# Air speed through a tube

## Main Question or Discussion Point

Hello,
I was looking for the name of the principle which governs the following-

given a constant air flow- air moves faster through a tube with a smaller diameter than a tube with a larger diameter.

Wouldn't you like to know what this has to do with singing?

Thank you
Debruyn

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Doc Al
Mentor
equation of continuity

DeBruyn said:
Hello,
I was looking for the name of the principle which governs the following-

given a constant air flow- air moves faster through a tube with a smaller diameter than a tube with a larger diameter.
The name of the principle is the equation of continuity (or the principle of mass conservation).

The conservation of mass leads, for an incompressible fluid, to the equation of continuity: the volume flow rate must be constant at all points in an air stream. The volume flow rate is given by Volume/time = Area x Speed. Thus, for a given flow rate, air will flow faster through a tube with smaller diameter.

Wouldn't you like to know what this has to do with singing?
Sure!

Q_Goest
Homework Helper
Gold Member
DeBruyn - Air speed in a tube is generally looked at as a phenomenon which is caused by a difference in pressure. It is not forced by some volumetric flow rate, though I suspect that's what you had in mind.

In fact, if you have a pressure drop in a given length of pipe, say a 100 foot long section of pipe and a 5 psi drop, the larger diameter pipe will have a significantly higher velocity, even though the pressure drop and length of pipe are the same.

Doc Al said:
The name of the principle is the equation of continuity (or the principle of mass conservation).

The conservation of mass leads, for an incompressible fluid, to the equation of continuity: the volume flow rate must be constant at all points in an air stream. The volume flow rate is given by Volume/time = Area x Speed. Thus, for a given flow rate, air will flow faster through a tube with smaller diameter.

Sure!

One of the main aims in classical singing is to keep the muscles of the neck relaxed thereby keeping the throat open and relaxed as opposed to constricted and tense. If a singer is not providing sufficient airflow- the body will automatically try to help out in the process by constricting the throat- thus concentrating the airflow in order to make more out of the airflow which is provided. This does not create a desirable sound! Providing the correct airflow is imperative for the most efficient tone.