By: Arjun Shankar, MCH Acoustical Consultant
Picture this: you have just seen your favorite band in your favorite music venue. The crowd is giving the band one last rousing standing ovation as they strike their final note and head off stage. You are still in a daze by the sheer excitement as you follow the crowd to the exit. Once outside of the venue, you begin noticing something: your hearing is awry. Your ears feel “full” or in pain, everything seems quieter than normal, or you are hearing ringing (high pitched tone). Don’t worry, this is all (mostly) normal. You have just experienced a Temporary Threshold Shift (TTS). As the name indicates, this is a temporary hearing reduction that tends to resolve in several hours. However, be cautious. If you regularly subject yourself to TTS, eventually this could lead to a permanent threshold shift (PTS), or permanent hearing loss.
To understand hearing loss, we must first understand some hearing basics. The human ear can be divided into three parts: the outer ear, the middle ear, and the inner ear.
The outer ear consists of the pinna, ear canal and eardrum. The middle ear houses the ossicles – three small bones known as the malleus, incus, and stapes. The inner ear contains the cochlea, an organ containing hair cells and the basilar membrane. Sound waves enter the outer ear, travel through the narrow passageway of the ear canal and excite the eardrum. The eardrum then connects these vibrations to the ossicles, which amplify and input those vibrations into the cochlea. These vibrations cause fluid inside the cochlea to form a travelling wave along the basilar membrane. Hair cells which sit atop the basilar membrane respond to these vibrations, creating electrical signals carried by the auditory nerve to the brain, which interprets the incoming sound into something we can recognize and understand.
This complex, intricate system should not be taken for granted. If we are not careful, this delicate system could be damaged, leading to tinnitus (constant ringing in the ears) or even permanent hearing loss. Noise induced hearing loss (NIHL) affects between 10-40 million adults in the U.S under the age of 70, according to recent CDC studies. It should be noted that hearing health and hearing loss varies depending on age, gender, history of noise exposure, and other environmental factors such as smoking or diabetes.
So how can you protect yourself from hearing loss? The Occupational Safety and Health Administration (OSHA) offers guidelines for noise exposure limits based on a given noise level (shown in the table below).
To easily see what kinds of noise levels you are exposed to, several smartphone apps provide an estimate (such as the NIOSH app for iPhone). A good rule of thumb is to simply wear earplugs in any environment with continuous loud noise or loud impulse noises. There are even flat frequency earplugs that attempt to attenuate noise equally across all frequencies – but at overall reduced levels. This results in a more realistic depiction of the sound when wearing the earplugs (think of it as a volume knob). It is also important to pay attention to volume levels of your earbuds and headphones – these can often reach levels up to 100dBA! Setting levels on your device to no more than 50-60% of the maximum volume can help reduce long-term hearing damage.
Don’t jeopardize one of your primary senses… Protect those ears!
