wattage

[Geoff St. Germaine]

Also a 4000W RMS amp would need at a minimum 30+ Amps - so you better have a dedicated circuit. Unless 4000w is a fake rating.

All the amplifiers that I've seen that do more than about 1000 W draw more than 15 A at full power. To run a QSC PLX3602 at max power (3600 W) requires a current of 63 A at 120 V according to the QSC website, which your typical North American outlet obviously isn't going to provide.

 

[HELLonWHEELS]

Oh really? well your wrong sonny, a 3 dB increase is a noticable increase and requires twice the power but it does NOT double the volume

IIRC volume "doubles" every 10dB? i think thats right anyways, but i can seriously tell you that 3dB is not doubling the volume

let me see if i get you,

the differance between a 100watt amp and 200watt is only 3dB and

1000watt amp is twice as loud as a 100 watt, right????

EDIT: then is 30 watt amp have 3dB more than a 15watt? I don't see a ratio here!

EDIT 2: unless dB kinda work like the gears in your car it takes you longer and longer as you shift higher?

 

[seanm]

let me see if i get you,

the differance between a 100watt amp and 200watt is only 3dB and

1000watt amp is twice as loud as a 100 watt, right????

EDIT: then is 30 watt amp have 3dB more than a 15watt? I don't see a ratio here!

You are correct. The problem is that the "ratio" is logarithmic, not a simple m:n ratio.

And I think one of the problems with "you need 10x the power for 2x the volume" is that most people do not have a feel for what twice the volume is.

Twice the volume is a +10dB change. That is a huge gain.

 

[Stubb]

unless dB kinda work like the gears in your car it takes you longer and longer as you shift higher?

Bingo.

I'm all for having a ton of power avaliable. It'd be nice to have 2k watts at your disposal for some situations, if not for volume, for headroom.

That said, my 100 watt (tube) head and my 240 watt GK head have gotten me by in a lot of situations through the right cabinets. I even played against a Marshall halfstack with only 240 watts, a 2x10, and a 1x15. Part of the trick is in EQ, part of it in having efficient cabinets if you only have this much power, and part of it is in that GK seems to rate their amps conservatively.

 

[Herman]

Twice the volume is a +20dB change. That is a huge gain.

I think twice the volume is just a +10db change in sound pressure level.

 

[i_got_a_mohawk]

You are correct sir. [This invalid link has been removed]

Some better info: Invalid Link Removed

There are numerous other charts out there with the same results.

HELLonWheels187: My amp produces 800 watts into 4 Ohm, currently producing 600 Watts into a single 8 Ohm Avatar CB112.

Cheers for the link to that, i wasnt 100% sure about the 10 fold increase part, not done physics involving that kinda stuff in about 5 years so im a little rusty

let me see if i get you,

the differance between a 100watt amp and 200watt is only 3dB and

1000watt amp is twice as loud as a 100 watt, right????

EDIT: then is 30 watt amp have 3dB more than a 15watt? I don't see a ratio here!

EDIT 2: unless dB kinda work like the gears in your car it takes you longer and longer as you shift higher?

you got it right, have you ever looked at an exponential graph? if you know what they are then you'll get it

 

[seanm]

I think twice the volume is just a +10db change in sound pressure level.

Oops, you are right. I was thinking about a 10x voltage gain.....

 

[paulraphael]

You are correct. The problem is that the "ratio" is logarithmic, not a simple m:n ratio.

And I think one of the problems with "you need 10x the power for 2x the volume" is that most people do not have a feel for what twice the volume is.

Twice the volume is a +20dB change. That is a huge gain.

Also, remember that these guidelines about how many decibles=twice the volume are approximations. Very, very general approximations. Volume is a subjective quality that can be influenced by tonal balance, harmonic content, and probably a lot of other variables.

An unrelated advantage of more powerful amps is their ability to control speakers. I don't know if this is related to damping factor or something else. At a comparable volume with the same speaker, my 1000 watt amp will give a much tighter, more controlled sound than my previous 300 watt amp did. You could see the difference, too. With the 300 watt amp, the speaker cones would jump around visibly. With the thousand watt amp, I can only see cone motion when things are starting to break up from being driven too hard.

 

[HELLonWHEELS]

Don't the frequencies change the amount of dB's? I know a 100 watt 100 guitar amp cranked it extremly loud while a 100 watt bass amp is a wisper. I know it takes more power to produce lower frequencies, but how does the actual volume change?

How amny dB does bass amp put out at 100 watts(i can do the math to find out the rest)

 

[billfitzmaurice]

How amny dB does bass amp put out at 100 watts(i can do the math to find out the rest)

None. An amp doesn't put out any dBs, a speaker does, and how many depends on its sensitivity. Since sensitivity varies with frequency there is no simple answer. I run with a 175watt amp, and seldom actually use more than 50 watts, but since my speakers are on average 10dB more sensitive than the average that's the equivalent of having a 1750 watt amp and actually using 500 watts output.

 

[i_got_a_mohawk]

Also, remember that these guidelines about how many decibles=twice the volume are approximations. Very, very general approximations. Volume is a subjective quality that can be influenced by tonal balance, harmonic content, and probably a lot of other variables.

An unrelated advantage of more powerful amps is their ability to control speakers. I don't know if this is related to damping factor or something else. At a comparable volume with the same speaker, my 1000 watt amp will give a much tighter, more controlled sound than my previous 300 watt amp did. You could see the difference, too. With the 300 watt amp, the speaker cones would jump around visibly. With the thousand watt amp, I can only see cone motion when things are starting to break up from being driven too hard.

Volume isnt subjective at all, volume is volume, dB is the units used to measure SPL which is the Sound-Pressure-Level, this is a specific measurement

The difference is if your making your amp pump out more lows it will be quieter because it uses more energy as for more low end the speaker needs to be pushed out more

What can be taken into account is the percieved volume, and that is mainly because the human ears pickup distotion more noticable and make that appear louder, and the human ears are not flat in thier response, ie not all frequencies are picked up at the same level, even if they are at the same spl level

 

[Groundloop]

Don't the frequencies change the amount of dB's? I know a 100 watt 100 guitar amp cranked it extremly loud while a 100 watt bass amp is a wisper. I know it takes more power to produce lower frequencies, but how does the actual volume change?

There's a difference between Sound Pressure Level (SPL), which is measured in dbs (key word-measured), and how loud a sound seems to us. The measurement is absolute, but perceived loudness is affected by so many factors ranging from the tuning of the human ear, to someone having worked in a factory for 20 years with no hearing protection.

The best example I can think to show this difference is the episode of "Mythbusters" where they're trying to produce "The Brown Note" (subsonic frequencies that make you **** your pants). IIRC, the first frequency they tried was 7 or 9 Hz, and the guys from Meyer Sound said the SPL was (again IIRC) around 120 dB, but nobody could hear anything because the frequency was too low for us to hear.

EDIT: Link to Meyer Sound where they talk about how the testing was carried out.

http://www.meyersound.com.au/brownnote.shtm

 

[paulraphael]

There's a difference between Sound Pressure Level (SPL), which is measured in dbs (key word-measured), and how loud a sound seems to us. The measurement is absolute, but perceived loudness is affected by so many factors ranging from the tuning of the human ear, to someone having worked in a factory for 20 years with no hearing protection.

Exactly. SPL is probably the greatest single influence on loudness, so out of convenience we often equate the two. But there are many, many influences. Your ears are much more sensitive to midrange frequencies around 1 khz than they are to trebble and bass frequencies. Your ears perceive certain changes in harmonic content as changes in loudness, even when the SPL stays the same.

A study showed that after the first one or two doublings of loudness, a trumpet played progressively harder stops increasing SPL significantly. But we hear it as continuing to get louder and louder. Researchers found the amount of energy in certain upper harmonics to be increasing progressively, and have hypothesized that this has a powerful influence on the loudness we perceive.

Musical signals are harmonically complex. Human hearing is even more complex. We're learning more about both subjects all the time. Whenever someone tells you something like "watts is watts" or "that's impossible, you can't be hearing that," be a little bit skeptical.

 

[i_got_a_mohawk]

Exactly. SPL is probably the greatest single influence on loudness, so out of convenience we often equate the two. But there are many, many influences. Your ears are much more sensitive to midrange frequencies around 1 khz than they are to trebble and bass frequencies. Your ears perceive certain changes in harmonic content as changes in loudness, even when the SPL stays the same.

A study showed that after the first one or two doublings of loudness, a trumpet played progressively harder stops increasing SPL significantly. But we hear it as continuing to get louder and louder. Researchers found the amount of energy in certain upper harmonics to be increasing progressively, and have hypothesized that this has a powerful influence on the loudness we perceive.

Musical signals are harmonically complex. Human hearing is even more complex. We're learning more about both subjects all the time. Whenever someone tells you something like "watts is watts" or "that's impossible, you can't be hearing that," be a little bit skeptical.

Thats percieved volume, and trust me, doesnt make as big a difference as you would think (with anything other than the midrange as you and i explained)

 

[paulraphael]

Thats percieved volume

perceived volume IS volume. There is no objective measurement for loudness. when psycyoacoustic researchers want to determine volume, they get a bunch of test subjects and ask them to rate sounds relative to other sounds, and they make graphs to figure out the averages.

 

[i_got_a_mohawk]

SPL is volume, the percieved volume is the volume we percieve

Say there was something that created 100dB and it was solid at 30 Khz, we wouldnt hear it, but it would still have a volume

 

[paulraphael]

SPL is volume, the percieved volume is the volume we percieve

Sorry, Mohawk, but there is NO objecive measurement for "volume." Or loudness. They're purely descriptive terms.

While we're on the topic of what the measurements mean, it's probably worth bringing up what a decibel is (and isn't). Not only isn't a decibel an objective measurement of loudness, it technically isn't a measurement of anything. The decibel scale is used to compare values. You could measure changes in power, sound pressure level, water pressure, speed, or the money in your checking account using decibel scale.

When we use decibels to describe loudness, we're comparing the loudness of the measured sound to 0db, which is defined by the sound pressure level presumed to be the quietest that most people can hear. 3db is the sound pressure level produced by twice the power that produced 1 db. 10db is the spl produced by 10x the power. It describes a general relationship between spl and loudness. It is mathematically perfect, but experimentally approximate.

The reason for the logarithmic scale (which is always confusing to the math challenged, like me) is to make it easy to describe huge ratios. The difference in SPL between the quietest sound you can hear and the loudest sound you can stand is over a million. The db scale lets us describe these changes with small, easy numbers. Also, human perception of loudness roughly follows a logarithmic scale, so this makes decibels doubly convenient.

In recording, decibels are used simply to compare signal strength. 0db is used as the reference point; often it's the clipping level. In this case, 0db is clipping, -3db is half that level, -10db is 1/10 that level, etc.

this is an excellent web page with information on loudness, decibels, and also some reference to the human psychoacoustic principles behind it all: Invalid Link Removed

 

[HELLonWHEELS]

None. An amp doesn't put out any dBs, a speaker does, and how many depends on its sensitivity. Since sensitivity varies with frequency there is no simple answer. I run with a 175watt amp, and seldom actually use more than 50 watts, but since my speakers are on average 10dB more sensitive than the average that's the equivalent of having a 1750 watt amp and actually using 500 watts output.

So your saying the rated wattage of a head means nothing it depends on the sensitivity on the speakers. Then why doesn't everybody get an 150 watt head and put in more sensitive speakers?

 

[Herman]

So your saying the rated wattage of a head means nothing it depends on the sensitivity on the speakers. Then why doesn't everybody get an 150 watt head and put in more sensitive speakers?

It's not that the power of the head means nothing but it's the combination of your amp's power and the speaker's sensitivity that you need to consider. This link has a good chart showing the SPL you can get with different power inputs and speaker efficiencies:

Invalid Link Removed

I would take this chart with a grain of salt but it does give you a good idea of the interrelationship between the three variables.

 

[Figjam]

I use about 300 right now. My new setup that I plan on getting will put out a similiar amount into a smaller cab. I can combine the 2 cabs together if I feel like it to get around 600 watts though, If ever needed. I have yet to encounter a situation that calls for more than 300 watts though, because I dont play large gigs at the moment.