2007 U.S. Courts Design Guide - Chapter 14.pdf

U . S . C o u r t s D e s i g n G u i d e l 2 0 0 7 Ac o u s t i c s l 1 4 - 1

ACOUSTICS

This chapter discusses acoustic design concepts and outlines specific acoustic criteria for courthouses. Criteria in this chapter focus on the court-occupied spaces.

Where detailed criteria are not provided for program areas, the requirements set forth in

GSA P-100 shall govern.

Introduction The two key factors that determine the acoustic performance of spaces in a courthouse are speech intelligibility and acoustic privacy.

Speech intelligibility is a measure of the ability of a listener to understand what is being said. A high standard of speech intelligibility is critical to ensure that all questions, testimony, and discussion can be clearly understood by all the participants and observers of the event.

Speech privacy is a measure of speech audibility between adjacent spaces and is a function of the acoustic separation provided by the separating partition(s) and of the background noise levels in the two spaces.

The acoustic performance of a space can be specified by a synthesis of acoustic parameters, which can be predicted and measured during design.

f Speech Intelligibility For unamplified speech, the two key parameters that determine the level of speech intelligibility are the level of background noise and room reverberance. For amplified speech, the third key parameter that needs to be taken into account is the performance of the sound-reinforcement system.

Installation of a sound-reinforcement system can help increase the level of speech intelligibility; however, poor room acoustic design cannot be compensated for with good sound system design. Both should be considered together from the outset.

Background noise is a product of several sources. The dominant component is typically noise associated with the heating or cooling system. This may include fan noise and regenerated flow noise associated with dampers, diffusers, and other mechanical system elements. Another component is noise ingress, either from external sources such as road traffic or from internal sources such as the activity of people in adjacent spaces. Noise criteria describe the desired level of background noise.

Achieving a high level of speech intelligibility requires that the signal-to-noise ratio, that is, the speech level over the background noise level, be optimized. This should be achieved by controlling the background noise level within the courtroom and optimizing the speech level through the room’s acoustic design and the design of the sound-reinforcement system.

Room reverberance is generally defined by the reverberation time, which is the time it takes for sound to decay within a room, expressed in seconds. Too much reverberance will result in late sound reflections (echoes), which will compromise speech intelligibility. Reverberation time is directly proportional to the volume of the room and inversely proportional to the amount of sound absorption within the room. Therefore, the reverberation time can be reduced by reducing the room volume and/or increasing the amount of sound absorption.

f Acoustic Privacy For any given courthouse space, it is important that speech from the activity within not be audible in adjacent spaces, and vice versa. Special attention should be paid at the earliest stages of planning to ensure that noise-producing spaces (building-systems equipment rooms, restrooms, circulation space, public lobbies, etc.) are not located directly adjacent (vertically or horizontally) to noise-sensitive spaces.

Internal partitions should be of a construction determined to achieve an appropriate level of airborne sound isolation, as measured per the ASTM E-90-99 standard.

Buffer spaces and vestibules should be included where appropriate. Impact isolation, to control footfall noise from adjacent spaces, should also be considered.

Noise-sensitive spaces must be protected from external noise ingress, such as road traffic noise, airplanes passing overhead, and pedestrian activity. All facade elements (walls, glazing, roofs, etc.) should be designed to provide appropriate sound isolation.

Another fundamental consideration when the building is located above or close to significant sources of vibration, specifically subways, below-grade or tunnel roads or railways, at-grade railways, trams, and metro systems, is the need to take into account groundborne noise and vibration in the building. In these areas, vibration isolation may be required to isolate the building structure from the vibration source.

Advice should be sought at the earliest available opportunity.

Supporting Documents A comprehensive guide to supporting documents can be found in Chapter 2, “Courthouse Programming and Budgetary Considerations.” That listing includes program and design criteria, courthouse planning and related guidelines, policies, and information on many facets of the design and construction of federal courthouses.

The reference listed below relates specifically to this chapter.

� American Society of Heating, Refrigerating, and Air-Conditioning Engineers (ASHRAE) Handbook of Fundamentals

Design Requirements This section of the Design Guide presents a definition of the acoustic criteria applicable to courthouse buildings as well as design guidance to ensure that the necessary criteria are met.

The design team should seek the advice of an acoustic consultant in order to ensure that the design recommendations are successfully implemented. It should be noted that minor changes in room shape, form, and finishes can have a significant effect on the room acoustics. The same is true for variations in the building systems, equipment, facade, and other construction design. Therefore, it should not be assumed, regardless of the prior experience of the design team, that targets can be met based on previous projects if changes are considered in subsequent designs.

f Speech Intelligibility Speech intelligibility is commonly measured using the Speech Transmission Index (STI). The STI uses a rating system from 0 to 1 to subjectively rate intelligibility, broken down as follows:

The design target for all critical spaces is to achieve an STI rating of > 0.6 for both unamplified and amplified speech. A sound-reinforcement system should be used to achieve an STI rating of very good to excellent. The STI should be measured when the audio system is completely installed, in accordance with the method laid out in IEC 60268-16 or ANSI S3.2-1995.

f Room Reverberation Times Critical spaces should be designed to achieve the reverberation times provided in Table 14.1.

1 4 - 2 I Ac o u s t i c s U . S . C o u r t s D e s i g n G u i d e l 2 0 0 7

U . S . C o u r t s D e s i g n G u i d e l 2 0 0 7 Ac o u s t i c s l 1 4 - 3

It should be noted that guidance elsewhere in this document regarding courtroom dimensions will result in a room reverberation time that, in the absence of sound-absorbing treatment, will exceed the targets indicated. Therefore, specific guidance should be followed to ensure that room reverberance is appropriately controlled. The relevant guidance is provided in Table 14.2. In all cases, the introduction of sound-absorbing finishes should be an essential component of the room design.

f Room Background Noise Levels Room background noise levels are comprised of the noise from building systems (HVAC, electrical, lighting, audiovisual systems, etc.) and noise ingress from external sources (road, rail, and air traffic; pedestrian activity; etc.) and internal sources (such as the activity of people or the operation of equipment in adjacent spaces). All sources of noise must be controlled to appropriate levels.

Acceptable levels of noise from building services systems depend on the sensitivity of the room function. In addition, constant noise such as that from HVAC systems also masks the ingress of external noise or activity noise in other areas of the building.

In accordance with the ASHRAE Handbook of Fundamentals, all spaces should be rated using the room criterion (RC) curves, that is, background noise.

If variable HVAC systems are used, the implications for the building design approach must be examined. This will also have ramifications for the design of the building facade (if used to control noise ingress from external sources) and internal room-to-room space privacy.

To maintain constant RC background noise levels, it may be necessary to introduce a sound-masking system using distributed loudspeakers. The spectral shape of the sound-masking system must be carefully designed and specified such that it does not exceed the target criteria provided in Table 14.2 and does not contain any tonal elements.

The increasing use of videoconferencing technology in the courtroom means that low-frequency noise needs to be adequately controlled to ensure that suitable levels of sound quality can be achieved in reproduction and recording.

f External Noise Ingress Noise from external sources may consist of road, rail, air, or pedestrian traffic or noise from the external mechanical equipment of the building or surrounding buildings. In all cases, the noise from these sources should be limited in order not to disturb court functioning.

In order to limit external noise ingress, an assessment must be made of future noise levels on the site. Step one will require that a site noise survey be conducted. An acoustic consultant should measure and record external noise at appropriate intervals during the operating hours of the court and document these as a baseline.

In the case of a new courthouse, any known future conditions, such as new or rerouted roads, new railways, airport flight paths, and so on should be reviewed and the noise impact determined. Future land use of surrounding areas may also contribute to external noise and should be reviewed with the local planning commission.

The acoustic consultant will then use this information to provide design guidance and improve the sound isolation performance of the proposed building facade using the Sound Transmission Class (STC) criteria.

f Internal Airborne Sound Insulation In order to achieve the required privacy between spaces, it is important to ensure that all internal partitions, walls, floors, and ceilings, as well as doors and windows, achieve an adequate level of sound insulation.

The guidelines presented here are expressed in terms of the Noise Isolation Class (NIC), a single-number rating describing the combined performance of all building elements in isolating one room from another. The in-field sound-level difference between adjacent spaces should be measured in accordance with ASTM E336-05 Standard Test Method for Measurement of Airborne Sound Insulation in Buildings, and the NIC value should be determined in accordance with ASTM E413-04 Classification for Rating Sound Insulation.

The higher the NIC rating, the better the privacy between spaces.

PRIVACY LEVELS

BACKGROUND NOISE (RC)

30 35 40

Inaudible NO

ISE ISO

LATIO

N

75 70 65 60

Confidential

CLASS

60 55 50 45

Normal

(NIC)

50 45 40 35

Minimal 40 35 30 25

It is the responsibility of the architect and acoustic consultant to minimize the use of heavy internal partition construction and full-height (slab-to-slab) partitions with the exception of areas where it is a requirement. Attention should be paid to the use of acoustically neutral spaces as buffer zones between sensitive areas. Where buffer zones or neutral spaces are used, the design team can use discretion in reducing the performance of partitions while ensuring that the subjective intent of the privacy standard is achieved.

The level of privacy also depends on the background noise levels in the spaces. For example, a room in which the partitions have a rating of NIC 50 and a background noise level of RC 35 will have the same le vel of privacy as a room in which the partitions have a rating of NIC 45 and a background noise level of RC 40.

The required sound insulation performance (NIC) should be defined by the background noise criteria (RC) and the required level of privacy, as shown in

Table 14.1. The levels circled in the table demonstrate a required privacy level of confidential.

Table 14.1 Room Partitioning Requirements f Impact Sound Isolation The Impact Isolation Class (IIC) identifies the requirement for control of impact noise (footfall, etc.) from adjacent spaces (horiz ontal or vertical). IIC values for the floor-ceiling assembly above key critical spaces (courtrooms, conference rooms, study areas, jury deliberation rooms, and attorney/witness rooms) should be a minimu m of 50.

IIC 50 can be achieved by using carpet as the floor finish or by using a resilient interlayer within the floor construction, such as Regupol QT, Sylomer, Enkasonic, or Kinetics Soundmatt.

f Raised Access Floor Systems Given that raised access floor systems are required throughout the courthouse, the design tea m must balance this against sound isolation performance very early in the design process. At the outset, building planning should try to separate sensitive spaces from each other by the use of acoustically neutral spaces (storerooms, risers, shafts, etc.).

Methods for improving the sound isolation of partitions at the head and base (e.g., “pan”-type floor tiles filled with lightweight concrete, packing with dense compressed mineral fiber, duct lagging or similar, use of cross-talk attenuators or similar) can also be considered. The use of access floors does not absolve the design team fro m achieving the required sound isolation performance, but places onus on the design team to consider these requirements from the earliest design stages.

f Vibration Vibration limits for key sensitive areas are specified in accordance with ANSI S3.29- 1983 Guide to the Evaluation of Human Exposure to Vibration in Buildings. Limits should be set on the basis of multiples of the relevant base curve. Appropriate multiples are as follows:

� Courtrooms: 1.4 � Other areas: 4.0

1 4 - 4 I Ac o u s t i c s U . S . C o u r t s D e s i g n G u i d e l 2 0 0 7

Table 14.2 1Acoustic Performance Requirements

SPACES

PRI VACY

LEVEL

REVERBERATION

TIME (RT)

in seconds

BACKGROUND

NOISE ROOM

CRITERION (RC)

curve

NOISE

ISOLATIONS

CLASS (NIC)

in decibels

SPEECH

INTELLIGIBILITY

INDEX (STI)

without sound system enhancement

COURTROOM

Courtroom Confidential 0.6–0.7 25–30 55–60 0.6 (Good)

JUDGES’ CHAMBERS SUITE

Judge’s Chambers Private Office Confidential 0.4–0.6 35 50 0.6 (Good)

Law Clerks’ Offices Normal 0.5–0.6 30 35 0.6 (Good) Judge’s Chambers Conference/Reference Room Confidential 0.5–0.6 35 50 0.6 (Good)

COURTROOM ASSOCIATED SPACES

Circuit Judge’s Robing Room Normal 0.5–0.6 35 40 0.6 (Good) District, Magistrate, and Bankruptcy Judge’s Conference/Robing Room Normal 0.5–0.6 35 40 0.6 (Good)

Attorney Work Room Normal 0.5–0.6 35 40 0.6 (Good) District, Magistrate, and Bankruptcy Attorney/Witness Room Confidential 0.5–0.7 30 55 0.6 (Good)

Public Waiting Areas Normal 0.5–0.6 40 25 0.6 (Good)

U . S . C o u r t s D e s i g n G u i d e l 2 0 0 7 ( R e v . 0 6 / 0 8 ) Ac o u s t i c s l 1 4 - 5

1 4 - 6 I Ac o u s t i c s U . S . C o u r t s D e s i g n G u i d e l 2 0 0 7

Table 14.2 Acoustic Performance Requirements (cont’d)

SPACES

PRI VACY

LEVEL

REVERBERATION

TIME (RT)

in seconds

BACKGROUND

NOISE ROOM

CRITERION (RC)

curve

NOISE

ISOLATIONS

CLASS (NIC)

in decibels

SPEECH

INTELLIGIBILITY

INDEX (STI)

without sound system enhancement

JURY FACILITIES

Jury Assembly Suite Normal 0.6–0.8 40 35 0.6 (Good)

Trial Jury Suite Inaudible 0.4–0.6 30 70 0.6 (Good)

Grand Jury Hearing Room Inaudible 0.4–0.6 30 70 0.6 (Good)

OTHER COURT UNITS

Library Lobby Minimal 0.6–1.0 40 45 N/A

Library Study Room Normal 0.4–0.6 30 55 N/A Probation and Pretrial Services Private Offices and/or Interview Rooms Confidential 0.5–0.7 30 55 N/A

Federal Defender’s Trial Preparation Suite Confidential 0.5–0.7 30 55 N/A

Office of the Bankruptcy Administrator Confidential 0.5–0.7 30 55 N/A Office of the Pre-Argument Conference Attorney Confidential 0.5-0.7 30 55 N/A

COMMON BUILDING SPACES

Shared Judges Conference Room Confidential 0.5–0.7 30 55 N/A

Judges’ Dining Area Confidential 0.5–0.7 30 55 N/A

All other courthouse spaces not listed reference GSA P-100.

U . S . C o u r t s D e s i g n G u i d e l 2 0 0 7 Ac o u s t i c s l 1 4 - 7

Courtrooms The primary requirement is for high intelligibility and natural-sounding speech in the courtroom. To ensure that this is achieved, the courtroom must have the following characteristics:

� Controlled background noise from building services systems and audiovisual and other building equipment

� Appropriate room shape, form, and volume to ensure a suitable sound-reflection sequence and natural control of reverberance

� Appropriate control of room reverberance through the use of acoustic treatments

� Suitable sound isolation from all adjacent spaces

Background Noise Control. Specific NIC/RC targets are provided in Table 14.2. The design team should ensure that these limits are not exceeded through the use of any equipment or system within the space.

Room Shaping and Materials. Room shape and form have a fundamental effect on room acoustics and should be considered from the outset. General recommendations are as follows:

� The courtroom must not be a long or narrow rectangle finished totally with sound-reflective materials. Such conditions can cause excessive acoustic fluttering. Reducing the room length, avoiding the use of long parallel walls, and using appropriately selected absorptive finish materials can alleviate the problems.

� At the front of the room, from the judge’s bench to just behind the location of the attorney teams, walls should be rectilinear and parallel to promote good distribution of lateral sound energy in the entire well area between the judge, jury, defendant, and attorney teams. Surface treatments should promote sound reflection. Some sound diffusion (through the use of surface texture or convex curvature) may be acceptable, as determined by a case-by-case evaluation.

Concave curvature should be avoided in this area as it can often lead to sound-focusing issues.

� It is recommended that the ceiling at the front of the room be flat and sound reflecting to maximize speech intelligibility in the well. Significant down stands, coffers, or similar elements should generally be avoided as they will reduce the effective sound-reflecting treatment area.

� At the rear of the room (between the rear of the attorney area and the main public entrance to the courtroom), room shaping may vary, being rectilinear or curved, either convex or concave. This wall area should be the primary location for sound-absorbing treatment. It should be noted that the extent to which treatment is required will depend on the shape of the walls as well as on the volume of the room. A concave curvature is likely to require the most significant area of sound-absorbing treatment, to control not only reverberance but also sound focusing.

� The ceiling at the rear of the room may require some limited area of sound-absorbing treatment to prevent late reflected sounds returning to the front of the room. This should be determined on a case-by-case basis.

� In all cases, carpet or carpet tiles shall be used for the floor finish.

Sound Isolation. Soundlock lobbies or vestibules should be provided at all entrances to the courtroom. This provides an acoustic buffer zone between the courtroom and other public or nonpublic circulation spaces. Sound isolation from external noise sources, where the courtroom adjoins an external facade, should achieve the requirements of Table 14.1. Internal sound isolation should be achieved by meeting the STC performance requirements. Space planning should minimize, as far as is practical, locating noise-producing spaces (mechanical-systems rooms, toilets, public circulation areas, etc.) directly adjacent to the courtroom.

Speech Privacy. In order to allow sidebar conversations at the judge’s bench to occur in privacy, the jury box should be located a minimum of 20 feet (6096 mm) away from the judge’s location. This will still require such conversations to be held in low voices.

If greater privacy or shorter distances are necessary, it is recommended that a sound-masking system be provided. Such systems require careful design but allow for the broadcast of a shaped noise spectrum through loudspeakers in the room. The judge should have the ability to turn such a system on from the bench. A mute function should also be provided for the microphone to ensure the privacy of sidebar and bench discussions.

Loudspeaker Type, Location, and Orientation. It is important, in order to maximize speech intelligibility in the room, that the type, location, orientation, and distribution of loudspeakers be very carefully considered. The acoustic consultant should specify the minimum loudspeaker requirements for incorporation into the audiovisual consultant’s or contractor’s design.

In some cases, it may be most efficient to locate loudspeakers on or at the bench locations (judge, attorneys, jury box, and defendant) to achieve maximum speech intelligibility. The need for a time delay and/or local volume control should be determined on a case-by-case basis. Additionally, audiovisual equipment should be specified and selected for low noise output, so as not to impair listening in the courtroom.

f Courtroom Associated Spaces Attorney Work Room. The primary requirement is for quiet and private working areas.

Appropriate control of mechanical-systems background noise, sound isolation from adjacent spaces, and acoustic control are the key issues. Specific requirements are provided in Table 14.2.

The attorney work room should be acoustically and visually separate from other areas of the building. However, the standard of sound insulation is reduced in comparison to the judges’ suites, such that a “good” standard of sound insulation is adequate.

The required reverberation time determines the degree to which acoustically absorptive finishes should be used in the attorney work room. See Table 14.2 for specific reverberation times.

District, Bankruptcy, and Magistrate Judge’s Attorney/Witness Room. The primary requirement is for quiet and private working areas with appropriate sound insulation from the courtroom. Appropriate control of mechanical-systems background noise, sound isolation from adjacent spaces, and acoustic control are the key issues.

Privacy is of paramount importance. All walls to these areas must achieve a high degree of sound insulation. They need not be slab-to-slab, providing that the construction meets the required performance set out in Table 14.1 and an appropriate sound-isolating ceiling is provided. Doors should be appropriately acoustically rated, with all necessary sound-isolating seals and hardware.

Internal sound isolation should be achieved by meeting the performance requirements outlined in Table 14.1. All penetrations in walls to these areas should be appropriately sealed to maintain acoustic criteria set forth in this chapter.

Recessed light fittings should be avoided, but where they are included they should be appropriately boxed in.

To ensure complete privacy of conversations, ducted systems should be provided with cross-talk attenuators at each wall penetration.

The required reverberation time determines the degree to which acoustically absorptive finishes should be used in the room. See Table 14.2 for specific reverberation times.

Public Waiting Areas. Public waiting areas must be separated acoustically from adjoining enclosed spaces. The same acoustic standards should be applied to public waiting areas as to attorney witness rooms.

f Judges’ Chambers Suites The primary requirement in judges’ chambers suites is for quiet and private working areas. Appropriate control of mechanical-systems background noise, sound isolation from adjacent spaces, and acoustic control are the key issues. Specific requirements are provided in Table 14.1.

Privacy in the suites is of paramount importance. All walls to the judges’ suites, private offices, and the reference/conference room must be slab-to-slab construction.

1 4 - 8 I Ac o u s t i c s U . S . C o u r t s D e s i g n G u i d e l 2 0 0 7

U . S . C o u r t s D e s i g n G u i d e l 2 0 0 7 Ac o u s t i c s l 1 4 - 9

Sound isolation from external noise sources, where the courtroom adjoins an external facade, should achieve the requirements of Table 14.1. Internal sound isolation should be achieved by meeting the performance requirements in Table 14.1.

Space planning should minimize, as far as is practical, locating noise-producing spaces (mechanical-systems rooms, toilets, public circulation areas, etc.) directly adjacent to the suites. All penetrations in walls to these areas should be appropriately sealed in accordance with the requirements of Table 14.1.

All equipment serving these areas should incorporate appropriate noise- and vibration-control mountings to a distance of 10 feet (3 meters) from the perimeter of the suites to ensure complete privacy within.

To ensure complete privacy of conversations, ducted systems should be provided with cross-talk attenuators at each wall penetration.

See Table 14.2 for additional detail on acoustics for judges’ chambers suites.

Plumbing runs must be isolated from judges’ chambers and conference/ reference rooms.

Jury Facilities f Trial Jury Assembly Suite Proper acoustics are important in the jury assembly suite because potential jurors receive instructions regarding their obligation. To enhance acoustics in the jury assembly area, a sound system should be provided. The system must be designed so that the loudspeakers distribute the majority of energy into the direct sound field, with minimum distribution into the reverberant field. This can be accomplished by providing a highly sound-absorbent environment, with a maximum reverberation time of 0.8 seconds. The acoustic privacy requirement for the jury assembly area is “normal.”

f Trial Jury Suite Trial jury suites must be acoustically enclosed. Trial jury suites adjoining other functional spaces must have soundproofed common walls. The acoustic privacy requirement is “inaudible” for the entire jury suite. To ensure intelligibility and privacy of speech within the trial jury suite, the soundlock entry doors must be fully gasketed.

f Grand Jury Hearing Room The acoustic privacy requirement for the hearing room in the grand jury suite is “inaudible.”

Central Court Libraries The entire library must be acoustically isolated from other court functions, including noise-generating functions within the library or adjacent spaces such as copier rooms or restrooms.

Probation and Pretrial Services Offices All interview rooms and offices of probation and pretrial services supervision officers must be acoustically separate from adjacent areas (acoustic privacy requirement: “confidential”), with 55-decibel (dB) NIC partitions, gasketed doors, and background noise levels of 30 RC. Special consideration must be given to the design and fabrication of ducts to minimize acoustic problems. Refer to GSA P-100.

Other Court Units f Office of the Pre-argument/Conference Attorney Both executive offices and conference rooms must provide acoustic confidentiality.

f Office of the Bankruptcy Administrator The executive office and conference rooms for the Office of the Bankruptcy Administrator must be designed for acoustic confidentiality.

f Trial Preparation Suite for the Federal Defender The trial preparation suite for the federal defender’s office must be designed to provide acoustic confidentiality.

f Design Requirements for All Other Court Spaces Refer to GSA P-100.

1 4 - 1 0 I Ac o u s t i c s U . S . C o u r t s D e s i g n G u i d e l 2 0 0 7