Why We Use The Decibel Scale To Measure Sound Level

Sound is an integral part of life as we know it. Physical sounds allow us to experience our environment in a way like no other, communicate with each other easily, compose beautiful music, and so much more.

As most people will know, sounds are actually pressure waves in the atmosphere around us that vibrate at frequencies that our ears are sensitive to. For various reasons, it is very important that we have a way to measure the strength and the intensity of these signals, and luckily we have developed a system to do just that.

This article will take a closer look at this specialized system of measure, known universally in technical circles as the decibel, or dB. It will help to educate our readers along the way, and it will answer some questions that are relevant to the subject.

These questions include, just what is a decibel, and how did it come to be so named? What are the decibel levels of some well-known loud noises? And, how does the science apply to everyday products? Let's answer these questions.

SO, JUST WHAT IS A DECIBEL, AND HOW DID IT COME TO BE NAMED?

Let's have a discussion about the amazing human ear to start with. These are the organs that help to give us an awareness of the sounds in our environment. They are marvelously calibrated auditory tools, and are quite capable of registering a wide variety of frequencies and intensities.

One of the gifts of the ear is its ability to sense sounds over a wide range of sound levels. This presents problems in some ways, though. This huge range means that when we attempt to measure the sounds the ears hear, the huge variation can make it impossible to perform the necessary calculations.

To make it easier to handle this huge range, a logarithmic scale was adopted, as opposed to the linear scale which is used by things such as rulers. To put things in a little perspective, linear scales measure straightforward changes in quantities, while logarithmic scales measure exponential changes.

For example, if we start at the number 10 on a ruler and count 10 spaces up, we will come to 20. On a linear scale, this is only twice as great as the original number. If we start at 10 on a logarithmic scale and count upward by only ONE space, this represents a 10-fold increase in quantity.

This method of representing numbers is of great value in situations where large variations in quantity are involved, such as the differences in sound intensity. This universal scientific scale is now known as the decibel, which is a logarithmic way of describing the ratio between two quantities.

The story of how it came to be so named is quite straightforward. Telephone circuits are prone to losses in signal power over transmissions lines, and thus a need existed to quantify the magnitude of these losses. The original telephone companies came to agree upon a measure of signal loss known as Miles of Standard Cable, (MSC). This is the amount of power or signal intensity that was lost over one mile of cable.

Over time, this measure was standardized and renamed as the Transmission Unit, or the TU. 1 TU is basically the same as 1 MSC. In honor of Graham Bell, this measure was eventually renamed again to the Bel. One tenth of a Bel is thus a decibel, which is the unit of measure now used universally.

WHAT ARE SOME DECIBEL LEVELS OF WELL KNOWN LOUD NOISES?

Normal conversation at 3 feet away - 60-65dB

* Traffic noise inside a car - 85dB

* A train whistle at 500 feet away - 90 dB

* A jackhammer at 50 feet away - 95 dB

* A loud rock n roll concert - 110 db

* Screaming Meanie Alarm Clock – 120 db

* Jet engine at 100 feet - 140 db

HOW DOES AN ALARM CLOCK APPLY THIS SCIENCE?

Let's face it, there are times and places in life when it is harder to wake up from a deep sleep than others. In times like these, it can be crucial to ensure that you wake up exactly at the time when you are supposed to. An example of this would be over-the-road truck drivers who are often forced to sleep in noisy environments, and thus require something a little stronger than ordinary to get them going.

The famous Screaming Meanie is that something else. Popular with truck drivers for two decades now, this modest device is only slightly larger than a deck of playing cards. Despite its modest size, it can produce alarms at a variety of sound levels up to and including 120dB. Even the heaviest sleeper in the loudest environment possible will be alerted to wake up when it is placed within a few feet of the bed.

Screaming Meanie developer Charles Louis, points out that the Screaming Meanie could be louder, but that at 120 dB, it’s at the limit beyond which hearing could be damaged. “The 120 dB limit is important, because a product for people is only valuable if it’s designed of, by, for, and around people,” says Liu. “When you hear a 120 dB alarm, believe me, the first thing you want to do is to turn it off. Next, you want to know how they can generate so much loud noise from just a 9 volt battery.” Thankfully, he had a useful scale, the decibel, to calibrate his loud alarm clock for consumer use.

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