Sub facing in, or out??

[NCSUmoomba]

Brian, I am just curious, did you guys try a down firing? Also for any of you guys, is there any way (I should say easy way) to get an idea of how far away from the object the sub is boundary loading into should be mounted from? Is it based on box volume? Speaker diameter? Woofer excusrion? Would the space for a port be similar?

I am considering moving my sub enclosure from underneath my helm so I can make room for a larger ballast sac under the bow seat. My two thoughts are making a custom seat base with the sub inside of it, or a bow filler cushion thing with the sub inside it. Either way downfiring will fit better, but I don't know how it will respond acoustically.

I love these discussions. It is great to have Brian, David, and Phil on this forum. You guys are awesome.

[EarmarkMarine]

BrianNCSU,
You will see home downfiring subs and ports that benefit from walls and corners. But give them a try on the patio and you might be surprised how much they labor. You will also see downfiring subs in automotive like the JL Audio Stealthbox for example. Before that Stealthbox design is finalized they have done exhaustive testing and listening in the actual vehicle for which it was designed. So if some aspect of the speaker and enclosure parameters change then this is compensated for in the design. Also, the vehicle is a very forgiving environment because it is an enclosed cabin with a second order per octave rise in the low frequencies. A woofer will couple very well in that rigid air mass. Now an open air environment of a boat is very different and unforgiving of any error or design that serves to choke the output. And, anytime you reduce the radiating surface area of a woofer you are initially doing the very opposite of what you need. Of course you are taking advantage of the sole as a reinforcing plane in a downfiring scenerio but if the sub is too close to that plane then you will change certain parameters and initially lose important gain. So our rule is this. Take half the diameter of the woofer. For example, if its a 12 then space it off by 6 inches and so on. Sometimes you are utilizing a downfiring scheme because you have a larger woofer in a very limited vertical space. In this case you may knowingly make that compromise...and we have many times when the situation dictates. Certainly never mix downfiring within an enclosed seating console or locker that must be venting to allow the bass radiation to freely flow from within that cavity. In this case you are choking the output twice. Again, we have done this when there was no better option. But we recognize the cost.
In general and when possible, we repeatedly do a sidefiring bass-reflex enclosure off the hull. We don't force a larger woofer and enclosure into that small space where there isn't ample room for the fluid-like bass radiation to flow. And we need adequate room for the woofer and vent to properly couple together without misalignment from the original design. A bass-reflex enclosure is a very self-dependent and contained circuit that is largely immune to the influence of the environment as long as you give it a little common and unobstructed space. All else in the way of boundaries, orientation and room dimensions are infuencing your perception but not the actual tuning. We have found this extra space around the woofer/port/enclosure is essential to good bass tonal construction. And I doubt there are many who have done as many marine subs and had the real world applicational experience over the last 12 or so years as us. There aren't many who understand acoustics as well. Having said that, there are those particualr boats that are the exception and you have to take the best option available. Its part of taking the best that a boat can give and choosing the leper with the most fingers.

David
Earmark Marine

[WaterBullDawg1980]

David, Phil and Brian;

Just reading through this thread again while I sip my morning coffee here in the office and I wanted to thank all of you for the support you provide on our forum. It's not everyday that an entire community can be educated by the experts with such open and honest dialogue.

This in particular is a fantastic read.

Well done!