Needing to be as sure as possible !!!

Good chance there isnt!

audiomik wrote: the Amplifier inputs aren't the critical ones, so long as there is a bi-phase source!

Mik

Yes, I am following you on this Mike, and not only are you making sense that appears to be based in solid logic, but I expect some experience as well! Since my experience with amps that had the correct internal circuitry was far better than very good and since my injury has limited both my ability to get funds for extremely powerful lightweight but very expensive amps and prevents me from being able to move around powerful but extremely heavy amps it is important to me that I explore this option.
If my understanding of your reply is correct I actually already have everything I need. The sub woofer output of my crossover is a summed , balanced XLR connection that part which is the initial vital part should work!
The next part is my adapter.... A have a 2 male rca to 1 female XLR adapter and I just opened it up to check the wiring. It looks correct. Previously I have tried this adapter using the female XLR as the source side and took the 2 RCAs to various amplifier connections. When used as stereo ins they work normally. When attached to a summed input I get dead silence. That is what I should get if the hots are 180 degrees out of phase. The inputs on the amp I want to bridge are RCA and are gender correct for this experiment.
The next thing is speaker cable... not a problem!
Then there is the small problem of I have insufficient test gear to do the precautionary test you wisely recommended! While I hate to not be able to follow that obviously good advice, I do have a suitable substitute! I have a brand name car audio sub that was free and in my mind isn't any better really than a "Test Dummy"!
I think I am in pretty good shape and with the controls on the crossover and the amp I shouldn't need the attenuator. It may be later today or early tomorrow before I can test it, but I will remember to post results....good or bad!

OK, well with a worst case of things failing then give it a try as you have described.
However do check the Impedance of your Car Sub driver before you try it as a Load.
I seem to think that Car Subs are often 4 or even 2 Ohm impedance!

And before others jump on this about using more professional Amplifiers with balanced inputs, I have on a number of occasions when needed used Hi-Fi Amplifiers in Bridge mode with much the same methodology as this thread describes. Mostly though for testing AC synchronous motors.

Sorry to hear of your back injury, getting old I have osteoarthritis so I fully sympathise with your condition
Mik

audiomik wrote: OK, well with a worst case of things failing then give it a try as you have described.
However do check the Impedance of your Car Sub driver before you try it as a Load.
I seem to think that Car Subs are often 4 or even 2 Ohm impedance!

And before others jump on this about using more professional Amplifiers with balanced inputs, I have on a number of occasions when needed used Hi-Fi Amplifiers in Bridge mode with much the same methodology as this thread describes. Mostly though for testing AC synchronous motors.

Sorry to hear of your back injury, getting old I have osteoarthritis so I fully sympathise with your condition
Mik

Thank you again for all your help! As to the impedance of the "crash test dummy" speaker, it is an 8 ohm speaker. Fortunately having used pro sound gear in my past including pro sound amps in bridged mono I am well aware of both the benefits and the dangers as well as the necessity of correct loads.
This test is really something I had to prove to myself more than anything. I certainly intend to use more professional amps when I can. After the test I do plan to reconfigure my system, but with even that amp in a mode of operation more suited to its design that still attains the same level of power. I am not even sure why I have to do this, I just do.And once again as I did throughout this thread I want to remind anyone that may be reading that this test has tremendous potential for disaster. Those disasters can range from destroying a driver all the way to smoke and fire coming from the amp. So do not try this at home! That being said, I think I will make some coffee and setup for the test, with all safety precautions ! Does anyone have a fire extinguisher I can borrow just in case!

audiomik, I have pretty much tested it to my satisfaction. Thank you again for your help. The results would work in a really sticky spot, but are pretty inferior compared to my system in a more conventional configuration. I might play around with it a bit more since I didn't even seem to have a heat build up going on. But truthfully I doubt it, I seem to have satisfied an itch and would prefer to get back to to getting the best out of my system without unnecessary risks.