Saturday, July 31, 2010

Cold Horn Intonation

Since I've played strings most of my life I associate "cold" with sharp and "hot" with flat. That the opposite is true for horns has been made obvious by experience, but I didn't know why. The explanation in this post made me realize I was thinking about the effect of temperature on the horn itself, not the air column inside it.

In Practical Hints on Playing the French Horn David Bushouse brings up another very practical aspect of playing the horn in tune, that of temperature.

"The tuning of wind instruments is affected greatly by temperature extremes. A cold instrument contains a cold air column which has greater density than warm air. Sound waves pass from air molecule to air molecule, and there are more molecules in the cold air than in the same volume of warm air. Therefore it takes longer for sound to travel in a cold air column, resulting in a slower velocity. This means the cold air column has a lower pitch than the same air column when warm."

This post by Prof. Ericson is one of a series he's been doing comparing and contrasting the positions taken by various texts on the issues facing horn players. While there is some agreement on some issues, there are a lot of different opinions on others, which tends to confirm my notion that the horn is the least settled instrument in the orchestra, both in terms of what the instrument is (single, double or triple) and the best way to play it.


  1. Prof Ericson has one part of this wrong. Air pressure has very little effect on the speed of sound in air, otherwise wind instruments would be dreadfully flat if played by the Denver Symphony, where air pressure is only about 83% of sea level pressure.

    It is temperature and composition of a gas which affects the speed of sound in air. The lighter the molecules of a gas, the higher the speed of sound at any temperature (hence the weird effects you get if you try to breathe helium).

    Leaving aside special cases like that, we can forget about composition, because give or take a bit of humidity, the composition of air doesn't change much from place to place.

    So the main effect on the speed of sound is temperature. Sound moves (a bit) faster in warmer air. The difference in the speed of sound between 15 Celsius (59F) and 30 Celsius (77F) is about 2.7%. Given a constant length of tubing to blow down, that makes you a bit less than half a semitone sharper.

    But the actual effect on you when playing is far less, because you are constantly blowing body-temperature air into the horn. So once you have warmed up the horn by blowing into it, the interior temperature variation is much less than the outside. And because the air is enclosed within the instrument, it doesn't cool all that fast because there are no convection effects to assist.

    If you ever get as much as 1% variation I would be surprised, and that would really only ever occur as a result of playing outside on a fairly cold and windy day where the horn cools quickly. 1% of variation in speed of sound is the equivalent of having to adjust your main tuning slide by about 1.8cm (3/4").

  2. Hi, Jonathan - Getting this far into the science of it all is a bit beyond me, but I think the man Prof. Ericson is quoting is talking about the temperature affecting the "density" of the air in the column, not the ambient air pressure, which I think are two different things.

    For me the revelation was it's the air column that's affected by the temperature (and not the metal of the horn) which in turn affects the intonation. One of the problems playing a lot of different instruments is that I tend to carry brain wiring from one to the other, and sometimes that just doesn't work.