Car Stereos: Car Audio Install, dual voice coil, internal amplifier

Question
Hi - I have an older car - Porsche 914 - and am experienced in wiring and installs.  My questions is related to installing a subwoofer.  I have an Alpine 9886, (2) 6 1/2 in speakers, and a 10 in subwoofer.  I do not have an amp of any kind (for now).  Which speaker leads do I connect the subwoofer to?  Or, do I need a separate amp to run it?  Obviously will connect the 2 speakers to the Front R/L connectors, but am not sure how to connect the subwoofer.  Most diagrams are for cars with 4 speakers, and/or an amp set up.  Looking for some help.  Thanks!

Answer
Hi Edmund,

There are a few head units that are specifically designed to allow you to connect a subwoofer to the rear speaker outputs, in place of rear speakers; but this is uncommon.  Your deck isn't one of these, so I wouldn't try to use a sub with the speaker outputs; you'll need to get an amp.  Even if your head unit did allow you to use the rear speaker outputs for a sub, I'd recommend getting an amplifier anyway.  A subwoofer really needs more power than a head unit's internal amplifier can provide.

If your subwoofer is a 4-ohm, single voice coil design, then I'd suggest looking for a 2-channel amplifier that can be bridged into a mono output; this is usually the least expensive option, and works very well with a single sub.  If it's a dual voice coil sub, you'll probably need to look for a mono amplifier that's stable with 2-ohm loads.  Either way, the amplifier will get its audio signal from the head unit's RCA pre-amp outputs.  You won't need to have the rear speaker outputs connected to anything at all.

Hope this helps!

Brian