Apparently this can be done wiith my new head unit...sony wx gt90 bt as i am only using the front speaker.....any experts...(non active sub btw)
Not sure if the head unit will provide enough power for a sub without an amp. Most head units give 50-55w output max.
If you were thinking of using the feeds from the rear speaker outputs to the amp you'll need a output converter from the speakers to the RCA inputs
The diagram with a 2 speaker set up shows one rear speaker wire going to a sub...the other speaker wire seems to be to an earth point......theres settings on the head unit too activate it as a sub.
With no amp inbetween?
Does it suggest what output that will give you?
I've just had a look at a set of tech specs for that unit and I think you are referring to the sub pre-out RCAs...
( m http://www.talkaudio.co.uk/index.php/in ... unit-r1489 (http://www.talkaudio.co.uk/index.php/index.html/_/reviews/source/sony-wx-gt90bt-bluetooth-2-din-head-unit-r1489) m )
These are non amplified outputs that supply a clean signal to an amplifier (or active sub) and won't be able to power the sub driver alone. Headunit internal amps just aren't powerful enough to move big sub drivers which is why they need external amplification.
I know it has the 2 sets of amp rca's and 1 set for a sub......but it does say 1 rear speaker can be used for a sub with no amp....direct sub they call it.....it also can enhance the rear speakers if fitted to sound like subs.
(http://i51.photobucket.com/albums/f368/MARKB68/IMG_00000201_zps72f055d0.png)(http://i51.photobucket.com/albums/f368/MARKB68/IMG_00000200_zps756b3dc8.png)
Ah ok...
It sounds like it'll work but I wonder how good it'll sound in the grand scheme of things. Although headunits often state things like '50W' per channel, the reality is that the amp hardware that you can fit in there isn't up to providing decent clean power (even if they could they'd overheat). When I had my old ICE setup in my Mini my old Helix amp was stated to be 4x50W but it was night and day difference in practice to my 50W Pioneer head unit output.
My presumption is it this setting effectively bridges the rear channels to give it a power boost to a single source. If you've got a sub handy it might be worth a test but, in my opinion, I wouldn't be laying out money to buy a sub specifically for this sort of setup.
Might give it a try just out of interest..lol,the head unit sounds pretty good but i like a bit of a kick.I have a Lanzer active underseat sub in the Rav,4 its very very good.
Looks like a really nice unit. I wouldn't be surprised if the bass amp arrangement is a bit weak though, as other have mentioned quoted peak power is a bit or a 'marketing thing'. The unit's amp should be able to drive normal tweeters and midrange well enough and it may help tweeters and midrange if you apply the HPF (high pass filter) to stop the bass coming through them as it wastes power and distorts when the volume is high.
Looking on the Sony website it looks like the bridged power could be 2 x 17W RMS as the specs say:
CEA2006 Standard
Power Output: 17 Watts RMS 4 at 4 Ohms < 1% THD+N
SN Ratio: 80 dBA (reference: 1 Watt into 4 Ohms)
Whereas looking at a low end 2 channel Alpine amp BBX-T600 (around £90), the 'marketing power' is 300W but the RMS would be 130W bridged for a bass speaker.
RMS Power Ratings
◾ Per Channel into 4ohms (≤1%THD+N): 2 x 50W
◾ Per Channel into 2ohms (≤1%THD+N): 2 x 70W
◾ Bridged into 4ohms (≤1%THD+N): 1 x 130W
Will be interesting to know what you think after trying it out but I suspect that even a small active/powered sub is likely to sound better.
sorry Op your on a hiding to nothing here. I've done this with my old pioneer HU for a laugh as it had the same functionality.
As the others have said to drive a real Sub (ie big heavy thing) with any kind of punch you're going to need a minimum of 50w RMS clean power. For that you will need a separate amp for sure.