Here's a quick and easy guide to help you understand the rim numbers which reveal a speaker's manufacturer and its production date. We'll use my picture below as an example.
The speaker reads C10N C7438 5 on the right: which describes the model and its construction. But what about the 6-digit code 220438 to the left? That's the code that reveals the manufacturer as Jensen and the production date as the 38th week of 1964.
Speaker companies, along with other electrical manufacturers, were assigned EIA (Electronics Industry Alliance) codes which were used to identify their equipment. The 220*** portion of the rim code is the number assigned to Jensen. Other speaker companies were assigned different prefix codes as follows (to name the main ones of our hobby).
The last three digits of the rim code, ***438 display the production date. The "4" gives the last digit of the year of production. I knew the cabinet from which this speaker came and knew the decade to be the 1960's - therefore this speaker was made sometime in 1964. The "38" refers to the calendar week.
Therefore the C10N speaker above was made in the 38th week of 1964. Right about the time The Kinks were in the #1 spot w/ You Really Got Me. Neat huh?
A speaker with the code 285312 would be.........................a Rola made in the 12th week of 1963 (or '53). Still helps to know the equipment from where it came to make a spot on age determination.