Jump to content

DSatz

Members
  • Content Count

    12
  • Joined

  • Last visited

About DSatz

  • Rank
    Member

Profile Information

  • Location
    New York
  • About
    Classical musician/location recording engineer
  • Interested in Sound for Picture
    Yes

Recent Profile Visitors

603 profile views
  1. Gazwas, the rotational symmetry of Schoeps' CMIT microphones is a feature that truly differentiates them from some competing brands. For other microphone or capsule types, however, such as omnis, cardioids and supercardioids that aren't "side-facing", rotational symmetry is the usual situation that users assume implicitly. Have you ever seen someone set up a pencil-type cardioid, aim it at the sound source, then rotate the mike until the logo (or whatever) was face up? That's not common practice, because it's widely understood that it makes no difference. When it does make a difference, it's the manufacturer's responsibility to say so, and to provide some way of showing how the microphone should be oriented. To my mind, if something isn't a distinguishing feature, it would be misleading to emphasize it in the sales literature--as if implying that other people's microphones aren't exactly the same way. --best regards
  2. Off-axis rejection in any shotgun mike is highly variable as a function of both frequency and the specific angle of sound incidence. That's the nature of the interference-tube technique, which is based on phase cancellation created by path-length differences. At one off-axis angle you might find 10 dB variation in response across a given octave or two of the frequency range (a degree of variability that wouldn't be tolerated in any other type of microphone). If you move the source or the mike just 10 degrees relative to the main axis, that entire response curve will change; its hills and valleys will occur at different frequencies from before, and the distance from the highest peak to the deepest valley will also change. As a result, no one overall decibel amount can possibly characterize a microphone's behavior in practical situations. If you graph the microphone's directivity factor vs. frequency, then you start to say something--but the sound quality in practice will still be affected significantly by factors that the graph doesn't reveal. The length of the interference tube determines three interrelated effects. One is that a shorter tube generally causes less violent ups and downs in the frequency response for any given angle of off-axis sound incidence. A longer tube causes a greater degree of variation or deviation from flat response, depending on the angle. Second is that, at any angle at which a given frequency is being (relatively) suppressed, a longer tube would generally suppress it more--though that's not an airtight statement, since the frequencies of maximum suppression at any given angle are also a function of the tube length, so it's true only in the aggregate. Third--and this is something that I'm surprised that people seem to forget so often, even in this forum sometimes--is that the length of the tube determines the frequency at which the tube begins to have any effect on off-axis sound pickup at all. For any given length of interference tube, there's a frequency below which the tube is transparent to sound and has no effect on the pattern. It's inversely proportional to wavelength. A longer interference tube will begin to narrow the microphone's pattern at a lower transition frequency than a shorter interference tube will do. (As an aside: The little microphones that have come onto the professional market recently, with slotted tubes only two or three inches long, can't possibly have any narrowing effect except on the highest sound frequencies. From their polar diagrams it's clear that the narrowing occurs above the range that matters most, and that the degree of suppression is also quite limited, as one would expect from their principle of operation. Yet people's wishful thinking seems to take over, like "Wow! A miniature shotgun microphone! Why didn't someone think of this sooner?" The answer is that the interference tube principle can't be miniaturized and isn't being miniaturized, since it depends entirely on sound wavelengths--and the slotted tubes on these little microphones are more for show than for real, no matter whose brand is on the microphone.) --best regards
  3. There's no extra charge for a warranty (?!!); for microphones it's two years, and capsules and amplifiers can be registered on Schoeps' Web site so that it becomes ten years. Certain conditions apply, e.g. the extended warranty applies only to the original owner, and must be registered within a year of the purchase. I think that the charges mentioned earlier must have been for non-warranty service. In that situation, yes--if you send Schoeps a complete microphone for service, its capsule and amplifier are considered separate items. This is spelled out on their Web site, and the flat rates are given there as well, which depend on the age of the product(s) involved. https://schoeps.de/en/service.html . --best regards
  4. Whenever I've bought used Schoeps equipment I've sent it back to the factory for checkout. Even capsules that were claimed to be in "excellent" or "like new" condition have needed some degree of repair about half the time. I don't blame the sellers; they can be 100% honest but unaware of internal problems that may exist. As far as changes over the years are concerned, newer capsules of some types (e.g. the MK 2 omni) are more sensitive than the ones from the first decade or two of the Colette series, thus lowering the equivalent noise of the microphone as a whole. A few types of capsule have also undergone improvements in frequency response at one or both ends of the range. For example an MK 8 with the newer, more open housing type will have more extended low-frequency response than the original type did; an older capsule can be remounted in a new housing to get this improvement. With older capsules that need more serious repair, Schoeps may update them to some extent when repairing them. That depends on the repairs that are needed, though. if a particular capsule has sonic characteristics that you want to maintain as closely as possible, you should let them know that when you send it in, in case they have to replace major parts; they can sometimes accommodate such requests. They keep records of every capsule they've made since 1953, and update those records when repairs are made, although as of last year they no longer repair microphones older than the Colette and CCM series. --best regards
  5. The RSM 190 and RSM 191 are exactly the same microphone. Neumann didn't sell these microphones separately, but only in sets with accessories and a carrying case, and it's the accessories (mainly the required matrix box) that differ by "generation". There have been three different types of matrix box (MTX 190, MTX 191 and MTX 191 A), with differences in cabling and powering arrangements between the MTX 190 on the one hand, and the two MTX 191 models on the other. But any of these matrix boxes can be used equally well with a microphone labeled either as "RSM 190" or as "RSM 191", as long as you use the right type of cable between the microphone and the matrix box. The main functional difference among the matrix boxes is that the MTX 190 requires external 48 Volt phantom powering, while the MTX 191 [A] offers a compartment for a 9V battery for when phantom powering isn't available, plus a toggle switch for battery vs. phantom operation. Specifications are identical for both types of powering. Battery life is claimed to be 8 hours for an alkaline, which I haven't tested. The MTX 191 has a low battery LED, while the MTX 191 A has a "battery test" position on its battery-vs.-phantom toggle switch. The MTX 191 and 191 A also have a 10 dB pad switch, a switch to shift the (always on) low-cut filter up from 40 to 80 or 200 Hz, and a switch that reverses the L vs. R outputs in either X/Y or M/S mode--none of which the MTX 190 has. Speaking of low-cut filters, there is also a gradual rolloff filter for frequencies below about 150 Hz for the "S" channel (figure-8) only, in the body of the microphone itself. This filter can be bypassed by unsoldering a bridge on the circuit board. Bypassing the filter makes the stereo pickup more spacious-sounding, but of course it also increases the risk of wind and handling noise. The filter is engaged when the mike comes from the factory, but if you buy a used RSM 190 or 191, this solder bridge should be checked (pages 9 and 10 of the instruction manual) to make sure that it's set the way you need it. --best regards
  6. As John B. said, the DC converter circuitry in modern microphones is part of this. First-generation phantom powered microphones generally took the incoming 48 Volts and routed that through a high-value resistor to polarize the capsule. Those mikes generally had a single FET as their only active device, with an output transformer--miniaturized so as to fit into a 20 or 21 mm-diameter housing--that brought the output impedance down into the standard 150 or 200 Ohm range. Transformers that small, however, saturate rather easily, especially at low frequencies. They restrict the maximum output voltage and thus the maximum SPL of the microphone. More modern condenser microphones generally add an active output stage which is direct coupled, i.e. transformerless. That arrangement requires substantially more operating current, but also offers much better headroom, and greatly improves the ability to drive long cable runs. The DC converter that John mentioned improves the sensitivity of the microphone, since all other things being equal, the sensitivity is proportional to the capsule's polarization voltage, and those converters typically put out around 60 Volts. They're also almost a necessity in a modern 48-Volt microphone, since the increased current draw of the output stage causes a larger voltage drop across the 6.8 kOhm resistor pair in the phantom supply. Thus a microphone that draws 4 mA, for example (2 mA per resistor -> 13.6 V drop across 6.8 kOhms), actually receives a voltage in the low-to-middle 30s rather than 48. It would cause a major step backwards in sensitivity if such a low voltage were used to polarize the capsule. So: The original, analog version of the Neumann KMR 81 is one of the last remaining holdovers from their fet 80 series, which began with the KM 84 microphone in 1966. It features the older, simpler, lower-current, transformer-output type of circuit, with lower headroom (as a wild guess, maybe 6 to 10 dB lower) than it could have with more modern circuitry. It still does well for its age, though--it can put out about 900 mV (when lightly loaded) if it has to, for a maximum SPL of 128 dB (again, when lightly loaded). It's a nice-sounding microphone in my opinion. I don't know how well it does in high humidity, though; it's a traditional DC-polarized condenser, and for situations with any risk of moisture condensation, RF condenser microphones are generally considered more reliable. --best regards
  7. The KM 180 series uses a DC converter to boost the 48-Volt phantom supply voltage up to 60 Volts to polarize the capsule. The converter basically is a radio frequency oscillator that drives a tiny step-up transformer; its output is then rectified and smoothed. With proper powering and a properly functioning microphone, the frequency of that oscillator is well above the audio range. However, if the microphone is defective or the phantom powering isn't up to specification, the oscillator frequency can dip down into the audible range. You can hear this if you connect the mike to an outboard phantom supply, run it for a minute, then turn the powering off while you continue listening to the microphone's output. As the stored energy in the supply and the microphone ebbs away, the oscillator will drop in frequency, and you will hear it descend through the audible range until it dies out completely. Since Sennheiser didn't find any problem with the microphone itself, I suspect that it wasn't being powered correctly when you ran it. There have been two different versions of the KM 180-series circuitry; the changeover occurred around 2002. The original KM 180-series microphones required 2.3 mA; the later version requires 3.2 mA (in return for which they are 3 dB quieter, while keeping the same sensitivity and maximum SPL). I suggest that you try your microphone with a different preamp, mixer or recorder, or with a known good outboard 48-Volt phantom power supply. The original version of the phantom powering standard set 2 mA as the recommended limit, and a lot of older equipment (and even some that's newer) falls out of spec trying to deliver the 3 to 5 mA that microphones commonly require today, let alone the 7 to 8 mA required in some extreme cases. --best regards
  8. The KM 183 is a "diffuse-field equalized" omni, which means that it was designed for distant miking. When used at medium or close range, it will have a considerable on-axis elevation in its high-frequency response--6 to 8 dB. That evens out when the mike is used at a distance in a reverberant space, since when you get far away enough, the sound reaches the microphone at more or less random angles, while that high-frequency elevation only affects the front quadrant. On the plus side, this type of microphone would have lower sensitivity to wind and handling noise than any directional microphone. But due to the pickup pattern, you would have to get almost twice (1.7 times, technically) as close to your sound source in order to pick up the same direct/reflected mixture as even a cardioid would give you. --best regards
  9. The factory can update older CMC 6-- amplifiers, but it's not cheap; it involves an entire circuit board replacement, not merely installation of that shield plate in the connector well. In effect it's a trade-in. There's no sonic difference, nor any change in performance or powering or anything else. And clearly, not everyone absolutely needs the more recent version. Still, I'm glad to have it because I record mostly live classical concerts, and I can't exactly tap the conductor on the shoulder and ask for a retake. --best regards
  10. In answer to the original poster's question: The two lobes of any figure-8 microphone have opposite signal polarity. Any positive-going sound impulse occurring in the front of the mike should produce a positive-going electrical waveform at the output, while if it occurs behind the mike, it should produce a negative-going waveform. The whole M/S principle is based on this characteristic: M + S = L, while M - S = R. Rotating a figure-8 mike by 180 degrees should cause the polarity of its signal output to be exactly reversed, assuming that it's truly symmetrical, as it should be. Normally, the 0-degree axis of the "S" microphone in an M/S pair should point to the left as you face the sound sources. If you set an M/S pair up with the 0-degree axis pointing to right instead, the "S" microphone's entire output will be the inverse of what is normally supposed. Take the above basic equations and invert the sign on S, and you'll see that the channels come out reversed in that case; whatever really occurred on the left will come out on the right and vice versa. So it does matter which way the dot goes, though if you get it wrong and realize it in time, it's completely fixable. --best regards P.S.: The (smaller) rear lobe of any supercardioid or hypercardioid is also opposite in polarity from the front lobe. If you like, you can think of those patterns--especially the hypercardioid--as figure-8s that came out lopsided to a certain degree.
  11. Hi, people. Sorry I couldn't join this conversation sooner, but I had to register with the sysop first. I'd like to reply to a few points. Yes, the CMC 3 and CMC 5 (for any given generation of circuit board) differ only in whether the bridge shown as "C" on the (decades old) schematic shown earlier in this thread is open or closed. The CMC 4 is a separate instance, and for many years was built on a different circuit board entirely, making conversion from a CMC 4 to a CMC 5 circuit much more difficult. The factory will gladly convert any CMC 3 to a CMC 5 or vice versa, but they don't convert to or from the CMC 4 (or CMC 6 for that matter). It's true that an unmodified CMC 3 can in a general sense be powered from a standard 48-Volt phantom supply--at least, that mode of powering is generally safe for the microphone. But the current draw will then be about 11 mA, which is is a little more than the standard for phantom powering requires--and unfortunately, many phantom power supplies and phantom-powered mixers and recorders don't meet, let alone exceed, the standard. So that approach is generally not recommended. There is no "alternative standard" for 9-54 VDC; phantom powering is standardized for 12 Volts and for 48 Volts. (For some years 24-Volt phantom powering was also defined, but nowadays it is just a footnote.) Different microphone circuits permit different ranges of supply voltage in practice, but also respond differently to inadequate powering. If the phantom supply is a few Volts below spec, some microphones will be fine, others will show only marginally reduced sensitivity, maximum SPL handling and s/n performance, while with still others, the maximum undistorted SPL will decrease far more than you would probably expect. With some microphones the internal DC/DC converter starts to leak high frequency garbage into the audio signal when the phantom voltage is too low. And all these different outcomes or symptoms can sometimes be found in different models from the same manufacturer. So it doesn't pay to assume too much; it's much safer to know what a given type of microphone actually requires, and to make sure that it reliably gets that. --best regards
×
×
  • Create New...