0 not able to send back an echo (= a sound that reflects off a surface): --
Those are lightweight building blocks made of some porous, anechoic material.
The ultrasound showed an anechoic mass located behind a normal bladder.
The anechoic chamber is used to test microphone performance.
12.5% of the nodes were anechoic.
The case presented in ultrasound studies as a large, solid, well-defined, heterogenous mass with anechoic areas.
In this study, 4 patients had an abnormal anechoic mass, 1 had an abnormal echogenic mass.
To overcome these problems it was decided to record heart valve sounds under controlled conditions deep in an anechoic water tank, free from reverberation noise.
Experiments in anechoic chambers have shown errors of more than two to one when subjects were asked to estimate the distance of a sound source.