Rowing’s original waterproof timer-amplifier now has a removable battery for easier charging, overmolded connectors for protection from wear and brightly colored rubber bumpers for durability and easy identification in the boathouse and at team events.

Note: The CoxBox comes standard with battery and rubber bumpers only.  Microphones and chargers must be purchased separately.

Availability: In stock

Cox Box Product Diagram

Step 1: Charge Your CoxBox

Each CoxBox leaves our factory fully charged. If it’s been awhile since you bought your CoxBox, or you have one that has been used before, use one of the two compatible chargers from NK. We recommend using the cradle charger over the basic charger because it causes less wear on the connectors on the front of the CoxBox. It’s also not a bad idea to take an extra battery with you out on the water.

Step 2: Connect the Microphone

NK makes two types of microphones: one with a BNC (metal) connector on the end of the wire, which is compatible with the old-style (metal can) CoxBox, and one with an R2 (rubber) connector on the end of the wire, which is compatible with this CoxBox (and all others made in 2008 or later).

Step 3: Connect Your CoxBox to the Boat

The wire you’re looking for in the boat is called the A+ harness. The connector on the end of this wire looks like the one at the end of the microphone wire, only bigger. Line up the pins inside this connector with the holes in the black plastic receiver that jut out from the face of the CoxBox. If it’s not connected, you’ll still be able to turn on the CoxBox, but you won’t get a stroke rating or hear any sound through the speakers.

To learn more about how to use the CoxBox, read the article CoxBox 101: How to Time Pieces and Store Data

Included in Package
  • CoxBox
  • CoxBox Can Protective Bumper
  • CoxBox Rim Protective Bumper
  • Hand/Shoulder Carry Strap
  • Rechargeable lithium-polymer Battery
Water ResistanceWaterproof (IP67, NEMA-6)
MemoryStroke rate automatically stored every 10 seconds, up to 42 minutes and 40 seconds stroke rate, count and time can be manually stored at the press of a button.
Control Unit Weight20 oz (567.09 g) for control unit
Unit Weight20 oz (567.09 g) for control unit, battery pack, bumpers; 4oz (113.4 g) for battery pack; 2lbs (907.2 g) for complete system for 8+ with 3 speakers
Unit Dimensions 4 in x 4.5 in (tall x diameter) (101.6 x 114.3 mm).
Display Dimensions2.75 x 1.5 in
Note: Control unit with battery pack installed and microphone attached floats. Control unit alone floats.Battery pack does not float.
DisplayHigh-contrast monochrome LCD
BacklightBlue/green electroluminescent backlight, auto-on.
ControlsKnob (on/off/volume), 3 buttons with tactile response (start/stop/split/memory).
Battery TypeThree cell lithium polymer rechargeable with on-board fuel gauging.
Battery Life Expectancy3 hours at typical use (3/4 of full volume, talking 50% of the time, using 3 speakers).
Charging Battery930 mAh, 10.3 Wh. Performance capacity varies greatly with volume and quantity of speech as well as number of speakers. 3 hours expected in Cox Box with 3/4 volume, talking 50% of the time, using 3 speakers. As much as 10 hours with more intermittent us
Battery TemperatureCharging: 32 to 113°F | 0 to 45°C; Operating & Storage: -4 to 113°F | -20 to 45°C
CaseInjection-molded polymer case, acrylic lens, injection-molded elastomeric bumper.
Warranty Period2 Year Warranty
Chronograph 00:00.00 00:00.00 - 59:59.99 Auto roll-over at 1 hour. 1/100th sec. resolution.
Stroke Count 000 0 - 999 Rate input from seat sensor, auto start with first stroke, auto roll-over at 1000 strokes
Stroke Rate 000 ½ 10 - 127 ½ Rate input from seat sensor, auto start with first stroke

CoxBox Boat Wiring

4+ 2 Speaker Setup

8+ 3 Speaker Setup

CoxBox Troubleshooting Documents

329090 pg 2 Speakerplug_repair 3031

CoxBox Operation, Maintenance & Troubleshooting Guide

CoxBox Customer Operation and Diagnostic Guide

Testing CoxBox Wiring in an 8 with a Multimeter

SpeedCoach/StrokeCoach Wiring


CoxBox Instruction Manuals

CoxBox Instruction Manual

CoxBox Maintenance Kit

CoxBox Panel Protector Installation Instructions

Product Questions

With increased airport security, traveling with your CoxBox is trickier than ever. We recommend you check the CoxBox in with your luggage. Include product literature that explains what the CoxBox is. Brochures can be obtained from NK, or product literature can be printed from the website. Another option that may work when traveling overseas is to ship your units through UPS. If you do so, be very clear that these are used units, being imported temporarily. Put a low replacement value on them, but do note that you run the risk of the replacement value being used for customs. VAT (tax) is quite expensive and if they decide to hold the units in customs until you pay you could be without your CoxBox for the race.

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Note:NK recommends troubleshooting any boat harness issues by substituting known “good” equipment in place, one at a time, to determine the location of the failed equipment.

See the following document for details on testing the Harnesses and speakers:

Testing CoxBox Wiring in an 8 with a Multimeter

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(Only needed for CoxBox Battery Packs Pre-August 2014)

NK recommends rebalancing your Cox Box battery twice a year. If you have not done so recently, this is a good time to re-balance them prior to winter storage. This procedure is also recommended for Cox Box Minis and Blue Ocean Batteries.

Steps to Re-balance:

  1. Run the unit until the battery dies. Generating audio while the unit is running will assist in draining the battery. Otherwise turn the units on and set them dark room so that the backlight is activated to cut down on time to drain the battery.
  2. After battery is drained, WAIT 2 DAYS to allow any remaining charge to drain out of the battery.
  3. After 2 days, recharge the batteries until they reach FULL. This will re-balance the cells in the battery and ensure they are ready to go for future use.

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  • Is the switch in the HOLD position?
    • If the toggle switch is in the HOLD (top) position, the unit will not read. Place the switch in the RUN (middle) position.
  • Is there a problem with the unit?
    • When there is no reading or there are irregular readings, the problem usually lies with the sensor, not the unit itself. To test the unit:
      • Turn the unit on; clear the memory and place in ready mode.
      • Using a pair of tweezers or a bent paperclip (unfolded into a “U” shape) gently poke into the two exterior holes of the CB plug (“A” & “D” sockets of the P5).
      • The stroke rate should update every other poke. If this happens, the Cox-Box is functioning properly and the problem exists with the rate sensor in the wiring harness. Order a replacement rate sensor (NK Part No. 0293) and install it according to the directions supplied.
      • If the rate does not update during this test, check the sockets to confirm that they are the same height within the plug and have not been pushed into the plug. If the sockets have become recessed, gently use a pair of needle-nose pliers to work the socket out to the same level as the other sockets.
      • Use the Audio System Maintenance Kit (NK Part No. 0230) to clean any imbedded dirt or debris from the sockets and inject a small amount of Nyogel into the sockets to prevent corrosion and ensure good electrical contact.
    • If the charger is not working correctly and you did get a voltage reading, it is probable that one of the pins has become disconnected or misaligned. Pins usually become misaligned due to debris in the plug—it is important to keep the plugs clean.
  • Is the wiring intact?
    • Check the wiring for pin alignment and cuts or nicks. Check the sensor and seat magnet placement for proper positioning and security. Clean all of the sockets and pins using the Audio System Maintenance Kit (NK Part No. 0230). Ensure all connections are tightly sealed to prevent water entry.
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  • Is the wiring clean of cuts or nicks?
    • Cuts or nicks in the wiring are the most frequent causes of audio problems. Be sure that all of the connectors (pins, sockets, plugs, receptacles) are not damaged and are positioned properly.
  • Is the microphone working properly?
    • The microphone may be the cause of failure. It is the most delicate component of the CB system. Test the system with a microphone you know is good. Note: A damaged microphone often causes static.
  • Are the speakers working properly?
    • Be sure all of the speakers are plugged in properly and are in working order (replace one at a time with a known good speaker to test). If you are getting a loud squealing noise, try pointing the speakers away from the coxswain to minimize feedback.
  • Is the audio signal balanced?
    • f you are familiar with how to use an ohmmeter, you can verify if the audio signal of the CB is balanced. Measure from the ground socket “A” to the audio socket “B”. It should read approximately 3.1 volts. Measure from the ground socket “A” to audio socket “C” it should read the same as “A” to “B”. If they are not balanced, return the unit to NK.

Never attempt to repair the CoxBox unit yourself. The units are specially sealed to make them watertight. Breaking this seal often causes very expensive damage and will void the warranty.

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Nielsen-Kellerman has been around since 1978. Our roots are in the sport of rowing, and we have been building performance products for athletes of all levels since the beginning. Year after year, we have created newer and better products for our customers, including novice coxswains, Olympic athletes, college coaches, masters rowers, and everyone else in between. Some of our products including the SpeedCoach family, have crossover unto other paddle sports(outriggers, dragon boats, canoes, kayaks, and stand up paddle boards). We have worked closely with partners and customers within the paddling community to make the best product we can. We are always open to new ideas and ways to make the products a better tool for your training, fitness, and racing needs.

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  1. Coxswain Tips: Listen and Count at the Same Time

    Question: When I’m counting out strokes for a drill, I often lose track of which stroke we’re on, especially if the coach is talking. I know that what the coach is saying is important, but I don’t want to mess up the drill. How can I listen and count at the same time? There is a stroke counter at the top right of your CoxBox screen. If you’re starting the drill from a standstill, press and hold the stop/start button (the big one) to re
  2. CoxBox 101: How to Time Pieces and Store Data

    We get many questions from new coxswains about how to use the CoxBox on the water. Here is a short how-to guide to get you started:
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