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

[soundcheck]

Originally Posted by Pano

More gain than you need is better than the reverse. Most of us work well within having enough gain. But systems with 20-30dB more gain than needed? Seems like bad planning, bad engineering, or both. But it sells, and that's important.

Find an amp with less or variable gain!!! (I'm not talking about fiddling
around with the feedback resistor of an opamp input stage)

Pretty much the entire Class-D market comes with a voltage gain of <> 30db. Solid state is not much better.


What most of us need is current and not voltage. That's what this thread clearly shows.


That's probably why those little 15W Class-Ds always sound powerless compared to it's fad 200W brothers.

If you run a 12V-15W amp with 30db gain or a 24V-80W amp with 30db gain. You'll end up with the same output voltage.

What'll probably make the difference though is the current delivery capability of that bigger amp.

Even on my 98db SPL/W speakers a 80W amp sounds better then its 15W companion.

Cheers

[Pano]

Most of us do need some voltage gain, as well. But usually not 30dB worth, I agree. With an active crossover the voltage going to my horns is actually lower than the voltage coming out of the DAC, but that's an extreme case.

On my ~98dB/W speakers a bigger amp does not sound better - usually worse. But I use small amps with plenty of power supply behind them. After all, what is an amp but a fancy variable power supply?

[AndrewT]

a fancy variable power supply

that sends current to meet the demand set by the speaker.


It's current that drives the voice coil of those transducers.

[AndrewT]

After two hours seaching I finally managed to work out how to and produce a CDR with those two test tones.

But, is it possible that the two tones are not recorded at the -9dB level?

I ask, because my 60W into 8ohms amplifier driving a 150W maximum recommended power 8ohms speaker gave a reading of 16.27Vac and 16.28Vac for the two tones at the speaker terminals.

Those tones if correctly recorded drive the amplifier to -3dB ref. max power !

[Pano]

Anything is possible, but it's not likely they are wrong. I've checked them on 2 different softwares and 2 different hardware. Always -12dB RMS and -9dB peaks.

Now when you say that the tones drove your amp to -3dB of max, where did you have your volume control? I've had amps that maxed out at about 10:00 on the volume knob from a CD input. Pretty silly, but that's the way they were built. Too much gain. Your 16.27V reading is 33 watts into 8 ohms, which is a lot for home use.

[AndrewT]

At the volume I wanted with my quieter CDs the volume knob was at max. Many of my over recorded CDs sound terrible at the max setting. That is the fault of the reproduction chain. I have to reduce the volume potentiometer to avoid all the clipping of the nearly continuous over recorded signal.

Yes, 16.xxVac is a lot, that is what your test is designed to reveal: How much voltage do my speakers need? To reproduce at the levels I want to listen at when I am in loud listening mode.

It indicates ~65Vpk is required at the speakers. I have only one amplifier that is capable of that.
I am not going to confuse the issue by looking at actual, or presumed, power figures.

That high power amp referred sits in it's box unused, after I inspected the quality of it's manufacture. It does not get near any of my music playing systems.

[Pano]

Thanks Andrew. Yes, if you got 16.25 volts from the test tones when playing the test tones at your preferred volume setting, then you need a lot of headroom. 65 volts peak or about 46 volts RMS. Of course your average level would be lower, but to keep the peaks from clipping you'll need that, 'cause that's where they'll be. I'm glad we determined that.

Do you have a very big room, low efficiency speakers, high SPLs, or a some combination of those things?

[AndrewT]

I didn't do the test in my listening room (lounge). I used my dining/kitchen area.
I used a chipamp powering an Acoustic Energy AE1 rated ~88dB/W @ 1m at a distance of ~2.1m.

If I reduce the vol pot to avoid clipping and the "noise" that results from that clipping, I end up with a much lower voltage at the speaker from the test tone.
But that vol pot setting does not represent the loudest I want to listen at. It represents my tolerance or intolerance of clipping distortion.

The test basically does not work, because it relies on the listener adjusting the preferred volume to suit whatever is in the system during the test.

I ignored what would happen during the loudest transients and came up with a completely different voltage from 89% of the pollsters.

The test as I have said all along is flawed.

I wonder what the result would be if I used a 5W amplifier and set the vol pot to avoid clipping and what would the result would be if I used a 400W amplifier within the same system.

[Pano]

No, the test is not flawed, it just has its limitations - as does any test. Those limitations have been discussed in the thread. You've given us a great illustration of one of its important limits; if you don't have enough power to begin with, then you'll have trouble with the test.

As you show, you turn down the level to avoid clipping because it sounds bad. So one might get to that level and say "Oh, that's as loud as I want it!" because the amp is clipping. You might actually play it even louder, if the amp wasn't clipping. On the other hand, many people have done the test and found that they are far under the maximum voltage of their amps. The volume limitation they set is probably not amp related. It may be room, speakers, ears, spouse, neighbors, etc.

I wonder what the result would be if I used a 5W amplifier and set the vol pot to avoid clipping and what would the result would be if I used a 400W amplifier within the same system.

That should depend on the speakers, the room and you. With my speakers in my room, I'm unlikely to clip a 5W amp (I've measured it) unless I want discotheque levels. Generally I don't - but there is the occasional rowdy party.

For you, I'd guess the 5W amp isn't nearly enough. The 400W amp should be plenty and allow you to turn up the average level to were you want it and not clip the peaks. Where those peaks would be, I don't know, but with very dynamic recordings, probably pretty high. The highest peaks I've ever seen on my system for very loud (non party) levels is 6V. Peak. Mostly far below that. You may need 60 volts or more. That's the point of the test, to find out.

It's been discussed before, but if you are at all close to your amp's clip point, you should try a bigger amp and do the measurements again. That's what the test is all about, it's not a flaw, it's the very essence of the test.

[Lavcat]

Originally Posted by Pano

Knowledge is good and this test will tell you just how much voltage (or power) you really need.

I have been following this thread almost since the beginning, but until now have been constrained from voting due to lack of an accurate meter. But now I can cast my vote!

Using the -12 dB 120 Hz test tone I measured 8.47 V. Loudness was set using Rossini's William Tell, Antonio Pappano conducting. (Listening to Tchaikovsky's 1812 now.)

The problem is 8.47 V (at -12 dB) works out to 142 W, if my math is right, and my poor little amp is rated at 35 W per channel into 8 ohms (FTC). Thus, for my amp, the maximum level of my test tone should be 4.2 V, again assuming that my math is right.

Fortunately much of my listening is late at night to chamber music, and for this my 35 Watts are plenty. Even in the middle of the day 35 W are more than enough for less dynamic music. Another limit is the point at which the police will come. True, I've only had the police come once, but it is a rather hard limit.

My listening room is L shaped, about 116 cubic meters, damped with eighteen Tube Traps, and open to other areas on each end of the L. Speakers are acousitic suspension rated at 8 Ohm and 85 dB sensitivity. For serious listening my listening distance is about four meters.

Oddly at a test tone setting of 7.1 V, which works out, I think, to 100 Watts per channel, the distortion indicators (which Crown calls IOC) never activate while playing music (or even fireworks).

At this point I have more questions than I have answers, but at least now I have some numbers! Let's keep this thread going!