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Erich,

I have found most versions of "Bernoulli Blower"  -- even the  
Exploratorium's, when it's placed in a smaller space -- to be too loud  
for my taste.  ( I suppose in truth the "modern world" is too loud for  
my taste, but what's to be done?)  There is a direct tradeoff between  
the CPM and the noise, but other factors are important too.  The path  
the air takes as it leaves the blower, and the aperture where it exits  
create resonances that shape the character of the sound.  We had a  
quite powerful squirrel cage blower in San Jose, driven by a 230 volt   
3 phase induction motor.  Someone discovered (or was brilliant enough  
to know) that placing a tennis ball at the aperture magically lowered  
the noise while only slightly reducing the height at which the ball  
flies.  The blower was also housed in a box lined with acoustic foam,  
fitted with air filters  on the intake to avoid sucking in strings and  
such and a grill on the outlet to keep coins etc from being dropped in.

My preference, to avoid all that bother,  is to forgo the heavier  
balls usually used, and go with balloons and a small quiet ventilating  
fan.   Yes, you will need to replace the balloons constantly, but  
then, beach balls don't last very long either -- and anything more  
durable takes considerably more air to lift.

Lastly, for all that it has been replicated over the years, I don't  
think the "Bernoulli Blowers" is a particularly rich exhibit, compared  
to the "air play table" you also mention.  The latter doesn't really  
need much air to be effective.  Here, for example, is a wonderful  
alternative, also from the Exploratorium, that uses just a window fan:

http://www.exploratorium.edu/pie/library/windtubes/index.html

quietly,

Tom Nielsen
www.TheExhibitGuys.com

On May 28, 2009, at 7:17 AM, Erich Rose wrote:

> ISEN-ASTC-L is a service of the Association of Science-Technology  
> Centers
> Incorporated, a worldwide network of science museums and related  
> institutions.
> *****************************************************************************
>
> For an "air play table" or a Bernoulli blower what would you suggest  
> as a minimum air flow? CFM? I have used different fans in the past  
> with different results. More often than not they were used squirrel  
> cage fans that we had laying around and had a wide variety of  
> outputs.  What I am looking for is some feedback from others about  
> what they found worked best.
>
> --
> Erich Rose
> Exhibit, Environmental and Industrial Design
> 807 The Living End
> Austin, TX 78746
> 512-626-9930; [log in to unmask]
>
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