Acoustics

Introduction

The fundamental role for any teaching and learning space or meeting room is to facilitate communication of ideas and information to an audience. The design of our spaces and the systems within them must support this by providing an environment within which appropriately prepared materials can be heard and assimilated easily.

Room acoustic design which supports intelligible communication with all participants is paramount to successful teaching. “Technology alone cannot solve the problems of reverberation, background noise and echo, which detrimentally affect so many cognitive functions. It is therefore important to ensure that the technology investment is complimented by sympathetic building and space preparation. The best technology in the world cannot deliver on its potential without appropriate support from the built environment.”

Additionally, whilst AV technology is refreshed frequently, the acoustic qualities of an individual space usually remain consistent until the entire space is rebuilt. It is important to build new spaces that support speech intelligibility throughout their design life, and to evaluate spaces to determine when their acoustics require adaptation to meet new ways of working and learning.

Well-designed acoustics are critical to the assimilation and retention of information delivered as spoken word or from recorded media in learning spaces. Designers should aim to provide an acoustic environment which enhances the listener’s experience, reducing the impacts of internal and external factors on the listening to or enjoyment of audio content. Technical managers should take an active role in the development of an organisation’s design standards and help other stakeholders appreciate the importance of good acoustics in space design.

In most teaching and meeting spaces, the discussion of acoustics has two complementary elements:

Physical acoustics deal with the properties of the room (and is described in this chapter)

  • Physical acoustics are important regardless of whether there is any AV technology in a space. The architect and acoustic consultant must work together to deliver appropriate outcomes for each space.

  • The acoustic consultant on a project is generally commissioned for their advice on the physical acoustics of the space, the control of noise from adjacent spaces, mechanical and other systems and sometimes to provide guidance on the management of construction noise and vibration impacts. Their scope will generally include calculations, modelling and advice on construction methods in order to achieve compliance with Australian/New Zealand standards, applicable educational design guidelines, and the organisation’s targets. It is vital that these considerations and appropriate standards are achieved whether or not an acoustic consultant is engaged.

  • Technical managers should engage with their facilities management teams to ensure the specific audiovisual performance criteria, appropriate standards and any organisation-specific requirements are included in their design and construction standards. It is these documents which are used to brief the design team, and information provided later may not be regarded as authoritative.

  • Technical managers should also engage with their teaching, learning and other key stakeholders to emphasise the importance of creating a suitable acoustic environment within which to communicate and share knowledge.

Electroacoustics concerns the electro-mechanical reproduction of sound (and is described in the next chapter - audio replay and PA systems)

  • The electroacoustic design requires close collaboration between the AV designer, AV consultant, the architect and usually an experienced acoustic consultant.

  • The solution will often be led by the designer of the room sound reinforcement systems, as it involves first-principles calculations and selection of active system components to achieve the target result. Scope may include electroacoustic modelling at key stages of the design, using the architectural design, accurate dimensions and surface properties.

  • Electroacoustic modelling is rarely briefed when appointing project consultants. If desired, the scope of service should be clearly described to allow selection of an appropriately experienced team.

This chapter provides an understanding of acoustics to assist readers in understanding why some rooms work better than others, and to provide valuable input to the development of briefs for capital projects and refurbishments.

Please refer to the glossary at the end of this chapter for definitions of terms related to acoustics.

Applicable standards

Standard

Title

AS/NZS 2107:2016

Acoustics - Recommended design sound levels and reverberation times for building interiors

AS/NZS ISO 717.1:2004

Rating of sound insulation in buildings and of building elements. Part 1: Airborne sound insulation

AS2021

Acoustics – Aircraft noise intrusion – building siting and construction.

IEC60268.16

Sound System Equipment part 16: Objective rating of speech intelligibility by speech transmission index

The AETM recommend professional advice from an Acoustic Consultant should be sought to design and detail the acoustic treatment required to achieve the required acoustic performance of teaching venues. The information in this chapter is provided only as guide to the design considerations needed.

Relevant Stakeholders

The stakeholders commonly involved in physical acoustics on any construction project are:

End users

  • The audience and the presenters are the primary reason for any acoustic design

Facilities management and capital projects teams

  • require finished spaces which are fit-for-purpose,

  • meet the appropriate national or international standards,

  • fit within each organisation’s targets for capital and maintenance costs

Architect and services designers

  • all members of the design team require a clear brief

  • acoustic consultants are generally the experts providing the acoustic report

  • AV/electro-acoustic designers provide feedback to design team to support the audio system to meet performance criteria

Organisational AV technical and project managers

  • Need guidance on required minimum standards and best practices

  • Should be prominent in helping to brief specific acoustic performance requirements of each space type

  • Need to budget appropriately for the design and installation of electroacoustic systems

Acoustic Briefing

Any good facility design starts with a clear design brief which will inform stakeholders from initial concept design and budgeting through to facility commissioning and handover. The brief will often be tested and may be modified throughout the project. An ill-conceived brief rarely delivers acceptable outcomes.

Identifying the requirements for each space

Many spaces are required to support multiple modes of learning as well as non-standard activities, and the criteria for these may heavily influence the physical design. Designers should strive to understand the intended use cases for each space, and brief criteria that support the most critical uses.

For example, AS/NZS2107 is the acoustic standard typically used to define background noise levels within space from building services plant and external noise ingress. This standard provides criteria based on typical uses. Where multipurpose spaces are proposed it is important that the design requirements for all modes are considered when finalising criteria for the space.

Some typical examples of the types of spaces found in education are summarised below.

Meeting and group study rooms

  • may also support audio/video conferencing

Learning spaces

  • Typical flat floor spaces have a flexible layout and may have voice amplification

  • Some small flat floor spaces may have no voice amplification

  • Collaborative/interactive group work spaces may have microphones at each group table as well as a wandering academic

  • Lecture theatres and auditoria are usually tiered or raked and almost always include voice amplification

  • Specialist spaces will have unique requirements, for example:

    • Discursive (Socratic or Harvard-style) are built to encourage discussion and debate

    • Superlabs may have multiple teaching stations with group benches flexibly assigned to each – more than one lab session may be conducted simultaneously

Multiple-use spaces, for example a teaching space may have a secondary role supporting

  • video conferencing

  • cinema/screenings

  • organisational events; and/or

  • live performances

Social learning areas

  • will usually be briefed on a project-by-project basis

Performance Criteria and User Experience

Once you’ve identified the roles each space must satisfy, you need to consider the performance criteria required to provide an appropriate user experience. Where the acoustics required for a secondary use are more critical than the general case, the tighter criteria should be applied.

For most organisations, a reasonably standardised set of criteria will be applied equally to all rooms of any type. These standardised criteria can also be applied to many specialist spaces with modification, but some use cases will necessitate departures, for example:

  • Teaching and meeting spaces fit-out with audience microphones may benefit from the application of more-stringent acoustic criteria where mix-minus systems are used

  • General acoustic criteria may apply broadly to a superlab, but must be evolved to allow the use of multiple discrete PA systems. Effective acoustic strategies that fit within the laboratory construction standards must be considered in the space design.

  • Acoustics in a lecture theatre with cinema style screening capability may need to meet SMPTE standards for playback in addition to those employed for typical lecture theatre. The specific standard required should be clearly defined during the briefing phase dependant on the needs of the cinema space or function.

Architectural & Building Services Design Considerations

Design and construction method including applied acoustic treatments

For the most common space types, it is desirable to employ a range of standard construction approaches to achieve the desired acoustic performance.

Typical advice formulated by the acoustic consultant might include:

Walls

  • Stud size and spacing

  • Thickness/density of plasterboard

  • Internal acoustic treatments

Façade/windows

  • Glazing systems

  • Extent of glass vs. solid walls

Ceilings

  • Type of ceiling (mineral tile, set plasterboard, perforated ply etc)

  • Appropriate treatment of slab in open/semi-open ceilings

  • Additional materials under roofs or plant floors

A standardised approach at any organisation helps control both capital and maintenance costs, but this must be evaluated against the unique character of each new construction project.

More complex issues or spaces will usually require multiple discrete approaches to the physical acoustics; in addition to the typical construction approaches above, including treatments such as:

  • acoustic treatments to limit noise from hydraulic or mechanical systems or other troublesome sources

  • diffusers, traps or other applied elements to control troublesome frequencies/bands

  • additional internal acoustic treatments to address problematic reflections

  • variable acoustics may be required for performance spaces to allow the room to change character to suit different types of performance

Reverberation and Reflections

What we hear comprises:

  • direct sound; that which arrives directly to our ears from the source

  • late-arriving sound; that which is reflected from various room surfaces before arriving at our ears

Reflected sound can either support or detract from the listener’s understanding of speech. One of the key factors in designing rooms to support speech is how long the reflections take to reach the listener. It is important to be aware that:

  • early reflections (<30 milliseconds) of sound largely assist with understanding

  • late arriving sound or reflections that arrive as an echo can detract from our ability to comprehend speech

Learning spaces designed in consultation with an acoustic consultant will often contain specific areas designed to reflect sound (to support speech) and areas which primarily absorb sound to control reverberation.

For critical listening spaces such as tiered lecture theatres or performance spaces the geometry of the space also plays a critical role in the acoustic performance of the space. Therefore early input from the project acoustic consultant is advisable when planning these spaces.

Background Noise

The ultimate utility and function of teaching areas is highly dependent on the control of both external and internal noise.

The following sources can be present and can increase background noise levels such that intelligibility is impacted:

  • Mechanical and hydraulic services (eg. air conditioning, plumbing, fire)

  • Noise emanating from equipment racks, projectors and other active equipment

  • Structure-borne noise and vibration from other locations in the building

  • Noise ingress from adjacent spaces, corridors, road traffic or outdoor activities (including rain, sports, events, etc.)

Rooms and buildings can be designed to reduce the ingress of noise into learning spaces, and specialist advice should be sought from an acoustic consultant to ensure that correct mitigation strategies form part of the design.

Space planners will need to consider a number of competing factors, including the relative sensitivities of each space to noise, adjacencies (the requirements areas surrounding each space) and logical ‘blocking and stacking’ of groups of spaces.

The choice of layout, construction methods, materials and finish should then be carefully guided by the space planning and the need to provide spaces with acceptable acoustic performance for the required use.

Particular care should be given to selection and detailing of walls, windows, doors and ceilings. Special treatment may be required in the vicinity of high noise zones such as plant rooms.

The acoustic consultant will need to provide a written recommendation of appropriate strategies to the architect (and other services teams) to achieve a level of ambient noise that is neither so high as to affect planned activities nor so low that users feel unnerved by the quiet.

Mechanical Services & Air Delivery

Noise from mechanical services is a common cause of degraded experience in presentation and learning spaces.

Lecture Theatres require high capacity air handling systems, which should typically operate at low velocity to minimise noise. Low velocity air handling systems invariably require larger and longer diffusers and larger ducts. This can present an acoustic and architectural challenge if not carefully planned at an early stage.

Air handling systems with local fan coil units (FCUs) mounted within the room or in the ceiling space are a potential risk to achieving the required internal noise criterion. Where practical, such units may be best relocated to outside the room envelope, or may otherwise need to be enclosed in an acoustically rated compartment designed to achieve a reduction in FCU noise.

Project engineers should take all steps to eliminate low frequency noise from mechanical plant, and to minimise the wide band noise generated by faster air flow in ducts and through diffusers. Vibration transmitted into the building from Fan Coil Units (FCUs) and other installed mechanical equipment must not cause sound levels to exceed the requirements for project-defined background noise levels or detract from the functional requirements of the space (e.g. generate projector or camera shake due to vibration).

Air handling systems with local (FCU) mounted within the room ceiling space are a potential risk to achieving the required Noise Rating (NR). Such units are best relocated if practical to outside the room envelope or otherwise fully enclosed in an acoustically rated compartment designed to achieve a reduction in FCU noise to below the room Noise Rating.

Project engineers need to take all steps to eliminate low frequency noise from mechanical plant compressors, and to minimise the wide band noise generated by faster air flow in ducts and through diffusers. Vibration transmitted into the building from FCUs and other installed mechanical equipment must not cause sound levels to exceed the requirements for Lecture Theatres NR 30 and Seminar Rooms NR30 within the band (63 to 8000 Hz).

Acoustic Design Criteria

It is important to know what constitutes acceptable acoustics for learning spaces. A range of standards are available to designers which provide definitions and measurements to ensure that spaces are acceptable.

Reverberation and Background Noise

AS/NZS2107 is the local standard which clearly defines design sound levels (LAeq) and reverberation times (RT60) for a comprehensive range of spaces in Australian and New Zealand buildings.

For most spaces there is a balance to be struck for background noise levels. Where background noise levels are too high there is potential for speech intelligibility to be impacted. However, background noise is also important for noise masking, which is an important factor in speech privacy.

Where background levels are too low, speech privacy could be impacted meaning either additional treatment is required to building partitions, or a noise masking system may be required to increase background levels. This would normally only be a consideration in a teaching environment where students are likely to be breaking into smaller project groups or in general workplace settings.

Similarly, the reverberation criteria is aiming to strike a balance between spaces being too reverberant (or lively) and too dead (or dry). A space with a higher reverberation time typically promotes higher noise levels during activity, which can impact on speech communication. Spaces which are used for dedicated audio or video conferencing may benefit from a lower reverberation time to support their functionality. Spaces with activities which result in high levels of noise may also benefit from a lower reverberation time to assist with noise control and reduce the effects of fatigue on users.

The table below from standard AS/NZS2107 summarises a range of spaces typically encountered in educational organisations. This list is not exhaustive, please refer to AS/NZS2107 for additional spaces.

Type of occupancy/ activity

Design LAeq Range (dB(A))

Design RT60 (s)

EDUCATION BUILDINGS

Art/craft studios

40-45

<0.8

Audio visual areas

35-45

0.6-0.8

Computer rooms

  • Teaching

  • Laboratories

40-45

45-50

0.4-0.6

0.4-0.6

Conference rooms

35-40

0.6-0.7

Drama studios

35-40

Curve 1*

Engineering workshops (Teaching)

<45

(Note #1)

Interview/counselling rooms

40-45

0.3-0.6

Laboratories (Teaching)

35-45

0.5-0.8

Lecture rooms up to 50 seats

30-35

Curve 3*

Lecture theatres

  • Without speech reinforcement

  • With speech reinforcement

30-35

30-40

Curve 3*

Curve 3*

(Note #3)

Manual arts workshops

<45

<0.8

Music practice rooms

40-45

0.7-0.9

Music studios

30-35

Curve 2*

(Note #3)

OFFICE BUILDINGS

Board and conference rooms

30-40

0.6-0.8

Meeting room (small)

40-45

<0.6

Video/audio conference rooms

30-40

0.2-0.4

PUBLIC BUILDINGS

Concert and recital halls

(Note #3)

(Note #3)

Courtrooms

30-35

Curve 1*

Video interview rooms

30-35

0.2-0.4

# Notes (from AS2107):

  1. Reverberation time should be minimized for noise control.

  2. Certain learning spaces, including those intended for students with learning difficulties and students with English as a second language, should have reverberation times at the lower end of the range.

  3. Specialist advice should be sought for these spaces.

  4. *Curves: Refer AS/NZS2107 Appendix A for a guide to reverberation times in these spaces.

Signal to noise ratio (SNR)

The signal (amplified or unamplified speech) to noise (all other sound) ratios at the listener position should be better than 25 dB to optimise intelligibility.

In some environments where high levels of background noise are present, this is still a good target to aim for but may not be practical (eg. 75dB background noise plus 25dB of signal would be 100dB overall, which is too loud to be comfortable for the users of the space). In these situations other alternatives such as closed-ear hearing augmentation could be considered.

It is worth noting that SNR is a generic ratio, applied to a wide range of acoustic and electrical system measurements. Therefore care must be taken to design to the correct SNR for each application.

Speech intelligibility

The audience is identified as the most important stakeholder. So it follows that unless a typical listener can clearly discern the transmitted audio and assimilate the communicated information then the acoustics may not be successful.

To be able to define the design target and to subsequently measure compliance we require a clear technical definition of intelligibility and a means of evaluating it. Intelligibility is defined in IEC60268:16 Objective rating of speech intelligibility by speech transmission.

According to the Standard,

“the Speech Transmission Index (STI) is an objective measure to predict the intelligibility of speech transmitted from talker to listener by a transmission channel.”

The standard describes intelligibility on a scale of 0 (unintelligible) to 1.0 (perfect), and plain-language labels are applied to describe performance to clients. As a general rule;

  • AETM recommends an STI design target in the ‘excellent’ band (0.75+) for all installed audio systems; however

  • an ‘excellent’ STI (0.75+) may not always be achievable in a large, tiered venue and so a minimum requirement of ‘good’ STI (0.6+) can be deemed acceptable in this category of building.

When briefing a design, technical managers should take care to ensure appropriate language is used to describe the required performance such that it is appropriate for the use cases and remains affordable by the organisation.

Testing ‘proper’ STI can be quite onerous, and the most commonly adopted implementation of IEC60268:16 is STIPA (Speech Transmission Index for Public Address Systems) which requires a far simpler test sequence and shorter testing time. The inexpensive test equipment typically found in contractor toolkits is often capable of STIPA testing.

Avoidance of acoustic anomalies

Early engagement with an acoustic consultant can be invaluable in helping avoid or minimise acoustic anomalies.

There are other potential acoustic performance issues that should be reviewed and addressed by the project’s acoustic consultant. The consultant will consider room size, shape and location of fixtures as aspects of the design that may give rise to issues of:

  • echoes or late arriving reflections

  • standing waves with resultant nodes and antinodes in the lower frequencies; and

  • focussed reflections, e.g. from curved rear walls

In addition to their general advice, the consultant may be requested to pay special attention to the geometry and proposed finishes of more critical spaces including:

  • theatres and large teaching spaces with raked or tiered seating

  • performance and function spaces

  • meeting rooms where a primary use case is video conferencing or unified communications

Electroacoustic Modelling

In some rooms, a detailed electroacoustic model may be commissioned to predict the coverage (SPL and uniformity) of amplified systems and unamplified speech in the space, as well as the STI that can be expected.

These models may be prepared in an acoustic simulation program designed to allow detailed acoustic analysis (e.g. Odeon) or in a proprietary environment (e.g. Bose Modeler). It is more common to use AFMG’s Electro Acoustic Simulation for Engineers (EASE) due to its wide user base and extensive library of speaker types. EASE also allows modelling of some infra-red assistive listening systems to test for predicted compliance with standards.

It is important to remember that modelling is a tool to validate the design. First principles calculations and the designer’s experience must still inform the type, location and power requirements of speakers. The level of detail in the model and the accuracy of surface material parameters directly affect the accuracy of the prediction, and the designer and modeller should agree the appropriate level of detail for each project.

Modelling is labour intensive and will be expensive in complex spaces. As discussed previously it cannot be assumed to be included in a standard AV or acoustics consultant’s commission. Ensure that it is documented in any scope of works that requires this specialist service.

Design methodology

New buildings

An acoustic consultant should always be included in the design team for new higher education buildings.

Acoustic design reports and/or specifications should be provided by the consultant at various design stages, with the design criteria for reverberation and noise control clearly articulated for each space type. In certain circumstances models may be developed to predict reverberation and investigate if acoustic anomalies are likely to be present.

The acoustic consultant should:

  • review the design and ‘for construction’ drawings of the mechanical services at the shop drawing stage, and prior to installation on site

  • advise the architect on required acoustic performance, as well as possible surface finishes and construction methods

  • coordinate with the electroacoustic consultant or AV designer to determine the impacts of likely sound systems on physical design

Prior to completion of the project, testing should occur to validate the acoustic performance of selected rooms against the design criteria. It is important to ensure that performance verification for background noise and reverb time is clearly defined in the scope of the acoustic consultant. Where electro-acoustic modelling is required, validation of performance criteria should also be included.

Existing buildings

An acoustic consultant is equally valuable on refurbishment projects to assess both the existing conditions and the planned modifications to each of the spaces. Especially in heritage buildings, where a good acoustic consultant can help the architect to develop acoustic treatments that complement the existing architecture.

Where an architect is not used on minor refurbishments, a suitably experienced AV consultant could perform measurements in line with the organisation’s design criteria to ascertain if there are likely to be any issues which require rectification or amelioration prior to commencement of other works. These measurements will also be helpful in guiding the electroacoustic design.

The consultant should also pay particular attention to mechanical services and hydraulic noise when evaluating the space so the organisation can consider the need for any remedial work.

Specialist spaces overview

Cinema

The standards applied to the design of sound reinforcement systems in cinemas are generally defined in SMPTE or manufacturer-specific standards (e.g. THX, Dolby) and will impose more detailed requirements than would typically apply for a presentation space.

Where a larger space is to be enhanced to provide a good quality screening environment, designers should consider both:

  • the physical acoustics of the space, aiming for cinema-like performance, and

  • designing electroacoustic systems which reflect the intent of the cinema-specific requirements to the extent possible

Also refer to: INTERNATIONAL STANDARD ISO 22234:2005 Cinematography - Relative and absolute sound pressure levels for motion-picture multi-channel sound systems - Measurement methods and levels applicable to analog photographic film audio, digital photographic film audio and D-cinema audio.

Superlab

Superlabs are large laboratory environments where multiple simultaneous classes can occur for a large number of students. They provide a challenging acoustic environment as there are no physical walls between each of the classes and extensive use of hard, reflective surfaces.

Addressing the acoustic and audio distribution challenges early in design is of paramount importance to the success of these spaces and it is essential that specialist acoustic and electroacoustic advice is sought where electro-acoustic systems are required in these less typical spaces.

Discursive spaces and Council/Senate chambers

Many new facilities will include one or more spaces intended for discussion and debate; typically

  • Discursive (a.k.a Harvard or case study rooms) are traditionally horseshoe-shaped or in-the-round; these spaces encourage cross-chamber discussion and interaction.

  • Council and Senate chambers are generally designed to support meetings of the organisation’s governing body with attendant advisors and a local audience.

Both of these space types should be designed to allow everyone to be heard clearly at conversational levels. This is best understood as peer-to-peer communication rather than just didactic (presenter-to-audience).

Whilst some form of distributed audio system is typically employed, the physical acoustics of the space must respond to the discursive/debate brief and aim to achieve high STI between each source and receiver position. Typical audio systems in these applications will target even voice lift and may comprise of:

  • individual or shared desktop microphones with local speakers

  • an array of ceiling-mounted microphones and distributed loudspeakers in flexible spaces.

These will often be augmented by lectern or wireless microphones for presenters, processed through complex mix-minus or congress system processors. In the case of multiple ceiling microphones, the physical acoustic design must account for the often large number of microphones which must be automatically processed. This is best achieved by reducing ambient and services noise as far as feasible. In learning spaces, the most critical criteria should be applied e.g. conference room rather than flat floor classroom.

Spaces with video conferencing and unified communications

With the increasing reliance on ‘soft codec’ Unified Communication (UC) systems, video conferencing technology is becoming ubiquitous. This requirement should trigger a discussion about which spaces are appropriate to be equipped, and should shift an organisation’s design criterion higher e.g. from meeting room (small) to video/audio conference room.

Typical project approach

The following is a guide towards achieving the most appropriate acoustics in an educational project.

Inception/Concept

The need for a new building may be identified some years before construction begins, and a detailed planning phase typically defines the desired number and type of learning and meeting spaces to be included.

Detailed acoustic input is unlikely at this stage, but members should work with their Facilities Management team to ensure general design standards always reflect the requirements of contemporary learning and meeting spaces.

Design and Construction

Once the project commences, the space planning will recommence and decisions affecting spaces will be made. This includes their location within the building and adjacency to plant, the façade, and other sensitive spaces.

Space planning is an iterative process, and the number and type of learning and meeting spaces will likely change several times before construction. The acoustic consultant will begin providing advice from concept design, and technical managers should take a prominent role by:

  • helping to ensure the organisation’s acoustic design criteria are defined clearly in the design standards

  • reinforcing the message to designers that an electroacoustic system is not a substitute for appropriate, optimised physical acoustics in each space

  • reviewing use cases for all proposed learning and meeting spaces, ensuring space-specific acoustic criteria have been agreed with facilities management (and clearly communicated to the project team)

  • reviewing advice and early designs to check criteria are being adopted, and to understand what performance is likely from each space. Where the performance appears unrealistic or unachievable, clarification should be sought from the design team and amendments agreed with all key stakeholders

  • reviewing testing and acceptance criteria, where appropriate, to ensure more critical spaces are verified to perform as required

  • during design and construction, several spaces will change function; and technical managers should check whether the applied criteria remain appropriate or need to change

  • technical managers should understand any as-built measurements or other testing being conducted at various stages of the project in order to identify any perceived issues as early as possible – when deficiencies can be remedied with the lowest possible cost and impact on the construction programme.

Glossary

Term

Definition

Decibel (dB)

The decibel is a relative unit of measurement used widely in acoustics. It is a logarithmic unit describing the ratio between a measured level and a reference value.

One common ratio to AV people is Sound Pressure Level (SPL).

Weightings are applied to sound pressure scales to reflect the performance of the human ear under certain conditions. Most typically encountered are:

  • A-weighting: Covers the range 20Hz-20kHz at lower sound levels

  • C-weighting: Used for high level measurements

Acoustic Consultant

Professional with specialist skills and experience in acoustics, usually commissioned to advise on the physical acoustics within a space/building and the noise and vibration issues associated with the construction process.

Designer/AV Designer

The professional or technical specialist with responsibility for designing the electronic and electroacoustic (PA) systems and coordinating with other members of the design team. May be employed by the organisation or an external consultant.

AV designer may also have responsibility for leading electroacoustic scope, where briefed.

Intelligibility

Speech intelligibility is a rating of how comprehensible speech is in a given environment.

Mix-Minus

An electro-acoustic system that is zoned and routed in such a way to allow microphones from one user to be routed to the speakers of other users for local voice lift functionality

Reverberation Time (RT60)

The reverberation time of an enclosure, for a sound of a given frequency or frequency band, is the time that would be required for the reverberantly decaying sound pressure level in the enclosure to decrease by 60 decibels

Signal to noise ratio

The difference between the measured sound level and the noise floor (all other sources). Expressed in dB

STI

The Speech Transmission Index (STI) is an objective metric ranging between 0 and 1 representing the transmission quality of speech with respect to intelligibility by a speech transmission channel

Audio Replay Systems and Public Address

Standards and Legislation

Standard

Title

AS/NZS 60065:2003

& Amendment No. 1 (January 2008)

Audio, video and similar electronic apparatus - Safety requirements

ANSI/INFOCOMM 1M-2009

Audio Coverage Uniformity in Enclosed Listener Areas

AS 60118.4-2007 Hearing aids

Magnetic field strength in audio-frequency induction loops for hearing aid purposes.

In Australia, requirements for the fitment of Hearing Augmentation systems are covered by the Disability (Access to Premises — Buildings) Standards 2010.

http://www.comlaw.gov.au/ComLaw/Legislation/LegislativeInstrument1.nsf/0/943923505EFF5F51CA2576E40008FFF9/$file/F2010L00668.pdf

System Functionality

A purpose designed audio system for teaching spaces should be installed to provide the following functionality:

  • Voice reinforcement (as a guideline the UK LTSMG Report suggests any rooms above 50 seating capacity should be considered)

  • High fidelity replay of program sources

  • Assistive listening / hearing augmentation

  • Recording (where required)

Overview of key components

Audio system components for a teaching room of 50+ students will, as a minimum, comprise of the following:

  • One or more high quality speakers installed so as to provide uniform sound coverage of the listener area;

  • Lectern microphone and provision for additional microphones to be connected;

  • Radio microphone (where specified);

  • Audio mixer to enable signal routing, level control, limiting/compression and equalisation of signals from microphones and line level audio replay equipment. The audio mixer will provide phantom power to microphones, interface to the lecture theatre control system and provide sufficient outputs for power amplifiers and recording devices;

  • High quality audio power amplifiers with overload protection;

  • Fit for purpose induction loop amplifier and room coil (AS 60118.4-2007) or other suitable assistive hearing technology: consistent with the practices/policies of the University’s special needs program. Other hearing augmentation technologies include infrared and RF systems

Large (>150 seats) or special purpose venues will have additional requirements, particularly where the venue is used for cinema studies, remote lecture telecasts/webcasts, or other theatrical activities. audiovisual representatives of the University are to be consulted on special purpose requirements as well as the general classroom requirements.

Design

The audio design shall ensure an electro acoustical system that is capable of producing adequate sound level with high intelligibility at the listener position, is stable under normal operating conditions, and is free from noise and distortion.

Effective design of the audio system and its components will require an understanding of the expected behaviour of sound in the room (refer Acoustics in Teaching Spaces). Acoustic modelling of the proposed space should be considered at an early stage of the project to provide valuable data for determining speaker type and quantity, placement, amplifier power, and expected performance against the guidelines. Computer modelling may be arranged through the Architectural Design Team, independent Acoustic Consultants, or Sound System Designers associated with major suppliers of professional speaker systems.

Speaker system options for teaching venues include, but are not limited to:

  • Single source Line Array

  • Front of House (FOH) Left-Right stereo pair

  • Distributed system (ceiling or wall)

  • Combination of FOH and distributed

  • Dolby/THX Surround system

Loudspeaker Selection and Placement

Loudspeaker type and position shall be based on achieving an effective coverage of the listening area while optimising the ‘gain before feedback’ of the microphone / loudspeaker system for the nominated presentation area. A practical electro-acoustical system design for teaching spaces should be capable of delivering an SPL of 65dBA-Slow at any listener position for amplified voice and an SPL of 85dBA-Slow for program material.

The uniformity of audio coverage shall be determined by measurement and validation standard ANSI/INFOCOMM 1M-2009: Audio Coverage Uniformity in Enclosed Listener Areas to “ensure that every listener perceives approximately the same direct sound from the sound system, no matter where the listener is positioned within the specified listening area of the sound system” . A conforming system shall achieve a tolerance window of 6dB within each of six ISO octave bands 250 Hz to 8 kHz when measured at the required test locations.

A combination of FOH and distributed speakers should be considered for medium to large venues to ensure all areas receive voice reinforcement which is direct, uniform in level and has high intelligibility. Electronic delay and speaker zoning should be considered where the delay between the sound arriving at the listener from the primary source and distributed speakers interact to significantly affect the intelligibility (STI) or spatial image of the sound source.

Smaller venues will require a minimum of two ‘front of house’ (FOH) speakers configured as a Left-Right pair for stereo imaging of program material in the primary listening area. Alternatively, a distributed ceiling speakers array may be used to provide a uniform coverage for both voice reinforcement and program content, albeit mono. Factors such as ceiling height and structure will determine the choice of speaker system.

Audio Mixing

Consideration should be given to using DSP technology for audio mixing and processing due to its inherent flexibility, cost/performance benefit and ease of external control.

The mixer shall accommodate a combination of microphone and line level sources, either as balanced or unbalanced connections. The increased use of domestic digital equipment in teaching venues requires review of practicality of connecting digital audio to audio mixers using HDMI, optical (TOSLINK) or coaxial (S/PDIF) for transfer of multichannel signals as an alternative to multiple analogue inputs.

Mixer size shall be determined by the specific requirements for microphones and replay equipment related to the use of the venue, but at least two additional inputs and outputs should be considered to enable future expansion during the operational life of the system.

Audio Inputs:

  • Lectern microphones

  • Radio Microphones

  • Conference microphones

  • Auxiliary input for Laptop Computers

  • Resident computers

  • CD / DVD players

  • Blu-ray players

  • HD/SD ‘Set top box’

  • Video conference CODECs

  • External feeds

Audio Outputs:

  • Program audio LEFT/RIGHT

  • Speech reinforcement*

  • Speech reinforcement delay channel/s*

  • Recording output

  • External feeds

* Larger venues may require multiple channels of delay for distributed speakers to achieve uniform coverage, particular where balconies are present.

Audio Recording to Lecture Recording Systems

Where audio recording is possible under the lecture recording system in use by the organisation, a line level output containing a post fader mix of all microphone and line sources should be available under the audio switching and mixing specification. This output shall be capable of supplying a balanced feed at +4dbm. If requested, an unbalanced output at -10dBm may be supplied for direct connection to the recording appliance.

Audio Equipment - System Performance

System design and gain settings should provide for a nominal operating level such that:

  • Peak or Maximum operating level (headroom) is 10 dB above nominal operating level

  • System Noise (S/N) with all inputs assigned is at least -65 dB unweighted below nominal operating level

  • Total Harmonic Distortion < 0.5% at peak operating level

  • System frequency response 50Hz – 18kHz +/- 2dB at nominal operating level

  • Nominal operating level of the electronic chain should be +4 dBm

High quality power amplifiers, matched to the power requirements of the loudspeakers, are required to achieve appropriate sound level to listener positions. Power rating should be such that at least 10dB headroom is available to handle peaks over the level required to achieve target SPL for program content. Consideration should be given to the location of the amplifier in relation to the heat generated and ventilation requirements as well as the likelihood of temperature impact on surrounding equipment. Speaker cabling should be run well clear of low level signal cabling to minimise the risk of interference and crosstalk.

Hearing Augmentation

In Australia, hearing augmentation/assistive listening systems are a requirement in all Class 9b buildings including (but not limited to) all spaces where a public address system is fitted.

The requirements are summarised in the Disability (Access to Premises — Buildings) Standards 2010 which form part of subsection 31 (1) of the Disability Discrimination Act 1992.

Other relevant standards and codes include:

  • BCA - SECTION D - Part D3 - Access for People with Disabilities

  • AS1428.5-2010 Design for access and mobility – Communication for people who are deaf or hearing impaired

  • AS60118-4. – performance requirements for hearing loops

In general, a “safe” assumption is that hearing augmentation systems are required in any University space which includes an audio reproduction system.

While a number of systems are permissible under the act, including Induction Loop, IR and RF systems, individual University Audio/Visual staff and Student Disability support staff should be consulted to determine local policies before determining the appropriate technology for particular spaces.

In University situations, classrooms are often closely adjacent and special care must be taken to ensure that the coverage fields of hearing augmentation systems do not overlap.

EWIS

Emergency evacuations systems may require room sound systems to be muted in the event of an alarm. Advice should be sought from a Fire/Electrical Engineer as to what is required of the sound system in relation to evacuation alarms/announcements.

Equipment Installation

Audio systems shall be installed in accordance with sections 2.9, 2.10, current industry best practice models (refer Infocomm AV Installation Handbook ‘The Best Practices for Quality Audiovisual Systems’) and related Australian Standards.

Grounding

Audio system noise performance may be compromised by poor management of equipment earthing. A single phase, star power earthing arrangement to the AV equipment rack or technical earth for all AV equipment within the room should be explored with the Electrical Consultant. Appropriate consultation and earthing design will minimise the potential for issues from ground loops and multiple phase connection of AV equipment. Balanced audio systems with high common mode rejection ratio (CMRR) provide maximum protection against ground loops and other sources of interference and are the preferred audio design.