I finally have had some time to finish up my fiberglass work for a sub box. I only need to attach the MDF top to the box and I'm done. When I taped things off and built up some cardboard walls in the trunk I made things a little bit bigger here and there not knowing how thick the fiberglass walls would end up and things like that. I estimated with a bag of packing peanuts.
My result is a sealed box for my Boston 10.5 which measures 0.6 cubic feet by measuring how much water it holds. Design calls for 0.5 cubic feet. I know I can add something like wood blocks to take up 0.1 cubic feet but what should I expect it to sound like at 0.6 cubic feet? Which way will the system Q be effected by an extra 0.1 cubic feet?

thanks!

 

Did you take into account how much volume your sub will displace once it's in the enclosure? A 10" will take up about .1 cu/ft of space. And even if 0.6 is your final number, that extra .1 won't make any audible difference IMO.

 

Keep in mind most sub manufactures list the minimum airspace in the specs. In many cases...it's by no means the best sounding airspace. Usually in a sealed box, bigger is better for extension and flatter response(less boomy sound). THe trade off being slightly less power handling and a bit less peak spl.

All that being said...0.1 oversized will not make much difference.

I'd say your good to go.

 

I assumed one thing on the speaker basket. BA recommended 0.5ft3 and then listed a box size that would net 0.525ft3 internal volume. I assumed they were taking speaker basket into account so I'm not really sure on that one now. What I did do is figured out how much my MDF spacer rings would take up and added their number and mine to get 0.545ft3. Then the actual box ended up 0.107ft3 larger than that.
I've talked to a guy at BA becuase the overall system Q was listed at 0.95! in the owners manual and he assured me that I can't go by that one number on paper. With the transfer function of the car and everything else that effects car audio that their recommendations are made by extensive in car listening and if I go by the owners manual I'll be happy.
Sounds like I may have ended up with the recommended size or just a little bigger. When I think about it, it seems pretty small to have a basket take up only 0.025ft3. I'll just plan on leaving it the way it ended up and now hope it is a little big since I don't want it boomy.
My amp should be here Wed. and hopefully I can make a quick post soon on how everything turned out.

 

Where's your pics BJ?

 

Ah, they are still on my hard drive. I thought I would wait until the box is in the car and my new amp comes in. I've got to get them organized to present them. I've got hundreds so I've got to pick them out and host them and post them! The weather still looks good around here this week but I am behind at work (11hr days) so something may give. Amp should be here Wed. and I already had another old amp in there and my old Bazooka temporarily for a couple of days so it shouldn't take much work I hope.

 

When manufactures specify enclosure volume, it's always going to be usable air space. This air space will never include the air volume taken up by the rear of the sub. If the manufacture calls for 0.75 cubic feet and the sub displaces 0.25, you must build a box with 1.0 cu feet of air space.

 

Actually, Boston Acoustics states their airspace including driver displacement. If they say .5 cubic feet, you should built it .5 cubic feet. In this application .1 cubic feet is so minimal it should not make a difference.

 

This is the impression I got from BA when I talked to them about system Q. He basically said build a 0.5ft3 enclosure and you will be great. They take everything into consideration for their box size.
I forgot to put the gaskets in last time I test fit the box and now the grille is a little high to clear the factory trim. I've checked and checked and believe that I can shave 0.2" off the height of the box and be just right plus have the 1/2" air space behind the driver for cooling that they recommend. It's getting down to splitting hairs now I've got the space under the driver except for one corner where the floor starts to ramp up. 0.2-0.25" is max space I've got left!
I'll be glad when it's done. Now I will be just under 0.6ft3 but am not going to go to the trouble of measuring it again. I trust now that I will be OK. Thanks for the advice.
Remember to test fit your stuff fully assembled! I just put the trim back in with the box like this then once again with the mounting ring and grille in...

Adding both gaskets to seal the driver adds a lot of depth. They both measure 0.2" thick. Even when they compress I bet I'll have close to 0.2" total to deal with. Cutting the box height should get me back. I guess another way out might be to use silicone instead of the BA gaskets but that would make it more difficult to take apart.

 

Leave the box alone - no fill.

I get way better sound quality out of my 10.5 subs in a box 0.6-0.65 cu-ft. Much better low end. 0.5 cu-ft box will hit harder but doesn't have the SQ of the larger box. I also put about 30-50% poly-fill in my boxes too.

 

I spent a long time last night with my fit problem. There were a couple of ways out theoretically but the way I cut the spacer rings I had to fix it by cutting down the height of the fiberglass tub. If I cut down into the rings more I would have reached a spot where I would be cutting them apart from each other if that makes sense. They are not the same diameter. There are definately a couple of things I could have done beter but it turned out in the end. As a result of sanding down the top edge I am left with a pretty level plane to attach the MDF to now. This is definately a tough project to get right but it will be worth it.
I was wondering if I would have better luck with the finished product if I run a bead of silicone around the f.glass/MDF joint before I start laying glass accross that gap. I thought it would help seal it better. Any opinions??

 

Shouldn't matter much. If you fiberglass the joint properly it will be more then adequete.