Understanding amplifier power

So, this doesn’t have much to do with Roon but since that’s my main source I hope people won’t mind me asking here.

I have been test driving a few different integrated amps recently, ranging in power from 40w RMS to 250w per channel into 8 ohms. I have purchased the 250w amp. They’ve all been driving 8 ohm speakers with a rated sensitivity of 90 dB. I use room correction via convolution along with -4dB headroom and volume levelling set at -14LUFS, the combination of which eliminates any clipping from the filters. I normally listen at somewhere between 73dB and 77dB at the listening position.

What’s confusing me is, despite the significant variation in output power, to achieve the lower end of this volume all the amps have needed to be set to, very roughly, 60% of max volume. I obviously don’t understand how this works as would have presumed it would vary significantly by power rating. What very obvious thing am I missing? I realise that doubling amplifier power only equates to a 3dB increase in volume level but this still seems surprising. Feel free to point me to an idiots’ guide somewhere.

I guess the other query that follows from this is if the speakers are rated to a power handling of 120w RMS and I’m feeding them with a 250w amp (but still achieving the same loudness as with the 40w amp), might I do some damage? Today I was listening at 75% volume on this 250w amp but only achieving 76dB at the listening position - ideally I would have liked things a little louder but I’m fearful of damaging the speakers.

Apologies if this is all a rather silly question - I fear I am missing some basic knowledge! Thanks for any pointers.

You are more likely to damage a speaker with an under-powered amp, rather than an over-powered one. He speaker will simply get the power it needs to deliver the volume you require even if the amp was 1kw. But trying to make a low powered amp produce more power than it can cleanly provide will cause distortion and potentially damage the speaker if you persist. Input sensitivity and gain will affect volume settings, so you could end up with quite different volume settings on different amps.

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Thanks @jobseeker, it sounds like getting a better understanding of input sensitivity and gain might be the answer, but in the meantime good to know I’m not going to be causing any harm at vaguely sensible volumes.

Just as an experiment, try turning off volume leveling and the headroom setting and see what difference it makes.

Personally, I haven’t seen a clipping problem with leveling. It’s usually lowering volume for modern loud mastering, so no need for headroom protection? In the rare case it’s increasing volume, it’s usually not much.

Also, you can try adding a procedural eq to boost gain. Seems counterintuitive with leveling and headroom adjustments, but I’ve used it to more closely match relative volumes to other playback devices and haven’t noticed any problems.

I’m no expert on how any of this works. Those are just my anecdotal observations.

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The volume control of an amp is logarithmic. That means the first 70% or so of volume control movement only represents a few watts worth of power, and that is helped by the fact you seem to run relatively benign speaker loads. All the power of a logarithmic scale comes at the end so it is only when turned right up that issues occur. Or if you induce clipping with a lower powered amp (not to be confused with clipping in Roon). I run Hypex Ncore 400 amps into speakers rated at 80wpc and have never had an issue, even on those very rare occasions something gets switched on while it is turned up too high. Just observe a little caution.

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Thanks @SKBubba - Just to be clear, the clipping is coming from the Convolution filters, not volume levelling - certainly turning off the two leads to needing lower levels from the amp, as you’d expect.

Aahhh - that would certainly explain this finding - thanks. I hadn’t realised that this was the default behaviour (I’ve seen some amps available with a choice of logarithmic or linear pots).

This is where Active and DSP active speakers have an advantage. The amps are designed with specific drivers in mind as a system so there is minimal wasted energy and no risk of being underpowered. Also no speaker leads to worry about.

Amplifier power in relation to perceived loudness is logarithmic. You need ten-times the power, to produce a doubling of perceived loudness. Eg. A 100watt amp has twice the perceived loudness of a 10watt amp.

To go twice as loud as a 100watt amp, you need 1000watts!

So… in your case, a 400w amp would go twice as loud as a 40w amp. That, is with the input fully saturated with sound and the volume full up!

You are applying volume levelling, so… for the majority of music (which has some dynamic range compression), there is quite a reduction in level on Roon’s output and, therefore, the input to the amplifiers, which is why you’re seeing 60% or more volume levels to get a reasonable listening level. A really dynamic recording may peak quite a bit louder though, but only momentarily, and those peaks would be handled better by a more powerful amplifier.

Also, as you apply more and more level to speakers, the cabinet and cone excursion resistance both have an increasing dampening effect, so you don’t get a linear change in volume as you push them harder.

There’s basically all sorts of non-linear factors at play here, including the logarithmic volume control.

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Thanks @Dan_Brown - although I’d played around with a handy amplifier power calculator I hadn’t appreciated quite how many factors were at play here. My conclusion from all this is that everything is probably working as expected and I’m unlikely to damage the speakers at a volume that I would want to listen to. It also now makes a bit more sense for me of things like the 1200w ICEPower module..

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It gets very complicated as although the loudspeakers will have a Nominal resistance of 8 ohms it will vary across the frequency range. Tricky devils.

In case anyone else has similar questions, there’s a helpful interview between John Darko and Vinnie Rossi which addresses some of these, in particular the difference between gain and power and how this relates to volume controls.