Viewing a single comment thread. View all comments

WoodenSporkAudio t1_iy1vzv1 wrote

Reply to comment by marvinNoMerge in What does it mean to properly “power” a headphone? by soldkeyboard57

Listening at 30dB huh? Ok. Well, have a good one then. Your math is way way way off.

Didn’t condescend to you, nor did I give any “condensation.”

Take it easy man.

2

marvinNoMerge t1_iy1w616 wrote

Correct it please. I got the 30db from your post, you said you often listen at those levels. If you listen higher, it uses much more power and we’re back to being far away from audibility of THD+N.

1

WoodenSporkAudio t1_iy29ujs wrote

-30dB meaning minus 30dB, not 30dB.

I just edited in the SPL marker when I realized you misread the factors and thought I meant listening at 1uW is 30dB- it’s ~68dB fwiw. 98dB/mW minus 30dB (a power factor of -1000x = 1uW)

With a stepped attenuator and signal meters on a pro unit, it’s easy to figure out with math that I am listening at the range I described, around 1-16uW and it is totally clear with HD650. Not everyone listens this low, but many do. When it’s even later I listen even lower. Again, Tons of people report topping out at around 70dB on many a listening session.

3

marvinNoMerge t1_iy2bwvg wrote

Aha I did misunderstand. Going from the spec of 100db at 1mW, it would be 52db at 15microwatts. I still think that’s acceptable, maybe you don’t. Certainly on the threshold of audibility and at low spl.

1

WoodenSporkAudio t1_iy2cuam wrote

1 microwatt is 1/1000 of a milliwatt. So spec of 100dB/mW divided by a power factor of -30dB or minus 10^3 is 70dB/uW not 52dB at 15 microwatts, which would be around 82dB SPL for that load.. give or take.

Can I help you with the fundamentals of the decibel (in relation to power output) which is a logarithmic scale? -3dB is half power, -6dB is 1/4 power, -10dB is 1/10 power. And vice versa for positive factors. 2x, 4x and 10x.

-6dB is a halving of voltage

-12dB is quartering voltage

So you can take any efficiency at dB/mW and figure out the equivalent at a microwatt by subtracting 30 decibels. 10 microwatts is subtracting 20dB from the dB/mW rating, etc.

Be mindful of dB/Volt ratings

5

marvinNoMerge t1_iy2ghgd wrote

https://physics.stackexchange.com/questions/366774/twice-the-audio-source-3-6-or-10-db-spl

Not once did I mention mV. I haven’t confused them. Double the spl is 6db additional. You might be confused about perceived volume vs power.

1

WoodenSporkAudio t1_iy2hbht wrote

I didn’t say you did. I said be mindful of headphones rated in dB/V since it is different than dB/mW - IE - HD650 ~98dB/mW or 103dB/V

You might be confused about the output power levels we are discussing (in relation to the amp’s distortion and noise at these levels) and how the decibel scale reflects power output factors of amps and therefore SPL… factoring for certain efficiencies at certain nominal impedances and the associated decibel levels they produce.

You’re tripping over your shoelaces correcting me, when my math is spot on.

3

marvinNoMerge t1_iy2lklo wrote

Edit: I am wrong! See below

here’s a calculator, let’s try. https://reference-audio-analyzer.pro/en/splfull.php#gsc.tab=0

Enter 100db/mW sensitivity, 300ohm, and 0.0001 mW load on amp gives 60db. 66db at 4microwatt, 72db at 16microwatt. By 70db, the THD+N of the apple dongle is audible transparent. If you’re listening less than that and can pick up noise over background sounds on your open back hd650s, then you can surely justify spending more than $9 on an amp.

Remember we’re talking about THD+N of 0.05% which is 66db below the fundamental measured. You’re not gonna hear that at 70db signal with open back headphones.

It’s a ~6db change for double output power (as I hope you found by using the calculator!) 10db is a doubling of perceived volume. Please read the link, I think it would bridge this gap. Instead, you assumed that I don’t understand logs lol. This won’t go much further, but I do encourage you to at least read it. Fun talking with you.

1

WoodenSporkAudio t1_iy2p4gz wrote

I’m done arguing with you. You are either trolling or stubbornly confused.

+6dB when referring to amps and power/voltage as we are here and have been, is a voltage factor of 2x, which is a power factor of 4x. Hard fact. Period. Written in stone. +10dB (when talking about power factors of amps) is a factor of 10x power. Again, hard fact. Period.

Arguing points on something we aren’t taking about which is SPL in the air you are bringing up, aside from what the peak output level will be from a given power level serves nothing except to prop up your broken talking points and bad math.

You typed in 0.0001 mW rather than 0.001 mW

0.0001mW or 0.1 uW is at a power factor of ten less than a microwatt, again, a microwatt of power into this load makes for 70dB SPL output in this example. 100nanowatts is 60dB.

So, if people want to believe you, they are free to. But you are mistaken about we have been discussing, well, trying to. While I’m sitting here listening to a mastering converter with amp at no more than 4 uW and down to about 0.25uW or 250 nanowatts on this song that is averaging about -12dBFS with HD650. All known variables.

You know how I know this? A Stepped attenuator with 1dB steps, a known power output and also professional dBFS meters with peak values and average values. Along with the actual math needed to figure all this out. Even ~approx calculation is possible for a one dB step with an easy to remember power factor.

So, when I say to people, yes, an Apple dongle can drive most headphones pretty well… I mean it. I use one too. With many headphones. But it doesn’t mean it sounds exactly the same as a mastering oriented pro voltage level DAC/amp, especially when listening rather low.

4uW for 74dB peaks isn’t that outlandish is it? It’s like 33dB ambient right now.

Have a good one man.

3

marvinNoMerge t1_iy2pqst wrote

Oh my goodness it’s true! I mistyped it! It is 70db and you were right my bad. Yeah I could imagine at low levels THD+N could be high then. I am sorry, I was thrown off by the tone rather than content

Legitimately, thank you for helping me better understand real world listening level distortion.

1