AMP POWER - significance of watts

[mmr7]

Could somebody explain watts and how it relates to power. What gives with amp power ratings. (seriously) I am confused. Mesa and Marshall make 150 watt beasts and line 6 and randall are rated at 300 watts. Overkill? "ghetto boxes" are rated at 400 watts these days. My wifes hair dryer is rated at 1850 watts. I don't understand. A portable cd player smokes a modern guitar head in watts but can't compete in volume. Why? Is a 200 watt head 2x as loud as a 100 watt head?

Also, why don't guitar players use (those that use rack equipment) the preamp of choice and match it to a PA style power amp (on the level of 500-2000 watts) for gigging, not bedroom practice. I've seen guys slave 5 marshall heads together, why not just use one very powerful power amp? I know this sounds like stupid questions, but I really don't understand the coorelation between watts, power, and volume.

Finally, I heard that a bass player's amp should have at least 3x the watts of the guitar players amp to be heard because of the demands of powering those low frequencies. Does that mean if a guitar player uses thick strings and tunes way low (A or G) that he effectively lost volume, power or whatever?

Finally #2 So about my question of power amps, is it feasible to get more volume and presence by using a PA power amp (1200 watts) hooked to a head or preamp so long as the cabinets are power matched for handling?

Thanks

[rickboot]

Watts, Power, Loudness (volume)

Watts are a unit of power so they are directly related. I think what you want to know is how does wattage affect our perception of loudness. First, an important thing to know is that doubling power does NOT equate to a doubling in loudness. As a matter of fact, doubling power makes the sound *slightly* (just noticeably) louder. To get a double your loudness and double your fun you need 10x the power. So a 10 watt amp is half as loud as a 100 watt amp. A 10 watt amp is still REALLY loud.

Guitar VS PA Power Amps

You could hook a guitar preamp to a PA power amp, but it would probably not sound good. I suspect it would be a little harsh sounding. PA power amps are designed to faithfully recreate the sounds they are amplifying. They are more hi-fi. Guitar power amps are purposely designed to shape the tone and the tone changes when cranked.

Low Freqs

Yes. Lower frequencies require more power, so a tuned down guitar could use a little more power.

Turn that #$%^ down!

You seem to be very concerned about getting a ludicrous amount of power. Where are you playing that requires this much volume? Madison Square Garden? Please warn me because I don't want to go! I still want to have kids one day. :biggrin:

[bammbamm]

Don't confuse output power with power consumption.
I.E. A "ghetto box" is rated at 350 Watts, that is not going to be how many watts of out put power you will get. More likely you'll see around 6 Watts at the speakers. Look for the "output power" , *RMS , or Peak output values. *An amp that is capable of putting out 100 Watts is probably drawing close to 4-500 Watts to run the whole system. Power is derrived by this formula
Watts = Volts x Current *or P = I x E ( P = power, I = Current, and E is Volts) if you have for the sake of ease, an amp that is capable of 120 Watts, you can determine that you are drawing around 1 Amp of current or 1000 Milliamps 120 x 1= 120
Output power is typically measured at the output transformer or speaker.

Rick is correct about the perception of sound VS. power, you effectively double the amount of power to increase your output by 3 DB *.

Hopefully you're not completely confused at this point.

Bamm

[rickboot]

And we haven't even talked about speaker efficiency inaccurate mfg ratings yet. This a truly complicated topic. I suggest researching more on the net. All this info will sink in over time.

[ChrisReedSmith]

So if a 100 watt head is only 3db louder then a 50 watt, then why use it?

[ardell henderson]

I have to throw this in on this post -

I hear people say that 50 "tube" watts is much louder than 50 "solid state" watts. *How come "tube" power has different results than "solid state" power?

And then, I hear people say that, for example, Mesa Boogie's 50 watts is more powerful than, say Marshall's 50 watts, etc.? *How can this possibly be?

Does the answer to these questions have something to do with the frequencies & bandwidth that the amp pushes/enhances? *Just reaching in the dark on this...

[rickboot]

Mesa watts are not more powerful than Marshall watts. Watts are watts.

As I alluded to earlier, some manufacturers are more conservative in their power ratings. Mesa is known to be conservative or at least more honest. Other manufacturers may exagerate their claims. Also, there are different weighs to measure power and other specs (like THD), so it is really easy to exagerate claims legally.

There are many factors with affect how what sound pressure an amp puts out is. Wattage is only one factor. How efficiently an amp uses those watts is a big factor. The same is true of cars. A car with more horsepower may not be as fast as a car with less horsepower even if they weigh the same amount.

As ardell hinted at, how we perceive loudness is a big factor. It is believed that tube amps sound louder (even at the same sound pressure levels) because of the even harmonics that tube amps add. The distortion and compression characteristics of tubes also affect perception. In addition, if an amp accentuates certain frequencies it may be perceived as louder even though on measuring equipment it isn't.

That's it for now. My brain is tired. It must not have enough power.

[mmr7]

Man I thought I was confused before... :-) OK 2 more question then since speakers are a factor. Would a fifty watt amp going through 2 speakers be as loud as a 50 watt amp (everything same and equal) going through 8 speakers. Also, since it seems you need a ten fold increase in watts to get a *3 fold increase in volume, using a pa power amp (say 750 watts per channel) hooked to a pod pro or other preamp is not really overkill at all and seems a good way to get headroom and not max your amp all day (unless its tubes which I guess need full volume for good sound) Thoughts?

[7 Dying Trees]

Speaker ratings are there to make sure that you don't put an amp on them with that'll blow them. Generally speakers with lower wattage rarings will distort faster.

THink of your stereo, you normally want speakers with a higher rating than the amp, lest you blow them up/damage them!

And yes, different frequencies will sound louder to the ear (you dstinguish changes more). This is how mp3 works, by the way, it compresses certain frequencies more than others because the human ear is insensitive to them. So a valve amp might be the same wattage on paper, but might accentuate a frequency range that the ear percieves as louder. Then again it might be a "preconception" or bias that people have ingrained into them. I've always wondered what a blind listening test would yield in terms of results...

In the end it's one of these things where manufacturers will tend to "fudge" results a bit to make their product more attractive. I'd go with the general rule of look at the approximate power rating people put on the amp to choose a range of things you are looking at, and then go by ear...You ear will tell you more than anything else.

(P.S:I often find that annoying/bad/abysmal sounds are louder than anything else as well, so I am thinking that if I ever need more volume that I can just dial in a really crappy sound and be louder than everyone else! )

P.S: my brain is starting to hurt as well....

(Edited by 7 Dying Trees at 9:51 am on Aug. 24, 2001)

[bluenote]

its a misconception that speakers are blown do to watts......how the get blown are by either an abrupt spike or by pushing them hard for a long period of time.....in other words, a 25 watt greenback doesnt always blow faster than a 75 watt speaker

most 100 watt amp heads arent 100 watts...almost all of them run a little over 100 watts whne cranked.....its a estimate

the reason people choose 50 watt heads over 100 watt heads( or vice versa) is personall prefrence....some say that 100 watt heads have more headroom.....i dunno about that.....what always struck me as funny is when i would hear guitarists say they need a 100 watt head so they can be heard over the drums(etc.)....thats a sure sign that that person is a beginner or just plain scary.....read other posts about the db change in watts.....i have a 30 watt amp that i still cant crank up cuz its too loud........

hairdryers use a lot of electricity.....more than your TV....just as long as the amps are low, youll be ok on your bill

more speakers, more loud.......simple, more of a vehicle for the sound to travel

you can use a 100000 watt power amp if you like......you wont get to user all the watts unless you like to turn it up all the way.......then youd be deaf and all the glass would break in your house

in reality, dont worry about the watts......worry about impedence

remeber, its the amps that kill.....the volts just throw you across the room

[Vaibanez]

I'm still a bit confuzeld, my self.
I've read a lot about an amps power consumption as it relates to wattage, but no one has touched on how wattage relates to output.

Loudness, and its relation to wattage aside, can be explained by different voicings. Fender 100 watt amps sound totaly different than Marshall 100 watt amps that sound different than Legacy 100 watt amps that sound blah, ba-blah, ba-blah.

What I am curious about, is the output to the speaker(s). I was under the impression that Wattage is the rate of cunsumption in electrical terms.

Volts = the number of electrons
Amps= the current (how fast)
Ohms= pressure in the line(heat)
Watts= rate(how much in a given time period)

J>:thumbsup:

[mmr7]

also, people have been telling me its much worse to UNDERpower speakers rather that overpower them. In that case, a 100 watt marshall head attached to a full stack (600 watts for the speakers *[75x8]) it would seem the head is woefully inadequate to power these speakers and they are at risk for damage. But obviously that is not so, so what gives?

[keith]

So...we're looking at amps with two different ratings on them. Input power and output power.

Let's take my amp for example...a 30 watt valve affair.
it's output is 30watts, yet it's input is 100watts. You ask what gives. Nothing is 100% efficient. Watts is equal to Joules per second in terms of power, and 70watts is the amount of joules per second used or lost throughout the circuit as any type of energy other than sound. [i.e. - the output rating on amps is the amount of energy it actually manages to convert to sound in one second from the entire amount which the amp sucks from the wall outlet]

Now, those 70 watts are usually lost as heat energy and light energy.

Now, speaking in linear measures [i.e. - not db's], when you compare a 50watt amp to a 100watt amp, the 100watt amp is in fact delivering double the sound or sonic energy of the 50watt amp in one second. Thus one can say that the 100 produces twice the sound energy
of the 50 watt amp. However loudness is different. Typically, if loudness has increased by 3dbs, it already means it has doubled.

Decibels or db's are not your typical linear measure. That is, 100db is not twice as loud as 50db. It's much more than twice as loud. I read in a review somewhere that switching a 100watt amp to the 50watt option 'only' lowered the volume by 3dbs. Hell, that's already quite soemthing.

AND. mmr7, about that underpowering issue. Speakers will not be damaged by underpowered amps. This only occurs in hi-fi systems where an over eager user pushes a small amp over the limit with his big speakers and fries everything. The 100watt Marshall you're talking about typically delivers power spikes of up to 250watts, so that 100watt is only a stable average.

BTW - all of this is ultra basic O level physics...there's a lot more to know.

[SalemB]

A typical school exercise is to calculate the shortcut current of an amp as well as the open circuit voltage.

The shortcut current is the the current running through your speaker if the speaker was a wire. The open circuit voltage is the voltage on the output if you disconnect the speaker. If you multiply these values to get the effect, you are getting an insane amount of Watts. This is the effect that many manufacturers are labeling their ghetto boxes and car stereos with.

It is complete rediculous as the shortcuted circuit would burn your output transistors or tubes and you can't get the open circuit voltage and shortcut current at the same time. From a marketing point of view it's great though.

[bluenote]

again, the watts of the head have nothing to do with the speakers....all you need to worry about is the ohms( load) on the speakers

oh, i was thinking this morning on my drive into work....steve vai used to use PA power amps in his guitar rig......as did Eddie Van HAlen......steve used those carvin FET1000(or was it FET1500) power amps...eddie of course used H&H power amps......this is a common practice in guitar rigs to power the speakers in a stereo rig......because of the clarity in the power amp wont color the tone of the amp heads