Two 4 ohm cabs in series??

[col.mustard]

I have an SWR SM400. It is the original without the fan and extra power of the SM400s. I have two 4 ohm Avatar cabinets. The manual claims the amp will run (inefficiently, but run nonetheless) at 2 ohms in stereo.

The manual also says the power output is as follows: 140wattsx2 @8ohms stereo, 220wattsx2 @4ohms stereo, 200wattsx2 @2ohms stereo, or 400watts bridged into either 4 or 8 ohms.

I thought that perhaps I could run the amp briged into the cabs in series ("daisy chained") for a total load of 8 ohms. that way I'd get approximately the same power as any of the other configurations without adding unnecessary stress to the amp. I especially don't want to overheat the amp since it lacks an internal fan, and I'm not really concerned with running in stereo in order to biamp or anything fancy like that. I just wanna send the full signal through both cabs, if possible.

Is that valid logic? What are the negative aspects of running cabs in series, if any? I appreciate any advice.

 

[KJung]

I believe running two 4ohm cabs bridged in series would be literally identical to running each cab separatedly from each side of the amp into 4ohms. I assume series would require a rewiring of the jacks on the speaker, so I wouldn't bother. Run each cab non bridged and you will be good to go IMO.

 

[T-Bird]

Hi.

I really see no problem there, You can build/buy a series box and run the amp bridged, but why?

You'll get 2*220W by running in stereo and 400W in bridged mode. That 40W You won't notice, but the ease of using the system is always reduced when adding components.

Bridging old amplifiers can be tricky, at least You should get the amps biased, any differences between the amps can trigger the protective circuits. Also as both of the amps are in "floating" mode the differences can result a shift in the 0V of the output, IOW there's a DC component in the signal that reduces the X-max to one direction.

Running cabs (speakers) in series shouldn't be done when using tube amps, but the only problem with SS amps would be a total silence if either of the cabs (or speakers) would break down and create an open.

Regards
Sam

 

[joegeezer]

I believe running two 4ohm cabs bridged in series would be literally identical to running each cab separatedly from each side of the amp into 4ohms. I assume series would require a rewiring of the jacks on the speaker, so I wouldn't bother. Run each cab non bridged and you will be good to go IMO.

+1 Yup!

 

[jarrod cunningham]

i wouldnt rewire or add a component to run them in series . i would look at possibly selling that 400 and looking into 2 ohm stable amps .

 

[slyjoe]

I believe running two 4ohm cabs bridged in series would be literally identical to running each cab separatedly from each side of the amp into 4ohms. I assume series would require a rewiring of the jacks on the speaker, so I wouldn't bother. Run each cab non bridged and you will be good to go IMO.

The specs are little odd in that the amp has the same power output at 4 or 8 ohms when bridged. Going just by the specs, you are correct, but again this seems odd. Two 4 ohms bridged in series creates an 8 ohm load. If the amp truly doesn't care whether it's 4 or 8 ohms bridged, +1

There is a downside to rewiring - somewhere you'll probably get the two speakers out of phase. Also, if you blow a speaker, you lose all sound. Running two sides in parallel will allow you to keep one speaker up if the other blows.

Series wiring is a pain with speakers - I wouldn't do it.

 

[KJung]

The specs are little odd in that the amp has the same power output at 4 or 8 ohms when bridged. Going just by the specs, you are correct, but again this seems odd. Two 4 ohms bridged in series creates an 8 ohm load. If the amp truly doesn't care whether it's 4 or 8 ohms bridged, +1

There is a downside to rewiring - somewhere you'll probably get the two speakers out of phase. Also, if you blow a speaker, you lose all sound. Running two sides in parallel will allow you to keep one speaker up if the other blows.

Series wiring is a pain with speakers - I wouldn't do it.

There would be no way to bridge to 4ohms with two 4ohm cabs anyway.

However, +1... the only thing you will get bridging that head into two 8ohm cabs is a lot of heat and IMO eventual trouble!

It works fine either bridged into a larger 8 ohm cab, or run 'stereo' 4ohms per side.

 

[col.mustard]

Thank you all for your insight. My band and I have our first concert this weekend, and I'll probably just bridge to one cab or the other for simplicity sake. Either of the two speakers can handle the power individually (thanks avatar/eminence ), and that will still be plenty of power as an on-stage monitor since I'll have sufficient P.A. support. I'm gonna try running it stereo today to see if that's a viable option for later. I'm not to concerned about the amp being capable of running in that configuration(since swr claims it will handle the load) as much as I'm concerned about shortening the life span of an amp that's already dated.

Anyone wanna trade me their sm400s?

 

[JTE]

The manual also says the power output is as follows: 140wattsx2 @8ohms stereo, 220wattsx2 @4ohms stereo, 200wattsx2 @2ohms stereo, or 400watts bridged into either 4 or 8 ohms.

I thought that perhaps I could run the amp briged into the cabs in series ("daisy chained") for a total load of 8 ohms.
Is that valid logic? What are the negative aspects of running cabs in series, if any? I appreciate any advice.

A. Daisy chaining the cabinets is still a parallel electrical connection, so it'll still be a 2 ohm load. So, no, that's not valid logic.

B. The negative aspect of running cabinets in series is that if you have a failure of one cabinet, the curcuit is broken and you have nothing coming out of either speaker.

Now, the spec says it's 140W x2 at 8 ohms. So both 8 ohm speakers, one hooked to either side of the power amp gives you 280 WRMS. It also says 400 WRMS bridged into 4 or 8 ohms (that's weird as mentioned above). You COULD make a special speaker cable to hook the two cabinets together in series (it's be Y-cable sort of thing with the a common plug to go to the amp, and the ground of one speaker plug hooking to the hot of the other plug) so you'd get the 400 WRMS @ 8 ohms, but I'm suspicoius of the rating. Just doesn't make sense that a solid-state power amp would have the same rating at 4 or 8 ohms, especially considering that the stereo ratings are different at different loads.

I'm betting that in bridge mode at 8 ohms it's only about 280 watts anyway.

jte