Acoustics

The purpose of this section is to give guidance on the acoustic performance requirements of the various areas and spaces within a school so as to encourage and foster an environment conducive to learning.

Noise refers to the sounds that we would prefer not to hear.

The noise levels within a space can either assist or hamper the ability of both students and teachers to hear each other and work together in the learning environment.

The acoustic design of rooms and spaces should address the following parameters:

• Internal noise levels
• Room acoustics (principally reverberation time)
• Noise emission (to the environment)
• Room to room noise control

Generally, the design of all building components, including acoustic components should consider the ‘Whole of Life ‘framework and ensure that the equipment or materials used are of appropriate quality, cost efficient, without compromising the overall efficiency and effectiveness.  They should provide longevity, low maintenance and overall Value for Money to the school and its users. For further details refer to the Whole of Life section of the Design Guide.

Room acoustic design considerations include:

• Reverberation time
• Reverberant noise control
• Speech intelligibility (Speech Transmission Index, STI)
• Late acoustic reflections

The extent to which room acoustics parameters will have to be considered and the extent of acoustic treatment required will depend upon:

• The use of the room or space and therefore an appropriate reverberation time for the use
• Whether or not noisy activities are expected in the room
• Whether or not speech intelligibility is fundamental to the use of the room, e.g.: general learning areas
• Whether the room or space is a specialist performance space with large dimensions and where late acoustic reflections are considered a risk.

The reverberation time within a room must be within the range stipulated in table Table 11.06.1 of Section 11.6 Acoustic Performance Guidelines or Table 1 of the AS/NZS 2107:2016 standard. The more stringent of the two should be met.

Reverberation Time

In the context of educational rooms and spaces, the principle room acoustic consideration is reverberation time. Reverberation time is defined as the time taken (in seconds) for sound to reduce by 60 dB in a room or space and is hence given the notation RT₆₀. Reverberation time is fundamental to describing the ‘acoustical liveliness’ of a room.

Reverberation time within a room or space is a function of the room volume and the acoustic absorption coefficients of room internal surface finishes. Where a room volume is defined (elsewhere in the guidelines), the area and absorption coefficient of room internal surface finishes can be selected to provide an appropriate reverberation time and therefore appropriate room acoustics for educational spaces.

For most educational spaces, the performance guideline reverberation time is the average of the predicted or measured octave band values at 500 Hz and 1000 Hz.

In acoustically critical environments (such as teaching spaces for students who are deaf or hard to hearing), it is desirable to define and design for the required reverberation time at all octave band centre frequencies between 63 Hz and 8000 Hz. This is a more onerous requirement and advice should be sought from an acoustic engineer for individual cases.

Controlling reverberation time provides the following main benefits:

• It serves to improve speech intelligibility, and
• It controls the build up of reverberant noise (i.e. sound levels being sustained by reflecting off multiple surfaces with minimal energy loss)
• To limit the ‘Lombard effect’, as described in ‘Internal Noise levels’.

Speech intelligibility is an important acoustic consideration in teaching rooms and spaces. Control of reverberant noise is important in teaching spaces and other spaces where a build up of noise is undesirable (e.g. practical activity areas, gymnasiums and halls).

Component Design Range (CDR)

School halls that are part of the Component Design Range (‘CDR’) incorporate acoustic design advice and achieve a known reverberation time (when constructed exactly in accordance with CDR design drawings and specifications). The reverberation time performance requirements for these spaces are therefore provided for information only.

School classrooms that are part of the Component Design Range (‘CDR’) achieve a known reverberation time and Speech Transmission Index (when constructed exactly in accordance with CDR design drawings and specifications). The reverberation time and Speech Intelligibility requirements for these spaces are therefore provided for information only.

Considerations include:

• Ascertain a room or space noise level and determine constructions (both walls and ceilings) required to control noise emission to an adjacent space
• Ascertain a room or space sensitivity as a noise receiver and determine constructions (both walls and ceilings) required to control noise intrusion from adjacent spaces.
• Consider airborne noise and impact (footfall) noise

The extent to which room to room noise control will have to be considered and the required acoustic rating of constructions between adjacent rooms will depend upon:

• Whether noisy activities take place in the room or space
• Whether a room on an upper floor has a hard floor surface (when considering footfall/impact noise)
• Whether a room is sensitive to noise intrusion
• The ambient noise level in the receiver room
• Whether the construction between adjacent rooms includes an operable wall, a door, a glazed section or other potentially ‘acoustically weak’ construction.

Airborne Noise

For the School Facilities Guidelines, the weighted sound reduction index (notated R_w) is the airborne noise assessment parameter. 

When a Post Occupancy Evaluation is conducted for room-to-room noise, the parameter is the apparent weighted sound reduction index (notated R_w).

The required design value of construction between adjacent rooms can only be defined when the use of both rooms is known. Refer to Tables 11.06.1 and 11.06.2.

Impact (Footfall) Noise

Refer to the guideline standardised impact sound pressure levels L_nTw values presented in Table 11.06.2. Design advice should be sought from an acoustic engineer for multi-storey buildings with noise-sensitive spaces below hard-surfaced floor areas. 

Prescriptive Constructions

The following elements have prescriptive acoustic performance or construction requirements:

• Operable walls (between general learning areas, all schools): R_w 45
• Entry doors to occupied teaching, music, drama and sports spaces: Solid core, minimum 35 mm thick with acoustic weather (where external) seals on all rebated closing faces. Gap at floor to be minimized. 
• Internal glazed sections in walls and vision panels in or adjacent to internal doors: minimum 10.38 mm laminated glass. In some situations acoustic windows may be needed for satisfactory noise separation.
• Construction separating wastewater pipework from occupied spaces: R_w 40
• Where adjacent to an occupied space (and not serving that space), hydraulic supply pipework and wastewater pipework shall be separated from the adjacent occupied space. Construction between the adjacent spaces in this instance shall be a ‘staggered stud’ arrangement or otherwise discontinuous.

Post Occupancy evaluations are often undertaken to assess the performance of recently completed or existing facilities. Where a Post Occupancy Evaluation is to be undertaken it should be conducted by the  project team or acoustic engineer and should be undertaken of selected acoustic parameters only. The following provides a guidance on the extent of work to be undertaken:

Internal Noise Levels

Generally, post occupancy evaluation of noise levels would involve short-term (typically 15 minutes to one hour) attended measurements of steady state L_Aeq noise levels in the centre of a room or space. Longer, or more detailed measurements of specific sources (e.g.: rail noise) would only generally be required;

• if the subject noise source has been identified as an issue once the building is occupied;
• if assessment and certification of a particular source (with a defined measurement procedure and duration) has been mandated for a particular project, or
• if certification is required in relation to State Environmental Planning Policies.

Measurements would take place in a room that is furnished and ready for occupation, but without people present (unoccupied).

Room Acoustics Post-Occupancy Evaluation

Generally, post occupancy evaluation of room acoustics would only take place in spaces with a specified reverberation time. Reverberation time would be reported as the arithmetic average of the measured values at 500 Hz and 1000 Hz, rounded to the nearest 0.1 of a second.

More detailed measurements and reporting (e.g. stating the reverberation time at all octave bands between 63 Hz and 8000 Hz) would only generally be required;

• if reverberation time has been identified as an issue once the building is occupied, or
• if the room or space has more detailed reverberation time requirements (e.g. teaching spaces for hearing-impaired students). 

Measurements would take place in a room that is furnished and ready for occupation, but without people present (unoccupied).

Noise Emission Post-Occupancy Evaluation

Generally, post-occupancy evaluation of noise emission would only occur if required by a condition of development consent or where noise emission (from either a stationary noise source or school activity-related noise) is identified as an issue after the room or space is occupied.

Room-to-Room Post-Occupancy Evaluation

Generally, post occupancy evaluation of room-to-room acoustic performance would take place only for airborne noise between occupied teaching spaces such as general learning areas and occupied spaces adjacent to noise producing spaces such as halls, or as directed for a particular project.

Airborne noise tests performed according to ISO 140:1998 Part 4 would be performed both ways in the case of two adjacent rooms, and the lowest R_w value reported according to ISO 717:2013 Part 1 would be reported as the result.  The measured value is considered acceptable if it is within 5 points of the guideline design value, R_w.

Measurements would take place in a room that is ready for occupation, but is not occupied.