BG 20 Cross – Mobile Audio System

Motivation and Requirements

Till now I focused on stationary audio systems for inside. As you might derive from the title this project targets on a mobile audio system. There are different reasons, why I decided to plan and build the BG20 Cross. The most reasonable was the need of such a system for the yearly tour on Labour Day (in germany: first of may) with my sports club. Accordingly the system had to match certain requirements:

  • Powered by battery
  • Proper duration
  • Mobility
  • Adequate audio quality and volume
  • Low cost

Key Decisions

Regarding the battery and the low cost issue I decided to use an existing car battery from a diesel vehicle with 65Ah. This further implied, that a manual transport of the audio system would have been impossible. Fortunately my grandparent provided an old coaster wagon to build upon.

Another topic was to choose an amplifier. Due to the low cost requirement and the 12V DC from the battery I bought a used stereo car amplifier on the internet: Got a Kenwood KAC-821 with 2x75W (rated power), which should be enough for adequate audio quality and volume.

Construction and Result

After these fundamendal decisions the setting was clear. The only thing left, was to build the corresponding loudspeaker with an adequate form factor for the coaster wagon. For this task I used two fullrange drivers of Visaton, namely the BG 20 – 8 Ohm (see image below). The crossover and the bass-reflex opening for the speaker were computed using the simluation software Boxsim offered by Visaton.

BG 20 with Crossover

BG 20 with Crossover

All in all the speaker has a volume of 90 liters, 45 liters for each driver and the shape of a hexagon. The shape is due to the profile of the coaster wagon as it fits exactly into it.

BG 20 Cross Speaker

BG 20 Cross Speaker

Half of the coaster wagon is filled, if it contains the speaker. The car battery stands directly behind the box covered by a wooden frame. The amplifier is mounted over the battery and below the top cover upside down. In the end there’s one fourth of space left, which is covered with styrofoam. Here you can place drinks and food to keep them cold.

BG 20 Cross - Mobile Audio System

BG 20 Cross – Mobile Audio System

The previous image shows the final result of the BG 20 Cross. Volume and quality of the system are more than satisfying. In addition the battery holds very long (more than one day). Further the costs summed up to adequate 150€ (without car battery and coaster wagon). This year was the third time I carried the wagon for Labour Day and everything went well. Thus I can claim the requirements stated above are fulfilled.

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