Watts vs Volume

[bruce egnater]

This is the first of many "Tech Notes". These will be published on the Egnater websites in a few weeks. I think this is useful information so I thought posting here would be cool.

TECH NOTE #101
WATTS vs VOLUME and other stuff…..
November 2008

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. 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. What you are hearing in the Rebel is “the truth” about power tubes.

I hope this information is useful.
Bruce Egnater

[gldtp99]

Excellent info !!
I just built a 14/7 watt 2204-type head with pentode/triode switched cathode biased EL84's---- on the triode 7 watt setting it's still a LOT LOUDER than i thought it would be---- i've been testing it at highly cranked Vol/MV settings and the difference between 14 and 7 watts isn't so much a huge vol difference as a "feel" difference just as stated above---- with the triode 7 watt mode having a darker, thicker tone----absolutely way too much vol to be a bedroom amp when cranked.
Still a cool sounding amp but not exactly what i was expecting to come out with.

[tjmicsak]

I think this also illustrates the fact that much more of an amp's tone comes from the preamp circuit tone caps and filters than the power amp tubes. I was told by another popular amp maker that if you took any power stage and put a standard fender preamp circuit in front of it, no matter if the power stage is 6L6 or 6V6 or EL84s, it will pretty much sound like a Fender circuit, because most of the tone shaping is from the preamp. So choosing an amp for the power tubes rather than the overall circuit is kind of the wrong thing to do.
This also gives alot of credability to the MOD preamps by Egnator and MTS modules by Randall.
Although lowering the Wattage does not seem to make a large difference in volume, I would think the lowering of clean headroom would be a big factor in effect making the sweet spot available at a lower volumes overall and also add fatter tube compression (Sag) at say a louder "equivalent" volume, unless a solid state rectifyer option was available.
It would be really nice to have a Mod preamp feature coupled with a Rebel Power amp switching option so that the total amp Pre and Power circuits could be tailored/mixed/matched to provide the overall amp "models" that some might be expecting, and MANY others are dreaming of in one usable amp. Real Tube Modeling. One do-it-all amp that can give the tone of all the amps everyone loves.

[live-I-evil]

Wow, this was really helpful. I knew a lot of that stuff but hadn't ever heard of the Fletcher/Munson curvers. Thanks.

[oldmanmetal]

Interesting

[zenpeace69]

Just as an observation on the topic, I didn't read everything in this thread. I noticed the biggest difference with my Rebel 20's wattage knob when I was playing at lower volume. That's where it seemed to make a pretty big difference. Cranked, there isn't much difference in terms of volume.

[zenpeace69]

For what it's worth, I don't think you need to defend any of the options on that amp. It's a monster amp, and I appreciate (and use) the tube control and the myriad of lovely shades of clean to overdrive I can dial in between the master and the gain control.

Everything I used to love about my master volume JMP 2204 is right here in this tiny little package.

For me, after putting my Mullard ECC83 in V1 and a NOS 12AU7 in V2, all I have to do is set the three EQ knobs to 2 o'clock, adjust the master/gain accordingly for clean or overdriven tones, and sweep the tube knob all the way to EL84 for the overdrive and noon for clean tones. I run my pedalboard right down the throat of this thing and it freakin' loves it. I run a little delay on the clean tones for a splash of spacious echo. My RC Clean boost slams the overdriven channel beautifully. It even loves my fuzz without getting over compressed.

I think people who are nitpicking this amp are simply nitpickers. I think a lot of those people spend more time tweaking than playing. I've been there before, and it's a crappyu place to be. If you can't find some really sweet tones from this amp, your head may be in the wrong place. Just plug in, crank it, and let it rip!

[eurotrashed]

So basically the power scaleing and tube blending on the Rebel 20 is useless?

I keed, I keed

[Plague Dog]

I have never played a 20 watt or less amplifier that was loud enough to keep up with a band. I guess I just play with loud drummers and especially bass players. I swear, if the bass player can hear me at all, he turns up.

[big mike]

Bruce, these need to be in the MFR section.

[muddy]

regardless of toob diffs, that little amp (rebel) sounds phenomenal!


ml

[bkd_guitarist]

Bruce - great info, thanks for posting!

[mmorse]

How does your wattage control differ from a typical power scaled or power damped control? The reason I ask is because when I played through a Mojave Coyote with power damping, turning the control down had a very large effect on overall volume but the tone essentially stayed the same. Much like the effect of a UA.

As others have said, this was not the effect of the wattage control when I tried a Rebel. Just curious.