The latest offering from AKG, designated D321, is an addition to their much respected '300 Series' of microphones. Like the other models in this range (D310, D320 and the outstanding D330 BT), it is a rugged moving-coil design, intended primarily for hand-held vocal use, but with a performance that also facilitates employment with a variety of instrumental sources.

The D321 retains much of the distinctive styling that characterises the 300 Series, in particular the horizontally slotted lower head region. However the bright satin chrome finish of previous models has been replaced by an attractive dark grey metallic enamel.

The slotted housing is more than just decoration, for its purpose is to allow a certain amount of sound to reach the rear of the transducer, in addition to that entering from the front. This arrangement, referred to as pressure gradient operation, enables the microphone to achieve its directional effect by a complex series of phase cancellations. The die-cast zinc body is surprisingly lightweight, but the design is well balanced and handles very pleasantly. A heavy gauge wire-mesh elongated nose-cone completes the streamlined appearance and conceals the strong, resilient plastic cage which surrounds the transducer, further contributing to the impression of exceptionally abuse-proof construction.

Assembly

The complete transducer assembly, which is fitted with a hum-compensation coil to combat noise from stray magnetic fields, can be renewed, if necessary, by just two soldered joints, making for easy serviceability. In traditional moving-coil design, the transducer has needed to be effectively decoupled from the microphone body, using some form of resilient mounting, in order to prevent impact noise and handling effects from being transmitted directly to the diaphragm. However, the D321 takes a radically different approach, employing no conventional shock-mount element in its construction. Instead, the magnet is flexibly mounted relative to the diaphragm (absolute rigidity is normally required in this area), with the matched resonant frequencies of the components and their resulting combined vibrational behaviour, claimed to reduce handling noise by at least 20dB more than conventional transducers. New models from AKG invariably display such evidence of the constant innovation in the field of transducer technology that has given the company such an impressive list of significant worldwide patents.

The D321 incorporates a three-pin male XLR output connector, wired for standard phasing, with Pin 2 'hot' (ie. a positive air pressure on the diaphragm will result in a positive voltage at Pin 2), Pin 3 'cold' or 'return' and Pin 1 ground. The output is low impedance (nominally 300 ohms at 1kHz), and balanced, for maximum rejection of stray magnetic field interference - a 'balanced' mic cable employs two conductors and a separate overall screen, with any noise picked up by the cable being cancelled on reaching the 'balanced' input, whereas 'unbalanced' operation, using just a single inner conductor with the screen acting also as the return wire, has a much greater susceptibility to such 'pick-up' and is not often encountered in professional microphone systems.

Response Tailoring

The specified frequency response of the D321 is an unqualified 40Hz to 20kHz, but both the quoted extremes are actually well down in level. However, such figures don't really tell you very much at all in the case of a stage vocal mic, for in this application a theoretically perfect 'wide open and ruler-flat' response would be more of a liability than an asset, merely contributing to feedback at both ends of the spectrum, whilst doing nothing to enhance the sound of the voice, and therefore a certain amount of 'response tailoring' is to be expected in this type of mic.

It is well known that when a directional microphone is placed very near to a sound source, low frequencies are considerably boosted (the phenomenon is referred to as 'proximity effect'). Consequently, hand-held vocal microphones which are invariably used close to the mouth, normally have a portion of their low frequency response reduced to compensate for this. The D321 rolls off frequencies below 200Hz at about 6dB per octave, thus effectively preventing the bottom-end becoming uncontrolled and 'boomy', whilst still allowing the vocalist the facility of employing an acceptable amount of the enhanced warmth and power generated by close-up working.

A dedicated vocal microphone will usually also employ some form of 'presence boost' in its response, to give additional clarity and improve the intelligibility of speech or vocals. However, a sharp peak centred in the upper midrange, such as is often encountered in cheaper vocal mics, may give an initially pleasing impression, but will rapidly be found to have a rather fatiguing effect on the listener, as well as producing a very unnatural sound when presented with a wide-range acoustic source.

In contrast, the response of the D321 rises quite smoothly from about 2kHz, providing a maximum lift of +6dB at around 5 to 6kHz, before falling away equally gently and returning to a flat response at 15kHz. By using this fairly subtle emphasis, centred quite high in the frequency spectrum, in conjunction with a well controlled low frequency area, this model manages to avoid any tendency towards harshness or excessively obvious colouration of the sound, whilst still providing a well articulated and bright vocal sound. When used with a PA system of sufficient quality, the D321 gives the subjective impression of a more extended high frequency response than many dynamic vocal mics, resulting in a pleasingly smooth and 'open' quality in the reproduction of voices.

The D321 has a 'hypercardioid' pick-up pattern, which means that it is less sensitive at the sides than a true cardioid model, with the effective working area being limited to a relatively small arc on-axis with the mic. A narrow acceptance angle such as this (approx 35°) causes no problems when a mic is to be used predominantly at close range, as is invariably the case under stage conditions, whilst the superior rejection of off-axis sounds it provides, assists in minimising the risk of feedback when high levels are used.

The excellent feedback resistance displayed by this model is indicative not only of its tight directionality, but also of a well controlled polar frequency response (often specified graphically in the form of a 'polar diagram', representing the extent of the microphone's ability to respond equally to sounds arriving from different directions), which is seemingly free of the type of serious off-axis deviation that can provoke an early onset of ringing, and thus artificially lower the gain-before-feedback threshold. A further benefit of the narrow hypercardioid pick-up pattern under stage conditions, is the improved separation it creates, offering the maximum discrimination against 'spill' or crosstalk from other sound sources, consequently giving the system operator more control over each signal.

Performance Uses

The well balanced performance of the D321 makes it rather more suited than many dedicated vocal mics to use in certain instrumental applications, both in live sound reinforcement and recording. Dynamic mics are traditionally favoured in very high sound pressure level applications such as with close-miked brass instruments (the onboard pre-amps of condenser mics being considered vulnerable to overload), and the D321's contoured, rising midrange response seems to make it particularly well suited to this type of source, offering an impressive, incisive brass sound. Reed instruments, such as saxophones, can also be reproduced very well if an intimate, close-miked sound is desired, although when more distant placements are used (perhaps 18" or more), as is often preferable in the studio to achieve a more integrated sound, the results tend to lack a little in warmth, possibly indicating the extent to which the performance of this model has been optimised for close mic placements.

As expected, the D321 performed very well when used for miking up instrument amplifiers, sounding well rounded and full, whilst successfully avoiding the unpleasantly 'brittle' quality that often results from close-miking an overdriven guitar speaker.

Although a dynamic vocal mic such as this would not seem the most natural choice for use with acoustic guitar, the informative Owner's Manual recommends it, and in fact some surprisingly creditable results were achieved, with the tight directionality proving an asset in PA work with this type of instrument.

On the drum kit, the D321 readily produced a most respectable, crisp snare drum sound, assisted only by a little lower midrange EQ cut, at around 600Hz, and also offered plenty of scope for a variety of typical close-miked tomtom sounds. Overhead cymbal use proved less successful, but this was not entirely unexpected as very few vocal mics are suited to this application, the majority tending to make cymbals and hi-hat sound rather 'splashy' and harsh, whilst the drums, picked up without the assistance of any proximity effect, can sound rather thin and distant.

Vocal Results

Not unnaturally, the D321's main area of excellence is as a vocal microphone, its fine performance in PA use standing up very well under studio conditions, displaying an impressively detailed top-end that necessitated very little extra equalisation. With close-up use it provides a manageable degree of added depth, without the thick or 'muddy' quality often evident in moving-coil models. The D321 cannot be said to be a neutral microphone, but its response is nevertheless well balanced and as a good vocal microphone should, it assists the sound of a voice most effectively.

Resistance to handling and impact noise is obviously an important feature of a mic primarily designed for stage use, and the innovative transducer design has obviously been effective in this area. Low frequency components such as stand-borne stage rumble are well controlled, and very little HF noise is evident when rubbing the mic body or connector.

'Popping' and 'blasting' produced by explosive breath sounds close to the mic, were effectively filtered by the integral foam screen, although I feel that the use of an additional foam 'pop' shield is always advisable when recording. Whereas a stray noise is soon forgotten in live performance, a destructive 'pop' in a recording remains a repeated source of annoyance.

Sensitivity, quoted at 1.4mV/Pa (equivalent to an open-circuit voltage of 0.14mV for the reference 74dB SPL, or -77dBV ref 1uB), is more than adequate for this type of microphone, whilst the maximum recommended sound pressure level figure of 128dB, in practice, imposes no limitations.

Summary

Like all AKG models, the D321 is supplied very well protected by a shaped foam insert within a rigid vinyl carrying case, which also houses a suitably indestructible looking stand adaptor. No lead is included, however, but it could be argued that, given the potential variety of circumstances of use for this type of product, it is perhaps preferable for the purchaser to be able to select a combination of cable and connector to suit the exact requirements of his system, rather than having any of the cost of manufacture dissipated in supplying possibly inappropriate accessories.

The high quality of performance, ruggedness and versatility of this model certainly makes it seem most reasonably priced, and with AKG's unsurpassed reputation for reliability, the D321 can be recommended as offering excellent value.

The D321 retails for £113.85 inc VAT. Further details from AKG Acoustics, (Contact Details).