Two microphones as matched pair, what properties are matched?

[MagnetoSound]

I think the part of loosest tolerance in a microphone is generally the capsule, and it seems even those are much more consistent nowadays than 40-60 years ago. Manufacturers can practically guarantee close matching in most cases, much more so than previously. Circuit changes and PSU variation notwithstanding. Components are a lot more consistent in manufacture.

 

[k brown]

@MicUlli: Those plots look weird. If measurement conditions for both were identical, I'm pretty sure the mic with the red plot is out of spec and should be serviced (i.e. needs a new capsule). Even for non-matched KM 184 the difference is way too big, and there seems to be quite some bass loss.

Here's a plot of my own pair of KM 184. I bought them as the standard matched pair set.

View attachment 109630

Regarding the difference between the KM 184 and the KM 84, I have a feeling people are exaggerating. I often read that the KM 184 is a bright mic. As the plot shows, that's not the case. I worked as a reviewer for close to 20 years and during that time I measured quite a number of small diaphragm mics, and just about all of them had a (much) bigger treble boost.

I don't own a KM 84, but I have a vintage KM 86. Here's a comparison plot of the KM 184 vs KM 86 in cardioid mode (please excuse the slightly different scaling; those plots were not done a the same time):

View attachment 109631

I might add that other factors than frequency response can give a mic a sound that is subjectively 'bright', such as a bit more distortion in the fr range that ears are most sensitive to, even though that range of the mic isn't higher in level.

 

[RCAguy]

I bought two “matched pairs” from a “professional” mic maker I’ll not deal with again (for several reasons). They only matched sensitivity, easily compensated by any user by adjusting preamp gain. But ignoring the far more important matching of frequency response curves

 

[Cqwet Dbdfte]

Orchestra and large jazz band recording typically uses stereo microphone configurations, and it is very convenient to have microphones which are close in sensitivity and frequency response for those cases.

Yes, like I stated in my remarks about "Blumlein and far field applications".
Old 1960's RCA "Living Stereo" recordings were reportedly done live with 3 mikes, left right and center, hung above the "talents".
The well considered and famous "Jazz at the Pawnshop" recording was done with 7 ea. U47 mikes into a Nagra tape recorder, sometime mid 70's. The mikes were suspended from the ceiling. I was not there, that day.

 

[terry setter]

As I posted on a different DIY topic, I had a friend who retired from Electro-Voice. He swore to me that they'd take two new microphones (of the same type), put them in a room such that their capsules were as close and identically pointed as possible, then play pink noise into the space. They would check that the output levels were within (as I recall) 1/2 dB, then throw one out of phase. If the combined signal dropped by 20dB, they were sent out as a "matched pair". I wasn't there, but he was a reliable guy and not prone to exaggeration .

 

[Cqwet Dbdfte]

That makes sense. I hope more mfg does this too. Checking the out of phase difference with a spectrum analyzer would be a step further

 

[MicUlli]

After a lot of work spent on this issue i found a (probably too complicated) way to match SDCs.

The idea behind it: The relationship of the omni part vs. the directional part of the mic sensivity shall be the same (< 1dB deviation) for the two mics over the whole frequency range.

->Obtain FR(0°) and FR(180°). Then apply windowing (10ms is a good choice) and calculate (FR(0°)+FR(180°))/(FR(0°)-FR(180°)) for the two mics.
Then equalise both mics for the same FR(0°) and determine the level difference.

You may be a lucky guy when FR and sensivity match anyway...

 

[SubSpec]

I wanted to get a rough idea of how close my KM84s are to each other. This was a super simple setup, side by side a couple feet in front of an uncalibrated monitor pumping out pink noise, with identical gain (digitally controlled).

They are not "matched" with a ~2db difference in some spots but close enough for my usage. That said, I will likely sell the pair before long and would like to provide prospective buyers with a reasonable assessment of how much they differ.

Does this seem sufficient for that purpose or would I be a better steward to have a more in-depth analysis and If so, what would you recommend?

 

[abbey road d enfer]

The on-axis responses are close enough to be consiered "matched".
An extra step would be comparing the 90° and 180° responses.

 

[SubSpec]

The on-axis responses are close enough to be consiered "matched".
An extra step would be comparing the 90° and 180° responses.

Excellent, thanks for that feedback! They certainly are better matched than I expected given their age and the fact that every cheap "pair" of SDCs I've bought definitely differed more than these. I'll get the off axis responses as well for full coverage!

 

[cyrano]

I don't know if it is general practice, but I've known more than one studio owner who bought mics in multiple pairs, tested and measured them and keep the "good" ones. They either sold the lesser ones or sent them back to the seller. Even with current Neumanns.

One of them also told me it's better to have a dozen identical mics than a dozen different ones. He didn't do rock or pop, just classical, some folk and jazz. He had way more SDCs than LDCs. I always admired his recordings.

 

[abbey road d enfer]

One of them also told me it's better to have a dozen identical mics than a dozen different ones. He didn't do rock or pop, just classical, some folk and jazz. He had way more SDCs than LDCs. I always admired his recordings.

Looks like inheritance of the ex-ORTF school of thought, where someone decided that mixing mics was wrong.
It resulted in generalization of Schoeps mics, which is not all that bad, but also earlier in having DO21's used as vocal mics in rock concerts...

 

[cyrano]

Never even seen that LEM DO21. Not a cheap mic. What was wrong with using them for rock vocals?

 

[abbey road d enfer]

Never even seen that LEM DO21. Not a cheap mic. What was wrong with using them for rock vocals?

Omni!
Not a bad ENG mic, though.

 

[cyrano]

Sorry, missed that it was an omni.

Never seen one on stage here. Despite the fact that the nowadays omnipresent 57 or 58 wasn't all that common either. Sennheiser, RCF... that kind of stuff.

Maybe it created a market for feedback killers?

 

[abbey road d enfer]

Sorry, missed that it was an omni.

Never seen one on stage here.

Well, if you watch a replay of the 60's french TV music shows, you will see them a lot.

Despite the fact that the nowadays omnipresent 57 or 58 wasn't all that common either. Sennheiser, RCF... that kind of stuff.

I'm talking about the 60's. Shure Unidyne were available, as well as Beyer M67/M88 and EV RE16..