A question of Ohms

In the different posts people ask about how to wire an amp for a 2 ohm load or 4 ohm load using 4 ohm subs.  Or the amp sees a 2 ohm load.  What is that exactly.  With a mono amp its easy to understand. You wire a 4 ohm SVC sub in parallel, you have a 4 ohm load.  How does it work for a stereo amp?  Looking at the different RF wiring diagrams they refer to one channel of an amp.  Is it the same for 2 channel or a 4 channel amp.  If you wire  (2) 4 ohm subs one sub to channel 1 and the other sub  to channel 2 will the amp still see a 4 ohm load?

Harvey

In general, and amplifier "sees" whatever you connect to it and each channel of an amplifier operates independently.  SO, in a mono system, there is only one amp so it will "see" the entire load.  If it is a 4 ohm load, it will operate into 4-ohms, etc.  If you are running a stereo amp, it is like having two mono amps (indeed in the best equipment it is exactly that.)  Each channel will operate into whatever impedence load is connected to that channel.  Connect a 4-ohm load to each channel and each amp operates into 4-ohms.  If you are operating a stereo amp in bridged mode, this means you are connecting the two amplifiers together into a common load.  Each channel will "see" HALF of the load.  So if you bridge a stereo amp into a 4-ohm load, each amplifier channel will operate into 2-OHMS.  Connect a 2-ohm load and each amplifier channel will "see" 1-OHM.  Etc.

Problems arrise when inexperienced installers try to wring more out of an amp than it is capable of safely producing.  Lowering the ohm loading on an amp will force it to produce more current.  When forcing more current through an amplifier, it generates more heat, more noise, more distortion, and shortens its life expectancy.  Loweing the ohm load too far will overload the amplifier output stages and it will fry (a condition known as "Max Smoke.")  This is a condition to be avoided.

A 4 channel amp is really just a 2 channel amp split in half to allow more hookups.  Channels 1 and 2 are left and right stereo.  Ditto for 3 and 4.  A channel has + and -, and connects to one speaker load.  If you have one sub on channel 1 and one sub on channel 2,  you are actually running a pair of speakers in stereo.  Both speakers must match impedence.  So if the subs are each 4 ohms, then you have a stereo load of 4 ohms.  If each is 2 ohms, the stereo load on the amp is 2 ohm stereo.

Most people will combine the 2 subs together first, then connect to the amp...it depends on what you're working with.  If each sub is in its own enclosure, then go with the stereo load.  If they share a box, the two 4 ohm subs can be wired together to form a 2 ohm load.  Very few amps can handle a 2 ohm bridged load.  That's why you see so many subs now with dual voice coils of 4 ohms per coil.  2 DVC subs like this can be combined for a bridged load of 4 ohms.