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Calculation of frequency-triggering

post #1 of 10
Thread Starter 
I attend a music technology school, and I need to deliver in some papers tomorrow, answering several questions. I have problems understanding this one, however, and was hoping for some opinions:

"We usually describe sound in 3 dimensions. Time (s), Level (dB) and Frequency (Hz). How many milliseconds does it take to start the vibrations in a pianostring, in a trumpet-tone and in an organ-tone?"

1. I don't really understand the question here, cuz I don't know if the startpoint of the calculation should be upon the impact of the piano-key, or when the piano-hammer hits the string within the piano. The question doesn't state that the result should be audible, so it's just a matter of vibration within the string. And one vibration equals one periodic swing, which is different from each pianostring - due to different frequencies being generated.

2. The trumpet starts (I believe) when the first breath of air comes into the chamber. Then it's a matter of finding the frequency-response of a trumpet, and calculating the speed of sound together with the periodic swing, and the length of the chamber. However, I don't know the amount of reflections within the chamber before the sound reaches the end, so it seems impossible. Because a trumpet functions in a way of multiple reflections back and forth with resistors breaking up the waves to alter the timbre and pitch. I'd have to be a engineer/mathmatician/genius to calculate the time from initial breath to actual tone at the end.

3. The organ-tone is also very absurd to me, as it's produced by electric signals. So I have to calculate the time from the triggering of the electricity, until the actual reproduction of sound from the internal speakers. That again will vary from organ to organ, depending on impedance, wire-lengt, speaker-size and speaker-material.

Hmmm...though one, this. I have no idea how to approuch it what so ever. Help
post #2 of 10
Whoever wrote these questions is an idiot. I wish I could help you but that isn't a question, it's a riddle.
post #3 of 10
Quote:
Originally Posted by b0dhi View Post
Whoever wrote these questions is an idiot. I wish I could help you but that isn't a question, it's a riddle.
X2.
It starts as soon as it is triggered, no time parameter involved.
If they mean how long it takes to form a standing wave: that depends on the length of the string or the size of the instrument and the precise form of the trigger impact.
I think this question might refer to some specific subject in a textbook that you are supposed to know, in which you may find the rest of the context you need to answer it.
post #4 of 10
Does it all begin at with the concept of making the move to make the sound using the device? Several seconds to minutes depending on how fast and how long the musician wants to think about the music.

Or does it start with the writing of the music? Years potentially.

Given the parameters of the question one could be as absurd in answering this question as the question appears.

Without test data showing the parameters requested it is hard to give answers as they appear to have actually been ask.
post #5 of 10
Thread Starter 
Oh, I'm laughing in joy to these answers! I actually have no idea how to solve the question, but I know one thing:

The piano-question only demands vibration. How long it takes to trigger vibrations in a piano-string. So it doens't have to be audible. And vibration in its definition does not equal one whole periodic swing (hz), imo. So it starts right after the hammer hits the string. No delay here what-so-ever.

The trumpet is just absurd to me. I have no idea how to solve that one. The same goes for the organ. It's a matter of electrical components in terms of impedance, lenght and quality.

Hey, thanx for sharing your opinions. Kees: I will dig deeper into the books to look for an answer, good idea But I've already read everything, and can't remember this topic.
post #6 of 10
My guess is: The answers are meant to be looked up rather than calculated, the question isn't about what you think it's about, and the organ tone is referring to a pipe organ rather than electric or digital. Could be wrong though.
post #7 of 10
Quote:
Originally Posted by Rempert View Post
The answers are meant to be looked up rather than calculated
The one main thing I dislike about education in general. Why can't someone get full marks for coming up with an answer creatively instead of regurgitating previously read material? If I was a teacher I'd reward unconventional approaches to stupid questions like this one.

Which may go to explain why I'm not in the teaching industry.
post #8 of 10
Thread Starter 
Hehe. The papers are delivered, and my answer described different issues that make this question impossible and undefined. So, I basically tried to unmanouver the correct answer (if there is any) by describing why it was technically unable to answer. Hope the teacher doesn't get offended. Who knows maybe he was proud of the question and had his way of thinking how to solve it. Nevertheless, the question was waaay too sloppy and broad to portay a correct way to solve it.

I hope it's a "got-cha!" question ;P The papers also asked for this question:

"How fast does sound travel at 0 degrees celcius?"

Yet again the question is a little undefined. It doesn't state in which material the sound travel, so I mentioned that. If he meant air, it depends on the molecular tension/ingredients of the air as well.
post #9 of 10
Quote:
Originally Posted by alexpea View Post
...
"How fast does sound travel at 0 degrees celcius?"

Yet again the question is a little undefined. It doesn't state in which material the sound travel, so I mentioned that. If he meant air, it depends on the molecular tension/ingredients of the air as well.
I realize it's a bit late for your purposes, but maybe you can just give an answer as a proportion to a known velocity at a given temperature. I'm a bit rusty on the thermodynamics/statical mechanics, but IRC kinetic energy is proportional to temperature and proportional to the square of the velocity of particles. So the velocity at 0 C should be proportional to the square root of the ratio of temperatures, e.g. 0 C and 25 C if you know the velocity at 23 C.
post #10 of 10
Hey, alexpea how did the class go?
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