Architectural Acoustics Basics

Acoustical Products and Systems

• Acoustical products and systems control noise to create comfortable, productive, and healthful environments.

Three Ways to Control Noise

• There are three basic ways to attenuate or reduce sound:
  • Replace the sound source with a quieter one
  • Block the sound with a solid, heavy material that resists sound wave transmission
  • Absorb the sound with a light, porous material that soaks up sound waves

Controlling Noise Along Its Path

• Reflected sound can be reduced by placing sound-absorbing materials on surfaces from which sound will be reflected.

Controlling Noise at the Receiver

• If source control is not practical, another approach is to treat the problem at the receiver.
• Temporary sound control: Direct ear protection (earplugs or earmuffs) is often used to protect workers' hearing when source and path noise control are not practical or possible.

Acoustics

• Acoustics is the science that deals with the production, control, transmission, reception, and effect of sound.
• Sound is reflected, transmitted, or absorbed by the materials it encounters.
• Soft surfaces (e.g., textiles, batt insulation) tend to absorb sound waves, while hard surfaces (e.g., gypsum board, ceramic tiles, wood) tend to reflect sound waves, causing "echo".
• Reverberation is the term used to describe sound waves that are reflected off surfaces.

Sound

• Sound is a mechanical wave and requires a medium to travel.
• Acoustics is classically divided into sound and vibration.
• Sound refers to waveforms traveling through a fluid medium (e.g., air).
• Vibration describes energy transmitted through denser materials (e.g., wood, steel, stone, dirt, drywall).

Sound Absorption Coefficient (α)

• The sound absorption coefficient describes the property of a material to convert incident sound into other forms of energy.
• The sound absorption coefficient of a material indicates the amount of absorbed portion of the total incident sound.
• α = 0 means no absorption occurs; α = 0.5 means 50% absorption and 50% reflection; α = 1 means the entire incident sound is absorbed.

Absorption Coefficient

• The sound absorption coefficient of a material is α = (1 - r), where r is the sound energy reflection coefficient.

Frequency

• Frequency is the speed of the vibration, which determines the pitch of the sound.
• Frequency is measured as the number of wave cycles that occur in one second.
• The unit of frequency measurement is Hertz (Hz).

Resonance Absorber

• A resonance absorber uses a resonance mechanism (e.g., enclosed air volume or vibrating surface) to absorb sound, mainly suitable for absorbing sound of medium to low frequencies.

Reverberation Time

• Reverberation time is the basis for ratings of room acoustic quality.
• The reverberation time depends on:
  • The volume of the room
  • The surface of the room
  • The furniture in the room
• Absorbing surfaces (e.g., carpets, curtains, sound-absorbing ceilings) reduce the reverberation time.
• The reverberation time of a room can be derived from the calculated total equivalent sound absorption area using the Sabine formula: T = 0.163 x V/A.

Noise

• Noise is any unwanted sound that annoys us, interferes with our hearing and communication, or may be hazardous to our health.
• A-weighted decibels (dBA) express the relative loudness of sounds in air as perceived by the human ear.
• Types of noise:
  • Continuous Noise
  • Intermittent Noise
  • Impulsive Noise
  • Varying Noise