From: Eric Benjamin <>
>
> Those who know me know that I tend to take an academic
> viewpoint on these things. I did a quick check of
> what has been published in the Journal of the Audio
> Engineering Society, and found a couple of helpful
> papers:
>
> "Microphones and Wind", Wuttke, Jorg; JAES, vol. 40,
> No. 10, 1992 October
>
> "Windnoise Meausrement using Real Wind"; Woolf, C,
> Prudden, O., AES preprint 5269, 109th Convention of
> the AES
>
> Jorg Wuttke is chief engineer of Schoeps. I'll try to
> give a brief synopsis of his paper here:
>
> Pressure microphones and pressure gradient microphones
> have different sensitivity to wind noise.
> Measurements presented at a wind speed of 18 kph for
> the Schoeps MK-2 (omni) and MK-41 (cardioid) show
> about 20 dB greater noise at low frequencies for the
> cardioid. The difference diminishes to about 10 dB at
> 500 Hz. There is still significant wind noise at 1
> kHz.
>
> Both basket-type and foam windscreens can be
> effective. Foam windscreens tend to merely attenuate
> the highest frequencies (about 2 dB in the top octave
> for the one evaluated in this paper) whereas the
> basket type has less overall attenuation but
> introduces narrow-band peaks and dips amounting to
> about 10 dB peak-peak.
>
> The basket type windscreen is more effective at low
> frequencies, but less effective at mid and high
> frequencies than the foam windscreen.
> Quote "
> Conclusions
>
> Foam windscreens should be used wherever the
> protection they offer is sufficient, for their
> negative effect on the sound is relatively small and
> easily correctible. On pressure transducers they are
> almost always the best choice.
>
> Basket-style windscreens must be used on directional
> microphones if foam types are inadequate to reduce the
> levels of wind interference. They do detract from the
> sound and directivity of a pressure-gradient
> transducer to the degree that they are small and
> efficient. A good compromise between the two types is
> a hollow foam windscreen. In all cases care must be
> taken to avoid overloading the microphone channel's
> input electronics due to the excessive very low and
> even infrasonic frequencies produced by the action of
> wind on the microphone diaphragm. Attenuating the
> system's low-end response at the earliest opportunity
> is always a good idea to ensure a clean transmission.
> *******************************************
> end quote
>
> Now, if you don't happen to agree with this, don't
> shoot me. I'm only the messenger.
>
> eric
I happen to think that both of these are not even investigating what we
are discussing. They are investigating a separate issue or set of
issues. Let's see if I can explain.
The question, at least to my mind, and what I looked for in the specs
when I first started researching wind protection and did not find can be
illustrated by a example.
I'm out at a recording site, there is a breeze. I take out my Kestrel
wind meter and measure the wind speed. It's 3.5mph horizontal. I also
note that due to various objects upwind it's not a laminar flow, but is
a mixture of eddies. The windspeed on the meter is not steady but varies
over a 2mph range about the median speed. The question is simple, what
mic will record with either no direct wind noise, or at least wind noise
that's well less than it's self noise? That's really the question we are
asking, not the dB level or the frequency distribution. We don't want
any of it.
When I say there is little or no difference in the need for wind
protecting a omni over a directional, it's because I've observed that
either will give me direct wind noise at the same threshold wind
conditions. It does not matter that one might give me louder unwanted
noise than the other, unless one is giving me quiet enough to sink below
it's self noise. With the MKH's self noise, that's just not going to happen=
.
While I don't totally trust the Kestrel's wind measurements when there
is less than a mph of wind, at even a few tenths of a mph the MKH-20 is
still not meeting my criteria for no direct wind noise in the signal. Of
course neither is the MKH-60.
Thus I wind protect both. And the amount of wind protection I need is a
function of wind speed and character, not the type of mic inside.
Note that most people only notice the effects on the signal of the
variable bursts of wind hitting the mic. But even laminar flow across
the mic produces signal.
Walt
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