Scooter Subwoofer: Effects of a putting a finished sub in another enclosure

[junkmail]

OK, so situation is I put a stereo system in my scooter, powered by a TDA1554Q chip amp. Two unbridged channels powering NXT exciters bonded to the scooter's body panels, and a bridged ~15 watts going to a sub. Not much, but i'm limited by what the scoot's electrical system can put out, and the goal of having a completely "invisible" system. With that in mind, the sub will be placed in the under-seat cargo area. I was in the middle of putting together a sub when I stumbled upon a computer subwoofer on the side of the road today. I tossed it in for giggles, and was surprised with how much output it put out. So much so that I might just keep it.

With my amp turned up the subwoofer sounds pretty bad (distortion from either the amp clipping or the ported sub unloading?). But I notice that when I close it up in the cargo area, the sound that I can hear is mellowed out and much more listenable.

For reference, the sub is from a Boston BA735 speaker system, essentionally this driver in a ~4L ported enclosure. The underseat cargo area is 20L (minus a few liters used by the amp) and is a big ABS plastic tub with an upholstered seat plopped on top. Looks like this:



So what I'm tring to figure out is: Is putting the enclosed sub within the larger cargo area affecting the overall performance of the system and causing the sub to perform better? It isn't exactly an enclosure per se, but the air in there must have some sort of suspension properties, right? Or is the sub still distorting away, but I simply can't hear the distortion because it's being muffled by the seat upholstery? Should I play it safe and turn the sub down to a non-distorting-in-free-air volume level before I button it up under the seat?

[mikee55]

Hello junkmail,

I think you need to establish whats happening with the driver. I'm just wandering if theres a possibility of a 'BANDPASS' enclosure type of action , going on here. If you could hook up a scope, or get a laptop with scope software, maybe you could check you got a good signal going in. But I think, the woofer is becoming un controllable, and when you close the cargo bay door, its helping to control things. So I'd say, you'd need to know if your signal is good.

Maybe, if the volumes could be calculated, a hole drilled somewhere, a port inserted, it could go Bandpass.

I think others need to chime in with opinions, to see what could be done.

Some come on then, people!

[richie00boy]

The bandpass thoughts are right, but the cargo area is much bigger than would normally be used for a bandpass design, and there may not be enough leakage as it is to get bandpass action. So I'm leaning towards the increased loading of the sub is stopping it shake itself to bits.