SWR Bass 750 into two 350 W cabs?

Newyorkduck · #1 06-12-2010, 05:57 PM

I've been using your forums for a while now as research, I figured I might as well join and ask a question or two:

I just bought a great SWR rig used. Bass 750, Goliath Jr. 2x10 and Son of Birtha 1X15. It sounds amazing, and the guy who sold it to me has been playing it for years live and otherwise.

My only question is about power handling:

The Bass 750 is rated at 450 W at 8ohms, 750w at 4 ohms. Each of the aforementioned cabinets are 8 ohms, rated for 350 w each. My question is, regardless of whether I am running them parallel or bridged mono (which is another question, because the SM-500 I had had a switch that denoted whether you were running parallel or bridged, while the 750 simply has two separate jacks), am I in danger of overloading the cabs? The last thing I want to do is blow out the speakers I just bought.

Thanks TB community, it's nice to have you as a resource.

Duck

muddycreek · #2 06-12-2010, 06:00 PM

You're not going to blow out the speakers. Most amps that go to 4 ohms a side, though, only go down to 8 in bridged mono, so if that's the case, you don't want to bridge the amp into two 8 ohm cabinets, which combine to a 4 ohm load.

The only reason to bridge, really, is to get all your power into one cabinet.

will33 · #3 06-12-2010, 06:09 PM

The bass750 isn't a stereo head, there is no bridging to do. You can either plug one cab in each jack on the back of the amp or run a cable from one amp jack to the top speaker and another cable from top speaker to bottom speaker, the end result is exactly the same.

Here's the manual
http://www.swrsound.com/support/manu...Bass750_OM.pdf

will33 · #4 06-12-2010, 06:11 PM

Should add that those speakers together are rated about the same as the head is. Shouldn't be any danger of blowing them but that doesn't mean you can't. It's still possible to send the speakers moving too far if you're using a lot of volume and bass boost. That holds true for any rig, not just that one. If you turn up to the point that it starts to sound distorted, it's time to turn down a little.

12bass · #5 06-12-2010, 06:17 PM

The thermal ratings of bass cabinets should not be taken as an absolute guide. Go ahead with that combination. It should work well. Without getting into the technical details, a good rule of thumb is to back off on the volume if you hear any signs of distress.

zuokinis · #6 06-12-2010, 08:04 PM

Quote:

Originally Posted by will33

The bass750 isn't a stereo head, there is no bridging to do. You can either plug one cab in each jack on the back of the amp or run a cable from one amp jack to the top speaker and another cable from top speaker to bottom speaker, the end result is exactly the same.

Here's the manual
http://www.swrsound.com/support/manu...Bass750_OM.pdf

except for lower gauge cables, connecting both cabs to amp would be better i believe.

will33 · #7 06-12-2010, 08:13 PM

The jacks on the back of the speakers cabs are wired in parallel and so are the jacks on the back of the amp, it's all the same no matter which way you do it. ie: it's acting the same as if you had one cable plugged into one 4ohm cab.

Newyorkduck · #8 06-13-2010, 03:28 AM

Cool. Thanks for the quick responses, guys.

That rule of thumb is a good one: I will certainly turn down if I hear the cabs straining at all.

Thanks for the tips.

Just for the sake of argument (and learning a little more), what if I plugged in a 4 ohm cab with one of the 8 ohm? That would run at 2.6 ohms and 850 watts. Does the head distribute that wattage equally, i.e. 425 watts per cabinet, or can it determine which cab can handle more power and distribute accordingly?

This may seem rudimentary, but I'm still pretty new to this and no one teaches it to you, so I have to learn somehow.

12bass · #9 06-13-2010, 05:16 AM

Quote:

Originally Posted by Newyorkduck

... what if I plugged in a 4 ohm cab with one of the 8 ohm? That would run at 2.6 ohms and 850 watts. Does the head distribute that wattage equally, i.e. 425 watts per cabinet, or can it determine which cab can handle more power and distribute accordingly?

The power is distributed according to Ohm's law. Thus, the 4 ohm cabinet will see twice the power as the 8 ohm cabinet, as it is half the impedance. So, hypothetically, it would be seeing 567 W maximum, while the 8 ohm would see 283 W. Equal impedance cabinets would see equal power.