First Snow on the West Hill
What is an Audiogram?
We live on the north slope of the highest hill for miles around (or kilometres around, since this is Canada). The picture above, taken from the large backyard, shows the west field in winter with the maple woods, which supplies sap for maple syrup and blocks the view of family members’ homes further along the road, although we hear the children’s voices, the crow of a rooster, and the barking of their dogs. Richard tells me an excellent drive would carry a golf ball 250 yards from Daniel’s spruce tree, in the middle foreground, diagonally across the field to its far corner in the center of the picture.
If you walk straight up the hill from the barnyard, you will have a clear view 3.5 miles (5.6 km) to Marmora, a village known for its open pit mine. In this springtime photo, the Marmoraton Mine slag heaps are a dark blue-grey line on the horizon under the budding tree branch. It gained province-wide attention when Toronto proposed dumping its garbage in the pit, which is half-full of water, a lake that would disperse soluble toxins south to a huge watershed. After a long battle, the villagers defeated the proposal.
View South towards Marmora
As you know a lot about your environs, we know people in homes and businesses scattered across the landscape and in the villages, the one we can almost see and two others about 10 miles distant east and west along the Trans-Canada Highway. Marmora is about equidistant from Ottawa and Toronto, which are 400 km apart. To the north, as we joke, is Santa Claus. We are 20 minutes away from the Pre-Cambrian shield that prohibits agriculture and stretches through forests and lakes into tundra and the Far North with only the occasional mining town to mark human activity in the vast wilderness.
Obviously, we don’t know everything there is to know about this territory. It could be studied from many points of view. So much is happening among its people that no one claims full knowledge about it. The very size of our map reminds us of how much we do not yet know.
The audiogram as a “map” of hearing is so constricted that it gives the impression that it contains all we need to know about a person’s hearing. The statement of audiologists about what constitutes “normal hearing” or “slight hearing loss” have been accepted and assumed to be correct and comprehensive by most people. On this page and at Secrets of the Audiogram I deconstruct a couple of things about the audiogram: (a) the misleading uniformity of the grid on which measurements are recorded and (b) the patterns of peaks and valleys that usually emerge after the measurements have been entered on the graph—because most people do not hear every frequency at exactly the same decibel level. The audiogram grid is a “map” of the audio territory being tested. But the graph or “curve” that appears does not fully reveal the way the person tested is experiencing that geography. Or, if it does, we don’t yet know how to read most audiograms that way.
If an audiogram were to realistically represent on paper what it means in decibels of sound, you would need all of that territory I described above as my environment, and more, to chart the audition of the hearing population. Pause for a moment to think about your own geography to personalize those distances from your point of view. Using the same sort of audiogram to chart the frequencies and volumes of sounds most people are exposed to, including damaging sound, would require a map of half the globe. Hard to believe? Here we go!
Decibels rise exponentially related to a base of 10, so they translate easily into metric distances (with the imperial measures used in the US calculated beside them).
Let’s assume the audiogram uses a grid of blocks 1 centimetre high (3/8 inch). (The ones illustrated below are actually half a centimetre.) The interval from 0 decibels to 10 dB is 1 centimetre (3/8 inch).
The interval from 10 dB to 20 dB will be recorded up to 2 cm (3/4 in) on your typical audiogram. However, that distance is very misleading. To be proportional to the increase in the level of sound, the 20-dB mark should be at 1 x 10 centimeters (4 in). The grid must be at least 5⅛ in long to record thresholds of hearing from 0 dB to 20 dB.
The 30-dB mark would be, not at 3 cm, but at 100 cm/1 metre (3.28 feet + the previous 5.12 in). Four sheets of letter paper taped together would be long enough to record a reading at this level. This covers the upper range of hearing considered “normal,” meaning “good,” for adults.
The 40-decibel mark would be at 1,000 cm/10 m (32.8 ft plus 3.28 ft plus 5.12 in). The sheet of graph paper would have to be 36 ft long, about the length of our old farmhouse.
The 50-decibel mark would be at 10,000 cm/100 m (328 ft/109 yards). The sheet of paper would have to stretch from the back deck to the maple woods, pictured above (an extremely fine golf drive, says Richard).
The 60-decibel mark would be at 100,000 cm/1 km (3280.8 ft) + 363 ft/1.11 miles ), a third of the way to the horizon in the second photo.
The 70-decibel mark would be at 1,000000 cm/10 km (6.2 miles) + 1.1mi/7.3 mi, about halfway to either of the more distant villages, east or west.
The 80-decibel mark would be at 10,000,000 cm/100 km (62 miles), about the distance, as the crow flies south from here, to Belleville (our nearest shopping center) and across Lake Ontario to Rochester, NY.
The 90-decibel mark would be at 100,000,000 cm/1,000 km (621.3 miles), the distance from our house to Quebec City in the east and to Toledo, OH (beyond Windsor, ON) in the west.
The 100-decibel mark, which ends the usual audiogram, would be at 1,000,000,000 cm (i.e. one thousand million, or 109)/10,000 km (6,214 miles). The distance across Canada from the east coast, Cape Spear, Nfld., to the westernmost point at the Yukon-Alaska border (141°00’W) is 5,514 kilometres, slightly over half that distance). 100 decibels is 1 billion times louder than 1 decibel (10 billion times louder by the old, long scale numeration no longer used in the US, Canada, or the UK).