bass problem in a sailboat

a small Bazooka cylinder-shaped active car-type sub might work out for you; they don't cost a whole lot. One model isolates & sums two-channel line-level inputs driving a single cone via an integral amp. I think their larger model handles the channels separately. Simply tee-connect the left & the right channels respectively at line level in either case.

I had Poly Planar head unit and speakers in my boat and in my hot tub. All factory installed.....and all way below average in every way. Overpriced as well. Not 45 watts constant power.....peak only. I would try new speakers first. Bigger, if possible. Look for something with a high sensitivity rating. Also pay attention to the specs as to how low they will go. If you do not get the bass you are looking for, at least you will have improved the sound dramatically. A passive bazooka tube may be the answer if your head unit will power it. Crutchfield will let you return it if it does not work out. The amplified version would shiver your timbers, but you have ruled that out.
By the way, bass shakers are made to go under your seat and vibrate to the music. They are not speakers at all.
Another idea (and probably the best)would be an inexpensive head unit with bass management. Crutchfield has lots of those. Look for one with lots of internal power. I would look at Crutchfield's comparison chart and focus on the watts per channel. I like the Alpines, but I think you will find Kenwood to be the watts winner. Good luck.

Baffled Bob,

Thanks! Your response is the most helpful so far! Right now I'm trying this: a dual voice coil subwoofer (hate that term) operated by two of the head unit's four channels. The other two channels will operate two of the original four PolyPlanar box speakers. We'll see. I intend to keep playing with this until I get it "right". I'm learning a lot!

Regards,
Troy

Linkster,

In fact, I bought my Cape Dory 36 from Robinhood Marine. I'm in the midst of a major refit now, doing the work in my hangar. When I'm finished, it will look like the R36 brochure boat!

Regards,
Troy

Folks,

If anyone here is still interested in my sailboat stereo project, here's the latest:
I bought the PolyPlanar model 250 amplified subwoofer (which includes a dual voice coil subwoofer) and added it to the system. When I adjusted the gain on the bass amplifier, it ended up very near the lowest level. The overall effect was a substantial improvement. The lowest notes were much better, but the upper bass still seemed boomy. Out of curiosity, I removed the bass amplifier from the system and connected the DVC subwoofer directly to the two front channels in place of the two bookshelf speakers that had been there. To my surprise, the subwoofer was actually LOUDER that the level I had set with the bass amplifier. Of course, without the bass amplifier there was no crossover for the woofer, so I had some out-of-place treble on the woofer. Another oddity: the sound from the subwoofer was not perceptively less when I added the two bookshelf speakers back to the front channels along with the subwoofer. However, to my ears the bass actually sounded better than the system sounded with the bass amplifier. Lesson learned: I think all I really need to do is add a very good DVC subwoofer to the set of four book shelf speakers. I've ordered an Infinity 12.1 dual voice coil subwoofer from Crutchfield, along with three different sets of low pass filters: 50hz, 70hz, and 100hz. I plan to try all three to see which works best.

Interestingly, almost everyone I've talked to about this problem has misunderstood. I'm after something subtle here, not a floating boom-box. We have an audiophile system at home, and I'm accustomed to hearing all the notes on my CDs. All I want to do is improve the system enough to hear everything clearly.

Regards,
Troy Scott