[citation needed] For example, a closed bulb connected to an organ pipe will have air moving into it and pressure, but they are out of phase so no net energy is transmitted into it.
The SI unit of pressure is the pascal and of flow is cubic metres per second, so the acoustic ohm is equal to 1 Pa·s/m3.
For a one-dimensional wave passing through an aperture with area A, the acoustic volume flow rate Q is the volume of medium passing per second through the aperture; if the acoustic flow moves a distance dx = v dt, then the volume of medium passing through is dV = A dx, so:[citation needed] If the wave is one-dimensional, it yields The constitutive law of nondispersive linear acoustics in one dimension gives a relation between stress and strain:[1] where This equation is valid both for fluids and solids.
In Newton's second law applied locally in the medium gives:[2] Combining this equation with the previous one yields the one-dimensional wave equation: The plane waves that are solutions of this wave equation are composed of the sum of two progressive plane waves traveling along x with the same speed and in opposite ways:[citation needed] from which can be derived For progressive plane waves:[citation needed] or Finally, the specific acoustic impedance z is The absolute value of this specific acoustic impedance is often called characteristic specific acoustic impedance and denoted z0:[1] The equations also show that Temperature acts on speed of sound and mass density and thus on specific acoustic impedance.
[3]) Such reflections and resultant standing waves are very important in the design and operation of musical wind instruments.