Auditorium Acoustic Design: The Complete Guide (2026)

By Daniel Natoli, Director, AKA Acoustics (MAAS, MAES). Last updated: 26 June 2026

Auditorium acoustic design is the engineering of a room to four measured targets at once: a Speech Transmission Index held above 0.60 at every seat, uniform early-reflection support (C50) across the seating plane, a reverberation time set to the room's volume per AS/NZS 2107, and a background-noise floor that preserves the speech-to-noise margin. Each target is specified, then verified by measurement, not asserted.

No single number fits every auditorium; the right reverberation time scales with room volume and use. A speech auditorium runs short and a concert hall runs long, and the same room measures roughly 0.3 s shorter full of people than empty. This page explains what makes an auditorium acoustically good, what reverberation and background-noise targets apply by use, how speech rooms and music rooms pull in opposite directions, how a multipurpose hall resolves that tension with variable acoustics, how you isolate the room from the foyer, plant and street, what it costs, and who can carry the whole job from brief to a measured result. AKA Acoustics is a Sydney acoustic design, build and supply firm: one team, one contract, one guarantee, with no handover from consultant to contractor.

What makes an auditorium acoustically good?

A good auditorium meets four parameters simultaneously: a Speech Transmission Index above 0.60 sustained to the rear rows; uniform sound-pressure coverage with early reflections inside 50 ms reinforcing the direct sound rather than returning as discrete echoes; a reverberation time set to room volume on the AS/NZS 2107 curve, not merely minimised; and a background-noise level low enough to hold the speech-to-noise margin under plant and traffic load.

The four properties are linked, and intelligibility is the headline result, measurable on the Speech Transmission Index. Reverberation that suits a lecture would smear an orchestra, and reverberation that flatters an orchestra would blur speech, so "good" is always relative to use. Even coverage depends on room shape and surface treatment placing early reflections where they reinforce the talker rather than arrive late as echoes. Background noise sets the floor the talker has to rise above: the standard that puts a number on the result is IEC 60268-16:2020, the Speech Transmission Index. STI runs 0.00 to 1.00, where above 0.60 is good and 0.45 to 0.60 is fair, and a noisy room drags that figure down. The point for a buyer is that "good" is not a finish you can see, it is a set of numbers the finished room has to hit.

What reverberation time should an auditorium have?

It depends on room volume and use, which is why no single figure is correct. Reverberation scales with volume over absorption, the Sabine relationship, so the target rises with room size; speech rooms are set shorter than music rooms; and audience absorption pulls the occupied result roughly 0.3 s below the empty room. AS/NZS 2107 gives the volume-dependent curve, consistent with established room-acoustics practice such as DIN 18041, not a fixed number.

The mechanism is straightforward. A bigger room holds more air and more reflecting surface, so sound takes longer to decay, and the standard's curve rises with volume to suit. Speech needs a short reverberation so consonants do not overlap, while music wants a longer tail for warmth and envelopment. The table below sets a reverberation ladder by use, at mid frequencies (500 to 2000 Hz), from AS/NZS 2107:2016, consistent with established room-acoustics practice such as DIN 18041. The exact figure for a given room depends on its volume and is read from the standard against the real room.

Two cautions a buyer should hold. First, always ask whether a quoted reverberation time is occupied or unoccupied, because the audience changes it by about 0.3 s and the two figures are not interchangeable. Second, concert, recital and opera spaces sit at the specialist end where the standard defers to dedicated advice, so treat the longer values above as a starting point, confirmed by specialist design rather than read off as a fixed target.

How is a lecture theatre different from a drama theatre or a concert hall?

Speech and music pull the reverberation target in opposite directions, and that tension is the core design decision. A lecture theatre runs short, about 0.7 to 1.0 s, to hold a high clarity index (C50) and a Speech Transmission Index above 0.60. A concert hall runs long, about 1.8 to 2.2 s, to build reverberance and bass ratio for warmth and envelopment, at the cost of consonant clarity. A drama theatre sits between the two, and the theatre guide covers it in full.

The reason is physical. Speech carries meaning in fast consonants, and a long reverberant tail lets one syllable overlap the next, so intelligibility falls. Music carries emotion partly in sustain, blend and lateral energy, and a longer tail lets notes merge and fill the room. Push a lecture theatre toward concert-hall reverberation and the lecture becomes hard to follow; push a concert hall toward lecture-theatre reverberation and the music sounds dry and small. This is why the single most important early decision in auditorium design is naming the room's dominant use, because it sets the reverberation target, and the reverberation target sets the absorption budget, the seating, and the surface treatment. The drama end of this spectrum, where staging, sightlines and the spoken voice all shape the brief, is covered in our guide to theatre acoustic design. Where a room genuinely has to serve both speech and music, splitting the difference fails; the answer is variable acoustics, covered next.

How do you design one room for both speech and music?

You build variable acoustics into a multipurpose hall so it hits two reverberation targets, not one compromise figure. Movable absorption such as retractable banners and curtains, adjustable reflectors, coupled volumes, and electronic enhancement let the room change its reverberation for the night's use, set short to protect speech intelligibility and long to build the reverberance and C80 balance music wants, rather than fixed at one value that suits neither.

The trap a multipurpose hall has to avoid is the fixed compromise, a reverberation around 1.3 to 1.5 s that is too long for clean speech and too short for rich music, satisfying nobody. Variable acoustics escapes the trap by making absorption and reflection adjustable. Deploying heavy drapes or rotating absorptive panels into the room pulls the reverberation down for a conference or a play; retracting them, and opening a coupled reverberation chamber, lets the tail lengthen for an orchestra. Some halls add electronic enhancement to extend reverberation beyond what the physical room gives. The design job is to set the two end-state targets, a short speech setting and a longer music setting measured on reverberation time and early decay time (EDT), then size the variable elements to move cleanly between them. Done well, one room genuinely serves a lecture on Tuesday and a recital on Wednesday, each at its own correct reverberation, which a single fixed room cannot.

What background-noise level should an auditorium have, and why does it matter?

Low enough that plant, ventilation and outside traffic never mask speech, set by use. Typical design sound levels from AS/NZS 2107:2016: a drama or theatre auditorium around NC-25 (about 30 to 35 dB(A)); a lecture theatre with speech reinforcement around NC-30 (about 30 to 40 dB(A)); a cinema auditorium around NC-25 (about 30 to 35 dB(A)) per ISO 9568.

The mechanism is the speech-to-noise ratio. Speech arrives at roughly 46 dB(A) at the listener; an NC-30 background sits near 36 dB(A), leaving about a 10 dB margin. Speech Transmission Index holds while that margin stays near or above 10 to 15 dB and degrades as it narrows: under IEC 60268-16, a background near NC-25 supports good intelligibility while one near NC-40 pulls it toward fair. This is why the in-design target is set tighter than the operational limit, about NC-23 to land NC-25, because real plant and real occupancy erode the margin. Background noise reaches the room by three paths, the foyer, the plant room and the street, and controlling it is as much an isolation problem as a quietness problem.

How do you stop noise from the foyer, the plant room and the street getting into the auditorium?

You isolate the three intrusion paths separately: the envelope against street noise, the plant and HVAC against mechanical noise, and the foyer against crowd and circulation noise. Sound insulation is rated by Rw and Rw+Ctr (airborne) and Ln,w (impact) in the laboratory, then verified in the finished building as field values, Dn,T,w, where flanking paths around a partition often govern the as-built result. The National Construction Code sets mandatory minimums between occupancies, distinct from the recommended in-room targets in AS/NZS 2107:2016.

This is the axis where regulation bites. AS/NZS 2107:2016 reverberation and background-noise targets are recommended, not mandatory, unless written into a development consent, whereas the NCC/BCA sets enforceable airborne (Rw+Ctr) and impact (Ln,w) minimums between occupancies and dwellings. The practical work is the same craft in three places: a heavy, sealed envelope to keep traffic out; an HVAC noise budget and isolated plant so air handling does not add to the floor; and acoustic doors and a sound lock or lobby between foyer and house so circulation noise does not leak in during a performance.

On a northern-beaches live-music hotel, AKA designed and field-measured the isolation: a boundary door specified at Rw 48 against an Rw 46 requirement carried the airborne separation, and a measured event found that adding 140 patrons lifted the L10 by only 2.4 dB. The reinforcement system, not the headcount, set the level, so control was applied at the source through a locked-gain limiter rather than at the crowd. An auditorium's isolation is the same work held to the same standard: controlled at the source and proven by measurement, from brief to a verified result.

Who designs auditorium acoustics in Australia, and what does a design-and-build firm do differently?

In Australia, most acoustic firms specify the targets and hand the drawings to a separate builder, so the specifier never controls the workmanship that determines whether the as-built room meets the number. The predictable failure points then sit with no single owner: flanking paths left uncontrolled, seals and mass substituted on site, absorption coefficients not achieved in the install. A design-build-measure firm closes that loop, owning the specification, the construction and the ISO 3382 verification.

That gap is the failure mode owners describe most. A consultant specifies a reverberation and background-noise target, a builder constructs to the drawing, and when the measured room misses, the consultant points at the build and the builder points at the spec. The client holds a room that does not perform and a dispute about whose fault it is. Single accountability removes the seam, one team owns the design, the build and the measured outcome, with no one to blame but the team that owns the number. AKA Acoustics works this way, and adds supply to the model, so the acoustic products specified into a room are the ones the team sources, installs and stands behind. Studio-born, delivery-minded: the work is not done when it is built, it is done when it performs.

How do I know the finished auditorium will actually hit the target?

You prove it by measurement. The finished room is measured to ISO 3382, which defines how reverberation time (T20, T30 and EDT) and the clarity metrics (C50 for speech, C80 for music) are surveyed and reported with stated accuracy, documented in full. The principle is simple: designed to AS/NZS 2107, measured to ISO 3382. A target without a measured as-built record is an opinion.

AKA applies that same measured discipline to its critical-listening rooms. On a Sydney Dolby Atmos post-production theatre, designed and built inside an existing shell, the finished room returned a measured NC-20 against an NC-25 requirement and a T30 of 0.17 to 0.20 s from 500 Hz to 8 kHz, modelled in DART, isolation calculated in INSUL, and confirmed in REW from a 20 Hz to 24 kHz log sine sweep, captured on a Class 1 microphone and spatially averaged over 18 positions. An auditorium's background-noise and reverberation targets are held to that same standard, from brief to a measured result.

What does auditorium acoustic design cost?

Cost scales with scope; there is no fixed price band for an auditorium, because it depends on room size, dominant use, distance from targets, and whether variable acoustics and isolation works are needed. The honest entry point is a half-day diagnostic acoustic audit at $1,500 to $4,000, which scopes the brief and the gap before a design fee is set.

A diagnostic audit measures the current room or assesses the design, defines the reverberation, background-noise and isolation targets, and produces a scoped fee proposal grounded in the actual brief. From there, cost is driven by the same factors that drive any acoustic build: the volume of the room, the depth of isolation the envelope and plant require, and the amount of variable or fixed treatment the reverberation target demands. The next step for any auditorium brief is an early-stage acoustic review before the design is locked. Talk to our team.

Is acoustic design mandatory for an auditorium?

Partly. The AS/NZS 2107:2016 reverberation and background-noise targets are recommended, not mandatory, unless a development consent writes them in as a condition. The National Construction Code sound-insulation minimums (Rw+Ctr airborne and Ln,w impact) between occupancies are mandatory. So the in-room comfort targets are best practice you choose to meet, while the isolation minimums between tenancies are law.

In practice the two work together. A council or certifier may make an AS/NZS 2107 reverberation or noise condition binding through development consent, at which point the recommended target becomes a compliance obligation for that project. The NCC minimums apply regardless, as the regulatory floor for amenity between occupancies. The distinction matters for budgeting and risk: treat the NCC isolation minimums as non-negotiable, and treat the AS/NZS 2107 in-room targets as the performance brief that makes the auditorium actually usable, whether or not consent has made them mandatory.

Frequently asked questions

What reverberation time should an auditorium have? It depends on room volume and use, so there is no single correct figure. Reverberation scales with volume over absorption, the Sabine relationship, so the target rises with room size; speech rooms are set shorter than music rooms; and audience absorption pulls the occupied result roughly 0.3 s below the empty room. Typical mid-frequency figures from AS/NZS 2107:2016: a lecture theatre about 0.7 to 1.0 s; a drama theatre about 1.1 to 1.2 s unoccupied; a multipurpose hall about 1.3 to 1.5 s; opera about 1.3 to 1.5 s; a concert hall about 1.8 to 2.2 s, where the standard defers to specialist advice. Always check whether a quoted figure is occupied or unoccupied.

What makes an auditorium acoustically good? A good auditorium meets four parameters at once: a Speech Transmission Index above 0.60 sustained to the rear rows; uniform coverage with early reflections inside 50 ms reinforcing the direct sound (C50) rather than returning as echoes; a reverberation time set to room volume on the AS/NZS 2107 curve, not merely minimised; and a background-noise floor low enough to hold the speech-to-noise margin. Intelligibility is the headline result, measurable under IEC 60268-16:2020, where STI above 0.60 is good and 0.45 to 0.60 is fair.

How is a lecture theatre different from a drama theatre or a concert hall acoustically? Speech and music pull the reverberation target in opposite directions. A lecture theatre runs short, about 0.7 to 1.0 s, to hold a high clarity index (C50) and a Speech Transmission Index above 0.60. A concert hall runs long, about 1.8 to 2.2 s, building reverberance and bass ratio for warmth and envelopment, at the cost of consonant clarity. A drama theatre sits between, about 1.1 to 1.2 s unoccupied. Naming the room's dominant use is the first design decision, because it sets the reverberation target.

How do you design one room for both speech and music? You build variable acoustics into a multipurpose hall so it hits two reverberation targets rather than one compromise. Retractable absorption such as banners and curtains, adjustable reflectors, coupled volumes, and electronic enhancement let the room run short to protect speech intelligibility and long to build the reverberance and C80 balance music wants. The trap to avoid is a fixed compromise around 1.3 to 1.5 s, too long for clean speech and too short for rich music. The design job is to set the two end-state targets, measured on reverberation time and early decay time (EDT), and size the variable elements to move cleanly between them.

What background-noise level should an auditorium have, and why does it matter? Low enough that plant, HVAC and outside noise do not mask speech, with the target set by use. Typical design sound levels from AS/NZS 2107:2016: a drama or theatre auditorium about NC-25 (30 to 35 dB(A)); a lecture theatre with speech reinforcement about NC-30 (30 to 40 dB(A)); a cinema auditorium about NC-25 (30 to 35 dB(A)) per ISO 9568. The mechanism is the speech-to-noise ratio: speech arrives near 46 dB(A) and an NC-30 background near 36 dB(A), leaving about a 10 dB margin, and intelligibility holds while that margin stays near or above 10 to 15 dB. The in-design target is set tighter, about NC-23 to land NC-25 in operation.

How do you stop noise from the foyer, the plant room and the street getting into the auditorium? You isolate the three intrusion paths separately: the envelope against street noise, the plant and HVAC against mechanical noise, and the foyer against crowd and circulation noise. Sound insulation is rated by Rw and Rw+Ctr for airborne and Ln,w for impact in the laboratory, then verified on site as field values (Dn,T,w), where flanking paths around a partition often govern the as-built result. The National Construction Code sets mandatory minimums between occupancies, distinct from the recommended in-room targets in AS/NZS 2107:2016. The practical tools are a heavy sealed envelope, an HVAC noise budget with isolated plant, and acoustic doors with a sound lock between foyer and house.

Who designs auditorium acoustics in Australia, and what does a design-and-build firm do differently? Most Australian acoustic firms specify the targets, then hand the drawings to a separate builder, so the specifier never controls the workmanship that decides whether the as-built room meets the number. The predictable failure points then sit with no single owner: flanking paths left uncontrolled, seals and mass substituted on site, absorption coefficients not achieved in the install. A design-build-measure firm such as AKA Acoustics closes that loop, owning the AS/NZS 2107 specification, the construction, and the ISO 3382 verification, so one team owns the design, the build and the measured outcome.

How do I know the finished auditorium will actually hit the target? By measurement to ISO 3382, which defines how reverberation time (T20, T30, EDT) and the clarity metrics (C50 for speech, C80 for music) are surveyed and reported with stated accuracy, documented in full as an as-built record. The principle is: designed to AS/NZS 2107, measured to ISO 3382. AKA proves that discipline in its critical-listening work, including a Sydney post-production theatre held to a measured NC-20 against an NC-25 requirement and a T30 of 0.17 to 0.20 s, confirmed in REW on a Class 1 microphone spatially averaged over 18 positions.

What does auditorium acoustic design cost? Cost scales with scope and there is no fixed band for an auditorium, because it depends on room size, dominant use, distance from targets, and whether variable acoustics and isolation works are needed. The honest entry point is a half-day diagnostic acoustic audit at $1,500 to $4,000, which scopes the brief and the gap before a design fee is set. From there, cost is driven by room volume, isolation depth and treatment.

Is acoustic design mandatory for an auditorium? Partly. The AS/NZS 2107:2016 reverberation and background-noise targets are recommended, not mandatory, unless a development consent writes them in as a condition. The National Construction Code sound-insulation minimums between occupancies are mandatory. So the in-room comfort targets are best practice unless consent makes them binding, while the isolation minimums between tenancies are law.