In the case of simple harmonic motion, the time factor being eiσt, the velocity potential Φ of the vibrations must satisfy the equation (Δ2 + k2) Φ = 0. Where k = σ /c in which c is the velocity of sound.
Proceedings of the Iowa Academy of Science
©1923 Iowa Academy of Science, Inc.
Hoersch, Victor A.
"New Vibrations within a Conical Horn,"
Proceedings of the Iowa Academy of Science, 30(1), 65-66.
Available at: https://scholarworks.uni.edu/pias/vol30/iss1/11