The web is a very visual environment,” he says, “and not enough people pay attention to sound and the very usefulness and power of sound – partly because we’re living in a house with other people, or we have headphones on or we don’t, so we turn off the sound, or we’re sitting in an office environment with other people and take the sound off.
The speaker is saying that in general, sound is not used much on the internet because of the many reasons people have for leaving their sound off.
They are listing the possible reasons people don't use sound on their computers normally, mixed with cases where they might be able to do so.
- They live in a house with other people who won't appreciate the noise
- We have headphones (so we can listen to sound)
- We don't have headphones on at the moment for whatever reason
- We're in an office-environment where the noise would be intrusive
It's a grammatical mess and it doesn't make sense when read literally.
As other answers suggest, this is a stream-of-consciousness sentence, the speaker has not taken the time to formulate his answer clearly and is producing words that sound roughly like what he's trying to express but don't quite work when you look closer.