A Test. How much Voltage (power) do your speakers need? - Page 13 - diyAudio
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View Poll Results: I measured the test tone at:
2 volts or less 143 37.34%
Between 2-5 volts 130 33.94%
Between 5-10 volts 51 13.32%
Between 10-20 volts 23 6.01%
Over 20 volts. 36 9.40%
Voters: 383. You may not vote on this poll

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Old 27th January 2012, 06:14 PM   #121
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Quote:
Originally Posted by Brett View Post
I'm not in a position today to do your test, but with the last proto, 6V into a 97dB MB (Re=6.3) driver was unbearable in room with tones or noise within it's passband (<300hz). Measured, 2 speakers and with a Fluke 287 at the terminals.
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Originally Posted by Brett View Post
That's the loudest I could stand being near them with a tone, which I would equate to an average level for dynamic content. Peaks could easily exceed that by 20dB and still be bearable, providing the system is still within it's linear range.

See Bob Cordell's dynamic content and power tests to get what I mean.
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Originally Posted by Pano View Post
I don't follow. Where is the 6V coming from? Is that what you need to get -20dB RMS at your listening level? Seems rather high, but possible.

If so, that indicates 60V peak, or 450W peak into 8 ohms. Or an RMS rating of about 225W into 8 ohms.
I did state later that the proto was 3 way active and I measured the voltage on the LF section as that was least efficient and I wanted to see what was needed. I mainly test with pink noise, full range, but I also measure with tones in the region above the impedance peaks at LF but below xover. Earlier I said it was my Fluke 287, but it might have been the 8010A or Wavetek, but all are true RMS, so the 6V would be RMS. Huge room, distant neighbours.

Did you read the Cordell article I linked today?
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Old 27th January 2012, 06:17 PM   #122
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Thanks Brett. So you got 6V with the -12dB test tone, or with something else?
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Old 27th January 2012, 06:22 PM   #123
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Read post 121.
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Old 27th January 2012, 06:25 PM   #124
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I did, that's why I'm asking. It's not clear to me were your voltage measurement came from. My test tone? Pink noise? Something else?
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Old 27th January 2012, 06:53 PM   #125
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Quote:
Originally Posted by Brett View Post
Did you read the Cordell article I linked today?

Hi Brett, I have seen that and can't dispute any of it as such.
So how much power do you really need for domestic listening ?

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I have a jazz disc somewhere here (I don't like the music) that noodles along at a modest level, which if I set it for a comfortable level at the LP (average of 80dB or so) is nice. Then all the horns come in at once and the difference on that initial note is easily >20dB, based upon your 9-12dB difference, artificially set, then I would be easily into clipping.
Can we look at this from another perspective.

Firstly, we need a reference such as CD (digital) in order to establish known levels. If we had vinyl test discs we could a similar thing of course.

Lets say for a moment this jazz track of yours was on CD.

You say "Then all the horns come in at once and the difference on that initial note is easily >20dB. So you have already set a listening level for your system and presumably it's not distorted. That peak level of the horns we could fairly assume to be near to the 0db level of the medium.

Do you see... it's hard to explain this easily.

You can't take a music track and say that some musical peak level "sounds/appears/mightbe >20db over the average level and so the amp will clip according to this test. You are already listening to that level and proving it OK. That is your current maximum level. And from that figure we can work out an approx amp rating.

Assuming the horns are +20db over the average is just that, an assumption They may or may not be but the horns are the pace setter at 0db.

Work backwards from that, not try and work up to what they may or may not be level wise.
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Old 27th January 2012, 08:21 PM   #126
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Originally Posted by Pano View Post
Yes it is the case. A sine wave has a peak voltage that is 3dB higher than its average (RMS) values. There is no doubt about that.
Do you think you made a mistake in the test when you measured 7V on the test tone?
i did it again more carefully.

7.7 volt but it doesnt change much.
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Old 27th January 2012, 10:08 PM   #127
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Originally Posted by Mooly View Post
Firstly, we need a reference such as CD (digital) in order to establish known levels. If we had vinyl test discs we could a similar thing of course.

Lets say for a moment this jazz track of yours was on CD.

You say "Then all the horns come in at once and the difference on that initial note is easily >20dB. So you have already set a listening level for your system and presumably it's not distorted. That peak level of the horns we could fairly assume to be near to the 0db level of the medium.
Quite right. There is an absolute maximum level with digital playback that is, as you said earlier "set in stone". It does not matter what music or signal is playing, that the highest level possible on the CD. For convenience, we call that 0dB. All other levels must be below that.

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Do you see... it's hard to explain this easily.
Not hard, you've done a great job of it.
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Old 27th January 2012, 10:23 PM   #128
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Originally Posted by Mooly View Post
No, 11.31 volts RMS... now there's a coincidence Maybe ! What's the impedance of a foobar ? Come to that, what's a foobar ?



But we are working in volts today (much nicer) and so we use the magic db =20logv1/v2 do-dah. That tells us that the db thingy for 11.3 volts and 4 volts is 9db or -9db depending which hemishere you are in.
Just like -11.31dB in my hemisphere ...
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Old 27th January 2012, 10:46 PM   #129
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Quote:
Originally Posted by Mooly
Can we look at this from another perspective.
Yes we can. And I think that persecutive is what is tripping up a lot of folks.
We need to think "Top Down" (digital), not "Bottom Up" (analog).

Because digital has an absolute maximum level it becomes a very handy tool for system measurements. If you know what that maximum is, then you know what all other levels are, too. It's pretty easy. Even easier is the fact that most CD/DVD players and DACs output 2V RMS as their maximum level (you should check that for your device). Ergo, all other levels will be below 2V RMS. 2V RMS is the maximum signal possible. 2.83 volts is the absolute maximum peak level. It's "carved in stone" so to speak.

If you measure a test signal that is 12dB RMS below maximum, we know that it's coming out of the CD player at 0.5V RMS. Pass that thru your preamp, volume control and power amp and that voltage will change, of course. It might end up as 5V RMS once it leaves the power amp and hits the speaker. But it's still 12dB below peak- that has not changed. Otherwise said, the peak level that your amp will produce is 4X higher. That's all it can be, unless your amp is clipping or has some other non-linearity.

Another thing that seems to be leading a number of folks astray is the -12dB level - maybe because it's close to the average level of a lot of music. But remember, you did NOT set your volume level to the test tone, did you? No, you set it to music. And on a digital recording that music, no matter what it is, will peak at 0dB, never higher. Your music might have an average level of -22dB, or -10dB or even Tom's fireworks recordings at -40dB. The absolute peak value will never be above 0dB. It can't be.

So why the -12dB test level? It was chosen so that you get a good measurement and don't blow out your speakers or your ears. Imagine that I had asked you to set a very loud level, than had you play a test tone that was recorded at -3dB. You'd complain to me that you had blown out your speakers, burst your eardrums and scared the cat!! (Poor kitty). The test tone could have been at -50dB, but that might mean a voltage so low it's hard to measure on some volt meters.

The test tone level could have been set anywhere, but -12dB seemed a safe and convenient place for it. It's just a happy coincidence that 12dB is 4X voltage for easy math. And even more fun is that the measured voltage squared = the 8 ohm power rating. That one just fell in my lap, I didn't plan it.

Sorry for the long post, but I hope this helps clear up what's going on.
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Old 27th January 2012, 11:06 PM   #130
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Hehehe I haven't yet got to try the test yet, will have to wait till I have the house to myself. I think I can see where the confusion is as Mooly and Pano have pointed out. I'll try and put it concisely.

Set your reference level using the recording you have with the greatest dynamic range, at the loudest you would listen to THAT recording. Then do the measurement of the test tone

Also as has been pointed out already you should be using the same source for the test tone as for the playback of the recording, otherwise you cannot be sure they are at the same level.

If you use the recording with the highest compression your results will be much lower (and not a true reflection of the voltage you really need).

If you know your music collection you should be able to pick the recordings which you know you normally crank the volume knob up higher on.
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