What causes musical instruments to have different sounds?

[iScience]

harmonics... got it.. but for instruments, whether they have a sound cavity (brass instrument or woodwind) or a string, to be resonating at say, 400 Hz, they should both have the same resonant frequencies no? if a string instrument resonates at 400 Hz, it should also resonate at factors of this frequency. Same with any other instruments; regardless of what they are made out of; if something, anything, resonates at 400 Hz, i t should also resonate at factors of this frequency the same way that the string instrument does. But this is not the case, why?

 

[rcgldr]

The string vibration is an input to the sound board on an instrument, and the instrument will produce harmonics even if the string only has a single frequency (ignoring the issue that some of those harmonics will be transferred back into the string at the sound board bridge).

 

[Delong]

I was wondering why harmonics occur at all which relates to your question. By harmonics I mean integer multiples of a sounds frequency.

 

[technician]

By their very nature stringed instruments have a string, under tension, fixed at each end. This means the ends of the string are nodes and the possible vibrations are when the length of the string is nλ/2
On the other hand a wind instrument may have nodes at each end, anti nodes at each end or a node at one end and an anti node at the other end.
These produce more possible vibrations ( harmonics)! Than a string.

 

[AlephZero]

harmonics... got it.. but for instruments, whether they have a sound cavity (brass instrument or woodwind) or a string, to be resonating at say, 400 Hz, they should both have the same resonant frequencies no?

No. For the simple cases you study in a first physics course on sound (strings and pipes with constant cross section) it is approximately true that the resonances are all multiples of the fundamental frequency. But for a pipe closed at one end the resonances are 1, 3, 5, 7 ... times the fundamental not 1, 2, 3, 4, ... which shows that your idea that "everything should have the same resonant frequencies" os wrong.

In real wind instruments the pipe is not a constant cross section, and the finger holes etc also affect the resonant frequencies.

The different sounds also depend on the relative amplitude (loudness) of the different harmonics. For example the sound of an acoustic guitar varies depending how close to the bridge you pluck the strings.

The acoustics of real musical instruments are MUCH more complicated than what you learn about in a first physics course, and there is still a lot of research being done into the details of how they "work".

 

[euni1968]

Also remember the indefinable element - the musician! I can play a note on a trumpet that sounds perfectly adequate. My cousin, however, is a professional musician, and he can play the same note on the same trumpet and it 'sounds' so much better. Nothing to do with the instrument in this case, but who is playing it and the technique being used.

 

[turbo]

@OP: Google on timbre. I played brass in HS, and though I could play the same note on a trumpet, French horn, and baritone, they didn't sound remotely like one another due to the design of the instrument.