Why you should never use multi pattern mics

[Marik]

Just to be clear about "phasing issues" I mentioned in the op. I am talking about introducing signal coming from rear diaphragm which is separated by the thickness of the backplate from the front one. So there is slight delay, although small it falls in the audible range.

Not only the thickness of the backplate, but also distance difference formed by external/internal passages between front signal and backwave reaching rear of the diaphragm. This distance can be pretty long. Depending on the parameters of the passage it can introduce an obstacle for lower frequencies, so the entire system is also frequency dependent. In reality the phase anomalies are all over the place, but (as already was mentioned) that's how we form the cardioid pattern in this type of the capsule.

There are ways to reduce those anomalies. One of them is optimization of the passage parameters using vented 3 chamber design (obviously, it comes to agreement with the very title of this thread). Another is using mass controlled system and introducing infinite back load with some backwave leak. The third is combining two native patterns--fig 8 and true pressure omni instead of using resistance controlled system, which by definition has intrinsic deficiencies to start with.

Best, M

 

[kingkorg]

Not only the thickness of the backplate, but also distance difference formed by external/internal passages between front signal and backwave reaching rear of the diaphragm. This distance can be pretty long. Depending on the parameters of the passage it can introduce an obstacle for lower frequencies, so the entire system is also frequency dependent. In reality the phase anomalies are all over the place, but (as already was mentioned) that's how we form the cardioid pattern in this type of the capsule.

There are ways to reduce those anomalies. One of them is optimization of the passage parameters using vented 3 chamber design (obviously, it comes to agreement with the very title of this thread). Another is using mass controlled system and introducing infinite back load with some backwave leak. The third is combining two native patterns--fig 8 and true pressure omni instead of using resistance controlled system, which by definition has intrinsic problems to start with.

Best, M

Awesome, thanks!

 

[Mark mth001]

Not only the thickness of the backplate, but also distance difference formed by external/internal passages between front signal and backwave reaching rear of the diaphragm. This distance can be pretty long. Depending on the parameters of the passage it can introduce an obstacle for lower frequencies, so the entire system is also frequency dependent. In reality the phase anomalies are all over the place, but (as already was mentioned) that's how we form the cardioid pattern in this type of the capsule.

There are ways to reduce those anomalies. One of them is optimization of the passage parameters using vented 3 chamber design (obviously, it comes to agreement with the very title of this thread). Another is using mass controlled system and introducing infinite back load with some backwave leak. The third is combining two native patterns--fig 8 and true pressure omni instead of using resistance controlled system, which by definition has intrinsic problems to start with.

Best, M

Not only the thickness of the backplate, but also distance difference formed by external/internal passages between front signal and backwave reaching rear of the diaphragm. This distance can be pretty long. Depending on the parameters of the passage it can introduce an obstacle for lower frequencies, so the entire system is also frequency dependent. In reality the phase anomalies are all over the place, but (as already was mentioned) that's how we form the cardioid pattern in this type of the capsule.

There are ways to reduce those anomalies. One of them is optimization of the passage parameters using vented 3 chamber design (obviously, it comes to agreement with the very title of this thread). Another is using mass controlled system and introducing infinite back load with some backwave leak. The third is combining two native patterns--fig 8 and true pressure omni instead of using resistance controlled system, which by definition has intrinsic problems to start with.

Best, M

That third option was used in the STC4033, a 1940s mic which had a ribbon and omni in the same body. You could choose between the three patterns - fig 8, omni. cardi. The STC 4033A

 

[ricardo]

makes me want to design a capsule that has intakes for the rear at almost the same place as the front diaphragm, routes it around the back and then back to the front.

The Calrec SDC cardioid is MUCH simpler than the AKG SDCs. IMnotsoHO, the Calrec stick cardioid is still one of the best SDC cardioids. What Clem Beaumont realised is that the 'mounting in the stick' has just as much effect as certain capsule intricacies and much easier to tweak. One of the parameters is the position of the slots/holes. If you have wonky back response, try moving them forward.

 

[egroys]

So my M49 pair live almost entirely as room mics in omni. I LOVE them. I track lots of drums, guitars, and various solo instruments in a medium sized studio.

If I were to convert them to M50s, how different will they sound? Is this a good/bad idea in anyone’s opinion?

And if I make cardioid only M49s using the current M7s I have, what (if any) difference does it make that they are dual sided vs single sided?

 

[Barry Hufker]

Keep the M49 as-is and make an M50 (instead of a cardioid only M49).

 

[Murdock]

So my M49 pair live almost entirely as room mics in omni. I LOVE them. I track lots of drums, guitars, and various solo instruments in a medium sized studio.

If I were to convert them to M50s, how different will they sound? Is this a good/bad idea in anyone’s opinion?

And if I make cardioid only M49s using the current M7s I have, what (if any) difference does it make that they are dual sided vs single sided?

Nobody can say if it will be better or not. Depends on your taste. But check the frequency responses of the originals. The M50 has extended lows and a smoother rising high frequency bump. Also the pattern response gets more directional at the high frequencies and is like a cardioid instead of a fig 8 of the omni M49.
I don’t know how big your “medium sized” studio is but the M50 was made for distant recording.

I would say the M49 is more of an Allrounder than the M50 and can be used for more tasks than the M50. But an M50, or better two, is a great addition. If you have the room.

The difference between “true” cardioid (one side only) and dual sided is a 4dB increase in level and a somewhat tighter pattern for the one side mode. I made the rear diaphragm switchable in my M49 clones and I really like the “true” cardioid mode.

 

[kingkorg]

If I were to convert them to M50s, how different will they sound? Is this a good/bad idea in anyone’s opinion?

They would sound nothing like your current mics in omni.

In omni K47 and m7 capsules create huge dip in midrange before sharp, high Q boost because of the phase discrepancies between the diaphragms, and chamber construction. Pointing to this was the original intent of this thread.

M50 capsules have very even, gradual boost towards high end. That high end boost is reduced off axis, and minimized at 180° which is not true with m49 in omni.

 

[egroys]

Thank you wizards for this!

My room mics hang ~10' up, ~18' away from the snare position on my "stage."
I love the M49 on female vocals, obviously, but it sounds like having a pair of M50s and a single, cardioid only, M49 would cover my bases at no loss.

I've never used fig8 on them but have enough ribbons and multi-pattern tube condensers in case the need arises.

 

[soliloqueen]

Not only the thickness of the backplate, but also distance difference formed by external/internal passages between front signal and backwave reaching rear of the diaphragm. This distance can be pretty long. Depending on the parameters of the passage it can introduce an obstacle for lower frequencies, so the entire system is also frequency dependent. In reality the phase anomalies are all over the place, but (as already was mentioned) that's how we form the cardioid pattern in this type of the capsule.

There are ways to reduce those anomalies. One of them is optimization of the passage parameters using vented 3 chamber design (obviously, it comes to agreement with the very title of this thread). Another is using mass controlled system and introducing infinite back load with some backwave leak. The third is combining two native patterns--fig 8 and true pressure omni instead of using resistance controlled system, which by definition has intrinsic deficiencies to start with.

Best, M

i've always been personally fascinated by the idea of a multipattern mic that uses a true omni and true fig 8 transducer instead of 180 degree (not even real) cardioids

 

[k brown]

They would sound nothing like your current mics in omni.

In omni K47 and m7 capsules create huge dip in midrange before sharp, high Q boost because of the phase discrepancies between the diaphragms, and chamber construction. Pointing to this was the original intent of this thread.

M50 capsules have very even, gradual boost towards high end. That high end boost is reduced off axis, and minimized at 180° which is not true with m49 in omni.

Not to mention the drastic difference in transient response due to the M 50 having a 12mm capsule.

 

[k brown]

i've always been personally fascinated by the idea of a multipattern mic that uses a true omni and true fig 8 transducer instead of 180 degree (not even real) cardioids

Or as AKG did in the CK6 (and I did a DIY version), an omni and a cardiod can also achieve all possible polar patterns (with more readily-available capsules).
https://groupdiy.com/threads/making-a-figure-8-with-an-omni-and-a-cardioid-capsule.87941/page-3

 

[terry setter]

So my M49 pair...

PLEASE don't hack into your M49s!!! You would be hard-pressed to replace them in the future, or in the near future if you find that the M49's (among the 5 most sought after mics in history) were giving you a bit of magic that you can't get any other way. And, you have a pair of them! Who would not give a large number of the best mics in their collection to have a pair of such mics. On the other hand, if you built them DIY, then go on and experiment to your heart's content. I'd just hate to see $40,000+ worth of irreplaceable mics become anything less than what they currently are.

 

[egroys]

PLEASE don't hack into your M49s!!! You would be hard-pressed to replace them in the future, or in the near future if you find that the M49's (among the 5 most sought after mics in history) were giving you a bit of magic that you can't get any other way. And, you have a pair of them! Who would not give a large number of the best mics in their collection to have a pair of such mics. On the other hand, if you built them DIY, then go on and experiment to your heart's content. I'd just hate to see $40,000+ worth of irreplaceable mics become anything less than what they currently are.

Goodness! I should have clarified that these are DIY M49s! I wouldn’t dare with the real thing!!

Poctop, Moby, Beesneez M7, 6S6B-V, and Chunger bodies.
Wouldn’t mind finding a reasonable, new source for that third body now that I mention it…

 

[Barry Hufker]

Now I feel a lot better!

 

[terry setter]

Thanks for the clarification. Let your curiosity guide you....

 

[abbey road d enfer]

i've always been personally fascinated by the idea of a multipattern mic that uses a true omni and true fig 8 transducer instead of 180 degree (not even real) cardioids

The issue with this solution is that the problem initially mentioned by kingkorg (post #1) about phase differences generated by the distance between diaphragms is even more pregnant. Not to mention the differences of tuning.

 

[soapfoot]

it’s been alluded to, but not explicitly said:

The M49 and M50 look similar externally, but are radically-different mics under the grille! An M49 in omni is in no way representative of what you can expect an M50 to sound like

a small-diaphragm, aluminum, single-membrane capsule in a lucite sphere versus a typical two-sided large-diaphragm capsule

I think your conclusion earlier is correct—it’s really worth having both

 

[k brown]

The issue with this solution is that the problem initially mentioned by kingkorg (post #1) about phase differences generated by the distance between diaphragms is even more pregnant. Not to mention the differences of tuning.

When a source is directly in front of a pair of vertically-mounted capsules, there is no time delay between them, and therefore no phase differences.

The only way a source can be equidistant from the two sides of a dual-membrane capsule is if it is directly above it!

 

[ccaudle]

When a source is directly in front of a pair of vertically-mounted capsules, there is no time delay between them

Most sources are large enough that that is not true for the entire soundboard, all the strings, etc. Probably brass instruments or voice, where the sound nearly all comes from a relatively small opening fit the criteria, but certainly a large ensemble in front of a stereo pair would not.
Just something to keep in mind when thinking about what spacing you can tolerate and what situations it may or may not cause a problem.