An anechoic chamber is a test facility in which there is no (or very little) reflection of sound.
Anechoic chambers are usually built from concrete, and lined with plates or wedges of a radiation absorbent material. These absorb sound and avoid reflecting it.
Car makers use anechoic chambers for detailed investigation into vehicle noise.
In car engineering, the facilities used are semi-anechoic chambers. These have solid floors, which make use of the facility more practical and also reflect sound the same way a road surface doors.