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Who wants to measure how much power (voltage) is REALLY needed?


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Am I reading this chart correctly? Are the listed numbers the "amplifier power rating... required to generate average sound pressure levels WHILE ALLOWING peaks 10 dB above average to pass without clipping" ? I was thinking the power listed is sufficient to handle the peaks? Have I got this wrong?

 

Edit: In other words, 6.3 watts will drive Khorn, LS, BK to both an average 105 SPL and also peaks 10 dB above... without clipping. [?]

Edited by Endo
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1 hour ago, tube fanatic said:

Not knowing your budget makes a recommendation difficult.  It pays to get a good one which will last you forever:

 

https://www.lowes.com/pd/Fluke-Digital-600-Volt-Multimeter/999970842

 

 

Maynard

Thank you for the recommendation. Longevity isn't as much of a concern as making it easy for a novice to set up and understand.  If there is something that would only  last for possibly 5 to 6 years and do the job as well for considerably less, it would be more justifiable for the budget. :)  If not, I can pick up that one because I am curious how much power I use.

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1 hour ago, Endo said:

Am I reading this chart correctly? Are the listed numbers the "amplifier power rating... required to generate average sound pressure levels WHILE ALLOWING peaks 10 dB above average to pass without clipping" ? I was thinking the power listed is sufficient to handle the peaks? Have I got this wrong?

 

Edit: In other words, 6.3 watts will drive Khorn, LS, BK to both an average 105 SPL and also peaks 10 dB above... without clipping. [?]

 

Yes ..... that is what PWK was stating in this paper. 

 

 

miketn 

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2 hours ago, Zen Traveler said:

Thank you for the recommendation. Longevity isn't as much of a concern as making it easy for a novice to set up and understand.  If there is something that would only  last for possibly 5 to 6 years and do the job as well for considerably less, it would be more justifiable for the budget. :)  If not, I can pick up that one because I am curious how much power I use.

Order one of these:

 

http://www.mcmelectronics.com/product/72-7720

 

 

Maynard

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7 hours ago, Endo said:

Am I reading this chart correctly? Are the listed numbers the "amplifier power rating... required to generate average sound pressure levels WHILE ALLOWING peaks 10 dB above average to pass without clipping" ? I was thinking the power listed is sufficient to handle the peaks? Have I got this wrong?

 

Edit: In other words, 6.3 watts will drive Khorn, LS, BK to both an average 105 SPL and also peaks 10 dB above... without clipping. [?]

 

8 hours ago, Endo said:

Am I reading this chart correctly? Are the listed numbers the "amplifier power rating... required to generate average sound pressure levels WHILE ALLOWING peaks 10 dB above average to pass without clipping" ? I was thinking the power listed is sufficient to handle the peaks? Have I got this wrong?

 

Edit: In other words, 6.3 watts will drive Khorn, LS, BK to both an average 105 SPL and also peaks 10 dB above... without clipping. [?]

 

A very good amplifier may deliver an extra 3 dB over its rated power.  Some high quality power amplifiers (but not usually receivers, including AVRs) may also deliver 10 dB above the rated power for a very short time, to accommodate very short peaks, milliseconds long.   But this refers to the rated power of the amplifier, not the 6.3 watts you refer to.  Let's say you have a 3,000 cu.ft. room, as specified in the chart, and your excellent separate power amplifier is honestly rated by the manufacturer at 6.3 watts (RMS).  If running nearly full tilt, it would cause your Klipschorn to produce 105 dB.  If there was a peak in the music, and if the peak was brief enough, your amp might produce 63 watts for an instant -- that's why they call them instantaneous peaks -- and at that instant, you would get 115 dB.  But note that that 115 dB would need 63 watts for just that instant -- 6.3 watts won't be nearly enough -- but some 6.3 watt amps would produce the 63 watts for that short duration.  I haven't noticed much agreement on how brief a brief peak is.  I seem to remember a range of up to 200 ms.(1/5 of a second).    Rated power should be with all channels operating, 20 to 20K Hz, at low distortion.  Don't bank on the rated power being honestly stated..  Sometimes, rated power is fudged, royally.  

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2 hours ago, Don Richard said:
21 hours ago, tube fanatic said:

 

Not true RMS, insufficient frequency response for audio use.

What a drag because it was considerably cheaper than the other one recommended. Is there another decent unit that isn't over $100 that would serve the purpose of conducting this test? It's not that I can't afford it as much as after I am done it won't get much use afterward. Thanks.

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what are you guys playing to do the tests? you can download 50hz and 1khz signwaves in mp3 format from mtx

 

a digital volt meter works with this signal even though they won't work with dynamic sounds for the previously stated reasons 

 

https://www.mtx.com/testtones

 

people use these to set amp gains in car audio. you're just doing the reverse here. you know the ohm load. play the signal, increase volume and see what you get for voltage. i tried a couple. an adcom 5300 puts out 28v into 8ohms which is 100w before the clip lights flicker. that's an 80wpc rated. i should run some of these marantz receivers and see what i get

 

 

 

 

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5 hours ago, tube fanatic said:

A true RMS meter is not necessary for measuring a sine wave!  This point was also addressed in the DIY link, posts #24 and #25.

 

Maynard

 

I thought  you were referring to PWK's power requirements paper where he said the numbers allowed for 10 dB peaks. He wasn't needing 10 dB for sine wave test signals now, was he? If good numbers from a test are what you want, you probably want to use pink noise or music for a test signal. A  true RMS meter with at least 20-20K frequency response is necessary for accuracy.

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1 hour ago, racebum said:

what are you guys playing to do the tests? you can download 50hz and 1khz signwaves in mp3 format from mtx

 

a digital volt meter works with this signal even though they won't work with dynamic sounds for the previously stated reasons 

 

https://www.mtx.com/testtones

 

people use these to set amp gains in car audio. you're just doing the reverse here. you know the ohm load. play the signal, increase volume and see what you get for voltage. i tried a couple. an adcom 5300 puts out 28v into 8ohms which is 100w before the clip lights flicker. that's an 80wpc rated. i should run some of these marantz receivers and see what i get

 

43 minutes ago, Don Richard said:

 

I thought  you were referring to PWK's power requirements paper where he said the numbers allowed for 10 dB peaks. He wasn't needing 10 dB for sine wave test signals now, was he? If good numbers from a test are what you want, you probably want to use pink noise or music for a test signal. A  true RMS meter with at least 20-20K frequency response is necessary for accuracy.

 

 

It would be helpful to read through the threads in the DIY link I provided in the first post as they will clarify the test quite well.

 

This test is not looking at how much power an amp can provide before clipping, and it is not looking at full bandwidth power requirements.  It is useful to determine how much power an amp needs to furnish for a given setting of the volume control.  This is why the initial requirement is to play music (instead of a test tone) and set the level to the loudest at which a person will ever want to listen.  It doesn't matter if the loudest level is 110 db or 75 db since each individual has a different requirement. Then, without touching the volume control, and using the same source device which played the music, you are going to play the 120 Hz and 220 Hz sine waves (which are recorded at -12 db) and measure the voltage at the speaker terminals.  Since zero db is the highest level at which a digital device can play, regardless of the recording, we then use the measured voltage to calculate how much power would be needed to satisfy the zero db condition.  Knowing that, for the chosen volume control setting, you will never need more power than the calculated value.  

 

Don, again, we're not worried about full bandwidth power requirements for this test.  It is simply a way to get a fairly good idea of how much power is needed to satisfy each individual's listening level.  I'm not sure I can explain this more clearly without getting too technical.  

 

Perhaps Albert can explain in layman's terms better than I can if he still happens to be following this.

 

Maynard

 

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So much confusion in here I reckon these blokes will never get this sorted out properly.  I don't konw how much more laymen it can get.

 

1) Listen to music

 

2) Play test tone

 

3) Measure.

 

The calculated result already accounts for max headroom as digital can only go to 0db. If it hasn't sunk in yet it never will. 

 

Purchase a megawatt arc welding amp and close thread, end of discussion.

 

 

 

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On 6/9/2017 at 1:50 PM, jimjimbo said:

Measured at the speaker terminals of an MC225.

 

Khorns - 4.96 vac at 120hz, 5.02 vac at 220hz (equates to almost 25 watts)

 

La Scala - 3.54 vac at 120hz, 3.62 vac at 220hz (equates to approx. 12.5 watts)

 

Belle - 3.51 vac at 120hz, 3.56 vac at 220hz (equates to approx. 12 watts)

Power is V squared over Z or R. So with say, minimum impedance of 5 ohms for a Khorn, 25 Volts divided by 5 ohms MIN is 5 WATTS MAX, not 25, and that's just for the bass driver. The Mid and Tweeter have much higher impedance through the Autoformer, so receive much less than a watt at the same level.

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1 hour ago, ClaudeJ1 said:

Power is V squared over Z or R. So with say, minimum impedance of 5 ohms for a Khorn, 25 Volts divided by 5 ohms MIN is 5 WATTS MAX, not 25, and that's just for the bass driver. The Mid and Tweeter have much higher impedance through the Autoformer, so receive much less than a watt at the same level.

 

 

Test tones are -12db. Jim's figures are correct for figuring max power. (into 8 ohms)

 

12db is 4x

 

5*4=20

 

20*.7=14

 

14^2=196

 

Divide 196 by whatever load you like

 

196/5=39

 

39 watts 

 

or 25 watts for 8 ohms et cetera

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As Albert demonstrated, there is more than one way to make the required calculations.  Pano devised the test for absolute simplicity.  You do not need to have any technical knowledge to do it (my wife did it correctly, without assistance, after reading Pano's instructions).  The only electronics skill needed is to be able to connect the probes of a multimeter to either your speaker terminals, or the speaker jacks of your amp.  Eight ohms was used as a reference because most amps specify power into that load impedance.  

 

Claude raised the question of power requirements into an impedance lower than 8 ohms.  For simplicity, let's consider 4 ohms as the minimum the amp will have to deal with (that will be approximately valid for most Klipsch speakers).  So, to find out how much power is needed for that impedance, simply do the test and then double the result.  So, in Jim's case with his K-horns:  4.96 X 4.96 = 24.6W into 8 ohms, or 49.2W into 4 ohms.  That's it.  For the volume control setting that Jim chose as his worst case (i.e. loudest) level requirement while listening to music, he now knows how much power is needed to satisfy ANY RECORDING  that he will ever play.  If his amp can deliver that amount of power cleanly, everything is good.

 

Maynard

 

 

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