But it's not audible noise that's the problem. It's infrasound below the minimum frequency response of the human ear, which is probably the cause of Tony feeling "unsettled" and the theme behind the article that's being commented on in this thread ...
What it 'sounds' like is not what's at issue
Arfa
The only place where the noise can be obtrusive is an oval patch usually between 1km and 2km downwind where wind shear causes the wake vortex of the blade tips interacting with the support to touch down. The slower air behind the blades will also turn condensing in the right conditions which makes it easier to see where to go and stand.
I don't normally find them obtrusive but the ones they have just put up in front of the North York Moors near Middlesbrough look a right mess.
Yes and I very much suspect that the sound thats left out of "noise meter" readings.....
I don't think that any of them go down that low in fact no audio equipment I know of does, they tend to filter off below 20 Hz just calling it wasted audio...
No I don't do that silly bu^^ers thing Harry...
They invariably use the A weighting curve when measuring noise as this follows the response of the human ear (ish). That's 10dB down at about
200Hz and 40dB down at 30Hz... (0dB @ 1kHz)
Except the equipment to measure turntable rumble?
They're my local ones (Between Hilton and Seamer). They're quite attractive. I pass them about 10 times each week.
We had better build some then.
>
There is no problem in the electronics: its the transducer that is the problem
Not sure where standard microphone capsule stops..
Chris
3 Hz-20 kHz broadband linear frequency range 16.6 - 140 dB *A-weighted* dynamic range with supplied microphone Type 4189
"A" weighting is USELESS for infrasound.
In message , harry writes
Of course it can be measured, it just requires special equipment fit for purpose, not off the shelf standard audio equipment
Can't see there being a problem there - moving things slowly is usually easier than fast. You'd likely need an omni type - directional ones use cancellation to give their DP which will be frequeciy dependant. But many decent ones will include some form of high pass filter to remove things below the audio band.
The DPA 4003 is flat 10Hz though that is more of the exception rather than the rule. The rule would be flat down to nearly 20Hz for decent microphones. If you can judge "decent" by price tag then think =A31000 o= r higher. Not a 5p electret capsule from maplin...
A these low frequencies it'll have to be a pressure operated microphone,= which are inherentally omni. Such low frequencies won't generate enough =
signal from a pressure gradient microphone.
But of course the problem with infrasound is not so much it's transmission through air as "sound" but through the ground or building structure as a "vibration".
They only look really bad when you are travelling southbound on the A19.
Close to I think they do look OK. But it is an act of gross vandalism to put them in front of the edge of a national park like that.
You are quite right, I missed that.
However, it looks like they produce a mike specifically for infrasound measurement:
It isn't clear which meter it can be used with.
Chris
Unfortunately there is nearly always a lot below the "audio" band. Just closing a door creates very high levels of infrasound, especially if the room is well sealed. In vehicles the effects can be extreme. I once measured sound pressure levels of around 140dB SPL at frequencies of around 10Hz with a B&K sound level meter in "flat response" mode in a "luxury" car travelling at high speed (with the windows closed). I think the A-weighted reading was around 70dBSPL.
Although such infrasound levels are barely audible, they exceed the dynamic range of most microphones, especially the cheaper electret types. To overcome this, the manufacturers of omni-directional electrets laser-drill tiny holes in the diaphragm to provide a controlled bypass leak which gives a high-pass frequency response curve. Without this, they would sound terrible under ordinary conditions as there would be frequent mechanical clipping.
Such microphones are used in many of the low-cost sound level meters on the market. This means that even if the A-weighting is disabled (which is seldom possible) they are still incapable of accurately measuring infrasound. There is certainly lots of scope for accidental or deliberate mis-reporting.
John
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