Running 4 ohm speaks on bridged amp...ok?

It's true, bridging does not change the speaker's impedance
but since each channel of a bridged amp drives half the wave form, it sees half the speaker's impedance. Most manufacturers of 4 ohm (or less) speakers advise against bridging. However, some amps will drve any load so it is best to check with the amp manufaturer.

One more time. The speaker impedance indeed remains the same (just like the song). The outputs of the bridged amp are in series, driven from a single input. This effectively doubles the output voltage swing driving the load (speaker) for a given input level. Thus the current requirement at any given input level is essentially the same AS IF the unbridged amp were driving half the load impedance in a two-channel configuration.

I find some of the posts so amusing. Half the people don't have a clue of what they are talking about and the other group is right on electronically speaking.

Bridging the amps does NOT change the Z of the speakers, nor impact the amps ability to drive it. All decent amps can handle 4 ohms. but not all amps should be bridged. Also a speaker may be nominally 4 ohms but over the entire 20 to 20K range the Z can dip to one or two ohms. This is the point where some amps have trouble. Also some amps cannot deliver high current. Some speakers need high current. Best to make sure what the speakers really need and what the Z curve is. Lastly, listen at home BEFORE YOU BUY.

I'll try again. When you bridge an amp and use it to drive a 4 ohm speaker, the amp sees a 2 ohm load. NO, the impedance of the speaker doesn't change, but the impedance load the amplifier sees driving the speaker is halved. I have had several conversations with dealers here in Phoenix, and I did talk to Jeff Rowland (the man) when he came here one weekend, specifically about this issue.
Some amps sound worse bridged, some the same, some better. I used a Parasound 1200II THX to drve a pair of Snell Sub 550THXs. Everyone who heard the system agreed the amp sounded stronger in stereo versus bridged.
Yes, a big power supply helps, but the quality of the bridging circuit counts too.
As always, listen & trust your ears....

Another unexpected problem of bridged amps is heat. Recently I added a second amp and bridged them and they heat the room up way to much.