Acoustics and dead zones

[Dukasaur]

Could one of the gifted scientists here take a stab at explaining this to me, because I've never understood it.

Why are there dead zones for sound in an auditorium? Yes, I know about constructive and destructive interference in standing waves, but every tone has a different wavelength. So, it would seem to me that while there should be dead zones for certain specific notes, each one would be specific to one note, and it seems to me unlikely that the same spot would be a dead zone even for all the notes in a single chord, much less for all the notes produced by an entire orchestra.

What am I missing?

[TA1LGUNN3R]

The differences between, say, the tones in a piece of music (so a couple octaves) are not that great when compared against all standing wavelengths. So while true that each tone has its own wavelength, there is enough overlap between such a short section of frequencies.

That's why there aren't single, precise spots where there is complete destructive interference, but rather a gradation area where the constructive interference subtract from each other.

Remember that the range of human hearing is pretty limited.

Edit: and I think you may be partly correct about areas being specific to certain tones, it's just minimalized for reasons I stated.

-TG

[Metsfanmax]

In most cases there's a sufficiently large range of wavelengths being heard, and a sufficiently large number of directions that the wave is approaching from (due to multiple reflections off walls). So you can think of dead spots as places where the sound hasn't been sufficiently smoothed out, due to poor focusing.

[notyou2]

I think you're missing your piano lessons.