There are three essential criteria in addressing courtroom acoustical design:
Acoustics should be clear, with no reverberations or echoes, and should be enhanced in the litigation area. All participants should be able to hear the proceedings clearly. Acceptable acoustics can be obtained only through the proper floor plan, and the appropriate balance of materials to reflect, absorb, or diffuse sound. Surfaces frequently are used to reflect sound that originates in the well area and absorb sound from the spectator areas. Generally, the front wall of the courtroom may be constructed with reflective materials to enhance the sound from the well area, while the back wall is covered with sound absorptive materials to reduce noise and echo. The side walls should be treated as needed, either to increase or reduce sound in the well area. The floor should be finished with carpet or padded vinyl to reduce noise.
Many older courthouses were built with wood paneling in the courtrooms, which often produced wonderful acoustics. When sound amplification systems are added to these courtrooms the result is often disastrous. Sound amplification systems require a different type of construction and different materials to produce the proper results.
While much of the research on acoustics design in buildings has focused on auditoriums and concert halls, courtrooms provide a unique challenge because they involve many complicated design issues. An acoustic and audio specialist should be consulted as part of any court design team.
Without an electronic amplification system, speech traveling directly from an average person to a listener will begin to fade at a distance of 30 to 40 feet. The standard courtroom is approximately 47-50 feet long, including the spectator area. Sounds coming from the judge's bench will begin to diminish near the public seating. A reflective ceiling will reinforce the intelligibility of the sound if the difference between the direct and reflected path does not exceed 45 feet. In a courtroom, sounds are generated from several different directions. If an attorney is talking directly to the jurors, then the judge, court reporter, witness, opposing counselors, and the public are not in the direct path of the speech. Most sounds radiate in all directions, but high-frequency sound, which is narrower and more directional, requires assistance to be diverted to other areas.
Electronic sound systems amplify sound. In courtrooms that are well-designed for reflection and diffusion of sound, an electronic sound system typically is not required. However, where audio- and video-recording systems are used, a good quality sound system is essential. This requires a specialized acoustical/audiovisual consultant to assist in the layout and design of the speakers and to help determine the amount of amplification. A courtroom with a poorly designed sound system can have worse acoustics than a courtroom with no sound system at all.
The need to limit the short reverberation time in a courtroom is critical to preserve speech intelligibility. A common standard for courtrooms is one occupant per 80 to 150 cubic feet (cf). Courtrooms, however, generally exceed this occupancy level, and it is necessary to treat the courtroom acoustically to provide a short reverberation time. The architectural/engineering team should undertake detailed planning for acoustics in conjunction with an acoustical consultant.
- The area behind the judge's bench and the two side walls should be balanced with sound-reflecting and sound-absorbing surfaces. The wall surfaces should reflect signals toward the clerk, jurors, and court reporter whenever an attorney speaks in that direction; but the ceiling should absorb sound to reduce reflected sound, which can restrict the judge's ability to hear.
- The rear of the courtroom in the spectator area should be treated as acoustically "dead," with highly absorptive materials on the floors, walls, and ceiling. This will eliminate serious reverberation in the back, where most of the sound will be directed. Additionally, this will reduce the noise level generated by the spectators and witnesses seated in the public area. Furthermore, because most courtrooms have hard benches, inclined at an angle, the seats might be upholstered to prevent uncontrollable reverberations in the room.
- Ceiling design in the courtroom should be carefully studied. If the acoustical treatment is inappropriate, barrel-vaulted and coffered ceilings can cause a fluttering echo or elongation of sound.
- Floors in courtrooms should be carpeted to prevent transmission of sound to the court room below as well as to absorb unwanted reflected sounds from the walls and ceilings.
Sounds generated and transmitted from outside the courtroom affect the acoustics in the courtroom. People talking in a corridor or an adjoining room, footsteps on hard surfaces above, traffic from the street, and loud air-conditioning systems can impair the room's acoustics and should be eliminated. On the other hand, some low-level background noise can mask irritating noises, such as pages turning, feet tapping, or even a person breathing heavily. Such noises can disrupt concentration. To protect the privacy of bench conferences in courtrooms with well-designed acoustics, "white noise" devices may be installed in the jury area. When activated, these devices produce sound patterns that prevent other courtroom sounds from reaching the jury.
Features such as soundproofing between courtrooms and surrounding spaces (particularly holding cells), double-door vestibules from public corridors and holding areas, and carpeting reduce the extraneous noise within the courtroom. Many materials that muffle sound are available for partitions, floors, and ceilings. These materials have been tested and rated for sound transmission by laboratories approved by the American Society for Testing Materials. The quality of their performance is based not only on the porosity of the material but also on its assembly and installation properties. Sound Transmission Class (STC) ratings for materials and assemblies provide architects with a reliable rating for walls, floors, and ceilings. In the STC classification, the higher the rating, the more privacy is provided in the adjoining space. In considering the need to eliminate intruding sounds in the courtroom, a high STC rating should be used for partitions.
Partitions around courtrooms should be rated with an STC of 50 and above. This is equivalent to an 8-inch concrete block wall with a one-half-inch furred gypsum board, which has an STC rating of 50. (A wood stud wall with five-eighths-inch gypsum board and two-inch isolation blanket has an STC rating of 39.) Other areas of the courthouse requiring a high STC rating are judicial chambers and jury deliberation rooms. It is also important that these walls be constructed to go from floor to floor so that sound is not transmitted from adjacent rooms. To further insulate the courtroom from noise, vestibules or sound locks and conference rooms should be placed between the courtroom and public corridor as a buffer zone. Door seals may be required to achieve a sound transmission rating of 50 or greater.