Creating Sound Environments in Police Interview Rooms
Interview rooms are key spaces within a police department. It's highly important that police investigators can hear the suspects they are interviewing clearly; and perhaps more importantly, that the interviewees are only heard by their intended police audience and not by others in adjacent rooms or those walking by. Additionally, since many interviews are recorded or videotaped, good acoustic performance is critical to the recording quality.
Acoustic control in an interview room is challenging due to the competing demands created by their relatively small size and proximity to other rooms, coupled with the necessity of abuse-resistant furnishings. Good acoustic control in interview rooms is a battle drawn on two fronts: sound transmission and reflected sound within spaces.
Sound transmission occurs when sounds leak out of a room and are heard in adjacent spaces. Making sure no one other than the police hears what a witness or suspect says in an interview room is particularly important to protect the privacy of the interviewee.
Sound Transmission Class (STC) is the measurement of how a wall attenuates airborne sound. High STC levels can be achieved with increased wall mass and elimination of structure-born transmission. Wall mass can be increased through multiple layers of drywall, as well as through the use of sound absorptive insulation. Another simple way of avoiding unwanted sound transmission is by providing neoprene or rubber acoustic seals around doors, as well as automatically descending door bottoms.
Structural-Born Sound Transmission
Structural-born transmission can be more challenging to combat, as sound waves can be transmitted through the simple vibration of surfaces, such as the metal studs found in many interview room walls. This can be lessened by adequately separating materials, using resilient channels that hold drywall off of studs and off of each other to create an air gap that doesn't allow materials to vibrate.
Sound waves also bounce around within spaces, which can obscure the reliability of recordings by making speech unintelligible. To avoid this, materials in an interview room need to absorb sound instead of bouncing it around the room.
Choose Materials that Absorb Sound
Noise Reduction Coefficient (NRC) is the measurement of absorptive qualities of a material. Hard and durable finishes, such as concrete floors and drywall or metal ceilings are favored in interview environments, but these materials have very low NRC values. Mitigate this issue by using fabric wrapped acoustical panels on the walls, ceilings, and/or acoustical ceiling tiles.
Conversely, balance higher NRC values and the desire for durable finishes by using metal panels with small perforations on their face. This allows sound to pass through and be absorbed by acoustical material behind the metal that is adequately protected.
While it is always a balance of space, cost, and durability, proper management of both STC and NRC values in interview rooms can ensure the best function of these critical interview environments and the success of any police operation.