Alternative Method for Loudspeaker Placement on Small Fiberglass Open Boats

Electrical and electronic topics for small boats
jimh
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Alternative Method for Loudspeaker Placement on Small Fiberglass Open Boats

Postby jimh » Sat Mar 28, 2020 5:03 pm

An alternative method for installing a loudspeaker system for reproduction of recorded music for entertainment on a smaller fiberglass open cockpit boat: buy an inexpensive 86-quart cooler. The cooler becomes a water-tight enclosure that will be the cabinet for two loudspeakers, will contain the audio amplifier, and will house an isolated storage battery to power the system. This method avoids having to make large circular holes into the structures of a fiberglass boat for loudspeaker mounting. Such large holes could affect the structural integrity of the hull, deck, or console of the boat. It also avoids having to route wiring to the loudspeakers from an amplifier located elsewhere.

For the loudspeakers, mount two 8-inch full range loudspeakers on one long face of the cooler, as far apart as possible. Select the cooler so it is as long as possible, to get the speaker separation to be suitable for reproducing a stereophonic recording.

For the speaker amplifier, buy a modest power-rating, say 25-Watt, 12-Volt-DC-operated high-quality audio amplifier with integral digital audio processor, and with Bluetooth wireless input. The wireless Bluetooth input will create the ability to use a tablet or smartphone as the source of recorded music, connecting to the amplifier wirelessly via Bluetooth. For even better sound, look for an amplifier that can have its frequency response adjusted by using an app on a smartphone that connects via USB. In this way you can make corrections to the frequency response as necessary. You won't have to do this all the time, so a USB connection to the smartphone will be fine for the initial set-up of the amplifier and its frequency response.

Buy a lithium-ion 12-Volt deep-cycle battery with its own charge management system. The reason for Lithium-ion chemistry is to save weight. However, this technology is expensive. If you don't mind added weight, a sealed lead-acid battery like an absorbed glass mat (AGM) deep-cycle battery will cost much less. If you need the loudspeaker system to play for hours without the battery being recharged, you will have to choose a large storage capacity battery.

The power demand of the amplifier will depend on how loudly you want the loudspeakers to be playing. Assuming an average drain of 5-Watts at 12-Volts, the amplifier will consume perhaps somewhere around 2.5-Ampere-hour per hour. So a 10-Ampere-hour battery ought to be good for an hour or two of audio reproduction. The actual power consumption will depend on the type of music you are playing, the efficiency of the amplifier, and the efficiency of the speakers, and where the volume control is set.

A 12-Volt 10-Ampere-hour LiFePO4 battery weighs 3-lbs but costs $120. An AGM lead-acid 12-Volt 10-Ampere-hour battery weighs 6-lbs and costs $25.

The better lithium-ion batteries have their own charge management system integrated into the battery. Note that lithium-ion batteries are best recharged when the are disconnected from all loads.

Provide an input connector on the cooler for connecting to a 12-Volt charging source, which could be the boat engine alternator output when the engine is running, or a 120-VAC charger when at the dock or at home if the boat is on a trailer.

To the floor of the cooler add a plywood floor, and mount the battery to the plywood in the center of the cooler. You may consider adding two divider walls on either side of the battery to isolate the two speakers from each other. Fill the cooler compartment behind each loudspeaker with woolen batten material (or inexpensive wool blankets) as sound baffling.

In this way you will have a portable sound system you can carry onto the beach if you like. You won't have made any large holes in the fiberglass structure of your expensive boat.

If I were really keen for having a loudspeaker reproducing entertainment system, I would use this concept. You may not need special marine electronics because the inside of the cooler should be water tight, but buying speakers that are rated for marine use is probably a good choice. Getting an amplifier that looks like it could survive some dampness is also probably a good hedge against any water intrusion into the cooler.