Acoustics in Concert Halls
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Questions and Answers

Deep balconies can enhance a room's acoustics by improving sound distribution.

False (B)

An acoustical shadow usually forms under a wide balcony.

True (A)

A room loses reverberance because sound that goes under a deep balcony returns with enough energy.

False (B)

The ceiling height in a concert hall is often the variable that controls room volume.

<p>True (A)</p> Signup and view all the answers

The absorption profile of the under-balcony volume is similar to that of a closed window.

<p>False (B)</p> Signup and view all the answers

As audience size increases, the sound strength also increases in music performance spaces.

<p>False (B)</p> Signup and view all the answers

Acoustical warmth is achieved by increasing the high-frequency content of a room.

<p>False (B)</p> Signup and view all the answers

A concert hall with 1800 seats and a 2.4-second unoccupied reverberation time typically requires a room volume of 815,000 cubic yards.

<p>False (B)</p> Signup and view all the answers

Gypsum board, owing to its composition, absorbs low-frequency sound effectively.

<p>True (A)</p> Signup and view all the answers

Chamber music rooms are generally less loud, with G values from $9.0$ to $13.0$ decibels.

<p>False (B)</p> Signup and view all the answers

Rooms with excessive low-frequency energy are described as being acoustically 'bright'.

<p>False (B)</p> Signup and view all the answers

Opera halls are known to be more reverberant with unoccupied RT values of $1.5$ to $1.9$ seconds.

<p>False (B)</p> Signup and view all the answers

Designing a room with brick surfaces can help to achieve warmth.

<p>True (A)</p> Signup and view all the answers

Balconies are used to relocate seats away from the source of the sound.

<p>False (B)</p> Signup and view all the answers

Balconies, when protruding from the rear wall, can create stronger echoes.

<p>False (B)</p> Signup and view all the answers

Side balconies redirect sounds to the ceiling which leads to an increase in loudness.

<p>False (B)</p> Signup and view all the answers

To minimize room absorption, use massive building materials with high sound absorption coefficients.

<p>False (B)</p> Signup and view all the answers

The audience plane in a concert hall provides less than 50% of the total sound absorption.

<p>False (B)</p> Signup and view all the answers

To promote loudness for the audience, you need to increase the absorption of the audience itself.

<p>False (B)</p> Signup and view all the answers

The absorption by the audience is a function of the number of seats, rather than the area of the audience plane.

<p>False (B)</p> Signup and view all the answers

A denser, more compact audience with smaller mean distances between seats translates to less absorption for a given room occupancy.

<p>True (A)</p> Signup and view all the answers

A configuration with more and smaller audience blocks absorbs less than one with fewer and larger blocks.

<p>False (B)</p> Signup and view all the answers

The total effective absorbing area of an audience with a maximal number of blocks approaches 1.4 times the total audience area as measured in plan.

<p>True (A)</p> Signup and view all the answers

With a shallow raked audience plane, less sound will be absorbed.

<p>True (A)</p> Signup and view all the answers

Wood in concert halls should be secured to stiff, massive materials with minimized air pockets behind and using a stiff adhesive so the panel and substrate act as one element.

<p>True (A)</p> Signup and view all the answers

Long wavelengths reflect off small surfaces, therefore large surfaces do not contribute to promoting warmth in an auditorium.

<p>False (B)</p> Signup and view all the answers

Small surfaces with angles similar to adjacent surfaces can appear as one single surface to short sound wavelengths.

<p>False (B)</p> Signup and view all the answers

The bass index is calculated by taking the sound strength at 125 Hz and subtracting the average of the sound strength at 250 Hz and 1000 Hz.

<p>False (B)</p> Signup and view all the answers

Rooms with a lower bass index will likely have a higher low-frequency loudness.

<p>False (B)</p> Signup and view all the answers

Rooms used for unamplified music will need low frequency support which would likely cause amplified music to sound less boomy.

<p>False (B)</p> Signup and view all the answers

Binaural response is the sense that sound arrives from a single point, usually the center, based on our bodies symmetrical nature.

<p>False (B)</p> Signup and view all the answers

Lateral reflections from the ceiling trigger a binaural response, giving the listener a sense that they are immersed in sound.

<p>False (B)</p> Signup and view all the answers

The lateral fraction (LF) method uses a unidirectional microphone to measure sound from only one direction.

<p>False (B)</p> Signup and view all the answers

The Binaural Quality Index (BQI) uses a model head with microphones placed in anatomically correct ears.

<p>True (A)</p> Signup and view all the answers

The BQI averages the 100-Hz, 1,000-Hz, and 10,000-Hz octave bands.

<p>False (B)</p> Signup and view all the answers

The early lateral fraction typically ranges from 0.05 to 0.50.

<p>True (A)</p> Signup and view all the answers

Target LF values range from a minimum of 0.20 to a maximum of 0.45.

<p>False (B)</p> Signup and view all the answers

Higher LF values always guarantee optimal sound quality in all cases.

<p>False (B)</p> Signup and view all the answers

The most-admired concert halls measure BQI values of around 0.65, while the least-admired halls average 0.45.

<p>True (A)</p> Signup and view all the answers

The just-noticeable difference measured when subjects judge BQI values is approximately 0.165.

<p>False (B)</p> Signup and view all the answers

Early lateral reflections arriving within 80 milliseconds of the direct sound contribute to listener envelopment.

<p>False (B)</p> Signup and view all the answers

The lateral fraction measured after 80 milliseconds is used to quantify apparent source width.

<p>False (B)</p> Signup and view all the answers

Before 1960, it was generally believed that early sound was the most important factor for spatial impression.

<p>False (B)</p> Signup and view all the answers

A large apparent source width gives listeners the sense that they and the orchestra occupy distinct spaces.

<p>False (B)</p> Signup and view all the answers

Late lateral loudness (GLL) has little influence on listener envelopment.

<p>False (B)</p> Signup and view all the answers

A room with a large audience area will likely enjoy high levels of listener envelopment.

<p>False (B)</p> Signup and view all the answers

The sense of acoustic intimacy is only a function of the reverberation level of a space.

<p>False (B)</p> Signup and view all the answers

Bringing earlier early reflections can make a big room sound smaller and more intimate.

<p>True (A)</p> Signup and view all the answers

Flashcards

Reverberation Time (RT)

The amount of time it takes for sound to decay to 60 dB below its initial level in a room. Measured in seconds.

Loudness (G)

The loudness of a concert hall measured in decibels (dB). Higher G values indicate a louder hall.

Audience Absorption

The primary source of sound absorption in a concert hall, absorbing sound waves and reducing reverberation.

Sound Strength

Used to describe the amount of sound energy present in a room. It's influenced by factors like room volume, audience size, and absorption.

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Balcony

A structural feature in concert halls that repositions seats closer to the performers. It also breaks up echoes and directs sound towards the audience.

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Sound Reflection

The process of sound reflecting off surfaces in a room, contributing to the perceived loudness and reverberation of a space.

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Chamber Music Hall

A specific type of concert hall designed for smaller ensembles and featuring a shorter reverberation time and higher loudness levels.

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Opera Hall

A specific type of concert hall optimized for opera performances. It is characterized by a quieter atmosphere and a shorter reverberation time compared to other concert halls.

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Compact Audience

A dense and compact audience with fewer aisles and smaller mean distances between seats leads to less sound absorption.

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Seat Upholstery and Absorption

Audience seats with thicker upholstery absorb more sound than seats with thinner upholstery.

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Audience Block Edges

The exposed sides of audience blocks, like the edges facing aisles, act as additional sound-absorbing surfaces.

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Raked Audience Plane

A steeply raked audience plane, where the seats slope dramatically upwards, leads to more sound absorption due to the geometry of sound wave spreading.

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Effective Absorption (Minimal Blocks)

The effective sound absorption of an audience with minimal seating blocks is approximately 1.1 times the actual audience area.

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Effective Absorption (Many Blocks)

The effective sound absorption of an audience with many seating blocks and aisles is approximately 1.4 times the actual audience area.

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Older Hall Design

Successful older concert halls often benefit from a compact audience configuration due to smaller audience size and comfort expectations.

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Acoustical Shadow

A deep balcony can negatively affect room acoustics creating an "acoustical shadow" underneath the overhang. This shadow reduces the sightlines and hinders sound reverberation by absorbing sound energy.

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Acoustical Warmth

The perceived fullness and richness of low-frequency sounds in a room. This is often considered desirable for unamplified music.

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Reverberation

The amount of time it takes for sound to decay in a space. It contributes to the overall character of the room's sound.

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Gypsum Board Absorption

Gypsum board, especially lightweight varieties, significantly absorbs low-frequency sounds (around 125 Hz) due to its panel absorber properties. This absorption can lead to a lack of warmth in a room.

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Acoustically Dark

Rooms with excessive low-frequency energy, contributing to a muffled and unclear sound quality.

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Sightlines

This refers to the ease with which people can see the stage or performance area from their seats.

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Material Selection

Materials used in a room can influence the overall sound quality. Brick, stone, and concrete are generally better for retaining low-frequency sound compared to gypsum board, which absorbs it.

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Warmth (Room Acoustics)

The perceived warmth of a room, usually judged by the relative strength of bass frequencies to mid-range frequencies. Warm rooms have a more pronounced bass response compared to their mid-range frequencies.

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Bass Index

The difference in sound strength at 125Hz (G125) minus the average sound strength at 500Hz and 1000Hz (Gmid). A higher bass index indicates a warmer acoustic environment.

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Spatial Impression (Room Acoustics)

The perception that sound is coming from all directions, creating a sense of immersion in the musical experience. This is often achieved through lateral reflections from side walls.

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Lateral Reflections in Concert Halls

In a concert hall, sound sources are perceived by the listener coming from the sides. This is due to the placement of our ears and how sound waves interact with our bodies.

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Binaural Quality Index (BQI)

A measure that quantifies the quality of a concert hall, encompassing factors like clarity, envelopment, reverberance, and intimacy. A high BQI suggests a great concert hall.

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Wood Paneling in Concert Halls

To achieve the desired warmth in a concert hall, wood paneling should be adhered to rigid materials to avoid sound reflection variations.

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Large Reflective Surfaces

In order to reduce sound reflection variations from segmented surfaces, large, smooth reflective surfaces are preferred for promoting warmth.

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Warmth and Amplified Rooms

For concert halls, warmer acoustics are desired. But in rooms with loudspeakers, the warmth would create excessive 'boominess'. This warmth can be digitally added in amplified rooms when desired.

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Lateral Fraction (LF)

A measurement used to quantify the spatial impression of a room, representing the proportion of sound arriving from the sides relative to the total sound.

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Typical Lateral Fraction Range

The range of lateral fraction values typically observed in rooms.

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Target Lateral Fraction Values

The ideal range of lateral fraction values for concert halls.

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BQI Range in Concert Halls

The minimum and maximum BQI values found in highly admired and least admired concert halls, respectively.

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Just-Noticeable Difference (BQI)

A measure of how much a change in BQI is noticeable to listeners.

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Lateral Fraction and BQI near Side Walls

The expected relationship between lateral fraction and BQI near side walls.

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Acoustical Quality and Side Wall Proximity

The relationship between side wall proximity and acoustical quality despite increased lateral fraction and BQI.

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Apparent Source Width (ASW)

Early lateral reflections arriving within 80 milliseconds after the direct sound create a sense of the sound source's width. It makes the sound feel wider and more spacious.

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Listener Envelopment (LEV)

Late lateral reflections arriving after 80 milliseconds contribute to a feeling of envelopment, where the sound seems to surround the listener.

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How does ASW affect the listener's experience?

A wide apparent source width (ASW) makes the listener feel like they're part of the performance, creating a feeling of unity between the listener and the orchestra.

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What influences LEV?

The late sound, which contributes to listener envelopment (LEV), is heavily influenced by the late lateral loudness.

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How does audience size impact listener envelopment?

Rooms with smaller audience areas tend to have higher levels of listener envelopment because there's less absorption of the late sound.

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Early reflections and intimacy

Early reflections arriving soon after the direct sound contribute to a sense of acoustic intimacy, making a large room feel smaller and more personal.

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How can designers create a sense of intimacy in a big room?

By bringing earlier early reflections, designers can make a large room sound more intimate and less cavernous.

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What factors determine acoustic intimacy?

A room's size and shape alone do not determine its acoustic character. The arrival time of sound reflections plays a crucial role in determining the perceived intimacy.

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Study Notes

Room Acoustics Qualities - Loudness

  • Concertgoers desire equal sound energy distribution across an auditorium, but sound levels vary greatly depending on the venue.
  • Halls with fewer than 1,000 seats may experience excessive loudness, contrary to most larger halls, which aim for increased sound energy per seat.
  • Halls with more perceived loudness often exhibit less sound absorption, more early reflections, and shorter distances between stage and seating.

Room Acoustics Qualities - Loudness (Formula for reflected sound pressure level)

  • The sound pressure level resulting from reflections can be estimated using this formula: Lp reflected = Lw sound power + 10·log (4/ (room constant * RT * 0.174r))

  • Where:

  • Lp is the sound pressure level from room reflections

  • Lw is the source sound power level of the orchestra

  • A is the total absorption in metric sabins (sq. meters times absorption coefficient).

  • r is the distance from the source to the receiver in meters

  • RT is the reverberation time

  • The sound pressure level is influenced by orchestra volume, room reflectivity, reverberation time, and proximity to the orchestra.

Room Acoustics Qualities - Loudness (Measuring Sound Strength)

  • Acoustic quality "loudness" is measured by sound energy at a listener position in comparison to the same sound source at ten meters in an open space.

  • The value is represented as G with a + or - decibel (dB) indicator.

Room Acoustics Qualities - Loudness (Minimizing Room Absorption)

  • Minimize massive building materials with low sound coefficients.

  • Minimize sound-absorbing surfaces (such as curtains).

  • Minimize the total area of surfaces exposed to sound.

  • The audience plane accounts for between 50-90% of total sound absorption.

  • Seat construction and upholstery material impact sound absorption significantly.

Room Acoustics Qualities - Loudness (Absorption by Audience)

  • Sound absorption by the audience depends on the surface area of the audience plane, not just the number of seats.
  • Denser, more compact seating configurations lead to less audience absorption for a given seating capacity.
  • Audiences with shorter distances between seats affect overall absorption levels.
  • Audience configuration's shape impacts sound absorption.

Room Acoustics Qualities - Geometry of the Volume

  • Steeply raked audience planes result in better sound absorption due to sound waves better approximating a plane perpendicular to their path.
  • Flatter audience planes facilitate sound reflection off various room surfaces.

Room Acoustics Qualities - Geometry (Optimizing Loudness)

  • Reduce the distance between the source and receiver positions of seats.
  • Minimize total surface area of room surfaces.
  • Maximize early direct sound arrival.

Room Acoustics Qualities - Loudness (Balconies)

  • Balconies relocate seats, bringing them closer to the music source.
  • They disrupt rear walls, diminishing echo potential.
  • Balconies redirect sound downwards, improving perceived volume.
  • Balconies are less effective and can be damaging if they create a large overhang, leading to an acoustical shadow.

Room Acoustics Qualities - Geometry (Balconies and Loudness)

  • Large balcony overhangs produce an acoustical shadow, reducing sound reflected through this space.
  • Shallow balconies allow for overhead reflection, improving perceived loudness.

Room Acoustics Qualities - Spatial Impression (Binaural Qualities)

  • People experience sound differently depending on the sound's direction of origin.
  • Sidewall reflections trigger binaural response (the perception of sound arriving from surrounding directions).
  • Spatial impression is heavily affected by the room geometry, especially the position and angle of sound reflecting surfaces.

Room Acoustics Qualities - Spatial Impression (Methods)

  • Lateral fraction (LF) evaluates the percentage of sound arriving from the sides.
  • It is a ratio of the sum of sound levels from two opposite directions, to the overall sum from all directions.
  • BQI (Binaural Quality Index) calculates correlation between sound level at both ears, using a model head.
  • The higher the proportion of side-arriving sound to total sound heard, the stronger the sense of spatial impression

Room Acoustics Qualities - Spatial Impression (Calculating BQI and LF)

  • LF metric is calculated by measuring sound at 125 Hz, 250Hz, 500Hz and 1000 Hz

  • BQI averages for 500Hz, 1000 Hz, and 2000 Hz

  • Higher values are interpreted as a strong sense of spatial impression

Room Acoustics Qualities - Intimacy

  • Big rooms typically sound larger than smaller rooms.

  • The time between the direct sound and its first reflection (ITDG) influences the perceived sound intimacy.

  • Shorter ITDG values signify more intimate listening environments.

  • Fan shaped rooms tend to create less of a sense of intimacy than rectangular rooms.

Room Acoustics Qualities - Warmth

  • Listeners prefer low frequency sound when listening to un-amplified music (robust low-frequency content).

  • Wall and ceiling panel configurations act as sound absorbers and impact the low-frequency response.

  • Rooms lacking adequate low-frequency reverberation feel un-warm.

  • Rooms with excessive low-frequency energy sound "dark".

Room Acoustics Qualities - Warmth (Bass Index)

  • Warmth is evaluated using the bass index.
  • The bass index compares the G value at 125Hz (G125), to the average G value at 500Hz, and 1000 Hz (Gmid).
  • Higher bass indices suggest warmer rooms.

Room Acoustics Qualities - Warmth (Materials Selection)

  • To achieve warmth in a space, consider more massive and solid material in construction

  • Lightweight materials generally absorb more low frequencies.

  • Gypsum board absorbs low frequency sounds much more effectively than concrete or masonry.

Room Acoustics Qualities - Concert Hall Types (Geometry)

  • Shoebox-shaped halls are good for promoting lateral reflections while providing a sense of a broad sound.
  • Fan-shaped halls help sound arrive closer from the stage.
  • Surround (Terraced halls) help create a sense of intimacy.
  • Reverse-fan shaped halls also enhance sound reaching the audience by directing reflecting off side walls.

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Description

Explore the fascinating world of acoustics in concert halls and performance spaces. This quiz covers concepts such as sound distribution, reverberation, and the impact of room geometry on acoustical properties. Test your understanding of how various factors influence sound quality in music venues.

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