How much power is enough?

Eric Jaeger · From: Oakland, California, USA

Does anyone have real hard data on power used? Different speakers have different efficiencies (usually expressed as "x" dB @ 1 meter @ 1watt). In addition, since achieving twice the apparent volume (+10 dB) requires more than 10 times the power (every 3 dB increment of volume requires twice the output power), most of us are probably using a lot less power than we think.

For example, if your little Radio Shack dBa meter shows 120dB (it hurts), do you have any idea how much power you're actually using? If it takes 200 watts to get 120dB, it would take 100 watts to get 117dB, 50 watts to get 114dB, 25 watts to get 111dB, 12.5 watts to get 108dB... pretty soon you're only using one watt and you're still over 100dB!

So why do we hear so little about speaker effieciencies and so much about the drawbacks of "low power" tube amps? A lot of guitar players are going to ridiculously low power amps (Carr has a $2000 8 watt/12" amp) in search of better tone at "normal" volumes.

Are we all wasting our time on this high powered amp thing?

-eric

Donny Hinson · From: Glen Burnie, Md. U.S.A.

Eric, you pose a lot of questions, I'll give you my opinions on some answers.

First off, speakers are terribly inefficient devices. I suppose that the average efficiency for all speakers used in our applications would be around 5%. You feed in 100 electrical watts, and you get 5 watts of actual audio out. Different frequencies take different amounts of power to produce the same perceived loudness, due to the non-linearity of our hearing response, and to the non-linearity of our speakers. (Most amps have a non-linear response, too, but we'll ignore that for the time being.)

Amps are usually blessed with "cut" tone controls. The tone controls don't add anything, they only attenuate or reduce specific frequency bands to give us the tone we desire. A 200-watt amp needs all the controls maxed out to produce those 200 watts we're looking for, but amps usually sound terrible with all the tone controls turned all the way up. So, you turn down the treble, and you lose a little output. You turn down the mids, and you lose a little more. Finally, you turn down the bass some (to keep the "woofing" down), and you lose a little there, too! So, now in addition to the speaker losses (which, as you recall, were about 95%), you've got all those losses due to contouring, or shaping the particular tones to your liking.

Sure you can get speakers that are more efficient, but they usually sound terrible. Remember those little amps the barkers used to use at carnivals and fairs? They were usually 5-10 watt amps that drove one of those little metal horn speakers. Oh yeah, they could be heard a quarter-mile away, even with all the noise, but the tone was lousy. They were only reproducing a very narrow band of (voice) frequencies. However, when you want good solid tone, amp power has to go up, and speaker efficiency has to go down, that's just the way it usually works. Bass-reflex (closed-back) speakers are more efficient, but they get that efficiency at the expense of distribution. They focus more sound out front, and therefore are more efficient. Bad thing (sometimes) is that they're also more directional. You don't hear much to the sides or in the back.

Now, let's look at all this together...

You start with a 200-watt amp, and you lose 190 watts just converting that to audio. Then you take that audio and contour it so it has the qualities you want, and now you lose a good portion of that, so your husky 200-watt amp actually puts out about 7 or 8 watts of clean audio, the sounds you want. I emphasize "clean" because that's what we pedal steelplayers are looking for. Sure, a guitarist can make out with much less. He's not interested in a clean signal (they actually LIKE distortion). He wants those highs and mids to really crank. Also, he's not interested in bass response. It's bass that takes "lotsa watts". Reproducuing treble sounds (where our ears and speakers are most efficient) only takes a few electrical watts. I can still remember a textbook in my electronics class about 50 years ago that stated..."5 watts of power fed into an efficient speaker system is more than the human ear can stand". I guess it goes without saying that that guy wasn't a bass player or a steeler!

Summing all this up, you could say that we need as much as we need. Depending on the tone we like, and the speaker efficiency, we may need tons of power...or we may need just a little. I can guarantee you, though, that an 8-watt amp (even if it costs $2,000) would be pretty useless on stage if we didn't mike it, and also pretty useless if we were interested in a really full, clean sound. We steelers also like to sustain notes with our volume pedals, so we need even more volume than a lead player, who just uses distortion for sustain. That's why you can't compare amps in different applications. A screaming Tele player may only need 40 watts, whereas a solid-sounding steeler may have to have 200. A crude analogy would be one with vehicle horsepower. That 100hp that drives a cycle like a rocket will barely push a sedan down the interstate...same horsepower, but in a different application, it performs much differently. Low frequencies are like the weight of that sedan - taking much more power to push 'em.

As far as the "It takes 10 times the power to make an amp twice as loud" thing, I don't find that to be true. To my own ears, it only takes about 4 times the power; a 200-watt amp sounds twice as loud as a 50-watt amp.

Speaker efficiency is just a dark subject. It doesn't generally sound good, so they (the manufacturers) don't like to talk much about it. Would you buy a speaker that bragged it was only 3.5% efficient? (Actually, that's pretty good, a lot are 3% or less.) But those little numbers can mean big changes in perceived output. A one-percent change in speaker efficiency might have the same effect as raising the amp power 25-50 watts!

Something to think about, anyway.

[This message was edited by Donny Hinson on 07 July 2006 at 02:56 PM.]

Robert Leaman · From: Murphy, North Carolina, USA

Here is a realty check. The United States Army Band with a full complement of musicians and each musician playing at double fortissimo can achieve 25 watts of actual audio. I have no idea what the sound pressure level is for this example.

Eric Jaeger · From: Oakland, California, USA

Donny, great feedback. I'm an engineer by profession, so this stuff interests me. I'm really beginning to wonder about our ideas about power based on some of my own experiences, as follows:

I play bass, guitar, and steel:

For bass, I have two amps (350 and 900 watts) and 2 enclosures (4x8 and 1x18). I pick the amp based on the venue, whether I'm using the 6-string (that low B)or not, and the enclosures I want to use. I've NEVER turned either amp past 6.

For guitar, I have an early 70's silverface Twin that I haven't used for more than 10 years, because I haven't played any gig where I could turn it up past about "4", so it sounds terrible. I have a '65 Deluxe Reissue that's too loud these days, as well, since it needs to be over "7" to sound decent. I think I need a smaller amp. (I treat lap steel as a conventional guitar). I also use a Mesa Maverick and a Mesa 20/20 sometimes, but neither of those get turned past "5" most of the time, so they're not doing their best either. I see more and more guitar amps with multiple output power settings (1/10, 1/2, 1, 5, 30 watt, for example).

For pedal, which I'm still pretty new at, I'm trying various combinations of the above. There are a lot of possible combinations (using a Mesa Studio Pre into the SWR 900 into the 18" will rattle your foundations, but the highs are ugly Smile

). None of them provide good tone at a reasonable volume yet.

A couple of other datapoints: 1/2 watt into a Klipschorn will make a small auditorium uninhabitable. My 100w PA amp into two 10" PA speakers can overwhelm the Twin (!).

So, for those of you with high-power rigs, how high do you ever turn it up?

-eric

(By the way, the 2xpower=+3dB, and "twice the volume = +10dB" are in the textbooks, which doesn't make them right Smile

).

[This message was edited by Eric Jaeger on 07 July 2006 at 04:03 PM.]

Eric Jaeger · From: Oakland, California, USA

p.s. on volume pedals and sustain...

I may be missing something, but I don't see how it implies you need more power. If you pick hard, and generate, say, 600mw with the pedal attenutating the signal to 100mw, and as the pickup volume/output drops, you ride the pedal so the volume stays constant, you're maintaining that 100mw into the amp, and your amplification needs don't change at all.

Am I missing something?

-eric

Donny Hinson · From: Glen Burnie, Md. U.S.A.

Not really, Eric, you just have to consider overall available gain.

Here's an example...

Let's say a 60-watt amplifier needs half a volt to drive it to full output. Now, if your pickup only puts out half a volt, that half a volt starts decaying almost immediately. If the amp gain and pedal are both maxed out, there's no way you can maintain the 60 watts output, right? Okay, now, let's take the same scenario with a 200-watt amp. (It too takes half a volt to drive to maximum output.) So, we give the amp (which is wide open) a little less than half pedal on the volume. The amp's only seeing 2 tenths of a volt, so it's not putting out it's full 200-watts, but somewhere's closer to 60 watts. Now the signal starts to decay, so we ease the pedal down, maintaining that same 2 tenths of a volt, so the amp's still putting out that 60 watts. (Remember, we couldn't do that with the 60-watt amp.) The signal decays more, and so we max out the pedal...still (temporarily) maintaining that same 60 watts output. Of course, in time, the signal level falls to the point that, even with all that extra gain we have with the bigger amp, it starts to fade...and the output drops down below 60 watts. Nonetheless, we've managed to maintain that same 60 watts' output a lot longer with a 200-watt amp than we ever could with the that 60-watt amp.

That's a layman's explanation of how a high-powered amp gives us more sustain than a low or medium-powered one.

David Doggett · Posted 7 Jul 2006 6:48 pm

Let me try to say the same thing as Donny in an even less technical way. The volume pedal, like the typical passive tone controls, is a cut-only control (active pedals do give a little signal boost, but it is just enough to keep the tone even over the whole pedal range). If you played pedal steel with the volume pedal bumping maximum, you would only need an amp as big as a regular guitar players amp. But what would be the point of having a volume pedal then? You could not use it to get any additional sustain. In fact steelers typically attack notes with the volume pedal only maybe 1/3 of the way on, and the rest is reserved for sustain. So whether you measure in db or watts, you need an amp 3 times more powerful than a guitar player. But you are playing with finger picks, not flailing away with your whole arm and a flat pick. So you need even more power. Finally, guitar players like to play in the top 10-25% of the amps output range, to get that "bloom," crunch, and grit. Guitar amp makers count that distorting top 25% as usable power (it's the top 50% for some guitar amps). If there is any such distortion in the top of the amp's range, steelers would avoid it. So steel amps are made conservatively and only count the clean volume, and limit the controls so the amp can't be pushed into distortion. Again that means more power. Put it all together, and I figure a steeler needs 4 to 8 times more power than a guitar player. So if the Tele player is using a 25-50 watt amp. The steeler needs 100-200 watts, just to keep up.

Having said that, it depends on the style of music. When I play rock and blues on steel, I play more like a guitar. I can use the volume pedal 2/3 or 3/4 of the way open. I don't need a lot of sustain. I don't mind if the amp distorts some. I might even use a stomp box for distortion, and that might add sustain. So for that, I can use an amp the same size as the guitar player, or maybe a little bigger. But if the group also plays some country or country-rock, then with the smaller amp I am bumping the volume pedal to maximum, and running out of sustain on the long notes. So I have to bring a bigger amp, just for those numbers.

If you can mike the amp, then you only need an amp loud enough to match the stage volume. But I sometimes play with ex-punkers playing alt country at very loud rock club volume, and nothing is miked but the vocals. Neither a 200 watt ss NV400 nor a 135 watt Twin are loud enough. A 180 watt Super Twin is, and a 300 watt NV1000 probably would be too (but I don't like loud ss tone).

The bottom line is, you can't necessarily calculate how much power you need theoretically. But trial and error teaches you how much power you need to keep your volume pedal from bumping.

------------------
Student of the Steel: Zum uni, Fender tube amps, squareneck and roundneck resos, tenor sax, keyboards

Jim Sliff · From: Lawndale California, USA

One of the biggest misconceptions is measuring power and using it to compare volume levels.

The two are basically unrelated. you have to know the THD (total harmonic distortion), at what ferequencies, the speaker efficiency, the total volume of air movement from the speakers, the type of waveform (a tube amp has an apparently louder volume level, all else being equal, than a solid state amp because of the different harmonic content).

There are far too many variables. I have a 30-watt Holland 2x10 combo that is far louder than a friend's 100-watt Marshall JCM 800 4x12....and much, much louder than a 100-watt solid-state Marshall through anything we could find.

A Vox AC30 is blisteringly loud and can keep up with a 100-wat Twin without breathing hard. It's a 30-watt amp.

What I'm indicating is that "how much power is enough" is a question that can't be answered.

Ask instead - "How loud an amp do I need?" describe where you play/site conditions and read descriptions posted.

Power is simply useless as a volume measurement.

Donny Hinson · From: Glen Burnie, Md. U.S.A.

jerry harkins · From: kingsland tx

Do you mean ^^%*^%%$@%$#!#@!%$$*&^%(*)(*_)+_)^(%*%$$%#^*_)? Think I'll just turn a nob and push my pedal. Yall lost me somewhere!

Eric Jaeger · From: Oakland, California, USA

Jim and Donny - great info. Jerry, some of us are too curious for our own good :-)

I'm beginning to see the light in here, I think. We need power to move air. Also, the steel register is lower in pitch than your average guitar. As Jim notes, steelers like cleaner tones than most 6-stringers, so we don't want to drive the electonics into fuzz, but we do want a little crunch, or we'd all be using 400 watt hi-fi amps. And we need enough power so that the input sensitivity of the amp allows us to deliver enough output at relatively low input values.

So, since lower pitch tones reguire more power for a given volume (as in my bass amps), and we want less distorion at any given output level, and we want a reasonable output level with lower input voltages, steelers generally use amps more powerful than your average guitarist but less than your average bassist. How am I doing so far?

That being said, where do you set your master volume? "7"? "11" (thanks Spinal Tap)?

And why not combine a tube preamp with an FET output stage, since high-powered tube amps are ferociously expensive? Then you could compensate for the low input voltage in the preamp stage and get by with an output stage a little lighter and cheaper?

Just some thoughts....

-eric

T. C. Furlong · From: Lake County, Illinois, USA

Loudness and percieved loudness is a very complex subject. I have been doing lots of research in the area for an article that I am working on for a trade mgazine. The two main things that need to be considered when talking about how loud something is are simply distortion and headroom. If a signal is distorted, the waveform is much harder on the ear and is percieved to be louder than an SPL meter will measure. That's why a distorted guitar amp with a Stratocaster can have 20 watts and seem like it's ripping your head off. Many steel players like to avoid a distorted sound. Clarity of tone is part of the "sound". The key to clean, undistorted sound is headroom. Headroom is the difference between the average demand on the amplifier (typical musical content) and the instantaneous demand on the amplifier(peaks such as the attack of a picked note). I think that a steel guitar amplifier should have a decent amount of headroom. In my research, 400 to 500 watts with a reasonably efficient speaker (JBL, Peavey, EV, etc.) will allow enough headroom to allow clean playing in a typical stage environment. If you play with a loud band, double it. You gain 3dB of headroom when you double the watts or you gain 3dB when you double the cone area of the speaker. If you double both you get an increase in headroom of 6dB. I think that the popularity of stereo rigs is partially due to the fact that you double the power and double the cone area resulting in 6dB of additional headroom. If you like a distorted "edge" to your steel guitar sound, a lower power say 50 to 100 watts will provide a distorted sound. But then you are kind of stuck with that sound. In the early days of steel, players such as Vance Terry, Leon McAuliffe, and Joaquin Murphey would compete with large bands using smaller amplifiers that were somewhat distorted. Lots of single notes were used to limit the demand on the amp.

Also, Donny is right about low frequencies requiring more power that high frequencies. The rule is four times the power for every octave lower you want to reproduce. So...C6th players who like the 8th pedal (boowah) should have plenty of available power.
TC

Twayn Williams · From: Portland, OR

A Vox is a bass shy amp. Whether this is due to the EL84 power section, or other design elements, it's not exactly a function of "power". My 22 watt DRRI has quite a bit more bass than my AC30. OTOH, it's true that the power required to create low notes is greater than high notes, which is why bass amps tend to use so much more power -- but there are so many parameters involved, that it can be difficult to give hard and fast rules. Also, one person's trash-tone is another's treasure.

I'm pretty much of the opinion that if a well-tuned Twin doesn't give you enough power, then you're going about it wrong. One sure way to get more power on stage is to tip the amp up towards your ears, and not deafen the back of your knees!

Eric Jaeger · From: Oakland, California, USA

Interesting. I didn't know the bit about the effect of cone area. Since an 18" speaker has more than double the cone area of a 12", and a 15" is more than 60% bigger than a 12", I can see why steelers have more of a preference for 15's than 6 stringers. I think I'll start looking for a 15...

-eric

Jim Sliff · From: Lawndale California, USA

Donny - absolutely correct about lows, but IMO it's more critical in the bass guitar fequencies - that's why bass players use 1500-watt SS power amps, but very inefficient speakers (intentionally).

OTOH, for steel a mid-power range...say 100 watts of typical tube power (AKA Twin Reverb) through a tighter speaker like an EV or Weber California will handle STEEL bass fine (note I omitted JBL's - personal preference, I don't think they sound good with anything).

The Twin Reverb was THE steel amp for a long time, at least on the west coast. With EV's or even stock CTS speakers a Twin can do the job. So IMO, power is mostly critical in how it interrelates with the speaker AND bias settings. 400-500 watts of SS power "sounds" kind of like 100 watts of tube power because of waveform diferences, but they will both handle the full range with the right transducer.

Bobby Lee · From: Cloverdale, California, USA

I use a 40 watt tube amp. It's enough for most of the small venues I play.

John Bechtel · From: Nashville, Tennessee, R.I.P.

I don't know how this statement adds to the foregoing comments, but; I'm using the 85-Watt ’65 Re-Issue Twin~Reverb Custom™ 15 and have never set my volume above (4) in public! Seems like quite enough, so far!

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“Big John”
a.k.a. {Keoni Nui}
Current Equipment

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