Gear / Technical Help > Microphones & Setup

Mic mods and tinkering...

(1/3) > >>

goodcooker:

I bought a pair of Cascade M39 small diaphragm mics for super cheap yesterday and I'm thinking about doing the capacitor swap that people say makes them perform better and with more closely matched output.

Anyone done a mod on a cheap mic? Most of them are based on the based on the Schoeps circuit (for SDCs) or the Neumann U67 circuit (for LDC).

The real difference is in the capsule and diaphragm but I'm hoping to get a decent pair of second stage mics out of the deal for well under $200.

DSatz:
Hmmm. Mass-produced capsules vary in their frequency response and sensitivity far more than electronics commonly do nowadays, so if closer matching is really a common result (a claim that surprises me somewhat), that could be a function of component choices that you could just as well make with the existing circuitry.

There's no reason that the Schoeps output circuit shouldn't be used with large-diaphragm capsules. The Neumann U 67's circuit is peculiar because the capsule itself is inherently quite bright sounding, so the amplifier purposely rolls off the high end by about 5 dB. There's also a fairly steep low-cut filter below 40 Hz, which was the subject of a patent back in the day. The only reason I can see for using that circuit is if a particular capsule is overly bright--but then again, that applies to a lot of mass-produced capsules. Still, even Neumann didn't use that rolloff in the mikes that they specifically designed for more distant pickup using those same capsules, such as the stereo and quad mikes ((U)SM 69 and QM 69).

I have had several professional condenser mikes modified, with mixed results. Some of the claims for the mods held up in practice but there were "down sides" that weren't mentioned before the surgery occurred (e.g. one pair of AKG mikes got 4 dB better dynamic range, but were sensitive to RFI after the mod; one pair of Neumanns became different- and arguably more interesting-sounding, but had reduced headroom and no longer matched one another well). More often than not, the results didn't live up to what I was assured would occur. Some people who are in this line of development seem to believe in what they're doing, to a degree that isn't always met by the actual results of what they offer. In all cases, no matter how prominent the person was who modified the microphones, I have had difficulty reselling them at all, and have "taken a bath" on the prices I was able to get.

TL;DR: This is a realm of smoke and mirrors, though with some benefits to be gained--but all in all, one is better off starting with good capsules, since they determine 80% or more of the sound quality of a microphone.

--best regards

Gutbucket:
I've long thought about what might be most effective strategy for optimizing less than stellar microphones that suffer from frequency, phase and sensitivity tolerance variations between units.

What about taking a measurement with each microphone, comparing those against the same made with a reference mic, and inverting the difference to create a corrective filter for each microphone that either directly emulates the response of the test microphone or goes on from there to further tailor the response as desired?  That should effectively match on-axis frequency, phase response and output level within the available dynamic range limit of the microphones.

Most of the work would be in performing the measurements and creating the correction filters.  The recordist would then label each microphone to keep it associated with its own corrective filter, then apply the filters to the files prior to doing any other post production work on the recording.

Many folks here may be familiar with DIY speaker builders doing this as standard practice these days using a measurement microphone and a DSP box or software that applies the crossovers in addition to corrective filtering. So this kind of thing is now within the domain of the DIY enthusiast.

Directly analogous is the TetraMic (and now OctoMic) ambisonic microphone systems from Core Sound which use such a method to linearize and match the responses of its four cardioid capsule elements (eight in the OctoMic) sufficiently such that the ambisonic A-format to B-format conversion applied on the computer after a recording is made works correctly.  Each of these microphones is provided with a set of dedicated corrective filters which are associated with that specific microphone by its serial number.  In fact, I'm overdue to send my TetraMic in for re-calibration, after which I'll have a new correction file to apply to any new recordings made with it.

Such a discussion seems to me to fit the thread title, but I'm more than happy to make a dedicated thread to discuss it if you'd prefer, goodcooker.

goodcooker:
[quote author=Gutbucket link=topic=198572.msg2369375#msg2369375 date=164064455
Such a discussion seems to me to fit the thread title, but I'm more than happy to make a dedicated thread to discuss it if you'd prefer, goodcooker.
[/quote]

I included tinkering in the title to encourage this very line of thought.

goodcooker:

--- Quote from: DSatz on December 27, 2021, 03:45:49 PM ---Hmmm. Mass-produced capsules vary in their frequency response and sensitivity far more than electronics commonly do nowadays, so if closer matching is really a common result (a claim that surprises me somewhat), that could be a function of component choices that you could just as well make with the existing circuitry.

TL;DR: This is a realm of smoke and mirrors, though with some benefits to be gained--but all in all, one is better off starting with good capsules, since they determine 80% or more of the sound quality of a microphone.

--- End quote ---

I agree 100% with these statements. A lot of the Chinese manufactured mics look exactly the same and are in fact in the exact same machined housings but differ in sound quality from brand to brand and often from mic to mic within the same brand. Whether that is a function of design choice, manufacturing tolerances or something else is anyone's guess.

Significant performance value can be had when swapping components. I used a pair of Oktava MK012 modified by Joly for a while. The capsules were good quality and included serial number specific graphs from the factory but the amplifiers were almost an after thought. It was speculated that since components were difficult to keep in supply in Russia that pretty much any capacitor that was close in value and would fit went in the circuit. Mine were rebuilt with closely matched higher quality capacitors and resistors and it changed the harsh peaky sound of the mics considerably. I did a side by side informal comparison with the hypercard caps and a pair of MK41 and was quite surprised. I found the Oktava to be much more pleasing.

I'm hoping that the Cascade mics that I bought are decent enough to be useful on their own and that changing the cheap ceramic capacitors for better quality closely matched metal film and polypropylene components can improve them. The change is likely to be negligible but you never know until you try. I'm out $20 and an hour of tinkering if it doesn't amount to much. I'll do some informal tests along the way.

These aren't going to be my main mics. I'm going back to MBHO subcardioid capsules next year. Most versatile mic in the tool kit (and best bang for the buck) if you ask me...

Navigation

[0] Message Index

[#] Next page