The sound-absorbing properties of some common out-door materials

Abstract

The sound absorption coefficients of pure sounds of frequencies from 125 to 4000 cycles per second have been measured at random incidence for specimens of some commonly occurring out-door materials, among them, gravel, turf, sand, ashes, railway-track ballast and snow. They mostly share the common characteristic of increased absorption with rising pitch. Some of the materials (e.g. loose gravel soil and ashes) are highly absorbent, snow is remarkably so, while others (e.g. compressed gravel and wet sand) are indifferent absorbents. Some practical aspects are discussed, and also the influence of nearly grazing incidence, such as often obtains with out-door sounds, in raising the degree of absorption.