A Test. How much Voltage (power) do your speakers need?

[Pano]

Here is a simple test to determine what voltage your speakers need to play their loudest. From that you can determine how much power you need.
Knowledge is good and this test will tell you just how much voltage (or power) you really need. Efficient speakers in a small room may need only a volt or two. Less efficient speakers in a big room may need a dozen volts or more.
I've included a poll so that we can see what's typical. If you want to also post your speaker details and room details, that would be nice.

For the moment, I'll leave this as a voltage test, we will talk about power later. Those of you who know Ohm's law can figure it out for yourselves. Amp power tends to be an emotional issue, so we'll post the results in volts for now. Since most amps are voltage devices anyway, it's not a bad way to measure. And a voltage measurement removes the speaker impedance from the equation.

All you need for this test is some sort of digital playback (CD, iPod, Squeezebox, computer, etc) and a volt meter with a low AC scale. Any scale 20V or lower should be OK. Meters with only 200V AC scale won't be accurate enough for this test.

Next post has the test tones and instructions.

NOTE: The test tone provided is not used to set you system levels, it is used to measure your system levels. You will set the levels by ear, or by pink noise if you wish.

[Pano]

Attached you will find 2 test tones in MP3 format. They are simply sine waves in 44.1K/16 bit format. The tones have an RMS value of -12dB. There is 120Hz for mains with woofers and 220Hz for systems that use a subwoofer.

• Download one of the files below.
• Unzip the MP3 and burn it to a CD or put it in whatever digital playback gadget you use.
• Select and play back a few dynamic music tracks as loud as you ever do (like rocking out after a few beers.) Take note of your volume settings.
• Use the highest setting you found when playing back music really loud and leave the volume there for the following measurement.
• Playback the test tone and measure the voltage at your speaker terminals. Measure at the amp or at the speaker, either is fine.
• Post the voltage you measured.

The principal of the test:
With digital playback, there is a maximum value "set in stone", so to speak. That value is 0dB. All other levels are below this. Knowing that, it's easy to figure out what the peak level is; it's 12dB more than your measured voltage. That means peak is 4X the voltage. That's as high as the voltage to your speakers will ever go.

Because you've played back a few CDs and determined the maximum level you use, the loudest level you ever want, you've established your peak voltage.
Playing back and measuring the test tones will tell you what that peak level is. The peak voltage will be 4X higher than your measurement.

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.

Thanks for taking the test. It will be interesting to see what voltages are used across a wide range of speaker types, room sizes and musical tastes.
Please post the voltage you measure and fill out the poll. Thanks!

[pinkmouse]

Right, a quick test on the second system shows that a good loud level in a 4x3x3m room takes 2.9V. However, this is taken on the 8ohm low mid driver of an efficient, (92dB), actively crossed over sub/sat system, so not typical I suspect.

[tuxedocivic]

So are we supposed to post our measured voltage, or the measured voltage x 8?

You said the peak voltage will be 4x's the measured voltage and then later said 8x's, but I'm pretty sure 12db makes it 8x's, right???

[Pano]

Please post your measured voltage. We'll do the math to figure out peaks and averages. Sorry if that was not clear.
The poll is for measured voltage from the -12dB.

12dB voltage is 4X. Thanks for catching the typo, I fixed it.
Peak will be 4X your measured (posted) voltage. Maximum RMS of a sine wave will be 2.83X.

[Pano]

Originally Posted by pinkmouse

Right, a quick test on the second system shows that a good loud level in a 4x3x3m room takes 2.9V.

Thanks Al. That sounds about right for 92dB and that size room.

[tuxedocivic]

Ah, ok. Thanks. Will try this later. I have insanely ineffecient speakers (82db, 8ohm), so it'll be interesting to see what I come up with.

[Pano]

Yes, I'm very interested to know! Thanks.

[weltersys]

Originally Posted by Pano

Here is a simple test to determine what voltage your speakers need to play their loudest. From that you can determine how much power you need.
Meters with only 200V AC scale won't be accurate enough for this test.

I have tested a rather efficient (around 101 dB 1 watt 1 meter) four ohm tapped horn speaker (B&C 18SW115-4) with 120 volts at 60 Hz, a 200V AC scale worked fine at that level .

That speaker could have used more voltage to play louder, but the amp shut down after a few seconds each time I tried three times in a row, and I don't have an amp capable of more voltage swing than 120 volts.

An AR-2 hits about 10% distortion at 45 Hz with 10.9V.
A pair burn up quickly with 64V at 60 Hz applied .

I once burnt an Eminence Alpha 8 using about 35 volts, would that be too low to read accurately on a 200V scale ?

Art

[Pano]

You using 120V at -12dB on speakers in your living room, Art?

I did not include a 100V+ scale because most folks here aren't trying to fill a stadium. Home systems are the aim of this test.
But your points are valid and I appreciate the data points, thanks.