Topic: The Myth of Microphone Reach by Shure

[Matt Quinn]

Hey all, long time, no talk, haven't had much time for taping stuff lately.

Anyway, got this cool article in an email from Professional Sound Services (they have a great monthly email they send out, always has lots of neat location recording stuff, sign up here: http://www.pro-sound.com/ ). I know DSatz has tried to hammer these points home in the past on this board, but figured a little more info always helps.

The Myth of Microphone Reach by Shure


Shure is often asked "How far away will my microphone pick up?'" or "Which microphone has the best reach?" Both questions are based on a misunderstanding of how microphones work. This bulletin attempts to debunk the myth of microphone reach.

 

Myth: A microphone reaches out to capture sound.

 

Fact: A microphone only responds to sound waves that travel to its location. A microphone measures local rapid variations in air pressure and provides an electrical output that mirrors these variations. These rapid air pressure variations are sensed as sound if they are within the hearing frequency range of 20 - 20,000 Hertz. The microphone is stimulated only by the sound waves that travel to its location. It cannot "reach" out and capture the sound wave from a distance.

 

Myth: A directional microphone enhances sound waves which approach from the front.

 

Fact: A directional microphone merely rejects sounds from directions other than the front. An omnidirectional microphone "hears" equally well in all directions. It does not reject any sound as it is insensitive to the direction of the passing sound wave. A unidirectional microphone "hears" well in certain directions and not so well in other directions. As an example, a cardioid microphone does not reject sound waves which approach from the front; is slightly “deaf” to sounds approaching from the left or right; and is very “deaf” to sounds approaching from the rear. So a cardioid microphone appears to enhance sound waves from the front, by being far less sensitive to sound waves from the left, right, and rear.

 

Myth: A microphone has a reach specification that can be measured in feet or meters.

 

Fact: A microphone’s effectiveness at different distances is primarily dependent on the background noise level. Let's use an example. For a nature film, you want to record the call of a wolf in the wilderness of Canada. The recording conditions are superb. There is no wind; the closest town is 100 miles away; your equipment is a state-of-the-art digital recorder with a quiet mic preamplifier. Your microphone is an omnidirectional dynamic. You spot a wolf about 1/2 mile away and start the recorder. The wolf howls for two minutes and you obtain a fantastic recording. [If you believe in microphone reach, your microphone has a reach of at least 1/2 mile.] The next week you are back in New York City. A wolf escapes from the Bronx Zoo, takes the subway to Manhattan, and is now howling on 6th Avenue at 59th Street, which happens to be 1/2 mile from your studio. You immediately activate your digital recorder and hang the same omnidirectional microphone outside your window to record the wolf, but much to your surprise all you hear is traffic and wind noise when you play back the recording. The wolf cannot be heard even though you saw it howling through your binoculars. Did the reach of the microphone somehow change? No, only the ambient noise conditions changed.

 

Myth: A shotgun microphone is like a zoom lens on a camera.


Fact: Using a shotgun mic is like taking a photo with the lens aimed down a cardboard tube. The image being photographed is not brought any closer, but the unwanted images to the sides are reduced or eliminated. A shotgun mic seems to bring the desired sound source closer because the unwanted sounds from the side and rear are attenuated. It is tempting, but misleading, to compare light with sound. Light waves and sound waves do have similarities, but many more differences. The most important difference is in wavelength. The wavelength of light is measured in millionths of an inch. The wavelength of sound is measured in inches and feet. For a zoom lens to be effective, its diameter must be hundreds of thousands times larger than the wavelength. A typical camera zoom lens is approximately 3 inches in diameter. But a "zoom lens" for sound waves (using the same ratio) would have to be tens, even hundreds, of miles in diameter. There is an acoustical device, called a parabolic reflector, that can be combined with a microphone for distant pickup. However, it too will be limited by unwanted ambient noise. To be effective at lower frequencies, the parabolic reflector must be six to eight feet in diameter. It is the extremely long wavelengths that make sound so difficult to control, manipulate, and focus.

[Hypnocracy]

I need to look up an old tape...back in the early 90's I patched once for a Flectones House of Blues show with a guy running Shure SM57's (I came prepared to  )...as I was doing it I thought "Oh Well...it's just tape" and it should sound better than these RS lav Omni's I got...

But I was pleasantly surprised....the quality of sound I really liked was the vocals...very natural and the rest was believable....I've brought home worse sounding pulls...

[absnj]

Myth: A microphone has a reach specification that can be measured in feet or meters.

The explanation for this myth is faulty:  Wolves are not allowed on NYC subways.

[it-goes-to-eleven]

Myth: A microphone has a reach specification that can be measured in feet or meters.

No, it is a known fact.

[Gutbucket]

Common TS myth: Omnis behave omnidirectionally when worn on your person.

[F.O.Bean]

Common TS myth: Omnis behave omnidirectionally when worn on your person.

Arent they tho? Theyre just baffled omnis

[Gutbucket]

Theyre just baffled omnis

Sort of like being dead is just an inconvenience. 

Each mic will no longer pickup sound omnidirectionally for a large part of the frequency spectrum.  It will instead act more like a cardioid facing outwards, perpendicular to the baffle.  Sure it's still omni at the lowest frequencies but more directional than many cardioids up top.

[F.O.Bean]

Theyre just baffled omnis

Sort of like being dead is just an inconvenience. 

Each mic will no longer pickup sound omnidirectionally for a large part of the frequency spectrum.  It will instead act more like a cardioid facing outwards, perpendicular to the baffle.  Sure it's still omni at the lowest frequencies but more directional than many cardioids up top.

Hmmm, never knew that. Thanks for the heads up

[ero3030]

Myth: A microphone reaches out to capture sound.


^^^^^ even on my greenest moment, that never crossed my mind when asking taping questions.  ed

[newplanet7]

Common TS myth: Omnis behave omnidirectionally when worn on your person.

This is what I've always thought.
Thus putting all these peeps insisting  omnis over cards are really getting more of a card tape WHEN WORN.

[Gutbucket]

Common TS myth: Omnis behave omnidirectionally when worn on your person.

This is what I've always thought.
Thus putting all these peeps insisting omnis over cards are really getting more of a card tape WHEN WORN.

Depends on how you wear them.  Not many wear cardioids so they are facing 180 degrees apart, facing left and right, which is the rough directional equivalent of HTRF style head-worn omnis.  Headworn with both mics parallel and facing forward, and considering the pickup pattern of both mics used together as a stereo pair, cards will be less sensitive to sound from behind as would be expected, where omnis will not.  Yet an omni on the front of a baffle facing forward will have greatly lowered sensitivity to sound coming from behind the baffle.

[SmokinJoe]

First of all I agree... there is no such thing as "reach", it's just a perception.

But AT has some diagrams for AT853 capsules which show exactly how much reach they have.  It shows some ratios where cards have a reach of 1, omnis are 0.7, hypers are 1.2, and the miniguns are 1.7 (those figures are from my memory).  If a manufacturer publishes those, it propagates the myth.

[Gutbucket]

But AT has some diagrams for AT853 capsules which show exactly how much reach they have.  It shows some ratios where cards have a reach of 1, omnis are 0.7, hypers are 1.2, and the miniguns are 1.7 (those figures are from my memory).  If a manufacturer publishes those, it propagates the myth.

True.
Those numbers may be incorrectly described as reach, but are still useful.  A more accurate description would be that they indicate the difference in reduced sensitivity to off-axis sounds between various AT853 patterns in relation to the cardioid.. but that's more of a mouthful and an eye glazer.

[zowie]

Common TS myth: Omnis behave omnidirectionally when worn on your person.

I hear what you're saying but don't agree.  The mic is still "behaving" exactly the same.  It's just that the sound reaching it is more directional.

[Gutbucket]

There is more to it than simply a barrier baffleing the sound.  There is also some boundary mounting effect depending on the surface, it's shape and hardness.  Think of PZMs and other boundary mounted mics, the classic Neumann M-50 and its decendants with an omni capsule mounted in the surface of a small sphere within the microphone housing, the DPA Acoustic Pressure Equalizers and the Neumann equivalents, the larger stereo sphere microphones from Shoeps and others, etc.  All of those use omni capsules, but none behave the same as omnis without those things.

[Gutbucket]

Another common myth: The '3:1 Rule' apples to recording with a stereo pair of omnis.

It does not, and would actually be impossible to implement that way or nearly so.

[Gutbucket]

Common TS myth: Omnis behave omnidirectionally when worn on your person.

I hear what you're saying but don't agree.  The mic is still "behaving" exactly the same.  It's just that the sound reaching it is more directional.

I came across some back-up on this while browsing TS today, from a source more credible than myself-

..body-mounted microphones can't possibly function as omnis at mid or particularly at high frequencies..

Here's the full post from the recent 'anyone using omnis exclusively?' thread- http://taperssection.com/index.php?topic=150689.msg1918573#msg1918573

[John Willett]

First of all I agree... there is no such thing as "reach", it's just a perception.

But AT has some diagrams for AT853 capsules which show exactly how much reach they have.  It shows some ratios where cards have a reach of 1, omnis are 0.7, hypers are 1.2, and the miniguns are 1.7 (those figures are from my memory).  If a manufacturer publishes those, it propagates the myth.

These are directivity ratios, but I have never seen them quoted as you have them.

An omni is 1.0
A cardioid is 1.7
A super-cardioid is 1.9
A hyper-cardioid is 2.0
A short-gun is 2.2

This means that a cardioid at 17cm distance will pick up the same sound as an omni at 10cm.

It also means that a short gun (like a 416) will pick up at 2.2m what an omni does at 1m - so a short gun will only just over double the distance compared to an omni.  (and a mini on-camera gun is more like a hyper-cardioid than a gun mic. and even shorter).

It's nothing to do with "reaching out", it's the directivity ratio based on the polar-pattern and the fact that the more directional patterns pick up less reflected sound.

[Gutbucket]

More specifically, those directivity ratios indicate the difference in sensitivity to sound ariving on-axis verses sensitivity to sound arriving from in all other directions. I think those ratios are misleading when converted to actual distance measurements, because that variable aspect will be different in different rooms.  In normal spaces there is more direct sound in proportion to diffuse sound closer to the sound source, but how quickly that changes with distance depends on the environment.  And because it changes with environment, and also with distance within each environment it makes those comparitive distance numbers misleading. For example- in an anechoic chamber, the effective difference between on-axis sound and off-axis sound is identical for all microphone patterns, simply because there is no off-axis sound arriving at all.  That is not a typical recording scenario of course, but emphasises the point that in addition to the the directivity ratio of the microphone, the environment in which it is used also determines how various patterns will behave at various distances.