ACOUSTIC DESIGN IN BUILDINGS

AKSHAY SINGH AHLAWAT | DIVAKAR JHA | KRITIKA DHUPAR

Since sound travels in all directions from the source, each listener will hear just the segment if the overall sound wave that is traveling in a direct line to his hear (in a space free from reflecting surfaces). As the distance from the source increases, the sound pressure at the listener's ear will decrease proportionately.

Direct Sound

Diffusion

Room Acoustics

Shape

Volume

Materials

What influences ROOM ACOUSTICS

Room Acoustics

SOUND RE-ENFORCEMENT

Reflect

Absorb

Room Acoustics

BC

REVERBERATION

A

The shape of a space determines the sound path within the space

Parallel reflective surfaces generates unwanted reverberation

Reverberation time must match room function•Pure speech requires short reverberation time•Symphony blends notes with long reverberation time•A classification of typical rooms by acoustical environments

"Dead" : Very Absorptive

"Live“: Highly Reflective

• Carpet• Soft ceiling tile• Rigid foam• people

• Masonry• Wood – smooth panels• Smooth concrete• Glass

Absorbing Materials Reflecting Materials

Auditoriums, theaters(for music)

Obtain proper reverberation time to enhance musical quality.

Provide reflective surfaces near source to reinforce sound; absorptive surfaces toward rear.

Conference and board rooms

Normal speech must be heard over distances up to about 35 ft.Allow middle section of ceiling to act as a reinforcing sound-reflector.

Apply absorbent to periphery of ceiling or to wall surfaces (not both). Additional treatment will contribute little to noise reduction.

Live Medium Live

Cafeterias (school or office)Reduce overall noise level.Use highly sound-absorptive ceiling; also use quiet equipment such as rubberized dish trays.

GymnasiumsInstructor must be heard over background noiseUse acoustical material over entire ceiling to reduce noise; walls remain untreated to permit some reflected sound.

Elementary-grade classroomsTeacher must be heard distinctly; reduce noise level produced by children.Acoustical ceiling essential. Supplementary acoustical space units on upper rear and side walls are desirable.

Music rehearsal roomsUnlike music hall, instructor must hear individual notes distinctly; minimum reverberation desired.Entire ceiling, sidewalls, and wall facing musicians would be treated; wall behind musicians may be left sound-reflective for proper hearing. Room should be located away from normal use rooms.

Medium Medium Dead

Hard, massive, non-porous surfaces, such as plaster, masonry, glass and concrete, absorb generally less than 5% of the energy of striking sound waves and reflect the rest. Such materials heaver absorption coefficients of .05 or less.

Porous materials such as acoustical tile, carpets, draperies and furniture are primarily absorptive. They permit the penetration of sound waves and are capable of absorbing most of the sound energy. These materials may have absorption coefficients approaching

Reflective materials Absorptive materials

Poor acoustical characteristics in this lecture room.

Reflective surfaces near the speaker.

In lecture rooms more than 40 feet long, the rear wall should be absorptive to prevent echoes.

Background Noise As a rule, we can tolerate, and even welcome, a certain amount

of continuous sound before it becomes noise. An "acceptable" level neither disturbs room occupants nor interferes with the communication of wanted sound.

Recommended category classification and suggested noise criteria range for steady background noise as heard in various indoor functional activity areas as indicated in the

Preferred Noise Criterion (PNC)Curves.

Type of Space (and acoustical requirements) Concert halls, opera houses, and recital halls (for listening to faint musical sounds)

10 to 20 db

Large auditoriums, large drama theaters, and churches (for excellent listening conditions)Not to exceed 20 db

Broadcast, television, and recording studios (close microphone pickup only)Not to exceed 25 db

Small auditoriums, small theaters, small churches, musical rehearsal rooms, large meeting and conference rooms (for good listening), or executive offices and conference rooms for 50 people (no amplification)Not to exceed 35 db

Bedrooms, sleeping quarters, hospitals, residences, apartments, hotels, motels, etc. (for sleeping resting, relaxing)25 to 40 db

Private or semiprivate offices, small conference rooms, classrooms, libraries, etc. (for good listening conditions)30 to 40 db

Type of Space (and acoustical requirements)

Living rooms and similar spaces in dwellings (for conversing or listening to radio and TV)30 to 40 db

Large offices, reception areas, retail shops and stores, cafeterias, restaurants, etc. (for moderately good listening conditions)35 to 45 db

Lobbies, laboratory work spaces, drafting and engineering rooms, general secretarial areas (for fair listening conditions)40 to 50 db

Light maintenance shops, office and computer equipment rooms, kitchens and laundries (for moderately fair listening conditions)45 to 55 db

Levels above PNC-60 are not recommended for any office or communication situation.

Minimize Background Noise Level

- Overall noise levels which may interfere with wanted communication should always be anticipated and corrected. To provide maximum quiet, typical methods include the following: 1. Elimination of outside noise by sound attenuation in walls, ceilings, and floor

2. Use of quiet mechanical equipment wherever possible.

3 .Control of remaining noise by absorption -- carpeting, upholstery, and acoustical treatment placed above and behind audience.

4. Individual handling of unusual noise sources -- for example, isolation of a noisy movie projector.

5. Electronic amplification of the wanted sound level above the background noise level -- usually done as a last resort.

The control of intruding sound ideally begins with the initial building concept and continues to be a consideration through the life of the building.

1. site selection2. building orientation on the site3. room orientation within the building4. design, detailing, specification5. construction6. inspection. Predictable sound attenuation can be achieved by careful attention to detail

during all phases of planning and construction.

Sound Isolation

Sound BarriersIf the noise source is intense and no natural sound barrier exists, a man-made sound barrier should be considered as part of the design. A solid fence-type barrier may remove from 10 to 20 db from the noise level. High-frequency sounds will be reduce more than low frequency sounds. The cost of an outside barrier may be less than the cost of reducing the sound transmission in the construction.This type of sound barrier must completely shield the building from the noise source. It should be placed as close to the sound source as possible to obtain the greatest sound-shadow angle. If a fence or wall is used, no louvers or openings should be permitted.

AbsorptionThe amount of sound energy dissipated depends on the thickness of the material, its density (which determines the amount of difficulty that the sound encounters in traveling through), and it's resiliency (flexibility with the ability to spring back to its original shape). Mineral wool insulation because of its porous yet dense character, is highly effective in this application. Sound attenuation blankets are manufactured with higher density than thermal insulating blankets to obtain optimum attenuation. Mineral fiber sound attenuation blankets, placed between the studs in a resilient partition with resilient channels, retard movement of the air column and convert considerable sound energy into heat. However, if the diaphragms are directly connected to rigid studs, the partition will act as a single diaphragm, rendering the wool ineffective in dissipating sound energy.

Jamshed Bhaba Auditorium

TREATMENT FOR CEILING

TREATMENT FOR ECHO

TREATMENT OF WALL SHAPE