A Test. How much Voltage (power) do your speakers need? - Page 46 - diyAudio
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View Poll Results: I measured the test tone at:
2 volts or less 155 37.80%
Between 2-5 volts 139 33.90%
Between 5-10 volts 52 12.68%
Between 10-20 volts 25 6.10%
Over 20 volts. 39 9.51%
Voters: 410. You may not vote on this poll

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Old 7th February 2012, 12:31 AM   #451
a.wayne is offline a.wayne  United States
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Old 7th February 2012, 12:36 AM   #452
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Quote:
Originally Posted by revboden View Post
How did you get 1.47w? distance ~2.5m from the three fronts ~2m from the sides and ~3m from the rears. I did measure at 1m from the front right main 85dBc before measuring the voltage for the -18dB 220Hz sine. this room has a lot of absorption built in, 6" of medium density closed cell foam covering the walls under the drapes.
Then it's hard to tell how resistive your room is , but your speakers may have an anechoic rating or 86db/1w/1m ... well if the numbers you gave me were correct..



@ Pano: I'm assuming 8 ohm nominal speakers .....
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Old 7th February 2012, 12:37 AM   #453
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Quote:
Originally Posted by a.wayne View Post
Then it's hard to tell how resistive your room is , but your speakers may have an anechoic rating or 86db/1w/1m ... well if the numbers you gave me were correct..



@ Pano: I'm assuming 8 ohm nominal speakers .....
You are correct 8 ohm.
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Old 7th February 2012, 01:02 AM   #454
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As we've had active loudspeakers mentioned quite a bit here it's worth examining them in a little more detail perhaps as my loudspeakers are active too.

Below you will see the transfer function/gain of the individual networks within the main three way part of the loudspeaker.

Click the image to open in full size.

As can be seen the gain varies by a huge amount vs frequency over the bandwidths that the drivers are asked to reproduce and as a result the voltage the amplifiers will be asked to reproduce vs 0dBfs will also change considerably depending on the frequency. So what do you do?

First lets look at the midrange driver (net gain 2) as this is the easiest one to make this work for. It can be seen that the point of maximum gain for the midrange is at around 750hz. This is useful because music easily has the potential to contain a lot of energy at this frequency. As a result it would make sense to run this test for the midrange driver at 750hz and it would give accurate results.

Next lets look at the tweeter (net gain 1). Here we've got a huge problem. As you can see the gain goes up as frequency increases (and by a large amount too), but at the same time we know that on the whole music contains less and less energy the further up in frequency you go. If I wanted to play this on the safe side I could measure at 20khz, but by doing this I would probably oversize my amplifier requirements considerably. If I did the measurement at 10khz for example I would need an amplifier with half the voltage swing then if I had done the test at 20khz.

It's similar for the bass driver too, here there's a LT circuit in place that adds a peak of gain at 35hz. But once again most music doesn't have a lot of content down that low, but then again some will. Here I am saved by the laws of physics though because in its specific cabinet that driver runs into xmax with around 28Vrms, which is what the amplifier can provide, so in that sense it's an easy enough task to size the amplifier for the driver.

For the tweeter however this test is showing one of its limitations and a scope really is required. In this case it is more informative to play a wide variety of music through the system, at the max volume, with a scope hooked up and see how high the peaks reach. Don't get me wrong however, using the test at 20khz would have given me an absolute 'worst case' requirement for the tweeter amplifier and would be the 'safest' bet, but it would also oversize it for the vast majority of music.
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Old 7th February 2012, 01:37 AM   #455
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Hi Tom,
I'm sorry if you feel like you haven't been getting thru, but it's been just as frustrating from this side.

You seem to be reading into this test things that aren't there. You are not alone. This isn't a set up or optimization test, or a loudspeaker performance calculation, it's just a voltage measurement under normal operating conditions. Let me see if I can explain better

Quote:
Originally Posted by Tom Danley View Post
I tried to explain why the sine test has a tenuous connection to what is required for some kinds of program material but fine for others.
And you did. But the test is not set up like that. The sine wave test tones that I provided in no way set any level. None. They bare no direct relation to any average levels.

Quote:
The issue was supposed to be what is required to drive the speakers, that includes what is hard for them, not just compressed music or tones ..
That is certainly not the issue in this test. Never was. Nowhere is "required" mentioned. It is simply a measurement of the voltage going to your speakers. In this case, the voltage going to your speakers when playing loud. That's all.
Quote:
I tried to explain that one’s impression of loudness is not necessarily an indicator of producing all the signal or strongly tied to what one measures while what one measures IS what the system is doing.
Yes, and it's an important point. The spectral content of the music can make you turn it up or down, even with pieces played at the same SPL. Bass heavy music is a good example, as we tend to tolerate that much louder.
I did suggest listening to a few tracks to get an idea of were your maximum level is.

Quote:
I tried to explain (since some folks are tempted to try to measure ) that the meters people are likely to used if they don’t have real test equipment HAVE a frequency response which may or may not allow them to be accurate other than around 60Hz or with changing signals.
That is precisely why I picked a 120Hz sine wave for the test signal. To quote myself in post two.
Quote:
Originally Posted by Pano
We use a sine wave to test with (after setting the level) because it's easy for a voltmeter to measure accurately, unlike music. All the meters I've tested have been accurate at 120Hz and within a small fraction at 220Hz.
Quote:
I have suggested that in order to tell if one has enough power, that the BEST TEST is one examining the actual Voltage signal going to the speakers at a level your happy with, with the program material you like to listen to and look for signs of limiting with an oscilloscope.
Yes it is. But if you understand digital recordings and this test, you will understand that it is not needed for this test. The tone you measure will be precisely 12dB below the highest peaks. With a digital source, it can be no other way. Period. Once you understand this, then you understand the test.
Quote:
Honestly, I don’ see why this is a bad idea here, this kind of test has revealed many problems in larger sound systems too where gain structure (not just amp limits) can be an issue too..
Again, it is not a bad idea and no one here has ever said that it was. We've been over this before.

Quote:
In a effort to illustrate that the peak electrical power or Voltage required and the apparent loudness ARE NOT strongly tied, I suggested two kinds of artificial test signals which would clearly illustrate that, in the case of the pink noise signals with various music like peak to average ratios, these if played back at the same apparent loudness, requires as much as tens thousands of times more peak power to be the same subjective loudness.
All fine and dandy, but of no real use in this test. See above. It's not a set up test - it's a test of what voltages you are actually using.

Quote:
A sine wave, requires even less peak power for a given apparent loudness than the 6dB crest pink noise and that more compressed than any music one can find.
You are still stuck on this and it does not apply to this test.

Quote:
All this may seems like an excessive focus on the dynamics of the signal but that’s what I wish to preserve /reproduce.
While it was a mistake to contribute to this thread, I am not asking people to believe what I am suggesting, just to look using tools that will show the engineering reality at the root of this.
This is because you are reading something into the test that is not there. You are coming from a design point. This is NOT a design exercise. It is simply a test of amplifier output voltage under (near) normal conditions. Please don't take it for anything else or read into it what is not there.
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Old 7th February 2012, 01:47 AM   #456
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I was thinking about something. not sure it will catch but...
maybe we should select one "worst case song" (classical with a large peak-to-average ratio and headroom) and have people do the test with it. that way, after the test is performed as Pano described it, knowing the SPL and impedance of the speakers, the required power and listening distance we can get a rough estimate of the SPL. the song can be analyzed in CoolEdit to get mean/peak power and SPL can be derived from there.
one problem I'm seeing is a song selection that would not get anyone into legal issues.
other is testing with music that might not appeal to everyone. some might turn it down if they dislike it
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Old 7th February 2012, 01:48 AM   #457
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5th-E. Thanks for the 3-way system plots and explanations. This is where I hoped we would be about 25 pages ago.

Yes, and active crossover system is going to be much harder to calculate, especially at the top end. You explained that very well.
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Old 7th February 2012, 02:04 AM   #458
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Quote:
Originally Posted by Pano View Post
How go you get 1.47 Watts from 0.72V
you multiply by two? LOL
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Old 7th February 2012, 02:36 AM   #459
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I thought about adding a test track too, something classical and very dynamic, the trouble is the copyright involved. I've got a high res 24/176.4 recording of Tchaikovsky's Hopak that was free to download from some website ages ago, I'm guessing that that would be okay? It's not too long and has some very large peaks relative to the quiet start and is rather fun to listen to.

I have converted it down to 44.1k 16bit and compressed it to a reasonably high quality FLAC and here's a download link. I also altered the level slightly so that the peak signal level of it hits 0dBfs too. How long the download will exist for I don't know

Tchaikovsky Hopak.flac

Pano may wish to download it and convert it perhaps into something different.
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Last edited by 5th element; 7th February 2012 at 02:39 AM.
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Old 7th February 2012, 03:36 AM   #460
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did a listen on my headphones (Senn HD448) and it sounds like a good choice.
here's what CoolEdit says:

Left Right
Min Sample Value: -31858 -29823
Max Sample Value: 30453 32178
Peak Amplitude: -.24 dB -.16 dB
Possibly Clipped: 0 0
DC Offset: 0 0
Minimum RMS Power: -63.46 dB -66.44 dB
Maximum RMS Power: -4.21 dB -5.49 dB
Average RMS Power: -22 dB -22.17 dB
Total RMS Power: -19.25 dB -19.5 dB
Actual Bit Depth: 16 Bits 16 Bits

Using RMS Window of 50 ms


exactly 18dB peak-to-average, isn't that nice. no clipped samples, some headroom, should do the job.
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