Music- Why Are There Different Bass and Guitar Amps?

That is an excellent question! When you look at them, they are about the same shape. There are even bass practice amps that are smaller than guitar amps. What is the difference and why are guitar and bass amps different?

Amps can be really complicated but at a basic level there are two ideas driving amps--size and power level.

Size

Size-- Although we cannot see them, except when they make liquids move (like the cup of water when T-Rex approaches in Jurassic Park) sound waves have size.

Pitch, or how high or low a sound is, is determined by how close together or far apart the crest of one wave is to the crest of the next wave. Higher pitched sounds are closer together and lower pitched sounds are more spread out.

For guitar, most of the sound waves it produces would be measured from a several hundred millimeters to a few centimeters. Bass notes, on the other hand, are most often measured in meters.

In order to produce such large sound waves successfully, bass amps require larger speaker cones or several different sized cones for different frequency ranges.

In terms of size, bass amps are most likely going to be larger overall than guitar amps. However it is the size of the speaker cone inside the amp and not the overall dimensions of the outside, what we call the cabinet.

Thinking about the size of sound waves, using a bass amp for a regular guitar would mean that the higher pitches would not sound as good as if they were from a guitar amp with smaller speaker cones. Likewise, playing a bass with a regular guitar amp would mean that the lowest notes would not sound as good (or not sound at all) than if it were played on a bass amp.

Power

The second layer of how amps work involves the amount of power it can output. More or less power equates to how loud the amp can get, but the size of the sound waves or frequency, also changes how much power is needed. Remember sound waves? The height of the wave is how loud or quiet the sound is.

On average, the very low bass notes require more power output than higher notes played at the same volume. This means that a bass amp playing at the same perceived loudness as a guitar amp would need more wattage.

It’s also the power idea that makes selecting the correct amp important as using an amp at a loud volume with an instrument that it is not designed for can eventually damage the amp.
But how can I tell which amp is which? Here’s a hint- they usually are labelled somewhere on the unit. If you do not see the word “guitar” or “bass” on the amp, find the make and model number name/number and look it up. Google should be able to tell you.
Another difference between guitar and bass amps that is more subtle has to do with the EQ settings available or rather the focus of these settings.

In order to understand the purpose of them, first we need to understand how instrument pitches work.

Every note has a main frequency (sound wave shape) that gives it the pitch-- we call this the fundamental pitch. But fitting within that wave are other related waves. These other waves are called overtones. While the fundamental pitch is what gives the note its letter name, it is these overtones that give the note its quality of sounding like a bass guitar and not a piano, tuba or other low instrument playing the same pitch.

The EQ settings on an amp are obviously not going to make a bass turn into a tuba, but it can enhance or repress certain overtones so that different frequency ranges (sound wave sizes) are brought out.
Going back to the sound wave sizes, the low, medium, and high frequency ranges for a bass is going to be different than the low, medium, and high frequency ranges for a regular guitar. Meaning that the medium knob on a guitar amp will not affect the same frequency range as the medium knob on a bass amp.

Guitarists are notorious for chasing the perfect tone with complete pedal boards to assist in that process. Often the focus for bass is more on defining the fundamental and how tight or reverberant the player wants that sound. For a bass, lower EQ boosts would give it more power and depth whereas higher EQ boosts would give the notes more clarity.

Hopefully this post has not confused you more. You should be glad I did not talk about keyboard amps and how they have to work for a wider frequency range than either bass or guitar amps. Unlike many products that are simply marketing gimmicks, bass and guitar amps are two separate products that serve different needs.

Please let me know if you have questions!