The front door speakers in a 400E are 4 inches in diameter, and the rear deck speakers are 6 1/2 inches in diameter. You can also check out a product fit guide, such as the one on the Web site for JBL speakers, to get more information about speakers sizes and mounting depths.
Deutsches Institut für Normung e.V. (DIN; in English, the German Institute for Standardization), which sets standardized measurements and designations for many items - sizes, electrical contacts, part designations, and a broad spectrum of things. See Deutsches Institut fur Normung - Wikipedia, the free encyclopedia.
More relevant to your car, it specifies the size of the dashboard opening for audio equipment. A designation just of DIN is single height; its frontal size is 7" wide x 2" tall. A Double DIN opening would be 7" wide and 4" tall. DIN designations are also used when describing Mercedes COMAND units. A COMAND 2.0 unit is two DIN units tall, and COMAND 2.5 is 2-1/2 DIN units tall.
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2005 S500 4-Matic
with Gateway 500 iPod integration
Formerly: 2000 S500
with Ice>Link iPod integration
Moto V710 phone with MikBox
Upgraded Voice Control