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Pad Porosity Study

jbtsax

Distinguished Member
Distinguished Member
#1
The pad porosity study is finally getting underway. The goal of the study is to test the porosity of the covering of several different brands and types of pads and then compare that data with the acoustic losses of each pad. There are 12 different pads being tested from Pisoni, Music Medic, and Jim Schmidt. The set-up for testing the porosity of the pads is shown in the following photos.

All pads being tested are 30mm and are without a center hole or resonator. A perfectly airtight pad made from neoprene is used as the control. The amount of closing force (weight) on the key cup required to register 0 with the control pad is the weight used in the study. All of the pads were tested with both 4"H2O and 2"H2O initial pressure.


Once the tests have been replicated by another tech to check the accuracy of the data, the pads will be sent to Dr. Pauline Eveno in Paris to measure the acoustic losses of each of the pads. Once these tests are completed, the results will be made available for anyone who is interested.









 

Carl H.

Distinguished Member
Distinguished Member
#3
Will there be a further look at resonators impact on porosity and acoustic loss once this baseline has been established?
 

jbtsax

Distinguished Member
Distinguished Member
#4
Will there be a further look at resonators impact on porosity and acoustic loss once this baseline has been established?

I don't believe so. The previous resonator (pad cover) study done by Dr. Eveno is quite comprehensive in and of itself.
 

jbtsax

Distinguished Member
Distinguished Member
#6
Thanks Toby from this acoustic nerd. :) I had forgotten about this study. Coltman's "Acoustic Losses of Bassoon Pads is also closely related to what I am looking into.

All of the "porosity testing" of the pad samples has now been completed with help from my trusted "lab assistant" Igor (Jory Woodis) who replicated the measurements independently. Both sets of measurements were found to be in close agreement. Those few pads whose measurements showed minor discrepancies were retested and the more common figures were used.

The weight necessary to register a zero reading with the neoprene control pad was found to be 206 grams so this was the weight used to test all the pads at both pressure levels. This sounds like a lot of force to close a key, but both my assistant and I pressed a finger against the postal scale as if closing a saxophone key with a very light finger pressure and both recorded a "push" of well over 300 grams!

Hopefully the acoustic absorption tests will be completed by the end of August to compare the data. In the meantime, I will be attempting to measure the acoustic pressures in decibels inside a sounding saxophone to convert those pressures to pascals and then to inches of water to see how much air pressure the installed pads are actually being subjected to.
 
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