Tuesday, July 3, 2012

Gefell M 900 - The Arty Condenser Mic

There is not a more exotic looking mic than the Gefell M 900 ($995). Part ray gun, part Venutian gynecological instrument, the cardioid condenser M 900 (and its hyper-cardioid cousin the M 910), are striking in their appearance. 
The M 900 is a transformerless, large-diaphragm condenser microphone with a single cardioid pattern. The membrane is a standard 1-inch gold sputtered Mylar membrane. The capsule was designed and computer-modeled at NIKFI in Moscow. According to GPrime, the US distributors, it has a ceramic backplate that is more stable to temperature changes than the often used brass. The conductive side is then chrome-plated. Over that is evaporated a one micron coating of Teflon. The Teflon acts as an insulator between the membrane and backplate and prevents damage as a result of incidental contact between the two. 

* Studio/Live Condenser Mic
* Cardioid Pattern
* Next to imposible to find

Frequency response is quoted as 40Hz to 18KHz. Sensitivity of the M 900 is 17mV/Pa. Due its tighter pattern, the hyper-cardioid M 910 version is slightly less sensitive, at 14mV/Pa. Incidentally, sensitivity is the ratio of the acoustical input to the electrical output. The M 900's active transformerless output removes the limitation on the output capability that would be imposed by a transformer. 
The MV200 amplifier (impedance converter) in the M 900, converts the large capacitive impedance of the capsule down to about 150 Ohms. The electronics also contain a switching power supply to generate the polarization voltage for the capsule, which is independent of the phantom voltage. This allows the mic to have a higher polarization voltage than the phantom voltage. This higher polarization voltage results in higher sensitivity and lower self noise. For compactness and mechanical robustness, all components of the MV200 amplifier are zero-clearance, surface mounted (SMD) on the board. 
When compared to the ubiquitous U87 Neumann and AKG C414, all through A.P.I. mic preamps at Flite Three in Baltimore,I observed the following similarities and differences.
The M 900 is at least as quiet as a U87 (not the U87ai), with a slightly higher output. The M 900 is much warmer than the U87, especially at a working distance of less than 4 inches. Due to the proximity effect and the mild sensitivity to popping, the closest I'd want to position the mic for voice work would be 4 inches. Cozy it any closer than that and the bottom overwhelms, unless the voice or sound is thin to begin with. 
The M 900 loses proximity fast. At a distance of 8 inches, it is only slightly warmer than a U87. Back off to about a foot, and the bottoms are almost the same. While each mic has a peak, the M 900 has a brighter top, with a peak somewhere in the 7K-9K range versus the U87's 3-5K peak. 

M 900 vs. C414
The M 900's bottom is similar, but slightly less than that of the C414. The C414 develops it's bass farther down than the M 900. The M900 has more in common than the U87 in their high-frequency responses, with the M 900 being slightly more peaky and the C414 extending out slightly farther. At a distance of 8 inches, the high-frequency bump of the M 900 gives a heavy-pitch delivery an edge. 
The M 900 has less proximity effect than the C414. A distances of 12 inches or more, the loss of low-frequency response thinned-out the mic's sound, making it sound slightly "canny".
Perhaps the most distinguishing feature of the M 900, apart from it appearance, is its off-axis high-frequency response. In fact, one of the design goals was an extremely uniform polar pattern. The M 900 achieves this better than most mics I've heard. A lot of cardioid-patterned mics appear to be more directional because of their lack of their off-axis high frequency response. 
Compared with both the U87 and C414 in cardioid pattern, the M 900 "hears" an amazing amount of high frequencies even at 90 degrees off axis. If performers wandering off mic a bit have caused you problems, the M 900 may be a solution. Given its wide-angle acceptance to high frequencies, I'd like to try a pair of M 900s as drum overheads. Of course, this same feature would likely make them less successful in applications where you were trying to keep extraneous, nearby high frequencies out of the mix. 
The most curious result of the tests was the difference in sound depending on which mic preamp was used. Both the in-board and lunchbox version of the A.P.I. mic preamps made the M 900 sound rough and edgey. There was no such edge when using the Amek/Neve 9098 and Mackie 1604 preamps. 
The M 900 is about as sensitive to popping as a C414. Because of its unusual open-back design a slip-on, foam sleeve pop filter has been designed. I tested the prototype and found that it greatly reduces the popping, without changing the sound of the mic much. 
I spent an afternoon at 1137 Recording in Baltimore, working with the M 900 and the Amek/Neve 9098. Not surprisingly, the combination sounded as good on vocals as it had at Flite Three. Next we set up for instrument recording. Our source was a Fender Strat through a vacuum tube, 130 watt, Music Man amp-head to a Crate closed-back cabinet with four 12" Celestion 30 watt speakers. In the studio, the speaker cabinet sounded like nothing special, your typical cranky guitar amp sound. 
The M 900 sounded nice, but a bit too thin, until we got it to within four inches of the cabinet and centered on one of the speakers. BINGO! Platinum ribbons of sonic beauty. The hair stands up on my arm every time I tell this part of the story. For comparison we plugged in a Rode NT2. It sounded edgey and harsh, so we quickly went back to the M 900. 
To be sure, the M 900 is not linear. It was adding warmth (and a lot of other things) to the sound of the bare cabinet, which by itself, did not sound anywhere near as good in free air to the human ear. The M 900 provided a sense on connectedness to the sound of the guitar. Maybe the increased warmth was filling in or masking holes in the guitar rig's frequency response. And, maybe, in the wrong situation, where too much bottom would get in the way, a closely positioned M 900 would not fare as well. 
For both looks and sound, the M 900 definitely makes the grade as a mic that deserves serious consideration for addition to your mic locker. 

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