Quake3World

found this - hope it makes sense:

http://cnx.rice.edu/content/m12589/latest/#s1

iirc a single string in theory will not create harmonics.
But when fixed to a guitar body, it's not only the string that resonates. The interaction of the string(s) and the body is what causes most of the harmonics.

mabe you woen be doing that billy any favours if you doent really understand the material.

no offence, jus sayin

"reflected waves" such as those you send down a dangling rope by "plucking" it are not fundamental frequencies or harmonics. They are forced harmonics. The dominant sound comes from the length and tension of the string, so you're not getting sound by a bunch of these little traveling waves going up and down the guitar string. Rather, it's the whole guitar string vibrating up and down over its whole length. If you've ever heard a guitarist do a "pinch harmonic", where the sound kinda squeals, then you're hearing them force one of these traveling waves into the string. It's not a natural sound, and it's used for effects (The first note in the outtro solo in floyd's "comfortably numb" song is a pinch harmonic).

What the natural sound comes from are the "natural" frequencies of the vibrating components, coupled to the natural harmonics of those frequencies, which are 1/2, 1/3, 1/4, 1/5, 1/n the fundamental wavelength of the vibrating component. In a guitar string this fundamental frequency is determined by the length and the tension. In a flute or trumpet it's determined by the length and width of the tube (how much space is there for the pressure to work positively against before it equals the outside pressure and begins to work negatively).

The "fixed" end of a wind instrument is the volume between where the vibration occurs and a reference pressure (pressure difference between the instrument chamber and the outside air pressure). If you blow accross a long tube you'll get a sound. This sound is made from the pressure differences between the chamber and the outside air that are built up at the mouth. These pressure differences are determined by the volume of the chamber (the length being the predominant determining factor for the volume). In effect, the volume of the chamber is the same as the length and tension of a guitar string. As such, the vibration of the guitar string is analagous to the changes in pressure as one blows accross the chamber.

If you were to have a short straw and blow accross it, the frequency would be determined by the length of the straw. Increasing the length would cause a larger volume in the straw and would make pressure changes accross the mouth of the straw to be slower, resulting in a lower pitch. If, however, you increase the length of the straw indefinitely, the pitch would not lower linearly. It's lowering would be limited by localized air pressure buildup. Blowing accross such a straw would build pressure in it, and that pressure would not ahve any place to go, so it would work against itself, since the thinness of the straw would provide enough resistance to prevent the length of the straw from coming into effect for the pressure. In this case, the thickness of the straw would be the determining factor for pitch.

Overall, the pitch is determined by the effective volume in the wind instrument, and this volume is mostly determined by length.

...shit i'm rambling. I hope i'm answering something in all this.

plained wrote:mabe you woen be doing that billy any favours if you doent really understand the material.

no offence, jus sayin

what do you think i'm trying to do right now?

Hr.O wrote:iirc a single string in theory will not create harmonics.
But when fixed to a guitar body, it's not only the string that resonates. The interaction of the string(s) and the body is what causes most of the harmonics.

from what i understand, the guitar soundbox amplifies the harmonics - a string by itself will produce sound, just not very loud.

well till tomorrow isnt alot of time for a full uderstanding to fluently answer from every angle opinion/

jus my opinion

[xeno]Julios wrote:

Hr.O wrote:iirc a single string in theory will not create harmonics.
But when fixed to a guitar body, it's not only the string that resonates. The interaction of the string(s) and the body is what causes most of the harmonics.

from what i understand, the guitar soundbox amplifies the harmonics - a string by itself will produce sound, just not very loud.

Yes. The string produces the frequency, with some tonal qualities. The soundbox is just an amplifier with more tonal qualities. You are not using the volume in the soundbox to create a fluctuating pressure difference between the inside of the soundbox and the outside air. Rather, you are using the soundbox to resonate plucked frequencies through the sound box's material, which amplifies it and modulates its quality just like you use your mouth to modulate a set frequency into harsher or smoother sounds taht can be used to create words or noises at that set pitch.

Canis wrote:"reflected waves" such as those you send down a dangling rope by "plucking" it are not fundamental frequencies or harmonics. They are forced harmonics. The dominant sound comes from the length and tension of the string, so you're not getting sound by a bunch of these little traveling waves going up and down the guitar string. Rather, it's the whole guitar string vibrating up and down over its whole length.

yep i understand this I think:

[xeno]Julios wrote:Since the string is fixed at the ends, the reflected wave and incident wave produces a standing wave pattern. The harmonics are just those standing wave patterns which are coherent with regular nodes/antinodes.

Canis wrote: If you've ever heard a guitarist do a "pinch harmonic", where the sound kinda squeals, then you're hearing them force one of these traveling waves into the string. It's not a natural sound, and it's used for effects (The first note in the outtro solo in floyd's "comfortably numb" song is a pinch harmonic).

nice - i'll be sure to check out that note

Canis wrote: In a flute or trumpet it's determined by the length and width of the tube (how much space is there for the pressure to work positively against before it equals the outside pressure and begins to work negatively).

Canis wrote:The "fixed" end of a wind instrument is the volume between where the vibration occurs and a reference pressure (pressure difference between the instrument chamber and the outside air pressure). If you blow accross a long tube you'll get a sound. This sound is made from the pressure differences between the chamber and the outside air that are built up at the mouth. These pressure differences are determined by the volume of the chamber (the length being the predominant determining factor for the volume). In effect, the volume of the chamber is the same as the length and tension of a guitar string. As such, the vibration of the guitar string is analagous to the changes in pressure as one blows accross the chamber.

I think i'm beginning to understand - similar to what is said here:

At an open end of the tube, there is nothing to stop the air rushing in and out, and so it does. What the air cannot do at the open end is build up any pressure; there is nothing for the air to build up against, and any drop in pressure will just bring air rushing in from outside the tube. So the air pressure at an open end must remain the same as the air pressure of the room. In other words, that end must have a pressure node (where the air pressure doesn't change) and (therefore) a displacement antinode.

http://cnx.rice.edu/content/m12589/latest/#s1

so in other words, the fact that the air pressure at the end of air chamber must remain fixed, it acts as almost a barrier against which the air waves can reflect?

plained wrote:well till tomorrow isnt alot of time for a full uderstanding to fluently answer from every angle opinion/

jus my opinion

I understand it fairly well already - that doesn't mean I'm arrogant enough to suppose i couldn't understand it better.

you'd be surprised at how many people who claim to understand a subject have never even thought of the more penetrating questions.

but you're right - this is last minute but it's the best i can do right now. My alternative is to give up and just give him a surface understanding, but i'd rather try and give him some real insight.

[xeno]Julios wrote:
from what i understand, the guitar soundbox amplifies the harmonics - a string by itself will produce sound, just not very loud.

Yeah...that's what I meant...the amplification thing.

Canis wrote:Rather, you are using the soundbox to resonate plucked frequencies through the sound box's material, which amplifies it and modulates its quality just like you use your mouth to modulate a set frequency into harsher or smoother sounds taht can be used to create words or noises at that set pitch.

Yeah...that's what I meant....the modulation thing.

welp - moff to work - hopefully lesson will go well.

thanks a lot to all, especially canis

Nightshade wrote:YEAH, LEARNING SUCKS! IGNORANCE AND MEDIOCRITY FUCKING ROCK!

you used to bash people for having a college degree

fucking hip0

Yes. The "barrier" is the frequency at which the pressure changes from positive to negative accross the mouth piece ONLY. This pressure change is determined by how the chamber (the tube or bottle) interacts with the surrounding air to equalize the pressure differences. If you had a small sound hole and a small amount of air going over it with a small chamber, you'd get a pressure build-up in the chamber that would fluctuate. However, if you increased the size of the chamber to a vast degree and then blew the same amount of air accross the same sized soundhole, there would be no pressure build-up, or rather, the pressure buildup would be so slow that it would not cause an audible frequency. There would also be other turbulence and interference in such a system.

arg now i'm even more confused - no worries he's only learning about waves on a string - tho it would be nice to understand wind also.

so just to clarify (won't get this answer till after work) - there actually are no reflected waves in a standing instrument?

so how exactly is the standing wave pattern produced?

you proly already answered this somehow, but i'm not getting it yet.

hate wrote:

Nightshade wrote:YEAH, LEARNING SUCKS! IGNORANCE AND MEDIOCRITY FUCKING ROCK!

you used to bash people for having a college degree

fucking hip0

Not once. You're mistaken.

[xeno]Julios wrote:arg now i'm even more confused - no worries he's only learning about waves on a string - tho it would be nice to understand wind also.

so just to clarify (won't get this answer till after work) - there actually are no reflected waves in a standing instrument?

so how exactly is the standing wave pattern produced?

you proly already answered this somehow, but i'm not getting it yet.

It doesnt matter how a standing wave is produced in an air instrument. All that matters is that the closed end of a pipe forces a node and the open end forces an antinode at that position. Thats all he has to know.

Initially a wind instrument's chamber (the tube) is at the same pressure as the outside air. In essence they are all just like a bottle. Blowing accross the top of the bottle (the mouth) causes a pressure difference between the moving air and the stationary air in the bottle. The air inside suddenly is more dense and has more pressure (just like an airplane wing producing pressure underneath via faster moving air above the wing). This causes the pressure inside to move air outwards, allowing the pressure inside to reduce. However, since you're blowing on the mouth, you re-pressurize the container and the cycle continues. This cycle's rate is determined by how fast the pressure builds up in the container, and is mostly effected by the volume of the container.

The sound is produced right at the mouth of a flute or pipe organ, and then resonates down the tube itself just like the soundbox of a guitar (except this "soundbox" is involved in determining the pitch of the sound). Hold a bottle by your fingertips and you'll get good resonance in the glass. The sound will be of the pitch determined by the volume of the bottle, but sound quality will be bright. Grip the bottle with both hands and cover it as much as you can, and then blow accross the top and you'll get a deader sounding tone, but it will be at the same pitch as before.

There arent any reflecting waves in a wind instrument, as there is no way to induce them. You'd have to have a small air-bursting puffer in the instrument to induce such a wave. An example of this sort of wave is an echo. If you're in a tunnel and you shout, you created a sound in the tunnel that then reflects. You didnt, however, use the tunnel's volumetric properties to create that sound's pitch. It's theoretically possible to create reflecting waves in an instrument, but isnt going to happen since the frequencies produced are all natural frequencies. Inducing pinch-harmonics in a guitar string is not a natural sound, but it is a lot easier to do on a string because our hands are capable of doing it. We just dont have the tools to do this on a wind instrument. One thing you can do is drive the second harmonic to be the main pitch by blowing really damn hard on a bottle or into a whistle. I'm not sure of the dynamics behind this process, but its possible. With a well-tuned instrument you can force enough air into it to theoretically reach any harmonic.

Yeah...that's what I meant...the theoretically thing.

[xeno]Julios wrote:
from what i understand, the guitar soundbox amplifies the harmonics - a string by itself will produce sound, just not very loud.

What i'm talking about is NOT the amplification of a guitar box. What i meant is the resonance of the whole body/neck construction. Even without strings it has a certain resonance frequency. Very low freq but it's there.
Hollowing out the body and making it into a soundbox just makes the whole story worse. That's why acoustic guitars have audible sweetspots.

[edit] One thing you also need to consider when buying a bass-guitar (ohh and i know, i was that dummy who didn't [/edit]

ToxicBug wrote:
It doesnt matter how a standing wave is produced in an air instrument. All that matters is that the closed end of a pipe forces a node and the open end forces an antinode at that position. Thats all he has to know.

he already knows how to solve all the problems - what would be the point of learning if all you knew was how to solve problems - deeper learning requires insight into these issues rather than just "learning what you need to know to pass"

Hr.O is right. All the harmonics you hear on guitar are entirely dependant on the wood of the guitar, it's construction, etc. That's why there even IS worry over what woods are used, etc, because they influence the overtones so much that some people don't even like guitars made from certain woods.

But one thing I'm not sure about, however, is if the octave overtone is made from the guitar or can the string itself create overtones of the octave?

Hr.O wrote:

[xeno]Julios wrote:
from what i understand, the guitar soundbox amplifies the harmonics - a string by itself will produce sound, just not very loud.

What i'm talking about is NOT the amplification of a guitar box. What i meant is the resonance of the whole body/neck construction. Even without strings it has a certain resonance frequency. Very low freq but it's there.
Hollowing out the body and making it into a soundbox just makes the whole story worse. That's why acoustic guitars have audible sweetspots.

[edit] One thing you also need to consider when buying a bass-guitar (ohh and i know, i was that dummy who didn't [/edit]

yes but my question was specifically about the resonance of the string, not the sound box.

Canis wrote:Initially a wind instrument's chamber (the tube) is at the same pressure as the outside air. In essence they are all just like a bottle. Blowing accross the top of the bottle (the mouth) causes a pressure difference between the moving air and the stationary air in the bottle. The air inside suddenly is more dense and has more pressure (just like an airplane wing producing pressure underneath via faster moving air above the wing). This causes the pressure inside to move air outwards, allowing the pressure inside to reduce. However, since you're blowing on the mouth, you re-pressurize the container and the cycle continues. This cycle's rate is determined by how fast the pressure builds up in the container, and is mostly effected by the volume of the container.

The sound is produced right at the mouth of a flute or pipe organ, and then resonates down the tube itself just like the soundbox of a guitar (except this "soundbox" is involved in determining the pitch of the sound). Hold a bottle by your fingertips and you'll get good resonance in the glass. The sound will be of the pitch determined by the volume of the bottle, but sound quality will be bright. Grip the bottle with both hands and cover it as much as you can, and then blow accross the top and you'll get a deader sounding tone, but it will be at the same pitch as before.

There arent any reflecting waves in a wind instrument, as there is no way to induce them. You'd have to have a small air-bursting puffer in the instrument to induce such a wave. An example of this sort of wave is an echo. If you're in a tunnel and you shout, you created a sound in the tunnel that then reflects. You didnt, however, use the tunnel's volumetric properties to create that sound's pitch. It's theoretically possible to create reflecting waves in an instrument, but isnt going to happen since the frequencies produced are all natural frequencies. Inducing pinch-harmonics in a guitar string is not a natural sound, but it is a lot easier to do on a string because our hands are capable of doing it. We just dont have the tools to do this on a wind instrument. One thing you can do is drive the second harmonic to be the main pitch by blowing really damn hard on a bottle or into a whistle. I'm not sure of the dynamics behind this process, but its possible. With a well-tuned instrument you can force enough air into it to theoretically reach any harmonic.

thx canis - makes a bit more sense now.

so a standing wave in a wind instrument is produced by a completely different set of wave dynamics than that of a string instrument.

I guess they're both the same in that they're coherent stable wave patterns (but they come about through different ways).