Sennheiser MKH 40 Microphone

Sennheiser, a German firm, manufactures a wide variety of dynamic and condenser microphones, headphones, wireless microphone and headphone systems, and related electronics. The designation "MKH" refers to their line of studio condenser microphones, each of which employs what the company calls the "RF Principle." Instead of applying a high d.c. voltage to the capsule, about 10 V of 8-MHz r.f. bias is applied from a low-noise oscillator. The capacitance variations of the capsule modulate the oscillator, and this modulation is translated into an audio signal. Since the capsule is a capacitor, the impedance of its 8-MHz output is low compared to the audio-frequency output of an equivalent d.c.-biased microphone. Sennheiser says that this renders the MKH microphones less susceptible to popping and sputtering noises caused by high humidity, thus making them suitable for outdoor use. The MKH line includes an omnidirectional, a figure-eight, and a cardioid mike, short and long shotgun models, and a special-purpose omni unit which features flat response down to 0.1 Hz. All of these microphones, except for the last, feature very low noise levels.

I've had some previous experience with the MKH mikes; it came in 1980, when I was refurbishing the 1970-vintage RCA console in the Grand Tier broadcast booth at New York's Metropolitan Opera House. The console inputs came from a number of short MKH-416 shotgun mikes hung 40 feet above the orchestra and stage. (This was low, compared to the reported 100-foot proscenium height!) The MKH shotgun mikes yielded excellent audio in spite of their long distance from the performers, and the very long cables between the mikes and the power supplies in the booth did not impair that quality.

The appearance of the MKH 40 is best described as "understated." The satin-black cylindrical housing is quite plain, save for the flat surfaces along two-thirds of its length. These surfaces serve the practical functions of providing secure mating to the swivel mount and acting as a "panel" for the 120-Hz filter and output attenuator switches. The microphone is very lightweight compared to many other professional condenser microphones.

The specifications for the MKH 40 indicate that it has a very wide dynamic range, uniform frequency response at all useful pickup angles (e.g., a polar pattern independent of frequency), and low distortion. According to the published frequency response curves, it also is flatter than the MKH cardioid that came before it (MKH-406) and has lower noise. It is recommended by the manufacturer for digital recording and, like the MKH-406, is said to be appropriate for outdoor as well as indoor use.

The MKH 40 requires external phantom powering; not wanting to gamble on introducing noise from a lab power supply, I opted for the battery supply, MZA 16-P48U. This was a good choice because it includes a 20-dB attenuator and response-shaping filters-flat (20 Hz) plus 80 and 140 Hz positions-which supplement those on the mike. The power-supply switches offer flexibility in recording and are an advantage in any live concert setting where you can't access the mike to make changes. At $678 for a pair, these battery supplies are a bargain, at least compared to one that I've tested which cost in excess of $1,000.

Use and Listening Tests

Using my low-noise microphone amplifier, I compared the Sennheiser MKH 40 to another condenser microphone with a wide frequency range, a Nakamichi CM-700 electret. The CM-700, a premium consumer-grade microphone, sounded very hissy in a quiet room, whereas the MKH 40 reproduced the room noise with no audible hiss. Very impressive!

Clipping level with close, loud speech was seen on a 'scope to be approximately 134 dB, as rated. Vibration noise pickup was less than with the CM-700, and magnetic hum pickup was lower too. On the other hand, the MKH 40 had somewhat more "pop" sensitivity with its windscreen mounted than the Nakamichi did. With voice as a source, the Sennheiser sounded identical to the Nakamichi at angles from 0° to 135°. This was quite remarkable, as the Nakamichi has exceptionally uniform polar response because of its small diameter (16 mm, compared to 25 mm for the Sennheiser).

I loaned the Sennheiser mike and battery supply to my associate Jack Shaw, who used them in recording piano and voice on videotape for a cable TV show. He reported that the resulting tape sounded "clearer, cleaner, and had less room noise than a tape made with the Nakamichi." However, after a few selections were recorded, the battery supply became noisy, and he had to switch to the Nakamichi. Later, I sprayed the battery contacts with contact cleaner, and the noise ceased

I had the good luck to be able to record a concert which featured 18 brass and percussion players from the Philadelphia Orchestra, plus pipe organ and large choir. The concert took place in the United Methodist Church in Haddon-field, N.J. An AKG C-422 polydirectional stereo condenser microphone is permanently flown about 16 feet above the place where musicians perform in this church. In order to make a good comparison between the Sennheiser and AKG mikes, I mounted an X-Y pair of MKH 40s on a tall Shure S-15 stand, which raised them to a level only about 2 feet below the C-422.

I had to position the Sennheisers for an included angle of 90° to match that of the C-422. The AKG, which is normally set for figure-eight (Blumlein) stereo, had to be set for cardioid patterns to match the Sennheisers. There was thus a potential sacrifice in stereo perspective, because the included angles were less than the usual 120° recommended for crossed cardioids.

Not having a 4-track recorder on which I could tape the outputs of these mikes simultaneously, I used two cassette machines from Aiwa, the AD-F990 and the AD-3700, with metal-particle tape and Dolby C noise reduction. Because the 990 has the HX-Pro headroom-extension system but the 3700 does not, I switched the units at intermission, to record with each mike on each machine.

The tapes were auditioned on two systems. One, in my home listening room, includes modified and equalized housed in large sealed boxes. In audio quality and stereo perspective, the tapes made with the MKH 40 mikes sounded almost identical to those recorded with the C-422. The bass notes of the organ sounded exactly the same on each tape, proving to me that the slight measured roll-off the Sennheiser is insignificant. The C-422's response is very uniform from 20 Hz to 20 kHz. The sound of trumpets and cymbals was slightly brighter with the Sennheiser, indicating that the measured brightness was not an artifact. I should note that some commercial recordings do sound a little bright on my system, whereas the many recordings I've made using the AKG sound neutral.

The second listening test was conducted in the living room, using three Klipsch horns. I found that the sound of tympani was better on the horns than on my direct-radiating 15-inch speakers and that it held up very well at higher playback levels (100+ dB). At first, the stereo perspectives seemed astoundingly wide, because the speakers, as recommended by Klipsch, were set along the long wall of the room. The speakers subtended a 90° angle at the listening position, compared to 60° in my own listening room. However, a very even spread of sound was maintained.

In the bass, both microphones sounded identical. In the treble, the MKH 40 sounded neutral, whereas the C-422 sounded a little dull; trumpets and cymbals sounded brighter with the Sennheiser. Referring to Fig. 4 in Heyser's Klipschorn review, I see a gentle downward trend in the speaker's response from 1 to 15 kHz, as compared to my Altecs, which are equalized to measure flat to 10 kHz and to be 5 dB down at 15 kHz. Obviously, Klipsch has adjusted the response to sound well balanced with commercial recorded material. I confirmed this by playing a few CDs. This leads to the conclusion that recordings made with the Sennheiser will have response balance comparable to that of commercial material, without additional EQ.

At the risk of repeating a statement from a previous review, I find that an X-Y pair of MKH 40 microphones is an excellent portable substitute for the reference AKG, which is more often permanently flown than used on stands, and which costs more. The Sennheiser's 122-dB dynamic range makes it suitable for use with digital or dbx-encoded analog recording systems.