Speakers lose sound when engine is sped up

I am posting this for a friend.<br /><br />He has an 18 foot aluminum boat with an older Envinrude 50hp. I don't know the exact year. He installed a modern stereo on it, using gear that he knows works. With the engine off or just idling, the stereo system works great. However, when the engine is sped up, the speakers fade. It's definitely not just the engine noise just getting louder. The speakers very noticably lose sound. Turning up the volume has no effect. The head unit stays on and powered up. A multi-meter shows consistant power going to the HU when this happens (ie: no power change from idle). <br /><br />The speakers (just two) are 6-inch and are flush mounted into a locker about three or four feet forward of the transom. <br /><br />Does anyone know what's going on here? We're both pretty good with electrical but this has me stumped, since I've never heard of it happening before. The only thing that I can remotely think of is that it has something to do with the alternator or its field line, but I don't see how. No other electronics are onboard (except lights).

Re: Speakers lose sound when engine is sped up

Your Evinrude has an unregulated charging system.<br /><br />Recheck your voltage readings. Those systems can easily reach nearly 17 volts at cruising speeds.

Re: Speakers lose sound when engine is sped up

What DJ said. Nearly every electronic device these days has an over-voltage protection circuit that shuts down the unit if voltage gets to high. Go to Radio Shack and buy a 12V voltage regulator (1 ot 2 amps would work) and install it in the 12V feed to the stereo. This will regulate the voltage to the radio. It will NOT regulate voltage to any other devices. Becuase the current rating is low, do not connect any other devices to it.

Re: Speakers lose sound when engine is sped up

Thanks, but the HU stays energized the whole time and continues to function. It's the speakers themselves that lose sound. All controls and functions on the HU work. This is all according to my friend. I have not seen this problem personally. He does insist that the voltage stays at ~12.

Re: Speakers lose sound when engine is sped up

If the voltage is at 12, the engine is NOT charging.<br /><br />Recheck.