A Quiet Day at the Office: Acoustics for People who are Hard of Hearing
Presented by Donald Bataille
Mr. Bataille began his presentation by noting that people can have hearing loss only at certain frequencies (e.g. above 1000 Hz) or at all frequencies, and that some acoustic treatments are effective only for certain frequency ranges.
He gave some examples of sound levels in common environments to give people a feel for the commonly used decibel scale. A quiet library is typically around 35 db, and a quiet office around 60 db. People with normal hearing can hear sounds from 0 db to about 120 db. They can also hear sounds above 120 db, but those sounds cause pain.
He also noted that our ear’s sensitivity to sound varies with frequency, so that some frequencies sound louder than others, even though the measured decibels are the same. As an example, for people with normal hearing, a 1 kHz sound at 60 db sounds as loud as a 20 Hz sound at 103 db.
Sound is simply changing air pressure, and the rate at which it changes determines the frequency.
Mr. Bataille pointed out that noise is detrimental to understanding for people with normal hearing. In a normal classroom (70 to 80 db), students with normal hearing can miss as much as one third of spoken communication. People with hearing loss, of course, miss much more. Understanding in the presence of noise requires work and causes fatigue; people with hearing loss have to work harder and become more fatigued.
Some additional interesting facts:
– 98% of the noise striking a hard surface is reflected back into the room, causing reverberation.
– “Poor acoustics” is the leading cause of workplace dissatisfaction.
The signal to noise ratio (SNR) denotes how much louder the desired signal (usually speech) is than the background noise. A high ratio means that the signal is considerably louder than the noise. People with normal hearing require a SNR of about 6 db to be able to understand speech clearly and without a lot of effort; people with hearing loss typically require about 15 db. When someone with hearing loss complains that they can hear the speech, but just can’t understand it, it’s likely that the SNR is below 15 db.
There are three methods to control unwanted sound; it can be absorbed, blocked (dampened) or covered (masked by competing sounds).
Absorbing the sound within a room contributes to better speech understanding by decreasing the reverberation. Available materials can absorb up to 90% of the sound that strikes them, and are very cost-effective as a means of improving speech understanding. Carpets, acoustical tile, sound absorbing wallboard, and draperies are effective sound absorbers.
Another good way to reduce unwanted sound in a room is to block sound coming from outside the room. One effective way during construction is to be sure that room walls extend all the way to a hard ceiling. (It’s fairly common now to have a suspended ceiling a few feet below the hard ceiling, and to build room walls to be just above the suspended ceiling. This leaves a gap of a couple of feet for sound from adjoining rooms to get through undampened.)
Pay attention to heating and air conditioning systems. Something as simple as rebalancing the HVAC system can significantly reduce transmitted noise.
The use of QuietSolutions type wall and floor coverings significantly reduce sound transmission from adjacent rooms, and sound attenuating blankets can be used in walls and laid over suspended ceilings. Also sealing all openings around electrical boxes and other wall openings can significantly reduce sound transmission.
Covering or masking unwanted sounds is really more for ensuring privacy by covering speech (e.g., in a doctor’s office), but it can also be used to cover unwanted distracting sounds. The common method is to introduce white noise, which is noise that contains all frequencies of sound. This technique is generally not helpful for people with hearing loss, because it actually raises the background noise level.
Another effective option might be to turn DOWN the PA system. If it is so loud that it is distorting, turning it down will increase speech clarity.
Also effective is simply moving closer to the sound you want to hear. It not only makes the sound louder (without distorting), but also makes it clearer.
Additional tips for improving communications include facing your desk towards the door, so you are aware when people approach, placing yourself so windows, lights, and hard surfaces are behind you, raising the height of your cubical walls, getting an office away from copiers, printers, etc., and partially closing your office door.
Q. How about furniture? Do you have some recommendations there?
A. Any upholstered furniture will absorb sound, so will help reduce reverberation.
Q. I have a problem with interference when I try to use my t-coil. Do you have any recommendations for that?
A. The first step is to determine the source of the interference. If it’s your computer monitor, changing to a flat screen will likely eliminate the problem. Another common source of t-coil interference is fluorescent light ballast. Replacing the lights with low-interference ballast will correct this problem. Interference caused by a motor can often be reduced by reorienting the motor. If it turns out that the source is something that can’t be easily corrected, increasing the distance from the source is a good option.