What Makes an Amplifier Loud?

There is quite a bit of confusion out there when it comes to measuring the “loudness” of amplifiers. When most guitarists think of volume, they think about the amplifier’s wattage specs. However, just because one amp has more watts than the next, it does not mean that it’s “louder,” by any means.

While wattage is undoubtedly a critical element to consider, there are plenty of other things that must be factored into the loudness equation. Before we hop in and explore those elements, let’s first discuss what “loudness” is.

Decibels and Levels

Decibels, often labeled as “dB,” are logarithmic measurement units that provide a ratio between two numbers. Without getting too deep into the math, logarithmic scales don’t allow us to simply add numbers in a typical fashion. For example, on a logarithmic scale, a doubled number does not mean that number is twice as much. Let’s take the example of 200dB.

200dB is not twice as much as 100dB. Instead, it is many times greater than 100dB. While we visualize loudness in dBs, we measure it using SPL or Sound Pressure Level. We use a 10dB increase in sound pressure level to double perceived “loudness.”

If we have an amplifier that generates 50dB SPL and one sitting next to it that generates 60dB SPL, the amp next to the first one will likely be perceived as twice as loud to the average listener.

So Watts The Deal?

The question you might be asking is,

How many watts are needed, to get a sound that is twice as loud as another?

First, let’s make sure wattage is understood.

Wattage = Amps (Amount of electricity) x volts (pressure on that electricity).

Essentially, the higher the wattage on an amplifier, the more that particular amplifier can drive the speaker before it begins to clip the signal. This does NOT translate to perceived loudness. Instead, this translates to the amount of headroom the amp has before it hits that “pushed” sound.

Let’s begin by taking one amp rated at 50 watts and another rated at 100 watts. The 100-watt amp has twice the power of the 50-watt amp, though doubling the power only means that the 100-watt amp gets a 3dB SPL increase.

For the second amp to be twice as loud as the first amp, it must have a 10dB increase. The same thing goes for amps with lower and higher wattages as well. For example, a 20-watt amp will only sound 3dB louder than a 10-watt amp, and so on.

Speakers

The speakers have a lot to do with the volume of an amp. To get a good reading on the loudness capabilities of a speaker, we must look at the size, quantity, and quality of the speaker setup. The best thing that you can do if you’re looking for loudness is to match the impedance of the speakers and the amp. Otherwise, the amp will not be able to deliver its potential power.

Speakers come with efficiency and sensitivity specifications, which notate their ability to convert incoming electrical signals into acoustic energy. Surprisingly enough, speakers found in guitar and bass amps are relatively inefficient when it comes to converting electrical signals. Most of that signal is converted into heat rather than something audible.

Typically, manufacturers will measure a speaker’s sensitivity in a soundproofed, non-reflective room, otherwise known as an anechoic chamber. You may have seen speaker specs that say something like:

90dB @ 1W/1m

This simply means that the amp gets 90 dB SPL with one watt of power, measured at a one-meter distance from the front of the speaker. The better or more efficient the speaker, the higher that number will look.

Let’s take your average, cheap 12” speaker, for example. You’ll likely get around 94dB out of it. Take it a step up in terms of quality, and you might get 100dB out of your speaker, which would give you twice the volume. Beyond dBs, you must also look at dispersion and projection. If you have more speakers in one cabinet, they will push more air, creating a much louder sound.

Plus, an amp will sound much louder in a smaller room than it would on, say, an open-air amphitheater due to the reflections in that space.

Cab Size

While we’re on the topic of pushing air, it is essential to note that the same science comes into play when looking at the cab size. Put the same speaker in a larger cabinet, and you’ll get a larger and louder sound since the speaker is pushing more air.

A 4×12 cabinet will be ground-shakingly loud compared to a 1×12 cabinet, which is why most sound guys roll their eyes when they see guitarists rolling through the back door of a venue with one.

Compression

One thing that many guitarists never consider when it comes to their amp is its ability to compress the signal. For example, a clean signal may sound quieter than a signal with gain, distortion, or compression.

Think of your favorite tube amp. Due to the nature of tubes, these amps are typically very compressed. This is one of the reasons that many people favor their sound over solid-state models. When you crank the volume on a tube amp, it breaks up much faster than a solid-state as well.

The beauty of compression is that it brings up all of the quiet sounds when engaged, providing our ears with the perception of loudness. If you’re looking for a “louder” sound, a tube amp might be far more favorable.

How Loud Do You Need Your Amp to Be?

Now that you understand where the “loudness” of an amp comes from, the question becomes, “How loud do you need your amp to be?”

If you’re practicing at home, we recommend going with a 1×12, 10-watt tube amp. If you stay low in wattage, you won’t have to turn it up so loud to get a nice, gritty distortion. I typically stay in this range for recording as well. There is simply no reason to have a 40-watt, 2×12 tube amp in the studio when a 10- or 20-watt will get the job done.

For those who play out at venues with other musicians (including a drummer), I recommend going with a 50-watt 2×12 tube amplifier, so you don’t get drowned out. Of course, you might have a microphone pressed against your amp with some monitors in front of you anyway, so size may not matter.

Loudness is all perception, though understanding the elements that go into crafting a loud sound with tons of headroom can be extremely helpful when looking to buy or upgrade an amplifier. Don’t let wattage alone guide you on your quest for a thunderous tone.