Screen fabric must lose under one dB yet remain porous enough to conceal speakers

Evidence

An acoustically transparent screen is a simple device for revealing truths, but it is essential to test the acoustical transmission loss of the material by performing a simple on-axis frequency response measurement, then place the material between the loudspeaker and microphone, and measure again. There will be a difference, but it should be less than 1 dB, even at the highest frequencies, as it is in a good grille cloth. Polyester double-knit is a commonly available possibility, and there are dedicated grille cloth fabrics in many fabric stores. However, care must be taken to ensure that the fabric when tested and used is under slight tension to open the weave—it is this that is responsible for the acoustical transparency. Because fabrics with low acoustical loss tend to be very porous (easy to blow air through and to see glints of daylight through) they can reveal outlines and sometimes more of the loudspeakers being evaluated. Minimize the light behind the screen and emphasize the lighting levels on the audience side to alleviate this problem—directional lighting helps. Be sure to cover any LED power indicators and other lights on active loudspeakers. — Toole, Floyd E, Sound reproduction- the acoustics and…, 1114

Categorization

• DEFINE: Defines the practical transparency criterion for blind-test screens: under 1 dB on-axis transmission loss, achieved by tensioning the weave open.