Understanding output power?
Jan 8, 2020 at 11:17 PM Thread Starter

#### Mhog55

I'm a bit confused about differences between power output - mW vs. Vrms. For example, I'm looking at the Shanling M5s, and it lists the balanced power output at 300 mW. My current dap lists the balanced power output at 3.4 Vrms. Which is greater in this scenario? Is there some sort of way to convert these measurements?

Jan 9, 2020 at 12:49 AM
I'm a bit confused about differences between power output - mW vs. Vrms. For example, I'm looking at the Shanling M5s, and it lists the balanced power output at 300 mW. My current dap lists the balanced power output at 3.4 Vrms. Which is greater in this scenario? Is there some sort of way to convert these measurements?

Watts = Amps x Voltage

No way to compare those two, since you'll have...

0.300watts = Amps x Voltage

Watts = Amps x 3.4volts

It's kind of like talking about a Corvette V8's torque vs a Ferrari V12's horsepower.

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Jan 9, 2020 at 12:58 AM
So how can I determine which offers greater power? What's larger, 3.4 vrms or 300 mW? Should I be looking for amps and voltage in the literature?

Jan 9, 2020 at 1:08 AM
So how can I determine which offers greater power? What's larger, 3.4 vrms or 300 mW? Should I be looking for amps and voltage in the literature?

I just showed you the equation.

You can't calculate and make a comparison because the equations are too incomplete.

It's like arguing about which car will be faster and all I'm working with is how much torque a Corvette V8 has vs how much horsepower a Ferrari V12 has. I need to know whether the torque rating is peak which can occur at lower rpm or what the hell the redline is and what the torque is somewhere near that redline, how high that redline is, what kind of corners am I going to expect, what the torque band is like on the Ferrari even if it's lower because it might be wider and more consistent all the way to what I can only presume is higher rpm, and in the end all I can tell you is what car I'm more likely to prefer to drive on a given circuit or how I'd tweak the gearing for a particular circuit, but in the end it's still down to who's driving what against who driving what.

Jan 9, 2020 at 1:11 AM
Seems like it shouldn't be so complicated, but I understand what you're saying. I'll look into it some more - thx

Jan 9, 2020 at 1:32 AM
Seems like it shouldn't be so complicated, but I understand what you're saying. I'll look into it some more - thx

It shouldn't be, which is why either manufacturers should just publish all specs or at least use watts.

Jan 9, 2020 at 2:13 AM
It shouldn't be, which is why either manufacturers should just publish all specs or at least use watts.

@ProtegeManiac,

This bothers me too, manufacturer specs should be consistent but that's like saying some shouldn't act a certain way about certain things but those people do just because.

Hope you have a great day !

Jan 9, 2020 at 11:31 PM
I haven't done algebra in ages, but I'm pretty sure you can calculate this.

Watts = Power = P
Amperes = Current = I
Volts = Voltage = V
Ohms = Resistance = R

P = V*I
I = V/R
So, P = V*(V/R) = V^2/R

We know that your Shanling M5s can do 300 mW into 32 Ohms. So we have power and impedance, so we just have to solve for voltage.

0.3 = V^2/32
0.3*32 = V^2
9.6 = V^2
V = √9.6
V = 3.09

I'm pretty certain this is correct, but if somebody can check my math, that'd be great.

Jan 9, 2020 at 11:40 PM
I was going to edit my last post, but editing on my phone is a @_&\$\$! So here's another post...

You can also figure out the power of your DAP into 32 Ohms in the same way.

P = 3.4^2/32
P = 361.25mW

Jan 10, 2020 at 10:15 AM
I'm a bit confused about differences between power output - mW vs. Vrms. For example, I'm looking at the Shanling M5s, and it lists the balanced power output at 300 mW. My current dap lists the balanced power output at 3.4 Vrms. Which is greater in this scenario? Is there some sort of way to convert these measurements?
As @megabigeye explained, the relation between max power and max voltage comes from the load(the impedance of the headphone/IEM you'll plug into it). Yes P=V*I but nobody really bothers with current values in audio gear specs, so all practical situations will rely on the impedance of the headphone: P=V²/R with R as that headphone's impedance.

Just remember that any given spec is only relevant to the impedance of the load it was measured with. Power into 16ohm is not power into 300ohm!!!!!!!!!!!! while voltage might be almost identical. As a rule of thumb you should not try to extrapolate when things aren't close to the impedance you need. Instead, if you're in need of more than average power/voltage for portable gears because you plan on using a low sensi non portable headphone for example, just assume you don't know enough based on incomplete or inadequate specs, and go get a device from a manufacturer that's less shady.

Jan 10, 2020 at 10:20 AM
As @megabigeye explained, the relation between max power and max voltage comes from the load(the impedance of the headphone/IEM you'll plug into it). Yes P=V*I but nobody really bothers with current values in audio gear specs, so all practical situations will rely on the impedance of the headphone: P=V²/R with R as that headphone's impedance.

Just remember that any given spec is only relevant to the impedance of the load it was measured with. Power into 16ohm is not power into 300ohm!!!!!!!!!!!! while voltage might be almost identical. As a rule of thumb you should not try to extrapolate when things aren't close to the impedance you need. Instead, if you're in need of more than average power/voltage for portable gears because you plan on using a low sensi non portable headphone for example, just assume you don't know enough based on incomplete or inadequate specs, and go get a device from a manufacturer that's less shady.
Couldn't you calculate the power for your specific load once you know the voltage? Since voltage should be constant?

Jan 10, 2020 at 10:49 AM
Couldn't you calculate the power for your specific load once you know the voltage? Since voltage should be constant?
Often yes, and on occasion no. Depends on the amp's design. So as with anything involving a non null possibility of being wrong, my personal approach is usually to dismiss the entire thing and go find more complete information somewhere else. As you know, I'm quite the skeptical chicken in this hobby.
But sure, if I had no alternative and no other mean of information, I'd do with the voltage even unloaded. I might then add like +6dB to how loud I want my headphone to go just in case that voltage fluctuates a bunch into a different load. But TBH I don't like to play guessing games with objective values. Any manufacturer measured the specs we need probably hundreds of times while designing the product and testing it. Them failing to clearly provide what any amplifier should have in their specs(any DAP is also an amplifier), is something I decide to interpret as incompetence or having something to hide. I'm biased like that now

Jan 10, 2020 at 11:12 AM
I'm a bit confused about differences between power output - mW vs. Vrms. For example, I'm looking at the Shanling M5s, and it lists the balanced power output at 300 mW. My current dap lists the balanced power output at 3.4 Vrms. Which is greater in this scenario? Is there some sort of way to convert these measurements?

It's been over a decade since I was in Electrical Engineering school (and failed at it by the way) so my electrical knowledge might be rusty. You'll forgive me if I give some information that is not entirely accurate, I'm sure more knowledgeable people can chime in and set things straight.

First of all mW, is a unit of power, meaning amount of work done in a given time, it's a unit that works both on electrical power and...physical power. The thing with electrical power, it varies according with the impedance of the headphone, in turn headphone impedance varies with the frequency. Some headphones have a fairly linear impedance, others have peaks at certain frequencies so the amplifier has to give more power to get the same sound pressure at other frequencies, or you lose some at that frequency. Which is why when looking at power output of headphone amps, always look for the Impedance at which that power is being given. I'll echo what another guy said here: 300 mW at 16 Ohms, is not that impressive. 300 mW at 600 Ohms, is very freaking impressive.

Second, Vrms. Is "Root Mean Square" Voltage, it is not a unit of power but a unit that measures how much work could be done, or how much work needs to be done to "move" against it. The RMS means that it's the comparable AC voltage generator (swinging up and down) would give, it if were DC (flat line). Vrms alone will not tell you how much power the amplifier is going to give. You need to know the load connected to it.

For most of us the power an average DAP has is more than adequate for a vast array of IEM and most headphones meant for mobile use. If you want to compare power of the two, look at the posts by megabigeye. Those two equations should be more than enough.

I'll add as well, any DAP manufacturer worth its salt should be giving more complete specifications and the conditions they apply to, if they are trying to appeal to the hi-fi crowd. Us audiophiles have built in frequency response graph generators. The most seasoned of us can determine the Total Harmonic Distortion, the Dynamic range up -123 dB and figure out at which frequency the distortion exceeds 0.5 dB, just by listening a single tone coming from an old earbub connected to what we are evaluating, some can even determine the Vrms by wetting their finger with saliva and touching the headphone jack, seriously. Any manufacturer must state all their proper specs at a moment's notice, less they'd be proven wrong by the next audiophile that walks into their store.

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Jan 11, 2020 at 3:51 AM
Thanks folks. I think I get it... For the most part. It was 32 mw into a 32 ohm load, but still not quite what I'm after. I like to use my 660s around the house, in the garage, etc. The Opus#1s drives it plenty loud, but I don't feel I'm getting the entire dynamic range of what this headphone is capable of with it. I'd like a dap that can push it closer to its full potential. Might get the Fiio M11.

Jul 23, 2021 at 10:02 PM
With that someone can show me Output Mw at 32 Ohms. It's Kann Alpha. Thanks.

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