Yes. Microphones designed for close in work (telephones, handheld voice mics, etc.) are not very good for picking up weaker or more distant sounds. They are made intentionally insensitive so as not to be overdriven by close in sources.
The ear is pretty good, but being attached to the human body, it comes with its own noise sources. In a very quiet environment, my breathing and heartbeat drown out sounds that could be picked up by a sensitive microphone.
-- Paul Hovnanian mailto:Paul@Hovnanian.com ------------------------------------------------------------------
Hi all.
Just been playing with some cheap (ECM-66B) microphone inserts and found they have a pretty poor performance compared with the human ear. I can hear some very quiet sounds in my room: the ticking of my clock and distant barking dog. This sensor can pick up sounds at this level but when the signal is amplified enough to hear them, there is a lot of noise with it.
The S/N ratio is quoted at 40 dB, and sensitivity at 60 dB/microbar.
It seems okay where it is next to or nearby a person's mouth, like a hand held microphone or a telephone. But if you stuck a pair on a dummy head and listened through an amplifier, you would not get a good sense of being in the room.
So, do microphones get much better than this?
Or is the ear such a marvellous organ that it is yet to be beaten?
In short, it's rubbish.
Professional condensor mics are often specified in terms of their dBA equivalent noise. I haven't heard of one lower than 12 dBA.
It is.
Graham
On Tue, 31 May 2005 02:33:49 +0100, Pooh Bear wroth:
Of course, the ear is supported by quite a bit of additional signal processing. If you looked at the nerve signals between the ear and the brain, I suspect that any useable information is thououghly buried in the "noise".
Jim
I
The way the ear hears is not exactly understood. The fact that it can apparently 'outperform' test instrumentation in critical istening tests in certain tests but not others perhaps adds to that puzzle.
Note that the ear hears partly by means of many cilia that are quite high Q 'tuned circuits'. I can't imagine a simple model of how humans or other animals hear. For example the ear can extract a signal that's 'buried in the noise' if it's of narrow enough bandwidth.
Graham
I do not know if it is true but this mike from Bruel and Kjaer has extremly low noise: The model 4179 is claimed to have -5.5dB(A) thermal noise only, that would be more sensitive than the human ear.
-- ciao Ban Bordighera, Italy
We can't beat the brain that processes the ear information, but as far as the ear itself goes, just what can it detect that test equipment cant?
Oh?
Care to support this with some references?
You must be using duff test equipment. I dont see that there is anything the ear/brain can hear that decent equipment can't measure. We just don't know what the measurements mean.
Kevin Aylward snipped-for-privacy@anasoft.co.uk
I didn't expect much for my £2. :-)
The dynamic range is certainly poor, but adequate for some applications.
It is sensitive enough it can pick up feint sounds, only buried in noise.
I was surprised by the amount of difference a simple plastic funnel made. Pointed out the window at a bunch of trees, the birdsong from them was much louder. Might be fun to play with a parabolic microphone :-)
How much does a reasonable quality transducer cost? I've seen mikes for several 10s of £, but much of that cost must go to make the robust housing for the transducer.
I suspect it has noise cancelling mechanisms. After all, it is buried in a mass of blood vessels and right next to airways.
As an aside, what is the noise heard when a sea shell is held to the ear? Usually explained as air currents, I find that hard to believe. I guess it is sounds coming from the head/ear itself, resonating and reflected back into the ear.
Yep, I did that (BC550 replacing BC547) and used a CA3140 op-amp.
I have a VOGAD (voice-operated gain adjustment) chip somewhere I will try out.
Yep, noticed that too.
I think the electronics are fine, so the electret is the noisy bit.
Recently heard of the "microflown", which is a silicon micromachine that senses the flow of air instead of pressure. Since it is very small (
FWIW, I once built a remote microphone for my handycam, incorporating a junkbox electret, a BC547 (as "frontend"), a 4558 (one half used) - to create a AGC mike amp with line level out (9V battery fed). The thing could "hear" things that I could ony detect with my "bare" (then still quite good) ears after noticing it on the headset. It would even feedback over thesound leaked out of the earphones.
In other words, I guess that with sufficient power line filtering and an adequate gain distribution - it may not be that bad.
-- - René
Try it with a satellite dish... the nice thing is that your microphone will point up and not cacth much ground noise while the reflector determines to which piece of ground you listen.
Thomas
most electret elements have an FET preamp built in so this bit of electronics may be adding some noise.
Mark
Yes, I'm just surprised that one FET can add so much noise.
What technology do decent quality microphones use?
Cheap fets I expect !
Professional conndenser mics use larger capsules and polarising voltages that produce more output for the same SPL. Hence the s/n is better. And they use quiet fets ( or toobs even in very old ones ! ).
Graham
It's a larger than average capsule ( see diameter ) which helps but even so that's an astonishingly low noise figure. Looking at the data it has a polarising voltage of 200V. That helps too.
Not too surpised at Neumann. Good products. I was thinking of more affordable mics !
I once owned an Neumann U87 - a classic mic. Last time I checked the RSP was £1600.
Graham
Okay, that makes sense.
If the bias voltage is 20 times my 9V battery, signal should be 20 times greater.
And that will be roughly multiplied by the area increase.
Hmm... I'm tempted to see what kind of output I'd get from two sheets of tinfoil (say 30 x 30 cm)held under tension very close to each other? Not the most practical stage mike, but it does provide a large sensing area. I imagine it would be pretty directional too.
Tried something like that using metallised melinex once as an experiment to make an electrostatic speaker.
I can see why it's best left to the experts !
Graham
Ah, but that is trying to put sound out, rather than sense sound in.
AFAICT the change in C needs to be as big a fraction of the total C for best results. Thus the sheets need to be close as possible. I think that is the hardest bit.
What a crap "design"....
(1) Shunt feedback stage with a pot as the source impedance.
(2) CB input stage... barf. For low noise you'd be better served with CE at low current and low VCE.
...Jim Thompson
-- | James E.Thompson, P.E. | mens | | Analog Innovations, Inc. | et |
Okay, it is pretty small so not got a great sensing area. And for £3 I did not expect much.
I went out and bought a dynamic mic insert for £5, and this is labelled as having 76 dB sensitivity. It is a lot bigger and heavier.
I made up this preamplifier
However I didn't find it was much improvement. There is noticeable hiss and buzz.
Hiss seems to be coming from the first transistor (BC109, common base) and the buzz from the mic insert, because the buzz disappears when the signal input is shorted to ground. The hiss and buzz disappears when there is no signal to the other transistors.
Circuit constructed on a bit of veroboard - not ideal but fairly neat and compact.
So, is this mic insert also crap, and if so how much would I expect to pay for a good one?
Also, is this BC109 transistor just too noisy?
Or am I going to have to make a much more complex pre-amp like this one:
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