bridge

what does bridging mean? how does it work? its advantages and disadvantages?

Bridging:  connecting two channels into one load.  Is done with a stereo amplifier for mono output.  Used for subwoofers.  Subwoofers do not benefit with stereo separation because the frequencies are too low, so bridging is a way to use a stereo amplifier to power subwoofers with a mono signal.  The two inputs, L and R, are mixed.

Modern amplifiers allow bridging because the signal is inverted and polarity is switched on one channel.  In this way, you can hook up positive from one channel to the load, negative from the other channel, and still get alternating current from both channels.  The older amplifiers just had signal from the positive and the negative was "ground", or more accurately, the "reference".

A drawback is that some people don't realize how the impedance of the load affects the amp output when bridging.  If a 4 ohm load is bridged across two channels, each channel outputs power into 2 ohms.  If someone were to load an amp, bridged, with a 2 ohm sub, he could cause amp failure if the amplifier isn't capable of a 1 ohm load per channel (most aren't).  Your amplifier will specify the minimum load that can be bridged, so if it reads "300 watts at 4 ohms bridged", and it doesn't give a spec for 2 ohms bridged, that means the minimum load you can bridge is 4 ohms.

Note:  there is no bridging on mono amps, as they are 1 channel.  They may, however, have two sets of terminals; if you use both sets the impedance is halved just like if you were bridging a two channel amp.  But that's something else entirely, it's just parallel connecting.  Not on the subject of bridging but a lot of people get confused with it.

Here's more information:  http://www.bcae1.com/             http://www.bcae1.com/bridging.htm

thanks stevdart!

i've read on bcae1.com that i also need to fuse my remote wire going to the amps. is that right or did i just read wrong? what if i use 2 amps, where will i get the 2nd amps remote wire?

Yeah, that's right, just to be on the safe side since it's hooked up to a source that supplies anywhere from 7 to 30 amps (whatever the fuse on that line is)...and the remote-on in the amp only needs about 1/5 of 1 amp.  You don't want to take a risk burning out something in the amp when all you need to do is put a dollar's worth of fuse/fuse holder in the wire.  For two amps, split the wire or run it to one amp and out to the next.  The fuse is placed near the power source and you can use a 500 mA (1/2 amp) fuse as bcae1 described. 

BTW, good to see you're reading that source!  Great information there.

RMS- root mean square, but don't worry about that- it basically means the amount of power a speaker can handle on a continuous basis.  Usually this figure is roughly half the peak power, but I wouldn't buy something that didn't have this listed somewhere (just a thought).