Rotating/swapping front with rear Microphone Capsules

[canidoit]

Are the front and rear capsules the-same on microphones?

I was testing a U87ai mic and noticed when in figure 8, that the rear capsule sounded fuller compared to the front capsule.

Are rotating the mic capsule from the front to the rear something that can be done to prolong life of a mic, especially for vintage mics, where the capsules may be expensive or rare to find?

 

[Khron]

"Testing", how exactly?

And yes, turning the capsule around is often a stopgap solution to more or less "reviving" a mic, especially vintage / valuable ones where service is risky or capsule replacement is unfeasible. And especially since they're most often used in cardioid anyway.

 

[MagnetoSound]

If you’re testing on headphones using your own voice you will need to flip the polarity when testing the rear capsule in fig-8 to eliminate phase cancellation from bone conduction in your head.

 

[canidoit]

I put the mic on figure 8. I record in my DAW, the-same speech on the front and the rear of the capsule in one take.

I listen back on the speakers and noticed that the rear capsule was fuller, sounded bigger and more bass.

Also, in general, does the front capsule likely wear out quicker than the rear as it is used the most?

 

[Khron]

I put the mic on figure 8. I record in my DAW, the-same speech on the front and the rear of the capsule in one take.

... While keeping in mind that the rear diaphragm signal has opposite polarity to the front?

Are you getting the same result if you split that clip, and flip the polarity of the latter half?

 

[k brown]

I put the mic on figure 8. I record in my DAW, the-same speech on the front and the rear of the capsule in one take.

I listen back on the speakers and noticed that the rear capsule was fuller, sounded bigger and more bass.

Also, in general, does the front capsule likely wear out quicker than the rear as it is used the most?

In average use, the front diaphragm often accumulates more contaminates from singers (if that's how it was mostly used).

 

[canidoit]

... While keeping in mind that the rear diaphragm signal has opposite polarity to the front?

Are you getting the same result if you split that clip, and flip the polarity of the latter half?

Not sure what you mean? I mean it is mono? Do you want me to flip a mono track?

 

[k brown]

Not sure what you mean? I mean it is mono? Do you want me to flip a mono track?

It's about making sure that the sound coming from the mic is in phase with the sound you're hearing in the 'phones, since in fig.8 the signal from the rear diaphragm is out of phase with the front one.

 

[canidoit]

It's about making sure that the sound coming from the mic is in phase with the sound you're hearing in the 'phones, since in fig.8 the signal from the rear diaphragm is out of phase with the front one.

Hi k brown, no I am not listening to it over the headphones. I record it into my DAW and then play it back to my speakers.

 

[GeorgeToledo]

It’s a common mistake, so members just want to make sure before you go down the rabbit hole.

 

[MagnetoSound]

I put the mic on figure 8. I record in my DAW, the-same speech on the front and the rear of the capsule in one take.

How can you be in front of both diaphragms at the same time?

 

[Khron]

Do you want me to flip a mono track?

Yes, i want you to flip the polarity on the part of the mono track that you recorded with the REAR of the mic.

 

[canidoit]

How can you be in front of both diaphragms at the same time?

Ahh MagnetoSound, you've caught me, its because I travel at the speed of sound

One take, just means not taken in two parts for each side of the capsule. There's a gap of me moving to the rear capsule in that one take

 

[canidoit]

Yes, i want you to flip the polarity on the part of the mono track that you recorded with the REAR of the mic.

Wouldn't I get the-same results on both front and rear capsule, if it was a case of phasing issue, since it is in figure 8 pattern?

I will give it a try.

 

[MagnetoSound]

Ahh MagnetoSound, you've caught me, its because I travel at the speed of sound

One take, just means not taken in two parts for each side of the capsule. There's a gap of me moving to the rear capsule in that one take

So that’s NOT one take then. One take would mean a simultaneous recording into both sides.

How can you be the exact same distance from the diaphragm both times?

 

[NoisyIndividual]

One take, just means not taken in two parts for each side of the capsule. There's a gap of me moving to the rear capsule in that one take

I think a more accurate test (though not necessarily having any noticable difference) would be to spin the microphone around, not the source, keeping the room and your body the same for each capsule.

 

[RoadrunnerOZ]

The front and rear diaphragms in a dual diaphragm mic are essentially identical. Reversing the capsule and its associated wiring will give you a brand new diaphragm at the front of the mic - unadulterated with contaminants and also with the elasticity of a relatively new one. It’s not just contaminants building up which increase the mass of the diaphragm and reduce the top end but also the continuous stretching of the diaphragm that occurs with regular use - however the rear diaphragm is still influenced by the air pressure feed from the front so it will age and stretch as well - just not as much as the front one.
As long as the centre pole (backplate) of the mic is at dead centre voltage wise in relation to the front and rear diaphragms then they should sound the same providing you flip the phase of the rear recording to match the phase of the front - this applies to a new mic, but in an older used mic there will be a difference between the diaphragms.
Rotating the mic 180deg and doing A/B comparisons keeping the room reflections the same is the most accurate test but there is still the difference between each vocal take. A truly neutral test would be to record a vocal on a mic (any mic of good quality) play back the recording through a good monitor speaker - then record the vocal from the speaker one side of the mic at a time, rotating the mic in place, on separate tracks, flip the phase of the rear recorded track, line the two tracks up in the timeline so they are dead in line and then flip between the two in your DAW - see which diaphragm sounds the best.

 

[Matt Nolan]

see which diaphragm sounds the best.

Hear which diagram sounds the best.

I know it is a usual figure of speech, but I suspect too many of us look at specs and graphs and see how things sound rather than just listening and hearing how they sound.

 

[canidoit]

Is it simple to add a switch on the U87, so that when in cardoid, you can switch to make the rear capsule as the front capsule?

Anyone know if its easy to swap the front head grill with the rear grill?

I'll do some further tests later on, as you are all correct, my initial test is flawed. It was better for me to spin the mic so that I get better consistency.

@RoadrunnerOZ, the issue with testing the mic with a speaker is that you are not capturing the behaviour of the mic when someone speaks and blows air onto the capsule which I believe is different to a speaker. I usually do your approach when testing at longer distances between sound source and mic.

 

[RoadrunnerOZ]

Hear which diagram sounds the best.

I know it is a usual figure of speech, but I suspect too many of us look at specs and graphs and see how things sound rather than just listening and hearing how they sound.

Good point - a figure of speech intended here (hear ). But now you mention it, you can also compare the recorded waveforms to the original and each other visually in your DAW and see which looks the best…….