AZ-TEC Micro-Module Microphone
Here is an interesting idea. Take a basic microphone body with detachable ball head, and add four interchangeable plug-in transducers, each with differing frequency characteristics. Sounds like a good idea for the home multitracker who just uses one mic input signal at a time and who perhaps would like a different frequency characteristic for each instrument or vocal track. AZ-TEC of Manchester, have come up with just such an idea and in reality the units do what they claim.
Because of the uniqueness of the arrangement we thought we would go a little further in this review than we normally do. We have measured the frequency responses of the AZTEC microphone modules together with four other well-known mics for comparison.
The AZ-TEC mic body is tapered à la SM58 (shush - you know who makes that?) and is speckled dark grey in colour with a silver-coloured, ball mesh head: all of solid, accurate construction. The actual Micromodules (as they are known) are nominally of 500 ohms impedance and each has a miniature 3.5mm jack plug in its base which fixes into the main mic body. It seems that AKG make the diaphragm - moving coil part for AZ-TEC. The modules do not just rely on the miniature jack plug to hold them in place, they also screw into the body proper. When screwing in place, it pays to hold the labelled base of the module and it is unnecessary to overtighten them as the electrical contact does not rely on this. A plastic dust cap on the business end of each module protects those modules not in use.
A stand mounting clip is supplied together with a good quality mic cable terminated in an XLR for the mic end and a ¼" jack for the equipment end. The mic can, of course, be used into balanced equipment with a suitable lead. The whole system comes in a neat plastic presentation case which lays all the items before you in its many foam lined compartments.
It was obvious with the initial usage that the capsules offer differing sound spectrum balances. Two of them particularly so. We felt that AZ-TEC should supply typical curves for each module, but we understand that it is a deliberate policy not to do so. Therefore we thought HSR should 'fill the gap'.
The author has used a particular set-up for such tests over the years. One can have faith in the system, as essentially a comparison is being made and provided interpretation takes into account various likely vagaries of the system. The set-up is shown in Figure 1.
One third-octave bands of filtered white noise from a Tutching's Electronics test tape are played on a Revox B77 through that very fine loudspeaker, the Quad ESL63 full range electrostatic. The signal from the tape is displayed also on one pointer of a BBC twin pointer PPM (peak programme meter) made by Ernest Turner with Surrey Electronics drive circuitry.
The mic to be tested is placed on a stand one metre from the centre of the ESL speaker and its output (after amplification) is displayed on the other pointer of the PPM. Basically, the difference between the readings of the two pointers is noted for each of the test frequency bands. The test tape covers bands with centre frequencies between 40Hz and 10kHz. This eliminates any tape playback response errors.
The tests are done in the author's monitoring room, allowances being necessary for anomalies, particularly for frequencies below 1kHz. Single sine waves cannot be used, as standing waves are created and enormous errors produced. The bands of random frequencies (white noise) do not set up standing waves so this particular 'room' difficulty is avoided. Sine wave testing requires anechoic conditions, ie. very absorbent non-reflective boundaries (with no reverberation) - the sort of test rooms where one can hear one's own blood circulating! But ordinary listening rooms will affect the performance of a loudspeaker no matter how 'flat' its response. However, this should showas a general trend in all the mics measured and therefore allowance can be made, particularly if some reference mics are chosen that are known to be reasonably flat. The mics were all set up at the same measured distance from the ESL and from the carpeted floor.
Suffice to say, that the method does show up known differences between well known mics and always seems to be repeatable. We only made 'on axis' (direct sound) tests-evaluation of 'off axis' responses could be a subject in itself!
Let us look first of all at the frequency curves in Figure 2. Here we have three 'flat' response mics and an example of a 'tailored' response type. Room effect trends show in all the mics measured. For example, there is a common dip around 200Hz with a rise below and above this frequency. Similarly around 800Hz.
Looking particularly at the curve of the £500 plus Neumann U89 capacitor mic, we see that the HF end is particularly flat! And assuming (justifiably) that its the room disturbing things below 1 kHz, the sort of allowance to be made can be seen. The double moving coil AKG D202 is a flat response mic also and the general trends of the curve shows this. Similarly for the Beyer M201 moving coil. The Shure Unidyne B however, is a tailored response mic and just how tailored it is can be seen from its curve. The bass end is definitely curtailed and includes the room effects up to 1kHz, above this can be seen what is meant by a presence peak. This also shares with the 'flat' mics the measurement induced dip around 3kHz.
Figure 3 shows the test results for the four AZ-TEC Micromodules. The black and yellow coloured modules are the most similar but with a subtle and usable difference. The region between 1kHz and 2kHz seemingly producing the differences heard. The yellow version in fact sounds the most like the Shure Unidyne B and as the curves are similar this is indeed just as well.
The AZ-TEC white and red units deviate greatly from each other and from the other two, the white module having more below 1kHz and a noticeably early HF decay but without a presence peak as such. It's thus ideal for low frequency instruments or where the top-end needs depressing. The red module on the other hand, is entirely the opposite. Now that is what I call a presence peak. Positively mountainous with a sound to match! But usable to good effect, no doubt, in many circumstances.
AZ-TEC do not state 'this head is for this purpose and that head is for that'. Having sussed out what is going on with each, in this comparative way, at least one is better armed for the decision about which module to use.
A few words of warning. We have only tested one particular set of AZ-TEC heads. Discussion with a company representative confirms that the response variations are deliberate to each colour-coded module and we can expect a sensible repeatability with other sets. This really needs to be so if a reputation is to be garnered.
As it turned out that the sounds from the modules related very well to the measured curves, it is going to be pointless to launch into a long-winded description also. Multitrack 'pop' recording does indeed need microphones with an other than 'flat' response. Also, it is essential that the low frequencies be attenuated and so the AZ-TEC modules have rolled-off responses below 100Hz. With the exception of the white version they are also depressed relative to the presence region from 100Hz to 1kHz.The result is a forward sound from the yellow and black versions compared to the lower, middle heavy, white module. The red insert is, of course, out on its own, being very 'telephonelike' in quality as the response curve shows.
The LF cut switch, which also has an on-off position, introduces a low frequency roll-off at 6dB per octave by introducing a tantalum capacitor in series with the moving coil element. Feeding the author's mic preamps, the -3dB point is around 200Hz. It is to be expected that the turnover point will be affected by preamp input impedances different from those used. For instance, half the impedance will double the turnover frequency. For the record, the test set-up has a nominal 2 kilohm input impedance.
On the question of input impedances, this order of impedance suits mics between 200 and 600 ohms nominal source impedance. I mention this in case readers are under the impression that a 200 ohm mic must 'see' 200 ohms and that a 600 ohm mic must 'see' 600 ohms. This is not the convention, and it is usual to connect modern low impedance mics into impedances 3 to 5 (or more) times their nominal source impedance. Often however, it is matching for best noise performance that is specifically involved in a mic preamp's design when it comes to what impedance mics should be connected.
Handling noise and 'P' blast popping were generally around average with the AZ-TEC modules. The big surprise technically was the small amount of directional cardioid characteristic. This was very much below the other 'reference' mics in the test set-up. They all showed around 15dB front to back discrimination mid band, whereas the AZ-TEC only managed around 6dB. This was in fact obvious from the initial listening tests. Also the HF bands showed a marked on-axis beam: moving the mic only 10° to the side dramatically reduced the level. The 'flat' response mics overall were very much wider in their HF acceptance.
Whether this novel idea of interchangeable modules to give users differing options in mic sound will catch on, only time will tell, as they say. It deserves to be considered by home recordists particularly, as a very cost effective way of obtaining versatility, for it is a well thought out and made system which does what is claimed. In discussions with the manufacturer it seems that 'spare' mic bodies will be made available and this must add to the attractiveness of the idea, as it would double the number of mics available instantly.
Finally, HSR would like to hear from Home Recordists who have invested in the AZ-TEC set-up, and how they find the flexibility in their practical conditions. We have given you some guiding measurements, so over to your letters for your longer term impressions.
The AZ-TEC package sells for £89 including VAT.
Further details from AZ-TEC, (Contact Details).
Review by Mike Skeet
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