I’ve come across a couple of general purpose powered monitors recently, for which the power ratings have got me scratching my head. I wonder if anyone here can tell me what’s going on.
The first is a Behringer monitor that I bought for use in the band. It’s marketed as a 200W unit. However, the rating next to the kettle lead socket says 35W. The only rating info in the user manual says ‘Power consumption at 1/8 full power = 35W
The second is a Yamaha monitor/PA speaker that a friend just bought. It’s similar in that it is marketed as 400W, but the rating next to the kettle lead socket says 60W.
Both units are plenty loud, certainly way louder than I would have expected from the 35W or 60W ratings on the back of each, so neither unit is particularly deficient. I just like to see a rating that means something.
i get that this type of equipment is often quoted with peak and RMS ratings, but the consumption at 1/8 full power seems like witchcraft to me.
can anyone enlighten?
Thanks
Comments
The Kettle Lead ratings are most likely 'average' ratings.
But it's all a bit unclear how they test these things.
As olafgarten says, consumption is a sustained level and will typically be much lower than RMS figure. You always need to take the 'power rating' on PA speakers with a large pinch of salt. There doesn't seem to be a standard and many of the budget systems quote peak power or that great marketing invention - music power.
As well as the amplifier's power you also need to consider speaker efficiency. The most reliable measure is spl (measured in dB). Again, not all manufacturers will measure this the same way but it's a better indicator. It's also quite telling when no figure is quoted.
dB is a logarithmic scale. It is generally accepted that a system with between 6 to 10dB additional level will be perceived to be twice as loud.
https://en.wikipedia.org/wiki/Sound_power
https://en.wikipedia.org/wiki/Electric_power
R.
Eqd Speaker Cranker clone
Monte Allums TR-2 Plus mod kit
Trading feedback: http://www.thefretboard.co.uk/discussion/60602/
I tested my ‘200W’ Ampeg Micro VR - which is about as loud in use as my old 100W Peavey Century - and has a quoted power draw of 150W. I was expecting the true power output to be somewhere around 100-120W, but to my great surprise it *does* actually put out 200W... and draws 288W, ie almost double the quoted power.
So the problem is that you can no longer rely on adding up the quoted power consumption on all your equipment if you need to assess whether you can run it from a single socket or a particular extension cable... because the numbers are now basically meaningless.
"Take these three items, some WD-40, a vise grip, and a roll of duct tape. Any man worth his salt can fix almost any problem with this stuff alone." - Walt Kowalski
"Only two things are infinite - the universe, and human stupidity. And I'm not sure about the universe." - Albert Einstein
The wattage of your monitors is confusing. For marketing purposes, the rating that is generally the product name is usually the max output of a powered and unpowered monitor. Something to do with ohms. A single powered monitor is usually half that figure.
R.
Eqd Speaker Cranker clone
Monte Allums TR-2 Plus mod kit
Trading feedback: http://www.thefretboard.co.uk/discussion/60602/
The trouble with audio is your dealing with AC currents across reactive loads and feeding the system a sine wave of 50 \ 60 Hz so you need some maths to do the correct calulations
For AC 230V \ 240 it's power factor X amps X volts roughly ... inductive loads have a PF of 0.7 \ 0.8 ... to get watts
But you see stupidly low wattage ratings next to IEC sockets all the time ... the Mackie SRM1801 are marked 150W or so despite the fact the unit's will draw 700 odd watts at full power
This actually makes sense if the risk factor is overheating the supply cabling, since that is cumulative over quite a long time (since PVC is a very good thermal insulator), but it's going to be a real problem if you hook up a total of "2KW" or so - from adding up the power consumption figures - to a 13A socket, and the short-period power draw is more like 4KW... resulting in a blown fuse.
"Take these three items, some WD-40, a vise grip, and a roll of duct tape. Any man worth his salt can fix almost any problem with this stuff alone." - Walt Kowalski
"Only two things are infinite - the universe, and human stupidity. And I'm not sure about the universe." - Albert Einstein
One or two of you have mentioned acoustic power/energy. It occurs to me that I’ve always assumed that amplifier output ratings are stated in terms of electrical power delivered to the speaker(s). I appreciate that not all speakers are equal in terms of efficiency,but I must admit I had never thought of the output rating as taking into account the speaker efficiency.
@ICBM, I’d be interested in how you measured/calculated the input and output power of the two amps that you mention.
From memory I think audio products are tested at 1/3rd maximum output power.
The logic is that for music reproduction, the average power when the peaks are clipping is about 10% of maximum power, hence the surprisingly low apparent power requirements for many products.
Eqd Speaker Cranker clone
Monte Allums TR-2 Plus mod kit
Trading feedback: http://www.thefretboard.co.uk/discussion/60602/
Not totally accurate but close enough to tell which of the two quoted power ratings was true.
"Take these three items, some WD-40, a vise grip, and a roll of duct tape. Any man worth his salt can fix almost any problem with this stuff alone." - Walt Kowalski
"Only two things are infinite - the universe, and human stupidity. And I'm not sure about the universe." - Albert Einstein
The website that @robinbowes linked to has answered my original question quite nicely. Apparently, in the audio/PA world the 1/8 full power measure indicates the power consumed when a device is occasionally clipping a musical signal, meaning that the output from the device will be as loud as it will go while sounding acceptable from the distortion point of view. It makes sense to assume that this refers to a typical dynamic music signal and therefore represents power consumption in typical usage.
Speaker efficiency has nothing to do with the power of the amp or the power rating of the speakers. It's certainly a factor in the overall volume a system will produce, but not what we're talking about here.
The problem is that 'typical' is not a very good reflection of real-world use.
Suppose you're going to use the same PA for a folk band, and a metal band. The ratio of average to peak power will be completely different in both cases.
"Take these three items, some WD-40, a vise grip, and a roll of duct tape. Any man worth his salt can fix almost any problem with this stuff alone." - Walt Kowalski
"Only two things are infinite - the universe, and human stupidity. And I'm not sure about the universe." - Albert Einstein
See https://en.wikipedia.org/wiki/Sound_power
R.
Eqd Speaker Cranker clone
Monte Allums TR-2 Plus mod kit
Trading feedback: http://www.thefretboard.co.uk/discussion/60602/
It's the same measure, putting 1 watt of electrical power through a perfectly efficient speaker will produce 1 watt of sound power.