I have a pair of sennhieser momentums, and i was just wondering if listening at 80% with lots of different types of music could blow them out
I might listen to them for upwards of 3 hours with music that varies from low bass to high bass
the actual power output of 80% volume level can vary quite hugely across devices....
generally you're more at risk of causing permanent hearing damage before damaging headphones like that. as long as you can listen comfortably you should be fine.
You should be more concerned about hearing damage than headphones damage. Hearing damage is usually permanent.
Long listening periods on loud volumes using headphones is not at all recommended.
Some headphones create more distortion as you play louder. Which can be a good thing since you will naturally turn down the volume. But on well designed headphones like sennhieser you will not have much distortion and hence you are at higher risk of playing at ear bleeding levels.
How loud a particular headphones will play depends on,
the headphones and
the source to some extent.
On some devices 70% volume would be as loud as 100% on other devices when using a particular headphone.