Sound Advice by Leon Sievers Sound Professional September 02, 2009

For more than 15 years I have made a living from my ears. As a studio and live sound engineer I have been exposed to damaging sound pressure levels. This is to be expected in the music world, but many churches operate at equally dangerous levels.

Your ears are very delicate and prolonged exposure to sound pressure levels above 85dBA will cause damage to your hearing. If you have ever been to a party or to a concert where loud music was played, you may have experienced Temporary Threshold Shift (TTS). This temporary loss of hearing can become permanent if exposure is done on a regular basis.

One way to tell if you've been exposed to excessive sound pressure levels is that you tend to hear a ringing in your ears. Ringing in your ears, hissing, clicking or buzzing sounds all represent the effects of tinnitus, which is often a side effect of noise-induced hearing loss. Inner-ear cells are sensitive to vibrations. But if they're damaged, the ears will still record ringing or buzzing, even when there's no sound.

How does long-term exposure to excessively loud music cause hearing loss? Basically, hearing loss occurs when the tiny hair cells in the inner ear are blasted away from repeated exposure to loud music. Our ears contain microscopic hairs as a fringe on the ends of auditory cells in the inner ear. When healthy, these hairs move in response to the pressure of sounds that vibrate the eardrum. This movement leads to chemical changes that in turn produce small electrical signals. The electrical signals excite nerve cells in each of the some 30,000 fibers that spiral away from the cochlea, a snail-shaped and fluid-filled structure in the inner ear. This spiral of fiber fuses together to form the auditory nerve and carries stimulation from the ear to the brain, where sound is perceived. Continued or repeated exposure to loud music can damage the tiny hairs, leaving them twisted, bent, fused, and no longer able to respond properly to sonic vibrations. Where there are no healthy hairs, erect and swaying to each sound that travels to the ear, there will be no stimulus to the brain from that particular nerve, and perhaps nothing more to be heard. The ear's ability to hear sound is degraded even when only a relatively small number of hairs are damaged. There has been some research into microscopic hair cell regeneration in the ear, but unfortunately, the damage to the hair cells and the resulting loss of hearing appear to be permanent.

Remember that it is your high frequency hearing that deteriorates first. Think of what music would sound like if you couldn't hear anything above 10KHz: just like with a crummy old transistor radio or listening to music over a telephone (no cymbals or high pitched instruments, voices sounding deadened). Protect yourself or just turn it down! The high frequencies are lost first, so you may have difficulty hearing high-pitched voices. Loss of high-frequency hearing makes many words sound alike, especially those containing the high-frequency sounds S or soft C, F, SH, CH or H. Words like "hill," "fill" and "sill" may sound exactly the same.

Experimental evidence

Researchers at the University of Florida tested the hearing of some middle and high-school students. The investigators found that about 17 percent of the children had some degree of hearing loss. Most of the hearing loss was in higher pitches, which are usually the first ranges of sound to be lost after hearing damage. The investigators believe that exposure to excessive noise results in a serious hearing impairment at an early age. Significant hearing losses were detected in a group of students who had a history of frequent attendance to pop music entertainment. Losses due to loud noises in jobs, gunfire, etc. were also identified. A ‘guinea pig' showed hearing impairment in his right ear after listening to high-intensity rock music for 88 hours over a two month span. The left ear, protected by a plug during most of the music, demonstrated no cytological changes. The damage to the right ear was permanent.

Why We Like It Loud

It turns out that loud sounds directly affect our autonomic nervous system (also called involuntary - it controls the body functions that you hope never stop, like breathing and digestion), in a way similar to many stimulant drugs. Adrenaline is released, the heart rate speeds up, the guts tighten up and move. This is the rush you get from loud music - it's real and it's beyond your conscious control. Sounds' addicting doesn't it?

So How LOUD is LOUD?

Our ears can distinguish a wide spectrum of sound intensities roughly equivalent to the lowest note on a pipe organ to the highest overtone on a violin. Because humans can perceive such a wide spectrum of acoustic energy, the units for measuring sound intensities are compressed using a logarithmic scale (based on the powers of 10) on which the sound intensity multiplies by ten every 10 decibel (dB) increase. For example, the sound of a rock concert, approximately 120 dB, would have 1,000 times the intensity of a motorcycle (90 dB). The amount of noise and the length of exposure determine hearing loss; one can experience hearing loss or damage if there is a one-time exposure to a loud noise, repeated or long exposure to noise, or extended exposure to moderate noise. In 1970, the Occupational Safety and Health Administration (OSHA) developed a scale indicating the length of time a person could listen to a given dB sound level before experiencing hearing loss or damage.

OSHA regulations permit exposure to 80 dB or less for eight hours a day, 95 dB for four hours a day, 100 dB for two hours, 105 dB for one hour, 110 dB for a half an hour, and 115 dB for less than 15 minutes.

The National Association for Hearing and Speech Action (NAHSA) also reports that exposure to 85 dB or more for any length of time is potentially dangerous.

Rock concerts expose most audience members to 120 dB of sound, and often last longer than two hours - imagine the extent of damage to the hearing of audience's members not wearing ear protection! NAHSA reports that anyone exposed to more than 10 rock concerts without proper ear protection (such as earplugs) is likely to develop hearing loss.

Operating Parameters

I recommend operating your church sound system at no more than 80dB peak during worship and averaging 65-70dB during the service. Sound Pressure Levels, which exceed these parameters, will cause ear fatigue, loss of concentration and potential hearing damage. Similarly, operating your system at too low of level will also cause people to strain to hear the spoken word, resulting in ear and brain fatigue. Purchase a simple sound level meter from Radio Shack and monitor your stage and house levels so that you maintain a balance. Most environmental noises include a wide band of frequencies and, by convention, are measured through the "A" filter in the sound-level meter and thus are designated in dB(A) units. Proper adjustments of your system and room acoustics also play an important part in maintaining moderate SPL while maximizing intelligibility.

As a rule of thumb, the average listening level in a church should be 25dB above the noise of the room. Make a measurement of the ambient room noise prior to the service. These measurements should include the noise generated by the air conditioner, local traffic, etc. Typically, if the church noise levels are under control, good listening levels are generally in the low 60dB range. In some churches, the room noise is so low, that a PA system is not needed for speech or a good listening level of 55 to 60dB is OK, (but this is so rare.) If you have to always drive your sound system higher than 68dB, chances are you have a noise problem that needed to be address.

Since many church populations have a high number of people with hearing problems, background noise becomes a greater problem. Generally I use the following as a guideline. If more than 60% of the church members or over 60 years of ages, increase the signal to noise (S/N) ratio standard from 25dB to 30dB. This allows many older people with minor hearing losses to hear better without driving the sound system harder and offending others with average hearing abilities. If these people continue to complain, then they will need a personal hearing-impaired system of some kind.

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