your recording.


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A Touch Of Magic

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Rack Attack!


Sound On Sound - Copyright: SOS Publications Ltd.
The contents of this magazine are re-published here with the kind permission of SOS Publications Ltd.

 

Sound On Sound - May 1993

Topic:

Microphones


Feature by David Mellor

Previous article in this issue:

> A Touch Of Magic

Next article in this issue:

> Rack Attack!


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