Valve Amp Wattage and Perceived Volume

jaymenon · September 2023

While not microscopically precise, I found it interesting - because dropping down from a 50W to 20W amplifier does not make it significantly quieter in practical terms...

In a nutshell - it would appear that to halve the perceived volume, you need to reduce wattage to 1/10th (10%) of what it was.

Compared to a 50W amp:

40 watts is 94% as loud as 50 watts.

30 watts is 86% as loud as 50 watts.

22 watts is 78% as loud as 50 watts.

20 watts is 76% as loud as 50 watts.

18 watts is 74% as loud as 50 watts.

10 watts is 62% as loud as 50 watts.

5 watts is 50% as loud as 50 watts.

1 watt is 31% as loud as 50 watts.

0.5 watt is 25% as loud as 50 watts.

ICBM · September 2023

Yes, although it does depend on what you mean by perceived volume, and in what context. You can't put figures as accurate as those percentages on it. It's often said that a 10W amp is half as loud as a 100W amp, but anyone who has ever played a proper 100W amp turned up full knows that is very far from the whole story... 100W just has a much more aggressive, visceral power that makes it seem a lot more than twice as loud as 10W. (Even through the same cab/speakers.)

In a band mix it's even more noticeable, especially when you go from an amp that's about 3dB quieter than the rest of the mix - basically inaudible - to one that's 3dB louder than the mix - overpoweringly loud. That's only a 6dB change, which is equivalent to four times the power, but it can be nearly as much as that with only a 3dB change (twice the power) if it's also from 'under the mix' to 'over the mix'. EQ/voicing also makes a big difference, especially in the upper mids where the ear is most sensitive.

Modulus_Amps · September 2023

Its all fine and well comparing numbers like that but how we all perceive loudness is down to personal perspective/reference point.

For example, if your max squat in the gym is 50kg, if someone loaded 100kg on the bar the extra weight would be crushing.
I can squat 100kg easily, but if you put 200kg on the bar it would be crushing for me.

So similarly I play guitar quite loud at work, cranking a 50w amp is not out of the question - just not for very long. Most people who don't get to do that would find that sort of volume overpowering because most home situations don't allow more than 5w of audio output before neighbours start getting annoyed.

ecc83 · September 2023

Phoar! Can of worms this! To even start to get an idea of Perceived Loudness the first thing you would need to do is setup two SPL C meters very close to the persons ears. "P L" is only loosely related to nominal power.

Loudspeakers are far from pure resistances and so you would have to have a true rms voltage and amp meter in the circuit and use a signal such as band limited pink noise. The amplifier would also need to be a very low distortion solid state design because valve OP stages have a high output impedance that complicates the issue. Low distortion because we perceive a distorted sound as louder than a clean one.

Once you have some figures for RMS V and I at various levels you can calculate the power involved then refer that back to speaker sensitivity. (you would really need Cellys to give you a calibrated speaker!) .

But! Loudspeakers and especially GUITAR speakers are not linear. SPL at one watt will not directly relate to SPL at 100W. THEN there is Thermal Compression!

And lastly there is the Temporary (but not forever!) Threshold Shift effect to take into account. After about ten minutes exposure to very loud sounds our ears start to shut down.

Dave.

BillDL · September 2023

Modulus_Amps said:

I can squat 100kg easily, but if you put 200kg on the bar it would be crushing for me.

Show off

Fingers657 · September 2023

2 pints on the bar is just about right.

p90fool · September 2023

Percentages are meaningless in a band mix. I use valve amps set clean in my band and a 50w amp is fine, but a 20w amp (supposedly 76% of the perceived volume) is almost inaudible.

jaymenon · September 2023

In a band mix, I agree, but for playing at home relative / subjective volume is quite relevant

Nerine · September 2023

People that claim “I can’t imagine why you’d need more than 20w” have never played in a loud band with a 100w monster (2203) behind them.

jellybelly · September 2023

And then you throw speakers in the mix!

A 30w with a Vintage 30 supposedly as loud as a 60 watter through a Creamback!?! Impossible to even try and account for all the variables.

Modulus_Amps · September 2023

jaymenon said:

In a band mix, I agree, but for playing at home relative / subjective volume is quite relevant

Your Stock TV probably has 5 - 6w Speakers in it.

Modulus_Amps · September 2023

Fingers657 said:

2 pints on the bar is just about right.

No Joke, I can't handle 2 pints - puts me straight to sleep!

BillDL · September 2023

Modulus_Amps said:
No Joke, I can't handle 2 pints - puts me straight to sleep!

Aye, but that's 2 pints of Witblits

ecc83 · September 2023

To return to the 'science' for a moment? IMHO it would help the consumer if amplifier power output was specified at a certain level of harmonic distortion. For a guitar amp that could be "X watts at 10%THD" . That might seem horrendous in these digital days of three decimal place interfaces but in fact 10% THD is actually perceived as just starting to "sound a bit rough". Though of course, you would not want to listen to a Bach choral at that THD!

For example the ubiquitous EL84 can deliver 4-5W at 10%THD from a single, cathode biased valve. A pair can give you around 15-18W at the same distortion level.

Such a specification would I think ease some of the confusion delivered by reviewers and daft YT people claiming "monster 'king loud" from a pair of 12W valves...We would know they are telling porkies (or don't know WTF they are talking about!).

The stated power would be measured with a true rms voltmeter across a stated resistive load and expressed as "P=V sqd/R for a 1kHz sine. None of this "RMS watts" bollocks! The measuring gear and the THD software is readily available now to anyone, even boutique back shed builders. In fact the software is free! Mind you! Anyone capable of putting a guitar amp on the market should be easily capable of building their own THD rig.

Dave.

slacker · September 2023

Perceived volume is in the ear of the perceiver. You have to play at the volume suitable for the application and the right amp and speakers to do it.

ecc83 · September 2023

slacker said:

Perceived volume is in the ear of the perceiver. You have to play at the volume suitable for the application and the right amp and speakers to do it.

To a limited degree yes. But you HAVE to start somewhere and having a solid figure for the ACTUAL V times I into (say) 16 Ohms at least makes comparisons a bit more realistic.

You also cannot play amplifier A at 95dB SPL for ten minutes then switch to another. Your hearing is *****d and you need a good 2 hours to recover before checking amp B.

Dave.

ElectricXII · September 2023

Context is really important. The sound engineer asked me to turn down my mic'd AC15 at Saturday night's sound check because it was apparently so loud that he had the fader on the mixer channel barely above off. The master volume on my amp was at between 10 and 11 o'clock, which is roughly where I run it at rehearsals in a much smaller room.

I get that he needs to set an overall mix that he can control in the context of an overall FOH volume level, but I need my amp to be at a half decent level on stage or it's just not very enjoyable. The room had a capacity of 200 people. so it wasn't a wee pub. and the FOH level was such that you had to talk loudly into people ears to be heard, so it wasn't exactly a quiet gig.

I just can't see me ever needing a 50 watt or 100 watt amp, unless I was playing an outdoor gig.

ecc83 · September 2023

Then the sound engineer was a t**t! Even the cheapest mixers have gain pots and channel faders. There should be no problem setting a usable fader level for any dynamic mic on a cab. Some capacitors mics maybe but then any decent sound guy would have some XLR attenuators in his gig bag!

Dave.

slacker · September 2023

There's so many factors here. Sidewashing the amp or angling up can reduce for volume. Speaker efficiency. Pedals. Sound engineer.

All variable.

I use various amps and pedals to get a good sound at various volumes. I actually don't like it too loud as I sing and there's a top volume before things start howling.

impmann · September 2023

Nerine said:

People that claim “I can’t imagine why you’d need more than 20w” have never played in a loud band with a 100w monster (2203) behind them.

I have - I gigged with a (real) plexi in my first band when they were worth a pound a watt. Sold that to buy a Marshall Jubilee 100 - bad idea, dreadful sound, different story. I also gigged with two AC30s most of the 90s with the originals band. It was all too bloody loud, but back then PAs were shite and it was all we knew.

Today, playing in 99% of pubs 20w is more than sufficient especially if you have a decent PA, unless you have someone else on that stage being a prick.

ElectricXII · September 2023

ecc83 said:

Then the sound engineer was a t**t! Even the cheapest mixers have gain pots and channel faders. There should be no problem setting a usable fader level for any dynamic mic on a cab. Some capacitors mics maybe but then any decent sound guy would have some XLR attenuators in his gig bag!

Dave.

His point was that the amp was nearly loud enough in the room not to need mic'd. I didn't turn it down much though.

slacker said:

There's so many factors here. Sidewashing the amp or angling up can reduce for volume. Speaker efficiency. Pedals. Sound engineer.

I always have my amp at around 45 degrees to the front of the stage and also angled up to avoid beaming the audience and so that the other guys in the band can hear me, especially if the amp isn't in the monitor mix.

ecc83 · September 2023

"His point was that the amp was nearly loud enough in the room not to need mic'd. " Well it was still within his gift not to amplify you at all! Not get arsey about it!

Dave.

ElectricXII · September 2023

ecc83 said:

"His point was that the amp was nearly loud enough in the room not to need mic'd. " Well it was still within his gift not to amplify you at all! Not get arsey about it!

Dave.

Absolutely!

slacker · September 2023

Sound people are variable.

I played bass in a band that had ahem a sound engineer. The band played whilst I transposed the chords. Soundman shouted at me I was too loud. I said I wasn't playing. He said if you were you would have been too loud. Band leader asked him to stand down shortly after.

There were a series of gigs in one week two bands a night short changeover. soundman. was nearly deaf. He had an assistant who helped him and they did a great job. One night the assistant was ill. He still did a better job than most I've worked against.

Modern venues and presumably modern sound engineers want a quiet stage. It's sound reinforcement not sound control.

Secret_Sam · September 2023

BillDL said:

Modulus_Amps said:

I can squat 100kg easily, but if you put 200kg on the bar it would be crushing for me.

Show off

He's including his own body weight :-)

ICBM · September 2023

slacker said:

Sound people are variable.

I played bass in a band that had ahem a sound engineer. The band played whilst I transposed the chords. Soundman shouted at me I was too loud. I said I wasn't playing. He said if you were you would have been too loud. Band leader asked him to stand down shortly after.

I assume he wasn't just joking...

Once, at one of the only gigs I've ever used my own 4x12" at, as I wheeled it onto the stage a voice came from the monitors - "John, you're too loud!"

. I recognised the voice though (a sound engineer I knew quite well), and knew it was a joke, so I thought "I'll show you what Too Loud is... " and set up my 50W Fender Bassman head at 7/7/7 - into full power stage overdrive - and played a few chords. The Voice then said "Are you *really* going to play at that volume?" To which I replied "Is it a problem?"

There was then a long pause, and finally he said "Actually, you're about right" (this was quite a big club) "so it will save me the bother of mic'ing you up. Have fun!". I played the whole gig at that volume and it was the best sound I've ever had on stage.

GoldenEraGuitars · September 2023

When music and volume gets broken down into numbers like that I just switch off.

Barquentine · October 2023

I've often played with a 50w combo turned up about half way. Does this mean I could have used a 5w combo turned all the way up?

ICBM · October 2023

Barquentine said:

I've often played with a 50w combo turned up about half way. Does this mean I could have used a 5w combo turned all the way up?

Maybe, maybe not. It totally depends on the taper of the volume control - it might be putting out 90% of its maximum clean power at halfway up. So many people don't realise this when they're trying amps - it's probably why companies make amps with ridiculous tapers like the Fender Hotrod, which typically reaches full power at about 4 or 5 out of 12, so they seem far louder than ones with sensible tapers... and we all know that louder is better

.

When I had a 100W 2x12" I used to typically play it with the MV at about 11 o'clock. One day after having to carry it back up to my 2nd-floor flat, I decided to measure the power output, and buy a smaller amp of whatever power that was - to my surprise it was only 11W, so I bought a 15W amp. It *was* "loud" enough, but it had nowhere to go in terms of dynamics, and it sounded a bit 'small'. Over the years I traded up to bigger and bigger amps, until finally I got 'my sound' back when I reached a... 100W 2x12".

And I still play at the same volume I always have, about 10-15W. It's total nonsense that a big amp is too loud, or overkill, or being wasted, or doesn't sound as good turned down as a smaller one turned up - it all depends on what you want from it, and personally I prefer the big amp sound. It may be too heavy or I may be too old, but that's a different problem

.

Dave_Mc · October 2023

Barquentine said:

I've often played with a 50w combo turned up about half way. Does this mean I could have used a 5w combo turned all the way up?

You could probably replace that 5W combo with a fuzz pedal...

...in other words pretty much what @ICBM said. A 5 watt amp won't sound the same as a bigger amp, especially if it's cranked into meltdown and the bigger one isn't...

Yorkie · October 2023

Barquentine said:

I've often played with a 50w combo turned up about half way. Does this mean I could have used a 5w combo turned all the way up?

Besides power, there’s also the speaker factor — most 5W combos I know have a 10” speaker.

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Valve Amp Wattage and Perceived Volume

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