[pianotech] SWELL was What is bloom

[John Delacour]

At 10:12 -0700 17/03/2011, Delwin D Fandrich wrote:


>It's that "swelling of the tone" that I have a problem with. Your
>explanation nicely accounts for the change in the rate of decay that pianos
>exhibit following the initial chaotic attack but I fail to see where any
>extra energy is coming from to "swell the tone." It is this "swelling" that
>I have not seen measured.

Very timely!  Since now people are giving another meaning to the 
'bloom' I was talking about, I had just decided, before you wrote, to 
change my term to 'swell' and let them get on with the other matter.

Swell is another very appropriate word, perhaps more so, for the 
phenomenon I'm talking about.  I think some harpsichords are fitted 
with a Venetian swell device, and certainly some organs, and the 
effect I am talking about gives very much the impression of the swell 
being opened.  Another analogy would be switching suddenly from mono 
to stereo.  There is no doubt that the effect could be measured.

Of course there is no "extra energy" as you say.  It seems to me it's 
what happens to the existing energy that is the point, and the main 
question in my mind is why it doesn't happen on most pianos.  Suppose 
I play a good loud rich chord.  The strings held down continue to 
vibrate and induces forced vibrations in the soundboard/bridge at all 
the frequencies delivered.  These forced vibrations distributed 
throughout the whole resonant structure in turn set up sympathetic 
resonances wherever there is an undamped duplex (for example), a 
loose screw, anything that will dance to that tune.  Some of that 
energy will be converted to heat and I would suggest that whatever 
short-lived vibration is excited in the unplayed (and therefore 
damped) strings is lost as heat.

When I now raise all the dampers, the energy imparted to the 
previously damped strings is no longer converted into heat.  Some of 
the strings will begin to vibrate strongly in sympathy with the 
played notes and all their partials, and others less strongly, having 
less sympathy, fewer shared frequencies or possibly none.

I would suggest therefore that the effect is caused by the system 
using the available energy to produce and recycle vibrations which, 
when the dampers are down, is converted into heat.

JD