MS mics placement

[abbey road d enfer]

The net output is not necessarily what is seen at the ribbon ends or voice coil ends voltage wise - the following circuit inside the mic can alter the phase of the signal.

How?
Phase-response in the head amp is intimately correlated with frequency response, by virtue of being Minimum-Phase.
Any deviation of the frequency response from a flat response is an attempt at correcting the capsule's quirks.
If done correctly, response variations in the head amp are intended to correct the frequency response variations in the transducer. Due to the MP behaviour in the validity domain, the phase-shift introduced in the head amp should cancel those created by the transducer.

 

[RoadrunnerOZ]

How?
Phase-response in the head amp is intimately correlated with frequency response, by virtue of being Minimum-Phase.
Any deviation of the frequency response from a flat response is an attempt at correcting the capsule's quirks.
If done correctly, response variations in the head amp are intended to correct the frequency response variations in the transducer. Due to the MP behaviour in the validity domain, the phase-shift introduced in the head amp should cancel those created by the transducer.

I’m only talking about what occurs inside the microphone and the difference between two differing capsule types and their phase relationship - nothing to do with amplification outside the body of a dynamic or ribbon mic and what it does. It seems you are denying that there is a maximum voltage output at zero acoustic pressure wave crossing point where the diaphragm is moving the fastest for a coil or ribbon mic, either that or denying that maximum voltage output for a condenser occurs at maximum + pressure/excursion - 90deg away from the ribbon/coil.
Why would many professional audio texts be written cautioning the use of mixed mic types at the same location due to phase inconsistencies.
However, if what you are implying is what I think it is, you’re saying that a ribbon or coil and a condenser at identical locations will be perfectly in phase using the same type preamp - including the use of vintage mics and preamps. Or not?

 

[molke]

However, if what you are implying is what I think it is, you’re saying that a ribbon or coil and a condenser at identical locations will be perfectly in phase using the same type preamp - including the use of vintage mics and preamps. Or not?

That’s the whole point, at least for the range where frequency response is reasonably similar (e.g. flat). And “identical locations” is rather hypothetical, so I wouldn’t say “perfectly”. I’m not sure what the preamp or vintage mics would have to do with it.

 

[RoadrunnerOZ]

That’s the whole point, at least for the range where frequency response is reasonably similar (e.g. flat). And “identical locations” is rather hypothetical, so I wouldn’t say “perfectly”. I’m not sure what the preamp or vintage mics would have to do with it.

Just covering all the various types of mics and preamps including the vintage tube mics and transformer coupled mic preamps of previous years.
The thing that makes me curious is that in the days of tape we had to be cautious of mic placement to ensure phase correlation - all the mainstream consoles had a phase meter which you could use to check phase relationship between two channels panned opposite - +=in phase, -=out of phase! This was used to check phase cohesion between left and right of a stereo mix or two elements of a recording in progress or off tape, you just needed to pan them opposite - whatever came through the monitor stage. There was no sliding of audio tracks to correct phase errors in those days - you had what you recorded - all you got was a phase flip switch on the mix console channel strip.
There must have been a good reason to caution about the mix of condenser and dynamic or ribbon type mics and I remember it was common to check their phase using a phase meter, adjusting position and ensuring common phase, or doing it by ear, to minimise cancellations and frequency holes or peaks.
Quote: Handbook for Sound Engineers p505 diags p506
“Further, the diaphragm and its attached coil reach maximum velocity, hence maximum electrical amplitude—at point c on the acoustic waveform. This is of no consequence unless another microphone is being used along with the moving-coil microphone where the other microphone does not see the same 90° displacement. Due to this phase displacement, condenser microphones should not be mixed with moving-coil or ribbon microphones when micing the same source at the same distance.”
(Note - point c referred to above is on diag fig16.35 - where the acoustic pressure curve crosses the zero pressure line, halfway between positive peak and negative peak.)
This text co-authored by Volker Schmitt, from Sennheiser I believe.
This is only one of many texts to caution this mix of condenser and magnetic induction mics with relation to phase.

 

[molke]

“Further, the diaphragm and its attached coil reach maximum velocity, hence maximum electrical amplitude—at point c on the acoustic waveform. This is of no consequence unless another microphone is being used along with the moving-coil microphone where the other microphone does not see the same 90° displacement. Due to this phase displacement, condenser microphones should not be mixed with moving-coil or ribbon microphones when micing the same source at the same distance.”

There may be many valid reasons not to mix ribbons and condensers. As far as I’m concerned, an inherent “90° displacement” is not one of them. Textbooks can be wrong too.

 

[RoadrunnerOZ]

There may be many valid reasons not to mix ribbons and condensers. As far as I’m concerned, an inherent “90° displacement” is not one of them. Textbooks can be wrong too.

Audio Technica would disagree with you on that one - they clearly state a 90deg phase difference between condenser and dynamic and that they solved this for their dual element ATM250DE.

 

[RoadrunnerOZ]

A ribbon and a moving coil both exhibit the same electrical response phase relationship.

 

[molke]

Audio Technica would disagree with you on that one - they clearly state a 90deg phase difference between condenser and dynamic and that they solved this for their dual element ATM250DE.

That’s the marketing video; the actual product description is much more careful in its description:

Elements are positioned in a perfect phase relationship, something practically unachievable with two separate microphones

I’m not saying that I’m necessarily right, but an inherent 90° phase shift between both elements (without the special Audio Technica treatment) should be pretty easy to show by putting a condenser and a dynamic (or ribbon) in front of a speaker and testing some frequencies.

 

[RoadrunnerOZ]

All I’m driving at is that the generator elements of both types are electrically 90deg out of phase - this is simple electronic engineering 101. When the moving coil or ribbon stop producing an output voltage at excursion reverse, the condenser is at its highest output, when the condenser is at the crossing of the diaphragm rest position the dynamic voice coil is at its peak output voltage.
Edit: for the same acoustic wave input, at the same distance.

 

[RoadrunnerOZ]

Then there’s DPA Microphones - see point 11:
https://www.dpamicrophones.com/mic-university/10-statements-on-condenser-microphones-vs-dynamic

 

[emrr]

And anyway, MS with omni mid is the least flexible/useful; all you end up with is two cardioid patterns aimed 90 degrees left and right - how often is that really useful?

I use it all the time. Great for close work.

 

[RoadrunnerOZ]

I use it all the time. Great for close work.

“An omnidirectional microphone will in principle pick up sound equally from all directions. The microphone will though become more and more directional the higher the frequency. The smaller the capsule, the more true omni the microphone is.”
Courtesy DPA Microphones
At higher frequencies the M/S factor would kick in

 

[GabrieleP]

Audio Technica would disagree with you on that one - they clearly state a 90deg phase difference between condenser and dynamic and that they solved this for their dual element ATM250DE.

Tested their AE2500 a few years ago. Not sure if it got the same "treatment" but @ 80 Hz the two waveforms were fairly matching although not exactly matching. If I recall correctly, it was a matter of a few dozens of samples @ 48 kHz (i.e. not even 1 millisecond).

 

[RoadrunnerOZ]

That’s the marketing video; the actual product description is much more careful in its description:

I’m not saying that I’m necessarily right, but an inherent 90° phase shift between both elements (without the special Audio Technica treatment) should be pretty easy to show by putting a condenser and a dynamic (or ribbon) in front of a speaker and testing some frequencies.

We do it in the studio by using headphones and moving mics - with broad spectrum audio such as distorted electric guitars and using twin miking it makes a lot more sense in a session rather than using test sine waves at various frequencies - you can hear positioning results immediately.
It would be interesting to see the results of equiposition miking on a single point source on a scope. I might do a line-up and record the results and post it here.
There is a point when using two different mics like a pencil condenser and a ‘57 on the same speaker from an amp where by moving them away from each other they gel and they are not usually at the same distance from the speaker. We usually get the first mic sounding right, then set up the second to sound right, then listen to both together and slide one in and out to achieve best results.

 

[molke]

Then there’s DPA Microphones - see point 11:

Then I must be doing something wrong. The setup now is with a Shure SM57 and a Haun cardioid condenser. Note that the frequency responses in this position are without a reference microphone because I’m too lazy to put one up.

 

[RoadrunnerOZ]

Then I must be doing something wrong. The setup now is with a Shure SM57 and a Haun cardioid condenser. Note that the frequency responses in this position are without a reference microphone because I’m too lazy to put one up.

Looks like nearly 90deg out of phase at 100Hz. Which trace is the condenser? Green or red?

 

[molke]

Which trace is the condenser? Green or red?

The condenser should be green. Going by the relative low-frequency amplitude response, a shift of the low-frequency phase response would be the expected result.

 

[abbey road d enfer]

Then I must be doing something wrong. The setup now is with a Shure SM57 and a Haun cardioid condenser. Note that the frequency responses in this position are without a reference microphone because I’m too lazy to put one up.

Very interesting and enlightening. The absence of phase-shift between dynamic and condenser at 1kHz is self-speaking.
The differences at 100Hz can clearly be attributed to the flat response of the condenser and the rising slope of the dynamic.

 

[RoadrunnerOZ]

Very interesting and enlightening. The absence of phase-shift between dynamic and condenser at 1kHz is self-speaking.
The differences at 100Hz can clearly be attributed to the flat response of the condenser and the rising slope of the dynamic.

Doesn’t seem to be that much of a level difference on the scope between 100Hz and 1KHz of the dynamic relative to the condenser - is that enough to give a 90deg shift?

 

[abbey road d enfer]

I’m only talking about what occurs inside the microphone and the difference between two differing capsule types and their phase relationship - nothing to do with amplification outside the body of a dynamic or ribbon mic and what it does. It seems you are denying that there is a maximum voltage output at zero acoustic pressure wave crossing point where the diaphragm is moving the fastest for a coil or ribbon mic, either that or denying that maximum voltage output for a condenser occurs at maximum + pressure/excursion - 90deg away from the ribbon/coil.

Constantly re-hashing the same incomplete theory leads nowhere. If it was the only truth, the frequency response of dynamic mics would be a 6dB/octave slope. Fortunately, teh diapgragm's tuning and added damping result in a mechanical low-pass that not only corrects the frequency response, but simultaneouly phase.

Why would many professional audio texts be written cautioning the use of mixed mic types at the same location due to phase inconsistencies.

Many professional audio texts are written by non-technical people, e.g. KH. The DPA article has probably been written by junior in the marketing dept.

However, if what you are implying is what I think it is, you’re saying that a ribbon or coil and a condenser at identical locations will be perfectly in phase using the same type preamp - including the use of vintage mics and preamps. Or not?

I believe you have perfectly understood, and the last experiment from molhe describes and proves that very well.