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Subwoofer help. Need the Experts

Randy

Well-Known Member
Famous
Ok, so this a car audio kinda question, but I have a problem and I desperately need help. I am redoing the stereo in my boat and I want it done right. I am planning to add 2 subs located in the gunwales right next to each front seat. I have done a lot of homework and I think this is the best place to put them. They will go in a wedge shaped box very similar to the one I used in my old truck with great success.

Hence the problem, I am planning on using 2 Alpine SWR 1243d (dual 4 ohm) subs with an MTX Thunder 801D amp (400 watts RMS at 2 ohms at 12v) going to each one. I have gone through several box designs and keep going back to sealed because of the marine environment. I am going to coat the boxes in spray on bed liner to seal the MDF from the moisture associated with the marine environment.

According to the T/S parameters of the subs, they should be ideal in a sealed box application.

http://support.alpine-usa.com/products/documents/OM_SWR-10+12_23D_43D.pdf

The Qts of 0.53 indicates it would work well in a sealed enclosure.
The EBP, or Efficiency Bandwidth Product = Fs/ Qes of 31hz/0.57= 54.386 indicates that it should work fairly well in a sealed box.

And, Alpine states that it will work well in a sealed box of optimum size .90 ft^3 gross internal volume and a net internal volume of .75 ft^3

But, every one of the car audio GOOFS that I have spoken to about getting my boxes built, and nearly everything I have read online says that the Alpine Type R's do not work well in a sealed box, unless it is considerably bigger than Alpine's specs, and you almost have to go ported.

WTF gives??? Soundhound, Flint, DIY'ER, SMGreen (my car audio freaky brother), I need help. I joined caraudioforum.com like 3 weeks agao and still can't post or start threads.
 

-B-

Well-Known Member
Off topic slightly, build the box and get it sprayed with Line-X. Looks good and renders it waterproof.
 

Randy

Well-Known Member
Famous
Not that kind of boat Matt. Although if the subs keep those F'in Asian Carp from jumpin in my boat while on the river, than I am all for it.

B-" I am going to coat the boxes in spray on bed liner to seal the MDF from the moisture associated with the marine environment."

Already addressed that part. :eek:bscene-buttred:
 

-B-

Well-Known Member
Totally missed that Randy...... :oops: It might be worth the extra dough to go with the Line-X brand as it's about as good as it gets. Whatever you go with make sure it's a 2 part catalyzed type product. If it's a straight air dry type product it may have a tendency to retain moisture.
 

Randy

Well-Known Member
Famous
Thanx B I will double check before I have it done. I have access to a couple of brands, Line-X being one of them.
 

Dentman

Well-Known Member
Randy,

Keep in mind that much of the car audio crowd cares much more about out put then they do about the quality of the sound. Along with this there are many people who just don't understand the whole sealed VS ported enclosure thing. I would stick with the manufactures listed dimensions for the sealed box. They should know the drivers needs better then anyone. they should anyway.
 

Flint

Dog Faced Pony Soldier
Superstar
Using a larger than ideal enclosure will give you more perceived deep bass output as the enclosure will not be restricting the motion of the cone as much as with a smaller enclosure.

That does not mean it will sound better or play louder if you build a larger enclosure.

The ideal enclosure will give you the least distortion, cleanest sound, and highest SPL capabilities - especially in an open air environment like a boat. Really, for a boat you need use PA sub designs rather than car audio designs because of the lack of cabin pressure.

I recommend following the guidelines from Alpine and any good enclosure calculator for a decent sealed sub. It may not play as deep, but it will be cleaner and louder in the range it is designed to operate in.

If it doesn't play deep enough (to the lowest frequencies you desire), then you are using the wrong sub drivers.
 

-B-

Well-Known Member
I'm thinking the environment dictates a sealed box strictly due to the moisture factor. It's also my opinion that there will be less of a noticeable difference based on the environment it's being used in. In my experience (limited) sealed boxes have been the most used. The output crowd always seemed to go with the bandpass boxes. Been quite a few years since I fooled with car audio though.
 

Randy

Well-Known Member
Famous
Thanx for the help so far guys. The common excuse given is that the manufactures publish specs the buyers want to read. People want their subs to perform well in small(er) boxes, we all know this is true, so they publish specs that will appeal to a broader audience even though that may not be where the sub performs best.

Flint,
The published F3 is 43hz with an Ftc of .90 so I guess that is about as good as one can expect consdering the environment. I was hoping the smoother rolloff of the sealed box would give me a little lower extension and I am hoping to get "some" cabin gain by placing the subs in the sides of the boat where there is a bit of room for the sound to be reinforced. The common thing to do in boats is slap subs under the rear bench seat, because it is a convenient place to put them with little effort. The enclosure is often completely overlooked, but they guy can tell his friends, I have four 12" subs, and it looks impressive.

That being said, Alpine reccomends for an optimum sealed box with dimensions of 14.5" x 14.5" x 10.5". These dimensions don't account for the "Golden Rule" ratio of 1:1.62:.62 and I can not use these dimensions anyway, cuz there would simply be no place to put them. So, will I be okay with my wedge box design as long as I get the gross volume and net volume down and have sufficient space behind the driver (magnet) for cooling?
 

Flint

Dog Faced Pony Soldier
Superstar
Forget the "Golden Ratio" as these are bass frequencies with wavelengths ten times longer than any dimension. The golden ratio is only for midrage stuff.

T/S specs are T/S specs. Woofer manufacturers have no reason to lie about those.

I can see them recommending smaller enclosures, but if you plug the T/S specs into an online enclosure calculator the results will be the ideal cabinet volume.
 

malsackj

Well-Known Member
If you want to improve the bottom a little. You could consider with a sealed enclosure to run a custom EQ to bring more out of the sealed sub. When working with my EV TL15-1 subs for band work they are ported and will not work very well with frequencies below the tuned port.

I have used a Behringer Feedback suppressor to do some EQ adjustments on my subs. If you can find a parametric EQ to attach a shelving low pass adjustment to improve the response in the 40 and below range by a small amount of boost than you might not create a large demand from the amp. Remember as Flint says that every 3 db will require twice the power in the amp. Also how much is the cone moving? I can push my 6.5 inch to 40 hz and create 120 db with how much distortion? Using the sub and crossing over and sending 100 hz and up to the 6.5 is much better.

Anytime your outside you will find that subs are not playing much below the 40 hz because the PA is filtering the 40 and below out of the mix for a band. I have the TL15-1 and the feedback suppressor getting my subs down to 32 because I choose the blocking of one port and adding 6 db to flatten the signal on the subs. My output to the amps is down at 40 percent for most but I have been up to 60 percent and they were putting out 120 db outside. ( Wedding church organ feel )
 

Deerhunter

Well-Known Member
Your subs are going in a open boat. It not like you going to really do critical listing with it. Just build your box to fit the area your after. Seal it well in-side and out. I would even Line-X the inside to reduce the resonance frequencies. Then see how it sounds, you can always add poylfill (pillow stuffing) to it from their.

I would keep it sealed just for the moister factor and use some sub grills, so a foot does not end up through it.
 

Randy

Well-Known Member
Famous
Deerhunter said:
Your subs are going in a open boat. It not like you going to really do critical listing with it. Just build your box to fit the area your after. Seal it well in-side and out. I would even Line-X the inside to reduce the resonance frequencies. Then see how it sounds, you can always add poylfill (pillow stuffing) to it from their.

I would keep it sealed just for the moister factor and use some sub grills, so a foot does not end up through it.
Thanx again guys.

Deerhunter, I agree with you and normally if it were going in a trunk or somewhere else that is the route I would take.
Unfortunately it is a one shot deal. I am going to have to take the interior of the boat almost comletely out, including the Bolster seats. The seats come out the subs go in and ther they stay. I will not be able to take the boxes in and out for tuning purposes as I would normally do in a car or truck.
 

Deerhunter

Well-Known Member
Ok then, I see your point. Try this sight the12volt.com its a good car audio sight. They also have several calculators for sub boxes and just about anything else you need. I am on their from time to time under my normal screen name Dragon51

Hope your able to come up with something that works right for you.
 
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