The space absorbers were long cylindrical shells of perforated metal, containing glass fiber. The absorbers were to be used in an aero‐engine test cell, and these conditions were simulated in the measurements by mounting a few absorbers in a long concrete pipe, so that the cross‐sectional ratio (absorber/enclosure) was the same in each case. The direction of propagation of sound was parallel to the axis of the cylinders so that absorption occurred at grazing incidence. The concrete pipe was terminated by a rigid reflector, and the attenuation figures were deduced from the resulting interference pattern using impedance tube theory. The theory was extended to the case of octave bands of noise, when the interference pattern for the mean squared pressure is(p2) = [cosh2ax sinh(2ax/3)]/(2ax/3) + [cos(2kx) sin(2kx/3)]/(2kx/3), whereais the sound attenuation constant,kis the wave number at the center frequency of the band, andxthe distance along the pipe measured from the reflecting end. Experimental results were obtained which followed this pattern, and the required sound attenuation constant was obtained by a graphical method. Measurements were made at low frequencies only, 300 cps and below.