How to test resonance frequency of spring using sound? I've done experiment with spring and mass to determine the natural frequencies of 4 springs. The first experiment went well but I had some problem when I want to test the resonant frequency. I'll explain the context first.
After the spring test, the spring was tested for its resonance frequency using frequency generator, amplifier, and speaker with tube to focus on the wave. I set up the spring stretched vertically and blasting the sound perpendicular to the spring. The string were stretched about 1.7x of its length (it was clamped both side).
In theory the resonance is at 26 Hz but after trying for 4 hours blasting the sound, I can't make the spring in resonance, the same goes for the other 3 springs
What did I do wrong?
I still unfamiliar with the correct methods to find the resonant frequency
 A: The resonant frequency depends just as much on mass density as on stretch and spring constant.  You also have to consider whether you are looking at a transverse wave or a longitudinal wave.  Blasting from the side is a transverse wave, similar to a wave on a string.  A mass hanging from the spring is a longitudinal effect.  I don't know what kind of spring you have, but many springs experience a significant change in loop density, and therefore mass density, when oscillating.
Unlike a string, stretching a spring vertically can result in a non-uniform tension and mass density.  Loops at the top must support the force due to the stretch and the weight of the spring.  If they are further apart than loops at the bottom, tension at the top is greater and mass density is smaller.  Both of these would contribute to a greater wave speed at the top than at the bottom.  A greater tension would make the spring force a greater effect at the top and make loop distances more uniform.
You don't say enough about your spring to know what does or does not matter most, but these are the first things thatcome to mind.
