Topic: Proximity effect with mount (and cable vibrations) on microphones?

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I'm currently working on building another mount since my last one was lacking in several areas. Unfortunately to reduce weight and other problems, my current design has the capsules at roughly 130degrees from the shockmount, and about 5cm away from it. I remember DSatz commenting on the reflection from the mic stand and positioning mics away from the stand, and wonder what sort of distance is required to reduce that reflection (or if some dampening measure can be taken on the object if it has to be close). Any ideas?

[DSatz]

Speak of the devil and he'll turn out to be awake and bored early on a Sunday morning. I'm not sure whether I'm visualizing your setup correctly, but I think that you might not have much of a reflection problem, and I'd suggest a bit of testing to find out.

Set up one of your microphones in an ordinary room with as much free space all around it as you can, and listen to its output over headphones (just picking up ordinary room sound, or the sound of a radio or TV playing at moderate volume). Take any object with similar dimensions to your shock mount (or the shock mount itself for that matter), and move it into and out of position near the microphone capsule while listening for changes ("phasey" sounds especially) in the upper midrange and treble. Small objects don't pose any obstacle to low- or most mid-frequency sound waves, so they're not an issue here.

If all you're concerned about is a normal mike stand or boom, it's usually not that big a deal--small, rounded surfaces create a variety of path lengths for reflections, so the small amount of distortion they create in the sound field isn't too heavily concentrated in any one very narrow range of frequencies. Larger solid objects and/or flat reflecting surfaces near a microphone (particularly a directional microphone) would be much more of a problem.

--best regards

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Excellent! I was secretly hoping my trap would work, thank you for the reply. 

I'm hoping that since this is a smallish mount (a shure a53m) and the angle of reflection would be toward the back of the cardioid pattern that it won't amount to much. I'll take some samples later today and see how it goes. Thanks.

[DSatz]

The way the A53M is designed, its only smooth hard surface is on the outside of the circle holding the rubber donut. But that is small, and unless your microphone is very short, it shouldn't be too close to the microphone capsule. I really don't think you need to worry about it.

A bigger issue with that shock mount is that its design totally ignores the mike cable as a pathway for vibrations to reach the microphone. Some length of loose cable should be isolated (tied off) somewhere or the shock mount won't do much good.

For the long run, you might want to save your pennies for a pair of Rycote "InVision" shock mounts--they take care of both problems very nicely.

--best regards

P.S.: Just to be pedantic for a moment, "proximity effect" actually means something else--it's the effect that emphasizes the low frequencies (sometimes by quite a lot) when a sound source is close to a directional microphone.

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The way the A 53 M is designed, its only smooth hard surface is on the outside of the circle holding the rubber donut. But that is small, and unless your microphone is very short, it shouldn't be too close to the microphone capsule. I really don't think you need to worry about it.

Yeah, now that I get everything setup, I think it will be ok, I've run it in a similar fashion before and I've been generally content with the results.

For the long run, you might want to save your pennies for a pair of Rycote "InVision" shock mounts--they take care of both problems very nicely.

I'm really tempted, I looked at them before going with the shure mount and there are times that I think they would be more suited for what I'm trying to accomplish. Notice the slight forward sag. Another problem with the shure mount and my current design is that I can't change bars to another configuration without pulling everything a part on one end (including retaining screw).

P.S.: Just to be pedantic for a moment, "proximity effect" actually means something else--it's the effect that emphasizes the low frequencies (sometimes by quite a lot) when a sound source is close to a directional microphone.

Yeah, I couldn't think of a better term at the time. Reflective effect related to proximity of other objects would be more accurate but it doesn't roll off the tongue as well. 

[notlance]

A bigger issue with that shock mount is that its design totally ignores the mike cable as a pathway for vibrations to reach the microphone. Some length of loose cable should be isolated (tied off) somewhere or the shock mount won't do much good.

Looking at the above photo and making some assumptions, you may get quite a bit of cable borne vibration to the mics.  I am assuming the mics pictured are low mass.  The mic cable is not looped to decrease its spring constant.  I cannot tell how flexible the cable is, but it looks kinda stiff.  All this means the cable borne vibrations may be a larger amplitude and a higher frequency than you want.

What's a guy to do?  Any combination of increasing the mic mass, decreasing the cable's spring constant, or increasing the system's damping will work.  Since you probably don't want to increase the mic mass, you'll have to work with the other two variables.

An effective way to decrease the cable's spring constant and probably increase the damping also is to use a few loops of very flexible mic cable between the mic and the larger standard cable.  A source of such thin, flexible mic cable are the cores of a snake cable.  Morgami and Canare both make snake cable with thin flexible cores.

[Church-Audio]

The way the A 53 M is designed, its only smooth hard surface is on the outside of the circle holding the rubber donut. But that is small, and unless your microphone is very short, it shouldn't be too close to the microphone capsule. I really don't think you need to worry about it.

Yeah, now that I get everything setup, I think it will be ok, I've run it in a similar fashion before and I've been generally content with the results.

For the long run, you might want to save your pennies for a pair of Rycote "InVision" shock mounts--they take care of both problems very nicely.

I'm really tempted, I looked at them before going with the shure mount and there are times that I think they would be more suited for what I'm trying to accomplish. Notice the slight forward sag. Another problem with the shure mount and my current design is that I can't change bars to another configuration without pulling everything a part on one end (including retaining screw).

P.S.: Just to be pedantic for a moment, "proximity effect" actually means something else--it's the effect that emphasizes the low frequencies (sometimes by quite a lot) when a sound source is close to a directional microphone.

Yeah, I couldn't think of a better term at the time. Reflective effect related to proximity of other objects would be more accurate but it doesn't roll off the tongue as well. 

Also is that the silver / Teflon cable everyone is raving about if so its way to stiff for use with microphones.. Especially if you dont want vibrations getting into your mics. Thinner cable would be better at least from the stand to the capsules. Then use the thicker silver cable to the thinner cables. I would be someone could make you some adaptors that would do the trick. That way your less likely to have issues. I would suspect that at least 50% of your vibration issues are from that stiff cable you are using.

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Ironically I have more limbre cables (the stock beyers) but they are wicked short which to me defeats part of the purpose of running remote capsules.

Would having a tie off (ala the rycote invisions tie off near the base of the shockmount) attenuate the vibrations into the cap or by that point is it moot to try and stop it (other then switching cables)?

[Church-Audio]

Ironically I have more limbre cables (the stock beyers) but they are wicked short which to me defeats part of the purpose of running remote capsules.

Would having a tie off (ala the rycote invisions tie off near the base of the shockmount) attenuate the vibrations into the cap or by that point is it moot to try and stop it (other then switching cables)?

Nothing will help the vibrations of these cables. Because they are way to solid they are like a steel wire. Make short jumpers out of the other cables you have and get male ends put on the one side so you can plug them into your Teflon cables. Then you will have much better isolation.

Chris