DIY subs...... with car drivers....

[Drewbert]

Ok..... hear my out. I was looking around for some wood in my shed, and I found my old car stereo stuff.... Phoenix Gold cross over and base cube... and my Rockford Fosgate DVC 15... :B 2000 peak and 1000 RMS.... I drove it with 800 all day long ;x(
So because they are not really doing anything I want to incorportate it in my HT. I know the crossover is fine to use... and the sub would sound great with 500 watts.... but I can go 4 ohm and use 1000 :T
But my question is.... Can I get away with a smaller box? 2 or 2.5 cubes?
Im sure the smaller box will affect the subs ability to go low... wonder if it will matter that much?
And hate sealed boxes....IMO slower and weaker response... but I know for a ported box its better to go larger.

So what do you think?
Its like Christmas all over again over here :B

[cjd]

Problem with car subs inside, which are made worse with a small box: they depend on cabin gain to have anything below 40 or 50Hz often.

Ported, with the right driver it will extend low response and give it a lot more presence, yadda yadda. Sealed is not slower, though. With the right driver, sealed can sound SOOOO much better. The extreme end here is the IB.

What you really need is to design a box around the T/S parameters like most of us here do. Got that info for these drivers?

C

[Drewbert]

No

and IB?

[ThomasW]

We live in a bit of a different world here....

1)saying 2000 watt speaker is like saying 2000hp tires, it really doesn't make any sense.

2)the alignment of the box has no relationship to the 'speed' of the sound coming out of it.

3)Like Chris said if you have the T/S parameters of the driver it's possible to design a box for it.

4)generally speaking drivers designed for car audio are less than optimal for home audio, however there are a few exceptions.

[Drewbert]

Thomas, I meant speed as in response time.... IMO it seems slower and a little less responsive...
I figured Id give it a shot as its sitting around collecting dust.....

[ThomasW]

Once again if you have the T/S parameters (at least the Fs of the drivers) it's certainly no big deal to design a box, either ported or sealed.

[cjd]

Have you tried Google? If you have the speaker model number, I bet you can find someone out there that's posted T-S specs for it.

Or, if you live near someone that has a testing rig, they *could* run the specs for you.

C

[Drewbert]

Finally I found it....

4 ohm x2
Fs 20 hz
Qts .35
xmax in MM 13.5
sensativity 89Db
and the enclosure volume 2.5 ft both sealed and vented.
Here is the manual, 2215 is my sub

And can I get away with using the BASH 500w amp?

[AndrewM]

When Rockford recommends a 2.5cu/ft enclosure, they're talking about for a car (cabin gain in a vehicle let's you "cheat" when building subs). The spec sheet doesn't have all the T/S specs, but doing a little guestimating for those and you're going to need a MASSIVE enclosure for those drivers. I get around 9cu/ft for a low Q sealed alignment (with response that drops off in the 40Hz range). And around 11-12cu/ft for a vented enclosure tuned in the low 20's, but you're still nearly 10db down at 20Hz.

These don't sound like very good subs for home use, there are other options out there that will give better performance without the need for fridge sized enclosures.

Andrew

[Drewbert]

damn no fridge size box......
thanks.
and amps Im looking at the EP1500 or 2500....

[AndrewM]

I'd decide on a driver and alignment before just getting an amp, you may go in a direction where you don't need kilowatts of power. To give some examples, your Rockford subs in those super-sized enclosures will run past their x-max limits with less than 500 watts of power, pumping 2500W to it offers no benefits.

There's a program out there called Unibox (if you have MS Excel) that will allow you to model a driver/enclosure and all of these other things. If you don't have Excel you should be able to find WinISD which is arguably not as accurate, but is also free.

Andrew

[Dennis H]

That driver looks fine to me with parms much like a good 15" home driver -- Fs 20, Qts .35, Vas 260 l. For a small box, 2.5 cu.ft. sealed with some stuffing works out about Q=.7 and F3 around 40Hz. Then it would be easy to EQ the lowest octave. You'd need to go quite a bit bigger for a good ported alignment but I still don't get a box nearly as big as Andrew's - maybe 7 cu.ft.

[Drewbert]

Im going to make a 2.5 cu ft and use the EP1500... least thats what my plans are for today.... lol

Thanks guys

[AndrewM]

Even in WinISD I get 9cu/ft for a .507Qtc alignment, and that only gives an F3 of 46Hz and F10 of 20Hz.

In 2.5cu/ft it's around .74Qtc with an F3 of 43Hz and F10 of 25Hz

Andrew

[Dennis H]

Even in WinISD I get 9cu/ft for a .507Qtc alignment, and that only gives an F3 of 46Hz and F10 of 20Hz.

In 2.5cu/ft it's around .74Qtc with an F3 of 43Hz and F10 of 25Hz

Andrew

Either one will need EQ -- it's just the nature of sealed boxes. Adding stuffing will drop the Q of the 2.5' box a bit so a simple shelving filter will do the trick without a fancy Linkwitz transform. Or with a bit more effort, a BFD can handle the EQ well enough. The T/S parameters of this driver are actually a bit better for a small box than the old Tempest -- lower Qts and smaller Vas.

Big boxes are nice if you have the room but, if you don't, small boxes can be made to work pretty well.

[Drewbert]

So Im thinking for the money.... it will work great.
Add the amp, BFD and some insulation and call it a day. Sound good to you?
Guys thanks for the help on this!

[cjd]

Build it right and you could add a Tumult or something down the road.

C

[Drewbert]

Build it right and you could add a Tumult or something down the road.

C

LOL true and thats an expensive upgrade.... :E
34mm excursion :T

[Drewbert]

I have been crunching numbers for the box to see what I can live with. seems that 3.5 cubes is something I can stand... would that be a lot better than the 2.5?

[Dennis H]

Bigger is always better for SQ with sealed boxes, up to the ultimate of an IB which is just a really huge sealed box. Remember to subtract the volume of the driver and the bracing when you're figuring net volume.

[Marzen]

So Im thinking for the money.... it will work great.
Add the amp, BFD and some insulation and call it a day.

That's the approach I took. I found a pair of Rockford 10" subs while cleaning my basement & wanted to build a low cost HT sub, quickly. I knew I'd make mistakes on my 1st project, so why invest in a lot expensive components when I'm not sure what I really need? I bought an amp, spike feet, & laminate for around $200. Is it great? No, but it was a blast to design & build. Surprisingly it does sound better than the more expensive ones my friends bought from the big box stores. I recently bought a Rane PE17 to tame my room response. As mentioned above it is large at over 4 cu/ft. You can see it here http://akins.no-ip.info/

[Drewbert]

Sweet! Like mentioned above.... if I do it right I can always change drivers.
Looks good, did you use screws or just glue?

Could one get away with using finishing nails and glue? That MDF cracks so easily. Even with pilot holes....

[Brian Bunge]

I use wood glue and 18 gauge finishing nails all the time with no trouble (as long as you shoot the nails in straight!). It sure helps with quick assemble of the enclosure.

[Marzen]

Looks good, did you use screws or just glue?

Could one get away with using finishing nails and glue? That MDF cracks so easily. Even with pilot holes....

It was glued and screwed with #6 x 1-1/2". Some notes on screws 'tho - I use a bitex drill bit for pilot holes/counter sink. Then drill the countersink hole oversized for the screw threads. This keeps the threads from engaging the outside piece. You only want the threads to bite into the inside piece. Then I re-drill the inside piece pilot hole to the actual diameter of the screw body & depth. You can download a reference sheet like this one off the web: http://www.aaronswoodscrews.com/freetable.htm
Assuming you're using 3/4" MDF (I haven't found 1" in my area), your pilot hole would be 6/16 on center from the edge, properly drilled & countersunk, you shouldn't have any problems with crushing or break out. Remember, you don't have to torque it down really tight, snug is fine. If you spread the glue on both edges, it will do the work. If you had clamps, you wouldn't even need the screws.

Probst!
Marz