Put yourself in my shoes for this simple experiment: Find a place that is completely quiet, devoid of any mechanical or natural noises (like a listening room, or maybe bedroom late at night) and sit in peace and quiet for a few minutes. Do you hear anything? I certainly do. I get a constant high-pitched ring. I currently suffer from a symptom called Tinnitus, which is defined as the sensation of sound in the absence of an external source. What is the cause of this problem? Well to get at the problem, we should first understand the complicated organ that is the human ear.
I’ll turn this over to a handy explanation from the British Tinnitis Association.
Essentially it is a very sensitive vibration sensor but is particularly designed to receive the minute longitudinal vibrations in air that make up sound waves. The human ear is broken down into 3 parts: the outer, middle and inner ears. The outer ear is in essence a funnel that ‘catches’ and focuses sound waves down onto the ear drum or tympanic membrane. The middle ear takes the relatively low intensity vibrations of the eardrum and ‘magnifies’ them through 3 little bones: the malleus, incus and stapes respectively. Finally the vibrations of the stapes are transmitted through the oval window membrane to the fluids of the inner ear (cochlea). It is here, in the inner ear, that the fluid vibrations lead to bending of the minute hair cells of the cochlea. It is this bending that causes tiny electrical signals to be passed through the auditory nerve to the brain where they are interpreted as sounds that we can then make sense of. The human ear can detect sounds from 20Hertz (very low pitch) to 20,000Hertz (very high pitch) but is particularly sensitive to sounds in the range of 500-5000Hertz. These are the so-called speech frequencies and are especially important for human social communication.
The ear is also able to deal with a huge range of sound intensity (volume) from the quietest whisper or rustle of grass, to the sound of a jumbo-jet taking off! As the range of sound intensities (volume) which the ear can hear is so great, a logarithmic scale is used to measure the sound levels. This scale is called the decibel scale. So a sound of 20dB is not twice as loud as a sound of 10dB but in fact is 10 times as loud! Unfortunately, the ear, and in particular the cochlea or inner ear, can also be damaged by exposure to too much of the energy it was designed to detect. In other words, too much noise can cause damage to the ear and even make you deaf!
So too much noise could cause the ringing I experience? What have I done lately that involves excessive noise?
I took this picture at the Ministry of Sound, one of two live events I went to recently that had very loud music. And although the MoS boasts a system capable of putting out 150dB worth of sound waves, I don’t think that this is the only problem. I wore musicians earplugs which are designed to attenuate the sound without limiting the frequency range. It is normal to experience hearing loss or ringing in your ears after an event like a concert, this is called a Temporary Threshold Shift. It is believed that TTS is due to metabolic exhaustion of the hair cells of the cochlea. This can recover with a period of ‘rest’ as the background noise levels fall, and most people recover within a day or two.
So if it isn’t concerts, what are some other reasons for my tinnitus? Most of you will probably suggest that I always have music playing and that music usually funnels through my headphones. While I acknowledge that it is possible that my ears are exhausted because of my constant music playing, I’m not convinced that this is the cause either. The volume of music pumping through my Sennheisers is not really much higher than the background noise where I work, I just prefer to listen to The Black Keys rather than the refrigeration unit on our -80C freezer or an annoying labmate. And actually, I would argue that I listen to music all the time because of my tinnitis. I do not enjoy silence because I never actually get it, so instead I drown out the ringing with music. I have thought about this one a lot, and it hits home.
In fact, the more I think about it the more I am convinced I have suffered from tinnitus for a long time. Individuals that have experienced a Permanent Threshold Shift won’t necessarily notice a loss in hearing, but but often report difficulty understanding what people are saying, particularly in the presence of background noise. Again this one hits home as I have a hard time hearing people in the pub or when out to dinner, which may be part of the reason I am loud (not discounting alcohol and the fact that I am American though.) PTS is due to damage or even death of the delicate hair cells of the cochlea, and this is very likely what has happened to me.
Then again, it is also possible that the fluid in my head due to a cold that won’t go away is the cause, and the caffeine in the tea I drink all day actually stimulates the nerves in my ears, amplifying the ringing. Perhaps this is true and my symptoms will disappear once I get healthy? Not a lot of hope in this possibility from me, I’m sure that I’ll always suffer a little bit.
The good news is that my life has not been seriously affected by the ringing in my head. I don’t lose sleep at night or have problems concentrating like some people, probably because my brain filters out the noise most of the time and I have learned to live with it. I might also try to give my ears a break for a couple of weeks to see if the “rest” helps those little cochlear hairs to stop going crazy. I’ll be sure to let you know once I don’t hear anything.