Have you been to the movies recently and left with ringing ears? The deafening volume levels is becoming a common complaint amongst avid moviegoers.
A study in the US done by researchers at the University of Hawaii found that some films showed peaks of 130 decibels during car chase scenes, gun fights and explosions. This is the equivalent of standing 100 metres away from a jet during take-off. They also found that the children's movies sampled in the study had an average exposure similar to those of action movies, and could potentially cause hearing loss in children.
How loud is too loud?
Ideally the sound for movies in the cinema and in home theatre system should be between 80 and 85 decibels as a maximum.
"Any loud sound above 85 decibels is regarded as potentially dangerous for the nerve cells of the cochlea in the ear. The length of exposure is also important as audiologists regard a period of more than 20 minutes of exposure to excessive sound potentially damaging. This is due to the fact that a protective reflex in the middle ear, which is in place to specifically to protect the cochlear, is unable to hold its position for more than that period of time, " explains Cape Town Audiologist, Natalie Buttress.
Prolonged exposure to loud noise can damage the hair cells in the inner ear. Loud movies can further cause headaches, tinnitus (ringing in the ears) and short-term shifts in hearing. High noise levels can also raise blood pressure, heart rate and increase stress levels.
Who's to blame?
Sound in movies is a combination of different soundtracks: one for dialogue, one for music and one for special effects. These are each recorded at different sound levels with special effects often recorded at the highest volume level to stir up dramatic response. The soundtracks are then combined to form a single fixed mix.
The researchers suggest that the increase in sound level can be blamed on two causes: producers have made a habit of cranking up the sound levels and cinemas also want to show off their surround-sound speaker systems by turning up the volume.
Audio experts also suggest that a lack of regular maintenance on sound systems, haphazardly placed speakers and under-specification of speakers for the size of the cinema are also common culprits.
The researchers also found that movie sound levels were higher than the limits set by the Occupational Safety and Health Administration (OSHA) for sound exposure in the workplace. Workers should not be exposed to more than 85 decibels over a period of eight hours.
"The (sound) volume of movies is not regulated or calibrated by each and every cinema. The risk of damage to hearing is increased in smaller cinemas, due to the confinement of the loud sounds. In addition projectionists in South African cinemas seldom remain inside the projection booth during the film to ascertain the level of the sound. Sound would need to be accurately measured inside the cinema itself in order to gauge whether the sound is at a safe level."
"Unfortunately, many films contain excessively loud sounds - particularly those with action sequences, and animated or high-energy films that are designed for children. The fact that the industry does not regulate sound leaves the public exposed to volumes that are not only potentially dangerous, but are usually uncomfortable," says Buttress.
Can sound be regulated?
About a decade ago research done by the British Standard Institute found that cinema adverts were louder than feature films, averaging 88 decibels and reaching noise levels up to 95 decibels. The British standards institute and cinemas in Britain have agreed to restrict the noise levels in films to under 85 decibels.
Recently the Cinema Advertising Council (CAC) in the US announced recommended industry-wide guidelines for audio levels of on-screen cinema advertising. The loudness standards state that audio output levels should average between 82 and 84 decibels, in comparison to the Trailer Audio Standards Association 85 decibels volume level.
"Unfortunately the South African industry does not apply the same regulation. Typically the acoustic reflex in a normal hearer is elicited above 80 decibels. Excessive exposure to very loud movies may damage people's hearing in subtle ways, and in a gradually progressive manner," says Buttress.
Protect your hearing
Audiologists can provide members of the public with acrylic hearing protectors which allow speech and sound below 80 to 85 decibels into the ear, but prevent sound above 85 dB from entering the ear and damaging the cochlea.
"Alternatively the only way that members of the public have of protecting the hearing during entertainment such as movies is to be more aware and lobby for regulation. If you are uncomfortable with the sound which you are experiencing during a movie you should ask the projectionists to turn down the volume, "says Buttress.
(Leandra Engelbrecht, Health24, September 2009)
IPod generation risk losing hearing
- Natalie Buttress, Audiologist
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