Reply To: I could use some advice…

Blog Forums DIY Speakers and Subwoofers I could use some advice… Reply To: I could use some advice…


Bridge mode is special way of dealing with the inputs and outputs.

Many (read that as most) amplifiers are what you call single ended, ie they run between a certain voltage and ground (0 volts). Many of those take the supply voltage, split that in half, and then the amplifier can only go a certain amount above and below that 1/2 way point, pushing through an output capacitor, into the speaker, and out to ground. So your output is limited to a percentage of 1/2 the supply voltage. Yes, there are other amps that run + and – power supplies in order to get that much more voltage swing, but that’s another post.
Now, if you reconfigure things a bit by adding a second part to the input where you get both a “positive” (upward going to start) and “negative” (downward going to start) signal, then apply that to 2 of your power amplifier sections, connecting the output of the amps to the speaker + & – (no ground reference is used), you get twice the voltage swing as before. Say you had 4 volts RMS output before (single ended), now you have 8 volts RMS (bridged). What you have done is actually quadrupled your power output.


(RMS V)^2 / Impedance

(4^2) / 8 = 16 / 8 = 2 watts

(8^2) / 8 = 64 / 8 = 8 watts

(^2) is “squared” or “raised to the power of 2”

As for the impedance of the bridged mode being rated @ 2 or 4 ohm, you will be fine with 8 ohm, generally, since it is solid state (transistor) which has no real problem seeing greater and greater impedances. Granted, the higher the impedance mismatch, the more it affects the bandwidth (shrinks). But 8 ohm should be no problem. Just know that the power will be about 1/2 the 4 ohm rating.