Classroom Acoustics

Acoustics

Important definitions Frequency

▪ def. [The number of sound waves created in a given amount of time, indicating the pitch of the sound, expressed as Hertz (Hz)]

Wavelength

▪ def. [The distance between corresponding points on consecutive sound waves].

Amplitude

▪ def. [The magnitude of a sound wave, indicating the intensity of the sound]

Important definitions

▪ Decibel (dB):A unit measurement of the loudness of a sound. Louder sounds have larger decibel values.

▪ A-Weighting (dB(A)):A measure of sound pressure level designed to refl ect the response of the human ear, which is less sensitive to low and high frequencies.

▪ Speech Intelligibility:A measure indicating to what extent speech is understood in a given environment

▪ Reverberation Time (RT):The time it takes for sound to decay by 60 dB once the source of sound has stopped. Reverberations occur when sound waves strike surfaces (e.g., fl oors, walls, ceilings) in a room and are refl ected back into the space. Reverberation will continue until all the sound waves have been absorbed or have dissipated

▪ Signal-to-Noise Ratio (SNR):The ratio of desired sound (e.g., teacher’s voice) to undesired background noise (e.g., mechanical noise). Larger numbers denote better acoustic performance

▪ Sound Absorption: Sound deadened upon striking a surface

INTRODUCTION

▪ In a classroom, speech is conveyed from the teacher to students through a combination of direct and reflected sound.

▪ Direct sound travels from its source in a straight line to the listener without being reflected.

▪ Reflected sound strikes one or more objects or surfaces in a room before reaching the listener.

▪ Direct sound energy is most prevalent at distances close to the teacher, and reflected sound is the major source of energy at distances removed from the teacher.

▪ When combined appropriately in a quiet classroom, direct and reflected sounds enhance classroom communication and enable all students in the classroom to hear the teacher.

Acoustics in CLASS ROOM▪ WHY ACOUSTICS MATTER

▪ WHO BENEFITS FROM IMPROVED ACOUSTICS?

▪ FUNDAMENTALS OF SOUND AND ACOUSTICS

▪ UNDERSTANDING THE PRIMARY ACOUSTIC PROBLEMS IN CLASS ROOM

BACKGROUND NOISE

REVERBERATION

SIGNAL-TO-NOISE RATIO

▪ ACOUSTICAL DESIGN STRATEGIES

GENERAL CLASSROOMS

CLASSROOMS FOR THE HEARING-IMPAIRED

OPEN-PLAN CLASSROOMS

OTHER EDUCATIONAL SPACES

WHY ACOUSTICS MATTER

▪ Classroom acoustics are an important, often neglected, aspect of the learning environment.

▪ Up to 60% of classroom activities involve speech between teachers and students or between students, indicating the importance of environments that support clear communication.

▪ However, classrooms that have been constructed in the last 20 to 30 years to better engage students in hands-on activities or discussions have often resulted in active, noisy environments.

▪ Additionally, HVAC systems have created distracting background noise in classrooms

Sound movement

WHO BENEFITS FROM IMPROVED ACOUSTICS?

▪students▪ ■ Children, especially those younger than 13 years of

age, have an undeveloped sense of hearing, making the impacts of background noise on hearing, comprehending, and learning more pronounced for children than adults

▪ ■ Temporary illnesses causing mild hearing loss (e.g., middle ear infections) are on the rise

▪ ■ Students with learning, attention, or reading deficits are more adversely affected by poor acoustic conditions than the average student.

▪ ■ Hearing-impaired students require a significantly better acoustic environment to adequately hear than the average student .

WHO BENEFITS FROM IMPROVED ACOUSTICS?

▪ TEACHERS

▪ Loud or reverberant classrooms may cause teachers to raise their voices, leading to increased teacher stress and fatigue.

▪ ■ Teachers speaking in noisy classrooms may be at risk for voice impairment .

FUNDAMENTALS OFSOUND AND ACOUSTICS

▪ Technically, sound is air pressure fluctuations resulting in audible vibrations. These vibrations travel in wave patterns away from the sound’s source, and the waves are characterized by their frequency, wavelength, and amplitude. When a sound-wave contacts a surface, for example a wall in a closed room, the energy and direction of the sound is altered. These alterations are perceived as sound reflections and reverberations, which can affect auditory perceptions

▪ The human auditory system is less sensitive to extremely low (below 500 Hz; e.g., mechanical or automotive rumbling) and high (above 8000 Hz; e.g., light fixture buzzing, mechanical ringing) Frequencies. Low frequency noise tends to have the detrimental effect of masking speech, particularly consonants. Individuals with hearing loss are particularly susceptible to the masking effects of loud low frequency noise.

UNDERSTANDING THE PRIMARYACOUSTIC PROBLEMS IN CLASS ROOM

▪ The teacher’s voice decreases 6 decibels as the distance from him/her doubles.

▪ Ambient classroom noise may mask the teacher’s voice for students sitting in the middle and back of the classroom.

Reverberation

time

Room geometry

Background noise levels Single to

noise ratio

Speech intelligibility

UNDERSTANDING THE PRIMARYACOUSTIC PROBLEMS IN CLASS ROOM

▪ Background Noise▪ Excessive noise in classroom has a negative

impact on student learning and performance While a 1 decibel (dB(A)) change in sound level is barely noticeable, background noises are perceived as doubling in loudness every10 dB.

▪ Background noise in unoccupied classrooms should not exceed 30-35 dB(A)

▪ Major sources of background noise include:□ HVAC noise (vents, ductwork, A/C unit)□ Outdoor noise (automobiles, airplanes)□ Reflected speech sounds (echo)□ Noise from adjacent spaces

Background Noise Sources▪ Through walls from adjacent classrooms

▪ Over the ceiling from adjacent classrooms

▪ Through doors, around the frame and under the door

▪ Through ventilators or louvers above door units

▪ Through HVAC ductwork from adjacent rooms

▪ HVAC noise from ceiling diffusers

▪ Through the light fixtures

▪ From outside, through exterior walls and windows

▪ From floor above

Reverberation

REDUCING REVERBERATION▪ Excessive reverberation can cause echoes that

interfere with speech intelligibility. Smaller classrooms generally have shorter reverberation times than large classrooms. However, sound waves may be rejected more frequently and can create a masking effect. It is important to develop design strategies that minimize reverberations to improve speech intelligibility.

ACOUSTICAL DESIGN STRATEGIES

▪ ■ Separate particularly sound-sensitive spaces (e.g., classrooms, counselling offices) from both external and internal sources of noise (e.g., playgrounds, gymnasiums, band rooms) by using non-acoustically sensitive areas (corridors, storage spaces) as buffer spaces.

▪ ■ For new construction school projects, avoid locating classrooms or core learning spaces below gymnasia, dance studios, or other spaces with a high level of activity

PLANNING THE CLASS ROOM▪ ■ classroom doors in hallways to create longer, less

direct paths for noise to travel between rooms.

▪ ■ Avoid placing adjoining doors on shared classroom walls, as this will limit sound isolation

▪ ■ Avoid open-plan classrooms and classrooms with thin or partial partition walls between instruction areas to reduce sound transmission between rooms.

Classroom Acoustics Goals▪ High Speech Intelligibility

▪ Requires proper Reverberation Time, ▪ Low volume, high sound absorption

▪ Requires low background noise level.

▪ High Hearing Comfort

▪ Requires proper overall geometry

▪ Indicated by detailed acoustical metrics

Acoustical Comfort and Hearing Comfort

Acoustical Comfort Requires high speech intelligibility,▪ Clarity, and▪ pleasant tonal spectrums

Ease of HearingDepends on Early Energy Patterns

• Speech Intelligibility depends on RT, dBA

All Classrooms (speech communication)

Strategies to Improve Acoustic Access

▪ Ceiling

▪ Floors

▪ Windows

▪ Walls and Doors

▪ Seating and Furniture

▪ Ventilation

▪ Lighting

▪ Special Purpose Areas

Areas to Consider

STRCTURAL CONSIDERATION▪ Place acoustically absorbent materials (e.g.,

mineral wool board) on top of concrete foundation flooring

▪ ■ Install double-skin steel roofing with acoustically absorbent materials (e.g., mineral wool board) to increase the structural roof’s sound insulation

▪ ■ Consider the impact of rain noise on occupants when designing lightweight roofs or incorporating roof lights into a design

▪ ■ Install pads underneath the school’s supporting structure to reduce structurally-borne background noise .

Ceiling• Installing acoustical ceiling tile is the most effective way of

absorbing distorted middle and high frequency noise and improving speech perception ability.

• A ceiling height less than 12 feet is optimal for the listening environment.

• Suspend banners, student work, and hanging plants from the ceiling

Types

▪ Drop Ceiling Tiles

▪ Ceiling Grids

▪ Light Panels & Louvers

▪ Surface Mount Ceiling Tiles

Ceiling

Floors

• Carpeting

• absorbs excessive reverberation of high frequency consonant sounds

• dampens noise from students and movement of classroom furniture

• Use rubberized or resilient tile versus flat, reflective tile

• Use area rugs or carpeting for uncarpeted areas

Floors

Exterior Wall Construction▪ ■ Install dense, insulated external walls with few openings

(e.g., doors, windows) near sources of high external noise .

▪ ■ Add several layers of gypsum or plywood board (5/8” minimum) to exterior frame walls or thickness to exterior concrete or block walls to increase wall sound transmission class values .

▪ ■ Fill cracks or gaps in exterior walls with elastic bonding to improve noise isolation .

▪ ■ Insulate walls with absorptive materials (e.g., fiberglass insulation) between wall studs to increase their sound insulation.

▪ ■ Air cracks, gaps, or insufficient amounts of insulation can compromise the sound isolation of a wall. Carefully construct exterior walls without gaps and monitor their degradation to improve their sound isolation.

Windows

• Drapes on the sides of windows absorb sound

• Keep windows closed to prevent outside sounds from entering the classroom

• Pvc, alluminium windows are used with double glazing to avoid d sound entry to inner part of the building to outside

• The small openings in the windows are closed using rubber strips

Windows

Walls and Doors• Place rectangular extension rods in opposite corners of the

room and hang a curtain

• Creates round corners to reduce reverberation

• Provides small storage area

• Place cabinets at angles in the corners –soften the fronts with fabric curtains on magnetic rods or cover with cork boards

▪ Acoustic wall types

▪ Fabric Wrapped Acoustical Panels

▪ Cleanable Acoustical Panels

▪ Black Acoustical Theater Board

▪ Recycled Cotton Wall Panels

Walls and Doors

Seating and Furniture• Place a drape or cork on the front of solid areas

teacher’s desk

• Use curtains to cover/conceal open shelving units

• Use tennis balls or rubber chair leg caps on tables and chairs

Seating and Furniture

Cautionary • Think about traffic flow in the room: where is

supplies kept in relation to your teaching zones

• Place noisy items (pencil sharpener) away from teaching areas

• Create assigned zones during small group work so that groups are spread out

Ventilation

• Replace noisy blowers

• Cover ventilation openings with strips of material

• Do not use desk or floor fans

• Avoid HVAC system inside the room

• The maximum noise can be cut down by placing these systems outside

Lighting

• Make sure florescent lights are functioning correctly

• Ballast will make high frequency sounds when they begin to burn out

• If your room is equipped with a motion sensor, position students with hearing aids out of the directional path of the doorway

Special Purpose Areas• Carpeting

• Use rubberized or resilient tile versus flat, reflective tile

• Hang banners or flags from the ceiling

• Place material or cloth banners on the walls

▪ Done by

▪ Vikas.R

▪ Shekar.S.R

▪ Thejas.M.T

▪ Vinay.M.V