Technics SB-4500

Variations of the SB-7000, SB-6000 and SB-5000 to a lower price-point.

Phase Linear placement of the drivers
Adjusted with a special phase measuring system that includes a Bucket Brigade Device ; corrected with this were thee inter-related elements : drivers' locations, their frequency response rang and the crossover network.

Wide-range woofer
The 25cm woofer has a response extending as high as 4Khz and its voice-coil bobbin is made of hardened aluminium foil for good heat dissipation

Wide-range tweeter
A newly-developed sythetic resin prevents air-leakage around the 6cm tweeter and supports it with high compliance. The voice-coil is made of copper-clad aluminium wire for excellent conductivity and heat dissipation ; response extends to 28Khz with a fo very low at 350Hz.

I don't know of any differences between the 4500 and 4500A.
Finish was either matte-ish grey or, as seen here from a 1977 USA leaflet, wood veneer - maybe that is the sole extent of the differences between A and non-A ?