What’s the deal with Watts
Did you know that at no point in the entire run of Seinfeld, did Jerry ever start a joke by saying, “What’s the deal with…” except for one time when he was intentionally trying to bomb? The more you know…
So, what makes an amp loud?
Here’s a little thought exercise to prove that I don’t use AI to write this: So, when we look at an amp, wondering how loud it will be, we first have to understand that amps— per se— aren’t loud or quiet. Amps produce output voltage that is then translated into sound by speakers. So, in reality, the volume of an amp is heavily reliant on the speakers through which it is being played.
On a related note, watts don’t measure sound. On some level we all probably know this, but we’re so used to describing the power of amps in watts that we’ve come to think of it as a measure of how loud the amp will be. But it’s only part of the story.
Like amps, lightbulbs are often measured in watts, but watts also aren’t a unit of brightness. That would be lumens. So, watts is an old, rough descriptor for the power of things when we don’t have a relatable way of talking about it. We’ll get into decibels later, and those things are just nuts.
Think of your amp’s output as potential energy for pushing speakers. The more energy you have available, the easier it is to push the speaker. But not all speakers are created equal.
Speakers are rated in several ways: Impedance (the amount of resistance the speaker offers to the amp’s output transformer), Power (how much power from the amp the speaker can handle before it fails), and sensitivity (how loud the speaker is capable of being at full output). There are other speaker measurements, but for the sake of this conversation, we’ll leave it at this.
Impedance: Every speaker has an impedance rating, but this does not mean the impedance is absolutely fixed. Generally, you match the output impedance of the amp’s output transformer to the impedance of the speaker. This is recommended for optimal operation, but it’s not absolutely necessary in most cases as the impedance of the output transformer and the speaker will shift as you play the amp.
Power: Speakers are rated for maximum power. So a 100 watt speaker is rated to handle output voltage in an amp that is running at 100 watts plate dissipation. This can become an issue if you don’t take a few things into account. First, as mentioned above, watts are not a good unit of measure for amplifiers. For example, most amps have a wattage rating based on when the amp starts to overdrive. See the problem? Your tube amps is likely more powerful than its rating. So, if you hook a 100 watt amp that is actually capable of 130 watts up to a speaker rated for 100 watts, it might blow.
Sensitivity: This rating describes how many decibels a speakers is capable of producing. Before we even do this, let’s talk about the totally bonkers way that decibels work.
Decibels measure the loudness of sound, but it is not a linear scale. So, the volume difference between 40dB and 50dB isn’t 20%, it’s actually over 300%. See, every increase of 3dB is an effective doubling of the sound pressure, which is what decibels are actually measuring.
Fun fact: The capital “B” in dB is because the “bel” in decibel is named after proper noun, Alexander Graham Bell.
When it comes to how fiercely your amp is melting your face or the faces of your loved ones, sound pressure is what you are actually experiencing. At the end of the day, that is what volume is: the sound pressure created by your amp’s output voltage, translated into forward and backward motion by the speaker, which then projects sound waves into your delicate ears.
Now that you know that the watts in question are simply the heat dissipation from the plates of the power tubes as you play the amp, doesn’t it seem weird that we use this as a standard of loudness? And yet…
Part of the reason for this pickle is the fact that there are a number of different, sometimes modular, components that will, together, determine how loud an amp ultimately is. Certainly, the amount of power that the amp can produce is a big part of that. That is the potential. The reality is what happens when that power hits the speakers.
We often refer to speakers having high or low “efficiency,” and this simply means how much power can the speaker handle. So a 15 watt Blue Alnico would be low efficiency, while a 200 watt Fane Crescendo speaker would be incredibly efficient. Essentially, how much sound can the speaker make with a given amount of output voltage. This also, typically, conforms to how easily the speaker breaks up, with low efficiency speakers breaking up more quickly than high efficiency speakers.
The speaker’s sensitivity is also a major factor. Some companies publish specs on their max dB level, but some don’t. There isn’t a uniformly agreed upon method for taking this measurement, so this too can feel a bit misleading.
The loudness of an amp is also greatly affected by how many speakers you are using. While the difference between a 1x12 cabinet and a 4x12 cabinet may not seem like a big deal, each of those additional speakers (as long as they are the same spec) effectively double the volume of the cabinet.
So, as you can see, lots of variables. But probably the most interesting scenario is one I see all the time.
“Well, I bought a 5 watt amp because I thought it would be quiet, but it’s still super loud!”
With the right setup, a 5 watt amp can easily achieve 100dB. And a 100 watt amp isn’t 20 times louder than a 5 watt amp. None of this is based on a linear scale, and you have to factor in a variety of variables in order to get anything like an accurate calculation.
So, why do we use watts then?!
As you’ve read this, has any other method that stood out to you as a better way of describing how loud an amp will be? Output voltage is meaningless without doing math, and decibels don’t work because it’s a matter of the speaker’s potential, not the amp’s potential. So, we stick with watts. Knowing it’s not a very good descriptor of volume but without any other logical options. Maybe we could use lumens!