When I soloed the violins, my mouth dropped open! The two Mojaves sounded like a high-resolution stereo mic — not at all like a pair of typical “pencil” mics put together into an X-Y arrangement. The imaging was rock-solid and, most importantly, the sound of the violin was extremely smooth and true.
I subsequently tried them on piano, choir, and organ, and each time came away with the feeling that these relatively low-priced mics can easily substitute for many of my custom-modified vintage microphones. They seem not to have any of the “solid-state sound” that I find objectionable in other, considerably more expensive, small diaphragm European microphones.
The Evolution of Small Diaphragm Microphones
Back in the day, the most widely used small diaphragm microphones were made in Germany and Austria by Neumann, Schoeps, and AKG. They had approximately 1/2”-diameter diaphragms and, due to various proprietary capsule manufacturing techniques and amplifier designs, sounded quite different from each other.
All three companies made vacuum tube models in the 1950s and early 1960s, and all eventually switched to solid-state amplifiers, which changed their sound somewhat. Nonetheless, there were still several sonic qualities common to all of them.
First, due to their small diameter diaphragms, their response to sound arriving indirectly at the diaphragm’s axis was almost as linear as the direct response — only lower in amplitude. Second, the cardioid and hypercardioid capsules could always be expected to be deficient in low frequency response, below about 150 Hz. The omnidirectional diaphragms — which responded to pure pressure variations — were flat all the way down to at least 30 Hz.
Due to these seemingly unavoidable characteristics of small diaphragm microphones, certain recording techniques evolved for taking advantage of their strengths, while avoiding their weaknesses. For example, the use of three small diaphragm omnidirectional Schoeps vacuum tube microphones, spaced across the front of an orchestra, became the standard for audiophile recordings in the fifties and sixties, as pioneered by the Mercury Living Presence LPs produced by the late Bob and Wilma Fine.
This technique was continued into the present digital era by Telarc. When a more precise stereo image was desired for chamber music recordings, coincident cardioid small diaphragm mics were used because their fine off-axis response complemented this technique; a little bass boost from a high-quality equalizer usually fixed the low end problem sufficiently.
The large (approximately 1”) diaphragm condenser microphones (from Neumann and AKG) had much better low frequency response, but terrible off-axis response. So different uses evolved for them — as spot microphones for vocalists (where their euphonic colorations and proximity effect when used as cardioids were deemed favorable) and, in general, for most multi-microphone situations in pop and jazz music recording.
There actually existed an in-between-sized, 3/4-inch diaphragm mic — the vacuum tube Sony C-37 (and its descendants, whose 3/4” diaphragm capsules constituted basically the entire Sony electret line, such as the ECM-22 and 33P), but it was rather noisy. Although it had its champions, the C-37 wasn’t used nearly as widely as the German and Austrian mics, and certainly not for classical music recording.
And let's no forget Western Electric and Altec. The Western Electric 640A predated the Schoeps mics by more than a decade; The Altec M-29 capsule was shared with AKG (C-28, C-60 and C-61).
Microphone capsule and diaphragm research and development, however, did not stop during the sixties. Throughout the 1970s and 1980s, modern mic pioneers — among them the late Stephen Paul and David Royer — experimented with different diaphragm material and thickness, and by the mid-eighties, Stephen Paul became the first person to produce large diaphragm capsules made of, initially, 3-micron thin gold-sputtered Mylar, and later, 1.5-, 1-, and 0.9-micron Mylar. These new diaphragm materials produced mics which exhibited far better transient and off-axis response than the older 6-10 micron PVC.
Stephen Paul also produced 1/2”-diaphragms with 3- and 1-micron Mylar, which showed analogously improved characteristics. I own more than a dozen of his modified Neumann and AKG vacuum tube microphones — both large and small diaphragm models — and can personally attest to their high resolution and superb sound pickup qualities.
When American vacuum tube importer and microphone manufacturer, Aspen Pittman (Groove Tubes) was exploring the possibility of outsourcing capsule manufacturing to China in the 1990s, he specified a 3/4”-diaphragm — in an attempt to improve the typical falling low-end response of small diaphragm microphones. He told me he was trying to build a vacuum tube microphone that “sounded like a Neumann KM 54, only better.”
In the low-frequency domain, this capsule was a success, but its 6-micron thickness, and early Chinese electronic design still exhibited uneven off-axis response. Thus, the GT-40 and its various successors were still not suited for coincident miking, despite their smooth, warm, and large sound.
But progress continued, and that Chinese manufacturer went on to make newer versions of this capsule for other companies, including M-Audio, in the form of their Pulsar, Aries, and Pulsar II. These were improvements upon the GT-C1 cardioid capsule, but it remained 6 microns thick, and still rather “slow” sounding, with not much better off-axis response. And the amplifiers were nothing special.
David Royer, however, came upon the perfect solution that solved all the aforementioned problems of transient and off-axis response, and designed a new capsule for the latest version of this evolving microphone. He instructed the Chinese lab to skin a variation of their 3/4”-capsule with 3 micron Mylar, à la Stephen Paul, properly sputtered with gold. This design is the heart of the Mojave MA-101fet microphone.
—Dr. Frederick J. Bashour