In the beginning, there was omnidirectional: all microphones start out as omnis and are tweaked to acquire various directional characteristics. As the science of making microphones progressed (aided in no small part by Georg Neumann), unidirectional designs found favor for P.A. systems, broadcast, and music recording.
Thankfully, Neumann has continued to design and offer omnidirectional mics, including benchmarks such as the famed M 50. Now the venerable mic manufacturer has updated the Neumann KM 83 (the omni sibling to the well-known cardioid KM 84), logically christening the latest family member the KM 183 (see Fig. 1).
All KM 180-series Neumann mics are small-diaphragm, phantom-powered condensers employing transformerless FET electronics. At just over four inches in length, the transducers are extremely light and easy to position. All 180-series mics are manufactured in nickel and matte-black finishes, and accessories are available from the manufacturer. Although it appears that the threaded microphone capsules, which screw on to the preamp bodies, can be swapped (as is the case with the modular 100-series Neumanns), the 180-series capsules are not interchangeable.
Generally, small-diaphragm omnidirectional microphones are favored for critical recording applications in which flat frequency response, accurate transients, and neutral, uncolored sound reproduction are prime concerns. For classical recording, film sound, and sampling, that transducer class is highly regarded. In contemporary pop recording, however, omni mics are more of a specialty item. That is partly because of the dominance of close-miking techniques and perhaps also because of a prevailing notion that omni mics don't offer adequate low-end response.
Regarding the latter view, it's true that small-capsule omnis provide neither the enhanced midbass warmth of a large-diaphragm mic nor the proximity-dependent bass boosting inherent in all focused-pattern microphones. However, most quality omnis, including the KM 183, offer low-end response that is flat to 20 Hz and below. That translates to window-rattling lows when recording orchestral bass drums, organ pedals, gongs, acoustic and electric basses, and thundering rock drums (with the omnis used as room microphones).
Another aspect of the KM 183's frequency response deserves a note of explanation. It is technically possible to design an omnidirectional microphone with ruler-flat frequency response beyond the audible frequency range: the Neumann KM 131 is such an item, as are models by DPA (formerly Brüel and Kjær), Earthworks, and others. But the neutrality of a flat microphone is not always desirable and can result in washed-out sound and lack of high-end detail, especially in concert-hall and studio recordings.
To compensate for the high-end loss that occurs when miking with an omni at a distance of three or more feet, Neumann designed the KM 183 to have a rising presence boost similar to that of its ubiquitous vocal mics. Diffuse-field equalization — a smooth increase in high-end response above 4 kHz, peaking with a 7 dB boost at 10 kHz — allows the KM 183 to sound crisp on distant sources.
That characteristic also lets the KM 183 compete in the studio as a close-miking tool, because it can enhance detail yet remain free of the muddiness that often attends bass boosting caused by the proximity effect. Because omni mics exhibit no proximity effect and off-axis coloration on high frequencies, they are surprisingly easy to position on complex instruments. Omnis are championed by a growing number of engineers for recording acoustic guitars, for example. Like other omnis, the KM 183 can be placed directly in front of a guitar's sound hole to capture rich resonance and plenty of high-end sparkle with little of the boominess and unfocused lows that afflict cardioid mics in that position.
NO MATCH MADE IN HEAVEN
For this review, I received a pair of matte black KM 183s packaged as a set complete with swivelmounts and foam-rubber windscreens in a single wooden jeweler's box. Although the KM 183s are sold both individually and in stereo pairs (with sequential serial numbers), the stereo pairs are neither provided with frequency-response graphs nor sonically matched. According to Sennheiser and Neumann product manager Karl Winkler, the caliber of construction and the quality-control process for Neumann mics ensure that any two mics of the same model will sound enough alike that, in general, they should work fine for stereo-recording applications. But again, no extra testing is done to precisely match the stereo pairs.
In loudspeaker tests with a two-way speaker system playing full-range rock mixes, I was surprised to hear distinct differences in frequency response between the two KM 183s. For the signal path, I used Baltic Latvian Universal Electronics (BLUE) Kiwi mic cables and a Langevin Dual Vocal Combo or Focusrite Green preamp, with gain matched by meters and by ear. All signals were recorded to DAT.
I initially positioned the KM 183 pair about two feet from the speaker, with the capsules approximately one inch apart. But I ended up moving the mics back to a distance of six feet from the source to minimize discrepancies caused by the relative proximity of the tweeter or woofer. At that distance, listening sessions in the studio (and later in my mastering suite) revealed marked dissimilarities in presence and in high-end reproduction between the two mics and subtle differences in bass pickup. I tried switching both mic preamps and mixer channels but received the same results.
Specifically, one KM 183 had a noticeably bigger sound; it enhanced the mix's high-frequency components such as hi-hat, snare, and vocal sibilance, and it added a bit more punch to the kick drum. I also heard minor variations in the lower midrange, which affected the timbre of electric bass and distortion guitar in the mix.
I also recorded an acoustic guitar with both mics and compared the results. One mic was obviously brighter, and the other had a thicker, more woody-sounding midrange quality. However, both microphones sounded good, and the differences were not as pronounced as in the loudspeaker tests. The mics' output levels were closely matched too. But still, the KM 183s were not sufficiently matched for critical stereo recording. Were I to audition a pair for the purpose of buying just one KM 183, the obvious sonic differences would prompt me to do a lot of testing before deciding which flavor I preferred.
To test the suitability of the KM 183s for classical-style recording, I set them up as a spaced pair to record composer Dan Plonsey's Portcullis Ensemble. Incidentally, during that session, I also tested an MBHO MBNM-622, a unique stereo mic that employs boundary-layer mics on either side of a modified Jecklin disk (see the review in the October 2001 issue).
In general, the KM 183 pair conveyed a realistic, unexaggerated left-to-right balance with a blended center image and an authentic-sounding ambience. Although each recording system had its strengths, the Neumann pair timbrally was the more natural, displaying open, airy detail that was particularly appealing when monitored on a pair of Grado SR 125 headphones.
Compared with the sharp separation and drier quality of the MBNM-622 recording, the imaging of the KM 183 tracks was sometimes blurred with slight shifting in the perceived position of high-end instruments such as cymbals and piccolo. However, part of that could be attributed to room reflections (which are minimized by the MBNM-622) and to the aforementioned differences in high-end response between the KM 183 transducers.
Positioned about four feet in front of a Taylor acoustic guitar, a single KM 183 added a world of subtleties when mixed in with an XY pair of close mics (Oktava MK012s). Low-end fundamentals, pick sound, sparkling harmonics, and early reflections from the room were accurately represented by the KM 183, contributing an exciting, three-dimensional realism to what would otherwise have been a fairly standard foreground guitar track.
Throughout the tests and especially for ambient miking on quiet sources, the KM 183's low self-noise and relatively high output were a boon. The only hitch in that session came when the KM 183 faithfully conveyed some machine noise from another part of the building. A low-cut filter on the mic preamp effectively dealt with the unwanted rumble, and I made a mental note that industrial buildings and omni mics don't always get along.
I discovered another noteworthy use of the KM 183 as a distant microphone while recording the improvisational trio Maybe Monday. When cellist Joan Jeanrenaud (formerly of the Kronos Quartet) entered as a guest artist, I decided to isolate her in the drum room, away from the trio's electric guitarist, Fred Frith, and saxophonist, Larry Ochs. I left the door to the wood-floored drum room open and supplemented Jeanrenaud's close mic (a Royer SF-1 ribbon) with a KM 183 taped to the floor a few feet away.
Employing the KM 183 as a boundary-layer mic added some interesting and rather dark live reverb to the mix. The mic also picked up amazingly clear artifacts from Frith's amp, which was 30 feet away, around a corner. Mixing that room track in with the close-miked cello track contributed a pleasant high end to arco passages. Used in moderation, that track filled in the instrument's sound transparently without adding boominess or boxy coloration.
In addition to being a reliable, smooth-sounding performer in conventional omni applications (distant miking of instruments and ensembles), the diminutive KM 183 also has some big surprises to offer as a stand-in for standard cardioid-pattern close-miking duties. For a session engineered by my studio partner, Bart Thurber, I proposed using the KM 183 as a single mic on a Hammond M-3 organ and Leslie Model 51 combination. At a distance of four feet and routed to a vintage Telefunken V72 tube preamp, the KM 183 delivered an even, airy sound with just enough ambience to grant the organ a spacious character. The Leslie cabinet had no problems with harshness or mechanical noise, and positioning the mic between the high and low rotors yielded plenty of low end. The only drawback was that the Leslie's speed control was installed on a homemade metal switching box, and even from ten feet away, the KM 183's big ears picked up the click of the switch.
I used the two KM 183s as a spaced pair on a set of three conga drums while recording rhythm tracks for a CD by singer and songwriter Jen Faith. Although I never tried that with omnidirectional mics before, after a couple of quick positioning adjustments, the Neumanns allayed any reservations I had. The low end of the conga set was rich in tone but never boomy, there was plenty of slap and skin sound, and the overall tone was tightly focused with a perfect amount of organic room sound.
Encouraged by those results, I threw caution to the wind and used one of the KM 183s during a session with jazz drummer Milo Francis — not as an overhead microphone, but in front of Francis's double-headed bass drum. When positioned as close as I usually like — one to two inches away, aimed at the outer rim of the head — the +25 dB gain setting on a Neve 1272 mic preamp provided way too much gain for my analog recorder. The mic has no attenuation pad, so I simply moved it back about four inches from the head and slightly lowered the preamp trim setting. The KM 183 never complained, and after a few EQ cuts in the low end and a small boost at 4 kHz, I had a solid, present bass-drum sound that provoked enthusiastic comments throughout the mixing session. I was knocked out by the KM 183's ability to capture that elusive jazz boom and appreciative that the leakage from the kit, though a bit more pronounced than with the usual cardioid mic, was even and uncolored.
PLAIN SOUNDS GREAT
As an engineer who savors the rich qualities of room ambience in studio recordings, I have developed a great appreciation for omnidirectional microphones over the years. Some in my collection will do something to enhance room sound or contribute a unique equalization curve to close-miked sources. I have also tried ultra-flat instrumentation omnis in the studio but have generally found that they lack character for my preferred recording style.
Excluding the top-dollar mics, nothing that I've heard in the omnidirectional class compares to the pleasant neutrality and sweetened high end of the Neumann KM 183. Purists may debate the merits of diffuse-field equalization, but my ears reveal that this little mic has an amazing reach, and its high-end compensation delivered astounding nuances from near or far without ever sounding overly bright or fizzy.
As with all Neumann KM 100-series mics, low noise, lifelike transient response, and clear resolution of delicate acoustical details are hallmarks of the KM 183. The pair I tested was not sufficiently matched for use as a stereo set, which was a disappointment given Neumann's stature and reputation. Nonetheless, the mic just plain sounds great, and it should provide years of sonic revelations in the studio and for live recording. I highly recommend the KM 183 to those looking to branch out into ambient miking, expand their miking techniques, or simply upgrade from budget omnis.
Myles Boisenis a guitarist, a producer, a composer, and the head engineer and instructor at Guerrilla Recording and the Headless Buddha Mastering Lab in Oakland, California. E-mail him firstname.lastname@example.org.
small-diaphragm condenser mic
RATING PRODUCTS FROM 1 TO 5
PROS: Clean, high-resolution reproduction. Low self-noise. High output. High SPL handling. Diffuse-field equalization provides sweet highs at a distance. Easy to position. Viable for a variety of studio close-miking applications.
CONS: Microphone pairs not matched for critical stereo use.
KM 183 Specifications Elementexternally polarized (DC bias) capacitor (“true” condenser)Diaphragm½", 3-micron, gold-vapor-deposited MylarPolar PatternomnidirectionalFrequency Response20 Hz-20 kHzDynamic Range124 dBSensitivity12 mV/Pa (±1 dB; @ 1 kHz into 1 kΩ)Signal-to-Noise Ratio78 dBASelf-Noise16 dBAMaximum SPL140 dB (for 0.5% THD)Power48V phantom (±4V)Dimensions4.21" (L) × 0.87" (D)Weight0.18 lb.