Topic: Chinese mics, omni capsules, foam windscreens and recording in the diffuse field

[Chuck]

I’ve been thinking a lot about the specifics of diffuse field recording with omni-directional microphones recently. I generally prefer the sound of a well placed pair of omni-directional microphones over recordings made with more directional microphones. To me, omni recordings tend to sound much more real and involving than cardioid or other directional microphone recordings. But, omni-directional mic recordings sound much better when the mics are placed closer to the sound source then is possible sometimes.

What got me started thinking about it was my recent experiments with modifying Chinese SD condenser microphones. Typically these microphones, for example the MXL 603, CAD GXL1200, Nady CM-90, and Avantone CK-1, to name a few, have a pronounced presence boost around 6kHz to 9kHz.

Many microphone manufactures make omni-directional microphones and capsules specifically designed to be used the in diffuse field. These microphones or capsules typically have a presence boost in the 6kHz to 9kHz range. Now, for those manufactures, the diffuse field generally means that the microphones will be placed a little further away from the sound source than near field microphones would typically be placed.  For example, when recording an orchestra with mics placed closer to the stage lip or just off stage rather than right over the conductors head.

The diffuse field as it relates to tapers often means recording from a much greater distance to the sound source than the diffuse field omni microphones are meant to be used from.  A pronounced presence boost in the higher frequencies can make the source sound closer than it really is from a less than ideal recording distance. This may account for why some tapers prefer brighter mics. If they generally record from far away, they like the reach that the brighter mic gives them. So, tapers knowingly or maybe unknowingly like and specifically use the brighter sounding microphones when recording concerts in the very diffuse field that they often find themselves recording in.

I have been doing some controlled tests with stock and modified cheap Chinese condensers. I’ll play noise or music through my home playback system and record that using the different microphones that I have. When comparing the Chinese mics with the omni capsules to my reference AKG C-480 with CK-62 capsules the Chinese mics, sound much more up front than the AKG’s from the same distance. They also don’t have as much omni room boom as the AKG’s.

Some people have found that by modifying the Chinese mics either electronically or physically they can tame the brightness and make the mics sound more neutral in near field recording applications. But, the modifying to eliminate the presence peak inherent in the microphones can only take you so far.

I got to thinking about how to tame bright mics when used closer to the sound source.  So, I started to experiment with several different foam wind screens I have bought over the years. I noticed that I prefer the sound of the Chinese mics with small foam windscreens installed over the sound of them without the wind screens. I will start using them more because of this.

I generally don’t like the sound of my AKG’s with windscreens. When recording indoors I don’t usually put the screens on if there is not a lot of air movement in the venue. But, they are closer to neutral sounding then the Chinese mics.

That extra brightness I hear in the Chinese mics can be used to advantage when recording from further away with the omni capsules. I can also tame that brightness with various foam wind screens when recording closer to the source.

[SmokinJoe]

I don't have a lot to offer except some general agreement...

Until recently I owned some JZ BT201's (from Latvia).  They have a fairly pronounced high end boost too, probably not as much as your Chinese mics, but some.  I found I really liked these mics with the omnis outside, with the "big ass shure" windscreens.  In fact at "Gathering of the Vibes" where the OTS is about 100' from stage, I liked them more than any other mic I've tried.  Even with the distance, and the heavy windscreens, they still pulled detail, in a place where other mics can turn to mud.
These are the open cards, but you get the idea... http://www.archive.org/details/qmb2010-07-29.bt201.flac16f

[Chuck]

Yeah, that's exactly what I was getting at. Use the perceived negative attribute of the mics to your advantage.

[illconditioned]

If you're going to record omni, get small capsules (ideally a point sensor), so the shape of the microphone has negligible effect.


Also, get best quality capsules.  For amplified music, a pair of Countryman B3 will sound better than *anything*, that is anything short of a DPA/Gefell/etc measurement mic.


  Richard

[Chuck]

I've read about your recommendation of the Countryman B3 mics many times Richard. But, I have never used them. Maybe it's time I try them because I still haven't found my perfect omni mics.

[Chuck]

The closer you get to a point source, the more you will eliminate diffuse-field response, as the microphone will get progressively more omni by removing the on-axis HF boost.

The other way to go, and this was done with classic omni recording techniques, is to accent the on-axis HF boost, such as with the Neumann M50.  It's probably safe to say more concert recordings have been done with that method rather than the former.

Thanks for that post mshilarious.

Here is a good read on the Neumann M50:
http://recordinghacks.com/microphones/Neumann/M-50

[illconditioned]

The closer you get to a point source, the more you will eliminate diffuse-field response, as the microphone will get progressively more omni by removing the on-axis HF boost.

The other way to go, and this was done with classic omni recording techniques, is to accent the on-axis HF boost, such as with the Neumann M50.  It's probably safe to say more concert recordings have been done with that method rather than the former.

The appeal of the M50 is both the HF boost and the fact that it is an excellent capsule,  A one half inch metal (nickel) diaphragm.

  Richard

[DSatz]

The type of diffuse-field pressure microphone for which the original Neumann M 50 is the prototype was developed in the mono era of recording, when a very large ensemble (say, a full orchestra and chorus performing the Beethoven Ninth) could be picked up by a single microphone at a considerable distance from all the performers. The design of the M 50 (as with the M 49) was done in the research laboratory of the NWDR; Neumann was then awarded the contract to manufacture those designs.

More recent versions of this type of microphone, developed since the growth of stereo recording in the mid-1950s, have less of an on-axis rise and are typically placed closer to the "reverberation radius" (a/k/a "critical distance"). That is even true for Neumann's later versions of the M 50 (at least three different capsule types were used throughout the series). The classic "Decca Tree" arrangement used this type of microphone, but by the time Decca adopted it, it no longer had a fully diffuse-field equalized response, and the placement was certainly not all the way back to where the sound field is predominantly diffuse.

A fully diffuse-field omni that is used too close to the sound sources is rather uncomfortable to listen to. I know, because for a few months in the early 1970s I used to record with a spaced pair of Neumann KM 83s. Nowadays, to listen to those tapes without massive regrets I have to cut the treble by several dB. And if I had placed the mikes far enough back to make up for their on-axis rise, the sound would have been all "washed out" with reverberation, and there would be no effective stereo localization in the recordings at all.

I guess what I'm saying is that a fully diffuse-field equalized omni isn't often a useful choice for stereo recording. If they're all you have available, you could place them where the reverberation balance sounds the best, then cut back the high frequencies in post-production.

[Gutbucket]

The other way to go, and this was done with classic omni recording techniques, is to accent the on-axis HF boost, such as with the Neumann M50.

DIY sphere mounted small omnis providing a bit of on-axis HF boost & increased HF directionality (as well as reduced eye-pokiness potential in the FOB zone)

[Chuck]

Cool! What's that sound like?

[Gutbucket]

Like deep-dish lasagna to a starving man. 

[Chuck]

...in my on going fascination with cheap (omni-directional) microphones...

I had a hunch that the capsules for the Samson CL2, Superlux S241 and CAD e70 lines of microphones were interchangeable with the MXL 604, CAD GXL1200, Nady CM-90 etc... capsules.

So, I talked a CAD rep into sending me a CAD e70 omni capsule to check out.

I was able to screw that capsule onto one of my modified CAD GXL1200 bodies.

The pictures below show the CAD e70 capsule (black and shorter) along side of the (silver and longer) CAD GXL1200 capsule.

I plan to do a test to see if the e70 style capsule sounds any better (or different) than the stock 604 capsules. The common complaint about the stock 604 capsules is that they are too bright due to an 8kHz frequency bump. Some people that modify the Chinese microphones have found that by removing the extra chamber in front of the capsule, they can tame that 8kHz bump.

I'm hoping that the e70 style capsule does that without being modified.

If you look at the e70 capsule, it does not have the chamber in front like the 604 capsule does. The e70 capsule has a resonator disc in front of the diaphragm too.

I plan to do a test in the next couple of weeks to see how the e70 capsule compares to the 604 style capsule.

[illconditioned]

...in my on going fascination with cheap (omni-directional) microphones...

I had a hunch that the capsules for the Samson CL2, Superlux S241 and CAD e70 lines of microphones were interchangeable with the MXL 604, CAD GXL1200, Nady CM-90 etc... capsules.

So, I talked a CAD rep into sending me a CAD e70 omni capsule to check out.

I was able to screw that capsule onto one of my modified CAD GXL1200 bodies.

The pictures below show the CAD e70 capsule (black and shorter) along side of the (silver and longer) CAD GXL1200 capsule.

I plan to do a test to see if the e70 style capsule sounds any better (or different) than the stock 604 capsules. The common complaint about the stock 604 capsules is that they are too bright due to an 8kHz frequency bump. Some people that modify the Chinese microphones have found that by removing the extra chamber in front of the capsule, they can tame that 8kHz bump.

I'm hoping that the e70 style capsule does that without being modified.

If you look at the e70 capsule, it does not have the chamber in front like the 604 capsule does. The e70 capsule has a resonator disc in front of the diaphragm too.

I plan to do a test in the next couple of weeks to see how the e70 capsule compares to the 604 style capsule.

Hmm.  The CAD E70 *may* be an electret mic.  May be, maybe not.  Hard to tell.  I could tell by looking at the circuit board, though.

  Richard

[DSatz]

Among low-cost condenser microphone capsules the pressure (omni) transducers can certainly offer better value per dollar than the pressure-gradient (generally directional) transducers. They're much simpler internally, and less expensive to build to any given standard of performance and consistency. I cringe when I see people here offering conclusory statements about super- and hypercardioid microphones, for example, based solely on what they've heard from third- and fourth-rate examples of the type.

In addition, since omnis are usually used spaced apart, unit-to-unit consistency matters somewhat less than it does with directional microphones that are placed close together or coincident. Another plus for the omnis, if you're restricted to low-cost versions.

But even where omnis are concerned, I think it would be a shame if people were to deprive themselves of working with better-quality microphones at some point in their lives, once they have a clue as to how to use really good microphones and what to listen for in a recording. There is something very real that one is paying for with the better microphones--including pressure transducers--in terms of smooth frequency response, good transient response and low distortion.

That difference truly doesn't show up in specification sheets. Published response graphs are nearly always "smoothed," and few manufacturers disclose their production tolerance limits. There isn't even an agreed-upon way to specify distortion in microphones, except for the method of specifying maximum SPL (which typically excludes the capsule anyway). But most manufacturers outside the top tier make little or no attempt to conform to such standards in the first place; their specifications more often reflect their marketing goals rather than actual performance.

I truly don't mean to disparage the experimental interest and the hobbyist enthusiasm (and good old American cheapskate-ism) for finding out the best results are that can be gotten for the lowest price. I just want to point out that better microphones really do tend to sound better--assuming appropriate usage, of course. Also, some of the things that less good microphones might do to the sound of a performance can't be undone or overcome no matter how good the equipment or the processing further "downstream" might be.

As long as people don't completely lose sight of that, by all means carry on! I'm reading this discussion with as much interest as the next guy.

--best regards

[chris319]

The CAD E70 *may* be an electret mic.  May be, maybe not.  Hard to tell.  I could tell by looking at the circuit board, though.

There is a partial view of the circuit board here:

http://taperssection.com/index.php?topic=128078.0

The e70 is a very bright mic.