Berry Gordy of Motown had his house engineers (Mike Miller, et al) built replicas of AM car radio systems in-house to replicate the sound of an automotive sound system. Many Motown songs were then re-equalized, re-mixed and run through this system to assure punch and clarity in cars, which was of course, a primary outlet for music in the heyday of AM Soul and Top 40 radio.
I understand the most elaborate of these test setups even used a CBS Labs Volumax AM radio processor, the predominant station signal processor of the era for dead-on replication of what stations used. There is a striking difference between the hard-panned 3-track stereo studio master tapes of early Motown (Vandellas on the left with rhythm, the rest of the Funk Brothers on the right, and Martha Reeves' lead vocal dead in the center) and the mono single release mixes.
(The "Motown Remixed" project of a few years ago re-did these 3, 4, and 8-track studio masters for clarity, even to the point of releasing alternate takes of familiar hits that sounded better than the original release versions. For instance, The Temptations' "My Girl" in the new series is 16 bars longer than the original 1965 release version, has a much better full stereo mix, and the orchestra plays the song to conclusion instead of fading out.)