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Crown xti Bridging

catwerk

Hi all,
I'm helping my buddy configure his PA system and he's trying to get maximum power out of a pair of Crown xti 2000's. For the subs, the idea is to run one amp in bridged mono (using the bridged subs xti preset). The question that I can't seem to find an answer to is this: When the xti is in bridged mono mode, can you connect 2 speakers via the Speakon connectors or do you have to use the bridged connection via the banana plug and drive only one cabinet from the amp? Max power in bridged mono from the xti is achieved at 4ohms and he has 2 cabinets rated at 8ohms. It would seem to figure that driving 2 cabs from the xti in bridged mono via the Speakon outs would drop the load to 4ohms...
Thoughts? Help? Clarity please!
Thanks!
-jd
August 14, 2008 @02:10pm
yeahforbes

I haven't looked into that model, but I have other crown amps (and qsc, they're all pretty much the same). In short, you MUST use the banana outputs, connecting both subs + to the channel 1 +, and both subs - to the channel 2 + (or of course daisy chaining in parallel... same thing). There is no "one cabinet limitation" just don't go below 4 ohms. Your 2 subs add up perfectly.
The reason is, putting the amp into bridged means it takes your channel 1 input (ignores channel 2 input) and sends it to channel 1 power amp like normal, but also sends an inverted copy to the channel 2 power amp. So when the input signal swings positive, one channel output goes positive and the other goes negative, causing the difference between the + outputs of each channel to be double! And so you hook up your speakers across those two + terminals. That's the beauty of bridging.
If you were to use the regular speakon outputs while the amp is set to bridge mode, you have that effect of "sending an inverted copy to the channel 2 power amp" and hooking up 1 speaker to each amp (and with each amp seeing that 8ohms mind you...). Then one speaker pushes while the other pulls and your sound disappears. Well, not entirely because the subs are in different places so you'll hear one more than the other except when standing equidistant from each. It's very counterproductive.
--
By the way, for anyone enlightened by that explanation, you can run a stereo amp bridged even when it lacks a "stereo/bridge" switch. Just get a Y cable with one female and 2 male XLR's (or TRS) and on one of the males, open it up and reverse pins 2 and 3 (or the T and R of the TRS) and mark the modified one. Pop the modded one into channel 2 input, the other into channel 1, and then hook up your speakers across the + outputs as described above. CAUTION: If you're sending the amp an unbalanced signal, your Y cable won't effectively invert one side and you will destroy your amp from connecting across the + terminals without opposite-swinging signals. CAUTION: Perhaps the amp lacks a "stereo/bridge" switch because the 2 channels are not closely matched enough to output exactly the same signal due to components with crappy tolerance ratings causing different slew rates, freq response, a million other things. [and don't even think about doing this trick across 2 different mono amps for that exact reason!] CAUTION: The minimum load impedance across the + terminals is double that of what each side is rated for in stereo operation. (2ohm minimum per ch = 4ohm min in bridged).
Plenty of reasons not to do it, but a cool experiment that's likely to work.
August 15, 2008 @08:06am
catwerk

Thanks for the info! So if I understand correctly, I CAN hook up 2 speakers to the + terminals on the banana plug connectors on the amp and it would perfectly cut the load down to 4ohms thereby achieving max power from the amp..? I thought along similar lines and suggested doing that with one speaker and daisy chaining the second cab to the first for the same result until I found that there aren't any parallel outs on the cabs...
Thanks again for the info.
-jd
August 15, 2008 @02:18pm
yeahforbes

Exactly. Many (most?) banana plugs are stackable, like the plug is male and female at the same time. That will allow you to connect both speaker cables to the same set of terminals. If yours aren't, snip them off and replace with something like this which I think is stackable.:
http://www.sweetwater.com/store/detail/BNA100/
http://www.sweetwater.com/store/detail/BNA260/
August 15, 2008 @04:40pm
Dave Burris

The XTi can operate bridged-mono using the Neutrik Speakon on channel A if you have a properly wired cable. If your speaker has a parallel Speakon output you can also daisy-chain multiple speakers as long as you stay above 4 Ohms.
The cable must be wired to connect 1+/2+ to the speaker +/- respectively.
August 15, 2008 @10:01pm
yeahforbes

Ah yes, I've seen a few amps with that capability (both outputs on the first speakon). But since your speakers only have one jack preventing daisy-chaining, you'll need to either...
1. Open up the speakon for one cable and move a wire from 1- to 2+, and mark that end of the cable because it NEEDS to go to the amp not the speaker, and then also take your other cable and put a banana for the amp end, connected to the 2 red terminals.
or
2. Make everything banana... probably less room for confusion down the road.
Whatever you choose, you need to ensure that your banana(s) are always plugged in to the red terminals correctly to avoid phase problems. Open up the connector on the sub's end of the cable, and note the color of the inner jackets for the 1+ and 1- (assuming it's also speakon). The color of the 1+, likely white but could be anything, is the color you want going to the amp's Ch1 red terminal on the banana end (or 1+ for the speakon on the amp's end in option 1). The color of the 1-, likely black but could be anything, is the color you want going to the amp's Ch2 red terminal on the banana end (or 2+ for the speakon on the amp's end in option 1). Kinda convoluted, let me know if it's hard to follow.
August 16, 2008 @03:59pm