Recently I have been considering putting a sub in my Fiero. I have decided that if I do, it will DEFINITELY be going under the dash, no question about that. Are there any tricks to making a box? It looks pretty straight forward but I have never done anything with subs before.

This is the box design I have been considering because it does not look too intrusive room wise and when it's nicely finished anyone this is not a Fiero person will not even know its there.




Would I pretty much buy 1/2in mdf cut to the measurements shown in the diagram and screw/glue it together, or is there more to it then that? When I calculated the cubic feet of space inside it, I came up with .239 is that enough space for an 8" sub? It seems a little small from what I have read, what effects will this have on sound? I am assuming that an 8" round or square sub would work with this box? Any help would be appreciated. Thank you in advance.

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Yeah pretty much cut each peice, glue, screw and then seal the seams with silicone or some other caulk. Get some spray adhesive (high strength is best) and attach the carpet. There are probably some 8's out there that will work in about a 1/4 cubic foot air space. I'd look for one of those. If you went with one that needed .5-1 cubic foot, you'd end up with shallow bass response. Yes 8" round or square should work. One thing to add, get some polly fill (pillow stuffing, you can buy it at Wal-Mart pretty cheaply) probably about 16-32 ounces of it and stuff the box with it before you put the woofer in. This will fool the woofer into thinking it's in a slightly larger box so a 8" needing a .25 min box would work good like that.

Edit to add:

Rockford Fosgate P1S48: .23 sealed
Rockford Fosgate P2D48: .23 sealed
MA Audio MA80QS: .25-.5 sealed

Just a couple of models I found with a quick search.

[This message has been edited by Khw (edited 04-18-2011).]

Mines not the ideal legroom for the passenger but it sounds a million times better than the flater boxes. 80% of the sound from a sub comes from the box so you don't want to cut conners on it, so make sure everything fits prefect. I made mine myself.

http://www.facebook.com/pho...93358&type=1&theater

One thing to consider is the size required i have a 10" woofer that only requires 1 square foot of box to work ideally. It is a dual voice coil woofer requires 2 x 2 channel amps pretty much unlimited power to drive them 2 ohmn stable.

Don't be fooled by size of the woofer my present woofer is 6" 150 watt and sits in the stock box and packs the punch of a modern woofer i dont see myself adding another.

Use 3/4" MDF, rather than 1/2". The 1/2" will provide weaker glue and screw points.

I have that same sub box in my car running a 10" sub that requires lower box volume, but I also stretched the design a bit to make the box larger internally.

To say the 10" will pound you out of the car is an understatement.
If I started over, I'd run an eight inch instead, simply for the space savings.

Remember to remove the thickness of the material when putting a piece 90 degrees perpendicular to another. You don't want the 4" ends to end up being five inches when building.

I actually have a few prototype "DIY" flat kits here at home that I am considering selling and letting others put together for their own identical sub boxes. I have not tested them yet, but they look like they would work OK. I just want to be 100% on them, and won't have time to mess with them for a while. The sub opening is not cut in them yet, which is one of the big issues.

3/4" MDF is awfully heavy stuff to be hanging.
For floor mount that`s fine, but I would go with something a little lighter like 1/2" birch or something along that line.
If you get the glue all the way across the surface of whatever you are glueing you won`t have trouble with the joint failing even if you use 1/2" MDF.
If anything the material will break before the glue joint fails.

quote Originally posted by TXGOOD: 3/4" MDF is awfully heavy stuff to be hanging. For floor mount that`s fine, but I would go with something a little lighter like 1/2" birch or something along that line. If you get the glue all the way across the surface of whatever you are glueing you won`t have trouble with the joint failing even if you use 1/2" MDF. If anything the material will break before the glue joint fails.

But you get resonance with anything other than MDF. There is a reason MDF is the primary material for most sub boxes.

I built a 12" sub box for my Sierra. I used 3/4" MDF.
I used dado joints & construction adhesive to adhere & seal everything. No mechanical fasteners needed!

I agree 3/4 will be a bit heavy to hang.

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86 GT
87 coupe restoration project.

quote Originally posted by zmcdonal: Recently I have been considering putting a sub in my Fiero. I have decided that if I do, it will DEFINITELY be going under the dash, no question about that. Are there any tricks to making a box? It looks pretty straight forward but I have never done anything with subs before. This is the box design I have been considering because it does not look too intrusive room wise and when it's nicely finished anyone this is not a Fiero person will not even know its there. Would I pretty much buy 1/2in mdf cut to the measurements shown in the diagram and screw/glue it together, or is there more to it then that? When I calculated the cubic feet of space inside it, I came up with .239 is that enough space for an 8" sub? It seems a little small from what I have read, what effects will this have on sound? I am assuming that an 8" round or square sub would work with this box? Any help would be appreciated. Thank you in advance.

Hi, This is my sub design and diagram and that picture is of my old yellow car. The box is constructed with 1/2" MDF and volume I calculated is 0.247cf. There are plenty of 8" subs out there now for that and I have found out by experience that if you use one with a little higher spec it won't cause no major difference. An 8" sub as some have mentioned above is plenty for the Fiero if you use a good sub and a good amp. Also you don't need 3/4"MDF at all. The 1/2" is plenty for this application. Personalyy I like Polk and JL subs but like I said any good brand will do the job.
For teh box you just need to plan and cut to get the final dimensions in the diagram. Use glue and screws. Also I sealed the seams with clear sealer. Good luck!

[This message has been edited by Alex4mula (edited 04-18-2011).]

For anything smaller than a 10" sub, 1/2" MDF should be plenty. Maybe 5/8" if you're feeling like you want something heavier. For 10"-12" though, I'd use 3/4" MDF. But you really don't need subwoofers that big in a Fiero. A good quality 6.5" or 8" subwoofer in a properly built enclosure with an appropriate amp, will vibrate the cabin plenty enough.

Use Gorilla Glue on the ends of the MDF where you're going to make sharp corners, and when screwed together and glue is dried up if it seeps out the edges, cut off the excess on the inside, and go around all the corners with some good caulking/sealer.

I just finished Dratt's 6" sub box for his Murci'. I also did a sub box for my Memphis 10" two weeks ago. 1/2" MDF is all that you need. In my box, I am running a shallow mount 10", with a box that measures .73 interior volume. It is nearly as tall as my passenger seat. I needed to put in support bracing to keep the 1/2" MDF from moving, but my point is this..... If you build it structurely sound, you do not need 3/4" MDF. Also, from doing much research on the subject, there is really no use for a ported box in the Fiero. Just not enough space, so stick with enclosed boxes. Seal everything up well, and don't be stingy with the glue. It is also a great idea to predrill your holes for the screws, or use a brad nailer to attach all of the pieces together.

Tony

quote Originally posted by Tony Kania: It is also a great idea to predrill your holes for the screws, or use a brad nailer to attach all of the pieces together. Tony

GAH! I can't beleive I forgot to mention that. You know, when you've built so many, little things like that become second nature and you just don't think about it.

[This message has been edited by Khw (edited 04-18-2011).]

quote Originally posted by Synthesis: But you get resonance with anything other than MDF. There is a reason MDF is the primary material for most sub boxes.

For an enclosure with small pieces, such as the one we're talking about in this thread, the resonant frequency of the panels will be much higher than anything the subwoofer will ever produce. And the hardwood plywood is strong enough to resist forced vibration, due to sound volume. So resonance should not be an issue.

Plus, the 1/2' hardwood plywood will weigh much less than the 3/4" MDF. And if you use the same external dimensions, the enclosure will have more internal volume.

[This message has been edited by Blacktree (edited 04-18-2011).]

I would not use nails in a speaker box. Nails can vibrate loose. Scews are much better fasteners.

As others have said, figure out how much space you have. Then pick a speaker that you like and that can use the space available. Then build the box.

There are three kinds of boxes you can build: band pass, sealed and ported. You don't have the space to build a band pass. Sealed will give a truer base but require more room than a ported box. Ported will be louder. You speaker has to be the correct kind for the type of box you plan to use.

quote Originally posted by Doug85GT: There are three kinds of boxes you can build: band pass, sealed and ported. You don't have the space to build a band pass. Sealed will give a truer base but require more room than a ported box. Ported will be louder. You speaker has to be the correct kind for the type of box you plan to use.

There is actually one more type, although it's very difficult to build and he wouldn't have the room to do it in that area.

Transmission line enclosure.


I've only ever seen it used in a vehicle twice. It's not a common type, but /shrug just for info's sake.

quote Originally posted by Doug85GT: Sealed will give a truer base but require more room than a ported box.

Think you got those size requirements backward. Sealed enclosure will be the smallest you can build, and it will repdroduce the notes the best. A sub that works in either sealed or ported enclosures, tend to require 1.5-2 times as much internal volume for the ported version, that I've seen.

quote Originally posted by dobey: Think you got those size requirements backward. Sealed enclosure will be the smallest you can build, and it will repdroduce the notes the best. A sub that works in either sealed or ported enclosures, tend to require 1.5-2 times as much internal volume for the ported version, that I've seen.

I need to learn to read a little better it seems. I skimmed right over that part .

quote Originally posted by Blacktree: For an enclosure with small pieces, such as the one we're talking about in this thread, the resonant frequency of the panels will be much higher than anything the subwoofer will ever produce. And the hardwood plywood is strong enough to resist forced vibration, due to sound volume. So resonance should not be an issue. Plus, the 1/2' hardwood plywood will weigh much less than the 3/4" MDF. And if you use the same external dimensions, the enclosure will have more internal volume.

So are you saying I should just use 1/2 MDF then, or some other kind of lighter wood?

Interesting information so far, it doesn't sound all that complicated just measure twice cut once kind of thing. Well a friend of mine gave me a 7 or 8 inch square kicker so I don't really need to shop for a sub. I think he said it was a 7 but when I go on there site, there is no such animal so I don't how big of a box it requires, unless it's an 8 and he got the required mounting hole size mixed up because for the 8's its a 7 and a 1/4, they have a minimum requirement of .33 would that be too much for this box even with polyfill? What do you do with the polyfill, it seems like you would want to keep it away from the speaker.

How intrusive is a box like this, it is kind of hard to tell in the pics.

quote Originally posted by zmcdonal: So are you saying I should just use 1/2 MDF then, or some other kind of lighter wood? Interesting information so far, it doesn't sound all that complicated just measure twice cut once kind of thing. Well a friend of mine gave me a 7 or 8 inch square kicker so I don't really need to shop for a sub. I think he said it was a 7 but when I go on there site, there is no such animal so I don't how big of a box it requires, unless it's an 8 and he got the required mounting hole size mixed up because for the 8's its a 7 and a 1/4, they have a minimum requirement of .33 would that be too much for this box even with polyfill? What do you do with the polyfill, it seems like you would want to keep it away from the speaker. How intrusive is a box like this, it is kind of hard to tell in the pics.

That should be okay with the polyfill in there. You just stuff the box with it, when you put the woofer in the woofer basket will keep it from interfearing with the cone travel.

And yes, it is probably the 8" woofer. The overall dimension should be about 8" with the cone are dimension being about 7".

[This message has been edited by Khw (edited 04-18-2011).]

quote Originally posted by Khw: That should be okay with the polyfill in there. You just stuff the box with it, when you put the woofer in the woofer basket will keep it from interfearing with the cone travel. And yes, it is probably the 8" woofer. The overall dimension should be about 8" with the cone are dimension being about 7".

Ok, not exactly sure what a woofer basket is though?

quote Originally posted by zmcdonal: Ok, not exactly sure what a woofer basket is though?

Okay, the basket is the metal thing around the back side of the woofer that the magnet is mounted to and the woofer cone/surround/voiecoil/spyder mount in.

In this picture it's the chrome metal.



Basically that structure will push against the poly fill and hold it away from the woofer cone.

Oh ok cool. I have always thought my stereo could use just a little more bass, but I never wanted anything crazy or a huge audio install project. This under dash box shouldn't be too bad for a first project I wouldn't think.

quote Originally posted by zmcdonal: Oh ok cool. I have always thought my stereo could use just a little more bass, but I never wanted anything crazy or a huge audio install project. This under dash box shouldn't be too bad for a first project I wouldn't think.

Actually, yeah it should workout pretty good. I've been considering getting some expansion foam and seeing how much room is actually usable up in there for a fiberglass enclosure. I've seen many done with tubes, the stock plastic enclosure and then the one you posted a picture of, but I wonder how much airspace could be gained with a enclosure that could more thuroughly fill the space.

This may be a dumb question, but what would be a good place to shop for MDF? Is that something a local home improvement store stocks, and how much should I expect to pay, I'm assuming for probably a 4x8 sheet because they probably don't sell it in smaller sheets.

quote Originally posted by zmcdonal: This may be a dumb question, but what would be a good place to shop for MDF? Is that something a local home improvement store stocks, and how much should I expect to pay, I'm assuming for probably a 4x8 sheet because they probably don't sell it in smaller sheets.

Check Home Depot or Lowe's somewhere like that. Yes most likely a 4X8 sheet although some places sell them cut down into a 4X4 or a 2X4 rip. A sheet will be about $15-$20 roughly.

[This message has been edited by Khw (edited 04-18-2011).]

quote Originally posted by zmcdonal: Well a friend of mine gave me a 7 or 8 inch square kicker so I don't really need to shop for a sub.

You might want to shop for a sub anyway. And a circular one. The square kickers aren't really designed to make quality sound. They're made to make loud bass for db competition, and are better in ported boxes. Circular speakers will reproduce sounds more correctly than speakers of other shapes.

quote Originally posted by dobey: You might want to shop for a sub anyway. And a circular one. The square kickers aren't really designed to make quality sound. They're made to make loud bass for db competition, and are better in ported boxes. Circular speakers will reproduce sounds more correctly than speakers of other shapes.

Yeah, I was hoping for more of a budget build on this, that all it will cost is the box, and some time. Maybe some where down the line if I have extra change to throw around I could try a different sub.

Kind of kicking myself right now because last year I gave a family friend 2 8" round kickers that were mounted in a box in the back of my dads gta when he bought it. Would one if those been a more suitable choice? So the square kicker may end up not sounding too good? It might be worth a shot anyway, if I don't like it I'm only out some time and the $$ for the MDF.

I personally would not use MDF less than 3/4" thick. MDF came to be used in speaker enclosures because it's relatively dense, which makes the panels heavy, which helps to dampen vibration. But MDF has less structural strength than normal lumber or plywood. So using thin pieces of MDF is usually not a good idea.

That's why I suggested 1/2" hardwood plywood. It's very strong (stronger than the generic construction-grade plywood, and better looking), and can be bought in 2x4 or 4x4 foot pieces at places like Lowes and Home Depot.

That said, you can probably get away with 1/2" MDF on a small, low-powered speaker setup. But since the hardwood plywood costs about the same, and is stronger, why bother?

[This message has been edited by Blacktree (edited 04-19-2011).]

quote Originally posted by Blacktree: I personally would not use MDF less than 3/4" thick. MDF came to be used in speaker enclosures because it's relatively dense, which makes the panels heavy, which helps to dampen vibration. But MDF has less structural strength than normal lumber or plywood. So using thin pieces of MDF is usually not a good idea. That's why I suggested 1/2" hardwood plywood. It's very strong (stronger than the generic construction-grade plywood, and better looking), and can be bought in 2x4 or 4x4 foot pieces at places like Lowes and Home Depot. That said, you can probably get away with 1/2" MDF on a small, low-powered speaker setup. But since the hardwood plywood costs about the same, and is stronger, why bother?

That's cool. I'm not doubting your knowledge Blacktree but just wondering if everyone else agrees that hardwood plywood would be a good choice? It seems like it would be difficult to screw into the edge of 1/2 plywood or is the whole thing supposed to be glued together? Any tricks or secrets?

For 1/2" thick panels, I wouldn't bother with mechanical fasteners (i.e. nails or screws). If you have a router, you can notch the edges of the panels so they interlock, then glue them. Use a high-quality wood glue, and clamp the pieces together while the glue dries.

If you don't have a router, or don't trust your woodworking skills enough to make the panels interlock, you can instead use strips of wood inside the corners. The idea is to assemble the box like you would if you were going to use screws to hold it together. But instead of using screws, you glue the pieces together. Then you cut thin strips of wood (or use strips of edge molding) to reinforce the corners. You glue the strips of wood to the interior of the box, so they're hidden from sight.

I've used both methods mentioned above, with good results.

quote Originally posted by zmcdonal: That's cool. I'm not doubting your knowledge Blacktree but just wondering if everyone else agrees that hardwood plywood would be a good choice? It seems like it would be difficult to screw into the edge of 1/2 plywood or is the whole thing supposed to be glued together? Any tricks or secrets?

Use glue and screws to hold the box together. You will need to predrill and countersink the holes no matter which material you use to prevent it from splitting.

1/2" MDF and screws are more than fine. I had my box for about 8 years with a good 200W amp and no issues. Now something to caution is the size of the sub magnet. If you get a high power sub with a huge magnet it will not fit the box.

quote [B]Originally posted by zmcdonal:[/

I just noticed that the mounting depth for the sub that I have is 4 3/4, is there any way that could work with this box design? Like what if I mounted it as far back towards the taller part of the box as possible, because the magnet has to be smaller then the cone area, would that be ok as long as it clears the 4" part?

Could the sub be mounted on the 7.5 by 8 side of the box and still work being mounted vertically? It would be pointing towards the front, would that be a bad thing?

I was just really hoping to be able to use the sub that I already have, at first I thought it would be alright and just add a layer of 1/2 mdf where the speaker is mounted to give it room, but then I forgot that those were outside dimensions of the box. Any ideas??

[This message has been edited by zmcdonal (edited 04-21-2011).]

I bought a Aus Fiero Sub box about 5-6 years ago and i am wanting to sell it. I was going to list in the mall tomorrow for sale, its the center console sub box that he stopped making a long time ago. Daniel

quote Originally posted by daniel87fierogt: I bought a Aus Fiero Sub box about 5-6 years ago and i am wanting to sell it. I was going to list in the mall tomorrow for sale, its the center console sub box that he stopped making a long time ago. Daniel

Thanks for posting another solution. I would really like to keep any stereo components as hidden as possible though, don't want to give anyone a reason to break-in. That's why I thought this under dash enclosure was perfect, if there's a way that I can make it work.

quote Originally posted by zmcdonal: I just noticed that the mounting depth for the sub that I have is 4 3/4, is there any way that could work with this box design? Like what if I mounted it as far back towards the taller part of the box as possible, because the magnet has to be smaller then the cone area, would that be ok as long as it clears the 4" part? Could the sub be mounted on the 7.5 by 8 side of the box and still work being mounted vertically? It would be pointing towards the front, would that be a bad thing? I was just really hoping to be able to use the sub that I already have, at first I thought it would be alright and just add a layer of 1/2 mdf where the speaker is mounted to give it room, but then I forgot that those were outside dimensions of the box. Any ideas??

I doubt you will be able to put the woofer in facing the firewall. What I would do, personally, is use a 3/4" spacer between the sub box and the woofer made out of MDF, that is if I didn't get a different woofer. That would increase your depth so it should fit.

quote Originally posted by Khw: I doubt you will be able to put the woofer in facing the firewall. What I would do, personally, is use a 3/4" spacer between the sub box and the woofer made out of MDF, that is if I didn't get a different woofer. That would increase your depth so it should fit.

Yeah I was thinking along those lines. But wouldnt it have to be more then a 3/4 inch spacer because you have to subtract 1/2 for the thickness of the wood on the top side right? Because a 3/4 piece would only give it 4 1/4 right?

I would also say 3/4, not 1/2. people always under estimate the pressure inside a sub box. 1/2 will flex and resonate weird. For real high powered stuff its common to double up and have 1.5 inch baffles. You wouldn't need that though...

quote Originally posted by TommyRocker: I would also say 3/4, not 1/2. people always under estimate the pressure inside a sub box. 1/2 will flex and resonate weird. For real high powered stuff its common to double up and have 1.5 inch baffles. You wouldn't need that though...

The largest side on the box is going to be 8" x 8.5". Go cut a 1/2" peice of MDF that size and try to flex it.