Explaining Sound

One method of explaining complicated things is to use an ‘analogy’.

An analogy usually makes a comparison using the ideas or processes of a familiar thing and making the logic or data apply to a more unfamiliar or complicated topic. For example, sometimes people will talk about electrical power by using an analogy between electrical power and water power.

They will say that you can think of electrical power the way that you think about water going through hose. Then they will explain all these ideas about bigger hoses (for Voltage) and kinks in the hose for measurements of resistance.

Each concept in the power and electricity story has a person’s name attached to it, all a long way back from the Golden Age of Electronics, Part II. (Some of the words come from the early Greeks who were responsible for Part I, but that is a different story.)

One of those names is the last name of Mr. Alexander Graham Bell. The unit he is associated with is called the Bel.

Wikipedia should get an award for having the most useless example of a circular definition when describing this term. Wikipedia says that a Bel is a unit of measure equal to 10 decibels. …which doesn’t tell you anything, of course.

We already know that when you put deci- in front of a word that it have something to do with 10. In this case, it is correct that there are 10 decibels in a Bel, but that doesn’t say much. Especially because most of us will go through our entire lives without ever hearing the term Bel used. But we will hear decibel a lot. Some of us will hear it when measuring sound. But it is also used in the most important measurement in our universe: the strength of our WiFi signal!

Engineers after Mr. Bell’s death started using the Bel as a unit of measurement when they needed to determine how much energy loss there was in a reel of cable. Communications would travel from one side of the city or country or ocean, and the communication wasn’t as strong at the end as it was in the beginning. But the Bel is such a large amount of energy that in normal use engineers divide it by 10 – and we then can use the more practical unit called a decibel.

The abbreviation is dB. You will notice in other electronic abbreviations which use a person’s name that the letter designating their name is capitalized like this. (Another example of this is millivolt, abbreviated as mV, because Volt was named after an Italian engineer named Volta.)

Power At The Source, Intensity When Measured

The way that we use dB is with sound intensity. 1 dB is about the difference of intensity of sound that a trained person can notice when the sound increases or decreases in level. The average person might hear change at 2dB, but most people can certainly hear the difference in two sounds that are 3 dB, 3 decibels, apart.

Now, one of the weird things about how sound is measured is that 3dB is a significant amount when we hear it, but it is also a significant amount because it takes twice the power to get that much sound energy going.

An example of this would be a person blowing a trumpet. The sound exits the trumpet kind of like light exiting a fire. The energy waves go in every direction at once – louder if you are right in front of the trumpet of course, but 2 people who are 5 meters away will get about the same amount of energy.

Using the fire example (as an analogy), if we add a 2nd fire or get twice the number of logs burning, the fire will be twice as hot or bright. But the person 5 meters away may not notice the difference of each individual log until they are all going.

Why? Because the heat and light is going all around – in a 360° circle. It isn’t all being focused at that one person. Actually, the energy disperses more the 360° – it disperses in a sphere, 360°s of 360°s.

So, any particular observer only receives the light from the few degrees that their eyes see. …or their body feels as heat. …or that the ear hears in the case of the instrument being played or the speaker being heard.

And, all that energy to those few degrees doesn’t add up to a significant amount – enough to tell the difference – until there is twice the power begin generated. And even though we don’t need to care about the math involved, for sound that ‘twice the power’ is measured as 3 dB.

It is only starting to get weird. We can tell the level difference between two sounds at 3dB, which is twice the power, but we don’t think that it is twice as loud until there is a 10 dB difference!

There is a Part 2. It touches on the explanation of the magic of 10dB. But take a break to rest your mind from this craziness for a bit. Calm water is ahead.

If you want to see a version of the water power/electrical power analogy, try this site. There are many others, but many get far too complicated far too quickly! And I don’t know about you, but my head is already boiling inside.

Understanding the basics of electricity by thinking of it as water

The important thing to remember is: The reason that all these analogies of fire and sound and water (and light and heat and many other sensations), the reason these can all be used as analogies of each other is that they are all energy. Analogies are never perfect – but when we speak about energy we are almost speaking of the same thing, but in different forms.