ARBUTIL: Module 5

ACOUSTIC DESIGN

1. Site selection

2. Space planning

3. Noise Control

4. Room sizing and design

5. Selection and application of materials

ACOUSTIC DESIGN CONSIDERATIONS (1-5)

ACOUSTIC DESIGN

Requirements

1. Consider ideal reverberation time

2. External and internal noise levels should be reduced

3. Proper size and shape of a room for diffusion, absorption, and reflection of sound

4. Reinforcing sound levels for all parts of a room

airborne noise and structure borne noise

Sound Generation Intrusive Noise due to:

Damping

To reduce the effects of stiffness

ROOMS FOR SPEECH

Considerations

1. Adequate loudness

2. Relatively uniform sound level

3. Appropriate reverberation characteristics

4. High signal-to-noise ratio

5. Low background noise levels

6. Free from acoustical defects such as long delayed reflections, echoes, focusing, and resonance

ROOMS FOR SPEECH

Loudness

• Distance between the source and receiver should be controlled

• Circular seating area minimizes the source-receiver distance

Grazing attenuation

Control ______ ______ (occurs when an acoustic wave interacts with an absorbing surface at a shallow angle of incidence)

Floor Slope' / sloping floors

can provide adequate sight lines and listening conditions

Arrival point of sight (APS)

lowest point of interest on stage

ROOMS FOR SPEECH

Sound Distribution

• Place hard surfaces in positions where they can distribute sound to the audience

• Reflectors must have sufficient size that they scatter the frequencies of interest and should be close enough so that the reflection delay time is less than 30 to 50 msec.

ROOMS FOR SPEECH

Sound Distribution

• A hard ceiling is preferred in a lecture hall and auditorium (50–500 seats).

• In small classrooms (< 50 seats) the direct field provides sufficient loudness and control of reverberant noise, an absorptive ceiling is enough

ROOMS FOR SPEECH

Sound Distribution

• Panels should not be used to reflect sound directly down, or back to the listener from behind

Reverberation

The more speech content there is to the sound, the lower the ideal _______ time

ROOMS FOR SPEECH

Signal-to-Noise Ratio

Background noise levels in small classrooms and lecture halls are designed to an NC 30 (35 dBA) and larger auditoria to an NC 25 (30 dBA)

Flutter echoes

are sounds that persist locally due to multiple reflections between parallel planes, concave, or chevroned surfaces

Flutter echoes, Coloration, Focusing, Shadowing

Acoustical Defects

Coloration

is the emphasis of certain frequencies or frequency bands over others, caused by room-mode buildup or by absorptive materials that only absorb in certain frequency ranges

ROOMS FOR SPEECH

Acoustical Defects

Focusing

is the buildup of sound energy in localized regions of a room, due to concave surfaces

Shadowing

is the blockage of sound traveling from the source, or from a significant reflecting surface, to the receiver.

Conference Rooms

• Ceiling above the table should be low, hard and flat.

• The area of reflective ceiling does not need to extend beyond the seating area

• Outside this area the ceiling may be absorptive, diffuse, or recessed

• Floors should be carpeted and absorption applied to the middle and upper portions of the walls

Classrooms

• Reverberation times should be less than 0.8 seconds for good intelligibility

• In small ______ the ceiling is the only absorptive surface.

• This requires a ceiling material of acoustical tile having an NRC of 0.8 or above for a ceiling height of between 2.7 and 3.6 meters

Small Lecture Halls

• Fan-shaped rooms bring the seats closer to the front whereas a rectilinear shape provides a more frontal view of the display areas

• Carpeted aisles are helpful in controlling the footfall noise due to latecomers.

• Automatic door closures without latches help to muffle the sounds of entry doors.

Small Lecture Halls

• As a room grows larger the direct field should be augmented with early reflections from hard surfaces.

• A stepped or sloped floor, along with a raised platform for the talker, aids in the useful reflections and reduces grazing attenuation

• Absorptive panels should be applied to the rear and side walls of the room to control reverberation and lateral reflections

(a 1:12 slope is sufficient)

The ceiling above the podium and the side walls surrounding the podium can be slanted ____________ to avoid flutter echo

ROOMS FOR SPEECH

Large Lecture Halls

In the case of large conference rooms, small auditoria, lecture halls, and legitimate theaters, a relatively low hard ceiling is preferable to an absorbent one.

1.8 to 2.0

Reverberation times in concert halls range from 1.5 to 2.2 seconds with preferred values between _______ seconds.

Concert Halls

• High ceiling (15m or more) and diffusive, with cofferred patterns having deep (15 cm) fissures

An opera house

is a mix of a legitimate theater and a concert hall, which constrains the design more than a pure concert hall. The stage house must be deep, with considerable wing space for set movement and storage

ROOMS FOR MUSIC

Opera Houses

The fly tower above the stage, which accommodates the lifting of sets, is about one and a half times the height of the proscenium opening above the top

of the arch.

ROOMS FOR MUSIC

Opera Houses

• The orchestra is seated in a pit below the stage to balance the level between the singer and the orchestra

• The conductor, who must be visible to both the orchestra and the vocalists, stands with his head just at stage level.

30m from the stage

• In an Opera House, The furthest seat is no more than __ meters and 30◦ from the nearest side of the stage opening.

• Smaller rooms are preferred since the vocal effort required of the singers is much less.

forestage

Walls surrounding the _______are often nearly parallel and decorated with large

ornate elements such as columns and balconies.

• The audience should feel enveloped or surrounded by the sound.

• The room should support instrumental sound by providing a reverberant field, whose duration depends on the type of music being played.

• There must be clarity and definition in the rapid musical passages so that they can be appreciated in detail.

ROOMS FOR MUSIC - General Design Parameters

• ( above 2600 seats)

In General Design Parameters, sound must have adequate loudness that is evenly distributed throughout the hall. When the number of seats becomes excessive ___________-, loudness and definition are reduced.

ROOMS FOR MUSIC - General Design Parameters

• A wide bandwidth must be supported. Musical instruments generate sounds from 30 Hz to 12,000 Hz, which is much broader than the speech spectrum.

• The room must not color the natural spectrum of the music

• The performers should have the ability to hear each other clearly and to receive from the space a reverberant return that is close to that experienced by the audience

• Noise from exterior sources and mechanical equipment must be controlled so that the quietest instrumental sound can be heard.

1750 to 2200

For a hall size in an opera house or concert hall, it is far easier to design a good sounding concert hall in the ___ to ____ seat range than at higher numbers.

rectangular or shoebox floor plan.

for a Hall Shape, the most consistent performer is the

Surround configuration

moving the orchestra platform toward the center of the room and arranging seating around the side and the rear.

at least 1” (25 mm) thick, and be backed with a solid masonry or concrete structure.

For a surface material, When wood is used it should be

• thin carpet walking surface.

• Floors are constructed of concrete or wood on concrete.

• When floors are concrete, the aisles are covered with a ______________

ROOMS FOR MUSIC

Surface Materials

• balcony

• A _____ brings the audience closer to the musicians and improves sight lines, while dividing the room vertically into separate spaces.

TRUE

TRUE OR FALSE

• The greater the balcony overhang the more it cuts the listener off from the reverberant energy in the main portion of the hall, and the shorter the early decay time.

• seated audience

In a room for music, the biggest absorbing surface is the

PADDED

In Rooms for Music, seats should be _____ so that there is little acoustical variation between the rehearsal and the performance.

ROOMS FOR MUSIC

Platforms

• Space must be provided for the musicians in a configuration where they can hear and be heard

• 1.25 sq m for upper string and wind instruments

  • 1.5 sq m for cellos and larger wind instruments

  • 1.8 sq m for double basses

  • 10 sq m for timpani

  • Up to 20 sq m for other percussion

  • 0.5 sq m for each seated choir member

ROOMS FOR MUSIC

Platforms

• Musicians like to spread themselves out and move forward toward the audience

• It is important to keep the players close together and near the rear wall of the platform shell or enclosure, as long as it is not too deep.

• wood on wood sleepers.

• The platform floor material is universally _________.

• Musicians appreciate the resonance they feel returning from the floor

• Risers

• ______ are important to minimize shielding of the instruments in the back.

• ______ that are arranged in a semicircular pattern around the conductor provide an unencumbered path for the direct sound and allow good visual contact between the conductor and the players.

1.1 m.

In platforms for rooms for music,

The height of the stage in a theater is just below the eye level of the first row, which is about ____

Orchestra Shells

• The support provided by the ceiling and walls of the shell generates strong reflections back to the musicians

• Pits

can be open or partially covered.