Newb with virgin build question.

kmplsv

Member
2011-01-22 10:07 pm
I'm a complete DIY audio newb and I'm trying to start tackling my first project. About 7 or so years ago I purchased a Dayton Audio SD315-88 12" subwoofer and a WF-100K plate amplifier. They sat new in the box and collected dust until now. I also have a pair of BIC America DV62si Bookshelf Speakers that are undergoing a crossover modification by GR Research. The speakers are hooked up to an Onkyo TX-SR606 receiver.

I want to build out a box for this subwoofer with some level of competence that will allow it to play nicely with my speakers. This setup is going to be for listening to music. Sources will be a turntable and a PC computer. I realize that all of the equipment listed is pretty much budget gear, but you have to start somewhere. I'm aware of programs like WinISD, Boxnotes, etc, but I'm pretty overwhelmed. Will the plate amp I mentioned even be enough to power the sub? Will it be an issue if the speakers are powered by the receiver but the sub is powered by the plate amp? Should I just say screw it and get a box from Parts Express and call it good?

Where should I start?
 

adason

Member
Paid Member
2004-11-10 8:31 pm
Maryland
It all sounds pretty doable.
when it comes to all your questions, most of the answers are 'yes', or it depends.
Plate amp will have no problem powering you woofer as sub, as long as you stay with reasonable volume.
Yes, you can use received speaker level to power it all, sub will only 'sniff' the signal, no problem there. I can not find any info on that plate amp, must be old. It would be good if it can accept speaker level and line level signal, but if not, its no problem to convert speaker signal to line with one resistor.
Bookshelf speakers with sub can sound decent, assuming all is correctly executed. I would even insert cap to filter low frequencies to the bookshelf to limit the midbass excursion, and thus lower the distortion. But that is minor thing.
Good luck!
 
This is great! Let’s get rolling.

It looks like you have a driver rated for 120W with a dual 8 ohm voice coil, specs that appear to be for 4 ohm (parallel) wiring, and a plate amp rated for 115W into 4 ohms. Seems like a very reasonable starting point, no reason to second guess it.

Start by plugging the parameters in the speaker driver’s datasheet into a box builder. I use

Speakerbuilder Pro 2.0

I went ahead and ran some simulations. Looks like a sealed box of 74 liters gives a -3db of ~50hz, -10 of ~30. That’s plenty to match with book shelves for music and it’s exactly what I’d build.

A ported box would go deeper without being much bigger but now you have get the tuning just right and worry about over excursion at high volumes. Not worth it IMHO given what you’ve told us. Sealed is just easier to get right.

Generally speaking dimensions and box ratios are less critical in sub woofers because resonances are far above the frequencies being reproduced. You could get some thick plywood and build any sort of rectangular prism with the intended internal volume (add, say, 10% to account for speaker) with some polyester fluff and get good results.

Others may offer other opinions. I suggest you keep it simple and get started as soon as possible. You’ll be happy when it’s done.


Brian
 
VB = 70.3 L, FB = 24.8 Hz
In a BR you need 320W amp, 4 ohms for Max. excursion. With a similar vol. sealed you need less than 50W. The bass-reflex takes advantage of the lower end but the small Bic speakers you have probably work good with a sealed sub and higher F3 or rolloff.
 

kmplsv

Member
2011-01-22 10:07 pm
Thank you for the help so far. I really do have a lot to learn. What do VB, FB, and BR mean? I've never even done any simple soldering, so that'll be a learning process too when I'm building this box. I don't know where to start with that either. How do you guys usually mock up your boxes? Use a calculator for the dimensions and then use something like Google SketchUp?
 
Thank you for the help so far. I really do have a lot to learn. What do VB, FB, and BR mean? I've never even done any simple soldering, so that'll be a learning process too when I'm building this box. I don't know where to start with that either. How do you guys usually mock up your boxes? Use a calculator for the dimensions and then use something like Google SketchUp?

I don't model mine up. Remember that you are targeting a certain internal volume and that the box dimensions are not critical in a sub woofer. For a book shelf speaker you need to think about ratios and not having equal dimensions or you may reinforce frequencies that you don't want to.

I'd think of it this way:

You have a 12" speaker, so one side of your box needs to be at least big enough in both directions for a 12" circle. Let's say is 15" square. The internal volume with be 15" squared minus the thickness of you plywood and multiplied by the internal depth of the box. If you are using 3/4 ply wood then subtract off 1.5" in each direction. So, 13.5" squared is ~182 in2. 1 liter is ~61 cubic inches so 70 liters is about 4250 in3. 4250 divided by 182 is 23.4 inches. If you made a wooden box that was 15x15x24" you're be in the right ball park. 24 is a bit long so maybe do an 18" cube or thereabouts.

If that made you nauseous then Parts Express sells pre-made sub woofer boxes. They have a two cubic foot with a 12" cutout (Double check the dimensions though!) and a three cubic foot that would need a speaker cutout in it. Two is a little small and three is a little big but they might reduce risk on the fabrication side of things if you aren't very handy.

Denovo Audio Knock-Down MDF 3.0 cu. ft. Cubic Foot Subwoofer Cabinet

Denovo Audio Knock-Down MDF 2.0 cu. ft. Subwoofer Cabinet for Dayton Audio 12" Ultimax Subwoofer


Hope that helps. Your main goal should be finishing.

Brian