Re: [Harp-L] Study of Harmonica cover resonances

["Vern Smith" <jevern@xxxxxxx>]

Congratulations on conducting an interesting experiment. 
I'm convinced that different cover shapes can have 
measurable acoustical effects.

Did you assess the effect of different mic locations on the 
sprectrograms?

Are we to understand that the effects measured arise from 
the shapes of the cavities under the covers and not from any 
acoustic activity of the covers themselves?   The materials 
of the covers would thus be irrelevant?

I assume that "blind" human listeners might, or might not, 
be able to perceive the differences. (I am reminded of the 
audiophile who plays a square wave through his hi-fi system 
to an oscilloscope.  ;o)  )

You can make a good pump of an old tank-type vacuum cleaner 
from a garage sale.  A 2kw light dimmer in series with the 
motor reduces the noise and pressure to usable levels.  A 
15" U-tube water manometer improvised of 1/4" clear plastic 
tubing and a yardstick will tell you what pressure you have. 
A well-gapped reed will start to speak at about 1/2" of H2O, 
will give you full volume at about 5" and will choke up 
around 15"  The pressure increase from 5" to 15" yields very 
little increased loudness.

Vern

----- Original Message ----- 
From: "geoff atkins" <geoffatkins@xxxxxxxxxxxxxx>
To: <harp-l@xxxxxxxxxx>
Sent: Wednesday, April 29, 2009 8:05 AM
Subject: [Harp-L] Study of Harmonica cover resonances


> The study of cover resonance seemed to create some 
> interest from members
> (though not the 2000 that Winslow scared me with  :).
> After about ten off-list requests from members, I have 
> posted the details of
> the study and findings in PDF file format onto the Google 
> groups Harp-L site
> at
>
> http://groups.google.com/group/harp-l/files
>
> It's called "Covers sound analysis 0 .pdf " and contains 
> all four postings.
>
> My thanks to Seth Galitzer, who introduced Harmonicaspace, 
> and Mox Gowland
> who showed me how to post to Google groups.
>
> Best Regards
>
> Geoff Atkins
>
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