Cogito wrote:For the RF determination I hold the blade at its grip and let a ball bounce from about 10 cm height. The noise is recorded by a microphone and audicity. After the measurement I select one of the sound peaks generated by the ball touching the blade and use the function "frequence analysis" to pick up the largest peak and read the indicated frequency.
I presume that you mean "Plot Spectrum
" for frequency analysis?
There are a number of issues with the test as you describe it that can probably be improved."about 10 cm height"
As someone with a scientific background I am very wary of unknown variables. In the design of experiments for quantitative analysis, it is generally best to reduce "unknowns" as far as possible, and where variables cannot be eliminated, to at least limit their range within a specified tolerance range. More about this later."I hold the blade at its grip"
This introduces many more unknown variables. How tightly are you holding it? How much variability is there in the angle of the blade? How much does the blade move due to inevitable unsteadiness of the hand that is holding it?
Perhaps the above two items could be improved by constructing some type of clamp to hold the blade, and a short tube clamped at a known height above the blade that is very slightly angled down from the horizontal (such as the cardboard tube from the middle of a toilet paper roll). Gently place the ball in the higher end of the tube so that it slowly roll down the tube and fall out of the other end, then drops down to the blade that is a known distance below. The tube and the blade clamp should be carefully aligned to ensure that the ball strikes the blade at the same position for each measurement."The noise is recorded by a microphone"
I would suspect that the majority of the sound picked up by the microphone will come from the ball rather than the bat.
Perhaps this could be improved by using a "contact microphone" (a piezo sensor stuck onto the bat) rather than a conventional microphone. A piezo polymer vibration sensor would be much better than a ceramic disk as the latter have strong resonance themselves whereas the former does not."Unfortunately it would create quite an effort to exactly reproduce the 10 cm (or whatever) height for different measurements."