For many hobbyists, the allure of RC flying comes from making their models look like “real” airplanes. Some are happy just approximating the profile of a certain airplane, while others spare no effort or expense to replicate every last detail. Regardless of the level of accuracy a builder pursues, one particular aspect has always been elusive: sound. Most models use screaming glow-fuel engines, growling gasoline engines, or whizzing electric motors. None of those power systems is likely to emulate the sound of the full-scale airplane’s engine. The one notable exception is turbine-powered models, which actually use miniaturized jet engines that sound (and smell) like their big brothers. The necessary flying skills and price point, however, keep turbines out of reach for most modelers.
Recent developments have revamped the sound equation. Several companies now offer sound systems for electric-powered RC models that play audio recordings of full-scale aircraft engines. These system are linked to the throttle control, so the sound revs as you increase power to the model’s motor. I know what you’re thinking: “How can you possibly get convincing engine sounds out of a system that is small and light enough to fit inside a model airplane?” I thought the same thing and ignored the growing popularity of these systems for a while.
My curiosity recently got the better of me and I watched a few YouTube videos of models with sound systems. The videos piqued my interest and I was soon investigating the various available products. One particular system stood apart from the others, the Mr. RC Sound V4.1 Sound System. What is most unique about this sound system is that it does not use speakers--at least not in the traditional sense. This is something I had to test.
What You Get with RC Sound
The heart of the Mr. RC Sound unit is a control board that measures about 1.75” x 2.5”. The board includes a “sound pack chip” with sound files recorded from six popular aircraft engines throughout history. The chip can be swapped for others with different engine options. In addition to the sound of the running engine, each selection on the chip also includes three auxiliary sounds such as chattering machine guns or the whistling of a falling bomb.
The sound board must be connected to the model’s RC receiver via standard 3-wire servo connectors. It is worth noting that male/male wires are needed rather than the male/female wires that are commonly used to extend servo leads. One wire is included, but you must provide others if you wish to use any of the auxiliary sounds. The wire lead for controlling engine sounds is connected in parallel to the model’s Electronic Speed Control (ESC: aka “throttle”) via a splitter, or “y-connector” (not included). Leads for each of the auxiliary sounds require an open port on the receiver.
The sound board can accept input voltage from about 11 to 34 volts. This means that models using a 3S LiPo battery (3 cells in series, 11.1v nominal) to 8S (29.6v) can siphon power from their flight battery to feed the sound system. This allows the vast majority of electric airplanes to avoid the additional weight of a separate battery for sound.
Rather than a speaker, the V4.1 system uses an electroacoustic transducer called the TT-25. It is basically a speaker without the frame or the cone. The TT-25 attaches directly to the airframe of the model, which then behaves similarly to a speaker cone. In essence, the entire airplane becomes a speaker.