A regular room may not have any mirrors in it, but may be chock-full of reflections — sound wave reflections, that is. Echoes aren’t merely those phenomena that repeat what you say, which are pretty rare. They’re part of your everyday life, when you hold a hand to your ear, when you sing in the bathroom, and generally anywhere and everywhere. Every sound that you hear almost always doesn’t come to you directly from the object that created it; before reaching your ears it most likely bounced around the different surfaces of the place you’re in–floors, walls, ceilings, tables.
So when scientists want to measure a sound just as it is, not as it is magnified through echoes, they want to do it in an echo-less room. They would also want to isolate the sound so that it’s the only one they hear, so they would want a room that blocks out the sounds from the outside, which may travel through the walls, roof, floor, air. In this situation, a room without echoes, an anechoic chamber, is just the thing the fulfills the need.
Testing for products such as microphones, speakers, ear plugs, and facilitating activities such as sound recording and music performances, these are just some of the things that anechoic chambers do. In fact, recording studios and concert halls are examples of anechoic technology applied in large scales.
Echo-less rooms are made by padding every single surface and corner with sound absorbing insulation. The outside is covered with special bricks and concrete, and even rubber, just to isolate the inside and keep external sounds and vibrations out.