Studio engineer Gareth Stuart puts this new VLM range of microphones through their collective paces.
Of the six Audix microphones under review, five come with a handy protective vinyl pouch and mic clip. The bottom of the range CD7H mic comes with a 15 metre XLR-to-jack lead instead, which I suppose compensates for the lack of a pouch. One minor oversight here is that the mic clips supplied do not conform to the standard 5/8-inch thread, so an adaptor is necessary (an extra couple of pounds should cover it) for fixing onto a mic stand.
The unique selling point of the Audix range is VLM technology. So what is it, how does it work, and should it influence your decision to buy VLM mics rather than traditional dynamic mics?
VLM stands for 'very low mass', and refers to the mass of the microphone diaphragm. Audix claim that this technology "represents the first major innovation in microphone technology in over a decade". Can this be true? I thought the working mechanism of the Sennheiser MKH40, using the radio frequency principle, was extremely innovative, and that was just over a year ago. Anyway, whether it's true or not, VLM technology does offer several advantages: a faster reaction time of the diaphragm, wider frequency response, lower handling noise, better tolerance of high sound pressure levels (up to 140dB), and improved off-axis rejection of unwanted signals. All this results in a more sensitive response than the typical dynamic microphone.
But how important is greater sensitivity in a dynamic mic if the normal applications are for close-miking of percussion, amplified instruments, and hand-held vocals? Well, I suppose the simple answer is that any technological advance which improves the performance of a dynamic microphone must be welcomed, so long as the research and development of that technology doesn't jeopardise the mic's competitive performance against traditional dynamic mics.
The Audix mics, or at least the top models in the range, would seem to be competing with the Shure SM58 and SM57, which currently retail at £120 (plus VAT). The Audix mics are priced as follows: OM1 £122, OM2 £118, UD360 £86, UD300 £80, UD50D £56, and CD7H £40 (all plus VAT). Let's look at each model in turn...
OM1 This is the flagship of the series, which Audix describe as being "like having a condensor in a dynamic". That's quite a bold statement to make, so in several practical tests I compared it and the rest of the range with a true condensor mic - the AKG 414. (See later.) The OMI has a hyper-cardioid polar pattern (not omnidirectional, as its name might suggest). It stands apart from the other mics in the series thanks to its interchangeable ball grille. It is sold with the standard hemispheric wire mesh grille but allows a narrow cylindrical 'probe cap' to be fitted, which considerably widens its applications from purely vocal to acoustic and amplified instrument miking. The review package didn't include this optional extra, but I decided to test the OM1's response to both vocal and instrumental recording anyway.
The OM1 frequency response ranges from 50Hz-18kHz and is 'flat' from 200Hz to 2kHz. Below 200Hz the response tails off at a rate of approximately 5dB per octave to 50Hz, but below that frequency no figures are given. This is not surprising as the bass response has had to be curbed to cope with handling noise. Above 2kHz the response climbs sharply by around 8dB in total to a pinnacle at 6-7kHz, peaking again - but at a lower level this time - at 9-10kHz. Above this frequency the OM1 tails off rapidly by at least 12dB per octave and comes to rest at 18kHz, 18dB below the maximum peak level.
These peaks are sometimes known as 'presence peaks', and they certainly give the mic a lively sound. They coincide with that area of the frequency spectrum most sensitive to the human ear, making for maximum clarity. All the microphones in the Audix range feature similar presence peaks.
OM2 This looks very different from the other mics - slim, cylindrical, and with a torch-like ball grille - but it is most like the OM1 in character, having a similarly high rejection of off-axis sounds and hyper-cardioid pickup response. However, it is more flexible than its counterpart, due to the extended frequency response, and has intended uses as both an instrumental and vocal microphone. Frequency response ranges from 40Hz-20kHz, and this produces a much more present and full-bodied sound than the OM1.
UD300 & UD360 These are both cardioid mics and, as you might expect, feature lower elimination of off-axis sounds. The one main distinguishing feature between the two mics is the on/off switch found on the UD360. Both mics are intended for instrumental and vocal use but are less sensitive than the two OM models (they're also cheaper). Their frequency responses are quite similar, with the UD360 giving a little more boost in the 100-400Hz band than the UD300.
UD50D The UD50D also has a cardioid response but a poorer frequency response than the other mics. Its main feature is a dual impedance switch allowing the user to alternate between high and low impedance operation as required.
CD7H A budget microphone with a cardioid response, a more limited frequency response than the UD50D, and a fixed (high) impedance of 50Kohm.
Armed with the above information, I proceeded with several practical tests based on the manufacturer's specifications and intended uses for the individual microphones. To ensure that I had some point of reference when appraising the mics, I ran all my tests using two other microphones alongside the Audix models, both of which were familiar to me - an AKG 414 and an AKG D12. Admittedly, the 414 is a more expensive mic than any of the Audix models, but as a high quality condensor it seemed as good a reference as any. The D12 is a typical dynamic mic in that its frequency response ranges from 40Hz-15kHz. However, it has no presence peaks in its response and doesn't utilise VLM technology.
For each test, the eight microphones (six Audix plus two AKG) were placed on stands and arranged as close together as possible - for coincident octet recording! It would have been better to have been able to place each microphone in the exact same position at the same time, in order to make totally meaningful comparisons, but I did my best. Each test was recorded on eight separate tracks of a Fostex E16 tape recorder, so as to facilitate immediate comparisons, and the following instruments/ voices were recorded:
- Acoustic piano
- Acoustic guitar
- Electric guitar
- Alto saxophone
- Female soprano voice
- Male bass voice
Before commencing the tests, I used an electronic metronome placed three centimetres away from each microphone to help equate their output levels. I only used this form of level-constant in the first of the recordings, purely to gauge the different amounts of gain needed to generate similar output levels (at that distance). This produced various gain settings - the AKG 414 needing least, and the Audix CD7H needing most amplification.
As you might expect, when the mics were moved further away from the sound source the changes in output level varied widely, dropping quite substantially with increasing distance. The AKG 414, however, remained very sensitive to the distant sound source, which is perhaps a little blow to the OM1's "condensor in a dynamic" claim. Without question, all the mics performed much better when close to the source, as seen in the other tests. The following table highlights the strengths and weaknesses of each microphone:
|Source||1st Choice||2nd Choice|
I certainly think the top four mics in the Audix range - the OM1, OM2, UD360 and UD300 - are worth using for 'close' studio miking. The other two models, the UD50D and CD7H, I simply wouldn't recommend. The top four mics may well be even better suited to PA use, but in the light of my studio tests I'm not really qualified to speculate on that. Certainly, the recording tests yielded very pleasing results, especially on voice and acoustic guitar. All the mics are very well made, and I'd expect them to survive many a rough knock if put to use regularly for PA work. In the hand, they feel well balanced and chunky. The OM2, because of its slimline cylindrical design, is particularly comfortable to hold for lengthy periods of time.
As I mentioned earlier, the Audix microphones' most obvious competitors are probably the Shure SM58 and SM57. Shure quote frequency responses of 40Hz-15kHz for these, and both mics feature presence peaks, so going by specs alone it would appear that the VLM technology has given Audix the edge. However, as I don't tend to make decisions based purely on paper specs, I would recommend you give these mics a trial run alongside the old 'standards'.
As to Audix's claim that the OM1 is "like having a condensor in a dynamic", I think it would be closer to the mark to describe the OM1 as 'a dynamic with all the features you'd expect from a top-of-the-range product plus the benefits of a condensor's sensitivity and extended frequency response' - and all for a very reasonable price.
Rose-Morris & Co Ltd, (Contact Details).
Review by Gareth Stuart
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