Acoustics in the Workplace, Part 1

By Bonnie O'Leary

October 2009

Editor: This may be a topic that you haven't thought much about. I mean, is there anything you can really do about it anyway? The answer is yes, and here's some information on what you can do to improve acoustics in the workplace.

This is part one of two parts.

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Hear to Work

Donald Bataille, AIA, CCS, is an architect with SWBR in Rochester, NY. As a professional with a hearing loss, Don is advocating strongly for better acoustics in the workplace. His presentation, Hear to Work, focused on workplace acoustics based on the classroom standard ANSI S12.60 (American National Standards Institute). Hear to Work is a personal project of Don's, which has the support of his firm. It has three main goals: (1) to foster a proactive approach to planning for a better acoustic environment, (2) to provide an understanding of ANSI S12.6 2002 Classroom Standard and its application in the workplace, and (3) to establish workplace standards for hard of hearing individuals.

Hearing loss is the most pervasive physical disability in the US, affecting approximately 31.5 million people. There are approximately 14 million employable hard of hearing people between the ages of 16 and 64. It may come as no surprise that "poor acoustics" is cited as a leading source of workplace dissatisfaction. In the office environment, office "noise" is cited as the primary distraction. Acoustic quality impacts work efficiency, attendance, and proficiency. It is the second most common point of litigation in multifamily construction.

Speech Intelligibility Issues

To function effectively in the workplace, we need to understand speech. This means understanding presentations and/or instructions, to effectively collaborate with others, to participate in group meetings. Speech intelligibility is dependent on what we call the signal-to-noise ratio. (Bonnie's note - Many hearing aid wearers might be familiar with that term; it seems that no matter how much money we spend on our hearing aids, understanding speech in a noisy environment can still be a challenge!)

Competing background noise in classrooms causes students to miss one third of spoken communication, and the effort to counteract noise creates fatigue. Someone with hearing loss is not as able to tolerate background noise or reverberation as well as individuals with normal hearing. Hearing people as well as hard of hearing people who share the same work environment can all benefit from a better acoustic environment.

Accessibility to Speech

Reverberation adds life and richness to speech, but too much of it degrades speech intelligibility which in turn decreases our ability to participate in group discussions. Noise from competing sources such as air conditioners, vents, outdoor traffic, etc., diminishes speech perception and comprehension as well as the ability to concentrate or to process speech sounds. Noise makes it difficult for people with hearing loss to locate the speaker and can impact our ability to participate.

Sound and Its Transmission

Sound is either airborne or structure borne vibration. Airborne sound vibrates at various speeds creating different frequencies, expressed in vibrations per second or Hertz (Hz) or how fast the air pressure changes. How much air pressure changes will determine the loudness, or volume, of the sound which is measured in decibels, dB, or average dB (dBA). A whisper in a library is about 30dB, a lawn mower about 107dB, and a jet engine at 30 ft would be 140dB.

Sound is transmitted, reflected, or absorbed by various materials. Competing sounds, or background noise, are often reflected (or bounced) off hard surfaces such as wood, tile, linoleum, concrete, glass.

Sound Measurements

STC (Sound Transmission Class) ratings refer to the ability to resist transfer of airborne sound at speech frequency levels through an assembly of materials; it measures Transmission Loss (TL). The higher the STC value, the greater the sound reduction across the acoustical barrier such as a wall, or a floor. A 5 dB increase would be required to be noticeable, and a 10 dB increase would be perceived as a 50% change in volume, or twice as loud.

STC ratings through a wall or floor system include:
STC 30 Loud speech well understood
STC 35 Loud speech audible but not intelligible
STC 45 Some loud speech is barely audible
STC 50 Loud speech inaudible
STC 60 Isolation for amplified sound

The Noise Reduction Coefficient, or NCR, is a measurement of the acoustical absorption efficiency of a material. A material with an 0.70 rating would absorb 70% of the sound which would help control the reverberation and reduce room flutter.

The Signal-to-Noise Ratio, or S/R, SNR, is the ability of speech to be heard and understood over the background noise. The average minimal SNR for perception by someone with normal hearing is +6dB.

Here's Part Two

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