Re: Projection

[Pat Missin <pat@xxxxxxxxxxxxx>]

Rick Dempster wrote:

>      I still do not see what the effective difference is between 
>the plucked and blown reed. I know that the airstream 
>amplifies the sound. 

No. In the case of the harmonica, the airstream IS the sound. The air
is chopped into a series of pulses by the action of the reed, in a
similar way to a siren. This pulsed airstream is what you are hearing,
not simply the sound of the vibrating reeds being amplified by the
column of air.

>      Can you explain what is the difference between the vibrations 
> produced by plucking, and those produced by an air stream? 

Simple. Pluck a reed and listen to the sound produced. It is nothing
like the sound that you associate with the harmonica being played
"normally". In the case of electric pianos like the old Hohner Pianet,
this is the sound you are hearing - the actual vibration of metal
reeds electronically amplified.

When plucked (or hammered, or bowed) lengths of material that are
fixed at one end produce overtones that are not harmonic - ie that are
not simple integer multiples of the fundamental frequency. This
produces a very complex timbre that is very different from the
perfectly harmonic timbre of an airstream that has been set into
motion by the chopping action of a reed.

>The reed must be producing the sound, otherwise what difference 
>would its mass/ length etc. make 

Simple - the length of the reed, the distribution of mass along that
length and the flexibility of the reed material all determine how fast
the air is chopped into pulses. The faster it is chopped, the higher
the pitch of the note produced. The width of the reed, the sharpness
of the edges, tolerances between reed and slot, etc., all have other
effects on how the reed interacts with the airstream.

>(I can see I'm going to have to conduct my own experiments to 
>understand this, ultimately!)

That's the best way to get to grips with these things.

>      Finally, can you imagine anyway of increasing the volume of 
>the harmonica without electricity? Is this the free-reed equivelant 
>of the quest for perpetual motion?

I can think of two ways straight off. Playing technique and an
acoustic megaphone.

 -- Pat.