[. . . ] The shape of the housing plays only a minor role with respect to the playback of low frequencies and, therefore, is rather freely selectable. However, try to avoid unusual shapes which require extensive work with respect to trimming and gluing. With a thickness of 18 to 25 mm are perfectly suited for building speakers. [. . . ] With a thickness of 18 to 25 mm are perfectly suited for building speakers. All abutting housing walls should be glued, screwed together and sealed to avoid a continuing detachment due to vibrations and environmental influences in the vehicle. Acoustic insulating material (sheep's wool or polyester web) which fills the inside volume to at least 50 percent increases the effective housing volume by 5 to 15 percent. The cables from the amplifier to the subwoofer should be kept as short as possible and have a cross section of at least 2. The finished subwoofer housing should be perfectly stable and airtight. If possible, use bass reflex channels with a diameter of 7 to 10 cm to avoid the air noises generally associated with smaller openings. PVC pipes are available commercially in different diameters, whereby the pipe sections can be routed inside the housing using appropriate joints and fittings. Use active (electronic) crossovers, such as those integrated into all Blaupunkt amplifiers. Prior to drilling the mounting holes, make sure that no cables and parts of the vehicle will be damaged. Do not install subwoofers on loose rear shelves (fastback vehicles) or at places open to the front. To dispose of the product, please use the available waste return and collection systems. Before installing the housing, please observe some fundamental design instructions: Subwoofers with infinite baffle can be installed in a vehicle by simply using a wooden board trimmed to size which ensures an acoustic separation between the front and rear sound components of a woofer. The wooden board is affixed in the trunk under the rear shelf or in the back of the rear seat bench. The shape of the housing plays only a minor role with respect to the playback of low frequencies and, therefore, is rather freely selectable. However, try to avoid unusual shapes which require extensive work with respect to trimming and gluing. MDF boards or high-quality plywood made out of birch with a thickness of 18 to 25 mm are perfectly suited for building speakers. [. . . ] The shape of the housing plays only a minor role with respect to the playback of low frequencies and, therefore, is rather freely selectable. However, try to avoid unusual shapes which require extensive work with respect to trimming and gluing. MDF boards or high-quality plywood made out of birch with a thickness of 18 to 25 mm are perfectly suited for building speakers. [. . . ]