[Anechoic]

I might be wrong on this, but I recall a hearing specialist advising me not to use earbuds at all, or at least limit the use to max 1 hour at a time.

The issue isn't necessarily about all "earbuds," the issue is that many earbuds (including the ones included with Apple iOS products) don't seal the ear canal very well, so a listener is exposed to outside sounds in addition to sounds from the player. Since the outside sounds have a tendency to mask the sounds coming from the earbuds, the listener will often turn up the volume to better hear the audio material and therefore be exposed to SPL's that can cause hearing damage over long exposure times.

The advice to use something like the Superlux HD 681 is that circumaural headphones offer some (not a lot, but some) shielding from outside noise, so a user won't be tempted to increase the volume level as much. Active noise canceling headsets and in-ear-monitors (like Etymotics-brand) provide better sound isolation so that users can keep the volume at more moderate levels.

[pierrec]

>the issue is that many earbuds don't seal the ear canal very well

For those wondering which earbuds do provide decent isolation, there are, as you stated, the pretty expensive "in-ear-monitors", but you can also go for cheaper earbuds based on isolating memory foam like the JVC marshmallows, which are pretty cheap and provide decent isolation.

[im3w1l]

For really high noise environments, like airplanes, I like using 30db dampening earplugs and then circumaural heaphones over them.

[bashinator]

Exactly. With my Etymotics in-canal buds, I can set the volume on my music player to about 25-30%. With the stock buds or even non-isolating over-the-ear headphones, the same subjective loudness requires about 60-75% on the volume control.

[markrages]

This is not a good measure, because different earphones have different efficiencies.

And the type of earphone changes the efficiency as well: The sound from the Etymotics all goes to your ear, but the others waste some sound out of your ear.