Alternating Pressure Why do 100 instruments in a band playing the same note always sound louder?
I've been told that a property of waves is that when two waves of the same frequency meet, they can either interfere constructively or destructively, depending on how much they are in phase with each other. However, in band, it doesn't matter how far apart they are, or where you, the listener are, if 10 trumpets play together at the same note, then they will always sound louder. It seems logically that if each instrument was creating individual alternating high and low pressure zones, then entropy would never allow those to all lign up perfectly, and eventually all those vibrations, if you had enough instruments, would just interfere so much that you were left with just regular air. But this never happens, the instruments always sound louder.
Sound is one of those fickle things. If you could track in on a set frequency I'm sure you would fine that the maximum amplitude of the 10 trumpets is equal to the sum of the amplitudes of the individual trumpets. However, that isn't how your ear works, certain bands (mainly mid range) are much more audible then others. In addtion, your brain filters out quieter noise and focuses on louder noise (especially if its in one of the mid range bands). You can override this by listening for a specific thing consciously, but if you were just sitting listening to a band, you would tend to focus on the main melody (which is usually played by trumpet rather then a trombone or tuba which amplitude wise are much louder).
The waves do interfere constructively and destructively, but you have to think on the order of hte wave length and the speed its moving as well as the arrangement you are sitting. The differences in phase of the wave will cancel out because chances are the instruments aren't tuned perfectly, so the music will have 'beats' to it - it will seem to get louder and quieter, if you ever tuned an instrument this is what you listen for to determine how in tune you are. No matter how well they are tuned, they will gradually detune as the instrument warms and cools, as well as the changes in ombesure of the musician. This will eliminate the perfectly in phase or out of phase argument.
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