I want to demonstrate some activities related to sound and tuning fork among kids.
I have a couple of these including C256Hz, C 380 Hz etc.
When I put these on a wooden resonance box the sound gets amplified and continues for about 10 seconds before the energy dissipates and it stops sounding unless it is brought close to the ears. What I want is that the sound should be more loud and it should keep coming for much more time. So I want to understand how to achieve this ? What factor are involved in tuning fork – resonance box system that will make the sound louder and continue for a longer time?
Shall I buy a higher frequency Tuning fork with a bigger resonance box ? Are there any materials which can be coated on inner surfaces of the resonance box so that it does not dissipate quickly ?
Kindly give some suggestions
Best Answer
You cannot make the sound both louder and longer without changing the tuning forks to make them store more energy. This is an issue of the conservation of energy. There is only so much energy you can put into each tuning fork when you set it vibrating. The limitation is set when the tines are touching. Once this energy has been dissipated the sound stops.
The stored energy can be dissipated over a long time with a quiet sound - this happens when you do not connect it to a resonance box. Or it can be dissipated over a shorter time with a louder sound - as when using a larger resonance box. Unless you change the tuning fork to make it store more energy, increasing loudness decreases duration, and vice versa.
You could increase the energy stored in the tuning forks by increasing the distance between the tines. You could also make them larger, but this would probably also make the frequency lower.
Tuning forks with higher frequency dissipate energy more efficiently. According to the article On the acoustics of tuning forks this efficiency is proportional to the 6th power of the frequency. So increasing the frequency will increase loudness but also decrease the duration of the note.
Coating the resonance box might increase the duration of the note but it will also reduce the loudness.
In order to sustain the duration of the note you need some method of continuously replacing the energy which is being radiated - eg some method of vibrating the tuning fork while it is attached to the resonance box.
See also Why do tuning forks have two prongs? and Why don't tuning forks have three prongs?