Concussion Bellows | Homemade Pipe Organ | Sub ITA

I built a Concussion Bellows for my Homemdade Pipe Organ to reduce the small pressure variation in the air supply system. Sub ITA for my countrymen

The result is quite good.

A concussion bellows is a small spring-controlled auxiliary bellows for a pipe organ for compensating slight variations in wind pressure.

Every electronics engineer knows that in a power supply you must install reservoir, or decoupling, capacitors to do away with voltage transients. This is a direct analogy to our air supply problem. Next thing is then to introduce the concept of 'acoustical capacitance'.

This is defined as C=DV/DP where DV is change in volume and DP is change in pressure.

In SI units V is in [meter3] and P in [Pascal=Newton/meter2], so capacitance is in [meter5/Newton], again pretty hopeless to grasp intuitively.

The prototype for an acoustical capacitance is a closed stiff container of volume V. When you compress the air inside it by pumping in that DV, then pressure will rise the amount DP.

By use of the gas law you can eventually derive the formula

C = V/(rc2) [m5/N] Acoustical capacitance of a closed volume V

CREDITS:

Pushing and bouncing air
Some reflections on the Theory and Practice of Pipe Organ Wind Supply
by Johan Liljencrants