Mic shock isolation

dosdan

Active Member
Examples of mic mechanical decoupling from 10 important facts about acoustics for microphone users

9. Mechanical vibrations
Mechanical vibrations in building parts result in audible sound. If a microphone stand is placed on a vibration floor, it may generate sound in the microphone. Also rattling of loose mechanical parts in a room will result in problems.

This audio sample demonstrates the effect of using a proper shock mount for microphones. A d:dicate™ 4017 B Shotgun Microphone is mounted on a microphone stand using three different fixtures. The recording engineer is kicking the legs of the stand. In each case the “stand kicking” is recorded without and with the 4017B low cut on.

The following mounts are used:
  1. Standard microphone clip UA0639. There is no damping, and the sound of the impacts enters the microphone via the microphone stand
  2. Shock mount UA0897. Now the sound is predominantly airborne
  3. RWK4017 Shock mount (optimized for DPA4017mk2). Less mechanical vibrations, and nearly only airborne kick noise
SoundCloud: Shock Mount - 48k.WAV



Dan.
 
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Terfyn

Active Member
All very interesting but how would you deal with microphone mounting and how does it work?
 

dosdan

Active Member
Rycote provides a number of universal shock mounts (USM) for camcorders:

Camera Mic Shock Mounts | Rycote

as well as boom-mounted mics:

Boom Shock Mounts | Rycote

The theory is a damped spring-mass system:

THEORY OF VIBRATION ISOLATION

Fig 20 in the link above shows that, at vibrational frequencies above the resonant freq of the system, the transmissibility of the suspended system decreases, providing more isolation.

This increased isolation can be seen in this measurement of a suspended Neumann TLM 104 in a Rycote USM-L mount:



The blue curve shows the vibration transference without a shock mount. The red curve shows how the isolation improves with the shock mount until its increasing effectiveness is not measurable on this graph when it goes below the measurement system's noise floor (black curve).

You can see at around 40Hz how the vibrational transmission is actually increased. I presume this is a resonant freq of the spring-mass system, but the peak is relatively subdued due to a fair amount of damping.

The Effect of Damping on Tranmissibility

Inside the mic body itself, there is usually another suspension system, isolating the mic capsule from its housing. See the "Internal Shock Mounts" and "External Suspension" sections here:

Handling Noise of Microphones | Knowledge Base | Shure Americas

The higher the mass of the capsule, the less compliant (elastic) the suspension needs to be to keep the resonant freq from rising too high. Conversely, the lighter the capsule, the more compliment ("softer") the suspension needs to be.

The capsule in a dynamic mic is usually relatively heavy due to the permanent magnet needed for this type of mic. This requires a less compliant suspension. (Too compliant, and the capsule would jiggle around.) The Shure SM57 and SM58 dynamic mics use a sophisticated pneumatic suspension to reduce handling noise:


However, a back-electret capsule is very light, and the suspension has to be very soft so that the resonant freq of the suspension doesn't rise into the audible band of frequencies. In cheap electret mics, the manufacturer just jams a bit of expanded foam around the capsule. As to how high the resultant resonant freq is, is anybody's guess. The high-quality back electrets I've heard have a fairly dead sound when you rub the body, while with the cheap electret mics, the handling noise is more abundant and, with more high-pitched components, sounds "scratchy".

And then you have the problem of foam deteriorating with exposure to ozone. I wonder what the condition of the internal suspension is in cheap electret mics, say 5-10 years after manufacture?

Dan.
 
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rogs

Well-known Member
I've find the Rycote Lyre mount that came with my Rode NT1 reference condenser mic to be very good - and the 1" capsule is itself mounted on a second Rycote lyre mount internally......which helps further.
Rycote certainly know what they're doing - although, understandably, you do have pay a bit more for their products than those from their cheaper rivals

The pneumatic shock mount in my Shure SM58 also works well - although it's probably not fair to compare it directly to the lyre mount for a side entry, fixes mount condenser mic....

I have made a number of mics using high quality Primo electret mic capsules, and because they are so light, mounting them in the centre of a roll of foam - fitted inside a mounting tube made from a length of plastic waste pipe - works very well.... as least as well as the Shure SM58 mount.

And if the foam should deteriorate in the future (that seems to depend a lot on the type of foam used, in my experience) then it's a simple enough job to replace it.

I've been very pleased with the results obtained from EM258, EM184 and EM172 capsules, interfaced with home made 48v phantom power balanced circuitry...
Excellent frequency response, low noise floors - and low handing noise - and all from mics which costs a fraction of the commercial equivalents...

Not for everyone of course, but if you are someone who enjoys experimenting.. :)
 
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12harry

Well-known Member
Mechanical isolation certainly does help . . . the more - the better I suspect.


Most Blimps use neoprene bands to hold shotgun mics in the centre of the blimp...thus providing a noise-less mount and very good isolation of handling-noise by the boom operator.
For outdoors, there can be the same issue, along with Wind-noise.​
We are familiar with fluffy-surrounds applied to blimps, as well as the somewhat cheaper alternatives where it just surrounds the mic.
My CX410, like the Stills camera NEX5 ( which does HD movie), both suffer from Wind noise outdoors... and a modest amount of Faux-Fur fixes most of that, esp if there can be a small air-gap before sound hits the microphone area.
I fail to understand why Mfrs like Sony don't throw-in a branded small Fluffy, which would advertise how good they are to their customers. However, as camera cases are rarely made to contain the Camera+Fluffy it seems we may be on our own.

Where it's important before recording something that matters.... is to do some Tests with good-quality headphones ( at the recording site) and decent speakers with sufficient Bass at the Edit. It's far too easy to discover there is LF noise on the soundtrack that shows up only when played on "better" equipment . . . Of course it's there beforehand, just you hadn't noticed.
I'm not at all a fan of LF-Cut filters to reduce wind-noise as they change the audio recording . . . far better to resolve the Wind-noise by having good fluffy/blimp combo. Standing with a shield (out of shot) can also lessen wind-impact if it doesn't touch the microphone.... I used this trick when filming waves at the seaside...caused by a mighty gale in progress. Filming the crashing waves at nearly 90 degrees, meant it was more spectacular as well as reducing the risk the camera (operator), could get wet.

Cheers
 
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