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[nathan Hulse]

I have just purchased from ebay 2 ramsa sub cabs. One of the speakers is blown, so I'm just gonna replace both drivers in each cab. These aren't the largest or ideal cabs for subs, but the guy that runs the band wont permit anything larger, even though he's not paying. (He's used to 50w vox pa's from the early 60's- it worked then so why all the huge speakers now).

My question is, will LAB12 drivers work. I quickly worked out the volume to be ~42lts which is lower than the recommended for a ported cab. Also if they would work, the other thing I was concerned with, is the amount the speaker moves. Would the speaker grill restrict it? I think the distance from were the speaker mounts to the cab to the grill is 2cm. I'll probably be running the cabs (2) of one channel of a QSC PLX 2502, which has a 33hz HPF, in addition to a DBX drive rack for band pass processing.


Picture of one speaker.

I look forward to your input and responses. Any more info required I'll be happy to supply. Also note, we normally only use our own PA for smaller venues, most larger venues it's supplied. We play early 60's music and don't need huge amounts of bottom end, just enough to take away from the tops and a little extra bottom end warmth.

[Silas Pradetto]

Not even close to the right woofer for that cab.

[nathan Hulse]

Fair enough, what would you recommend. Please note I'm in UK and some US products are difficult to get here. The frequency response of the cab with the original speaker is published as 35hz-150hz, if that helps. There is no internal crossover or band pass, it would all be done with external processing.

[Mike Smith]

Nathan, try an Eminence Definimax 4012HO, a B&C 12PS100, or any number of other similar 4" voice coil pro twelves from Beyma, Faital, 18 Sound, etc. Target parameters: driver SPL will be 93 to 97 dB 1W/1m, Fs below 45 Hz, xmax around 6 to 10mm, and a Qts below 0.30.

You will not end up with a subwoofer in the truest sense of the word but you will have a little thump down to around 45 or 50 Hz (if you have some decent power available) and give your top boxes some relief.

Keep in mind I'm making some very general recommendations! You will definitely want to look at specifics, like matching a particular driver's attributes and parameters to your box volume and port size. Other people on this forum (or dedicated speaker-building forums) can help you with that.

[nathan Hulse]

Thats great Mike, thanks for taking the time to reply. I'm better equipped with information now, to have a better idea of what to look for in a replacement for this cab (and other). Just a shame I'm trying to squeeze a pint out of a half pint glass.

[Mike Smith]

There's no problem trying to squeeze a pint out of a half pint glass -- unless you are expecting to get a barrel's worth! Good luck with your project.

[Art Welter]

nathan Hulse wrote on Thu, 25 March 2010 12:01

Thats great Mike, thanks for taking the time to reply. I'm better equipped with information now, to have a better idea of what to look for in a replacement for this cab (and other). Just a shame I'm trying to squeeze a pint out of a half pint glass.

I agree with Mike as far as replacement, but the original speaker works really well in that box.
I would check into reconing it, rather than replacing it.

[Art Welter]

Silas Pradetto wrote on Thu, 25 March 2010 09:30

Not even close to the right woofer for that cab.

Actually, Labs work pretty well in small cabs, tuned low enough.
The very long Xmax would require a grill standoff.

I still would go for a recone or a more similar cone to the original, as the alignment below would require longer ports than the Ramsa cab, but the size is not far off.
42 liters is 1.48 cubic feet.



Art Welter

[Silas Pradetto]

If it's limited to 113dB acoustic power, then I think he's going to need a bit more sensitivity to hear the sub at all. Even with a pair, 119dB is pretty much not even going to be heard when run with any decent mains plus guitar amps, drums, etc.

[Rory Buszka]

Actually, given the fact that the cab is essentially tupperware, I'd advise pairing it with a lightweight driver with a neodymium motor structure, like the Eminence Kappalite 3012LF. While it's unlikely that the OP will be filling auditoria with the sound from this box, pairing it with a lightweight driver would make it a convenient little thumper for bar band applications. The Kappalite has 9mm of linear Xmax, so it'll most likely have more grunt than the original driver. Of course, loading both enclosures with the new drivers is strongly advised so that the benefits of the better driver aren't negated by the distortion emitted by the overworked original driver.

Nathan, can you also give us an estimate on the diameter and length of the ports? If so, we can get an idea of which drivers will work best in the box.