Originally Posted by Eisenhower
I keep hearing this over and over again. It is usually advice given to a neophyte who just bought some sort of full sized headphone, and is less than pleased with their sound quality.
Of course, the issue is with voltage swing not being large enough to make headphones play sufficiently loud. It is actually low impedance headphones that drain all of your source's current, causing bad response.
It is unfortunately very hard to kill such myths, as many people keep repeating them without actually knowing what they are talking about, but the fact that it is so widely spread makes the myth look like generally accepted "science" that is backed by authority. In my opinion, these are the main sources of this belief:
- many devices have excess gain and clip at high volume, therefore the headphones could indeed end up being "loud enough" but sounding bad
- the allegedly loud enough volume might not be loud enough after all; humans are not very good at judging absolute loudness, especially when relying on long term auditory memory, and level matching issues are a major source of alleged differences between the sound of amplifiers
- it is not uncommon for devices with high maximum output voltage, such as tube amplifiers and the headphone jacks of speaker amplifiers, to have very high output impedance as well; this will typically boost the bass on full size dynamic headphones to some extent, giving the subjective impression that a (technically better) source with low output impedance is "underpowered"
- as usual, expectation bias plays an important role; after reading comments from many people that headphone X will sound bad from amplifier Y, it is hard not to expect that to be the case