Hear, See, Believe - AvNetwork.com

Hear, See, Believe

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It's summer and the sound of growling, humming, and purring two-wheeled vehicles is everywhere. For a certain segment of the population, there is a thrill in the challenge of relying on sound alone to identify the make and even model of the motorcycle cruising by. This guess is followed by craning of the neck, peering around parked cars, or leaping up to look out the open window to confirm the information by sight.

In this game, the sense of sound is being used as a primary tool, followed by sight. The Doppler effect plays a significant role here. If a motorcycle is rolling by a stationary observer there are corrections and adjustments to be made before the eyes follow the sound to the location of its source.

That's all fine and dandy, unless you live on a hill near a canyon in a valley. For reasons many readers of this magazine could explain, the Doppler effect here gets all tangled up by echoes and atmospheric conditions. As a result, often it sounds as though a motorcycle is approaching one's location rather than disappearing into the distance, which, after a glimpse out the window, it is in fact doing.

For someone who grew up in a prairie state, the alterations in sound in a mountainous region are very strange indeed. But for those who have lived among these hills, canyons, and mountains all their life, it's likely they always know the direction of travel related to any sound.

It's all relative, as is dictated by the definition of the Doppler effect: The change in frequency and wavelength of a wave for an observer moving relative to the source of the waves. Since we're talking about sound waves, the Doppler effect definition adds, "the velocity of the observer and of the source are relative to the medium in which the waves are transmitted." So, factors like air moving through a canyon, or across a hill in a valley, and low or non-existent clouds play a role in this game of "spot the motorcycle".

Actually, in general, our perception of events is altered a bit by something like the Doppler effect. Whether it seems like something is screaming toward us or howling away from us depends on our relative position in life. Day-to-day opportunities and challenges often seem to be hurtling themselves at us at uncontrollable speeds, while the bigger questions that affect the bottom line in a long-term way often seem to fade into the background. So as we all speed toward InfoComm this month, make sure to reverse the Doppler effect a little bit and think about the bigger picture of how the industry and your business are affected by technological change.


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