Hi Rich,
thanks a lot for the hint!! I'll buy a
sparker for my tests... I used keys, small bells,
small hammers, old ultrasonic remote controls,
generators connected to ultrasonic speakers...
all them useful to check if the mic catches
something, but not useful for comparison, even if
you record all mics together to be compared on
the same event they are not exactly in the same position.
- keys, bells and hammers are too variable...
- ultrasonic remote controls emit only few
frequencies and their directionality is highly variable
- the sound generator emits only a variable, but
single frequency, signal and at those frequencies
interferences and reflections might be very intrusive, and...
- ultrasonic speakers have often fuzzy emission lobes
The sparker seems to have the advantage of
generating an omnidirectional broadband signal with a very good repeatabili=
ty.
By the way, big sparkers are used to produce load
broadband pulses for geophysical research! By
modifying the geometry and spacing of the
electrodes (and the supplied current too) it is
possible to change the energy/bandwidth of generated pulses...
by reducing the spacing of a sparker we can
generate a smaller spark and maybe a less intense but broader acoustic puls=
e.
The only doubt I could have about this method is
about a possible (?) electrical/electromagnetic
interference maybe catched up by cables or electronics...
I'll do some tests...
Gianni
At 23.03 23/03/2007, you wrote:
>Yes keys do have ultrasonics too. It is such a complex signal that it
>leads to an easy ear check of a recording system.
>
>Too complex and long to give a good paper trail. The key compared to
>the spark have some things in common but on the amptitude display I
>also see strong different harmonics that I don't see on the spark.
>
>My car keys recorded at 3 inches. The spark was recorded at 1 foot.
>In the linked photo I have the key jingle first and then I have
>appended three separate spark sounds. Same mic, same recorder, etc.
><http://home.comcast.net/~richpeet/keyspark.jpg>http://home.comcast.net/~r=
ichpeet/keyspark.jpg
>
>For measurement of attenuation of different frequencies for my wind
>blimp I think I am better off with the spark. But am open to
>suggestions as I just hack at this.
>
>Rich Peet
>
>Rich Peet
>--- In
><naturerecordists%40yahoogroups.com>=
m,
>Lou Judson <> wrote:
> >
> > Have you tried a key jangling test the same way? I'd be curious to see
> > a similar image from that, the traditional test used for mic pre
> > distortion - care to do a comparison? Certinly safer than the spark, is
> > it as effective?
> >
> > How close was the spark to the mics?
> >
> > <L>
> >
> > Lou Judson =95 Intuitive Audio
> > 415-883-2689
> >
> > On Mar 23, 2007, at 11:32 AM, Rich Peet wrote:
> >
> > > How high will a standard mic go.
> > >
> > > Someone else with more experience than me would have to comment on
> > > what the freq response curve of a gas grill bbq piezo starter is but
> > > it seems to go into RF frequencies.
> > >
> > > Testing two standard mics with the bbq starter I noted that on
> > > multiple sparks that the spectrum display looks identical each time.
> > > Then changing mics I get a different pattern that once again does not
> > > change from spark to spark. So I conclude that an electrical spark is
> > > a way to check the freq capability of your equipment. I have no idea
> > > if this method could be dangerous to electronic devices and would not
> > > be surprised if there is a risk.
> >
>
>
>
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Gianni Pavan
Centro Interdisciplinare di Bioacustica e Ricerche Ambientali
Universita' degli Studi di Pavia, Via Taramelli 24, 27100 PAVIA, ITALIA
Phone +39-0382-987874 Fax +39-02-700-32921
Email
Web http://www.unipv.it/cibra
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