Building a sub enclosure

[DatDoug]

I have #2 cheap 8" subs & I want to build a box for them to go in the back of my gOOn. Anyone have some good input as to how I should go about building it. Size? Ports?

[Pacific coast Datsun]

I applied no math at all when i built the box for my Kicker 12's :cool: I made it half the size of the area & it sounds fine. Box is sealed & has a 200 watt amp powering them. Im sure theres a site somewhere that will tell you how much airspace needed for each speaker size. My box....

[thisismatt]

Don't: Build a box of random volume, port(s), or material.

Do: Build an enclosure tailored to the driver's thiele-small parameters.

 

Thiele-small parameters

 

If you don't have the necessary T/S parameters and they can't be looked up, then you'll just have to go with a generic sealed or ported enclosure (by generic I don't just mean a random volume and/or port(s), just one more-so based on a guess and not finely tuned to your individual drivers). Certain drivers perform better in sealed vs ported, and vice versa.

 

Generally speaking, the smaller the volume of a sealed enclosure, the more peaky the output will be at a higher frequency, and a sharper roll-off in output as you move lower down the frequency response curve (ie it won't have good output down low, but it can give you more output at a desired frequency like around 40hz for a kick drum). A bigger sealed enclosure will have a smoother response curve and slower roll-off, giving you more low-end output but not that kick drum boost that you might want. Moderate/large sealed enclosures make good sound quality enclosures in cars because, due to the small volume inside the car, they couple well with "cabin gain" and can produce a very flat frequency response.

 

For ported enclosures it's important that you build to a specific volume, port length, and port cross sectional area (doesn't have to be round, it can be any shape you want more or less). These three things define your tuning frequency and overall frequency response, although the T/S parameters of the driver(s) will effect how well the driver(s) do/does across the board. There are basic calculators for these here. Note that Vb doesn't typically account for the air displaced by the driver(s) itself/themselves so that may have to be added to the overall volume when you build the enclosure. For ported enclosures these three things affect the roll-off and peaks in frequency response. Changing the volume without changing the port has the same basic effect for a ported enclosure as for a sealed, so if you make it smaller the roll-off will be sooner/sharper and the response will become peaky higher and higher in the frequency response curve. To maintain the same tuning frequency as you lower the box volume, the port will have to get longer, or smaller in cross sectional area, or vice versa if you increase the volume. Shrinking the cross sectional area (size) of the port has the adverse affect of increasing port airflow velocity which becomes and audible chuffing if it become too great and your port inlet(s)/outlet(s) are sharp edged. If you want to play around and visually see how changing these aspects of an enclosure affect the frequency response, download WinISD, load up a driver and some enclosure parameters, and then fiddle around with the parameters to see how the response curve is affected. WinISD

[thisismatt]

I applied no math at all when i built the box for my Kicker 12's :cool: I made it half the size of the area & it sounds fine. Box is sealed & has a 200 watt amp powering them. Im sure theres a site somewhere that will tell you how much airspace needed for each speaker size. My box....

If you go sealed, like this, you really can't go wrong. It may not be optimal for output and/or sound quality, but it will work at least okay. The same can't be said for ported enclosures - if you err on the design of a ported enclosure and end up with a high tuning you will get terrible output and perhaps blow your sub(s). The driver(s) become unloaded (meaning they have no air spring/returning force) in the enclosure and it will be like running the driver as though it's sitting bare in free air, making it easy to overpower its mechanical limits.

[dennis]

x2 what matt said.

 

Also glue and screw, and use MDF not plywood like above (plywood has voids in the material). I like to double my speaker plates to 1.5" and use around 3 layers of sound deadening inside the box (not the silver stuff this is reflective) Just think sound quality for a sealed box and a ported/bandpass box for Sound pressure level.

[thisismatt]

x2 what matt said.

 

Also glue and screw, and use MDF not plywood like above (plywood has voids in the material). I like to double my speaker plates to 1.5" and use around 3 layers of sound deadening inside the box (not the silver stuff this is reflective) Just think sound quality for a sealed box and a ported/bandpass box for Sound pressure level.

MDF is the best bang for buck as far as enclosure building goes, plus it is really easy to work with (other than the toxic dust :P ). It'll hold edge screws well, just predrill with a 3/32nds bit, if you don't have a tapered 1/8" bit, and use 1 5/8" or 2" course thread drywall screws. I would also use a countersink and much prefer these bosch tapered bits w/countersinks: here They're kind of pricey for one job, though. Titebond is arguably the best wood glue to use, but even regular elmers wood glue is fine. Gorilla glue is also fine and will foam/expand to fill voids in your joints if you don't make perfect cuts, but it's messier and not water clean-up really. Even though it will fill small joint voids it will be weak in these areas because it basically turns into a foam. There are higher grades of plywood that are technically better than MDF for enclosures, but you'll have to pay 3x-5x as much as MDF to get them and the gains are negligible. For 8" subs your enclosure will be fairly small and likely won't need to double up on MDF anywhere. 3/4" will be fine. If you end up with any large spans/sides, you can easily add bracing - either a piece of 2"-3" wide MDF on edge attached to the panel or on end spanning across the enclosure to another panel. This is cheaper/easier/much lighter than layering sheets and will be very rigid. Doubling up the speaker baffle has other advantages, though, like more screw holding material for big, heavy subs.

[Braden]

you do not have to dick with screws of any sort, screws will cause you a headache and look like shit, i have built ported boxes for 13's that ran 143 db at the headrest with liquid nails and 1.5 inch brad nails, then you can paint the box since there is no screws to hide. My advice do not build a ported box for 2 8 inch subs, look up the manufacturers specs, 99 percent of subs 10 inches and under are recommended for sealed enclosures only. also do not forget to run a bead of the liquid nails on every inside joint to seal out all the air.

here are a few that i have built. and yes oneof those is my SINGLE CAB silverado (talk about building cardboard templates!)

[Braden]

http://mobile.jlaudio.com/support_pages.php?page_id=127

[matwood]

I am and have been an Electronics Installer for a LONG time now. Some of this info is great (thisismatt) and some of this info is himhawww.... haha.

 

Screws are def. unnecessary, use a brad nailer and a sufficient amount of GOOD wood glue.

 

10's, 8's, even 6's can all be ported, without a doubt.

 

I port JL 13TW5's all the time and they are a 13" flat super woofer that is NOT recommended for porting. Just be sure to use the Thiele small parameters and equations that you can definitely find around the net for a ported enclosure.

 

Even a sealed enclosure should be calculated as different amounts of airspace resonate at different frequencies, you should build a box to suit your subs liking either way.

 

MDF is DEFINITELY the wood of choice. Mask up cause the dust will make you congested for a couple days otherwise.

 

If you have any questions at all, dont hesitate to ask me, hell... give me some dimensions and the model of the subs and I will draw a box for you in ACAD.

[dennis]

MDF is the best bang for buck as far as enclosure building goes, plus it is really easy to work with (other than the toxic dust :P ). It'll hold edge screws well, just predrill with a 3/32nds bit, if you don't have a tapered 1/8" bit, and use 1 5/8" or 2" course thread drywall screws. I would also use a countersink and much prefer these bosch tapered bits w/countersinks: here They're kind of pricey for one job, though. Titebond is arguably the best wood glue to use, but even regular elmers wood glue is fine. Gorilla glue is also fine and will foam/expand to fill voids in your joints if you don't make perfect cuts, but it's messier and not water clean-up really. Even though it will fill small joint voids it will be weak in these areas because it basically turns into a foam. There are higher grades of plywood that are technically better than MDF for enclosures, but you'll have to pay 3x-5x as much as MDF to get them and the gains are negligible. For 8" subs your enclosure will be fairly small and likely won't need to double up on MDF anywhere. 3/4" will be fine. If you end up with any large spans/sides, you can easily add bracing - either a piece of 2"-3" wide MDF on edge attached to the panel or on end spanning across the enclosure to another panel. This is cheaper/easier/much lighter than layering sheets and will be very rigid. Doubling up the speaker baffle has other advantages, though, like more screw holding material for big, heavy subs.

 

I always doubled my baffle boards because it decrease box resonance, this is also why I used dynamat in my enclosures too. I won a bunch of IASCA 1 - 100 watt events with a single 15" Image Dynamics IDQ running a 60 watt Rockford Punch amp. I think my SPL would hit 135 on an RTA. Not bad but not great really didnt care a lot about SPL since it wasnt a huge point capture with that particular wattage class.

[thisismatt]

I always doubled my baffle boards because it decrease box resonance, this is also why I used dynamat in my enclosures too. I won a bunch of IASCA 1 - 100 watt events with a single 15" Image Dynamics IDQ running a 60 watt Rockford Punch amp. I think my SPL would hit 135 on an RTA. Not bad but not great really didnt care a lot about SPL since it wasnt a huge point capture with that particular wattage class.

I managed to do 146db @ 38hz on the dash with a termlab meter with my last ported enclosure and my 15" Adire Audio Brahma, but that was on a weee bit more than 100w :lol:. That was this beast:

 

 

I don't see how you're gaining anything if the baffle isn't dimensionally much bigger than the driver(s), which it probably isn't for a couple of 8" drivers that don't need much volume, but of course it's not going to hurt. I just think it's overkill in most typical instances and the same end can be had be a brace from the baffle to the back of the enclosure, or a strip on edge across the face.. Sure, I have my 45lb or so 15" Adire Audio Tumult in a double baffle, but it's 45lbs and down-firing in a large-ish home theater enclosure :P Here's an example of the type of on-edge bracing I'm talking about in my HT enclosure:

 

 

As far as screws vs 18ga brads go, to each his own I guess. Brad nails hold very poorly in mdf...frankly, they hold pretty poorly in almost anything other than a medium/hard wood, especially compared to screws. They provide little to no actual clamping force on the joint (it does help, however, if you pin them at alternating angles instead of straight in). They'll also split MDF as easy as a predrilled screw. And...uhh...you still have a bunch of 18ga holes. Either way you're going to be filling holes and a screw hole isn't much different to fill with bondo than an 18ga hole. If you make good joints you'll never have to caulk anything or screw around with liquid nails, which doesn't even cure very fast and can even take weeks/months to cure, and then it's still a flexible adhesive and it doesn't really penetrate wood grain all that great (haha, as though MDF had any grain ;)).

 

But anyways...I don't bother with much MDF anymore :D

 

[DatDoug]

Rite on! Thanks 4 all the great intel :cool: YYou guys are wicked smahrt! I ended up using 3/4" MDF which is awesome stuff. I am a craftsmen by trade so I have the tools & Know-how to make nice cuts. I srewed the box together & its a sealed enclosure. It sounds pretty good. No huge bass comin out but its good for the gOOn. Prolly just sprayn er bloack & call it good.

 

I angled the back same as the back seat so it would sit tite against

 

[thisismatt]

Looks good. Did you wire them optimally for the amp you're using (eg if they're single coil 4 ohm drivers and your amp can handle a 2 ohm load, did you wire them in parallel to produce a 2 ohm load)?

[izzo]

Wood glue and caulking are key too.

 

I used to work for R/T Enterprises in Kelso, they mfr speaker boxes. I have built many boxes, but its been about 10 years.

 

http://www.rtboxes.com/

[elmerfudpucker]

Rite on! Thanks 4 all the great intel :cool: YYou guys are wicked smahrt! I ended up using 3/4" MDF which is awesome stuff. I am a craftsmen by trade so I have the tools & Know-how to make nice cuts. I srewed the box together & its a sealed enclosure. It sounds pretty good. No huge bass comin out but its good for the gOOn. Prolly just sprayn er bloack & call it good.

 

I angled the back same as the back seat so it would sit tite against

 

 

Far as I can tell the box is clean work but a bit on the large size, most 8" subs do fine in 3/4 to 1 cube of air each. If you get a chance to reduce to depth of your box by half, you would get more boom out of it. That box is about the right size for 12" subs.

[DatDoug]

Looks good. Did you wire them optimally for the amp you're using (eg if they're single coil 4 ohm drivers and your amp can handle a 2 ohm load, did you wire them in parallel to produce a 2 ohm load)?

 

I wired them separately. The amp is an old pile that i found in the kigcab i got the speakers out of. its so worn i can t even tell what it is.

[elmerfudpucker]

I wired them separately. The amp is an old pile that i found in the kigcab i got the speakers out of. its so worn i can t even tell what it is.

 

You get some free time one weekend or if I do, we can meet up and I can help you out with it, I may even have some extras to donate to the cause!

[dennis]

I managed to do 146db @ 38hz on the dash with a termlab meter with my last ported enclosure and my 15" Adire Audio Brahma, but that was on a weee bit more than 100w :lol:. That was this beast:

 

 

 

I don't see how you're gaining anything if the baffle isn't dimensionally much bigger than the driver(s), which it probably isn't for a couple of 8" drivers that don't need much volume, but of course it's not going to hurt. I just think it's overkill in most typical instances and the same end can be had be a brace from the baffle to the back of the enclosure, or a strip on edge across the face.. Sure, I have my 45lb or so 15" Adire Audio Tumult in a double baffle, but it's 45lbs and down-firing in a large-ish home theater enclosure :P Here's an example of the type of on-edge bracing I'm talking about in my HT enclosure:

 

 

 

As far as screws vs 18ga brads go, to each his own I guess. Brad nails hold very poorly in mdf...frankly, they hold pretty poorly in almost anything other than a medium/hard wood, especially compared to screws. They provide little to no actual clamping force on the joint (it does help, however, if you pin them at alternating angles instead of straight in). They'll also split MDF as easy as a predrilled screw. And...uhh...you still have a bunch of 18ga holes. Either way you're going to be filling holes and a screw hole isn't much different to fill with bondo than an 18ga hole. If you make good joints you'll never have to caulk anything or screw around with liquid nails, which doesn't even cure very fast and can even take weeks/months to cure, and then it's still a flexible adhesive and it doesn't really penetrate wood grain all that great (haha, as though MDF had any grain ;)).

 

But anyways...I don't bother with much MDF anymore :D

 

 

Nice enclosure Matt.

 

When I used to do my fiberglass enclosures I would run 1 layer of fleece then two layers of chopped mat, I have even done a few in Kevlar and Carbon fiber. CF and Kevlar are a pain in the ass since it is really hard to get the weave to look really nice especially on some of the many contour enclosures.

 

Oh on that 15 Image dynamic sub I was at one time running a USD aperiodic membrane but it required way too much power to get any decent spl out of that thing. I ran that 15 in a 1.55 cubit ft sealed box and I was running it at 1ohm so I was pulling out 349watts out of my punch but I had to build one hell of a cooling rack for it or it would thermal after 5 min. I also ran USD and Image Dynamic horns up front but didnt like the sound so I started running Focal or Dynaudio. I really never mess with car audio anymore and havent worked in a shop in a long time. Now I just build my own crap but mostly home theater shit like my Focal filled Gemini II enclosures.

[thisismatt]

I wired them separately. The amp is an old pile that i found in the kigcab i got the speakers out of. its so worn i can t even tell what it is.

Ah, well, just some food for thought - if the enclosure is one shared space for both subs (as opposed to divided into two separate volumes), and when your run them separately off their own channels, then you risk having uneven power to the two subs, essentially making the subs fight each other and reducing output. It would be better if you bridged the amp and wired the subs together so they for sure receive equal output signals, or divided the enclosure into two volumes. Who knows, though - bridging a pyle amp might cause it to burst into flames :D

[mklotz70]

I like the fiberglass enclosure Matt. I've done a couple. I still have a bag of thixotropic powder in the shed! :) I'd to the outside in a heavy fleece, then coat the inside with about a 1/2" of resin and thixotropic powder....it was like a frigging rock and a lot easier to do than many layers of mat or cloth. It spreads out like peanut butter. Only needs to be about 1/4" to 3/8 for a kick panel. Saves a ton of time on the sanding and finish work on the outside!! Next time I come across my pics, I'll have to scan them and add them to my PB account. I've done several systems with MDF, but fiberglass is a lot more satisfying!

[elmerfudpucker]

I like the fiberglass enclosure Matt. I've done a couple. I still have a bag of thixotropic powder in the shed! :) I'd to the outside in a heavy fleece, then coat the inside with about a 1/2" of resin and thixotropic powder....it was like a frigging rock and a lot easier to do than many layers of mat or cloth. It spreads out like peanut butter. Only needs to be about 1/4" to 3/8 for a kick panel. Saves a ton of time on the sanding and finish work on the outside!! Next time I come across my pics, I'll have to scan them and add them to my PB account. I've done several systems with MDF, but fiberglass is a lot more satisfying!

 

I have a hard time working with fiberglass, the fumes burns my eyes, even with glasses on. I will only work with it outside.

[dennis]

I have a hard time working with fiberglass, the fumes burns my eyes, even with glasses on. I will only work with it outside.

 

What kind of resin were you using? I always use epoxy, it is quite a bit more expensive but the fumes are very tolerable.

[elmerfudpucker]

What kind of resin were you using? I always use epoxy, it is quite a bit more expensive but the fumes are very tolerable.

 

dont remember the name brand, got it from shucks, you got some name brands or a bit more detail of what I need? I would love to get on the pods for the 720! :D

[dennis]

dont remember the name brand, got it from shucks, you got some name brands or a bit more detail of what I need? I would love to get on the pods for the 720! :D

 

You don't need a particular brand. I used to go to tap plastics and just picked up what I needed for the job. They carry everything you will need there, The closest one they have to you is in Seattle.