How to Properly Place and Install Underwater Speakers
By Paolo Benedetti
From the car to the office to even a walk around the neighborhood, people love to take their music with them everywhere they go. Another big one: the gym — nothing takes away the drudgery of a workout than some fast paced tunes. So why shouldn't your swim workout benefit from music as well?
With the constantly dropping price of underwater speakers and a little planning, audiophiles can now relish their prized tunes even while in the pool.
Underwater speaker come in a few styles. My favorite are piezoelectric speakers: they don't have moving parts, nor do they contain magnetic or exposed metal parts that may make them subject to galvanic corrosion.
Sound travels better underwater due to the proximity of water molecules. A good rule of thumb to keep in mind: Space underwater speakers no more than 40 feet apart. (So if you're dealing with a 40-foot-long pool, a single speaker centered on the side wall is adequate.) Anything further apart and swimmers would experience fade out as they distanced themselves from the speaker.
Say you're working with a bigger pool that's 80 feet long. In that case, you'd need at least two speakers on the side walls (20 feet from each end, which would space them 40 feet apart). Another option would be to place them on the ends of the pool. Most manufacturers are more than willing to assist with speaker placement, as they have decades of underwater acoustical experience.
To ensure adequate dispersion of sound throughout the pool, the niche must be placed deeper than a typical light niche. The minimum depth is 24 inches. My firm specifies that the niche be placed at half the depth of the pool, with the top of the niche no shallower than 24 inches. Excessively deep pools may require even deeper placement, if swimmers are expected to linger at those depths (as is the case in scuba diving pools, for example).
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Some manufacturers require special proprietary niches for their speakers. Again, I prefer firms whose products can utilize any standard, full-sized stainless-steel light niche. No matter where the project is located, the rough-in components are readily available. Remember, though the niche will be housing low voltage electrical components, it still requires both external and potted internal bonding wires — it needs to be treated just like a light niche. An additional benefit is that the stainless steel niche will also provide the requisite "water bonding," as required by the National Electric Code.
Using a 1-inch conduit will ensure there is plenty of space to ease the pulling of wires. This conduit will hose the internal #8 bonding wire and speaker cord from the niche to the junction box. (A standard pool light junction box is all that is required.) The junction box is located and installed above the water level, just as if it housed the electrical connections for a pool light. The external bonding lug of the junction box must be connected to the bonding grid as well with a bare #8 copper wire. This ensures that there is equipotential bonding across all of the attached components. It is also the only means for the internal bonding wire to connect to the bonding grid.
A conduit is required from the music source (SOS – source of supply). The SOS can be from the speaker output of an amplifier, wireless network audio receiver or similar device. Many manufacturers provide an isolation transformer that is installed between the SOS and the speaker. The isolation transformer is just like a low-voltage pool lighting transformer in that it separates the signals, ensuring that the voltage from the primary (input) is not transmitted directly through to the secondary (output). Usually mounted adjacent to the junction box, the wires from the SOS connect to the isolation transformer. A cord from the isolation transformer is routed into the junction box, where the connection is made to the speaker cable.
Our vendor provides 400-watt isolation transformer as standard equipment. This means that a clients SOS can input up to 400 watts before damaging the transformer. Four hundred watts per channel is a lot of power!
Impedance matching to the clients SOS is also important to prevent damaging the SOS. Most home stereo systems operate at 8 ohms (though there are some 4 ohm systems) and 25 volts. Obviously, an automatic impedance matching 4 to 8 ohm transformer is ideal. Bear in mind that some commercial sound systems (e.g. schools, institutions) may utilize 70- or 100-volt sound systems. These projects will require specialized transformers. When specifying an underwater speaker, you will need to know the sound system's speaker output impedance and operating voltage.
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The NEC requires that the speaker be protected from damage by a metal grill. Our speaker vendor provides a stainless steel plate with perforations. Prior to plastering, we have the stainless steel grill powder-coated to match the finish materials inside the pool. We take care to ensure that the mounting holes are free of coatings that would interfere with a good bonding connection.
Another NEC requirement is that the SOS must be powered from a GFCI circuit or outlet. This additional layer of protection prevents short circuits in the SOS from potentially energizing the speaker with high voltage.
A simple monaural sound signal is all that is required. If multiple speakers are being used, right and left channels can be used to power them. However, clients should be advised to not expect the same high fidelity stereo or surround sound that they experience in their home theater or headphones.
When synchronized with the patio speakers, swimmers can now go from air to water without missing a beat!
