Thanks again for the feedback. We measured the space today, and 2.5cu.ft won't be an issue as long as I invert the sub. I thought about mounting it straight in the floor of the boat, and trying to create an infinite baffle using the hull of the boat's empty space, but the 2.5 cu.ft works perfect, so no sense in cutting up the boat more than I need to. I was seriously considering an Aperiodic membrane, but since I have the room for the airspace, I'll attempt it on another install maybe. Not sure how much people know about the aperiodic membrane setup, but an old buddy of mine did it with 2 10's in a Supra, and it sounded 20 times better than I thought it would. Tricky to get right though.
Thanks for the specs TLS Guy.
A number of issues.
As has been pointed out you don't know that driver will survive a marine environment. I don't eve know if this is a fresh or salt water environment. Both are harsh. Salt water is very harsh.
The driver has significant cone weight, high BL and relatively high sensitivity. So that means it has a precision voice coil/pole gap that will be very small.
I have no idea how well the adhesive they used in the coil will isolate it from the environment. Even if it sprouts a little green copper oxide, the voice coil will lock up and you will have a ruined driver. The same goes for the metal used in the magnet pole piece. If it exhibits any corrosion in this environment you will have a ruined driver.
So you need to check with TC Sounds. They may not know the answer, as I suspect they never thought of this possibility. If they have not designed and or tested for this environment, then far more likely than not you will have a ruined driver in a short space of time. Even if the cone does not lock up, I can tell from the specs, that even a small amount of corrosion will cause gap rub and a loud buzz.
The next issue is using the hull as the enclosure. Likely you will get away with this, but fiberglass is an unpredictable as to what will cause fatigue failure and what won't. You will have to Eq this device or you won't have a sub at all. It is therefore very likely you will have to use the full rated 2000 watts, as this will be a very inefficient sub. These designs by their nature are pure brute force. 2000 watts is 2.7 HP. So you will have a 2.7 HP oscillating jack hammer against the hull. I can not tell you what effect this might have on the hull compared to the stress of hitting waves. The biggest difference is going to be the frequency of the impacts. In general the higher the frequency the more destructive the impact. This is the principle of the jack hammer.
As to the membrane loading, I think you are referring to the so called aperiodic vent. These was first muted by the brilliant gadfly Ted Jordan back in the fifties when he was chief engineer at Goodman's. He published an article with a ton of math about loading an axiom 10 in this way, but in his hands it never saw the light of day. At that time loudspeaker transfer functions were not understood and so his arguments are not valid. Small of Thiel/Small included it in his thorough review of loudspeaker loading and concluded it was an inferior form of loading.
Dynaco used it and especially Dynaudio. There is not consensus on what this really is. So I will give you my view.
Before amp power was plentiful and driver design improved equalizing a low Q driver in a sealed enclosure was not practical. The point is that low Q drivers with this loading have a high F3 and so drivers with higher Q were and still are used. This usually results in some bass ripple, especially if the enclosure is smaller then optimal.
To illustrate here is a speaker I designed and built around 1984. This is the frequency response.
I designed it for minimal ripple. As you can see there is a peak of about 5db at 80 to 90 Hz. This speakers in fact sound very good, and are now my surrounds. However the enclosures are a little larger than the Dynaudio ones that had the variovent.
Everyone agrees that a resistive vent lowers the peak of impedance, as you would expect as it has increased enclosure losses (QL). So this adds up to lowering Qtc. However f3 is raised and roll off is now 18 db, third order, rather than 12 db second order. I don't think this is a good trade in most circumstances I can think of. In my view my speakers sounded better than the Dynaudio speakers of the period using these drivers. However my crossover was significantly different to the Dynaudio one, so this would also have to be taken into consideration.
So in your case I would not think it would be a good idea, as you are using a low Q driver. I can not get consensus of how much F3 is raised but one DIYer showed F3 increased by an octave in his case. I suspect there is wide variation as there is not enough study as to how to model this, as opinions vary as to what is really going on in this alignment. Leap claims to be able to model it. The validity if this model is disputed. This form of loading has never been widely adopted. Hard data is sparse and most anecdotal and therefore unreliable.
You certainly do not want to lower Qtc in your case.
There is no data on how this set up would respond the Eq, but I would think poorly, and very likely result in driver damage. In any event it is clear that Eq would have to start at a higher frequency and be 18 db per octave. That pretty much rules it out as an option in your case.
Just one last issue. There is a typo in my last post, stating that reducing enclosure size lowers Q, but of course it increases it. The large increase in the peak of impedance in an enclosure too small of course limits the power the amp can deliver to the driver.
