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For a standing wave, there are two kind of nodes: pressure nodes, where pressure remains constant and air molecules move, and displacement nodes, where air remains constant and the pressure varies.

If that is hard to picture, then think of a guitar string. It is anchored at the nut and the bridge. When you pluck it those points do not move, but the pressure varies. In the middle of the string the displacement is at a maximum and the pressure variation at a minimum. The former are displacement nodes and the latter is a pressure node. They are generally, but not always, equally spaced.

The string has more than one vibrational mode: it also vibrates in halves and thirds and quarters, etc. these are the harmonic components. So when the string vibrates in halves (at the same time as unitarily), the octave is created--the second partial. For that partial, the center point is a displacement node, and halfway between that at the ends--at the quarter points, pressure nodes form.

For the air column, the actual length of the instrument is half a wavelength--like a string folded in half with both anchor points at the mpc. This is because for each reed cycle the wave travels to the end of the tube where some is radiated, but where also a reflection is formed that changes phase and travels all the way back up the tube to start the next cycle.

But the air column is also vibrating in halves, thirds, fourths, fifths, etc--which adds harmonic content to what would otherwise be a pure sine wave sounding only the fundamental. With the harmonics the sound approaches a sawtooth wave.

Not that due to mode locking, the air column only vibrates at integer fractions of the total length of the air column, so the partials are (almost) always harmonic overtones.

It is also important to realize that the air doesn't bounce against the walls; at displacement nodes it pushed equidistantly around the body from the inside--like blowing up a balloon at those points.

In between nodes the areas mix moving air and changing pressure; the proportion depending on how far the point is from which kind of node.
 

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Is this node talk going to come back 'round the circle to addressing how material matters?
 

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... <server hiccup> ...
 

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Very clear, thank you

But the air column is also vibrating in halves, thirds, fourths, fifths, etc--which adds harmonic content to what would otherwise be a pure sine wave sounding only the fundamental. With the harmonics the sound approaches a sawtooth wave.
Since the component of the sound we usually talk about is the harmonic structure, does it involve that nodes relative to higher partials are physically closer to each other?

I am not thinking much of "bouncing" effect, but how (if) the vibration induced in the body by the main harmonics can interfere with the higher partials.
When I think of the shape of a saxophone or an oboe note I see more of a sawtooth (more high odd partials) than in a clarinet or a flute.
 

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Since my training is in General Physics, with the emphasis in Mechanics, rather than in aeronautical or acoustics, I may be wrong, but the illustrations in the referenced page in Oric Muso's post actually seem the opposite (although they would serve adequately enough for a basic understanding). The open reed, prior to the player's providing air velocity allows air to flow. The moving air lowers the air pressure in the mouthpiece/horn system, closing the reed, stopping the flow, thus increasing the pressure inside the horn (relative to the flowing air pressure). This pulse reopens the reed in a cyclic fashion, providing the pressure impulses in the air we perceive as sound. I'd venture a guess that the pressure pulses even playing at a loud level are barely above ambient. Curious if anyone has ever tried to install a strain pressure transducer inside a horn to see what pressures are achieved (it would need a reference transducer outside the horn). Also curious to see if anyone had considered to apply self adhesive strain gauges to a horns body to see how much actual stress a horn actually undergoes from pressure pulses from playing, although this would require a very controlled environment and involved fixtures to avoid the players hands from straining the horn.
 

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I'd go for what Benade says, whatever that is, or whatever is in the University of NSW site.
Both very reliable authorities.
 

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Discussion Starter · #108 · (Edited)
A player can't really induce much pressure change with their airstream.

If someone blows into a plastic Recorder, then there are no noticeable vibrations being induced into the body that I can remember from when I last played one, even though the player is probably using a similar airstream speed as a Sax.

The Recorder has standing waves and different pressures etc etc.

Of course, there is no reed on a Recorder.

Standing waves induced by human airstreams inside containers, don't seem to be responsible for vibrations in a very noticeable way.

The different pressure levels inside a Sax when it's played, are not that far away from the outside pressure as the Sax always has open holes coupled to the atmosphere and the Sax wants to go back to the outside pressure at any time, which is it's natural state when not being played.

Maybe Backus was right, and it's the beating of the reed that is mainly inducing vibrations into the mouthpiece/neck/body that the player can feel.

These vibrations would be connected to the reeds beating frequency and they still wouldn't interfere with the standing wave much at all from the research I've read and just because a player can feel vibrations it doesn't necessarily mean that they interfere with the standing wave in a noticeable way, because as I've already posted, humans can pick up vibrations in the micron/micrometre range and can easily feel that the vibrations are larger then they really are.

A cane reed beating against a solid material would induce what vibrations?

Cane isn't much of a solid material and is easily bendable in the region where the reed actually moves when playing, ie the tip of the reed etc.

So there is a bendable pliable material hitting a solid material and the solid material is going to take the reed hitting it and not respond to it much at all IMO.

IMO the reed movement wouldn't be able to induce very meaningful vibrations into a solid material, but the player might still feel them especially as they have their teeth and lips connected to the reed movement region.

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"A recorder is basically an open pipe which, when played in the normal way, develops a standing wave between the open end where you blow and the first open hole below the mouthpiece."

http://prezi.com/msbnisuf-_x6/physics-of-a-recorder/

"The recorder is made up of the fipple and the body, tapered at the end. Resonance is created in air columns by blowing air into them
In recorders, as an air column, resonace is created by blowing air into the fipple, made of the mouth, the passage and the windcutter BY REEM D. When air is blown through the mouthpiece, some air will flow into the the mouth of the fipple, leading an increase in internal pressure.
While some air stream flows across top of the windcutter, reducing the pressure at the mouth of the instrument and leading a decrease in internal pressure, this is called resonance - condition the frequency of a wave equals the resonant frequency of the wave's medium. The pressure of the air column lowers so more of the air stream enters the mouth and less air stream flows across the windcutter.
During a pulse of high pressure at the mouth, more of the air stream directs itself across the mouth and decreases the internal pressure, & sends low pressure pulse nack down the tube
Pulses of low pressure arriving at the mouth of the fipple draws air in the mouth, increasing its internal pressure and sends high pressured pulse back down the tube the air column of a recorder has several vibrating modes, affected by the holes to play a certain note; called registers and corresponds to each harmonic present to the instrument
Resonance In Air Columns By blowing air though the fipple, air would either come out through the other end or some would end up coming through the holes not pressed down
the air molecules inside the recorder can be compared to a string of pendulums hitting each other because each pendulum would receive a pulse from the next one and pass it on till it reaches the end and goes back to the source
the air column in a recorder is created by the continuous cycle of the air stream within the fipple, vibrating lengthwise
Resonance in Air Columns - Recorders
Continued for the low A note of the recorder, this graph shows the frequency and amplitude of the different harmonics, represented by peaks. Low A note of the recorder air columns can be shortened, along with the vibrating length if the holes were left open, giving off higher notes
however by closing the holes, the length of the air columns will extend
therefore, being an open-ended instrument, it will create half lambda per harmonics Conclusion of the Physics of the Recorder Recorders will achieve acoustic resonance, which forms a standing wave inside the air column and the entire instrument will vibrate and give off noise or create music
since recorders are open-end instruments, they create half lambda per harmonic or overtone"
 

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I'd go for what Benade says, whatever that is, ro whatever is in the University of NSW site.
Both very reliable authorities.
You seem to be suggesting Dr Murray Campbell and Dr Clive Greated arent' reliable sources? I don't think what they say differs from the two you mention. It's just the way it is explained that differs.
 

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Of course, there is no reed on a Recorder....
The airstream itself, oscillating, effectively is the reed. A reed made from air.
 

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Scargo said "I may be wrong, but the illustrations in the referenced page in Oric Muso's post actually seem the opposite (although they would serve adequately enough for a basic understanding)."

My thoughts, exactly. The illustration is out of phase and is useful only as an over simplification of what's happening. Unfortunately, as with many examples, the simplification comes back to haunt us. Blowing into the mouthpiece causes lower pressure inside the mouthpiece than outside. That has to be the case in order for the reed to close. Once closed, the pressure bounces back. Even though there is still pressure above ambient outside the reed (as the player keeps blowing), the pressure bounce back against the closed reed is high enough to open the reed against that pressure. Low when open, high when closed; exactly opposite of the illustration. It reminds me if the illustrations that use "sound arrows" to show how sound bounces around and out the end of the instrument. Another illustration that can do more harm than good by over simplifying a complex issue.

Ah, materials. Yes, material matters. A mouthpiece of bronze "bell metal" sounds better than a mouthpiece made from bronze "Roman coin" metal even if they are the identical alloy. Why? Because bell metal has a certain "ring" to it. "Ring" as in cache. Bell metal sells better. Bell metal sounds better (in advertising copy) and therefore has a higher profit margin for the seller and a higher value to the proud owner. It works with all materials. A sterling silver neck is good, but gold-plated silver sounds better. Just think how great a platinum neck would sound to those who can hear it calling to them. For the best sounding metals, just check the spot prices on the commodities market.

Call me a sceptic (I won't believe you), but the majority of the material questions seem to be driven primarily by issues of what "sounds" appealing to the consumer as a consumer. A vintage, secret formula, gold-plated, nodal weighted, made in Paris, expensive limited edition widget is going to sound better than the regular widget (played by regular players). Given that, it doesn't matter which one vibrates a micron more or less.

Mark
 

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but the majority of the material questions seem to be driven primarily by issues of what "sounds" appealing to the consumer as a consumer. A vintage, secret formula, gold-plated, nodal weighted, made in Paris, expensive limited edition widget is going to sound better than the regular widget (played by regular players). Given that, it doesn't matter which one vibrates a micron more or less.
Interesting. Marketing BS keeps getting brought up, but what I have seen is a pretty thoughtful attempt by some folks to discern whether, in fact, there might be some significant differences between hard rubber and metal when it comes to mouthpiece performance.
 

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Scargo said "I may be wrong, but the illustrations in the referenced page in Oric Muso's post actually seem the opposite (although they would serve adequately enough for a basic understanding)."

My thoughts, exactly. The illustration is out of phase and is useful only as an over simplification of what's happening. Unfortunately, as with many examples, the simplification comes back to haunt us. Blowing into the mouthpiece causes lower pressure inside the mouthpiece than outside. That has to be the case in order for the reed to close. Once closed, the pressure bounces back. Even though there is still pressure above ambient outside the reed (as the player keeps blowing), the pressure bounce back against the closed reed is high enough to open the reed against that pressure. Low when open, high when closed; exactly opposite of the illustration. It reminds me if the illustrations that use "sound arrows" to show how sound bounces around and out the end of the instrument. Another illustration that can do more harm than good by over simplifying a complex issue.
If you look at how the air column oscillates you'll see the air flow isn't like water through a hose. Blowing air in causes high pressure in the mouthpiece as the air isn't going straight through. When the reed is closed there is more pressure on it than in the mouthpeice. So the diagram might seem wrong, but it isn't.
 

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And, a player doesn't need to keep buying them :)
And on flute, the player can adjust them in thickness and strength while playing! A most amazing reed. :)
 

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If you look at how the air column oscillates you'll see the air flow isn't like water through a hose. Blowing air in causes high pressure in the mouthpiece as the air isn't going straight through. When the reed is closed there is more pressure on it than in the mouthpeice. So the diagram might seem wrong, but it isn't.
That's where we disagree. If there is high pressure inside the mouthpiece, what causes the reed to close? Higher pressure on the outside? That still means that the pressure inside the mouthpiece is relatively lower, causing the reed to close. Once the reed is closed, the pressure builds up on the outside, but not enough so that the reflected pressure wave can't open it up again. That actually only requires equal pressure to open it, as the reed has a natural flex that creates a normally open position under equal pressure. It's not like water in a hose (as the diagram assumes) because the mouthpiece causes the Bernoulli effect. The pressure differences would cycle through higher, lower, and neutral out of phase with the exact opening and closing of the reed tip. That's why I think that the diagram is as much of a hindrance as a help.

Why does high pressure in the mouthpiece cause the reed to close, as shown in the diagram?

Back to materials. I'm thinking about producing my own brand of mouthpieces and horns. I'm trying to decide what materials to use. What materials should I use in order to profitably sell the most mouthpieces and horns? Do you think that material will matter as much as my chosen brand name FlemTone?" Again, I'm not sure material would matter in this instance. Something tells me that a McGurk effect would influence the purchaser as to the sound of my products. I'm not sure I could overcome that prejudice with my sales jingle: "With a name like FlemTone, it's got to sound better than other similar products!"

Material matters, but generally to an immaterial degree.

Mark
 

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Discussion Starter · #118 ·
Some people seem to think that because Acoustic Science (and others echoing Acoustic Science at forums) say that material has a minimal non noticeable effect at best, then it doesn't matter what gear a Sax player then plays.

This isn't right.

There are still loads of variables in a Sax/Mouthpiece combo even if material is not one of them.

There are impedance variables (resistance to players) and inside dimension differences influencing the standing wave etc etc.

All of these variables are things a player can prefer or not prefer within logical Sax/Mouthpiece design boundaries.

Some players might prefer less resistance and use thinner reeds and just like a certain Keilwerth designed model.

Just because materials don't seem to matter, it doesn't follow that the other variables don't seem to matter as well.

Just how much a player has to have an exact fit for their preferences is up to them.

If someone can get things going on a Sax or instrument they might not prefer then they can worry about less about having to have exact gear requirements and having to have exact circumstances and surroundings IMO.

The variables from just playing in different rooms and the players mood, reeds etc, mean that a player has to adapt on the fly and not fall to pieces because everything isn't to their exact preference.

Are they playing the instrument or is the instrument playing them?

I think some players that seem to be highly concerned about materials would be better off focusing on other things involved in playing, rather than possibly thinking that the material is going to help them.

I have a 1956 Selmer Mark VI and I prefer other Saxophones to it including a Chinese one in terms of feel and playing, but I can also play the Selmer Mark VI even if I might not prefer it always.

I don't like playing with 4 reeds, but other players like to.

I do like high baffles, especially for Rock, others don't.

These are all preferences, having nothing or little to do with any possible material effects on the standing wave.
 

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That's where we disagree. If there is high pressure inside the mouthpiece, what causes the reed to close?
The Bernoulli effect. More air goes in the open mouthpiece which means there's then less pressure in the mouthpiece than outside and the reed gets sucked back.

It's not like water in a hose (as the diagram assumes) because the mouthpiece causes the Bernoulli effect. The pressure differences would cycle through higher, lower, and neutral out of phase with the exact opening and closing of the reed tip. That's why I think that the diagram is as much of a hindrance as a help.
Read the text. It explains all this. If you read the Backus it says basically the same thing.

Why does high pressure in the mouthpiece cause the reed to close, as shown in the diagram?
Consider the system without the air stream. If the pressure is higher in the mouthpiece it'll force the reed open. If it is lower it'll allow the reed to close. It isn't the high pressure closing the reed. The diagram shows high pressure in the mouthpiece with the reed open. With a more open aperture, more air goes in. The air flow causes a Bernoulli effect which closes the reed.
 

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The Bernoulli effect. More air goes in the open mouthpiece which means there's then less pressure in the mouthpiece than outside and the reed gets sucked back.
Correct.
Dangle two spoons below a tap with their backs facing each other & a a gap of approx half an inch between them. Now run the tap through the gap between the spoon backs.....they will come together, not separate.
 
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