Topic: Advantages/disadvantages of LD mics?

[DSatz]

Continuing my earlier post: The whole notion that large-diaphragm microphones pick up "better" bass or "more" bass because of their size is completely mistaken. When people make generalizations about "better" or "warmer" bass from large-diaphragm microphones, they are usually talking about a cardioid pattern and a dual-diaphragm capsule design. Very few large-diaphragm microphones are single-diaphragm, and the difference in the way the pattern is obtained matters greatly. As you go down in frequency, dual-diaphragm cardioids aren't cardioids any more; their patterns broaden out at low frequencies, often quite considerably. Thus they are picking up additional low-frequency energy from around the room, even from the back of the microphone where a cardioid shouldn't be sensitive.

But that's dual-diaphragm behavior, not large-diaphragm behavior; for better or worse, small-diaphragm microphones with dual-diaphragm capsules have the same characteristic. As an example, I've attached the polar diagram for the cardioid setting of the classic Neumann KM 56 small-diaphragm microphone, which had a dual-diaphragm capsule and three switchable patterns. Compare this to the polar diagram of any good single-diaphragm cardioid and you'll immediately see the difference in low-frequency pickup from off-axis. A good single-diaphragm cardioid can still be a real cardioid at 100 Hz or even 50 Hz.

It's one thing if you're close-miking something or someone in a studio with a cardioid, and quite another thing if you're making a stereo recording with a coincident or closely spaced pair of them. In the studio situation the spreading out of the pattern can be a good thing (warmth, roundness) but in the stereo situation it's a disaster: The low frequencies become more and more mono, which undermines the whole sense of spaciousness in the recording.

So this is one direct answer to the original poster about why most people here are using small-diaphragm condensers, apart from logistical reasons such as lower weight or the visual aspect: It's because we're recording in stereo with two main microphones (or two microphones, period), and in that kind of recording the consistency of the microphones' directional pattern across the frequency range is crucial, and large-diaphragm microphones (especially the most common kinds, which are dual-diaphragm) are never as good in that repect.

--best regards

[stevetoney]

Here's a transcription of a old but loved topic from another board, technical but not too technical.  And DSatz even wrote some of it!

http://www.itrstudio.com/MIC_CHAT.PDF

THanks for that.

And, a big thank you to yourself, Mr. Satz and all the others like you who have knowledge lightyears beyond mine and freely share it.

X2...I actually saved the .pdf on my machine and may print it for some coffee table reading (obviously deserves a better place in the house than my Relix magazines, which are bathroom reading.  LOL.)

[airbladder]

A lot of this is over my head.  I have SD and LD mics.  I like the LD's because I can get 5 patterns for less cash.  Now I am using U89s and the size is never and issue for me.  One thing that is nice about the 89s is that they are internally shock mounted, this gives you the ability to use ring mounts.  With out big shock mounts the mic size is less of an issue for me. 
I like the sound of LD mics.  Not sure if LD is better or worse than SD mics.  This reminds me I should do a good A/B between my u89s and km184s. 

[DSatz]

mshilarious, the very first example that I looked up just now, to check whether I was tripping or not, was the Neumann KM 84 vs. U 87. These two microphones were the paradigms of their respective categories when I was starting out as an engineer. The U 87 is hardly an inexpensive microphone, but the small-diaphragm KM 84 had the (slightly) lower noise figure.

Neumann reduced the noise of the U 87's amplifier by 4 dB some 20 years after it was introduced, and also increased its sensitivity by some 5 dB--which is interesting in the context of this discussion since the size of the diaphragm didn't change at all!

My point is that unless the extra trouble and expense is taken, as with the U 87[A], we can't assume that a large-diaphragm microphone will be quieter or more sensitive simply because it is large-diaphragm. Since the vast majority of microphones don't have optimal electronics attached, such assumptions don't hold up in practice. High sensitivity and ultra-low-noise performance have never been reasons for many people to choose one microphone over another, and manufacturers know this.

--best regards

P.S.: Definitely, the best impulse response performance comes from small-diaphragm, single-diaphragm condenser microphones that operate as pressure transducers. This isn't a matter of "fast" vs. "slow," though (which I think is a kind of audiophile myth); it's more like "clean" vs. "dirty."

[DSatz]

But mshilarious, I'm not saying that there's no relation between diaphragm size and equivalent noise. I'm saying that the economic realities being what they are--and given the fact that most users evidently don't feel that they really need a microphone to have the lowest possible noise--only a smallish minority of microphones are built to achieve the lowest possible noise (to within, say, 2 or 3 dB). Thus any buyer of a large-diaphragm microphone who doesn't bother to check out its actual noise specification can't safely assume that he's getting a quieter microphone on account of its having a large-diaphragm capsule. I'd be amazed if you would dispute that statement--and you'd be in error if you did.

The same goes for sensitivity, which depends on many variables that are essentially unrelated to the capsule. You can take the same capsule and put it into different (complete) microphones and get basically any sensitivity you want within a very wide range.

The requirement of "all other things being equal" is rarely met in practice, so certain of the generalizations that you listed are often misleading, even though there is something to them in the aggregate. It's just that individual people don't buy or use the aggregate of all possible microphones; they buy and use particular ones that are actually made and sold, and those often don't fit some of the generalizations that you listed.

Other generalizations that you listed were spot on, though. I've got to go right now, but if it isn't boring everyone to tears I could come back and say more about them--the ones having to do with directional response and high frequency response, mainly.

[twatts (pants are so over-rated...)]

I think this is a great discussion, even if I don't understand much of it...  At least it gives me beginning point if I really want to learn the Art of Mics.  Thanks very much to DS and MSH! 

Terry

[yug du nord]

As an owner of both large and small diaphragm mics, I really appreciate this info from you fellas.....  good stuff!

[DSatz]

(I've been going back and rewriting some of my postings because I was embarrassed at my wordiness. This posting was almost completely redundant, so I'm replacing it with something different that I should have said in the first place.)

When any object is placed in the path of sound waves, even if it's a microphone whose purpose is to register those sound waves as accurately as possible, it will disturb or distort the very thing that it is trying to respond to. This disturbance depends on the object's shape, but will generally become significant when the object is half a wavelength or larger in any of its dimensions.

Music contains a mixture of frequencies that span a 1000:1 ratio and therefore the physical wavelengths of sound span a 1:1000 ratio (wavelength and frequency are inversely proportional). Since sound travels in air at about 1100 feet per second, one wavelength at 1100 Hz = one foot. A one-inch "object" is therefore a concern at around 6.6 kHz and above; a two-inch "object" starts obstructing things at around 3.3 kHz, and so on (this is simplified, of course).

So this leads to two conclusions about microphones: Even the ones we call "small" are acoustically large at the highest audio frequencies; also, large microphones trip over themselves throughout the whole upper midrange and high frequency range, whicle small microphones can at least be out of their own way in the midrange and below, which is where most of the sound energy is.

(More later.)

[DSatz]

(message withdrawn by its author, who was really too tired to be allowed near a keyboard at the time)