"Circle of Sound" was a Zenith trademark used in the 1970s to designate a line of radios with slightly improved sound quality. I believe Zenith also used the term to describe some of its TV sets. In the radio line, there were some units that were cylindrical, playing up the circle theme. But that probably wasn't too practical, so instead Zenith made the C472-W3. I got mine in 1973 after the dial cord broke on my first clock radio, a US-made Westinghouse. For some reason, my parents just decided to get me a new one.
This radio served as my wake-up radio for seven years or so. It was replaced by a newer-model Circle of Sound clock radio with an electronic clock. In 1973, though, a digital clock meant a mechanical clock. Zenith used a Westclox alarm-clock movement which turned out to be prone to failure.
That's why the on-off switch on this radio is a little messed up. When the clock failed, somehow it reversed the "on" and "off" positions on the switch!
I also modified it to add a headphone jack, which the radio didn't come with. That's how I discovered how the radio produces a richer sound with a relatively small speaker: a substantial bass boost is added to the audio signal just before it goes to the speaker. It also helps that the speaker is a better-quality Pioneer speaker. The speaker fires downward into a plastic assembly that's supposed to direct the sound out and around the radio. In reality, that's a gimmick.
This radio has some signs of age. The backlit, semicircular dial has only one of its two lights working. The dial also reflects the circular theme. I have a portable Zenith radio, made about the same time, that also has a semicircular dial. It looks cool, but it's really not that special on the inside: it still uses a dial cord.
The plastic cabinet is in fair-to-good condition, but the fake-walnut veneer has worn off in many spots. The radio was made in Hong Kong, though I believe the mechanical clock was actually made in the United States.
AM performance is good, with good sensitivity and excellent gain control (i.e. weak signals sound almost as loud as strong ones). I haven't measured its AM audio response, but I estimate it starts rolling off around 4 kHz, with a gentle rolloff, typical of Zenith AM radios. FM performance is fair at best. This radio really can't stand up to the modern-day, crowded FM dial in most cities. It's sensitive enough, but not very selective and plagued with front-end overload, causing fake signals (images) to be generated across the dial. I've even found it interacting with analog TV sound to create images. That's not a problem these days, only because there's no analog TV any more.
Later Zenith Circle of Sound clock radios, the ones with electronic digital clocks, are more reliable but sound less robust. There seems to be less bass boost, and a lower-quality no-name speaker is used.
Another version of this radio was made without the clock, the Zenith H421W.
While this radio was good in its time, it wasn't really ready for radio dominated by FM stations. The clock went bust a long time ago but the electronics still seem to be good, and I bring it out every once in a while to find that it still works pretty well, despite the weirdness with the on-off switch caused by the broken clock.