Decibels vs. Watts - Demand the TRUTH!

[woodman]

somebody (not me!) needs to calculate a scale like the heat index or the wind chill factor that considers watts, dB, tube vs. solid state, mojo, and various other factors. trained monkeys could test the amps at the factory, and an American Bandstand panel could vet it before it goes out the door. "i'd give it a 9, it has a good beat and you can dance to it!"

[JohnnyCrash]

Originally Posted by woodman

somebody (not me!) needs to calculate a scale like the heat index or the wind chill factor that considers watts, dB, tube vs. solid state, mojo, and various other factors. trained monkeys could test the amps at the factory, and an American Bandstand panel could vet it before it goes out the door. "i'd give it a 9, it has a good beat and you can dance to it!"

I don't know if it's possible given all of the variables.

Biasing - cathode versus fixed.
Biasing - how hot or cold.
Running voltages.
Tube manufacturing tolerances.
Speaker sensitivity.

Also, as Dacious mentions, different amps and designs may emit different frequencies that may, or may not, handle traveling through meat (people in the front row) as well as other frequencies. The guy in the back may not hear any top end by the time our speakers hit him in the face.

Another consideration - dB's might not really help us now how good an amp will work as well... consider the work (wattage) low-mids and bass requires. To keep those from falling apart at gigging levels may mean an amp that goes beyond dB specifications. Wattage specifications can help here. We can turn down the frequencies ears are sensitive to and still have low-mids and bass on tap.

[casadyrocks]

I can't even hear what your writing

[Dogbear]

European or African?

Estimating the Airspeed Velocity of an Unladen Swallow

http://www.style.org/unladenswallow/

11 meters per second, or 24 miles an hour.

BRIDGEKEEPER: Hee hee heh. Stop! What is your name?
ARTHUR: It is Arthur, King of the Britons.
BRIDGEKEEPER: What is your quest?
ARTHUR: To seek the Holy Grail.
BRIDGEKEEPER: What is the air-speed velocity of an unladen swallow?
ARTHUR: What do you mean? An African or European swallow?
BRIDGEKEEPER: Huh? I-- I don't know that! Auuuuuuuugh! [ explodes and dies ]
BEDEVERE: How do know so much about swallows?
ARTHUR: Well, you have to know these things when you're a king, you know.

What's the true db of 15 watts......

Huh, I don't know that Auuuuuuuugh...........

Sorry couldn't resist........

[Mr_Catch_22]

Just a couple things to throw into the mix...

Here's the way wattage ratings were explaned to me by an amp tech a while back...Wattage really is a throwback, but in a different way than from a design stand-point. Just like horsepower is a simple way to describe torque in a linear sort of way, wattage is used to describe power consumption vs output. Back when everyone had a 4-fuse, 30-amp current to power their home, wattage was a big deal. I forget the formula for converting watts to amp usage, but I'm sure one could look it up easily.

Another point to note is the classic question of what distortion really is. When does an amp TRUELY distort? Sure, you can mention 'clipping' and whatnot, but in layman's terms, most guitar amps are distorted at the point that they put out audible sound. To an audiophile, or blissfully-toneful noise boxes are crap. Even a bad home theater receiver rated at 100 watts will usually be rated at something like 65 watts RMS @ >.05% THD. An amazing tube amp (of 100watts) might get a similar rating of, say 60 watts RMS @ eleventy-billion% pure warm and fuzzy electrified heaven.

[Stewart Ward]

Originally Posted by Dacious

I see why you are somewhat peeved - for instance, these car systems where an amp half the size of a housebrick is supposedly putting out 400 watts stereo, from a couple amps @ 12 volts input. It might do - at exactly 3,422hz for one millisecond.

But if you told me amplifier A was 97 db at 50 feet, and amplifier B was 102 db at 50 feet I would have no way to quantify size. Again, the 102 db might be only at limited frequencies and only for a spilt second. Whereas the 97 might be bass frequencies and shake the floor.

Snip...

Well, that rashional can be applied to watts just the same!

[Stewart Ward]

Originally Posted by woodman

somebody (not me!) needs to calculate a scale like the heat index or the wind chill factor that considers watts, dB, tube vs. solid state, mojo, and various other factors. trained monkeys could test the amps at the factory, and an American Bandstand panel could vet it before it goes out the door. "i'd give it a 9, it has a good beat and you can dance to it!"

"Watts" is a precise measurement of power. V x I (voltage x current), I² x R or V²/R. It cannot vary according to which technology created it.

Valve watts and Tranny watts are, therefore, identical! No arguemnets about that!

BUT! Old tranny designs see the speaker load more like a resitive load, whereas, a valve amp does not... it's more complicated!

To measure output power into a dummy load resistor is dead simple. But that's not representative of the true output power into the speaker for an amplifier which employs an output matching transformer... beit valve or trannies with an output TX! Many early tranny amps had output TXs too, so they would behave exactly like a valve amp!

Traditionally, for example, any valve amp would have it's power quoted measured across a resistive load... so does a tranny amp. However, the matching of the output TX is only absolutely correct at a very narrow band of frequencies and is also dependent on the speaker's characteristics. So, as it happens, a valve amp with an output TX, can be outputting more power than is measured across a dummy resistive load! This is because, at certain frequencies where the TX matches to speaker's impedance closely, it can be 'magnifying' the voltage across the speaker load - especially when the speaker is at resonance resulting in far more bass output than a tranny amp. There are other things going on, far too complicated to explain here. Valve amps are nothing like accurate... they just sound cuddly in the lower frequencies and the human hearing translates extra bass as 'louder'!

The TX cannot match the speaker at all frequencies efficiently! The speaker is only it's rated 'nominal' impedance at around 200Hz. At other frequecies, the speaker impedance is higher than the nominal quoted figure. More complications!!

But basically, this is why, watt for watt, valve amps 'can' sound louder than a tranny amp of the same power rating without a matching TX. If you were then to add a matching TX to that quieter tranny amp, then the tranny amp would sound as loud as the valve amp!

It's nothing to do with the valves... it's the output TX which creates this additional percieved output!!

I bet this is as clear as mud? Never-the-less it's a very simple explanation of what is actually going on!

[JayFreddy]

Originally Posted by TelZilla

The truth is, the designs are so varied that ther is no good comparison, but lots of us have memorized some of these basic wattage figures...

Originally Posted by Dacious

That's why we use watts. 20 watts implies amp in one hand, guitar in the other. 100 watts implies trolley/castors.

Originally Posted by woodman

somebody (not me!) needs to calculate a scale like the heat index or the wind chill factor that considers watts, dB, tube vs. solid state, mojo, and various other factors.

Thanks for the education guys, some of this might seem like common sense to you, but I hadn't considered the issue of frequency response as it relates to db level...

As guitar amp and speaker technology starts to catch up with the rest of the world, I really like Woodman's suggestion of a "Mojo Index" that incorporates different factors such as volume, tone, durability, portability, durability, efficiency (power output/power consumption), design quality, and general coolness.

Tone will always be subjective and elusive, but decible levels over a range of frequencies might be useful. Also, as electricity gets more expensive, people will become more aware of the amount of energy their audio toys consume. In an age of greener marketing, a rating like the "EnergyStar" system used for appliances and computers could apply to audio appliances.

For musicians, energy efficiency is probably less important than other factors, but in the not-too-distant-future, if you're trying to power your entire home on a 500 watt solar unit... It's nice to know you can jam out without having to unplug the fridge.

Another crucial element, at least to me, is weight. My aching back really needs to find an good-sounding amplifier capabale of producing quality clean tones, comparable to a Twin, without weighing in at 87 lbs. Solid state, digital modeling, and neodymium speakers are promising, but I don't think they can deliver yet...

[Stewart Ward]

Originally Posted by Mr_Catch_22

Snip...
I forget the formula for converting watts to amp usage, but I'm sure one could look it up easily.

Power (P), in watts, is the product of at least two factors. So to find the current (I) consumed, you would need to know what the voltage (V) and resistance or impedance (R) values are: I = V/R.

So, to find I for a 100 watt amp into an 8 ohm load:

First find the AC voltage value...
V = P/R = 100/8 = 28.28VAC
(Voltage swing across the load is: 28.28 x 1.414 x 2 = ~80V peak to peak)

Therefore: I = V/R = 28.28/8 = 3.535 Amps

But in practise, it is pretty much impossible to measure power into a reactive speaker load, so you would have to use a dummy load resistor... which is also inaccurate for a valve amplifier which employs an output trasformer. It's only an idea of ball park power being generated.

Have fun!

[hondo76]

i never protected my ear growing up guns racecars airlpanes never. i wish i had as i am ONLY 19 snd suffur from hearing loss.i love it loud and i paid for it dearly. louder is not always better. take it from me.

[Steve G]

This is very interesting and I understand about half of it.
Great to have you on the forum Stewart!

[Ted Witton]

Hi Stewart,
I am the happy owner of one of your Session Stockton amps, so I can at least confirm that you can produce fine sounding and bloody loud SS amps in lightweight 1X12 cabinets. My query extends to the tonality. Let me explain.The Stockton is of course voiced on one channel particularly to recreate HankMarvin/Shadows VoxAC30 type response as heard on a recording whilst the other channel is of broader scope. In both cases it can get in the ball park of the valve amps that it is deigned to emulate, but after a couple of hours playing, my ears seem to get more tired than with a valve amp. There seems to be a certain "hardness" to the sound - something slightly less organic. Is this my imagination or is this the reality of analog SS? Incidentally, I get the same feeling with Tech 21 stuff which is I guess, your nearest US peer group/competition. Ted

[kennl]

use your ears to compare and choose an amp, not the specs
the only accurate "scientific" comparison would have identical (preferably flat) tonal response through the amps compared, and that will never happen
Ken

[reverbbb]

The wattage of an amp is directly proportional to your back strain. 20 watt amps tend to be less iron in the transformers. 5 watts are almost toyish in weight. But 100 watts is a back breaker. (All this discussionis relavent to tube amps).

Therefore, I conclude that watts have more to do with weight than decibels.

I think it was mentioned above, that smaller speakers can greatly affect the db levels, regardless of the amplifier rating. The speakers are often rated to match the wattage of an amp, but there is a large margin of efficacy involved.

BTW, I think a truer form of measuring sound levels are with SPL (Sound Pressure Level). SPL apparently takes into account frequencies and distance anomolies.

A favorite quote from a guitar playing friend of mine: "It was so freaking loud, I couldn't even hear it.".

[gaddis]

This was suggested by some of the others but the bottom line is this. Watts are measured at the speaker terminals. Decibels are measured in the room, some distance away from the amp. This adds variables that the amp manufacturer has no control over. They are not selling you the room, only the amp. With that in mind, using watts makes perfect sense.

[Snide]

But mine goes to "11"

[Stewart Ward]

Originally Posted by Ted Witton

Hi Stewart,
I am the happy owner of one of your Session Stockton amps, so I can at least confirm that you can produce fine sounding and bloody loud SS amps in lightweight 1X12 cabinets. My query extends to the tonality. Let me explain.The Stockton is of course voiced on one channel particularly to recreate HankMarvin/Shadows VoxAC30 type response as heard on a recording whilst the other channel is of broader scope. In both cases it can get in the ball park of the valve amps that it is deigned to emulate, but after a couple of hours playing, my ears seem to get more tired than with a valve amp. There seems to be a certain "hardness" to the sound - something slightly less organic. Is this my imagination or is this the reality of analog SS? Incidentally, I get the same feeling with Tech 21 stuff which is I guess, your nearest US peer group/competition. Ted

Hello Ted,

I wish I could offer you an explanation... but I guess the 'valve fairies' are wispering in your lug 'oles naughty things like... "Are you sure you should be using this fake?" or "Of course, it's NOT the real thing you know" or "But it's not even got a single valve in it anywhere!"

Auto suggestion is a very real thing... not only that, but your Stockton is about 1/3rd the size of an AC30. And everyone knows a bigger box gives a far more satisfying tone. Well, at least, they should know that!!

Hey keep it fun Ted and thanks for your kind words.

[anacephalic]

I think percieved volume has a lot to do with how an amp is voiced as well as speaker area (amount of air moved) and speaker type. My 35 wt Dr Z can appear insanely loud through two 12 celestions. if i put it up against my home stereo it cuts right through.

Home rig consists of high current (big power supply) tube monoblocks with 6 6550s per side rated at 220 wts. speakers have two 5 in mids and a 10 in woof rated at at least 93 db/m and they may even be 98db/m efficiency. i think the high end stereo amps use a lot of the power for speaker dampning to keep the bottom controled though how that works, bewond requiring high current capacity, i have no clue. i just know that for 220 watt they are not that loud.


There's that rule of thumb that it takes 10x power to double your Dbs...all else being equal. thing is those other things ain't often equal

[Stewart Ward]

Originally Posted by anacephalic

Snip...

Home rig consists of high current (big power supply) tube monoblocks with 6 6550s per side rated at 220 wts. speakers have two 5 in mids and a 10 in woof rated at at least 93 db/m and they may even be 98db/m efficiency. i think the high end stereo amps use a lot of the power for speaker dampning to keep the bottom controled though how that works, bewond requiring high current capacity, i have no clue. i just know that for 220 watt they are not that loud.


There's that rule of thumb that it takes 10x power to double your Dbs...all else being equal. thing is those other things ain't often equal

Guitar speakers are extremely efficient over a narrow band of frequencies. They are F1 by comparison.

Hifi speakers, to get a broad range, are designed notoriously inefficient! So 220W in hifi can be nothing that special. Especially when hif speakers are generally only 93dB sensitivity. This is 9dB less than a good guitar type, so your 220 watts is, in guitar amp/speaker terms, only 27.5 watts loud!!

Heavy damping will make your tube amp sound like a tranny amp... tranny amps have extremely low output impedances and sound 'flat' (as in unexciting) in the low and higher frequencies! Regular tube amps are hopelessly inaccurate for hifi reproduction... but they 'sound' cuddly and flabby in the bass areas... if that's what you like, due to their high output impedance and resultant lack of LF 'cone control' or damping!

The only similarity between guitar amps and hifi is that they both use amplifiers and speakers... beyond that, there's no comparison at all!

Actually, 10 times the power is twice as loud! 3dB, is double the power... far less than twice as loud!

[anacephalic]

thanks for the explination of the "tranny amp" that shows why they can accomodate a 4 ohm nominal load with lower dips. Flat in stereo land = neutral where the source supplies the excitement so that makes sence too.

i did say 10x the power was double the volume