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Sub box volume. How precise?


minnmarker

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The WS-12S4 manual says you should have a enclosure volume of 1.1 cu. ft.  The QBOMB box (lazy way out) I have for it is 1.4 cu. ft.  The amp will be a Kicker CX-1200 (600 W at 4 ohms).

Should I add some wood to the inside of the box to reduce the volume - or is it close enough?

This is for my down firing "sub for pontoon" project.  Part of the project is adding a "sole" bolted 3" under the box, and I've double the amp power from 300 to 600 (thanks David).  If it makes a difference the sub will be placed on the deck in an open location where I would like to get sound radiating in 3 directions.

Thanks!

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It definitely makes a difference. 0.3 cu.ft. is a large percentage difference in this case. As you increase the enclosure size too much, you may lose power handling and lose output, even though the sub may reach a little lower. There's a sound difference when the sub enclosure is too large and the driver is under-damped. It sounds a little dead.

I believe a 12-inch sub enclosure should be all 0.75" thickness before any exterior coating. I'm not sure yours is. Pull the terminal cup and measure the wall thickness less the coating. Instead of inserting blocks of wood you may want to dedicate the needed displacement reduction to making internal stiffeners.    

 

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7 minutes ago, David said:

It definitely makes a difference. 0.3 cu.ft. is a large percentage difference in this case. As you increase the enclosure size too much, you may lose power handling and lose output, even though the sub may reach a little lower. There's a sound difference when the sub enclosure is too large and the driver is under-damped. It sounds a little dead.

I believe a 12-inch sub enclosure should be all 0.75" thickness before any exterior coating. I'm not sure yours is. Pull the terminal cup and measure the wall thickness less the coating. Instead of inserting blocks of wood you may want to dedicate the needed displacement reduction to making internal stiffeners.    

 

OK, good info.  Thanks.  The wall thickness is 3/4 inch MDF plus a thick bed liner coating.  As far as sound, does it matter what shape and orientation the braces are?

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The woofer should see the smallest cross section of bracing from the front to rear perspective.

I have two reasons for suggesting you check the thickness of the side wall by removing the terminal cup. The last Q box I used had a .75" thick baffle but all other walls were .50" thick. The Q boxes are much lighter in weight than other boxes of the same size. Yours may be different but it doesn't hurt to make the check.    

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David

I have a Q? Here, minnmarker not ment to hi jack. 

I just moved my stock RF 12"  Sub from out of the ski locker to under the helm. Reusing the existing sub box 

which is 3/4" thick ABS all around and added a new Kick panel out of 3/4" thick ABS.  I afixed the sub box

to the back side, cuting a matching hole and secured togeather with SS screws. We now have the sub ABS face 1-1/2" thick.

Sounds great but some base seems over boomie even with the sub amp set to min. Is this due to the location under the helm

or possibly the fact of to thick a face panel by 3/4"  changing the sub box volume, or the songs them selves?

As I mentioned,  sounds great with lots of different artistis and others not so. Never noticed this while it was

in the ski locker, & then again that does muffel the base.

 

http://www.themalibucrew.com/index.php?/forums/topic/58216-another-sub-story/&do=findComment&comment=904911

Edited by Dare2goBare
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Dare2,

I'm at a disadvantage since I am unable to hear what you are experiencing. But when I get to hear problems like yours, from the sound, I can usually pinpoint the cause.

Doubling up on the baffle depth will not change the box displacement by much because it is only around the woofer circumference, like a donut, instead of across the entire box cross section. My only concern with a double-thick baffle is restricting the air flow. You can always enlarge the back layer slightly and round-over the back side. But I doubt that detail is the cause of the issue you described.

I'm sure Rockford provides Thiele/Small parameters on your woofer and a sealed box size that corresponds to a particular 'Qtc' (a woofer loaded in box final system 'Q'). This 'Qtc' is often around .85. This represents a tuned acoustic circuit with a gradual roll-off with a slight midbass crest and is usually very musical sounding. The extremes are....If the box is too small the crest becomes too pronounced and you lose deep bass content. If the box is too large the midbass crest can turn into a null with greater deep bass extension, and a lack of the bass liveliness. You get low fundamentals but these aren't perceived with a great deal of tonal construction. Those are the general characteristics. Maybe this helps.

The location or orientation of the sub is not the problem.

Crossover selection and tuning could be the problem. Poor midbass contribution from the cockpit coaxials could be a problem because the coaxials carry much of the upper bass harmonics that provide the true tonal construction. If you don't have enough coaxial surface area, or a phasing problem, or poor coherency between the sub and coaxials, this can also contribute to poor bass quality. Any non-linear or abrupt change in the bass response can really stand out as boominess. If you are using any kind of bass boost, kill it.              

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2 hours ago, David said:

The woofer should see the smallest cross section of bracing from the front to rear perspective.

I have two reasons for suggesting you check the thickness of the side wall by removing the terminal cup. The last Q box I used had a .75" thick baffle but all other walls were .50" thick. The Q boxes are much lighter in weight than other boxes of the same size. Yours may be different but it doesn't hurt to make the check.    

Checked and all walls are 3/4" so we're good there.  Will do on the bracing orientation.  Thanks again.

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without crunching and numbers, I think 1.4 ft will be a little on the mellow side for that woofer. Too mellow? hard to say as this starts to get a little on the personal taste side of things. Personally, I like a sealed woofer thats a tad mellow rather then 'snappy" The good thing is, its easier to make a box smaller than larger :biggrin: for others, they like that very crisp tight response. 

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1 hour ago, IXFE said:

Which Q model did you get?

I'm asking because I believe it's listed at 1.3 cu ft. 

QBOMB 12S SINGLE

http://www.qpowerinc.com/index.php?id_product=35&controller=product

Yes, it says 1.3 but if you use their dimensions or measure it (interior or exterior dimensions minus 1.5") you get about 1.43 cu. ft.  Maybe they're bad a math.

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Question for David... 

Do you subscribe to the idea of using polyfill inside the box? I've read that has the effect of making a bigger sealed box seem smaller. 

Curious to hear your take. Might this be a solution for the OP??

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Polyester fiberfill can be used to simulate a slightly larger enclosure by converting energy. But not the inverse.

It can also be used to attenuate any coincidental or reflected waves within the enclosure. This won't make that much difference for longer wavelengths in a sub enclosure like it will for mids.

So leave the sofa pillows alone.     

Btw, the enclosure is internal gross. The woofer recommendation may be for net. So confirm this and the woofer displacement.

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14 hours ago, David said:

Dare2,

I'm at a disadvantage since I am unable to hear what you are experiencing. But when I get to hear problems like yours, from the sound, I can usually pinpoint the cause.

Doubling up on the baffle depth will not change the box displacement by much because it is only around the woofer circumference, like a donut, instead of across the entire box cross section. My only concern with a double-thick baffle is restricting the air flow. You can always enlarge the back layer slightly and round-over the back side. But I doubt that detail is the cause of the issue you described.

 

Thx David.

I'm going to take the kick panel off,  place the sub back into the sub box as the stock build and see how it sounds.

I'll start another post  or pm you on further discussons as I don't want to hi-jack here. It was the comment around sub box volume 

that prompted my Q.

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