Optimal line out level for WiiM Ultra + Audiophonics MPA-S250NC?

[Fralle]

No, if the listening level is fine, stay there.

When I said earlier that 22w are within the norm you have to put this into relation with the speaker impedance.
So now 11w are fine.

Thank you kindly! It is definitely enough for me. Kind of says something about how something about how excessively powerful these class d amplifiers actually are if 11w is more than enough

 

[Aquaman]

Thank you kindly! It is definitely enough for me. Kind of says something about how something about how excessively powerful these class d amplifiers actually are if 11w is more than enough

Well you must also keep an eye on the non-linearity of speaker impedances. A dip especially in the bass region and easily double the required output.
Also there is some source material for which you really need to crank up the volume.

And with your settings you are not limiting your amp‘s power, only the request for it. When more power is required the speakers will draw them and your amp can deliver.

Also, I cannot say why or what is happening physically, I do find that ‚exessive‘ power helps with bass control, even though it may not be need mathematically. It‘s a mystery.

 

[pieterv1]

So, what’s the general consensus among those who’ve actually tested both?

Best not to overthink it, is my suggestion!

With older amps with sensitive inputs, it is actually recommended to keep it at a lower value - to avoid distortion. With modern amps like your Hypex unit, you may set it to a lower value if preferred. No matter if you're using 500mv or 2v rms, if you then adjust the volume for the same listening level with your amp, you'll end up with the same signal-to-noise ratio.

The benefit of setting the line out level to 2v rms is that the volume increments will be higher, so you'll need less clicks or presses on the remote to make changes. The risk is that it will be very loud if you set it to 100% by accident

The 500mv rms setting will allow you to make more precise adjustments, with lower max volume. If you find the volume control to be a bit slow, there's the option to change the volume control resolution with the "Knob volume Step" setting in the WiiM Home app.

 

[harkpabst]

Personally, I wouldn't buy a 250 W amplifier and then limit its output to 22 W deliberately. There are cheaper, lower output versions for that.

2 Vrms will be fine, 1 Vrms if you want to keep the kids from destroying the house. Done.

 

[Aquaman]

Personally, I wouldn't buy a 250 W amplifier and then limit its output to 22 W deliberately. There are cheaper, lower output versions for that.

You‘re not doing that. That is a nominal output at a defined steady voltage input and a given speaker impedance.
But the input varies (the input voltage expressed in a single value is a root mean square) and impedance as well.
So you may well end up using 100watts or more in peaks even at a low setting.

 

[harkpabst]

You‘re not doing that. That is a nominal output at a defined steady voltage input and a given speaker impedance.
But the input varies (the input voltage expressed in a single value is a root mean square) and impedance as well.
So you may well end up using 100watts or more in peaks even at a low setting.

The voltage set in the Audio Output settings is the RMS value for a 0 dBFS digital input signal. It's the absolute maximum the WiiM Ultra will put out with a sine wave at full blast.

 

[Aquaman]

The voltage set in the Audio Output settings is the RMS value for a 0 dBFS digital input signal. It's the absolute maximum the WiiM Ultra will put out with a sine wave at full blast.

Exactly. With the peak of the sine wave being considerably above the nominal RMS voltage.

Combine that with impedance dips of a 4ohms speaker and your amp is going to have to work more than then nominal numbers suggest.

All of that may not be critical at low volumes. But when you‘ve had a dram or two and feel like having a party you WILL use volume levels that max out our moderate settings of input voltage and gain on the power amp. And you may want more!

I have my input set to 1Vrms and my amp‘s gain at 20.5db. This is good for all days but insufficient for a party, at least with my hungry 4ohms speakers.

My gut feeling tells me that an amp should have approx. 5 times the power of what the nominal values tell you. I can‘t prove it nor can I measure it.

That‘s what high-power amps are there for - to cover peaks at an otherwise lower level.

 

[Fralle]

Just to clarify: I have 8 ohm speakers so the Audiophonoics will output a maximum of 150 in my case. My bad.

 

[harkpabst]

Exactly. With the peak of the sine wave being considerably above the nominal RMS voltage.

Yes, but don't fall for this misconception: Peak power vs. RMS power of an amplifier has absolutely nothing to do with the peak and RMS values of the input voltage (or output voltage).

With any sine wave the ratio between the peak and the RMS value is fixed and the peak value is always 1.41 times the RMS value. You don't get a higher output wattage just because you look at the peak value instead of the RMS value. It's just a matter of how you describe one and the same signal. The peak power of an amplifier is still limited by it's maximum output voltage, no matter if you provide the peak or the RMS value.

Combine that with impedance dips of a 4ohms speaker and your amp is going to have to work more than then nominal numbers suggest.

Not much of an issue, either. These Hypex based amps are nearly ideal voltage sources. The maximum voltage into 4 ohms is almost identical to the maximum voltage into 8 ohms loads. As a consequence, the power into 4 ohms almost doubles that into 8 ohms.

That‘s what high-power amps are there for - to cover peaks at an otherwise lower level.

As I said before, you cannot reach these power peaks with insufficient input voltage.

Just to clarify: I have 8 ohm speakers so the Audiophonoics will output a maximum of 150 in my case. My bad.

This makes no difference regarding the output voltage.

Let's stick with the Audiophonics MPA-S250NC RCA for now. Max. power into 8 ohms is 150 W.
Power = voltage * current
Current = voltage / impedance
Power = voltage² / impedance
Voltage = sqrt(power * impedance)
=>
Voltage = sqrt(150 W * 8 ohms) = 34.64 V

This is an RMS value, but that doesn't matter, 34.64 Vrms are exactly the same as 49 Vpeak at the same time. No difference, just different ways to describe the same thing, no difference in output power.

The MPA-S250NC RCA needs an RMS input voltage of 1.66 Vrms (fully equivalent to 2.34 Vpeak) to generate an output voltage of 34.64 Vrms. This equals a voltage gain of 20 * log(34.64 V / 1.66 V) = 26.39 dB or in plain numbers a factor of 20.9.

You will notice that this factor is very close to that calculated by @Aquaman for a 4 ohm load. This is because the output voltage hardly drops into 4 ohms compared to 8 ohms. But here is the essential part: If you limit the input voltage to 0.5 Vrms then the output voltage is limited to 20.9 * 0.5 Vrms = 10.45 Vrms (which is exactly the same as 14.78 Vpeak).

Power = voltage² / impedance
=>
Power = (10.45 V)² / 8 ohms = 13.65 W

13.65 W is the absolute maximum power you can get from this amp if the output voltage of the WiiM Ultra is limited to 0.5 Vrms. There is absolutely no headroom. No higher peak wattage. No nothing. There is simply no way to get more than 13.65 W out of this amp into an 8 ohm load with the Ultra set to 500 mVrms. Period.

If the true frequency dependent impedance of your 8 ohm speakers dips down into 4 ohms at any given frequency, then the maximum output power at this frequency is roughly 22 W.

 

[Fralle]

Yes, but don't fall for this misconception: Peak power vs. RMS power of an amplifier has absolutely nothing to do with the peak and RMS values of the input voltage (or output voltage).

With any sine wave the ratio between the peak and the RMS value is fixed and the peak value is always 1.41 times the RMS value. You don't get a higher output wattage just because you look at the peak value instead of the RMS value. It's just a matter of how you describe one and the same signal. The peak power of an amplifier is till limited by it's maximum output voltage, not matter if you provide the peak or the RMS value.


Not much of an issue, either. These Hypex based amps are nearly ideal voltage sources. The maximum voltage into 4 ohms is almost identical to the maximum voltage into 8 ohms loads. As a consequence, the power into 4 ohms almost doubles that into 8 ohms.


As I said before, you cannot reach these power peaks with insufficient input voltage.


This makes no difference regarding the output voltage.

Let's stick with the Audiophonics MPA-S250NC RCA for now. Max. power into 8 ohms is 150 W.
Power = voltage * current
Current = voltage / impedance
Power = voltage² / impedance
Voltage = sqrt(power * impedance)
=>
Voltage = sqrt(150 W * 8 ohms) = 34.64 V

This is an RMS value, but that doesn't matter, 34.64 Vrms are exactly the same as 49 Vpeak at the same time. No difference, just different ways to describe the same thing, no difference in output power.

The MPA-S250NC RCA needs an RMS input voltage of 1.66 Vrms (fully equivalent to 2.34 Vpeak) to generate an output voltage of 34.64 Vrms. This equals a voltage gain of 20 * log(34.64 V / 1.66 V) = 26.39 dB or in plain numbers a factor of 20.9.

You will notice that this factor is very close to that calculated by @Aquaman for a 4 ohm load. This is because the output voltage hardly drops into 4 ohms compared to 8 ohms. But here is the essential part: If you limit the input voltage to 0.5 Vrms then the output voltage is limited to 20.9 * 0.5 Vrms = 10.45 Vrms (which is exactly the same as 14.78 Vpeak).

Power = voltage² / impedance
=>
Power = (10.45 V)² / 8 ohms = 13.65 W

13.65 W is the absolute maximum power you can get from this amp if the output voltage of the WiiM Ultra is limited to 0.5 Vrms. There is absolutely no headroom. No higher peak wattage. No nothing. There is simply no way to get more than 13.65 W out of this amp into an 8 ohm load with the Ultra set to 500 mVrms. Period.

If the true frequency dependent impedance of your 8 ohm speakers dips down into 4 ohms at any given frequency, then the maximum output power at this frequency is roughly 22 W.

2 Vrms can get dangerously loud with a baby in the house. 1 Vrms is at least a little bit safer I quess. and you think this will be beneficial compared to the 0.5 Vrms setting?

The only problem is that I dont know which one of you is right cause this is waaay above my head.

 

[Mr Ee]

Beneficial...
Choose whichever gives you the volume control granularity you want combined with the max loudness you want.
You can also use the wiim volume limit thingy.
Anything else is just scientific babble

 

[Aquaman]

Thank you @harkpabst for this explanation.
I was indeed of the conception that peak voltage was related to peak output wattage. So I will have to educate myself further in this direction and will stand corrected for moment.

@Fralle
harkpabst is probably right and I was wrong, or at least not 100% correct. But that must be of no concern for you. The practical implication for you is zero.

 

[dominikz]

Choose whichever gives you the volume control granularity you want combined with the max loudness you want.
You can also use the wiim volume limit thingy.

I second this advice!
There's no one 'correct' way to do it, so I'd advise the same as @Mr Ee - set a value that gives you good control of the volume level, without being too loud when volume is set close to 100%.

 

[harkpabst]

@Fralle, zero implications and scientific babble aside, whatever gives you the volume levels you want is good enough.

To me it looked as if you haven't bought this amolifier, yet. If so,.it makes sense to just pick the right amp for you in the first place. As I said it before, why spend money on a 150 W/8 Ω amp if all you need is 15 W?

They also make the cheaper MPA-S125NC RCA. It might probably even have lower THD+N in the range youigoing to use it in.If you have to pick between one of them it makes sense to look at the theory behind all this for a second.

 

[canard]

I second this advice!
There's no one 'correct' way to do it, so I'd advise the same as @Mr Ee - set a value that gives you good control of the volume level, without being too loud when volume is set close to 100%.

But that's also related to the speakers' efficiency, the listening distance, etc., and the precautions to take depending on their power handling...don't forget that in the equation...

and the sound levels you'll be using on a daily basis.

;-))

 

[canard]

PS

"Remind me of the effectif DR of the essential part of what you're listening to?"

with a little objectivity and honesty
;-)

 

[dominikz]

But that's also related to the speakers' efficiency, the listening distance, etc., and the precautions to take depending on their power handling...don't forget that in the equation...

and the sound levels you'll be using on a daily basis.

;-))

Assuming the OP already has the amp and can experiment with it, all of that is taken implicitly into the equation of "which value gives me the loudness I want?"

On the other hand, if @Fralle didn't yet buy the amplifier, then it might make sense to look into it a bit deeper. In that case perhaps this post can give a useful overview on how to calculate power requirements for individual needs.

 

[canard]

It's always interesting to examine real/factual needs, and a wonderful process to discover them... and not imagined ones.
;-)

The 700ch 6L v8 American car, on a straight 200km road at 110km/h or ...the same on the roads of Corsica?

"The assurance of a good margin...300w/8ohms..more is better!!"

""Muscle car""?
;-)

 

[dominikz]

To be completely honest I am not sure my ears are good enough to tell the difference. And after the time it takes to switch between the settings and the match the volume it is almost impossible to say for sure which settings sounds the best.

I am more curious about the science behind all of this since I know that I have read about the importance of gain settings before.

OK, perhaps this approach will be more intuitive:

Looking at the datasheet, we know that the MPA-S250NC reaches maximum power with 1.66 Vrms input - with this input voltage the amp will play the loudest it can (without going into clipping).

So if you set WiiM output to 2Vrms you will be able to push the amp to its rated maximum power, but you will also be able to push it a bit over that (and into clipping) if you set the volume too high.
On the other hand, you set WiiM output to 1Vrms (or lower) then the amp can't be driven to maximum power.

Let's try to see what exactly this means.

Since amplifier power doesn't relate to sound pressure level (SPL - i.e. what we actually hear) in a linear way, it can be difficult to understand intuitively what 'loudness' to expect for each power value. This is arguably even less intuitive when looking at input voltage.

So let me try to simplify by illustrating the difference in loudness (in dB SPL) you can expect by choosing different WiiM output voltage levels:

• 2 Vrms => +2 dB SPL compared to 1.66 Vrms input
  • I.e. with 2 Vrms output level you could theoretically push the amp 2dB into clipping.
  • Maximum power of MPA-S250NC would be reached with WiiM volume between 90%-95% (see the "output volume curve" section in this post), above that the amp will start to clip.
• 1 Vrms => -4 dB SPL compared to 1.66 Vrms input
  • With 1 Vrms output voltage level and output at 100% you lose 4dB compared to maximum power.
• 0.5 Vrms => -10 dB SPL compared to 1.66 Vrms input
  • With 0.5 Vrms output voltage level and output at 100% you lose 10dB compared to maximum power.
  • This is approximately half as loud as the level you'd get at maximum amplifier power.

Note how halving the input voltage reduces the SPL by 6dB.

As a rough rule of thumb:
-3dB SPL is considered a small decrease in perceived level, while -10dB is perceived to be about half as loud.
At the same time -3dB SPL requires 1/2 of the original power, while -10dB SPL requires only 1/10 of the original power.

This should hopefully illustrate that any of WiiM output levels can be fine, it just depends on your playback level requirements, and whether or not you want to limit it.

Hope you'll find this helpful!

 

[Mr Ee]

Hope you'll find this helpful!

I did.
A little bit of scientific babble can go a long way
I'm pretty sure you realised I was joking before - much appreciated.