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post #1 of 42 Old 10-24-2013, 01:41 PM - Thread Starter
 
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So I started a thread or two about amplifier power which I found very enlightening. Lots of opinions, some of it mixed, but I think I gained valuable information out of them.

My question is something I've wanted to know for a long time. How does one measure how much power is being used with the speaker? If I'm watching a movie, or listening to music, is there an easy way for me to determine how much power is actually being drawn from the speaker?

I'm anxious to test this out on my system. I don't think I'm running into any clipping issues at all, but I am very curious to know how much power is being used by my system. Any advice would be most appreciated.
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post #2 of 42 Old 10-24-2013, 01:56 PM
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Originally Posted by OllieS View Post

So I started a thread or two about amplifier power which I found very enlightening. Lots of opinions, some of it mixed, but I think I gained valuable information out of them.

My question is something I've wanted to know for a long time. How does one measure how much power is being used with the speaker? If I'm watching a movie, or listening to music, is there an easy way for me to determine how much power is actually being drawn from the speaker?

I'm anxious to test this out on my system. I don't think I'm running into any clipping issues at all, but I am very curious to know how much power is being used by my system. Any advice would be most appreciated.

Probably the best way to measure the power drawn by your speakers is to measure the voltage across the speaker terminals. Yes, its not power, its voltage but under most conditions, the voltage across the speaker terminals is the best way to determine if the power drawn by your speakers is causing your amplifier to clip.
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post #3 of 42 Old 10-24-2013, 02:08 PM - Thread Starter
 
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Originally Posted by arnyk 
Probably the best way to measure the power drawn by your speakers is to measure the voltage across the speaker terminals. Yes, its not power, its voltage but under most conditions, the voltage across the speaker terminals is the best way to determine if the power drawn by your speakers is causing your amplifier to clip.

How would I go about doing something like that? If I wanted to measure power, not voltage, is that something that a person can do, or is measuring voltage the only method people use for checking how much juice is being used?

Say I'm watching a movie like Master and Commander. I switch my subs off. Just want to measure the power on the most dynamic portions of the movie. I know that movie very well. Chapter 4 is when the cannons go crazy... very soft, to very, very loud.

I guess I'm just really curious to know what is going on here. If my speakers were only using, say, 40 watts, at the levels I listen at, I would find that interesting.

But as far as amp clipping goes, would it not be obvious whether it was clipping? I thought amp clipping was audible. I don't hear gross distortion at any point on my system, but I sure would like to know how much of the available power is being wasted. It would teach me not to spend money on things I don't need!
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post #4 of 42 Old 10-24-2013, 02:29 PM
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To measure current you would put a multimeter in series with one of the speaker terminals. Power is current (amps) X voltage.
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post #5 of 42 Old 10-24-2013, 03:15 PM
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Originally Posted by OllieS View Post

How would I go about doing something like that? If I wanted to measure power, not voltage, is that something that a person can do, or is measuring voltage the only method people use for checking how much juice is being used?

Say I'm watching a movie like Master and Commander. I switch my subs off. Just want to measure the power on the most dynamic portions of the movie. I know that movie very well. Chapter 4 is when the cannons go crazy... very soft, to very, very loud.

I guess I'm just really curious to know what is going on here. If my speakers were only using, say, 40 watts, at the levels I listen at, I would find that interesting.
To measure power accurately, you need to measure both voltage and current simultaneously and create the product.

Most multimeters are not accurate enough to measure wideband signal like audio. They don't have the bandwidth and they are too slow responding, and few are true RMS with a suitable bandwidth.

How I would do it, would be to measure voltage via a voltage divider and buffer into a soundcard. Current via a small resistor, amplified and scaled into another soundcard channel, with levels set for V and I to allow a good dynamic range without clipping the soundcard input. Sampled at 16/44 for both channels it would give instant values and suitable processed could give a rolling average over a few seconds so you could see instantaneous peaks and an average. I don't have the PC software coding skill or it would already be done as the hardware is easy for me.
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But as far as amp clipping goes, would it not be obvious whether it was clipping? I thought amp clipping was audible. I don't hear gross distortion at any point on my system, but I sure would like to know how much of the available power is being wasted. It would teach me not to spend money on things I don't need!
Clipping is seldom audible because of the short duration of most of it. Bob Cordell actually did this at an RMAF workshop in 2006. Read about it here in brief.
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post #6 of 42 Old 10-24-2013, 03:40 PM
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A multimeter will work fine. You just use a steady tone like a sine wave. You will never get readings from music.
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post #7 of 42 Old 10-24-2013, 04:03 PM - Thread Starter
 
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Originally Posted by FMW 
A multimeter will work fine. You just use a steady tone like a sine wave. You will never get readings from music.

Are steady sine waves a good alternative to musical signals?
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post #8 of 42 Old 10-24-2013, 05:00 PM
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No they aren't but they are all you can deal with using a multimeter.
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post #9 of 42 Old 10-24-2013, 05:15 PM
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The idea of using a volt meter can AT BEST give you a vague idea of the POWER going to the speaker.

This is because the impedance of the speaker IS NOT what it is rated at. The impedance varies quite a bit depending on the freq.

It can easily be 5 to 10 times higher than the rated impedance.

So using a voltmeter and trying to calculate based on the impedance will give a higher wattage than is actually going to the loudspeaker.

What I use is very old school. I have some old Simpson wattmeters.

These are put in series with the loudspeakers. They are pretty accurate. If testing with sine waves the wattage varies with the freq and when I calculated the actual power when using sine waves and the actual impedance of the loudspeakers at that freq-they were VERY close.

These are not easy to come by.

Another variable is the "reaction time" of any meter. Most meters that measure voltage (Durroughs excepted) will not be fast enough to measure the peaks.

TO get accurate ideas it takes a number of different approaches.

So I guess it really comes down to how accurate you want to be.

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post #10 of 42 Old 10-25-2013, 05:50 AM
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Quote:
Originally Posted by OllieS View Post

Quote:
Originally Posted by arnyk 
Probably the best way to measure the power drawn by your speakers is to measure the voltage across the speaker terminals. Yes, its not power, its voltage but under most conditions, the voltage across the speaker terminals is the best way to determine if the power drawn by your speakers is causing your amplifier to clip.

How would I go about doing something like that?

(1) Obtain a voltmeter with good frequency response. As others have pointed out, most multimeters cheap or not are designed to measure regular electrical power whose frequency ranges from 50 Hz to 400 Hz. It is not the least bit uncommon for the response of a common multimeter to drop like a rock starting around 1 KHz. Obviously, to measure audio voltages we need a meter that responds accurately over the regular audio band, from 20 to 20 KHz at minimum. Just to confuse the matter, the actual frequency response of common voltmeters is often not specified as well.

Here are some frequency response curves for common Digital Voltmeters (DVMs) that have frequency response that is at least above average:



One of the more available and cheaper of them (Fluke 27) retails for $475. Several such as the excellent and classic Fluke 8060 are discontinued. I've seen some likely candidate 8060s on eBay for around $100. Caveat Emptor.

(2) The second problem is that audio in general varies a lot and the digital displays on DVMs don't even pretend to keep up. If you want to accurately capture the peaks and variations, then you need something like a digital recorder that can withstand the relatively large voltages that one finds on speaker terminals - probably up to 50 volts RMS. AFAIK, you are on your own engineering project if you want such a thing.
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If I wanted to measure power, not voltage, is that something that a person can do, or is measuring voltage the only method people use for checking how much juice is being used?

There are such things as watt meters, either mechanical or electronic, but again they are typically designed for use with power line current and therefore only operate accurately over a narrow range of frequencies. I've measured true power delivered to speakers but I ended up engineering the equipment/software used myself and spent over $1,000 assembling it.

I believe that there are commercial audio test sets such as those made by Audio Precison that have actual power measurements as a standard feature, but even the first edition of AP equipment (AP System 1) now decades old in good condition is sold for thousands of dollars and takes serious training and experience to use competently.
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Say I'm watching a movie like Master and Commander. I switch my subs off. Just want to measure the power on the most dynamic portions of the movie. I know that movie very well. Chapter 4 is when the cannons go crazy... very soft, to very, very loud.

I know of no off-the-shelf options for you that don't require a big financial and time investment.
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I guess I'm just really curious to know what is going on here. If my speakers were only using, say, 40 watts, at the levels I listen at, I would find that interesting.

But as far as amp clipping goes, would it not be obvious whether it was clipping?

If one makes a digital recording of the voltage across the speaker terminals and looks at it with an audio editor even just freeware Audacity software, the flat-topping would be pretty obvious.
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I thought amp clipping was audible.

If there is enough of it, its readily audible and not nice to listen to.
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I don't hear gross distortion at any point on my system, but I sure would like to know how much of the available power is being wasted. It would teach me not to spend money on things I don't need!

I still think that AVRs should have clipping indicators. They are common features of pro audio amps, and many of them like the simple but highly sensitive and effective one that QSC uses don't cost a ton of money to implement. I think the QSC clipping indicator circuit is composed of 6 parts costing less than a dime each in production quantity (4 signal diodes, 1 LED and 1 resistor).
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post #11 of 42 Old 10-25-2013, 05:55 AM
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Originally Posted by Ivan Beaver View Post

The idea of using a volt meter can AT BEST give you a vague idea of the POWER going to the speaker.

This is because the impedance of the speaker IS NOT what it is rated at. The impedance varies quite a bit depending on the freq.

It can easily be 5 to 10 times higher than the rated impedance.

So using a voltmeter and trying to calculate based on the impedance will give a higher wattage than is actually going to the loudspeaker.

What I use is very old school. I have some old Simpson wattmeters.

IME the Simpson watt meters have very poor frequency response by audio standards.

http://www.kjq.us.com/images/SIMPSON_880_WATT_METER.pdf

"±0.5% from 54 Hz to 66 Hz Sine Wave"
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post #12 of 42 Old 10-25-2013, 06:28 AM
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Originally Posted by OllieS View Post

Quote:
Originally Posted by FMW 
A multimeter will work fine. You just use a steady tone like a sine wave. You will never get readings from music.

Are steady sine waves a good alternative to musical signals?

Depends what you want to know from your measurement and what you are measuring.
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post #13 of 42 Old 10-25-2013, 06:41 AM - Thread Starter
 
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I think this topic is a lot more complicated than I anticipated. What I'm asking just can't be done by the laymen, or at reasonable cost. That's unfortunate, because I'm sure lots of people would like to know how much power is being used on their systems. Or perhaps I'm the only one... I just know that after reading all the comments in my previous threads, I feel a lot more cautious now than I was before.

I think I read something on the DIYaudio forum about a test concerning maximum voltage required by the speakers, but I don't know if that would be relevant to what I'm asking.
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post #14 of 42 Old 10-25-2013, 08:38 AM
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For what you want, a voltmeter is probably just fine. Power is determined by the following formula:

P = (E * E) / R

Where E is the voltage reading (E comes from Electromotive force) and R is resistance (for example, 8 ohms for an 8 ohm speaker).

So, if you have 8 ohm speakers and are measuring 20 volts, your speakers are using 50 watts (20 * 20 = 400 / 8 = 50). Now, this will be pretty rough. As others have correctly pointed out, many A/C voltmeters are designed to be most accurate at 50 to 60 Hz, and can be pretty bad outside of that range. But if you are interested in bass, that's probably not as much of a problem as you might think. Also, an "8 ohm" speaker is a generalization because impedance varies by frequency, so 8 ohms is at best a guess of the overall impedance.

But if all you are interested in is a ball park number, this should work OK.

Mike

P.S. Don't be too surprised if you find power levels a lot lower than you expect. Many modern speakers will generate in excess of 90 dB at 1 meter when using only a single watt. 90 dB is pretty loud! Two watts would be about 93 dB, 4 watts is 96 dB, etc. So at 8 watts you'd be listening at around 100 dB which is way too loud for long term listening.
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post #15 of 42 Old 10-25-2013, 08:48 AM
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It isn't complicated. Measure the voltage and current as described above using sine wave test tones. You can do the measurements at a variety of frequencies if it makes you feel better and average them.
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post #16 of 42 Old 10-25-2013, 09:28 AM - Thread Starter
 
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FMW, I think I fear I would need a step by step approach on how to go about this. I have no idea how to average frequencies, what frequencies to use, etc etc etc . I never done this before, and I'm not a technical guy, so I basically would need to be spoon fed. I'm not trying to be rude, I'm just stating the truth. frown.gif

So far I've been told to get a good volt meter. Ok... I'll look into that. But then from that point? Could one explain this in an easy to understand process that a layman could understand?
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post #17 of 42 Old 10-25-2013, 10:06 AM
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Back in the day there would be amp display meter on dedicated amps, logarithmic scale, been a while since I saw those.

Here is a thread I found while searching google ""
http://www.tnt-audio.com/shows/burning_amp2012_e.html


between what Ivan posted, who does this for a living, I'm still curious your drive and desire to have this data?

ahh, found them! Just get these and be happy reading them!
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post #18 of 42 Old 10-25-2013, 11:45 AM
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Originally Posted by OllieS View Post

I think this topic is a lot more complicated than I anticipated. What I'm asking just can't be done by the laymen, or at reasonable cost. That's unfortunate, because I'm sure lots of people would like to know how much power is being used on their systems. Or perhaps I'm the only one... I just know that after reading all the comments in my previous threads, I feel a lot more cautious now than I was before.

I think I read something on the DIYaudio forum about a test concerning maximum voltage required by the speakers, but I don't know if that would be relevant to what I'm asking.

This gets us back to my first post, where I suggested estimating power based on measurements of voltage.

The rationale for this is that the thing that most people want to know is how close they are to clipping their amplifier.

Most clipping comes about when more voltage is demanded then the power amplifier can deliver with good linearity.

The remaining problem is the problem of measuring peaks, since most people's real world listening is to music not sine waves.
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post #19 of 42 Old 10-25-2013, 11:52 AM - Thread Starter
 
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Originally Posted by mtbdudex 
between what Ivan posted, who does this for a living, I'm still curious your drive and desire to have this data?

I am interested to know how much power I'm using at the loudest levels I generally listen at. It would give me a better idea of power usage. Plus I learn ... and I'm always up for that, even if I find it difficult.
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post #20 of 42 Old 10-25-2013, 12:17 PM
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Originally Posted by A9X-308 View Post


How I would do it, would be to measure voltage via a voltage divider and buffer into a soundcard. Current via a small resistor, amplified and scaled into another soundcard channel, with levels set for V and I to allow a good dynamic range without clipping the soundcard input. Sampled at 16/44 for both channels it would give instant values and suitable processed could give a rolling average over a few seconds so you could see instantaneous peaks and an average. I don't have the PC software coding skill or it would already be done as the hardware is easy for me.
Clipping is seldom audible because of the short duration of most of it. Bob Cordell actually did this at an RMAF workshop in 2006. Read about it here in brief.

+1, and well within a hobbiest price range.

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post #21 of 42 Old 10-25-2013, 12:49 PM
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Quote:
Originally Posted by OllieS View Post

Quote:
Originally Posted by mtbdudex 
between what Ivan posted, who does this for a living, I'm still curious your drive and desire to have this data?

I am interested to know how much power I'm using at the loudest levels I generally listen at. It would give me a better idea of power usage. Plus I learn ... and I'm always up for that, even if I find it difficult.

That's cool, as a hobby learning and connecting the dots is what drive me also.

My suggestion:
Do some analytical calculations, see this thread http://www.avsforum.com/t/1387083/list-of-reference-level-high-sensitivity-spl-speakers, figure out what you should need to get to 95db and 105db at your MLP with your gear and set-up.
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How Calculated

Speaking of which, I started off using the SPL calculator [URL=http://http//myhometheater.homestead.com/splcalculator.html]here[/URL] and I'm calculating with one speaker, away from walls, at 12 feet.


Later, as the errors mounted in having to calculate each speaker manually, I incorporated formulas, such as =(10^((Calcs!B$3-(I25+(20*log(3.2808399/Calcs!B$2))))/10)).

Then compare your paper study with your measure study - however you end up doing it - make sure its close & accurate, then grok upon the results and differences.
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post #22 of 42 Old 10-25-2013, 01:19 PM
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Originally Posted by OllieS View Post

I think I read something on the DIYaudio forum about a test concerning maximum voltage required by the speakers, but I don't know if that would be relevant to what I'm asking.
Because of the non flat impedance of speakers and the poor performance of multimeters in terms of FR and response time this is a very poor test, and I explained that to Pano when it started. But many there seem to think it gives some insight.

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+1, and well within a hobbiest price range.
I designed, built and tested such a rig some time back. Like you, I have been in electronics a long time and need to test and measure a wide range of stuff, so if something isn't available to do this, I build it. This rig I did to look at mains draw, so was limited to 1k because of the CT FR, but substituting it for a series resistor would ameliorate the BW issue for some slight changes in the electronics. I'm lucky in that I have a nice certified lab at work to test things in.

When and if I have the time and interest to do this again, if I can get someone to code it, the plan was to loan the rig to people so they could test their systems. I'd be happier doing that with line level than mains.
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post #23 of 42 Old 10-25-2013, 02:11 PM
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Originally Posted by OllieS View Post

FMW, I think I fear I would need a step by step approach on how to go about this. I have no idea how to average frequencies, what frequencies to use, etc etc etc . I never done this before, and I'm not a technical guy, so I basically would need to be spoon fed. I'm not trying to be rude, I'm just stating the truth. frown.gif

So far I've been told to get a good volt meter. Ok... I'll look into that. But then from that point? Could one explain this in an easy to understand process that a layman could understand?

OK. First you need a multimeter. Here is a picture of a typical digital multimeter.

fluke175.jpg

Multimeters can read resistance (ohms), current (amps) and electrical pressure (volts.) You need one that can measure AC current and voltage. To read the voltage at your speaker terminals you set the meter to AC volts and put a probe on each terminal. In other words the meter is connected in parallel to the terminals. Read the volts and write them down. To. read current, set the meter to AC amps Disconnect one of the speaker wires from the terminal, put one probe on the terminal and the other on the bare speaker wire. You are connecting the meter in series with the speaker terminal. Read the current and write it down. Power is the product of the two numbers. AC amps X AC volts = watts

You can find test tones all over the internet. Here is one place. Download them and burn a CD with the tones. All you need to do is play the test tones through your system and make the voltage and current measurements outlined above. You can do it with a number of frequencies and average the results. Or you can just take a 1000hz tone and be content with that. If you want to calibrate your work you will also need an SPL (sound pressure level) meter. If you are content with just playing the tones loud, then set the volume by ear don't worry about it.

There are better and more accurate ways to measure power dissipation but this will work with a relatively simple and affordable instrument. You do get what you pay for with multimeters. I have two good ones - a Fluke and an Extech. They were over $100 each perhaps 15 or so years ago. They are relics from the service department of my old computer company. You can probably buy a decent Chinese one for a lot less than that these days. Let me know if you need any further guidance.

If it helps, I have a recording power meter that I have connected to a speaker in the past and the highest power dissipation I ever measured was 18 watts on speakers with a sensitivity rating of 87 db for 1 watt at 1 meter. I may not listen as loudly as some people but amplifier power has never been an issue for me.
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post #24 of 42 Old 10-25-2013, 02:26 PM
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Quote:
Originally Posted by FMW View Post

Quote:
Originally Posted by OllieS View Post

FMW, I think I fear I would need a step by step approach on how to go about this. I have no idea how to average frequencies, what frequencies to use, etc etc etc . I never done this before, and I'm not a technical guy, so I basically would need to be spoon fed. I'm not trying to be rude, I'm just stating the truth. frown.gif

So far I've been told to get a good volt meter. Ok... I'll look into that. But then from that point? Could one explain this in an easy to understand process that a layman could understand?

OK. First you need a multimeter. Here is a picture of a typical digital multimeter.

The price performance of multimeters continues to improve. Someone tipped me off to the UniTrend UT61 which is better than average for audio.



The manual is here: http://www.uni-trend.com/manual2/UT61English.pdf

The specs and a small picture is here:

http://www.uni-trend.com/ut61e.html#

And a typical offer to sell one of these can be found here:

http://www.amazon.com/UNI-T-Digital-Ranging-Multimeters-Multitester/dp/B007THZMWI/ref=sr_1_1?ie=UTF8&qid=1382732719&sr=8-1&keywords=ut61e

They are also offered on eBay.

This particular meter has fairly decent frequency response, better than +/- 0.1 dB 20-20 KHz.
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post #25 of 42 Old 10-25-2013, 02:49 PM
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There you go. $55 is very affordable for an accurate digital multimeter.
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post #26 of 42 Old 10-25-2013, 03:50 PM
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Quote:
Originally Posted by OllieS View Post

I am interested to know how much power I'm using at the loudest levels I generally listen at. It would give me a better idea of power usage. Plus I learn ... and I'm always up for that, even if I find it difficult.


the trick may be that for non-heavily compressed sound, peaks of 10 dB or more (ten times the power or more) may last for a twentieth of a second. Likely less time than a typical meter could even register the increase, and faster than normal folks could read the meter.
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post #27 of 42 Old 10-26-2013, 07:12 AM - Thread Starter
 
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This is the thread I found on DIYaudio forum :

http://www.diyaudio.com/forums/multi-way/204857-test-how-much-voltage-power-do-your-speakers-need.html

What do guys think of this test?
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post #28 of 42 Old 10-26-2013, 07:54 AM
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Quote:
Originally Posted by JHAz View Post

the trick may be that for non-heavily compressed sound, peaks of 10 dB or more (ten times the power or more) may last for a twentieth of a second. Likely less time than a typical meter could even register the increase, and faster than normal folks could read the meter.

He's going to use test tones. Not music.
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post #29 of 42 Old 10-26-2013, 08:02 AM
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Quote:
Originally Posted by OllieS View Post

This is the thread I found on DIYaudio forum :

http://www.diyaudio.com/forums/multi-way/204857-test-how-much-voltage-power-do-your-speakers-need.html

What do guys think of this test?

I think it is pretty good.

The current results of the survey are:

2 volts or less 38.73%
Between 2-5 volts 33.97%
Between 5-10 volts 12.06%
Between 10-20 volts 6.03%
Over 20 volts. 9.21%

The highest voltage mentioned (20 volts) corresponds to 50 watts into an 8 ohm load. Well within the capabilities of your typical AVR. More than 90% of the respondents never go there, ever.

Notice that the test is based on musical selections and the sine waves are used as part of a measurement strategy that circumvents the voltmeter frequency response issue that we have been talking about.
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post #30 of 42 Old 10-26-2013, 08:07 AM
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Quote:
Originally Posted by JHAz View Post

Quote:
Originally Posted by OllieS View Post

I am interested to know how much power I'm using at the loudest levels I generally listen at. It would give me a better idea of power usage. Plus I learn ... and I'm always up for that, even if I find it difficult.


the trick may be that for non-heavily compressed sound, peaks of 10 dB or more (ten times the power or more) may last for a twentieth of a second. Likely less time than a typical meter could even register the increase, and faster than normal folks could read the meter.

The $55 True RMS/audio UT61E meter I mentioned has a peak-reading feature. I am in the process of testing it to see what duration peaks have to be to be measured accurately. I'm testing it by feeding it 4 KHz tone bursts of various durations and repetition rates. I can tell you that 10 millisecond peaks are too short for it to register in a meaningful way.
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