Equalizers - Use them, or no?

Interesting question. The truth is, producers and engineers try to make tracks that sound consistent across all sound systems. However, not all sound systems are equal, and the acoustical differences are even more so for the rooms they are in. If you were to put a sound system in to a small box-room, the lower frequencies would resonate to cause standing waves of bass. This is where you, as a listener, may want to turn the bass down slightly on a system, to literally "equalise" the sound. It's also worth noting that at the stage of listening to music (rather than recording etc), equalisation should only ever be subtractive (turning frequencies down) rather than additive (turning frequencies up). This is due to fact that boosting any frequency will always create more resonances elsewhere. To my understanding, most basic equalisers are only built in to sound systems through traditional force of habit from a time where both recordings and sound systems were unpredictable. As for the other things like reverb etc, well I have no idea why anyone would want these as a feature. So, in answer to your question, I would personally leave the equaliser flat, unless you feel there is too much of a frequency in your room. Otherwise, use whichever setting you enjoy. :)

These equaliser presets (Concert Hall, Echo, Rock, Jazz, etc…) are a joke to any audio professional. They really are just a silly gimmick and I'd be happy to never see them anywhere again. Actually using the equaliser on a music player to correct for the properties of your sound system and room is a valid approach but then you'd just leave it set that way for all listening and only change it when you changed the speakers or their position in the room. This use of the equaliser isn't a joke because you actually listen to the change and choose it based on how it sounds (instead of choosing by the name as you do with those presets). Ideally you have a reasonably neutral sounding system and room and you just don't do anything with the equaliser at all. That's the closest to hearing the work as intended by the artist / producer. It definitely isn't generally the case that artists intend for their music to be equalised by the listener. That's why they pay a mastering engineer to optimise the sound across the wide range of listening systems out there by making it have a neutral balance across the frequency range.

Every speaker or headphone has different response to frequencies. This essentially means there is an optimum EQ for each sound system. If you can set your speaker up to this perfect EQ, trust me, you'll feel and love the difference. Check this out: http://timeandtimeless.wordpress.com/2014/08/11/how-to-equalize-your-music-player-for-that-perfect-sound/

technically no. By the time the song gets to the consumer people have painstakingly equalized the hell out of a track to get it to sound the best they can across as many playback devices as possible. So you basically just poop all over their work when you adjust the EQ. That EQ should only be used for a specific reason, like you know your system is to bass-y so you turn your bass down, but you do that across the board for anything you play. Thats the kind of adjustments you should make. But you should not change anything from song to song, just overall settings that help improve your sound system.