Mono Bridged Setup - cable ends not long enough?

What causes the impact on sound quality with bridging?

There are probably a number of factors which contribute to that, to varying degrees depending on the particular amplifier and speakers. Including:

1)Most amplifiers will have lower distortion when driving higher impedances (e.g., 8 ohms of more) than when driving lower impedances (e.g., 4 ohms or less). As I indicated earlier, in bridged mode the amp will see the speaker's impedance divided by 2.

I suspect that effect will be mitigated to some extent in the case of your particular amplifier, because it includes autoformers having 2 ohm taps (which I suspect you would find to be the best choice when bridging with a 4 ohm speaker), as well as 4 ohm taps (which I suspect you would find to be the best choice when bridging with an 8 ohm speaker).

2)As you probably realize, speakers commonly have impedances that dip to considerably lower values at some frequencies than their nominal rated impedance. In many cases that happens at bass or mid-bass frequencies which typically require a lot of energy. Again, in bridged mode that impedance dip will be seen by the amp as half of its actual value, and the result may be too low a value for some amps to handle with good results.

3)Since in bridged mode both of the channels in the amp participate in the generation of the same output signal, to the extent that the two channels don't have identical characteristics distortion may be introduced in bridged mode that would not occur in stereo mode.

4)In bridged mode a phase inversion has to be applied to the signal on one of the amp's two channels. In some designs that will necessitate insertion of an extra active stage into the signal path, with possible adverse sonic effects.

There are probably other factors that may be involved as well, but those are some that readily come to mind. Despite all that, however, as ZD indicated it is certainly conceivable that there will be some cases in which an amp will sound better in bridged mode than in stereo mode, at least from a subjective standpoint and in the context of some specific systems.

Regards,
-- Al

"10-11-14: Andrewdanapoole
Thanks all, appreciate the input! What causes the impact on sound quality with bridging?"

Its one of those things that you have to try for yourself. Even if we both bridged the same amps, its likely we would get different results depending on the rest of the components in out systems. Its also worth noting, that there are some amps that are known to sound very good when bridged. In my experience, I liked both BEL and Bryston when bridged. Actually, I thought the BEL sounded better bridged.

Thanks all, appreciate the input! What causes the impact on sound quality with bridging?

You may want to get some basic cables just to test the 2 amps in your system first. When you bridge amps, it has an effect on sound quality that most people don't like. I'm not saying that will definitely be the case in your system, but its something to consider.

Blue Jeans Cable would be a perfect source for a custom cable like this that would be affordable. Get their 10 awg, it is good quality stff.

I don't think you are doing anything wrong, but that cable is unsuitable for the reason you stated. What I would suggest is that you contact a cable supplier of your choice and ask them if they would customize a cable which allows enough separation between + and - at the amp end.

Also, keep in mind that in bridged mode the amp will "see" a load impedance equal to half of the speaker's impedance, so you will probably want to connect to an output tap that is one value lower than you would use in stereo mode (for example, the 2 ohm tap instead of the 4 ohm tap).

Regards,
-- Al