Eleven Pipers Piping: the physics of orchestral brass

29 December 2016

Interview with

Alan Calverd, Physicist

According to the song, by the twelfth day of Christmas, 11 pipers were piping and 12 drummers were drumming. Alan Calverd explains to Chris Smith the physics of the wind section of an orchestra...

Alan - You have to start off by making what’s called a ‘buzz.’ Basically you blow a raspberry in a funnel.

Chris - Go on!

Alan - Pthhhhhhhhh or Pfffffff depending on which level of brass instrument you’re playing. And then that contains a whole lot of tones and you select the resonant length of tubing by pressing the valves up and down.

Chris - Why do the valves actually change the notes though? Why should the length of the tube affect what comes out?

Alan - What you’re trying to do is produce a standing wave within the tube. Now the end of the tube being open means that there’s got to be an antinode at the bell and there’s going to be a node where your lips are because the air’s not moving at that point.

Chris - What’s an antinode?

Alan - Antinode is where the air is moving at it’s most rapid and the node is where the air is not moving. Essentially, if you imagine the tube is stretched out you have something like about 15 feet of tubing, you can draw lots of sine waves within that 15 feet.

Chris - Wiggly waves along it?

Alan - Wiggly waves along it. And provided they all start at zero and end at maximum, then you can have waves of various different frequencies all fit in the tube.

Chris - Would it have to be all curled up like the tuba is or could you get the same tune out of a long straight piece of pipe - it’s just that we coil it up for convenience because it would be hard to move otherwise?

Alan - It’s very difficult to march with a 15 foot drainpipe. Also, it upsets the other guys in the orchestra.

Chris - Fair enough. Why are these instruments made of brass - is there a reason why they go for brass or could you make it out of anything?

Alan - In principle you could. You can play a hosepipe if you’ve got a decent mouthpiece.

Chris - I’ve seen people do that with a funnel on the end. And by swinging the hosepipe almost like you were going to do a lasso, you get a range of different sounds out. Very interesting.

Alan - Yes, that’s quite interesting. You get quite a harsh tone out of a hosepipe - very similar to a trombone because it’s the same diameter all the way down.

Chris - What are you saying about trombonists. They won’t be very happy to hear that.

Alan - Trombonists are always happy because they always get to play the loud bits.

Chris - Fair enough!

Alan - It’s because the trombone is, essentially, the same diameter all the way down the tube. That means you can get a whole lot of harmonics and overtones and you get this good rasping sound if you really blow it hard.

Chris - But the reason for brass?

Alan - The reason for brass is it’s an easy material to work; it’s ductile, it’s malleable so you can beat the shape of the bell that you want and you can draw tubes of any size and length. You can solder it quite easily, it doesn't corrode, and most important of all from my point of view is it’s a biocide. There’s so much copper in brass that bugs don’t grow on it.

Chris - And that’s quite important because you don’t want to catch tuberculosis do you?

Alan - Urghhhhh.

Chris - Are you saying then that, actually, this is a useful aspect of the instrument because of the you’re blowing all that moisture and warm air in there and a whole bunch of bugs from your mouth, presumably instruments do end up riddled with bacteria?

Alan - The first thing they tell you when you join a brass band is... never breath in.

Chris - And what about the brass section and other parts of...say woodwind - is it pretty much the same physics or is there a difference there?

Alan - Slightly different physics. The real difference is in the way that the first edge tone is generated. Instead of blowing raspberries, woodwind either use a reed or an edge like a whistle, which is the recorder and the flute have an edge and everything else is a reed. But the question is whether the saxophone is brass or reed?

Chris - What do you think?

Alan - I think it’s interesting, it’s almost entirely in a class by itself because of all the instruments it’s the one that sounds most like the human voice.

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