# What is really enough power output? here is my results



## tonyvdb (Sep 5, 2007)

So, given this topic comes up often and continues to be a topic with a lot of different views. I dont want to derail the latest conversation thats going on here so I want to continue it in this post instead.
I wanted to do my own test using what I have access to in my own house.

I have heard comments like: 
"most people only use 10 to 20 watts when listening at normal volume levels"
"doubling of watts is only a 2db increase"
and a few other statements. do I believe them, well I truly believe it is suspect to much more than hard numbers as things like room acoustics, furniture and speaker type all play into what really is needed and the above numbers will change depending on these other factors as well.

I have done my own tests using pink noise and although not scientific watching the 12 segment led on each channel of my Samson amp 0db would be 300watts output on each channel. I have reached reference level using my SPL meter at the listening position with the meter on the amp showing -4db that would certainly not be 10 to 20watts of power but I want to do another test tonight to see what approximately 20 watts would be like, see below in my second test.
Normal use during movies my amp is generally showing on the meters consistent levels of -12 to -8db.
I previously had a 150watt per ch Samson in the same class that would often come close to peak output with the same volume levels keeping in mind that I run them at full range with a filter at 30Hz

So, on to some tests.

My daughter has a JVC FS-T100 mini system and its stated output is 15 watts per channel so thats a good test to see just how loud that really is powering my EV sentry 500 monitors and me at the listening position first doing pink noise. The EVs are 95db efficient and ruler flat response even in my room.

The results were actually surprising, running the mini system. The volume control only goes to 50 and at 35 some distortion was present with a track I usually use from Lee Ritenours CD Rhythm sessions called Maybe tomorrow as it is a great dynamic mix with a female vocalist. Now I love to listen to good music at a nice level and my SPL meter on C weighting showed me between 60 and 68db with the volume as high as I could go and still clear with no audible distortion (believe me the EVs are very accurate and distortion shows up without having to strain to hear it). 
Next I simply played some pink noise to get a feeling on the SPL meter what that was like leaving the volume at the same spot. I was steady at 62db.

for the next test I dragged down my Mission 765 towers from my livingroom and hooked them up, they are 89db efficient but a 4ohm load. 
Playing the same track the volume level was much less before I heard distortion and given they are not quite as detailed as my EVs I suspect more forgiving before the distortion was noticeable. The volume was only at 56db with pink noise.

So although not a true scientific test I do believe that the statement "most people only use 10 to 20 watts when listening at normal volume levels" is a bit low I do believe that 40-60 clean watts would be more than sufficient as long as the speakers are above 90db efficient (many are not). If your running a sub then you could get away with a little less power.

So I did learn something today that surprised me. I really did think that anything less than 80 watts per channel was a compromise and it turns out that is not really true. I do still stand fast that a receiver with a large power supply with some weight to it will drive the amps properly. Distortion is the enemy here and when driving all channels hard this can factor into what we hear as poor sound/imaging or even loss of detail.


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## moparz10 (Sep 21, 2010)

Thanks for the tests tony,very informative reading,goes to prove that the marriage between speaker and receiver is very critical if one is to be satisfied with the end result,getting the balance between both is a major task taking in to consideration reviews and specs out there.


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## fmw (Aug 11, 2013)

tonyvdb said:


> So, given this topic comes up often and continues to be a topic with a lot of different views. I dont want to derail the latest conversation thats going on here so I want to continue it in this post instead.
> I wanted to do my own test using what I have access to in my own house.
> 
> I have heard comments like:
> ...


You misunderstand. When I say 10 to 20 watts is what a normal system will need at normal listening levels I'm not guessing. I have attached a wattmeter to one of my main speakers. My speakers are 88 db sensitive. My average consumption listening to music is around 1/2 watt with peaks in the area of 5 or 6 watts. For movies I crank it up to 1 watt with peaks of around 10 watts. If I play my system loud enough to be uncomfortable I have taken it up to 18 watts on peaks. I view my situation as pretty average or normal. Also, I use a powered subwoofer like most home theater enthusiasts and that certainly affects the power draw from my main speakers. Obviously having more overhead than you need or use is not harmful.


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## Tonto (Jun 30, 2007)

I have never given too much thougth to how to measure the actual "watts" being output by the receiver. I do know that my APC S15 does display total watts delevered & when cranking my system, has displayed up to 750 watts. This is the entire draw including my PB13-U. I'll try it tonight without the sub & in 2 channel. Interesting but since I don't have a sound meter, wont know how many dB's it will be.


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## Owen Bartley (Oct 18, 2006)

Thanks Tony, interesting comparison. I had a similar realization (kind of) when I fired up my vintage 70's Pioneer SX-424 receiver, rated for 15 watts. I paired it with some old mini-system speakers which are likely high impedance, and was really surprised at how loud they were at really low volume settings.


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## vann_d (Apr 7, 2009)

Here is some reference material for those interested in the subject. This is the JBL Sound System Design Reference Manual and it really goes into things with much more depth and aptitude than I can. I would call it a must read for those interested in how power levels relate to perceived volume levels, room acoustics, and a wealth of other topics. One of the interesting points is how rms values for sine waves don't relate well to rms values for real world sound (i.e. voice and musical) waves. Anyhow, good reading! See the attached file...

Oops, sorry gonna have to link to it. File is too large

JBL Sound System Design Reference Manual


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## selden (Nov 15, 2009)

But it's over 100 pages!?! We can't read all that!!! 

Thanks!


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## fmw (Aug 11, 2013)

Tonto said:


> I have never given too much thougth to how to measure the actual "watts" being output by the receiver. I do know that my APC S15 does display total watts delevered & when cranking my system, has displayed up to 750 watts. This is the entire draw including my PB13-U. I'll try it tonight without the sub & in 2 channel. Interesting but since I don't have a sound meter, wont know how many dB's it will be.


You will need a multimeter. Simply set the meter to read millivolts and measure across the terminals of one speaker. Then set it to read milliamps and put the meter in series with one of the terminals (disconnect the cable and put the meter between the cable and the empty terminal.) Multiply the two readings together to get milliwatts and multiply that by 1000 to get watts. Multimeters are not terribly expensive if you don't have one.

SPL meters run $50 and up for accuracy appropriate for home audio.


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## selden (Nov 15, 2009)

Sorry, but your arithmetic is slightly off for the units: milliamps x millivolts = microwatts.


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## lcaillo (May 2, 2006)

Most multi-meters will not be particularly accurate for current measurements with music.


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## fmw (Aug 11, 2013)

lcaillo said:


> Most multi-meters will not be particularly accurate for current measurements with music.


Nobody suggested music. Test tones would be the way to go.


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## fmw (Aug 11, 2013)

selden said:


> Sorry, but your arithmetic is slightly off for the units: milliamps x millivolts = microwatts.


OK, so use watts and amps. I was just trying to get the zeros away from the reading on the meter.


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## Sonnie (Apr 11, 2006)

I think it will be hard to guess the watts used without the proper measurement tool, no offense to your testing methodology Tony. I have a 24 watt per channel amp and it gets considerably louder than I want to listen to it at 3/4 volume on my Arx A5's. I have no idea if 3/4 volume equates to 18 wpc, but it wouldn't be more than 24 watts. My thinking is depending on the sensitivity of the speakers... 10-15 watts per channel is probably very close to normal.


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## tonyvdb (Sep 5, 2007)

I'm going to do the voltage meter test as soon as I have time, I'm very curious.


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## chashint (Jan 12, 2011)

This makes the math real easy http://www.csgnetwork.com/ohmslaw2.html 
I don't know how a home owner grade multimeter will respond if you try to measure the voltage level of white/pink noise, it might see it as a DC level and give a meaningful reading or it may just be gibberish.
The AC scale won't be able to decipher a complex signal, it's pretty much intended to measure 50/60 Hz line voltage.
An oscilloscope and a current probe would be much better instruments, but they don't cost $10 at the local hardware store.
Some speakers use 2.83V instead of 1 watt in the spec to make the efficiency look better, since Tony's speakers are nominally 8 ohms 2.83V at the terminals should be reasonably close to 1 watt amplifier output.


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## vann_d (Apr 7, 2009)

chashint said:


> This makes the math real easy http://www.csgnetwork.com/ohmslaw2.html
> I don't know how a home owner grade multimeter will respond if you try to measure the voltage level of white/pink noise, it might see it as a DC level and give a meaningful reading or it may just be gibberish.
> The AC scale won't be able to decipher a complex signal, it's pretty much intended to measure 50/60 Hz line voltage.
> An oscilloscope and a current probe would be much better instruments, but they don't cost $10 at the local hardware store.
> Some speakers use 2.83V instead of 1 watt in the spec to make the efficiency look better, since Tony's speakers are nominally 8 ohms 2.83V at the terminals should be reasonably close to 1 watt amplifier output.


Right but an impedance plot would help in assessing. Plus, we have no idea how the manufacturer assessed efficiency. That is, average over a range or at 1kHz or what?

Bottom line is that the home enthusiasts will not be able to make a good assessment without some good equipment.


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## hjones4841 (Jan 21, 2009)

Tony, a slight correction: twice the power is 3 db, not 2.

I agree that an average multimeter may not register true power, since a speaker is not a pure resistive load.

Speaker efficiency is a huge factor in how many watts to get a certain volume. For instance, 20 watts into my K'horns (104db/1watt/1meter) is MUCH louder than 20 watts into a 89 or even 95 db efficiency speaker. Paul Klipsch used to say "what the world needs is a really good 5 watt amplifier."

Then there is the factor of distance from the speakers to the measuring location. I don't remember the specifics, but at some point in most rooms as distance is increased, the reflective sound adds to the effective volume and the inverse square law is no longer applicable. Guess a lot of that depends on how much absorption is in the room, which for us can be rather high.


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## Savjac (Apr 17, 2008)

This statement is spot on, few meters that our external of the source cannot react quick enough to changes in power demands to be of much use in making close measurements. I remember well driving a set of the big Mac speakers, 4 woofers each, in the late 70's with one of their big amps said to be able to delivery 250wps, and during certain passages, the power guard lights on the amp would pop on and off as needed. I think that some demanding speakers and/or music passages will use a huge amount of power, if available.



lcaillo said:


> Most multi-meters will not be particularly accurate for current measurements with music.


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