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85 Barefoot

Box Size Recommendations

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85 Barefoot

Hi,

Have a relatively old MTX Blue Thunder 12 that I was going to put in the response. Problem is, the box won't fit through the opening under passenger seat. In fact, I can't find any good spot to mount the amp either (kicker 700.5). So, I'm going to have to build a box and, yes, I know it's not ideal, but was thinking of building a long and flat box to mount the amp on top of it. Amp is about 20" long. Initial design idea was to let sub fire downward. So, I was thinking let two walls extend about 6 inches past the flush side of woofer, and let woofer fire down, amp mounted on top. Any thoughts? Any recommendations on size of box? I have plenty of room but the box must be shallow (about 12 inches). Thanks!

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Earmark Marine

85 Barefoot,

Can you get the Thiele Small parameters on the MTX woofer? If you can, then this would be an easy to figure box size. Shoot for a sealed Qtc between 0.7 to 1.0.

Extremely elongated sub enclosures with one very shallow dimension tend to sound undersized and not very good. You also tend to lose power handling early. Normally box shape in a sub box has little affect but too shallow is the exception. So be careful of this. In a shallow enclosure, if you have a woofer with a vented pole piece, make sure the vent is a good distance from the enclosure rear interior surface. However, I would not call 12" shallow at all.

For a common downfiring 10-inch sub you would want 2.625" from the tip of the surround roll to the sole in order to not reduce the sub's radiating surface area. Cars will forgive you for a choked downfiring set up but boats are not so forgiving. And if its a choked dowfiring sub in combination with a concealed location within a console or locker then the losses and poor sound quality become very obvious.

David

Edited by Earmark Marine

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85 Barefoot

85 Barefoot,

Can you get the Thiele Small parameters on the MTX woofer? If you can, then this would be an easy to figure box size. Shoot for a sealed Qtc between 0.7 to 1.0.

Extremely elongated sub enclosures with one very shallow dimension tend to sound undersized and not very good. You also tend to lose power handling early. Normally box shape in a sub box has little affect but too shallow is the exception. So be careful of this. In a shallow enclosure, if you have a woofer with a vented pole piece, make sure the vent is a good distance from the enclosure rear interior surface. However, I would not call 12" shallow at all.

For a common downfiring 10-inch sub you would want 2.625" from the tip of the surround roll to the sole in order to not reduce the sub's radiating surface area. Cars will forgive you for a choked downfiring set up but boats are not so forgiving. And if its a choked dowfiring sub in combination with a concealed location within a console or locker then the losses and poor sound quality become very obvious.

David

David, thank you. Overall, what do you think of this "plan"? The 2.625 figure, is that the min distance between "floor" and surround if firing downward? I should clarify, The box can be no TALLER than 12" to get through the opening, even WITH the supporting "legs". Knowing that space limitation and also needing an amp location, what do you think? Scrap this plan and do something else? As to Thiele Small parameters (I assuem you mean the factory recommended figures?) I can't find them. Width I have about 20", height about 12". I can go as long as I need to. Still a bad idea?

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Earmark Marine

85 Barefoot,

Yes, the manufacturer specs like Fs, VAS, Qts, etc.

Its not sounding like a bad idea at all as you are providing more information. I am just pointing out where the landmines are buried in advance so you can avoid them in your initial design.

Yes, 2 & 5/8" from the highest point or peak of the surround roll to the boat's floor (sole). This takes into consideration the one way excursion plus the elevation at the circumference of the woofer so that it is no less than the woofer's effective radiating surface area. This will ensure that there is no compromise at all whether its a downfiring or sidefiring configuration.

You can pre-stud (S.S. bolts) and double-nut the enclosure in advance so that the legs will slide on and bolt on easily after insertion into the compartment. This way you will not have any trouble assembling the parts blind and the enclosure can be larger if needed.

David

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85 Barefoot

What about firing it up as opposed to down?

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Earmark Marine

I don't see how the orientation would matter in the context of what we have discussed thus far.

David

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martinarcher

Can you mount your amp to the "firewall" under your feet and still have ample room for you box? You could then use all 12" of the enclosure height and not loose any for the down firing enclosure's legs. I do like down firing subs though. Thumbup.gif

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85 Barefoot

Can you mount your amp to the "firewall" under your feet and still have ample room for you box? You could then use all 12" of the enclosure height and not loose any for the down firing enclosure's legs. I do like down firing subs though. Thumbup.gif

No, in my era response the footwell is but about a 6 inch wall, above it is all open space leading to the bow storage. So, I think the bass radiation should be good in that it's not closed off. But, I have no place to mount the amp other than the "ceiling" of the bow, which I'd prefer not to do.

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85 Barefoot

I don't see how the orientation would matter in the context of what we have discussed thus far.

David

I'm just saying if the box design will have to be what it is, (relatively short and wide), any advantage to firing up vs down?

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Earmark Marine

85,

As we discussed you do not want to have the woofer too close to the plane as this can change the woofer 'Q' in an extreme situation and will choke some of the output which is inefficient. As long as you have adequate separation then any reinforcing planes in close proximity to the woofer will enhance the bass whether sidefiring. upfiring or downfiring. However, I would not mount the sub enclosure to anything above because of the unwanted vibration that will be transmitted through that surface. A stiffening brace only might be okay if the main mounting is below.

Just to cover this in advance, I would never mount an amplifier upside down.

David

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85 Barefoot

David, thanks for your time and feedback. To clarify, I wans't going to mount the sub on the ceiling. In the bow area there is actually quite a bit of room, the problem is the size of the access, hence my height limitation on the box. Once inside, if I fired up, it would probably be 18" from surround to ceiling. Downward, and I'm limited because I can only build it off the floor so far as what will fit in the access. MAke any more sense?

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Earmark Marine

85,

Sure, its makes perfect sense.

I like the idea of loading the sub against a plane as long as it isn't "too" close to that surface. I think the added acoustic leverage will be welcomed. With an expansive compartment leading into the under-bow area you can use all the leverage you can get.

You should be in good shape to make the final plan.

David

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martinarcher

No, in my era response the footwell is but about a 6 inch wall, above it is all open space leading to the bow storage. So, I think the bass radiation should be good in that it's not closed off. But, I have no place to mount the amp other than the "ceiling" of the bow, which I'd prefer not to do.

Right on. That's a lot like my Skier was laid out. I mounted my amp on top of that box.

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NuBuGuy2011

fwiw - polk audio site has some good box design tools for sizing box specific to your sub's parameters - used them to size custom sub enclosures my son & I built for his jeep liberty :thumbup:

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Shaboy6

What year is your response? I have a 98 lx,Is your open or closed bow.I know exactly what your talking about. I had my stereo don't this time last year by a shop. They removed the front bow upholstery and built the box inside. There are 2 10's facing the rear when you open the passenger seat there right there. I have 3 amps and 3 battery in there including my onboard charger. It's clean but defiantly no storage now. Lol. But I can send you some pics if you want. Let me know.

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85 Barefoot

Closed bow 98. What you had done sounds great but not possible on this boat.

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Earmark Marine

85,

Have you managed to get the T/S parameters from MTX yet? Old TermPro programs may have those parameters in the database. If you are unable to score that info then let me know and I will give you the next best option.

David

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85 Barefoot

85,

Have you managed to get the T/S parameters from MTX yet? Old TermPro programs may have those parameters in the database. If you are unable to score that info then let me know and I will give you the next best option.

David

can't find anywhere. Don't go out of your way David but I appreciate it. It's not exactly earmark material!

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shawndoggy

good luck finding the ts parameters for that sub. I asked on a different forum about a pair of blue thunder 10s that I ran in my F150. I had the 10s in about .8 ft2 and they would not really go low. So my completely unscientific advice is to go sealed and go as big as you possibly can. The blue thunders aren't new school subs that do well on small boxes. They need all the room you can give them.

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Murphy8166

Why wouldn't you just call MTX's techinal support dept....

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Deephaven

Fs = 26.3 Hz

Qms = 9.72

Vas = 98.6 liters

Cms = 0.242 mm/N

Mms = 151.5 g

Rms = 2.58 kg/s

Xmax = 9.4 mm

P-Dia = 261.9 mm

Sd = 539 sq.cm

Qes = 0.65

Re = 3.17 ohms

Le = 2.4 mH

Z = 4 ohms

BL = 11.05 Tm

Pe = 250 watts

Qts = 0.61

no = 0.26 %

1-W SPL = 87.2 dB

Didn't model it, but WAY back in the day had one in ~2cuft sealed and it worked well.

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Earmark Marine

WOW! Good job on getting those specs.

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85 Barefoot

Thanks! But uh can someone interpret please ? Again I have room for plenty of cubic feet just must be less than 12" tall. Seal? Port? Thank you. Good project for the weekend

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Earmark Marine

85,

Try what Deephaven recommended. Its a fairly high 'Q' woofer so its going to need a bit more box. Go with the 2 cu.ft. internal gross (no need to figure the woofer displacement) sealed. With 3/4" thick construction material your external displacement will be about 2.68 cu.ft. So any box that would total 4628 external cu.in. It could be 25.5" X 16.5" X 11" for example. Any combination of H X W X D to = 4628.

David

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Deephaven

Exactly. Had to call a friend to get those, but same boat there. His was in 1.75 or so but it was better when stuffed. If you shoot for around 2cuft sealed you'll enjoy it. Definitely a great old school woofer.

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