700w rms

What could that possibly mean?

http://www.lg.com/us/home-audio/lg-CM4550-mini-shelf

Look at the specs... 80W power consumption:

http://www.lg.com/us/support/product...Sheet-2016.pdf

[Michael Edwards]

Probably rated the same way they do shop vacs.

[3 Phase Lightbulb]

I absolutely hate to say this, but it actually sounds absolutely amazing considering the following:

Speaker wires are probably 64 gauge. I think carbon nano tubes are thicker than the speaker wires that came with this system.
The speaker enclosures feel very light. I assume the magnets on the drivers are smaller than the magnets found on the tips of Philips screwdrivers.
All of the speakers have "ports" but the ports are obviously not tuned but somehow they do sound like they were tuned if I didn't know better.
Excellent bass, mid-range, and treble. I must be getting very old as it shouldn't sound this good.
The USB MP3 player is fantastic. Very fast. Immediately skips to the next song as fast as you can press the remote buttons.
This is going to be a really great shop stereo that is replacing an old one that I was too lazy to toss in the dumpster.

[Mark Rand]

That's funny. I think I saw either that unit or a very similar one in a recent 'Black Friday' sale. Was severely tempted to contact our local Trading Standards Officer and suggest that they might want to prosecute the vendors for selling goods with a 'False Trades Description'

To be fair, my rather large and efficient speakers can produce 116dB with my 80W/channel amp, but I don't usually need that much noise in the workshop...

[J Tiers]

Hah.....

1) it is probably a PWM (class-D amplifier) which is rather efficient, even at reduced output levels, where an analog amplifier has horrible efficiency.

2) The standard power consumption is with a specific signal (a noise signal, as I recall) while putting out an average power of 1/8 or 1/10 of rated power (don't recall which), which allows for the peaks of the music signal to come through mostly un-distorted.

While putting out 70W (1/10 max output) it would be possible for a PWM system to use only 10 added watts for an 80W total.

As for the speakers, there are options with the subwoofer. The port might be a real port. the speaker may be equalized and/or operating with motion feedback so that it is not very dependent on the box and port for re-inforcement. (that does limit output). It may have a passive radiator (a second weighted speaker cone that acts as a port does).

For the mid-high boxes, there may be no port (sealed box system), or the ports may be real, since the ports for a higher frequency are smaller in length.

[Mark Rand]

None of that relates to RMS power. That'll be the steady state power that the amp can deliver into a load, typically resistive, at the impedance that the amp is designed to drive. The law is very specific about this. The law in question is the second law of thermodynamics

[J Tiers]

None of that relates to RMS power. That'll be the steady state power that the amp can deliver into a load, typically resistive, at the impedance that the amp is designed to drive. The law is very specific about this. The law in question is the second law of thermodynamics

Not at all. You are talking about a different thing. While true, it is not relevant to the situation described.

There are TWO ratings here.

First, the amplifier power rating, which we will assume is correct, since the outputs may not all be available to check, and there is no reason why it could NOT be true..

Second, the average power draw spec, the 80W, which is rated with the unit producing a lower utput, more relevant to actual use with a music signal

[BCRider]

PWM or not there is clearly some short term peak pulse RMS value going on. It doesn't matter how good an amp it is or if it's doing the PWM thing. We can't get 700W of steady sinusoidal power out of only 80W input power. So there's some very specific conditions applied to get a 700W rating for some very short duration pulse sort of thing going on here.

Yes, the steady 80W can be technically stored up in some manner and then blasted out to temporarily provide 700W for a short duration pulse. And it may be that they are taking the RMS value of that pulse to justify the 700W rating.

Or it might be a bold faced lie depending on where it was made.

[danlb]

We are all guessing. The lettering says 700W over stylized speaker symbols. There is no reason to think that it has anything to do with input power. The symbols tend to indicate that it's output power to the speakers.

As Micheal Edwards said in post #2, "Probably rated the same way they do shop vacs. "

So if the MP3 player has capacitor that stores enough power to emit a 700w pulse to the speaker for even a milisecond, that would probably satisfy the legal requirements.

Thinking about it, 80 watts is a lot for an MP3 player. I had a pocket model in 1999 that ran for 4 hours on a pair of AAA cells.

Dan

[J Tiers]

We are all guessing. ......

YOU are guessing. I have reasons for my answer...... At a previous employer I had to actually have things like that tested, both analog and Class-D. I could probably look up the exact test details, but they are more-or-less just what I said. So the low power consumption is not in any way unusual.

And, given the typical efficiency of a class-D amplifier, as well as the fact that hardly anyone makes analog amplifiers at that power level, I make it a 95% chance they are class-D.

Bottom line, it is all consistent with those ratings being PERFECTLY LEGITIMATE.

[danlb]

Jerry, Not sure that you read post #5. That's where the argument is made that it's quite possible to have 70 watts output. Then there's post #1 where it's talking about 700 watts of something.

BCRider and I agree in post #8 and 9 that they appear to be justifying a 700 watt claim using a very short duration pulse. Since LG is using symbols instead of words, none of us can be 100% sure of what the label is supposed to mean.

Does not matter too much, since 3PL (the OP) is quite satisfied with it's performance.

Dan

[Forestgnome]

I'm not buying it. If your amp is 100% efficient, you'll put out 80 watts RMS with 80W power consumption. Physics.

RMS is probably the brand name of the sticker. Note that RMS isn't mentioned anywhere in the specs.

[J Tiers]

Jerry, Not sure that you read post #5. That's where the argument is made that it's quite possible to have 70 watts output. Then there's post #1 where it's talking about 700 watts of something.

BCRider and I agree in post #8 and 9 that they appear to be justifying a 700 watt claim using a very short duration pulse. Since LG is using symbols instead of words, none of us can be 100% sure of what the label is supposed to mean.

Does not matter too much, since 3PL (the OP) is quite satisfied with it's performance.

Dan

Dan:

I WROTE post #5.

I DO know about the test methods, and understand the rules under which these things are rated. I spent more than 30 years in the audio biz. Yes I CAN be sure of what the label is supposed to mean.

A point was made in the original post citing the figure of 80W power consumption, and by implication, questioning the 700W total output. You'd look at that and determine that they do not agree, unless you understood what the two numbers are, and why they are different.

There is a recognized test for obtaining the power consumption, the 80W. It involves using a particular signal, adjusted to produce 1/10 average continuous power output relative to maximum power. The power consumption of the device is measured and that is the power consumption used for the standard rating, i.e. the 80W rating. This is the way the "CE ratings" are developed, it is a standard method for both UL and CE.

The 80W power consumption is quite possible / logical for a 700W class-D amplifier using class-D amplifiers.

The power consumption is therefore not measured at max output, because you cannot use the amplifier at max output, it would sound like crap, because audio signals have peaks. This is not some "peak music power" scam rating, the point of the test is that used "normally" the power draw is that 80W.

The "rms power" (there is no such thing) ratings are a separate issue. There are Federal Trade Commission rules for determining those power ratings, which I assume were followed. (At least there WERE rules for the last 40years, if the current administration has not got around to repealing them). There is no reason to believe the FTC rules were not followed, since the quoted power draw is consistent with the ratings being true.

[Mark Rand]

So if I play the toccata for Widor's 5th symphony or Fireball by Deep Purple I'm going to hit 700W RMS? Sorry, not going to happen on 80W of input!

[ed_h]

You guys aren't listening to Jerry. He knows what he is talking about.

Ed