Raphi Giangiulio's Homemade Pipe Organ

Home
Construction
Specification
Dedication
Virtual Organ
Sound Samples
Videos
Hi Res Gallery
Prototypes
The Shop
Mathematics
References
Organ Builders
Organ Photos
Other Projects
About Me
Contact Me
Site Updates

Calculating the Windsheet Thickness

I found a formula on the following website to calculate the windsheet thickness (WST). The WST and mouth height are defined in the image to the right. I'll summarize here by saying that a scientist named Hartmuth Ising developed a number to characterize the mouth of a pipe. The Ising number should be between 2 and 3. I=2 gives you maximum efficiency. As you increase the number, you get more harmonics and anything higher than 3 will overblow. I've found that I=2 gives good results. Here's the equation for calculating the WST:

WST =I2f 2ρH3
2P
  • I is Ising's number
  • f is the frequency
  • ρ is the density of air
  • H is the mouth height
  • P is the air pressure

It's important to be careful with the units in this equation. Using 1.2 kg/m3 for the density of air and putting in a factor to correct for the units, the following equation will give you the WST in inches.

WST =I2f 2H3* 1.554 x 10-6
P
  • WST is the windsheet thickness in inches
  • I is Ising's number
  • f is the frequency in Hz
  • H is the mouth height in inches
  • P is the air pressure in inches of water