MANUFACTURER'S SPECIFICATIONS:
Model KM-83 Assembly
Capsule Model No.: KK-83.
Preamp Model No.: KMi.
Directional Pattern: Omnidirectional Frequency Range: 40 Hz to 20 kHz.
Transducer Type: Pressure condenser.
Model KM-84 Assembly Capsule Model No.: KK-84.
Preamp Model No.: KMi.
Directional Pattern: Cardioid.
Frequency Range: 40 Hz to 20 kHz.
Transducer Type: Pressure gradient condenser.
Model KM-85 Assembly
Capsule Model No.: KK-85.
Preamp Model No.: KMi.
Directional Pattern: Cardioid.
Frequency Range: 40 Hz to 20 kHz, L/F roll-off.
Transducer Type: Pressure gradient condenser.
Sensitivity: 10 mV/Pa =-40 dBV/Pa (may be reduced 10 dB by switch on preamp).
Output Impedance: 200/50 ohms.
Noise Level Expressed as Equivalent Sound Level (The frequency bandwidth is not stated): Approximate values, IEC 179, 18 dB; DIN 45-405, 25 dB.
Max. SPL for 0.5% THD: With sensitivity switch set at-10 dB, 133 dB.
Power required: 48, +6,-8 V d.c.
Phantom Powering: 0.4 mA. Operation Time with Battery Supplies: Approx. 200 hours.
Dimensions: V. in. (2.2 cm) D x 4 %8 in. (11.1 cm) L.
Weight: 2.82 oz. (80 gms). Accessories Supplied: MKV swivel mount and WNS21 (foam) pop screen.
Price: KM-84 microphone system, $260.00; KK-83 capsule, $110.00; KK-85 capsule, $110.00, and the N80 power supply, $50.00.
The Neumann fet-80 microphones are high-quality condenser units designed for professional broadcasting and recording. The advanced amateur who has invested $1,000 plus in a tape recorder, not to mention other accessories such as preamps, mixers, and equalizers, will also want to acquire professional grade microphones.
We first learned of Neumann microphones in the 50s when we read a "Target Report" by the U.S. Forces who occupied Germany at the end of World War II. They had "captured" the Neumann labs in Gefell and moved them to Berlin before the Russians arrived. They learned from Mr. Neumann himself about double-membrane, switchable directivity condenser microphone ... which was unknown in the U. S. at that time. We had an opportunity to test an early U-47 microphone with a Telefunken logo which was the commercial version of Mr. Neumann's invention. The U-47 had a wide range frequency response with a rise at 10,000 Hz. It was very popular with recording studios, and an FET version of it is in the latest catalog.
Today, the Neumann name is synonymous with high-quality studio microphones, just as RCA and Western Electric were in the 30s and 40s.
We evaluated three microphones of the fet-80 series, all 22 mm (%8 in.) diameter components. The KM-84 was received as a system, consisting of a flat response cardioid capsule, FET preamplifier, "pop" screen, and swivel mount. Two additional capsules were supplied separately, the KK-83 omnidirectional and the KK-85 cardioid with low frequency rolloff.
The N80 power supply was furnished, which provides 48 V d.c. "phantom" powering for two microphones. (Readers of our review of an AKG microphone in the August, 1977, issue will recall that phantom powering is a means whereby an ordinary two-conductor shielded microphone cable carries both the audio signal and the d.c. power.)
Moving-coil and ribbon microphones may be interchanged with phantom-powered condensers on the same microphone line without turning off the power supply.
No microphone cable was supplied as part of the KM-84 microphone, as the fet-80 series is a "component" microphone system where the user must separately order the capsules and power supply needed for his particular application. The preamp and power supply employ U.S. standard Switchcraft 3-pin connectors. The supply output is via two short cables which terminate in Switchcraft adaptors. These adaptors have male and female 3-pin connectors and are inserted in the output lines of one or two fet-80 microphones.
The capsules are easily unscrewed from the preamp and interchanged. Some care has to be taken not to bend the long gold-plated contact pin which protrudes from the capsule.
The head-end insulator on the preamp is a Teflon hemisphere which provides a long electrical leakage path to minimize humidity effects. The shape also provides a smooth (and non resonant) transition from the back part of the capsule to the atmosphere. The mechanical design and workmanship are flawless, and the nickel plated finish appears to be very durable. The sensitivity switch is recessed and can only be intentionally operated by a pointed instrument.
No individually drawn frequency response curves were supplied, even though other European manufacturers, such as AKG and Beyer, supply curves with their higher priced microphones, at least. This did not make us very unhappy because the instructions contain curves on each capsule with rather tight production tolerance "envelopes" indicated.
The instruction pamphlets supplied include data on many different models of microphones, power supplies, and powering methods. However, they are printed on rather thin paper, and we feel that Neumann should, for the benefit of audiophile users, print individual simplified instructions for each model of equipment in larger type and on heavier paper.
Laboratory Tests
Our first impedance test indicated a low Z value and the microphone appeared dead. We consulted the instruction pamphlet entitled "Compatible Central Powering ... fet-80 series" and failed to find a reference to the N80 Power Supply which we were using. Fortunately, individual circuit schematics were supplied separately for both the preamp and power supply. We learned that the N80 contains no output isolation transformer, so grounding either microphone line (a must for our impedance test) shorts out the d.c. power. The instructions show some (slightly complex) modifications for unbalanced operation, as required for some tape recorders, etc. We opted to use a high quality 1:1 isolation transformer for all tests. The UTC HA-108X is a well-shielded unit that will accept line levels without distortion. Gotham offers such a transformer as Model BV-40134.
Neumann states that in order to use their microphones with a grounded center tap input transformer, the center tap must be lifted from ground, which they state will do no harm.
However, the user should be cautioned that in some applications, particularly with long microphone lines, increased hum and noise may result due to lack of cancellation of "common mode" interference. Then the user will have to add an isolation or input transformer that rejects noise without a center tap grounded. (For example, the Shure line and input transformers do not require a grounded center tap. Editor's Note: Neumann states they have used mike cables several hundred feet long and encountered very few common-mode difficulties). Having solved this problem, the impedances shown in Fig. 1 were measured. The impedance is, for practical purposes, equal to that of a 200-ohm nominal value resistor.
The axial frequency response of the KM-84 is shown in Fig. 2. The "plane-wave without pop screen" curve fits within the envelope in the instruction pamphlet. The 12-inch data represents a normal proximity effect for a cardioid microphone, and an external roll-off equalizer is required for flat low-frequency response at distances closer than about two feet.
The pop screen does not live up to Neumann's claim of-1 dB at 10 KHz as our test shows. a 3.5 dB loss. They may be experiencing some quality control problems, as we have used these WNS-21 screens for many years on sound level meter mikes and with a GR ceramic mike where they exhibit no more than 1.5 dB loss at high frequencies. For voice applications, the new screen should cause no problem.
Our sensitivity numbers are 5 dB less than nominal.
Neumann does not state the tolerance on sensitivity, and our numbers will be at least 1 dB low due to our transformer. We are pleased with the 55 dBV/Pa value with the switch at -10 dB because it agrees with values for many moving-coil and ribbon mikes.
The cardioid directional pattern of the KM-84 (Fig. 3) is essentially uniform with frequency. (We consider the 180° response to be a perfect null if 15 dB or more below the 0° response.) Thus, the KM-84 is virtually a perfect cardioid mike and is the best one we have tested.
The response of the KK-85 capsule (Fig. 4) is similar to the KK-84 except for the low-frequency roll off. The KK-85 is suited for use close to the source or for attenuation of low frequency noise on distant sources. Our data falls within the specifications envelope.
Fig. 1--Impedance of the Neumann KM 84 microphone system, including the
UTC-HA108X isolation transformer.
Fig. 2-Frequency response of the KM-84 mike system.
Fig. 3-Frequency response versus angle.
Fig. 4-Frequency response with the KK-85 capsule and the KMi preamp.
Fig. 5-Frequency response with the KK-83 capsule and the KMi preamp.
Fig. 6--Noise spectrum of the KM-84 microphone system in one-third octave
bands, unweighted.
The KK-83 capsule response at 0° (Fig. 5) is slightly above the specification envelope at 50 and 8000 Hz, possibly due to differences between laboratories. Note that the KK-83 must be used at grazing incidence for direct sound waves or high frequencies will be boosted. When used for pickup of direct plus reflected sound, such as a single mike above an orchestra, the sound will be natural, because the response to random incident sound will be similar to the 90° curve. We believe that Neumann has made the correct choice in tailoring the response of the KK-83.
The one-third octave self-noise levels (Fig. 6) indicate a flat or "pink" noise characteristic at high frequencies, but the noise at low frequencies follows a 1/f characteristic. The low frequency noise will cause no problems, unless you're recording distant earthquakes. The one-third octave values in the important mid and high frequencies are as low as 6 dB equivalent SPL. This will be below ambient in most rooms.
(The KM-84 would be good for acoustic noise measurements, as the lowest third-octave level we've been able to measure with lab equipment is about 18 dB SPL!) We recently constructed and calibrated a "sound proof" box for another project and thought it would be an interesting experiment to attempt to measure the absolute self noise of the Neumann mike system. In this test, the ambient noise inside the box was at least 10 dB below the self-noise.
Our measured overall noise level of 33 dB was higher than the (approximate) Neumann values of 18 or 25 dB, but our bandwidth extended down to 2.5 Hz, so that the overall measured level was controlled by infrasonic noise. (The IEC or DIN methods roll off the low frequencies.) The 60-Hz magnetic hum sensitivity of the KM-84 is much greater than our BK-5B reference ribbon mike is undoubtedly due to the preamp output transformer. There is little room for shielding but our experience indicates that carefully balanced hum bucking windings will yield adequate performance. We had to move the mike and test box away from electrical equipment to avoid a 60-Hz peak in the noise graph, Fig. 6. Recording studios minimize electro magnetic noise (as well as acoustic hum) by using incandescent instead of fluorescent lighting and by keeping non-essential electrical equipment out of the studio. Thus, hum will not be a problem with the KM-84 in most studios, but the audiophile could encounter problems in the field while recording weak sound levels in a room with strong electro magnetic interference.
(Editor's Note: Neumann states that they have concentrated on r.f. interference problems and feel the mikes are nearly immune to these.) We observed clipping at 132 dB with the KM-84. This is close enough to the spec value and adequately high for most voice or music applications. The "pop" sensitivity of the KM-84 (with screen) was just a little higher than our BK-5B with its large 4-inch diameter windscreen. This good "pop" immunity apparently results from the trade-off of high frequency response and is caused by the high air-flow resistance of the foam screen.
Vibration sensitivity of the KM-84 was quite low, and equal to our BK-5B. Phasing was Pin 2 positive, in agreement with the proposed revision to the EIA Standard.
Subjective and Listening Tests The fet-80 series microphones were used without the "pop" screen for this portion of the review.
The KM-84 with speech or music at two feet or more sounded very similar to our BK-5B reference mike (M-flat response) except for a distinct lack of "presence." The BK-5B has a slight rising response trend from 50 to 15,000 Hz, and the response in the 2,000-5,000 Hz region rises a few dB above the trend. A similar result was obtained by comparison of the KM-84 to a 77-DX, except the top octave of the 77-DX was missing compared to the KM-84. The essentially flat response of the KM-84 may be acceptable without equalization in many applications. With pipe organ, for instance, all three mikes sounded identical, but for voice, brass, guitar, strings, and woodwinds, we would boost the "presence" region of the KM-84 2 to 6 dB with an external equalizer.
We obtained similar results with the KK-85 capsule in the high frequency region. The bass roll off is quite noticeable for distant sources, and the KK-85 must be placed at 6 to 12 inches from the source to obtain a natural bass sound. The KK-85 has obvious utility for close pickup of voice or music, as well as suppression of low-frequency noise in rooms or outdoors.
A proper A-B test of the KK-83 capsule would require comparison to a lab condenser mike. We did not do this because a change of the reference mike would require retraining our ears, as well as adding confusion to this report. Besides, in the real world, pressure mikes are compared to pressure-gradient mikes. For distant voice (in our dead room), the KK-83 yielded similar results to the KM-84 when compared to the BK-5B reference. Its lack of proximity effect is a great advantage for close pickup of voice or music. For voice, the mike may be used "on axis," but for certain high-pitched instruments the top octave is exaggerated and the mike must be oriented perpendicular to the axis of the source for a natural sound (if the mike is used close to the instrument). We feel the KK-83 would be excellent for classical recordings where a pair of mikes is suspended above the orchestra, if the room is not excessively reverberant. We'll leave this as an exercise for the audiophile and hope to receive some reports of their results.
Except for the slight possibilities of hum problems, the fet-80 series has excellent performance. The price is competitive with high quality ribbon and dynamic mikes, and we think the price is moderate for a top quality condenser mike.
We feel that the audiophile who has an octave band or preferably one third octave band equalizer will obtain maximum performance in varied field situations with these microphones.
We mentioned that improved instruction books would be desirable for the audiophile. We also feel that Neumann should incorporate an isolation transformer in the power supply which would prevent the shorting problems found with some mike inputs. This would save the audiophile from having to perform circuit modifications on mikes, mixers, or recorders in the event that shorting problems are encountered.
(Editor's Note: Neumann feels that for the audiophile the fewer transformers, the better, and recommends their KM-883 mike which is similar to the KM-83 but has an unbalanced output and requires no transformer.)
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(Source: Audio magazine, Jan. 1978; Jon Sank)
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