By Bruce Egnater
There is some confusion about the relationship between watts and volume (loudness). There is much discussion about how this many dB is twice as loud as that many and that many dB is double the power and blah blah…… lot’s of techie rambling but no real world explanations. I’ll try. Let’s say you have a guitar amp with a knob to adjust the power (watts). Now say this amp is 20 watts at its maximum power setting and 1 watt at the lowest knob position. It would be reasonable to assume that 20 watts should be loud enough to play with the band and 1 watt would be whisper volume. Anyone who has had the opportunity to test this theory has found quite the contrary. 20 watts through a reasonably efficient speaker is quite loud. 1 watt through the same speaker is also quite loud. What’s up with that? Have you ever seen the specs for a 12” speaker? A typical guitar speaker will produce about 95 to 100dB at 1 meter (about 3.3ft) with 1 watt of input power. Now put 2 or 4 of that same speaker in a cabinet and the output is even higher. What this is saying is that even with a mere 1 watt of power, that speaker will put out the volume about equal to a person yelling. Obviously not “TV watching” volume. To obtain that whisper volume, you might need as little as 1/10 of a watt but…….at that low a volume, most guitar speakers start to sound terrible. In addition, there is a phenomenon that occurs with human hearing that is documented by Fletcher and Munson (two really smart guys) that graphs the way we hear things at different volumes. Look it up on the internet. The Fletcher/Munson curves show how our ears, at lower volumes, are less responsive to low and high frequencies. That means the quieter you play, the more we tend to want to boost the bass and treble to compensate for our own hearing. Ever seen the “loudness” contour switch on a home stereo? That is what the switch does. It boosts the treble and bass to make it sound better quiet. On a guitar amp you often find knobs for boosting the low and high end in the power amp section. Typically these controls are called Presence for the high end boost and Resonance or Depth or Density (Egnater) for the low end. At low volumes you typically turn those controls up but the louder you play, the more you find you need to turn them down. Fletcher/Munson again.
Because we make guitar amps with variable power (Rebel) and switchable power (Tourmaster and Modular), we get inquires about this all the time. Often players will use one of our amps and it appears that the power cut feature doesn’t do much. Please allow me to explain. Let’s say you are playing an amp at home or in a music store at relatively low volume. Recall what was said earlier about how little power it really takes to get a fairly loud volume. If you’re playing quiet, you might be using even less than 1 watt to obtain the loudness you’re at. If you have a chance, try this on a Rebel. Play fairly quiet and turn the WATTS knob from 20 watts to 1 watt. What do you hear? Very little change! Why? Because at that volume you probably are not even using up 1 watt let alone 20 watts. Sort of like driving a car at 5MPH. It doesn’t matter if the engine is a 100HP or 500HP, you are still only going 5MPH and using very little HP to maintain that speed. Same with your amp. To cruise along at low volume requires very little power (watts). Having the extra horsepower (watts) doesn’t make the amp louder when you play at low to medium volume.
Now try this with your Rebel. Set the power to 20 watts, turn the master full up and turn up the gain knob until you start to hear some distortion. It will be loud. While you’re playing turn the WATTS knob down. You will clearly hear and feel the way less power creates a spongier, lower volume tone. Some players are saying the knob isn’t really cutting the power but is reducing the headroom. Call it what you will, the result of reducing power is more of a “feel thing” than a volume thing. Ultimately the idea is to set it to where you like the sound and be happy…..play your guitar.
While we’re on the subject of the Rebel, there has been some talk about how, when panning from the 6V6 tubes to the EL84 tubes, the tone difference is not what some expected. It is believed that by simply changing power tubes you can make a Fender (6L6 power tubes) sound like a Marshall (EL34 power tubes) or a Vox (EL84 power tubes). What you are hearing in the Rebel when you go from 6V6 to EL84 is the real difference in the sound of those two types of tubes. It may not be quite as dramatic as many believe but that is the reality of it. The tonal difference between various types of tubes is more subtle than many believe. A few people have even been disappointed when using the TUBE MIX features because their expectations of what should happen were really not based in fact. The intangible characteristic is the change in “feel” between different types of tubes. These subtle differences do become more apparent at higher volume when the power tubes are “pushed” a little more into overloading. What you are hearing in the Rebel is “the truth” about power tubes.