If you wish to add realism to your model, then pretty much the obvious choice would be an engine sound, ideally one which increases in pitch as you open the throttle. Take care that this is a realistic choice however as I doubt very much if you would have heard the engines of HMS Hood or the Titanic unless you pressed your ear to the hull and the very popular KD Perkasa was powered by three gas turbine engines, not petrol or diesel!
Such sound units are available in two basic types; those which simply simulate the sound of an engine by generating and modifying electronic noises, and those which replay digital samples of real engine recordings. In order for the pitch to be varied there is a connection either to the brushes of the motor itself or to the receiver throttle channel output, Figure 24
. In the former case it’s important to know the voltage of the main battery, because the sound card runs directly from it. In the latter case the sound card takes its signal and power from the receiver so the main motor battery voltage isn’t relevant. Sound simulators are generally adjustable for volume, pitch, idle and top speed and some sort of character or tone, e.g. number of cylinders in a diesel engine, while the digital replay types are usually only adjustable for volume.
In nearly all cases, engine sound cards will have an amplifier chip built into their circuitry, so the only other item to fit will be a suitable speaker. Make sure you use the correct impedance, which is usually 4Ω or 8Ω, but check the instructions. The exception is the ACTion P100 Noisy Thing, which requires an external amplifier to work. Most sound cards will benefit from the addition of an external amplifier to increase their volume, as few seem to be suitable for all but fairly small lakes. Model Sound Inc’s Shockwave digital system has a very powerful on-board Class-D amplifier which makes it suitable for large model aircraft and helicopters, but a high supply voltage and large speakers are required to obtain the optimum performance from this unit.
Note that a straightforward engine sound card doesn’t require a separate radio channel to operate, as it simply uses the throttle channel to vary its pitch. Some units, however, may require a second channel e.g. the Mtroniks unit needs one to start up the engine sound while the P100 carries up to eight other sound effects (horns, bells etc.) which can be activated by a second channel and selector switch.
Engine sound simulators are made by Technobots, ACTion, Harbor Models, Robbe, and JoTiKa while the more expensive digital types are from Mtroniks, Benedini, ACTion, Model Sounds Inc. (Canada) and Graupner. Model Sounds Ltd (UK) make a fixed-pitch sound unit called Master Blaster which is switched on manually and allowed to run for the whole sailing session. This is useful for a heavy marine-diesel sound, which varies very little with throttle anyway and other types are available. Note that the digital types can all be programmed with different engine sounds, some by the user and others at the time of purchase. Once again, check out the manufacturer’s website for all the details.