How Flooring Affects Acoustic Performance, Lecture notes of Microwave Engineering and Acoustics

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How Flooring Affects Acoustic Performance

2 |^ How Flooring Affects Acoustic Peformance

Noise is typically defined as unpleasant and unwanted sound. High noise

levels worsen patient and staff outcomes in hospitals, hinder teaching and

learning in schools, and negatively impact productivity in offices.

With flooring, one of the most abundant finishes in the built environment, the

opportunity to positively influence the acoustical performance of a space is great.

Acoustical Properties of Flooring

Different commercial floor coverings such as rubber, resilient/vinyl, carpet and

textile composite flooring control sound differently. Harder materials such as

rubber and resilient/vinyl absorb little or no sound and have greater potential

to transmit sound, contributing to a noisier environment. Softer materials such

as carpet and textile composite flooring absorb significantly more sound and

transmit less sound, contributing to a quieter environment.

Laboratories typically use two tests to measure the acoustic properties of

interior surfaces and finishes—airborne noise reduction and structure-borne

noise reduction.

Airborne Noise Reduction

The typical frequency range for normal human hearing is 100-10,000 Hz. The

human voice falls within the low-frequency end of the spectrum, at around

100 Hz. Building noises such as those emanating from elevators, HVAC

systems and mechanical systems fall near the 1,000 Hz range. Loud noises

such as alarms and bells are in the high-frequency end, up to 10,000 Hz.

The airborne noise reduction test, ASTM C423-02a,^1 measures a surface’s

ability to absorb these and other airborne sounds which contribute to ambient

(background) noise. A floor covering sample is typically tested in an anechoic

reverberation room. The test measures the product’s absorption of sound

at 15 different frequencies ranging from 100 Hz to 10,000 Hz. All of these

frequencies fall within the range of what a normal human ear can hear.

A floor covering’s measure of effectiveness in absorbing airborne sound

is expressed as a Noise Reduction Coefficient (NRC). The greater the

absorption, the higher the NRC number. A surface that completely eliminates

sound has an NRC of 1.0. Hard surfaces such as rubber and vinyl typically

have NRCs of about 0.0-0.015, meaning they absorb little to no airborne

sound. Commercial carpets used in hospitals, schools and offices have

NRCs typically ranging between .15 and .2, meaning they absorb about 15-

20 percent of airborne sound. A textile composite flooring’s NRC is about

.30, meaning 30 percent sound absorption.

Airborne Noise Reduction TEXTILE COMPOSITE

How Flooring Affects Acoustic Peformance |^4 Up to 60 percent of classroom activities involve speech.^15 High noise and reverberation levels hinder speech intelligibility, causing reduced understanding and reduced learning. Many U.S. classrooms have a speech intelligibility rating of 75 percent or less.^16 Inappropriate levels of background noise and reverberation can also hinder reading and spelling ability, affect behavior and attention, and affect concentration and academic performance. Children for whom English is a Second Language and those with learning, attention or reading deficits are more affected by poor acoustics. Additionally, teachers may need to raise their voices in loud or reverberant classrooms, causing greater teacher stress and fatigue.^17 A growing body of research links acoustics to student learning and achievement.^18 In one study, 97.9 percent of school principals indicated that acoustics had a somewhat to very strong influence on student achievement. 19 In a national survey of public school teachers, 81 percent of respondents believed that a quiet environment with good acoustics had a very strong impact on student performance. Another study found that students in classrooms with carpet scored higher on tests in math, language and other subjects than students in classrooms with hard floor coverings.^20 LEARNING ENVIRONMENTS: Noise Influences Student Performance Speech Intelligibility CONT.

A person must speak 12 decibels (dB) louder than the ambient noise to

achieve 95 percent speech recognition.^3 Every 10 dB increase seems twice as

loud to the human ear.

Materials with higher NRC ratings are much more effective in absorbing

ambient noise and improving speech recognition.

Reverberation Time

Reverberations are continuing effects of a sound. Like echoes, they occur

when sound waves strike a surface and are reflected back into the space.

Reverberation time is a measurement based on physical volume, areas of

different surface materials and the absorption coefficient of those materials.

Reverberation time influences a floor covering’s NRC.

Shorter reverberation times aid speech recognition. For example, the

recommended reverberation times for offices and classrooms are 0.

seconds^4 and 0.4-0.6 seconds^5 respectively.

Excessive reverberation interferes with speech intelligibility. To reduce

reverberation time, sound absorption must be increased or noise volume

decreased.

Test results show that soft-surface mutes reverberation. In one study,

reverberation times of a hand clap and human speech were measured in a

room with a hard, concrete floor. Measurements were taken again after carpet

was installed in the space. The measured reverberation time was 3.3 seconds

for the empty room and 1.6 seconds with the carpet^6.

Facility managers attending an APPA Facilities Drive-In Workshop co-hosted by Texas Christian University and J+J Flooring were polled on a variety of building performance issues. Noise was cited as a predominant concern with 90% of College and University Facility Managers note that noise is a problem in the buildings and spaces that they manage with class- rooms, administrative areas and dining halls having the highest noise concerns. APPA Drive-In Workshop Poll, April 2014

5 |^ How Flooring Affects Acoustic Peformance Noise is a leading source of employee dissatisfaction in offices. Research conducted by the Center for the Built Environment (CBE) at the University of California, Berkeley, reveals that office workers are generally poorly satisfied with acoustics, particularly in open plan environments. Additionally, acoustics is typically the lowest ranked category in CBE’s occupant survey.^21 In one particular CBE survey, people talking on the phone and people overhearing private conversations were reasons for acoustical concerns for 86 percent of respondents. Additional acoustical concerns included: people talking in neighboring areas, 84 percent; excessive echoing of voices or other sounds, 60 percent; telephones ringing, 36 percent; outdoor traffic noise, 31 percent; and office equipment noise, 29 percent.^22 Research by the General Services Administration (GSA) Center for Workplace Strategy, Public Buildings Service, also shows that work environments do a poor job of providing acoustical comfort. After seven federal offices were redesigned, employee surveys showed substantial improvements in all environmental factors except two—noise and voice privacy.^23 Of 3,700 respondents to a GSA WorkPlace 20- program survey, 60 percent said “they could get more done if it were quieter”, 56 percent said “the ability to insulate themselves from distractions was important” and 50 percent said “noise keeps them from being as productive as they could be”.^24 OFFICE ENVIRONMENTS: Noise Hinders Productivity Conclusion

All types of flooring, hard and soft, have merit for the right place and right

population. Acoustics is an important consideration when specifying flooring

and should be evaluated based on the needs of a particular environment.

An environment with good acoustical control supports the activities and

goals of that space, such as improved health outcomes and higher patient

satisfaction in hospitals, effective teaching and learning in schools, and

improved worker productivity in offices.

The two most important acoustical factors to consider when specifying

flooring are the product’s sound absorption and noise reduction capabilities.

Independent laboratory tests show that carpet and textile composite flooring

control noise more effectively than any other floor covering. Even so, no flooring

material can provide all of the necessary acoustical management within a

space. Depending on the goals for the space, acoustical ceiling tile, sound

masking technology and other noise-reduction strategies may be necessary.

Notes (^1) “Standard Test Method for Sound Absorption and Sound Absorption Coefficients by the Reverberation Room Method.” ASTM International. (^2) “Standard Test Method for Laboratory Measurement of Impact Sound Transmission Through Floor-Ceiling Assemblies Using the Tapping Machine.” ASTM International. (^3) Nelson, P., Soli, S., Seltz, A. “Classroom Acoustics II: Acoustical Barriers to Learning.” Acoustic Society of America. April 2003. (^4) “Project Design: Open Office.” Retrieved from http://www.acoustics.com/open_office.asp; accessed March 31, 2014. (^5) “Classroom Acoustics”. Acoustical Society of America. Retrieved from http://asa.aip.org/classroom/book let.html; accessed March 31, 2014. (^6) Russell, D. “Reverberation in a Small Room.” Retrieved from http://www.acs.psu.edu/drussell/Demos/ RT60/RT60.html; accessed March 22, 2014.