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Microphones - physics vs design/quality/R&D

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Microphones - physics vs design/quality/R&D

Postby Ramirez » Tue Jun 02, 2020 2:53 pm

I've been meaning to open a discussion on this for a while, as it's something that's intrigued me.

Generally speaking, of course, to what extent does a microphone's design and quality compensate for the compromises of its physical principles?

For example, off-axis response - it's generally accepted that a small-diaphragm has a more accurate off-axis response, and is the better choice when off-axis colouration and spill is an issue. But how true is this when comparing, say, an £80 Rode M3 SDC to an expensive, well designed workhorse LDC like an U87. Is the M3 still going to offer an advantage?

Or, instead of the U87, perhaps an LDC that's often prized for its off-axis response. A 414 B-ULS perhaps, or one of the new Austrian Audio OC818. A lot of work goes into designing these microphones and their off-axis response. Are they considered "good for an LDC", or just good, period?

Consider a scenario where you're rigging an ORTF pair for recording a choir or an orchestra. You have a choice of high-end LDCs (maybe Neumann TLM170 or the Austrian Audios) or mid-priced SDC (maybe Beyer MC930 or Rode NT55). What do you go with? Does the on-axis tonality trump all considerations?

Similar questions could be asked about polar patter consistency etc.

If I had a free day in the studio I'd try them all out, but alas I'm stuck at home!
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Re: Microphones - physics vs design/quality/R&D

Postby Hugh Robjohns » Tue Jun 02, 2020 3:32 pm

Ramirez wrote:Generally speaking, of course, to what extent does a microphone's design and quality compensate for the compromises of its physical principles?

Very little. In short, "you cannae change the laws of physics"... all you can do is try really hard not screw up the rest of the design. Some manufacturers do that better than others! :-)

For example, off-axis response - it's generally accepted that a small-diaphragm has a more accurate off-axis response, and is the better choice when off-axis colouration and spill is an issue. But how true is this when comparing, say, an £80 Rode M3 SDC to an expensive, well designed workhorse LDC like an U87. Is the M3 still going to offer an advantage?

Yes.

Here are the published polar plots of the current AKG C414XLS LDC and the Schoeps CCM4 SDC:
C414 cardioid polar.jpg
Schoeps cardioid polar.jpg


Ignoring the fact that one is upside down (!) you can see the Schoeps maintains a very accurate cardioid polar pattern up to 4kHz and only gets fractionally more 'pointy' above that. In contrast, the C414 is struggling to maintain the cardioid pattern at the back and sides above 1kHz, and the sides it collapses dramatically above 8kHz. The more pointy HF response is entirely due to the physics of a larger capsule, and the rear null business is largely due to its dual-diaphragm construction.

And it's exactly the same story with the Rode M3 and Neumann U87:

Rode m3 cardioid.jpg
Neumann U87 Cardioid.jpg


Consider a scenario where you're rigging an ORTF pair for recording a choir or an orchestra. You have a choice of high-end LDCs ... or mid-priced SDC ... What do you go with?

Which ever sounds nicest!

With an ORTF array, while a sizeable proportion of the wanted source will be off axis, it won't be all that far off axis, and as you can see from the diagrams above the LDCs retain pretty reasonable off-axis frequency responses out to 45 degrees or more.

If there's an audience that will be far more off axis, but most will actually be behind the mic and so sound terrible anyway... which is why a separate array for the audience is often a good idea!

But it's a safe bet that a 'better mic' is always a better mic, regardless of its size. It will usually have more 'resolution' (for want of a better word), and often less distortion, a more appealing response, and so on.... There are always compromises involved, so you just have to use your ears.
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Re: Microphones - physics vs design/quality/R&D

Postby CS70 » Tue Jun 02, 2020 9:30 pm

Ramirez wrote:Generally speaking, of course, to what extent does a microphone's design and quality compensate for the compromises of its physical principles?

My take is that they are somewhat complementary concerns.

Quality to me means two things: one is the quality of the idea and the R&D. These are fixed costs however, and not really so important at the end of the day. That is they are uber-important but they're hard to compare. The Geumann Microphone Company may have high fixed costs because they hire the best engineers, spend a ton in research (research is another word for lot of failures - aka money that ends up in nothing) and do a lot of testing of their design before commencing production. The Zehringer company may have low fixed costs because they do neither. But then the Tonald Drump Microphone Company may have high fixed costs and do neither research nor testing and have the same quality level of Zheringer because its management is all about pocketing as much money as possible by rebranding Zeringher mics. Or the Johnnis Bornson Microphone Company is spending all its high fixed cost in marketing and purchasing weekly full commercial pages of The Daily Mail. You get my gist.

So R&D quality is hard to justify. There are metrics, but are not straightforward.

That leaves the second meaning of "quality" - manufacturing quality. In the end, it boils down to how yo define which of your produced wares you throw in the "rejects" bin and which you don't. Meaning what tolerances you set in order to say that a produced item is "ok". The narrower the tolerances, the better the quality. Note that if you set narrow tolerances, high quality can be achieved either by accepting high marginal costs, or by taking in use innovations that reduce production errors without increasing marginal costs (in the last 30 years, that has meant mostly computers and automation. Plus a few other management innovations).

Physics on the other side, is physics. Being smart and accepting high fixed costs will occasionally produce clever workarounds, but cannot really do much about the fundamental limitations. Remember that 90% of modern science are really limitative results - they tell you what you cannot do. However, throwing money at research has proven more than once that it can produce a fundamental re-framing of the problem, so that previous limitations may no longer apply. It can, of course, also simply produce a huge waste of money.

Microphones will benefit as any other items, so long there are companies willing to put down the fixed cost to put scientific discoveries into use. Say the discovery of new materials with particular properties might allow a bright fellow at Geumann to address some of the current diaphragm limitations, and Geumann may have a management enlightened (if it works) or foolish (if it doesn't) enough, to allow him or her to pursue the research..

Basically a quality company, producing quality products, may have more of a culture able to benefit and produce innovations to overcome or work around the physical limitations. But that's as far as it goes imho, and it ain't much.
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Re: Microphones - physics vs design/quality/R&D

Postby Tim Gillett » Tue Jun 02, 2020 10:45 pm

It's so much easier to compare mics of the same type. So a U87 with a Rode NT2a. Or if comparing an LDC with an SDC, compare cardioids, or compare omni's, and in the same brand, again to avoid unnecessary complication. The scientific method may seem boring, slow, unflashy, but it tends to reap reliable, dependable results. Not even a top company like Neumann can change the laws of physics.
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Re: Microphones - physics vs design/quality/R&D

Postby Ramirez » Wed Jun 03, 2020 11:02 am

Thanks all, especially Hugh. Fascinating.

Tim, yes I know it's easier to compare like for like - that happens very often already - but it's not the point of my question.
I was interested in to which extent does the very best of one design principle overcome its inherent limitations, and how does that then compare to a poorer/cheaper example of a design where the same limitation is not as much of an issue. I don't wish to compare an U87 to a cheaper multi-pattern LDC yet again.
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Re: Microphones - physics vs design/quality/R&D

Postby Hugh Robjohns » Wed Jun 03, 2020 11:17 am

I think so much depends on the application, but it's always about balancing the compromises to achieve the 'best' result -- the definition of 'best' depending on your (or your client's) priorities.

A coincident stereo array will always be a more challenging role for a mic than a simpler 'spot-miking' application. This is because for a spot-miking application any off-axis sounds tend to be unwanted spill and inherently at a lower level than the wanted on-axis sound. In contrast, for a mic in a coincident array a large amount of off-axis sound is very much wanted sound, and is typically at the same level as the on-axis sound sources.

And the greater the mutual angle, the more difficult that role will be, so ORTF with a 110 degree mutual angle is particularly challenging and I would automatically reach for small diaphragm mics. The HF polar pattern of most LDCs is noticeably narrowed by 55 degrees off axis (see those diagrams in the post above).

However, for 'traditional' XY hypercardioids or XY fig-8s, the off-axis demands are less challenging as most LDCs maintain a uniform polar response with frequency out to 45 degrees.

But as I said, in choosing one mic over another, you're seeking the most appropriate compromise between off-axis colouration (or dulling), and on-axis tonal quality, as well as other details like noise floor (rarely a problem in practice), distortion, presence peaks, resonances, subsonic noise, and so on.
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Re: Microphones - physics vs design/quality/R&D

Postby Tim Gillett » Wed Jun 03, 2020 12:40 pm

Ramirez wrote:
Tim, yes I know it's easier to compare like for like - that happens very often already - but it's not the point of my question.
I was interested in to which extent does the very best of one design principle overcome its inherent limitations..

But if the limitation is inherent then... it's inherent.

So the large diaphragm of an LDC by definition reduces its off axis treble response re the SDC. No amount of quality engineering can change that.

In the same way the small diaphragm mic will always have higher self noise re the LDC.

All the manufacturer can do is optimise weaknesses that are not inherent to the design.
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Re: Microphones - physics vs design/quality/R&D

Postby Sam Inglis » Wed Jun 03, 2020 12:52 pm

Well, there are trade-offs that the designers can make here.

An interesting approach is the use of a long, thin rectangular capsule as in the Pearl ELM-series mics. Those are large-diaphragm mics, in that the diaphragm area is comparable to that of a typical LDC, but in the horizontal plane they have polar-pattern characteristics somewhat more like an SDC. The trade-off is that the polar patterns are not symmetrical, so off-axis pickup in the vertical plane is dramatically different. That's actually a useful characteristic in some recording situations.
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Re: Microphones - physics vs design/quality/R&D

Postby Ramirez » Wed Jun 03, 2020 1:11 pm

Tim Gillett wrote:
Ramirez wrote:
Tim, yes I know it's easier to compare like for like - that happens very often already - but it's not the point of my question.
I was interested in to which extent does the very best of one design principle overcome its inherent limitations..

But if the limitation is inherent then... it's inherent.

So the large diaphragm of an LDC by definition reduces its off axis treble response re the SDC. No amount of quality engineering can change that.

In the same way the small diaphragm mic will always have higher self noise re the LDC.

All the manufacturer can do is optimise weaknesses that are not inherent to the design.

Quite. So my question is how close can an expertly designed and built LDC come to the off-axis response of a cheap, but inherently superior in this regard, SDC.

That’s very interesting as well Sam, thank you. I gather this is also true for the rectangular capsules that Milab use? There are a couple of DC96s at the studio, I shall experiment when the time allows!
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Re: Microphones - physics vs design/quality/R&D

Postby Tim Gillett » Wed Jun 03, 2020 1:17 pm

Sam Inglis wrote:Well, there are trade-offs that the designers can make here.

An interesting approach is the use of a long, thin rectangular capsule as in the Pearl ELM-series mics. Those are large-diaphragm mics, in that the diaphragm area is comparable to that of a typical LDC, but in the horizontal plane they have polar-pattern characteristics somewhat more like an SDC. The trade-off is that the polar patterns are not symmetrical, so off-axis pickup in the vertical plane is dramatically different. That's actually a useful characteristic in some recording situations.

Yes but as you say, it's a trade off. Unless the application requires that particular dual polar pattern it's not "the best of both worlds".
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Re: Microphones - physics vs design/quality/R&D

Postby Ramirez » Wed Jun 03, 2020 1:19 pm

Tim Gillett wrote:
Sam Inglis wrote:Well, there are trade-offs that the designers can make here.

An interesting approach is the use of a long, thin rectangular capsule as in the Pearl ELM-series mics. Those are large-diaphragm mics, in that the diaphragm area is comparable to that of a typical LDC, but in the horizontal plane they have polar-pattern characteristics somewhat more like an SDC. The trade-off is that the polar patterns are not symmetrical, so off-axis pickup in the vertical plane is dramatically different. That's actually a useful characteristic in some recording situations.

Yes but as you say, it's a trade off. Unless the application requires that particular dual polar pattern it's not "the best of both worlds".

But he didn’t say it was! Or are the quotation mark referring someone else?
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Re: Microphones - physics vs design/quality/R&D

Postby Sam Inglis » Wed Jun 03, 2020 1:35 pm

Ramirez wrote: I gather this is also true for the rectangular capsules that Milab use? There are a couple of DC96s at the studio, I shall experiment when the time allows!

Yes, I think the Pearl and Milab capsule designs are essentially the same, and in fact the two companies have now re-merged after being separate entities for many years.

The capsule in the ELM series is much more elongated than those of earlier Pearl and Milab mics, so the asymmetry is more pronounced, but it's present in any mic with a rectangular capsule. Ribbon mics also typically have an asymmetrical polar pattern with the deepest nulls at the end of the ribbon rather than the sides.
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Re: Microphones - physics vs design/quality/R&D

Postby Tim Gillett » Wed Jun 03, 2020 1:37 pm

Ramirez wrote:But he didn’t say it was! (a trade off) Or are the quotation mark referring someone else?

Sam Inglis wrote:Well, there are trade-offs that the designers can make here...
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Re: Microphones - physics vs design/quality/R&D

Postby Ramirez » Wed Jun 03, 2020 1:39 pm

Tim Gillett wrote:
Sam Inglis wrote:Well, there are trade-offs that the designers can make here...

I meant the bit where you put ‘the best of both worlds’ in quotation marks.
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Re: Microphones - physics vs design/quality/R&D

Postby Tim Gillett » Wed Jun 03, 2020 1:47 pm

Ramirez wrote:
Tim Gillett wrote:
Sam Inglis wrote:Well, there are trade-offs that the designers can make here...

I meant the bit where you put ‘the best of both worlds’ in quotation marks.

I put "the best of both worlds" in quotes because it's a common saying. I didn't mean to imply Sam was claiming it was the best of both worlds. Sam said himself it is a trade off, which it is, as opposed to "the best of both worlds", which again, it only is in the specific situation that might require those dual patterns.
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