Changing sealed box shape?

[RSDXzec 10+ year member]

I'm looking at getting an ssa dcon 15" subwoofer soon, and due to space and preference I will be going with a sealed enclosure. I know on ported enclosures shape is crucial for performance, but I'd like to know how much it matters in a sealed enclosure?

Here is the recommended box

Now this will fit in the trunk, but I'd have to remove the boot cover and the box would be very obvious to anyone passing by. So I'd like to know if I could reduce the height a bit and enlarge the length/width in order to maintain the same volume. This way the sub wouldn't be visible from outside and would fit more nicely in the trunk. And how this would affect loudness/sound quality.

And I'm not sure why the front of the recommended box has two layers of MDF as opposed to just one. Was hoping someone here could let me know the importance of this, because if I could just use one layer of mdf I'd greatly increase the volume of the box.

the mounting depth for the 15" is 8.5" and I'm pretty sure my boot cover is about 12" from the bottom of the boot. So accounting for excursion I'd say a good height would be 10.5"

may go with something like (LxWxH) 23"x32"x10.5"

which if I use 1 layer of 3/4" mdf would give me an internal volume of 21.5"x30.5"x9"

so 3.41536 cuft

since the sub has a mounting depth of 8.5" and I have an internal depth of 9", could this cause problems or is this fine?

Cheers.

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[THATpurpleKUSH 5,000+ posts]

The dimensions of the box can change, you just need to make sure that the internal volume does not change. The box you have pictured there is 3.66 cu/ft before sub displacement, so you will need to keep this amount the same.

For a sealed box, that is a little on the large side. A ported box will only take up a little bit more room. If you are sacrificing that much space to big with, you might as well give up a little more and get the best performance possible. Sealed boxes are tremendous bottlenecks. A properly designed and build ported box will have better sq and output vs a sealed box.

The double layer where the sub mounts is crucial for providing rigidity to the box. When you mount any kind of speaker, you want the baffle (piece its mounted to) to be as strong as possible.

 

[RSDXzec 10+ year member]

The dimensions of the box can change, you just need to make sure that the internal volume does not change. The box you have pictured there is 3.66 cu/ft before sub displacement, so you will need to keep this amount the same.
For a sealed box, that is a little on the large side. A ported box will only take up a little bit more room. If you are sacrificing that much space to big with, you might as well give up a little more and get the best performance possible. Sealed boxes are tremendous bottlenecks. A properly designed and build ported box will have better sq and output vs a sealed box.

The double layer where the sub mounts is crucial for providing rigidity to the box. When you mount any kind of speaker, you want the baffle (piece its mounted to) to be as strong as possible.

Thanks for the info. That sealed box is listed as the optimum box size for the dcon 15" on the ssa website. I did consider making a ported box, but if I did I'd have to follow the manufacturer recommended box, and just like the sealed box it's too high for my liking. Considering this the the first box I'm gonna build I think I'd like to keep it simple because modifying a ported box I think would be very difficult for a novice like me, because from what I understand they are hard to get right.

Also, from what I've read about ported vs sealed, the sealed boxes appeal more to me. Sure ported hits lower notes better and is louder, but it seems sealed has better sq responsiveness and it (provides punchier bass) shakes a bit better which makes sense to me since there would be more pressure in the box, causing more shaking.

Also I'm trying to make this box light if I can, less parts in the box reduce weight, and I'm still thinking about how necessary the double layer for mounting. Information on the internet suggests it's only really necessary for subs that push a lot more power than 300WRMS.

 

[duanebro 10+ year member]

The shape does not matter in your case. It can make a difference sometimes. But what you want to do will be fine. If you are worried about weight, switch to plywood. Don't do the double baffle unless you want to recess the driver for looks. BUT you need to brace the box, I don't care how much power you are using. Bracing is much more effective than making the box thicker. I would just use several around the driver, from the baffle to the back of the box. This ties the two together so they can not flex. The bigger the panel the more important this is.

One other thing, buy some pillow filler, the correct name escapes me right now, poly something. And put in the box. This will make the box act bigger than it is. 1 pound per cf max is the general guideline.

one last note, sealed boxes are very forgiving, if you reduce the volume a bit - it won't make a huge difference. I would give a range of 2.5 - 3.5 cf would be fine for this driver.

If you would like to see how you like ported, I can help you out, with a design that can do both. //content.invisioncic.com/y282845/emoticons/wink.gif.608e3ea05f1a9f98611af0861652f8fb.gif

 

[RSDXzec 10+ year member]

The shape does not matter in your case. It can make a difference sometimes. But what you want to do will be fine. If you are worried about weight, switch to plywood. Don't do the double baffle unless you want to recess the driver for looks. BUT you need to brace the box, I don't care how much power you are using. Bracing is much more effective than making the box thicker. I would just use several around the driver, from the baffle to the back of the box. This ties the two together so they can not flex. The bigger the panel the more important this is.
One other thing, buy some pillow filler, the correct name escapes me right now, poly something. And put in the box. This will make the box act bigger than it is. 1 pound per cf max is the general guideline.

one last note, sealed boxes are very forgiving, if you reduce the volume a bit - it won't make a huge difference. I would give a range of 2.5 - 3.5 cf would be fine for this driver.

If you would like to see how you like ported, I can help you out, with a design that can do both. //content.invisioncic.com/y282845/emoticons/wink.gif.608e3ea05f1a9f98611af0861652f8fb.gif

Are you sure plywood would be fine? everything on the net suggests mdf is whats necessary, also I didn't think about bracing, so I'll have to look into that.

what your thinking of I believe may be polyfill which I should probably look into getting.

and as far as reducing the box size, I've done a bit of research into the "qtc" necessary for a good sealed box. I don't know too much about what the numbers mean yet but everyone seems to say a qtc of 0.707 is best. But using a calculator I found here Car Audio - Sealed Subwoofer Speaker BOX DESIGN - Qtc Calculator and the specs on the ssa website DCON Series Sub Woofer

Vas 37.8

Fs 33.5

Qts 0.44

and a box size of 3.66 as recommended gives me a qtc of almost 1.5, to get a lower qtc i'd need a much larger box so I think I'm doing something wrong here...

cheers.

 

[THATpurpleKUSH 5,000+ posts]

Also, from what I've read about ported vs sealed, the sealed boxes appeal more to me. Sure ported hits lower notes better and is louder, but it seems sealed has better sq responsiveness and it (provides punchier bass) shakes a bit better which makes sense to me since there would be more pressure in the box, causing more shaking.

Ported boxes provide just as punchy bass and sq, wherever you read that statement is completely false. A sealed box does have more pressure inside because the rear wave has no where to go, however this does not lead to more "shaking."

 

[Moble Enclosurs 10+ year member]

the shape of the enclosure, regardless of its type, can make a difference all the time. Its just a matter of how much of a change occurs. As far as plywood, birch is where its at. Double baffle is not meant for recessed looks. That comes with the detail if requested. It is mainly for support and reducing flex from excursion, especially with larger and stronger drivers and more so when they are vertically mounted. So it's not for looks at all. That's just an option.

As far as a sealed volume recommendation, I calculated 2.439 cubic ft and no smaller.

 

[Moble Enclosurs 10+ year member]

One more thing.....do not rely on manufacturer specs. Second, as far as depth of the box for mounting purposes, as long as the driver does not have a vented pole piece, you can put it that close, but be careful. Usually, 2-3inches from the magnet is recommended by me as a minimum allowable distance.

 

[duanebro 10+ year member]

Are you sure plywood would be fine? everything on the net suggests mdf is whats necessary, also I didn't think about bracing, so I'll have to look into that.
MDF is cheaper, and denser. Otherwise plywood is better IMHO.

What your thinking of I believe may be polyfill which I should probably look into getting.

Yep, that's it. LOL

and as far as reducing the box size, I've done a bit of research into the "qtc" necessary for a good sealed box. I don't know too much about what the numbers mean yet but everyone seems to say a qtc of 0.707 is best. But using a calculator I found here Car Audio - Sealed Subwoofer Speaker BOX DESIGN - Qtc Calculator and the specs on the ssa website DCON Series Sub Woofer

Vas 37.8

Fs 33.5

Qts 0.44

and a box size of 3.66 as recommended gives me a qtc of almost 1.5, to get a lower qtc i'd need a much larger box so I think I'm doing something wrong here...

cheers.

You just entered one thing wrong. The VAS you listed is in liters. The calculator expected cubic feet. The VAS is closer to 1 cf. The Qts is about .7 in the 3.6 cf box and .76 with a 2.5cf box. The difference is about 1 db in the model I think. Moble E. agrees that a smaller box would work. We came up with close to the same lower size limit. Makes me think I am doing something right. LOL.

One item I'd like to note. I had said that the change in box shape would be ok. I over looked the distance behind the sub. You have a vc vent there. You do need room for it to breathe. I don't know how much clearance is needed. I would like more than 1/2" though.

the shape of the enclosure, regardless of its type, can make a difference all the time. Its just a matter of how much of a change occurs. As far as plywood, birch is where its at. Double baffle is not meant for recessed looks. That comes with the detail if requested. It is mainly for support and reducing flex from excursion, especially with larger and stronger drivers and more so when they are vertically mounted. So it's not for looks at all. That's just an option.
As far as a sealed volume recommendation, I calculated 2.439 cubic ft and no smaller.

My explanation was to simple. The box shape shouldn't make enough of a difference to be a concern, in this case. Though the depth is a concern.

A thicker baffle does make a stiffer box. But the same thing can be done with bracing. And it will be lighter, plus take up less space.

 

[OmegaBunny 10+ year member]

If you want to port and are worried about the weight issue use a aeroport. They are very light weight and the box you have now might be a good size for ported already.

 

[RSDXzec 10+ year member]

You just entered one thing wrong. The VAS you listed is in liters. The calculator expected cubic feet. The VAS is closer to 1 cf. The Qts is about .7 in the 3.6 cf box and .76 with a 2.5cf box. The difference is about 1 db in the model I think. Moble E. agrees that a smaller box would work. We came up with close to the same lower size limit. Makes me think I am doing something right. LOL.
One item I'd like to note. I had said that the change in box shape would be ok. I over looked the distance behind the sub. You have a vc vent there. You do need room for it to breathe. I don't know how much clearance is needed. I would like more than 1/2" though.

My explanation was to simple. The box shape shouldn't make enough of a difference to be a concern, in this case. Though the depth is a concern.

A thicker baffle does make a stiffer box. But the same thing can be done with bracing. And it will be lighter, plus take up less space.

ah that explains a lot lol. Converted to cubic feet which was about 1.33 i think and now the qtc seems a bit low. Where you said qts there did you mean qtc? I don't know much about this but I didn't know the qts could change as it is listed on the ssa site as a specific value.

For the vent, would 1" be enough? Basically my problem is I have about 12" of space total height to work with and I figured that accounting for the excursion and whatever mounting distance I'd need externally that 1.5" would be good. Hence why I am making a 10.5" tall box. I guess I could make it 11" tall if I never used it with the trunk cover on, then I'd just have to account for external mounting depth and forget about whatever distance the excursion may add as I will have to remove the trunk cover to use it. My goal here is to not make the sub visible from the outside of the car so it doesn't attract attention while parked.

If you want to port and are worried about the weight issue use a aeroport. They are very light weight and the box you have now might be a good size for ported already.

Is adding a port with a box this size really as easy as just putting in the port? Many vented designs I have seen have 45 degree corners internally to get rid of "standing waves" so what internal modifications would be involved to make this work?

Also, I assume these ports come in a variety of sizes, from what I've seen the way the port is designed is what changes the tuned frequency of the box. If I go ported I'll most likely be aiming for 32hz, as the tuned boxes on the ssa site are tuned between 28-33hz and I'm not sure how safe it is to go for a lower frequency. (The sub has an Fs of 33.5Hz, not sure if that makes any difference to this or not)

 

[RAM_Designs 5,000+ posts]

That Vas isn't right, they simply put the Vas for the 10" model across the board to the others. It's around 5ft^3, if I remember correctly.

 

[Moble Enclosurs 10+ year member]

Yep

 

[RSDXzec 10+ year member]

That Vas isn't right, they simply put the Vas for the 10" model across the board to the others. It's around 5ft^3, if I remember correctly.

ok then, I'll see how the calculator responds to that.

Yep

care to elaborate? lol I don't know what you're responding to.

If you could answer my question on how much harder it is to go ported that would be greatly appreciated as I'm not sure how much more work I'd have to put into it. Or if it's as simple as making a hole then tuning the port to the right frequency.

 

[duanebro 10+ year member]

ok then, I'll see how the calculator responds to that.


care to elaborate? lol I don't know what you're responding to.

If you could answer my question on how much harder it is to go ported that would be greatly appreciated as I'm not sure how much more work I'd have to put into it. Or if it's as simple as making a hole then tuning the port to the right frequency.

I'm a little late on this reply. I believe that ME was just agreeing about the Vas being wrong.

As far as porting a box. I have never heard about the 45 degree angle standing wave thing. You do need a design to go by. I would use round ports so they can be easily plugged. This way you can try sealed also. I am not at my computer right now. but I can help with port sizing and tuning.