[Trombone-l] Leadpipe

[Jeff Albert]

On May 26, 2006, at 1:40 AM, Richardson, Timothy Mr. DAC USAG  
Franconia DPW wrote:

> Yeah, Jeff, sorry about that, but think back a while.  I used to do  
> this
> every six months, then once a year, and now it's been at least  
> two.  You've
> had a decent break, should be well rested.  <g>

True, and I often learned something before I started cursing your  
name and throwing my Guiness across the room.  I must say I was  
suprised you didn't get in on the King lacquer one a few weeks ago.

>
> .  By the way, I have given up Guiness and switched to
> Jever.  Good stuff, you should try it.

This is the kind of knowledge that needs to be shared in our community.

>
> The function of the airflow is mainly to move the mass of the lips  
> open and
> shut.

Agreed.

> It does not need to enter the horn.

Does not NEED to, but does enter the horn anyway.

> The proof of this is a recent
> demonstration at one of the big music conferences.  The bottom of the
> mouthpiece was sealed with a thin flexible membrane that would pass
> vibration but not air.  The side of the mouthpiece was drilled to  
> allow an
> escape path for the air.  The air did not enter the horn but it did  
> pass the
> lips.  The horn played fine.

I have no trouble believing that the horn played, I'll take your word  
for it that it played fine.  If they had manipulated the hole in the  
side of the mouthpiece to affect the resistance to the air escape,  
they would have manipulated the feel of the blow, much the way  
changing a leadpipe will.

> Now, I would love to be able to claim they
> then removed the leadpipe and the sound changed.  Unfortunately  
> that was not
> part of the experiment as far as I know.  I *think* that is what  
> would have
> happened.  But indeed, I cannot prove it.  But it is logical to me  
> that the
> leadpipe does more than restrict air, because it affects intonation  
> in a way
> that simple resistance does not.  At least, to my ears.

That is all fine with me.  I don't think I ever said that the  
leadpipe doesn't affect the sound.  I said that it also affect airflow.

>
> My estimate of back pressure is based on an inaccurate garage  
> experiment of
> my own.  We have to be careful to remember that resistance to flow  
> of air
> and resistance to sound wave travel are different things, I measured
> resistance to flow.
>
> I used a plumbing tee fitting and lots of duct tape between my  
> mouthpiece
> and my receiver.  I attached a home made manometer (aquarium tubing  
> with
> some water and a ruler) to the tee.  The differential pressure  
> between that
> point and atmospheric was approximately 1 inch of water.   
> (Engineers often
> use head differences dimensioned in length to measure pressure.  An  
> inch of
> water is about .03612629 psi)  I then put the tubing in my mouth  
> and played.
> It is stinking hard to get a good tone with hoses coming out the  
> corner of
> your mouth - but then not as bad as when Pepsi comes out your  
> nose.  At any
> rate, pressure in my mouth averaged from 12 to 15 inches of water  
> above
> pressure at the receiver, which was itself 1 inch of water above  
> pressure in
> the atmosphere (end of bell).

> This indicates that the majority of
> resistance is at the lips/mouthpiece end of the system and not in the
> trombone at all.

This is absolutely true.  The majority of the resistance is at the lips.

So you found about 15 inches in your mouth, 1 inch between the  
mouthpiece and leadpipe, and 0 inches at the bell. (If I read that  
right) That's how you got 1/15th of the resistance.  I guess if you  
include the lips, that could be true.  I wasn't including the  
resistance provided by the lips.  I was thinking of resistance  
provided by the equipment.  It would be interesting to follow that  
experiment up at various points in the instrument.

Jeff