Axiom Home Page Forums General Discussion Technical Questions Measuring power going to speakers?

Just curious how to measure how much power is going to the speakers in my system?

Last night I hooked up the other M3 to the centre channel in parallel and it sounded AWSOME. Wow, there was no sign of current limiting (while driving all 5 channels) and I had to decrease the trim by about -5db on the centre (I am sitting about 12 feet away from the centre channel).

I then watched about 1 hour of Battle Star Gallactica (I must say that the drums that play regularly in that series sound WICKED on the M22s and the EP500 sub, frackin' eh!) with the Parallel M3s.

I was listening for any signs of distorion at all...I thought I mabey heard some, so I disconnected one of the speakers (I should add here that my wife was totally freaking out for me pausing and rewinding this one scene where I suspected the distortion). After cutting it down to one M3 the scene sounded exactly the same (I was pushing the AV reciever a bit to -20dbs for a bit to see if the RX-V659 could handle the 4ohm load on the centre, not sure how loud that is, my wife again told me to turn it down ).

There was a major diference from parallel M3s down to 1 M3, the 2 M3s in parallel sounded just so awsome, I couldn't believe it.

Back on topic in my own topic...how can I measure the power going to each channel to see how much current they are all getting?

This is getting into the, too much time on my hands, things to do list.

I would use a multimeter and measure the AC amperage going out to the speakers and then the voltage, from that you can calculate the wattage. I don't remember the formula's any more. I checked my system real quick and found I had 270 milliamps at low listening levels, I forgot to write down the voltage, my kids were battling at the time.

I am guessing you are concerned about the parallel M3's power consumption?

Formulas and calculation Electrical voltage, current, resistance, and power

>>I am guessing you are concerned about the parallel M3's power consumption?>>

Exactly, in the manual is states that a 4ohm load is ok for the mains, but a 6ohm should me the max that should be used for the centre channel.

I suspect that all is well, I just want to make sure that I don't ruin anything. I bought the 5 year extended "exchange for any model for any reason" guarantee from Sounds Around, so at least I know that if someting blows in the 659, I am covered. But from the sounds of it, i thought that the amp was handling the load very well and judging by the fact that I had to trim down the centre channel -5db proves that there is no current limiting going on (right?).

Hi,

You're OK so long as you aren't hearing any distortion. If the amp goes into current limiting, then the overall power output is reduced so it could clip (distort) more easily.

You won't hurt anything because the amp's protection circuit would normally shut it down if the output transistors got too hot. All protection circuitry usually has thermal monitoring to shut down the amp if the output stage overheats.

Measuring real-time power output levels is really difficult because of the constantly varying music signal, so you'd want to know what the peak values are. In some ways, it would be easier to put an oscilloscope across the amp output signal and monitor the waveform for any evidence of clipping. You can see that when the top and bottom of the waveform is truncated. If that occurs, I expect you'd hear the distortion because it would be in the 1% to 3% range (at least), which is pretty audible.

Regards,

>>oscilloscope>>

Wow, never seen that word before, I think its a little out of my price range just to find out if the 4ohm load is ok (>$300).

I was thinking about playing some music through all the 5 speakers, cranking it up really loud and seeing if the centre channel distorts/clips at all. I already tested this method yesterday, but no louder than -20db.

The problem with that is that there is so much noise everywhere it would be hard to determine if the centre channel is indeed clipping.

So if there was a problem...I would hear the speakers coming in and out right? I also didn't notice any excessive heat coming from the amp after 2 hours of Dolby Digital 5.1 content at -30 db.

EDIT: Was just reading on AVS' RX-V659 thread, a user is using 2 surround channels that are 4ohm and only noted that the amp got pretty warm but not excessivly hot, and he didn't notice any distortion when watching a dts movie.

Seeing as I will only have one 4ohm load (even though the center is used more than the surrounds) I think the 659 can handle it. I am quite amazed at the speakers that this budget receiver can drive. I am probably going to watch a familiar movie tonite (or bits and pieces anyway) to determine for sure.

I am willing to bet your EP500 that you will not have any trouble with the Yammie. Have some more fun tonight watching and listening to your new HT. Wait a minute you still have work to do..hurry up and get that room done would ya.

Alan told you the correct way of doing it. What you need is either the scope or a peak reading power meter/ voltmeter.

Last year, one of the board members did exactly that and posted his results. As I recall, the peak to average power was about 25:1 which indicated to me that one needs to be concerned with both peak and average power.

Maybe someone can find those posts and put them here.

Is this the one.

Robb, there'd be no reason for the paralleled center speakers to be "clipping". When the speakers are operating in parallel there's an increase of 3dB in sound level, so dropping the level 3dB to keep it the same as before results in only half as much power being required, not more. Apparently, as strongly suspected, the 659 has no problem with that load, which drops below 4 ohms at certain frequencies.