Before we can talk about bass tone or equalization (EQ [eee-kyoo]), you need to understand a few basics about how sound works.
The science of acoustics can get complicated very quickly. But, in my usual style, I'll try to make it easy-to-understand and useful to you. Ready?
Sound is all about vibrations. When something vibrates the air around it, the vibrating air travels into your ears. Your ears react to the vibrations in the air and convert them into electrical impulses sent to your brain. In a nutshell, that is how you hear sound.
Everything which produces sound—a drum, a speaker, or your significant other—is sending vibrating air into your ears.
Frequency, Cycles, and Hertz
To understand how we measure and describe these sonic vibrations, we need to learn three new terms—Frequency, Cycle, and Hertz.
The speed of the vibrations, or sound waves, determines how high or low something sounds to you. We call the rate at which something vibrates frequency. Frequency is a measure of how frequently something vibrates.
The slower the frequency, the lower the pitch; the faster the frequency, the higher the pitch.
When a wave goes all the way up and down once, we call it a cycle.
Frequency is measured in cycles per second—how many times a wave has gone up and down in the span of one second.
These cycles per second are called Hertz (named after the German physicist Heinrich Rudolf Hertz).
Hertz are abbreviated Hz as in 440Hz, or 440 cycles per second. When the cycles per second get into the thousands, we call them kilohertz and abbreviate them kHz. So, 8,000 cycles per second may be written 8kHz.
The Human Hearing Range
On average, humans can hear between 20Hz to 20,000Hz at birth. The high-end declines as you get older (20s-30s) down to about 16,000Hz. Don't worry though. That's more than enough range unless you want to talk with dolphins who can hear up to 150,000Hz!
Frequencies and Musical Notes
In music, the notes you hear vibrate at particular frequencies. For example, when you play the open E-string on your bass guitar (the lowest note on a standard 4-string bass) it vibrates at about 41Hz—41 times per second.
While 41 times a second seems really fast, in terms of sound that's pretty slow. Remember, you can only hear between 20Hz and 20,000Hz or less. So 41 is pretty far down there.
To give you a visual: A hummingbird flaps its wings about 50 times a second, and that's what creates its humming sound. Think about that in comparison to your vibrating bass strings. The note G (3rd fret of the E-string) vibrates about the speed of the hummingbird's wings.
A Note Isn't Just One Note
To really understand bass tone and EQ, this is the essential part:
When you play a single note on your bass or another instrument, you're not only hearing one pure note vibrating at one frequency. Instead, you are hearing one strong main note along with many other weaker, quieter frequencies mixed in.
This strong, main note is called the fundamental. The faint, weak notes are called overtones.
The fundamental and overtones come from something called the harmonic series which we'll discuss next.
Up next: The Harmonic Series and Timbre.