Calculate actual power used?

[brubacca]

How can I calculate how much power I'm actually using?

Could i just use a meter to get the amps and just multiply by volts? I have a kill-o-watt meter. I'm thinking I can get amps from this.

Make sense?

[DYohn]

The power being generated at any instant can be calculated using Pout(RMS) = Vout(RMS) * Iout(RMS) where P=Power, V=Volts, I=current. Realize in an audio system the power is constantly changing depending on the dynamics of the content, the volume setting (line level voltage) and the impedance of the loudspeaker which changes with frequency. So you might be able to grab an average reading depending on how fast your meter is, or you could use a sine wave signal to hold the speaker's impedance at a relatively fixed value and stabilize the current to read it. I don't think your kill-a-watt meter will be up to the task.

Another indirect way to estimate power is to measure the SPL being put out by your loudspeaker at 1 meter and calculate an estimate based on the speaker system's sensitivity.

[Deleted]

Louder = More Power ;D

[goldenear2]

DYohn: Please explain the last sentence of your post at 4:03 pm. Give an example.

[DYohn]

OK. Let's say you play some program material and using your trusty SPL meter, you measure 109dbSPL at one meter in front of your loudspeaker. Now look at the loudspeaker specs, and notice the sensitivity is rated at, say, 88db/watt/meter. This means with a 1 watt input, the speaker is rated to produce 88dbSPL at 1 meter. Each doubling of power will create a +3db change in the output. So it goes like this:

1 watt = 88dbSPL
2 watts = 91dbSPL
4 watts = 94dbSPL
8 watts = 97dbSPL
16 watts = 100dbSPL
32 watts = 103dbSPL
64 watts = 106dbSPL
128 watts = 109dbSPL
256 watts = 112dbSPL
512 watts = 115dbSPL

So, your 109dbSPL reading means the loudspeaker is being delivered approx. 128 watts program power.

Note that I cheated by picking numbers that easily fit the power doubling math, and that this is approximate not exact as there are other factors in a room that can come into play. But it's a close enough for government work estimate.

Here's a handy calculator. Make sure you input the proper number of speakers (one in this case) and select "in phase." www.doctorproaudio.com/doctor/calculadores_en.htm#calc_spl

[brubacca]

Thanks for the ideas. I found an iOS app called decibel. It will track dB and peak dB. I go through an elevated volume listening session, with my normal music ending upwith the infamous telarc 1812 with the cannons to really hit some peaks. I,ll back calculate power required to see where i am.

Just want to see where i am power wise with my system. It is easy to convince onself that you need a xpa-2 or xpr-2, but do you really?

[davidas6350]

See this thread I started not long ago and draw your own conclusion.

emotivalounge.proboards.com/index.cgi?board=stupid&action=display&thread=29233

[brubacca]

Used the decibal app in my listening chair. Cranked up the volume as loud as I would have it, really louder than I ever listen. Ran through a couple of songs. Max dB reading was 88. Used the following website:
myhometheater.homestead.com/splcalculator.html
And came up with a power usage of..... 20W and that is with cheating the numbers so the power usage was higher.

Guess I don't need those XPR amps. Just a fun exercise to bring a little reality to the audio system. 125W is plenty formy speakers/space.

Regards,
Charlie

[Deleted]

Bingo, Charlie! *Very* few folks really need more than 150-200 watts/ch., but bragging rights always seem to insinuate themselves into the math...

-RW-

[davidas6350]

brubacca --> Are you sure the power usage is actually approx. 20W? I used a pretty much the same calculation formula and the results of my calculated power usage is 134w at 110dB, but my 1000w amp appeared to be near max load as indicated by red LEDs.

You can read all about it on the link I provided above your post. I never really got an answer.

[brubacca]

Davidas6350- I did peruse your thread. We have very different animals in terms of speakers. You have a tweeter, (2) midrange and one 8" woofer to drive.the lower frequencies really absorb the current.. I would believe the data you are seeing based on sending a full range signal to your speakers. They would be pulling gobs of current out of the amp to keep those drivers moving. To me it would be a very interesting experiment to run your speakers frequency limited ( 50 Hz and higher at say 80hz) and see if your results vary. I'm no expert, but I have always been of the opinion that Watts was a very bad way to rate an amp. In my mind they should be rated based off of the current capability. Current going through the drivers is what causes them to move. I work in the industrial world and we are always specifying variable frequency drives in horsepower because it is convenient, but current is what really gets the motors to turn. If you have a 5 HP motor ( speaker) you may need a 10 HP drive (amplifier) to operate that motor based on the application. I think it is the same with speakers/amplifiers. On the test bench with the test signal that amp is 1000W and that speaker is 88dB, but in the reality of your application you see the behavior you see.

Sorry if I am rambling. Good luck.

[davidas6350]

^ I agree, I think it will give me different results if I limit the frequency to 50-80Hz or higher. If you intend to use the amp solely for high frequencies then yeah... I don't think you'll need high wattage amps for those.

I don't really know the right answer to your topic question as it was my question too.

[DYohn]

There can be a huge difference between what your SPL meter can read and what's being produced instantaneously by the amplifier. And then there are power compression effects and other inefficiencies of a loudspeaker system, not to mention room effects, to take into account. That's why I said using the SPL calculation method only gives you an estimate.

[brubacca]

Definition of a Watt is a Volt times an Amp. If you accurately measure both at the same time you could calculate what is actually going on. I was going through the exercise to get an order of magnitude kind of estimate.

davidas6350- your numbers tell me that you absolutely need the amp you have.

Mine tells me that more power would be an absolute waste of money.

[brubacca]

So I admit that I'm crazy. Last night I powered my amplifier through my belken puraAV power conditioner. It measures volts ans amps in banks so I could isolate th amp.
120.9 Volts, 1.1 Amps max peak..... Calculated Watts- 133W.
dB calculation says 20 Watts, real world says 133W. (6 ohm speakers)

Thoughts?

[geebo]

What the Belkin is showing is power consumption of the amp. Power output is different. No amp is 100% efficient so it cannot output as much as it uses.

[brubacca]

Makes sense. Maybe I should just sit back and enjoy!