Author Topic: Is it a fallacy that dynamic microphones are better at rejecting room sound?  (Read 973 times)

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Offline sfs1

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I'm not having much luck with this question in music production circles, it very quickly goes into personal experience and received wisdom.

It's commonly said that a dynamic microphone is better at rejecting background noise / room sound / reflections compared to a condenser microphone. I don't understand why this should be the case. When I look at the polar response graphs for different mics, I don't see any pattern that would let me determine that I'm looking at a condenser mic or a dynamic. They're just all over the place (you can get a shotgun condenser and an omni dynamic for example). So if the polar response isn't characteristic, what else could make a difference? Maybe it's just that there are lots of dynamic mics that have a tight polar response and lots of condenser mics that have a wider response, so when you look at a typical mic cabinet in a studio, that rule of thumb holds. But people (and manufacturers) talk about it as if it was an intrinsic thing. I'm interested to find out if I missed anything or got anything wrong.
 

Offline dmills

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There is nothing intrinsic about either technology that impacts this, and contrary to popular belief in music circles the ONLY thing the mass of the diaphragm impacts is sensitivity.

What I think may be going on is that a condenser is often really a large diaphragm condenser and those (because the diameter is greater then the wavelength at high frequency) tend to have significant side lobes in the response at high frequency, thus making them more prone to pick up reflections from a badly behaved room.

Narrower patterns do of course pick up less room, and those are often (but not always) condenser designs.
 
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Online JohnnyMalaria

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I suspect it's because, for many cases, a particular dynamic microphone is chosen because it is cardioid (e.g., Shure SM57). Hence, many people would simply associate the two and claim a dynamic mic is better for rejecting room sound.
 
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Offline TimFox

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The basic sensitivity patterns are omnidirectional and figure-8.  The latter is the default pattern for a ribbon microphone, where both sides of the ribbon diaphragm are exposed to sound, and the voltage from one side is inverted in polarity from the voltage from the other side.
Summing these responses with appropriate weighting produces the "cardioid" directional pattern (heart-shaped) and its variations.  Some microphones (including condensers) incorporate electrical switching to set the response to omni, figure-8, or cardioid.
Cardioid is the usual choice when response to sound from one direction needs to be attenuated, for example when acoustic feedback in sound-reinforcement systems is a problem.
« Last Edit: March 08, 2021, 05:09:38 pm by TimFox »
 
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Online SiliconWizard

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I suspect it's because, for many cases, a particular dynamic microphone is chosen because it is cardioid (e.g., Shure SM57). Hence, many people would simply associate the two and claim a dynamic mic is better for rejecting room sound.

Well. Yeah. This point is certainly a major factor.

Another, more objective one, is that condenser microphones tend to be more sensitive than dynamic ones. One side-effect of this, is that you tend to get a dynamic microphone closer to the sound source - which in turn will tend to get you a better signal-to-noise ratio. But this approach doesn't necessarily work well for recording everything. So, as always, the right tool for the job.
 
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Offline mansaxel

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It is not the case. per se. I would suspect that it is more about the perception of what a typical microphone of either kind is; where
  • The dynamic often is a close-talk affair with suitable sensitivity and a pronounced directivity with resulting compromises in off-axis frequency response and proximity effect (SM58 type of crap-turned-legend)
  • The condenser is a "overhead mike" type of thing, with a slightly wider pickup pattern resulting in less proximity effect, higher output level (there's a buffer amp in it, for starters) and better off-axis response  (Neumann KM84 style)

You can do it the other way around, by tuning the output level, adopting the directivity, dealing with the proximity effect results, and you'll end up with the MD21 and the AKG C5900.  The MD21 is a Druckempfänger, ie. non-directional, has no proximity effect, hears the room, and is very dynamic. The C5900 has adopted output level, tighter directivity, some proximity effect, and works very well hand-held and is if not a true condenser at least a good electret.

Good engineering can do both, and good microphone designers can make either work. The rest is opinion.

My opinion is that average condensers often outperform the average dynamic in ways that will transform sound reproduction. Favourite example is guitar amplifiers. I would recommend anyone trying to get the sound of a guitar amp into an electrical current to try a large diaphragm condenser (It's quite sufficient with a china clone!), on-axis, instead of that "angle a SM57 at the edge of that Celestion and whack the console EQ" thing people have been failing at since the dawn of time.

And, I strongly dislike the SM58.

Offline VintageTest

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What Tim Fox has just said is completely true regarding polar responses of microphones. In addition, you must consider sensitivity and frequency response , as this will impact the use to which the microphone is put. The gold standard live vocal mic has been the Shure SM58 for a few decades, but unlikely to be used in a studio for the same purpose. Those that can afford it will use Neumann U87's, Electrovoice RE20's or the like, with AKG 414's or 451's being popular for drum kit overheads, AKG D12 for kick drum, Shure SM57 for guitar cabs etc. I'm old, so my reference was "techniques of the Sound Studio" by Alec Nisbett, but it was published in the late 70's, so there's probably a lot more current info available today.

Good luck,
Mel
« Last Edit: March 22, 2021, 03:40:55 pm by VintageTest »
 

Offline themadhippy

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Quote
Favourite example is guitar amplifiers. I would recommend anyone trying to get the sound of a guitar amp into an electrical current to try a large diaphragm condenser
And then try a shure ksm313, youll never go back to  condensers let alone 56/57s or 609's.
 

Online SiliconWizard

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Quote
Favourite example is guitar amplifiers. I would recommend anyone trying to get the sound of a guitar amp into an electrical current to try a large diaphragm condenser
And then try a shure ksm313, youll never go back to  condensers let alone 56/57s or 609's.

It's a ribbon microphone right? Pretty expensive stuff. It's 13x the price of a SM57... ;D
 

Offline mansaxel

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Quote
Favourite example is guitar amplifiers. I would recommend anyone trying to get the sound of a guitar amp into an electrical current to try a large diaphragm condenser
And then try a shure ksm313, youll never go back to  condensers let alone 56/57s or 609's.

Actually, something along those lines was what got me thinking on how to capture the amplifier sound.  I read an interview with Steve Albini at least 20 years ago, where he spoke warmly of the RCA ribbons, and also the Coles ribbons, as optimum devices for amplifier miking. He was very insistent that one puts the microphone about 25-30cm away, aiming for the center dome, trying to get the microphone ribbon/diaphragm exactly 90° to the movement axis of the cone.  I started wondering whether that would not work with a large-diaphragm condenser, and of course it does.

Offline Yansi

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Dave Rat to the rescue with a beautiful practical presentation.

 
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Offline Cerebus

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The basic sensitivity patterns are omnidirectional and figure-8.  The latter is the default pattern for a ribbon microphone, where both sides of the ribbon diaphragm are exposed to sound, and the voltage from one side is inverted in polarity from the voltage from the other side.
Summing these responses with appropriate weighting produces the "cardioid" directional pattern (heart-shaped) and its variations.  Some microphones (including condensers) incorporate electrical switching to set the response to omni, figure-8, or cardioid.
Cardioid is the usual choice when response to sound from one direction needs to be attenuated, for example when acoustic feedback in sound-reinforcement systems is a problem.

That is slightly misleading, as most cardioid (and supercardioid and hypercardioid) mics do not do any electrical manipulation to get the polar pattern but do it by physically channelling the sound waves around the microphone capsule in a selection of interesting ways. This is one of the things that leads to all the little oddities that give different microphones their 'character'. The same principle is at work, mixing the pressure and pressure gradient responses, but it's done physically.

One of the more entertaining examples, the schematic view of an Electrovoice "Variable-D" microphone from 1958, heavily engineered to have a cardioid response with low proximity effect. You can see the various paths at different frequencies (and path delays) leading to the back of the diaphragm as well as to the front.



From Eargle's Microphone Book. p103
Anybody got a syringe I can use to squeeze the magic smoke back into this?
 

Offline mansaxel

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On the subject of variable directivity, it is nearly always (if intentional) done with two diaphragms that are mixed electronically with varying levels and polarities. One counter-example is the AKG C1000 which comes with an extra physical attachment that is stated to make this dull-sounding cardioid into an equally uninspiring hyper.

The fixed directivity is achieved as Cerebus illustrated by channeling sound out of polarity to the back of the membrane. And, the "oddities" are indeed a lot of the character. That's my main issue with a Very Famous Vocal Mic. It's off-axis response is shit.

The most common directivity modification method, though,  is known as "cupping", where the hand turns a pressure gradient transducer into a pressure transducer. Having frequently done monitors for people known to perform this act of directivity vandalism, I can assure the reader that it is indeed effective, both as a pose to make the alleged talent look stupid and as a destroyer of monitor mixes.

Offline Bassman59

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Good engineering can do both, and good microphone designers can make either work. The rest is opinion.

This is the truth!

Quote
My opinion is that average condensers often outperform the average dynamic in ways that will transform sound reproduction. Favourite example is guitar amplifiers. I would recommend anyone trying to get the sound of a guitar amp into an electrical current to try a large diaphragm condenser (It's quite sufficient with a china clone!), on-axis, instead of that "angle a SM57 at the edge of that Celestion and whack the console EQ" thing people have been failing at since the dawn of time.

As a long-time FOH mix guy, I agree. What's the point of using the SM57 with its presence peak on a guitar amp which by its very nature already has a presence peak? And it's made worse when the cabinet is on the floor and facing the guitarist's knees, so he dials it brighter so he hears it the way he wants. And then you get odd looks when you suggest using those nice legs Fender puts on Twins to lean them back ... "But then it's too bright!"

Anyway in the early 90s I bought a pair of CAD E-100 large-diaphragm condenser mics at the NAMM show, specifically to use on guitar amp cabinets for live shows. I figured for $200 each (!) if they got broken or stolen, I wouldn't feel as bad as I would if an AKG C414EB got broken or stolen. These mics have a supercardioid pattern so the proximity effect is more pronounced than a cardioid, but the mic also has a built-in high-pass filter which mitigates that.

Before using them on a show we set them up in at the studio and directly compared them to the "standard" SM57 and the results were undeniable: condenser mics on a guitar amp cabinet are the way to go. The CADs had definition and air (extended HF response) without the presence peak that is a spike in your ears. We did put up for comparison a 414EB and a U87 and those two were also as you would expect excellent, but they are not something you'd want to take on an indie rock tour.

If you look at big stages these days (or when we can do shows again), you'll see that a lot of mix-people are using various condenser mics on amp cabinets -- certainly most of my touring mix friends use them instead of an SM57. I still use those E-100s, though I'm at the point where I'm considering retiring them so they don't get broken. (On a lead guitarist's amp, I use the E-100 and an EV 308, the latter being a dynamic with a larger diaphragm than a 57. For solos I punch in the 308 and it sounds different enough so the leads stand out. Old trick.)

And while we are bashing the SM57, I remember my first introduction to the wonder that is the Beyerdynamic M201. I did a show at a college and the sound company that came in had a case full of them. The company owner said, "you'll love these" and suggested them for all of the drums except kick, as well as the guitar amps. And he was right. Totally excellent. I own and use two of them. The 201 is my go-to snare drum top mic. As Steve Albini says, "The Beyer 201 is what the SM57 would be, if the SM57 was a microphone."

Quote
And, I strongly dislike the SM58.

Same here.

This is fun. I wanna do shows again!
 

Offline Bassman59

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The fixed directivity is achieved as Cerebus illustrated by channeling sound out of polarity to the back of the membrane. And, the "oddities" are indeed a lot of the character. That's my main issue with a Very Famous Vocal Mic. It's off-axis response is shit.

Its on-axis response isn't much better :) That microphone is the "gold standard" (as someone mentioned above) because it's cheap and familiar.

A recording-engineer friend has been ranting against the use of the Sennheiser MD421 on drums. Why? The off-axis response is terrible. Put one on a floor tom with the ride cymbal nearby. Listen to the 421 on the tom as the drummer plays on that ride cymbal. YEEEECCCCHHH.

Quote
The most common directivity modification method, though,  is known as "cupping", where the hand turns a pressure gradient transducer into a pressure transducer. Having frequently done monitors for people known to perform this act of directivity vandalism, I can assure the reader that it is indeed effective, both as a pose to make the alleged talent look stupid and as a destroyer of monitor mixes.

"Can you get my voice louder in these wedges?"

"Sure. Just hold the microphone properly and I guarantee you'll be able to hear your voice."

"But this is how I hold it."

"I'm a sound mixer, not a magician."
 


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