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Getting Acme B-2's - 4 ohm or 8 ohm?


SteveC

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So I'm going to order 2 Acme Low B-2 full range cabs. I am using a QSC PLX 1602. Here's the output info.

 

4 ohm

500 watts per channel stereo/parallel

1,600 bridged mono

 

8 ohm

300 watts per channel stereo/parallel

1,100 watts bridged mono

 

I want to be flexible. One cab for small gigs, 2 for big ones. Stereo, parallel, bridged, whatever works for the gig. Any thoughts?

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Originally posted by SteveC:

So I'm going to order 2 Acme Low B-2 full range cabs. I am using a QSC PLX 1602. Here's the output info.

 

4 ohm

500 watts per channel stereo/parallel

1,600 bridged mono

 

8 ohm

300 watts per channel stereo/parallel

1,100 watts bridged mono

 

I want to be flexible. One cab for small gigs, 2 for big ones. Stereo, parallel, bridged, whatever works for the gig. Any thoughts?

I'd go for 8 ohms if I were you. That way you'll get 1,100 watts into a lone B2 or 800W into each if you run a pair. Unfortunately I bought 4 ohm cabs and it's more effort than it's worth changing them so I'm upgrading to a PLX 3002 to get enough power. If you want to use the cabs as small PA (or as studio monitors!) you'll still have 300W per cab and as there will be greater HF content in program audio rather than a bass sound, by having less power you'll be less likely to blow the bulbs.

 

Alex

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I have one of each: an old 4 ohm B-2 and a newer 8 ohm B-2W. Man, this impedence matching thing is a hassle. I wish they just had a switch on the back.

 

My ideal setup would be a PLX 2402 driving one 4 ohm Acme with each channel. They'd be getting 700 W each (about ideal for an Acme) and the amp would be running a 4 ohm load so you wouldn't be straining it too hard. If you needed the other channel for something else, you could wire them both up on one channel and still get 600W per cab. (1200 into 2 ohms) I think this approach would be the best if you're going to use the full-on rig a lot.

 

Right now I have a Stewart World 1.2. Bridged into one 8 ohm cabinet, it puts out 700W. With two, you'd get 1200W. This is a good way to save bucks on the power amp, but for the larger gigs you'd be straining it by bridging into 4 ohms. That's okay for me because I only do it a few times a year. (I put a fan on the Stewart and it does fine.)

 

The 4 ohm B-2 isn't the best match for the Stewart. Run one channel (about 350 into 4) it sounds okay, but clearly could use more watts. Bridged, you get 1200 watts into 4 which is too much, and I've blown drivers this way. I think I'm going to convert the B-2 to 4 ohms ($170) and then I'll have the setup I described above.

 

In your case, if I had a PLX 1602, I'd probably get the 8 ohm cabs, run the amp bridged and be careful when running one cab (1100 into 8). If there's a way to send the amp back and get a 1202 for use with two 8 ohm cabs or a 2402 with two 4 ohm cabs, that would be ideal.

 

Good luck. I look forward to seeing hou your rig turns out.

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