Audio Help For The Stereo Noob

[Z3CO23]

I've always had the understanding that when you bridge any amp that you cut the ohms in half.

I've been doing some research online about possible changes to my system and found some things that say that's not correct and now I'm just totally confused. Can anyone clear up what bridging does to ohms?

My tower (4 rev10) is powered by 2 400.4 2ohm amps bridged to power the rev10's which are 4ohms. When my amps are being bridged what is happening to the ohm load to the rev10's?

I guess I'm just looking at an explanation of ohms when it comes to a 2 ohm amp and a 4ohm speaker.

[chpthril]

What you likely have a 2 ohm stable amp, meaning that a 2 ohm load (load being the speaker its driving) is the lowest safest impedance that can be run on each chnl. When you bridge a speaker across 2 amp chnls, each chnl "sees" half the speakers nominal impedance. But, the impedance of the speaker stays the same, its only the load the amp sees, that changes. So in your case, you have a 4 ohm speaker bridged across 2 chnls. Each of those chnls is seeing a 2 ohm load. Power wise, the speaker is receiving each chnls 2 ohm output x2. For example, lets say your 400.4 has a 50W x 4 @ 4 ohm, 100W x 4 @ 2 ohm and 200W x 2 @ 4 ohm. Ok, see the math? When bridged, the two 100W @ 2 ohm chnls become a single 200W chnl with a 4 ohm bridged load.

[Z3CO23]

I follow ya on everything except the 50W x 4 @ 4 ohms. What caused the single channels to be 4 ohms and 50W.... wiring hookup?

[chpthril]

The load, in this case a 4 ohm, results in the amps output. A lower impedance, like 2 ohm results in more amp output (with most typical amps, but not all) and conversely, a higher impedance would result in a lower output. Amp designers will build the amp so its output is what they are shooting for at a particular impedance. Since a 4 ohm speaker is very common in the mobile audio, thats typically why you see 4 ohm and 2 ohm specs listed.

[Z3CO23]

Ok, so the 4ohm impedance in the speaker cuts the power on the channel. Essentially if the speaker was 2ohm, you would see 100w instead of the 50W.

[chpthril]

Basically yes. The impedance, or load, determines the output. We cant change the impedance of the individual speaker, but we can manipulate the final load when wiring 2 or more speakers to a single chnls. But regardless, what ever the amp's output is at a given load, it is divided each speaker that wired to the chnls. Two 4 ohm speakers can = 2 ohm, so the amp chnl output would be 100W, but only 50W net to each speaker.

[Z3CO23]

Ok. So I'm assuming my 400.2 is wired in parallel to power the bow pair of xs650's and then the cabin pair of xs650's. giving a 2ohm load at the amp and 100w per speaker.

[chpthril]

The logical configuration with 2 pair of speakers on a 2 chnl amp, would be to wire each pair on parallel on each chnl. That results in a 2 ohm load per chnl, on the amp. What ever the amps 2 ohm x 2 output is, its then split by the speakers.

[Z3CO23]

Thanks for the help chp. Happy New Year man.