I just picked up a alpine head unit and a pdx -f4 4 channel amp. I am going to power 4 6.5" speakers with this set up. Then I remembered that I have 2 bose 6" subwoofers sitting in my basement collecting dust. Can I connect these 2 directly to the head unit and power them off the internal amplifier.

I would think the head unit will not have enough power to power the subs. A better way may be to connect the subs to the amp and the 6.5 to the head unit.

you definately cannot do that, you must purchase an amplifier for the subs

you will be very light on output power to drive a pair of 6" woofers ( I don't think you can call a 6" speaker a "sub woofer" )

Bose can, its all in the marketing !!!

Sometimes they do.....I know my 91 vette has Bose speakers and each one has it's own amp built in. Makes for a pain to change.

If it were me I would leave the Bose speakers collecting dust in your basement. They are not very good speakers, and are not designed to work in an open air environment. Usually these speakers are in a plastic bandpass box which gives it the boom of a slightly bigger speaker but only at a certain frequency. However, the sound quality is not there. I have 2 10" boston acoustic G5's in my boat and I'm quite happy with it but there also getting fed 600 watts RMS. Save up some money and do it right.

Bose does some amazing things with enclosures and small "subs", however a 6" sub is not going to get you far in a boat, even with a band pass set up like bose uses for enclosures. These "subs" are made for a small car, or the corner of a living room using well thought out enclosures.

My suggestion- quality audio components are relatively inexpensive today, get your set a quality pair of 10-12" subs and a good sub amp with a low pass crossover. When installing the subs under a seat you still want to build an enclosure under the seat, for sealed or ported subs.

Sealed sub boxes give tighter bass but require more power.

Ported subs make looser booming bass but are more efficient

I have seen (and fixed) a lot of subs that are just installed in the kick wall under the seat without an enclosure, the bass you give up with a setup like this is amazing, not to mention the speakers will last longer with the right enclosure. It is very simple to build a good box under the seat, build the sides and the top and seal the corners, a top is a must!

Subs make the best bass when the air from the front of the speaker is seperated from the air on the back of the speaker, or the air from one side is allowed out with a tuned port.

Many people think "free air" subs make bass just sitting there, not the case. The air from the front must be sealed from the back for max performance, free air just means the back "enclosure" can be any size.

[QUOTE=endeavour32;3259457]If it were me I would leave the Bose speakers collecting dust in your basement. QUOTE]

I agree!! You can get a decent pair of kicker, alpine, etc subs that will blow away anything you can do with the bose ones. I installed 10" alpine marine free air subs under my back seat this summer. They sound good, even with a somewhat small amp driving them. You can probably get a pair of them, with a decent amp for under 250 bucks.

if your Alpine head unit is the marine radio, id should be a digital. Alpine makes very nice marine ampa. I have personaly installed 4 amps in a customer's boat, dialed it all in and it sounded so good that you had to get out of the boat is so loud. each sub had its own amp. Cockpit speakers had their own amp and forward cabin had its own amp. also used alpines marine speakers as well and great sounds.