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Old    Jason Smith (snowslider76)      Join Date: Mar 2002       01-05-2012, 9:44 PM Reply   
So it's time for me to start a few winter boat projects, nothing too spectacular.

Anyway I have a slightly over stock system I put in my Xstar without really knowing what I was doing. I have 2 - 10"'s in separate band pass boxes one under the drivers seat and the other under the starboard back seat in the same compartment as the stock 10" free air JL sub. I sorta got lucky with how decent they sound considering I just ordered stock made boxes that fit in the compartments, I really have zero idea on how they are tuned or anything.

The subs are each powered with an Alpine MRP-M450 amp the specs on it are 220 watts RMS x 1 at 4 ohms (400 watts RMS x 1 at 2 ohms). I don't think these amps are around any more. I've always just run crappy subs to them, generally whatever series E where on sale and came close to meeting the amp specs. Problem is they blow all the time.

What I'd like to do is figure out what sub would go good with these amps either 10" or 12" I most likely need a 10" on the starboard size because of the space. I'll build new boxes to manufacturer spec's on box volume. I really like the way band pass boxes sound but could probably be convinced otherwise.

I'm open to recommendations, I would like to know the why though. Price really isn't a factor but I'm pretty sure the JL W's at $500 a piece really aren't a good fit for these amps anyway. So I'm expecting something cheaper then that, at least that's what I think.

Thanks for the help.
Old    Earmark Marine (david_e_m)      Join Date: Jul 2008       01-06-2012, 9:16 AM Reply   
You are right in that a $500 variety of subwoofer may be a little too much for those amplifiers to control.

A bandpass enclosure has an inherent steep lowpass filter that can make distortion inaudible until the damage is already done, especially if you have an enclosure within an enclosure (as in the seat console).

Its hard for a bandpass enclosure to be linear (relatively flat response) and still deliver a substantial boost in output for more than 1 1/2 octave. They can sound great but I doubt you could do well by using an off-the-shelf version. Those, like most off-the-shelf bass-reflex enclosures, are generally designed for maximum peak output rather than sound quality. And its harder for the output of a bandpass to seamlessly combine with your fullrange speakers in order to get decent bass tonal construction. While its all very possible its not likely to happen without a professional design throughout and a custom enclosure.

I would simpify the system by placing all bass drivers in a single optimum location, if for no other reasons, efficiency and phase coherency. You could have multiples behind the existing free-air woofer which could be removed and the opening could be converted to a large vent. Or, you could have one SERIOUS 2-ohm dual voice coil woofer driven by dual equal amplifiers (one amp per voice coil).

Start with the ideal location, from there determine the acceptable maximum displacement, from there determine the best enclosure type (whether bandpass, bass-reflex or sealed) in combination the right woofer size or multiples of woofers for that given displacement enclosure. The largest woofer doesn't always win although collective woofer surface area is one of the most important factors in an open boat. The sequence of location first, enclosure second and woofer selection third will serve you well.

Earmark Marine
Old    Jeff D (Jeff)      Join Date: May 2010       01-06-2012, 9:28 AM Reply   
I've always had good luck with the JL W0, or the Image Dynamics ID series. I've actually never had one blow when pushed within the limits of their power ratings even after years of abuse in a properly sized enclosure.

I'd be willing to bet that the reason your subs are blowing isn't due to power but due to the band pass boxes not being properly built for your subs' parameters. Also, even when properly designed, a band pass box tends to prevent the listener from hearing distortion. So you could push it past it's limits without even knowing.
Old    Jason Smith (snowslider76)      Join Date: Mar 2002       01-06-2012, 1:58 PM Reply   
Thanks for chiming in guys. I never knew band pass boxes worked that way, figured there way a reason you never see them in pro set ups.

Dave I like the idea simplify the system. The idea of placing them in one location is fine with me. I like the idea of the old free air sub becoming a vent but I really don't think that area is big enough to fit the properly sized box in. Sure if I gave up ballast but I'm not willing to do that, wake first stereo second.

So that makes my ideal location under the passenger seat and storage area, lots of room to work with there. So this is really "stereo systems for dummies" what exactly am I measuring to determine the acceptable maximum displace, the inside of the this area?
Old    Earmark Marine (david_e_m)      Join Date: Jul 2008       01-06-2012, 2:35 PM Reply   
The place to start is the location and now it sounds like you have already determined that.
Then design an imaginary sub enclosure that is the largest you can justify with all the other objectives that you need to satisfy like storage, access, mounting method, etc. The woofer and/or port outputs need to be relatively unobstructed relating to the confines and boundaries of the seating console interior.
And you have to include how exactly you plan to vent the bass radiation out of the seat console and into the open cockpit area.
Now you have a maximum external displacement of the enclosure which is easily converted to the gross internal displacement (simply the volume of air in cubic inches or cubic feet) by subtracting the enclosure wall thickness.
Simple enough thus far.
Now you can model which of the various size of woofers and which of the various types of enclosures will serve you best. At this point its a good idea to get the help of a pro. Many go through this analysis daily. The best option will always be the one that is custom for your scenerio.
Also, you have to balance the woofers responsiveness and thermal capacity with your existing amplifiers. This woofer to amplifier match up is not about extremes. Its about balance.

Earmark Marine
Old    Jeff D (Jeff)      Join Date: May 2010       01-06-2012, 3:28 PM Reply   
There are plenty of 10" woofers that can fit in a .5-.6 cu ft enclosure. If you really want a pair then you could put them in one box that's only 1-1.2 cu ft. That's probably smaller than one of your current band pass enclosures.


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