Ratshack Budget Subwoofer

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Hi all I thought I'd do little write up of my budget HT sub.

The drivers are the old Ratshack 15"s I picked a pair up for 35 off ebay.

I borrowed a PE tester and these arent anywhere near what the specs from RS say.

RS claimed a qts of .81 or something outlandish these are barely .40
maybe it's from use I dont know.

I plotted a sealed box with the .40 qts and a VAS of 12 and got a 4.5 cu ft box with an f3 of 35hz.

Not earth shakingly low but more than enough for HT.

The amp was scavenged from a 150w 12" KLH sub cost was 20 dollars used.

The rest was wood 3/4 Baltic Birch about 2 sheets of 4x3 ft .
Cost was about 30 including glue and screws.

The bafle is double thick 3/4 Birch. Sides are 1" MDF(The MDF came free hehe from old speaker racks.)

Total cost so far is well under 90 dollars.

Here a construction pic

Thats not the baffle thats the internal brace


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It's sealed.No drone wired in parallel they are 8ohm drivers.

Thanks for the critique,actually it's not finished literally.

The baffle and top you are seeing are raw wood.

And I still need to countersink the woofers(I don't own a router and my 8" 2ways in another thread I did with a razor and chisel definitely not an easy task doing 2 15s.) and make a grill.

Sounds very good not too boomy with a lot of low bass for only a 150w amp.

I could compare this to any sub I've seen or heard for under 700 and they wouldnt hold a candle to this.

Sounds very accurate too listening to some old JP recordings where the bass is very subtle it does extremely well.

I happen to have four of those drivers in my garage and have been wondering what the best sub for HT would be for a long time.
Would you mind posting the measurements you made, please?

In all honesty, I think the subs should play lower for HT. But that's not important if you're happy with them the way they sound now.

Here's what I have on the 15" Polycone foam surround RS woofer

150 watts rms

Qes .43

.Qts .40

VAS 11.96 Cu ft

SPL 91.2 1w@1m

Xmax 4.8mm

FS 24hz

8ohms nominal impedance

DC 6.2ohms impedance

I can't find the model numer its 40-1XXXXX lol I had it somewhere

Not as bad as I was originally led these drivers to be.I had passed on pair on clearance years ago.

anyway that should be enough to design a box it was for me.
Hmm, it should be stamped on the back of the motor, but with its inverted DC not like any RS woofer I've bought, though spec wise it 'reads' like a 40-1035.

I'm curious why you spaced it up off the floor and didn't configure it as a bipole since it's not turned around, firing into the corner. Also, while 4.5 ft^3 sealed looks fine for a corner loaded single driver, for two it's way under-damped.

Anyway, thanks for sharing, I really enjoyed embarrassing relatively expensive consumer systems with my 'el cheapo' RS loaded designs way back when.

40-1035 it is.

Actually it plots rather well a 4.5 cu box (I suspect the box is 4.8 but..)with two drivers on 2 different softwares.

As far as being 3db down at 35hz is not bad being in a corner believe me I put it in the middle of the room and then the corner it was a huge difference.And having 2 drivers still give me a 3db boost in spl.

As far bi-pole Ive had bi-pole and di-pole in this case it was a matter of practicality it would have been much harder to do another way .(Don't ask.)

Oh as far as spacing,well I was never a big coupler no spikes always rubber and in this case decided see how far I could take it with isolation .

And in the real world sounds and feels good too!
Interesting! All I've used had regular convex DCs.

Well, 4.5 ft^3 is a ~T/S max flat alignment, so two in ~ the same Vb will be a bit too under-damped IMO, but if it sounds good in-room, then that's all that really matters.

Yes, I agreed with you, ~35 Hz is OK in a corner for most music and movies, though for folks with the space for a largish cab, a pair of these can do pipe organ symphonies loud enough to make you think you're in a big church.

OK, fair enough. FWIW, in my own spacing experiments I had good luck spacing them so that the center point between the two drivers would be either at the midpoint null or at the 0.618 golden ratio or 0.46 point from the floor depending on the room and desired response.

Sorry for the late response and thank you for sharing the details.

I have not seen the inverted dust caps on these drivers either.
But mine are the 40-1301 Like most people know them.
Maybe your drivers were limited editions?

Still pondering on what sub to build for these four RS's.:(
Four? Manifold IB if you can. FWIW I loaded them in 9.5 ft^3/16 Hz MLTLs, though four would consume a lot of materials and listening room 'real estate'. Maybe Linkwitz transformed small boxes is the most practical overall, though power handling would drop to maybe 12-15% since these aren't exactly heavy duty drivers.

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