A few years ago, the term 'electret' was synonymous with low cost and poor performance. Since then, the development of back-electret technology has brought us microphones offering true studio capacitor quality at dynamic mic prices. Paul White rounds up three of the best.

Most live microphones work on the so-called dynamic or moving-coil principle, which is the reverse mechanism to that employed by loudspeakers. A moving diaphragm is attached to a coil suspended in a magnetic field, resulting in an electrical current being generated which bears a direct relationship to the sound impinging upon the diaphragm. Dynamics are inexpensive to build, they're very rugged and they need no external power or batteries to make them work. However, the relatively high mass of the moving parts means that they struggle when it comes to reproducing the upper registers of the audio spectrum, while their low sensitivity makes them unsuitable for working with quiet or distant sounds.

At the other end of the scale we have the studio capacitor microphone, with its gossamer-thin, metallised plastic diaphragm, using the principles of electrostatics to convert sound energy into an electrical signal. These microphones can work over the entire audio spectrum and are very sensitive. They are also very expensive and require power to operate, usually in the form of so-called 'phantom' power, which comes from either a special power supply or from the microphone input socket of a suitable mixing console.

The less costly electret principle is ingenious but is not without its problems. In essence, electret microphones work in exactly the same way as capacitor microphones, except that instead of the diaphragm being electrically charged from an external voltage, a permanent charge is physically built into the material of the diaphragm. Exactly how this is achieved is beyond the scope of this article, but suffice it to say that a properly designed electret capsule can maintain its electrical charge for many years and often decades. The real problem is that the process of making a permanently charged diaphragm requires a thicker and consequently heavier diaphragm material. This means more mass, so we're back in the land of limited audio bandwidth and reduced sensitivity.

The electret appeared to be doomed to serve as a 'cheapo' cassette recorder mic, until someone had the rather clever idea of fixing the charged material to the stationary backplate of the capsule and using a normal metallised plastic diaphragm as the moving part. This proved to be not quite so straightforward as was anticipated, but once the engineering problems had been overcome, the outcome was a microphone that was cheaper to build than a true capacitor microphone, yet could offer the same advantages — and it didn't need phantom powering. Some power was necessary to run the integral preamplifier but a battery would suffice. Nevertheless, as most modern mixing consoles have built-in phantom powering, most serious back-electret designs offer the choice of battery or phantom operation.

Today, many of the world's best microphones are back-electrets and have high price tags, but the spin-off is a range of relatively low-cost microphones that outperform dynamic microphones in virtually every area. We've brought together three similarly-priced models from three of Europe's best-known microphone manufacturers and were pleasantly surprised both by their sound quality and their comparatively low cost. All three are low-impedance, unidirectional (or cardioid) pattern mics designed primarily for vocal use.

All may be used either live or in the studio and have a variety of secondary applications, such as recording acoustic instruments. It is also worthwhile recording electric guitar using a back-electret rather than dynamic microphone as it gives a brighter, more 'American' sound.

BEYER MCE80 TG

The suffix TG stands for Tour Group, Beyer's range of vocal mics designed to be tough enough to survive life on stage as well as in the studio. Being a back-electret design, the Beyer MCE80 TG is the odd one out, as all the others in the Tour Group series are dynamic microphones. Conventional capacitor microphones are seldom used on stage, due to their inherently fragile nature, whereas a properly designed back-electret model is as tough as a dynamic. This particular model, as is to be expected for a vocal microphone, has a cardioid or unidirectional pickup pattern, meaning that it picks up sound predominantly from one direction. This not only cuts down on unwanted sound pickup from other sources, but also helps prevent feedback in live situations, where sound from the speakers enters the microphones and is recirculated at an ever-increasing level until it builds up into an uncontrollable screech.

With a frequency response extending from 50Hz to over 18kHz, the MCE80 TG displays a nominally flat response but with a slight, broad hump between 2 and 5kHz, which is responsible for its bright, forward character. This helps maintain clarity of diction in a live situation, but is also useful in the studio for capturing an intimate, breathy vocal performance or for registering the finer nuances of tone of a steel-strung acoustic guitar.

"All three of the microphones reviewed cost less than a top-flight dynamic microphone yet they have a wider usable frequency response and are significantly more sensitive."

Though finished in black, the body is in fact made from brass and screws into two pieces to allow the battery to be fitted. This is a standard 1.5V AA cell which can be used as an alternative to phantom powering. The battery can be left in place when phantom power is being used and it will not be drained, but it is important to switch off the microphone when the phantom power is turned off, otherwise the battery will go flat. In normal use, the battery life is around 80 hours.

As is standard practice with any serious microphone, the handle terminates in an XLR connector which accepts a standard XLR microphone lead (not supplied). The mesh windshield unscrews to reveal the microphone capsule, an unassuming cylinder about the size of an aspirin, perched on top of a plastic support structure. Directly below the windshield, on the handle, is a three-position switch which turns the microphone on, off, or into the battery test position; this causes the adjacent red LED to illuminate if a healthy battery is installed. The microphone is supplied in an elegant protective case with clip and stand adaptor.

In Use

On plugging in the MCE80 TG, the first thing to strike me was the clarity of the sound. Used at any distance, the sound is bright but without undue harshness and is very transparent. Though the sound could never be described as thin, there's little in the way of warmth unless the microphone is used very close to the sound source, in which case the proximity effect comes into play, providing a gentle lift at around 80Hz. This is very useful in live situations, as it allows a vocalist to 'work' the mic, but in the studio, larger distances are generally used to eliminate the proximity effect and to minimise any level changes caused by small movements of the performer.

The off-axis sound of the microphone is good in that the tonal quality doesn't change much if the mic is pointed at an angle to the sound source instead of directly at it. Of course the level drops, because this is, after all, a directional microphone, but there's a usable working angle of around 60 degrees. The microphone conveys a good sense of intelligibility and would probably benefit a singer who normally lacked presence and clarity. It is also ideally suited to detailed, acoustic instrumental sounds.

Further Information
Beyer MCE80TG £193.88 including VAT.

Beyerdynamic (GB) Ltd, (Contact Details).

AKG C1000S

Like the Beyer MCE80 TG, the C1000S can run from phantom or battery power, in this case a 9V PP3-type battery which will give between 100 and 200 hours of operation, depending on whether or not you're using an alkaline battery. The capsule is somewhat larger than the one used in the Beyer model and is protected by a sturdy, cylindrical basket with a foam lining. There is a recessed on/off switch on the handle but no battery test facility, and because of the large diameter of the microphone body, a special clip is provided. The aluminium body is finished in an attractive grey metallic enamel with a green trim band just above the half-way mark. A recessed, balanced XLR connector accepts a standard mic lead, which is not provided.

"Given their sensible pricing, all three microphones represent excellent value and in most applications, they far outperform a similarly priced dynamic model."

In The Studio

I've used a couple of these mics myself over the past few years and have come to know them pretty well. They have quite a warm sound for a back-electret mic, yet they also exhibit a degree of high-frequency clarity that simply isn't there with any dynamic microphone I've tried. Like most microphones, the response is only nominally flat and there are two little peaks in the response curve worth noting. There's a pretty well-defined presence peak at around 5kHz and another little wrinkle at around 9kHz. This latter peak may be intentional or may be due to interference from the basket and capsule support structure. On paper, the frequency response extends from 50Hz to 20kHz, though the high end response starts to roll off at around 17 or 18kHz. Like the Beyer model, the proximity peak occurs around 80Hz and at distances of 10mm from the microphone, a 10dB boost can be expected in this area. Again, in studio applications, the microphone is unlikely to be used close enough for the proximity effect to influence the sound.

I've used these microphones on a variety of sound sources and have found them to work especially well on vocals and acoustic guitar. A pair make a cost-effective stereo setup as well as doubling as drum overheads; they also make an interesting alternative to dynamic microphones for miking the electric guitar.

Further Information
AKG C1000S £203.28 including VAT.

AKG Acoustics Ltd, (Contact Details).

SENNHEISER 5032P

Like the other two mics, the Sennheiser 5032P can run either from an internal battery (around 100 hours from an alkaline AA cell) or from a phantom power supply in the range 12 to 48 Volts. Connection is via a standard XLR. The mesh grille unscrews to reveal a large-diameter (around 25mm), supercardioid pattern, electret capsule and extensive use is made of surface-mount electronic components to keep the size and weight of the preamp down. This is important, as the microphone is designed to be used as a hand-held, live vocal mic as well as for recording. The all-metal housing appears to be finished in black anodising, with the company name and Black Fire logo picked out in red. A case and clip are provided but, as is customary, there is no lead.

A switch is provided to turn the microphone on and off, and an attendant LED shows that the battery is functioning. A further recessed switch provides three attenuation positions at 0, -10dB and -20dB, enabling the microphone to cope with sound levels in excess of 140dB. The handle unscrews to allow access to the battery compartment and this reveals yet another switch, which brings in a low-cut filter to help suppress handling and wind noise.

The Sound

Unlike the other two microphones, which are nominally flat with discrete presence peaks in the 4 to 10kHz region, the response of this model rises gently from around 500Hz, reaching a maximum at around 6kHz before gently falling away again. Being a cardioid pattern mic, there is also a proximity effect which gives rise to a bass boost if used at very close working distances. The sensitivity of the microphone is subjectively similar to that of the AKG model reviewed here, though its supercardioid pickup pattern gives it the tightest focus of the bunch. In the studio, this makes little difference, but in live performance situations, the feedback rejection capabilities of this microphone are impressive.

"As vocal microphones, all have their strengths, though which one is best depends largely on the vocal character of the performer and on whether you like a bright, airy sound or a touch more warmth."

Despite the rising response curve, which provides almost 10dB of high-frequency boost over quite a large part of the mid and upper audio spectrum, the microphone has a very natural sound, with no tendency towards thinness. It doesn't have the warmth of the AKG model but is slightly warmer than the Beyer. Because the presence boost is applied over such a wide range, the response is smooth rather than being in any way peaky, which helps clarity of diction but not at the expense of obviously colouring the sound. The microphone is well-suited to a wide range of vocal styles and also provides a pretty true representation of acoustic instruments and percussion.

Further Information
Sennheiser 5032P £352.50 including VAT.

Sennheiser UK Ltd, (Contact Details).

Summary

All three of the microphones reviewed cost less than a top-flight dynamic microphone yet they have a wider usable frequency response and are significantly more sensitive. As is the case with most microphones intended for serious applications, they have balanced, low-impedance outputs and require a standard XLR microphone cable. All can run from either internal betteries or phantom power. Balanced microphones may be used with unbalanced equipment (such as most Portastudios), but a special XLR to unbalanced jack lead will be required.

The AKG seems marginally the most sensitive mic of the bunch and it also has the most distinctive sound — though that isn't the same as saying it's the most accurate. In comparison with the other mics, it seems almost artificially warm, yet it is a warmth that works well with most vocalists and doesn't detract from its clarity in any way. In some ways, it behaves like a large diaphragm capacitor microphone, most of which are flattering in some way rather than being particularly accurate. For those users who don't have access to phantom power, the AKG will cost slightly more to run in the way of batteries; though it has a longer battery life than the two other models, the more expensive PP3 battery makes the hourly running cost around three times as high. Even so, this still works out at around only 2p per hour, which means it isn't worth losing any sleep over.

By comparison, the Beyer and Sennheiser models produce a subjectively more precise, detailed sound, especially at the high end, and though they both have a good low end response, they don't seem to 'hype' the bass end in quite the same way. If anything, the Sennheiser model is a touch warmer sounding than the Beyer. As vocal microphones, all have their strengths, though which one is best depends largely on the vocal character of the performer and on whether you like a bright, airy sound or a touch more warmth. All are excellent on acoustic guitar, an area in which most dynamic mics tend to produce disappointing results, and though they do sound different, they all produce a 'quality' sound.

I've used a pair of AKG C1000S's as drum overheads for some years now and find them very suitable. The bright, transparent quality of the Beyer and the open clarity of Sennheiser indicate that these would work well in this application too, though I didn't have a chance to try them in this role.

Given their sensible pricing, all three microphones represent excellent value, and in most applications, they far out-perform a similarly priced dynamic model. They are sensitive enough to allow acoustic instruments to be recorded at a reasonable distance without noise becoming a problem, and the frequency response is wide enough to do justice to percussion or plucked string sounds without losing the transient detail. Each has its own distinctive tonal character, making it hard to come out hard in favour of one or the other, but then part of the art of recording is choosing the right microphone for each situation. I feel I can say with confidence that, within this price range, you'd not be disappointed by any of these mics, especially if your experience until now has been restricted to dynamic models. A top-flight, studio capacitor microphone will certainly outperform any of these models in terms of sensitivity and overall quality of sound, but given the immense price differential, I think you'd be surprised at by how little.