volume vs wattage

[JDC]

if I have say 100W head with a 200W cab, will this be the same volume as say a 50W head with a 250W cab?

I know wattage and volume are ment to be related but I've seen solid state and hybrid amps with crazy amounts of watts hence, me = confused

and do solid state amps get damaged without a speaker load?

[gwEm]

if I have say 100W head with a 200W cab, will this be the same volume as say a 50W head with a 250W cab?

essentially what speakers do is transform electric power into sound power.

all the matters is the input electrial power, and the efficieny of the speakers at performing the transformation.

the wattage rating of the cabinet refers to how much input electrical power the cabinet can handel without damage. it doesn't affect volume.

efficiency of the speakers is the 'sensitivity' measurement in decibels. decibels are a non-linear scaling. 3dB translates to twice as much. decibels are used as human hearing is also non-linear in a similar way.

a 100W head with a 97dB cabinet will be as loud as a 50W head with a 100dB cabinent.

I know wattage and volume are ment to be related but I've seen solid state and hybrid amps with crazy amounts of watts hence, me = confused

many hybrid amps have a solid state output stage, so for the purposes of this point, its kind of the same.

valve amps can produce crazy power too... but they'll need lots of very big valves, and a huge output transformer. it would generate alot of heat, and be somewhat heavy and impractical.

solid state amps don't need an output transformer, and operate more efficiently meaning the engineering challenge of getting big power is easier.

however the power rating of guitar amplifiers is given with an undistorted sine wave...

valve amps will produce more output power when the guitar signal gets distorted, and they sound good at the same time.

solid state amps have hard clipping after maximum output is reached, and don't sound good.

thats why many people talk about 'valve watts' being louder and so on... its not really true at clean levels, but with overdrive then its a different story.

and do solid state amps get damaged without a speaker load?

it depends ;) often not though

[Roobubba]

The "power rating" of a cabinet is merely a description of the maximum constant power that it can handle. An amp rating relates to the output power (which can peak higher, by the way) - this means that a 100W amp can put out 100W (peaking ocasionally at considerably more, maybe 150W? not sure on figures!)

A 50W head with a 250W cab puts out 50W and doesn't damage the speakers, we hope.  A 100W head with a 200W cab puts out 100W, and *should* be ok with the cab when cranked, but I thik a safe value for the cab is at least twice the power of the amp.

Volume is broadly speaking related to power output. A few notes to make though:
1) Valve amps *sound* louder, so a 50W valve amp with the same speakers equates to something like a 200W solid state amp (through the same speakers)
2) The volume of a speaker is not related to its power *handling*, it is related to the amount of power *put into it* and the speaker efficiency. Speaker efficiency is measured in decibels (dB) You might also see "SPL" knocked around - that's the sound pressure level - all the efficiency/SPL readings you see on the web for a speaker refer to the same thing. A 97dB SPL speaker will be *half* the volume of a 100dB SPL speaker with the same input, will in turn be half the volume of a 103dB speaker...
Different speakers have very different characteristics - some will make the bass sound much louder than the mids, or the treble - etc - you get the idea.

3) A 50W valve amp with efficient speakers is more power than you will strictly require anywhere - when a venue is so big that you need to mic up the guitar amp, this will definitely be the norm for that venue anyway.

4) Solid state amps don't *usually* require a speaker load like valve amps do. This doesn't really mean anything though: why would you want to turn on the amp with no speaker attached?

Hope that I've got this right, and that it helps :D

Roo

EDIT: beaten to it, damn!

[gwEm]

1) Valve amps *sound* louder, so a 50W valve amp with the same speakers equates to something like a 200W solid state amp (through the same speakers)

only a fool would deny that a valve amp appears louder than a solid state amp of the same rating.

i'm not sure about how much though, and i would be interested in an experiment to determine this.

we pitted a 20W handwired marshall against a 100W AVT and the AVT was noticeably louder. i'm going with a 50w valve amp equates to something like a 125W solid state.... any more ideas on that?

EDIT: beaten to it, damn!

;) i'm fast this morning

[Mr Ed]

I'm running my JCM900 on 50W mode through a 2x12 with a pair of V30's... am I going to die? :(

[indysmith]

^ well obviously it depends which amp you're talking about. My friend's Rockerverb 50 2x12 combo is significantly quieter than my jcm800 50W 2x12 combo...

[gwEm]

^ well obviously it depends which amp you're talking about. My friend's Rockerverb 50 2x12 combo is significantly quieter than my jcm800 50W 2x12 combo...

!!! wow, i'm surprised

[Will]

I think that I read somewhere that a 50w amp will peak at 80w
so for a 100w amp, a 160w cabinet would be advisable, presuming you had it constantly on 10

[JDC]

I think that I read somewhere that a 50w amp will peak at 80w
so for a 100w amp, a 160w cabinet would be advisable, presuming you had it constantly on 10

if a 50w amp peaks at 80w, then why does an engl screamer combo only have a 60w vintage 30 speaker

thanks for all the quick replies, I deffo learnt something new today

[indysmith]

^again, it depends on the amp, and especially how it's rated! i.e. british manufacturers usually rate the wattage of their amps CLEAN, whilst in the states they tend to rate them dirty. (therefore meaning that usually a 50W british amp is louder dirty than a 50W yankamp) Also - modern speakers can usually handle a bit over what they're rated at.

[Mr Ed]

So, again, running a 100W head (although running at 50W) through a pair of V30's isn't gonna kill them?

[gwEm]

So, again, running a 100W head (although running at 50W) through a pair of V30's isn't gonna kill them?

amp rated at 50watts continuous, into a cab rated 120W continous - very much doubt thats going to be a problem.

if it was me i'd run the amp at 100w and not sweat it - i play a 50w amp into a 60w cab.

[indysmith]

of course not! you could probably run it at 100W and not do any damage
EDIT: mymy Gwen, you are on the ball today

[Mr Ed]

Hmmm, I only use it on 50W so I can crank the smeg out of it at practise without killing anyone...

[Roobubba]

yeah 50W into 2 x 60W speakers is definitely OK.

Another point to note is that the rated wattage on amps is really only usually a marketting ploy. Some companies (eg Matamp) are more modest with their ratings. I'd be willing to bet that a 50W matamp would be VERY loud through some efficient speakers!

Oh, and speakers often take more than their rated maximum, as has already been alluded to. These numbers that are banded around are really only ballpark figures for every day use. The testing is done in "non real-world settings", often with sine-wave sounds etc.

Roo