Cnoidal wave is the wave height, "λ" is the wavelength, "c" is the phase speed and "η" is the trough elevation. Further cn is one of the Jacobi elliptic functions and "K"("m") is the complete elliptic integral of the first kind; both are dependent on the elliptic parameter "m". The latter, "m", determines the shape of the cnoidal wave. For "m" equal to zero the cnoidal wave becomes a cosine function, while for values close to one the cnoidal wave gets peaked crests and (very) flat troughs. For values of "m" less than 0.95, the cnoidal function can be approximated with trigonometric
Sound pressure Since formula_18, the amplitude of the specific acoustic impedance is given by Consequently, the amplitude of the particle displacement is related to that of the acoustic velocity and the sound pressure by When measuring the sound pressure created by a sound source, it is important to measure the distance from the object as well, since the sound pressure of a "spherical" sound wave decreases as 1/"r" from the centre of the sphere (and not as 1/"r", like the sound intensity): This relationship is an "inverse-proportional law". If the sound pressure "p" is measured at a distance "r" from the centre