Thank you for the response!
Everything is stock and all works, I have the stock head unit BUT I should've have mentioned sorry!! I use a bluetooth transmitter to connect my phone to the stock head unit (this exact one: https://www.amazon.co.uk/gp/product/B07Q82LRDK/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1 )
The stock radio (i.e. BBC radio 1) plays mono, bluetooth transmitter (phone to transmitter to car stereo) plays mono. I work with audio as a side business so i know about speaker setups, mixing & mastering etc but not for cars.
The sound from every speaker is the same, exactly like if you unplugged your earphones (i.e. stereo sound) and listened to music through your single phone speaker (i.e. monophonic sound). For an 'audio engineer' like myself this really kills the fun of the music and is very noticable - But maybe every E12 corolla does this?
All im really asking is: will changing the head unit resolve this and give 'surround' stereo sound? (i.e. L speakers play L channel, R speakers play R channel) Any head unit, even the older single din aftermarket ones.
Each speaker can fade & balance i.e if i wanted only front L speaker to play: it does. Dont think the speakers/faders themselves are damaged but its confusing why if thats the case: it plays mono rather than using stereo.
I would be extremely grateful if you could point me in the right direction regarding this, thank you.