Cox box

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A Nielsen-Kellerman Cox Box in a rowing shell together with a SpeedCoach XL

"Cox Box®" is an internationally registered trademark belonging to Nielsen-Kellerman®, a US manufacturer of performance equipment for rowing and paddling. An NK® Cox Box® coxswain's amplifier combines an electronic timing, stroke rate measuring and voice amplification unit with rechargeable batteries for power. It is used by the coxswain in competitive rowing. "Cox Box" is sometimes written "Cox-Box" or "CoxBox" by users. It is not a generic term for a coxswains amplifier and should not be used as such.


Mainly used in Eights and Fours the read outs are used by the coxswain to monitor the performance of the crew and manage the race. Whether a multi-lane race or a time-trial style "head race", every rowing race involves strategic shifts in stroke rating to adjust speed and make moves on other crews while preserving the energy level of the crew. While higher ratings generally produce faster boat speed, rowing is an extremely physically taxing sport and high ratings cannot be sustained for long. A typical 2000M race plan will involve a series of short strokes to get the shell moving from the stationary start, followed by high stroke rate (34 to 36 SPM) strokes to build boat speed, then a "settle" or reduction in stroke rate to row the body of the race, and finally a high stroke rate sprint near the finish line. Higher rating "power 10's" can be taken during the race to catch a competing crew, which can build momentum if they succeed, or dishearten a crew if they fail.

The Cox Box® contains an on-board rechargeable battery to power the audio amplifier and circuitry. Earlier models relied upon Nickel–cadmium battery packs but environmental concerns and regulations have resulted in a switch to Nickel–metal hydride battery packs, while the newest models rely upon removable Lithium polymer battery packs. The self-powered amplifier is linked to one or more waterproof loudspeakers along the boat making it easier for the crew to hear commands. This is particularly important for the rower in the bow seat as they are often furthest away. The coxswain wears a headband-mounted microphone, which is attached by a wire and waterproof connector to the Cox Box®. An inline accessory connector allows a walkie-talkie style radio to be connected so the coach can use the amplification to speak directly to the crew as well.


Before the development of the Cox Box® a megaphone strapped to the head of the coxswain was used to make the cox easier to hear. The Cox Box® was invented by Nielsen-Kellerman Co. in 1978 and has been in continuous production since. Other brands of coxswains amplifier systems have also been introduced to the market, including CoxMate and CoxOrb by Active Tools. All deliver amplification of the coxswain's voice using a microphone and series of wired waterproof loudspeakers, and most offer stroke rate monitoring and timing features. Some, such as the Coxmate SCT and SX units can receive input from a speed measuring impellers or GPS to report boat speed, typically measured in Meters/second or 500 meters predicted split time.

Strokes per minute (SPM) or rating[edit]

The Cox Box® has a liquid crystal display, showing the strokes per minute (SPM). On the NK Cox Box® systems, a magnet is positioned under nearest rower's seat (stroke or bow in a bow loader). As the rower moves up the slide (moving forward to prepare for the next stroke), a measurement is taken, and fed to the Cox Box®. The Cox Box® also features a timer which can be stopped, cleared, and reset, along with a stroke counter. For rows in poor lighting, the Cox Box® is also equipped with a backlight.