Unfortunately, i'm pretty sure the series/parallel setup will not give you equal volume from all speakers because those speakers in the parallel portion of the wiring will get half the power, and the other half will be split amongst those wired in parallel. I can only think of one approach that would give you equal volume from each speaker. I would run the speakers from each side of the the boat in series. That would give you 12 ohms per side (4+4+4). Then run those two series' in parallel. That would give you a single channel with impedance of 6 ohms (12/2). Then, bridge the two-channel amp and hook that single channel up to it. An amp that is bridged will "see" one-half of the actual impedance present (6/2=3 ohms) and its output will increase accordingly. Since i dont know what particular amp you have, i'll state a hypothetical one. Assuming an amp that outputs 75Wx2 @ 4ohms. Its output at 2 ohms woud theoretically be 150x2 @2 ohms. Most likely, because of regulation in the amps power supply, it will put out about 125W x 2 @ 2 ohms. Its bridged power would probably be about 250W x 1 @ 4ohms, with an unregulated yield of 300Wx1 @ 4 ohms In calculating the power output at 6 ohms, i'll start from the theoretical yield of the amp at 300Wx1 @ 4 ohms. (300W x 4ohms) / 6 ohms = 200W. The amp power supply wont clamp down as much on a 6 ohm load as it would on a 4 ohm load, so i would make a rough guesstimate that you would probably get about 180Wx1 @6 Ohms. That would give you an equal 30W RMS to each of the six speakers. Thats probably enough for the passengers to hear; you've got the tower speakers to get the sound off the boat. Also, the fact that you're using a sub and a high-pass crossover makes this more feasible. It takes more wattage for an amp to tightly control a woofer cone to prevent distortion than it does a mid or tweet. The only problem with this setup is that you lose the "stereo effect." All the speakers will output the exact thing, as opposed to having separate left and right channels. I dont consider this to be a big deal. I'm really hoping that boat audio has not gotten to a point where soundstaging is really an issue. Regardless, this method will work, and will not burn up your amp; even if its just a temporary thing until you can invest in another amp. Thats just my $0.02 based on my experience with several installs in cars. Cheers, DKJ
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