I frequently hear questions like “Is a 15 watt amp loud enough to cut it with a band?” or “How can I get more clean headroom out of my amp?” I just as often hear people saying, “a 15 watt or even 30 watt amp just can’t cut it in a band setting.”
Have you ever stood in front of a cranked Vox AC30 loaded with two Celestion AlNiCo Blues? It’s LOUD! Probably louder than a 50 watt half-stack loaded with four less efficient speakers Celestion Greenbacks.
The Celestion Blue is rated at 100dBb while the Celestion Greenback is rated at 97dB. It’s convenient, but simply coincidence that these two speakers differ by 3dB in terms of efficiency. Convenient, because it takes a doubling of wattage to gain a 3dB increase in volume. In other words, to get those Greenbacks as loud as the Blues, you’d need 60 watts pumping into them.
So while you might have thought that wattage was the most important factor when shopping for an amp, the speakers you play it through and their efficiency is equally as important.
I like to use this analogy when talking about speaker efficiency. Think of it in terms of a car with an internal combustion engine. A more fuel efficient car will go further on one tank of gas than a less efficient car. A compact car might go 35 miles per gallon (mpg) while an SUV or truck will only do 15 mpg. In the same way, the more sensitive (efficiency is usually referred to as sensitivity) speaker is more efficient at turning your amps output into sound. So if you feed the same signal into a 97dB speaker and a 100dB speaker, the 100dB speaker will be louder.
"You might even say that the more efficient speaker gives you more bang for your amp power and that it takes twice as much power to get the 100dB speaker to be as loud as the 103dB speaker. A 3dB gain is a doubling of power."
As Anthony Lucas from Eminence Speakers explains it, “You might even say that the more efficient speaker gives you more bang for your amp power and that it takes twice as much power to get the 100dB speaker to be as loud as the 103dB speaker. A 3dB gain is a doubling of power.”
Let’s bring this into the real world. I have a Vox AC15HW that came with a 97dB Celestion Greenback. It sounded great, but every now and then I wished I could get a little more clean volume before breakup. My solution: I installed the 103 dB Eminence AlNiCo Red Fang. Now I have plenty of clean volume when I need it.
On the flip side, let’s say you have an amp that won’t start to break up until it is running at ear-bleeding levels. In this case, sure, you could use a pedal to create distortion or use an attenuator. But you could also switch to a less efficient speaker.
If you want the best of both worlds – an amp that will keep up with the band but also offer sweet power tube distortion at a reasonable level, Eminence might just have the solution for you. The Flux Density Modulation (FDM) in their Maverick and ReighMaker speakers allows you to twist a dial on the back of the speaker and go from 91.5 dB to 99.5 dB. According to Anthony Lucas, “with the FDM technology, we are decreasing the strength of the magnet. When you turn the knob to attenuate, the magnetic strength decreases, and thus lowers the efficiency of the speaker.” It’s the perfect way to experience firsthand the impact of speaker efficiency on the volume of a guitar amp.