What do headphone amplifiers do for efficient/sensitive headphones?

[iucoen]

I recently purchased purchased the Sivga Phoenix. I wanted a pair of efficient open-back to use with my phone without hauling an amp around. I power them with the Apple lightning to 3.5mm dongle and it gets plenty loud enough. And they sound great.

But when I read/watch reviews online, everyone out there says that you need to use an amp to get the most out of these headphones, specifically bass. Why is that? According to calculations, at 32 ohm, 103 dB/mW, the lightning adapter should provide more than enough power. Also, according to measurements, the Apple dongle is one of the best DACs.

So my question is, given enough power, what does a good headphone amp do that the Apple dongle doesn't?

 

[bobbooo]

So my question is, given enough power, what does a good headphone amp do that the Apple dongle doesn't?

Audibly? Nothing.

 

[solderdude]

I recently purchased purchased the Sivga Phoenix. I wanted a pair of efficient open-back to use with my phone without hauling an amp around. I power them with the Apple lightning to 3.5mm dongle and it gets plenty loud enough. And they sound great.

But when I read/watch reviews online, everyone out there says that you need to use an amp to get the most out of these headphones, specifically bass. Why is that? According to calculations, at 32 ohm, 103 dB/mW, the lightning adapter should provide more than enough power. Also, according to measurements, the Apple dongle is one of the best DACs.

So my question is, given enough power, what does a good headphone amp do that the Apple dongle doesn't?

103dB/mW in 32 Ohm is 117.95 dB/V SPL.
The dongle can provide 1V so can drive it to impressive levels.
So in this case it is rather pointless to use an amp.

That said.. not all dongles are created equal and not all headphones are created equal.
There can be situations/combinations where 1V isn't enough or when there is some (sub)bass roll-off due to components used.
In such cases it helps.

The problem is that when someone encounters these issues they generalize it to 'all other' circumstances too and hand out incorrect advice.
Afterall on the interwebs everyone is an expert.

 

[iucoen]

There can be situations/combinations where 1V isn't enough or when there is some (sub)bass roll-off due to components used.
In such cases it helps.

Is that something than can be measured? Which part of Amir's measurement graphs would show this effect?

 

[A Surfer]

This is of course cofounded even more when you consider that one major variable will always be the music the transducer is being tasked with reproducing so there is an almost infinite amount of variability. Infinite is perhaps a tad strong, but most certainly a very large degree of variability. Ultimately my understanding has always been that if all else is equal, the robustness of the power supply and delivery rail in any amplification circuitry matters most when it comes to determining the stability and fidelity of the amplifier design under variable loads.

 

[solderdude]

Is that something than can be measured? Which part of Amir's measurement graphs would show this effect?

Yes very measurable. That would mean FR would also have to be measured at 10 Ohm or so not just at 32 Ohm. Most headphone outputs get into to trouble with low impedances which are not that uncommon, certainly not in the IEM world.
I don't think Amir tests for this.
I would be too time consuming to test for all circumstances I reckon.

 

[iucoen]

Yes very measurable. That would mean FR would also have to be measured at 10 Ohm or so not just at 32 Ohm. Most headphone outputs get into to trouble with low impedances which are not that uncommon, certainly not in the IEM world.
I don't think Amir tests for this.
I would be too time consuming to test for all circumstances I reckon.

Is that because the the impedance drops to 10 ohm in the bass frequency? So for a set of efficient planars then it wouldn't matter at all?

 

[solderdude]

For planars it would be an even bigger issue as A: they rarely have boosted bass and B: they do not have a rising impedance at the lower frequencies.

 

[maverickronin]

So my question is, given enough power, what does a good headphone amp do that the Apple dongle doesn't?

With your particular headphones and the Apple dongle it may not make an audible difference.

Another important case to keep in mind is IEMs. Many are extremely efficient (120dB/mW+) but still benefit from a good amp - not for the power, but for the lower noise so there is no constant background hiss.

 

[pk500]

So my question is, given enough power, what does a good headphone amp do that the Apple dongle doesn't?

Possibly clean up the sound a bit and remove a lot more bills from your money clip.

 

[BillG]

So my question is, given enough power, what does a good headphone amp do that the Apple dongle doesn't?

Nothing. The Apple is already transparent and powerful enough for sensitive transducers. It can drive my IEMs, one of which is rated at 106dB/mW and the other at 113dB/mW, to such volume levels as to be quite uncomfortable.