Tech/maintenance Saxophone Pad Acoustics Study

[Dibbs]

Yes, 2 Pa or 2 Newtons per square metre is a tiny pressure. You can refer to jbtsax's post to convert that to other units.

Isn't there a another pressure component too, unrelated to sound pressure but just because there is air being blown into the tube?

 

[jbtsax]

Isn't there a another pressure component too, unrelated to sound pressure but just because there is air being blown into the tube?

This is an excellent question. It is a common misconception that the air blown into a saxophone actually travels through the instrument. If one plays the mouthpiece and neck apart from the saxophone and feels the open end, it becomes apparent how little air is actually moving. In a famous test a tuba player took a big drag on a cigar and then played this tuba. It took several minutes for the first traces of smoke to waft out the bell.

Band teachers commonly tell students to "blow through" their instruments when they play which of course doesn't happen. It is merely a concept that helps to achieve the proper air pressure or breath support.

 

[Dibbs]

This is an excellent question. It is a common misconception that the air blown into a saxophone actually travels through the instrument. If one plays the mouthpiece and neck apart from the saxophone and feels the open end, it becomes apparent how little air is actually moving. In a famous test a tuba player took a big drag on a cigar and then played this tuba. It took several minutes for the first traces of smoke to waft out the bell.
...

So it's small enough to be negligible. Fair enough. It's pretty obvious that a tuba can hold a few lungfuls of air.

 

[kevgermany]

There's a test mentioned in Teal about trying to blow paper out of the end of the sax... Too little air.

 

[aldevis]

Still, on clarinet I could blow open some keys with weak springs. I seem to miss something.

 

[Jeanette]

Still, on clarinet I could blow open some keys with weak springs. I seem to miss something.

You are just full of hot air

(You can delete this if you want) 🙂

Jx

 

[jbtsax]

Still, on clarinet I could blow open some keys with weak springs. I seem to miss something.

Good point. I don't yet know the physics of this, but I do know that the larger the surface area the air "pushes" against, the more force is applied. Try holding up a 4'x8' piece of plywood in a moderate wind to really understand this principle. It shouldn't be that difficult to set up an experiment to see what air pressure it takes to force open a clarinet low Ab or Gb key. It is probably less than the pressure needed to open a C#/G# or a side key due to their smaller pad surface.

 

[aldevis]

It shouldn't be that difficult to set up an experiment to see what air pressure it takes to force open a clarinet low Ab or Gb key. It is probably less than the pressure needed to open a C#/G# or a side key due to their smaller pad surface.

 

[kevgermany]

It shouldn't be that difficult to set up an experiment to see what air pressure it takes to force open a clarinet low Ab or Gb key. It is probably less than the pressure needed to open a C#/G# or a side key due to their smaller pad surface.

It's going to depend on spring tension and the Id of the tonehole. Remember that area goes up with the square of the dimensions, in the case of a tonehole, the square of the radius. So if the clarinet has a 6mm hole and the sax a 16mm one, we get 9 compared to 64 units of force on the sax pad. My money would be on the clarinet taking more pressure to open it against the spring. But this is based on pad lifting and completely fitting/sealing.

 

[aldevis]

Wait.
If a tonehole has 20 mm diameter, its area is 3.14...

in case of 130 dB we have about 2 grams pressing against that pad.
Still not much from the spring point of view.
(where is @BigMartin when you need him?)

 

[kevgermany]

Wait.
If a tonehole has 20 mm diameter, its area is 3.14...

Nope. The circumference will be 20*3.14, the area is 10*10*3.14

 

[aldevis]

Nope. The circumference will be 20*3.14, the area is 10*10*3.14

=314 square millimeters, = 3.14 square centimeters (I was after kg/sqcm)

Wait.
If a tonehole has 20 mm diameter, its area is 3.14 sqcm

 

[kevgermany]

Tut tut. Shouldn't mix units like that without specifying.

 

[jbtsax]

Let's see: 130 dB = .62 mb = .632 grams per square centimeter.

A 20mm pad's surface area is 3.1416 x 10 squared = 314.16 square mm = 3.14 square centimerer

3.14 x .632 = 1.99 grams

Give Aldevis a cigar!

 

[Jeanette]

Give Aldevis a cigar!

Far too bad for his health, how about a couple of reeds 🙂

Jx

 

[aldevis]

Far too bad for his health, how about a couple of reeds 🙂

Jx

Clearly you never tried to smoke them.

 

[Jeanette]

Clearly you never tried to smoke them.

I was waiting for something like that but expected @Targa Actually never smoked, just a couple of drags to try it out but couldn't see the point.

Jx

 

[Targa]

I was waiting for something like that but expected @Targa Actually never smoked, just a couple of drags to try it out but couldn't see the point.

Jx

Can't be here all the time, six hours of BTCC coverage to watch.

 

[aldevis]

Give Aldevis a cigar!

I'll leave it to you if you replace the high F pad with a weight detecting device. We would know its area and it would be easy to see the actual pressure.
In particular I am deadly curious to see if it changes when a node ends up there.

 

[saxplorer]

Just came across this ... Clarinet - Wikipedia, the free encyclopedia

There's an interesting explanation of wave motion in the clarinet. I did also note this point particularly.

"The ‘puff of air’ or compression wave (around 3% greater pressure than the surrounding air) travels down the cylindrical tube and escapes at the point where the tube opens out. "

... which seems to imply pressure variation of +/- 3% atm, (the article later describes a rarefaction wave, which presumably is of the order of 3% lesser pressure than the surrounding air)