ACME cab rebuild

Depends on the design of the crossover in B1 vs. B2. If the woofers run full range in both cabs (no low pass filter) then you can use the crossover and drivers from the B2 to create a B1 plus a spare woofer. If there is a low pass filter on the woofers, you're out of luck.

 

True that. All the more reason to just ask Andy!

 

There's no electrical low pass filter on the Acme cabs, it's all done with the woofer design. So yes, your plan should work!

 

Yes, the 4-ohm cab will have two 8-ohm drivers in parallel. Since the cab is used, it's best to check resistance with a multimeter to verify nothing has been swapped out. 4-ohm cabs will read about 3 ohms of DC resistance. Each 8-ohm driver will read about 5-6 ohms of DC resistance.

 

In your place I'd just use the working B2 as it is. It's a small fairly light cabinet with a unique sound all of its own. When I play a gig I tote a pair. I feel that the B2 would be worth more than a cobbled together B1. It also seems to rub me the wrong way to destroy a functional cabinet to get a lesser one working.

Edit: Tonight I'm using my Series II pair.

 

Thanks for the information Alex, I should have known you would have taken one apart!!

I've always assumed it was both a high and low pass crossover. See? We all learn a little sumpting new every day.

 

I seem to recall something about the midrange driver and tweeter being more padded on the B2 than they are on the B4, and more padded on the B1 than they are on the B2 - in order to keep the relative output of woofer(s) to mid-driver and tweeter relatively consistent from one model of cab to the next. Allegedly necessary due to the ratio of woofers to mid-drivers and tweeters differing between the cabs, i.e. 1:1 for the B1, 2:1 for the B2, and 4:1 for the B4.

If true, this could certainly have a bearing on the outcome of a components swap from a B2 into a B1. FWIW...

MM

 

No, I haven't taken one apart (other than taking a woofer out to change the bulb) - years ago I was asking about having a switch to take the low pass out of the crossover to give you a mid boost and Andy said there wasn't a low pass filter because he didn't like having chokes in series with woofers because of their effect on the damping factor and thus cone control and because they're a big heavy component which isn't terribly easy to secure permanently in something which will be gigged.

I remember also discussing the padding on the mids and tweeters and I remember that the 4 ohm B2 and 8 ohm B4 have no fixed pad, 8 ohm B2 and 4 ohm B1 has about 3dB, 8 ohm B1 has another 3 dB. So with the innards of a 4 ohm B2 in a B1 you'll need to turn the L-pad knobs down. Something Andy wrote about the challenges of the crossover for the B1 bothers me though - I wonder if there's something else going on in there? One of the biggest problems with crossovers is avoiding impedance dips, especially when the phase is negative, because that's tough on amps. I know Andy had done a lot of research into the effect of back EMF and was thinking of writing a paper on it, but I guess business has got in the way of finishing that!

 

Thanks for the fuller answer Alex. My Series II pair sang all last night. I've never played so damn loud in my life. All in all it was a great Christmas party!!