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 Post subject: Re: What is a mode
PostPosted: Wed Aug 28, 2019 5:21 am 
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Modes of vibration. A flute is a tube open at both ends, which means that you can't have pressure changes at either end as they are open to atmosphere. So it can in theory resonate at any wavelength which crosses the horizontal axis at both ends. This image from UNSW Physics Flute Acoustics may confuse you further.....

Image

Fortunately, you are not dependent upon theory and diagrams. Take up thy flute, finger xxx xxx and blow softly. You'll get low D, mode 1

Now tighten the embouchure and blow again. You'll get middle D, mode 2.

Tighten some more and blow again. Mode 3, 2nd octave A

Tighten more and try again. Mode 4, 3rd octave D.

Mode 5, if you are that good, will be 3rd octave F#

And so it goes on, in theory forever, but practically limited by the cut-off frequency, a factor of bore and fingerhole diameters, above which the flute becomes very uncooperative. You might have achieved 5 modes on xxx xxx, but try other fingerings. Heh heh heh.....


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 Post subject: Re: What is a mode
PostPosted: Wed Aug 28, 2019 8:19 am 
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benhall.1 wrote:
PB+J wrote:
I couldn't get your E being a third of the (sting length?) and G being a fifth of the length. Were you just picking notes haphazardly (being a pedant, I won't use the term "at random" in this context :wink: )? If not, you've lost me ... :-?


Surely he meant, Tune your string to the pitch 'C', no?


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 Post subject: Re: What is a mode
PostPosted: Wed Aug 28, 2019 8:42 am 
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JackJ wrote:
benhall.1 wrote:
PB+J wrote:
I couldn't get your E being a third of the (sting length?) and G being a fifth of the length. Were you just picking notes haphazardly (being a pedant, I won't use the term "at random" in this context :wink: )? If not, you've lost me ... :-?


Surely he meant, Tune your string to the pitch 'C', no?

How does that help? G is higher than E, so, even if E would sound at a third of the string length on a C string (which it wouldn't), the G wouldn't make any sense at all ... :-?

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 Post subject: Re: What is a mode
PostPosted: Wed Aug 28, 2019 11:15 am 
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benhall.1 wrote:
How does that help? G is higher than E, so, even if E would sound at a third of the string length on a C string (which it wouldn't), the G wouldn't make any sense at all ... :-?


Yes, you're right. Trying to interpret PB+J's statement, I got things backwards. The interval of a fifth ( C --> G) is achieved at 1/3 the length of the string, and the interval of a major third (C --> E) is achieved at 1/5 the length of the string. I think.

It's been eons since I've thought about this theory stuff, but I'm enjoying trying to follow along.


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 Post subject: Re: What is a mode
PostPosted: Wed Aug 28, 2019 2:08 pm 
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JackJ wrote:
benhall.1 wrote:
How does that help? G is higher than E, so, even if E would sound at a third of the string length on a C string (which it wouldn't), the G wouldn't make any sense at all ... :-?


Yes, you're right. Trying to interpret PB+J's statement, I got things backwards. The interval of a fifth ( C --> G) is achieved at 1/3 the length of the string, and the interval of a major third (C --> E) is achieved at 1/5 the length of the string. I think.

It's been eons since I've thought about this theory stuff, but I'm enjoying trying to follow along.

Actually, yes, I get that, now. That must have been what he meant. With a fourth (F) at a quarter the length of the string.

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 Post subject: Re: What is a mode
PostPosted: Wed Aug 28, 2019 2:21 pm 
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Terry's post, complete with circles and arrows and diagrams clearly explains 'modes of vibration' in both acoustic air columns and strings. Modes of vibration get a lot more strange and interesting when we examine the patterns formed on surfaces whilst vibrating. This is a bit further afield from flutes-but can include guitar and fiddle backs and fronts on our way to applying them to static structures like bridges and dynamic structures like jet plane aerofoiles. . .

Bob

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