When i puschased my octy there was a sony aftermarket headunit it has very little bass, there is a sub out. I was wondering if there is a compact sub to fit under say the passenger seat?

First thing I would do is check the wiring to the speakers, if they are aftermarket its possible that one side has been connected out of phase. If wired out of phase, then the bass is effectively canceled out by the incorrectly wired speaker.

Check by moving the fader all the way left/right. If there is more bass at the full left/right position one speaker is wired wrong.

cheers, I'll see if this is the case and let you know.

If it's a mk1 octy don't expect any tbh, imo the speakers are pooh

Has the headunit got a cross-over activated on it perhaps?

OTOH IMHO, the Octy 2 has too much bass. (With the Stream MP3.)

A member (Decron) is selling this

http://briskoda.net/items-sale/alpine-underseat-subwoofer-swd-1600-a/122878/

I was never impressed with Sony's head unit bass out put. even with their xplode range...was naff!

I found Panasonic really good, and my Blaupunkt even better.