ADS L620's are exceptional speakers and some of the best 2 way "bookshelf" speakers that were available at any price from any manufacturer during the late 1970's - early 1980's. There were two generations of L620's; the first generation introduced in 1978 had cloth grills - the second generation introduced in 1980 had metal grills and featured a number of enhancements including improved drivers, crossovers and speaker terminals. No matter what generation you have, you'll find that the woofer surrounds are made of butyl rubber, which won't rot over time like the foam that was used by most other manufacturers of the era.
To get the best sound out of your L620's, be sure to use speaker stands. ADS sold optional stands for most of their 2 and 3 way speakers that elevated / angled them to the proper listening height. You'll find the sound to be much improved when you get them off the floor.
For detailed information on ADS L620 speakers, see page 12 of the 1980 ADS brochure that can be found here ...