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AKG CMS Modular Condenser Microphone System

Dave Lockwood presents his report on the C451 condenser mic with associated capsules and passes on a few tips on how he uses them in the studio.

The CMS series by AKG, pioneered the concept of the modular condenser microphone system, and continues to be renowned for its excellent performance and inherent flexibility. Based on the C451 FET preamplifier, designed for universal phantom powering (9-52V), or the '48V only' C452 version, the system offers a most comprehensive range of capsules and inserts to facilitate the assembly of a suitable configuration for almost any conceivable application.

The basic C451E model is a very slim and lightweight tubular unit, almost entirely without feature, other than an XLR output connector at one end, and the capsule fitting at the other, with the alternative preamp modules; the C451EB and C452EB, being practically identical, with just the addition of a deeply recessed bass roll-off switch. I have always found this to be a useful facility on these microphones, for its action is variable and can be selected to subtly roll off frequencies below 75Hz right down to -7dB at 50Hz, or to operate rather more noticeably with a cut-off point at 150Hz, thus giving -20dB roll-off at 50Hz.

All the preamp models feature a low impedance output (200 Ohms), which is balanced, with the standard pin configuration of Pin 2 'hot' or in-phase, Pin 3 'cold' or out-phase, and Pin 1 earth or ground according to your preferred terminology.

CK1 Capsule

Although a number of different capsules are available, the standard cardioid capsule, designated CK1, is by far the most commonly encountered for it is the most practical for normal music recording applications. The CK1's specified frequency response of 20Hz to 20kHz is impressively flat, with just a very gentle upward slope above 1kHz which rises to +3dB at 5kHz before levelling off, while the bottom-end response slopes away slightly between 50 and 20Hz, thus avoiding any low frequency noise problems in an area where there is normally very little useful musical information.

This results in the typically smooth but detailed sound of the C451/CK1 combination, which is capable of giving a fine performance in a wide variety of both distant and close-miked applications. The classic cardioid pickup pattern is almost perfectly independent of frequency, resulting in negligible off-axis colouration, and making this model excellently suited to crossed-pair stereo techniques, where even the widest angles of incidence (the relative angle from which sound arrives at the mic) will usually be contributing some significant information.


In close-miked work, the C451 can be particularly favoured where a clean, bright top-end is desired; small plucked stringed instruments such as acoustic guitars and mandolins are reproduced with a 'sparkling' quality that manages to retain the delicacy of their sound, whilst revealing its transient nature.

I often employ C451/CK1s in pairs when recording acoustic guitars, placing the mics up to eighteen inches apart, with one pointed at the body, opposite or behind the bridge, and the other further down towards the neck. When panned to opposite sides of the stereo mix, this can give an unusual and pleasant sense of ambience and movement to the sound, with the left hand's fingering noises and the bright harmonic content of the neck microphone's signal being displaced, and clearly discernible as a separate source to the main body of the sound and the percussive effects of the right hand's technique.

This is particularly effective for an acoustic guitar that is integrated into a rhythm track. However, the sound image instability can be detrimental to the sound of a more prominently heard instrument, and consequently I would always tend to record something like a solo classical guitar with a coincident stereo technique, the mic capsules being placed as close as possible, at an angle somewhere between 90 and 120 degrees.

The C451's natural and uncoloured sound allows it to perform very effectively as a reinforcing 'spot' microphone within an orchestral balance, giving fine results with all strings and woodwind, although very close miking is always best avoided with these types of instrument, for even such a smooth sounding microphone can tend to overemphasise bowing and finger noises, or key and breath sounds, when placed too close.

Drum Miking

A particularly fine transient response, combined with the wide frequency range, makes the C451/CK1 combination well suited to drum kit overhead use, reproducing cymbals and hi-hat with great precision and fidelity, and drums with presence and attack.

With a good sounding drum kit, in a reasonably favourable acoustic, I often prefer to dispense with conventional tom-tom mics, and pick up the whole kit with just bass drum and snare mics, and a pair of high quality condensers (usually C451s) overhead. This gives a very 'open' sound to the kit, and a lively and natural sound to the drums that I prefer to the more artificial close-miked sound, with the additional advantage of usually requiring considerably less damping and detuning of the heads, thus resulting in a happier drummer.

Experimentation is sometimes necessary to achieve the best compromise in the balance between drums and cymbals, however, I find that the uncoloured off-axis response of the C451/CK1 will allow very low positioning of overhead mics, often level with the cymbals pointing down at the toms, with the reduced sensitivity of the side area pick-up able to reproduce clean sounding cymbals that do not overpower the drums.

Among the CMS microphone accessories is a choice of 10dB and 20dB signal attenuators, which can be fitted between the capsule and preamp to prevent overload on very high level signals. I have found it advisable to employ an attenuator when using a 451 for close-miked snare drum, an application in which it performed very creditably, and also when close-miking loud and very directional brass instruments, particularly trumpets.

Piano Miking

The C451/CK1 seems to be an excellent piano microphone, with its high sensitivity (0.95mV open circuit voltage for 74dB SPL, or -61dBV), and gently rising midrange response, helping to produce a pleasingly bright sound with plenty of overtone content, which can cut through an instrumental mix, while still sounding convincingly natural. The use of two microphones is invariably preferable, even when 'stereo' piano is not required, for it can be very difficult to achieve an acceptable balance between the upper and lower portions of the keyboard with just a single directional mic.

When close-miking a piano, it is common to place one unit over the bass strings, with another close to the hammers, somewhere above the middle of the keyboard, although with certain types of music, particularly jazz where an upright acoustic bass is employed, I will place the bass-end mic also close to the hammers in order to achieve better definition and separation in the mix. I find that the smoothness of the 451's response allows me a great deal of flexibility in the use of EQ to precisely tailor a piano sound to the requirements of the music, and to complement the instruments around it.

Modular Benefits

A modular system allows different capsules to be employed with just a single preamplifier, thus enabling the user to extend the facilities of his microphone collection in a very cost-effective way. As an alternative to the standard CK1 cardioid capsule, the CK1S offers a similar performance, but with the addition of 'presence boost'. The response rises above 5kHz to +6dB at 10kHz, offering a fairly subtle enhancement of vocal or speech clarity, but without introducing the 'hardness' associated with a midrange 'presence peak'.

The CK5 capsule facilitates hand-held vocal use, for it incorporates both effective shockmounting of the transducer, and a large wind/pop shield, thus minimising handling noise and problems with explosive consonants and breath sounds. Acoustically the capsule is fairly similar to the CK1, producing the smooth and extended, natural sound that distinguishes the condenser vocal mic from the more common moving-coil models.

The CK22 is an omnidirectional capsule (equally sensitive to sound from all directions), which has built-in wind and pop filters. Its beautifully smooth and wide response is within 2dB of 'flat' from 20Hz to 20kHz, and exhibits only the slightest directionality at high frequencies. I have recently heard of CK22s being used very successfully in high quality, discrete sound reinforcement work, where the complete freedom from 'popping' and proximity effect, inherent to omnidirectional models, enables a remarkably natural sound to be produced from very close mic placements.

The other capsules in the range are highly specialised, with the CK8 and CK9 shotgun capsules being more appropriate to film and TV work, than normal music recording, although the shorter CK8 capsule has been usefully employed in 'live' recording, where high volume on-stage conditions demand particularly tight directionality in order to achieve adequate separation of sounds for multitrack recording.

Other accessories in the CMS range include a very useful series of extension tubes, for insertion between the capsule and preamp, thus allowing the placement of the tiny capsule to be optimised, even when space is at a premium, while the preamp and its bulky microphone stand are kept at a distance. This can be useful in TV work, where discreetly placed capsules on extenders can leave viewers hardly aware of the presence of microphones. To assist in accurate capsule placement, an ingenious swivel-joint insert is available, enabling the capsule to be set at any angle within a 180 degree arc, relative to the mic body or extension.


AKG's CMS system has become something of an industry standard, being inherently non-obsolescent, with new components able to be introduced to meet new or changing requirements. However, even the most modest recording system will benefit from the use of a high quality microphone, and the addition of a modular condenser system would be a considerable asset to any small microphone collection. Where no phantom power is available, a C451 can be conveniently operated by an individual battery supply (B46E), making the quality of a true condenser microphone available for use with any equipment.

The reputation of the C451 and its associated capsules relates not only to its excellent performance, but also to its proven reliability, for the CMS system maintains AKG's renowned, professional dependability. Although it is certainly not cheap, it offers a standard of performance that will never disappoint the purchaser, and can therefore be said to offer value for money, and to be a most worthwhile investment for anyone seriously interested in music recording.

The C451E retails for £97.75, CK1 capsule £64.40, CK22 capsule £126.50 - all inc VAT.

Details from AKG Acoustics Ltd, (Contact Details).

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Fostex SPA-11 Powered Monitors

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Third Generation CMF Amplifiers

Home & Studio Recording - Copyright: Music Maker Publications (UK), Future Publishing.


Home & Studio Recording - Dec 1984

Donated & scanned by: Mike Gorman

Review by Dave Lockwood

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