<Tr> <Th> Characteristic </Th> <Td> Symbols </Td> </Tr> <Tr> <Th> Sound pressure </Th> <Td> p, SPL </Td> </Tr> <Tr> <Th> Particle velocity </Th> <Td> v, SVL </Td> </Tr> <Tr> <Th> Particle displacement </Th> <Td> δ </Td> </Tr>

Fundamentals of telephone communication systems. western electrical company. 1969. p. 2.1