Sharp WQ-T354
The Sharp WQ-T354 first appeared in the year 1987. It has a total of 5 speakers, including two 12cm full-range speakers, two tiny piezo tweeters at the far edges, and a 10cm "X-Bass Super Woofer" on top. This Super Woofer has its own dedicated amp, as well as a band-pass filter that limits it to bass tones. Please be aware, the surround on this Super Woofer is made of foam, which disintegrates with age. So it will need to be replaced if it hasn't been done already. A lot of Ebay sellers won't tell you this. They also use dark, low-resolution photos to prevent you from seeing the rotten foam.
Here are some drawings from the service manual, showing the X-Bass system. The Super Woofer is attached to an accordion-shaped plastic chamber hidden inside the boombox (it's the object labeled "Extra Bass Box" in the drawings). This box has baffles inside that extend the bass response. Its outlet is connected to the large bass port on the front of the boombox.
This is exactly the type of radio I fantasized about when I was young, because I loved bass ports. I'd go into stores and look at radios like this, trying to figure out whether the ports were real or fake. Were they actually connected to the speaker chambers? Or were they fake, sealed off, cosmetic only? Sometimes I would bring a flashlight into the store and shine it into the ports to learn the truth. 
Fortunately the one on this Sharp is real, and it works great.
Another interesting feature is the "Twincam" cassette deck that accepts 2 tapes in the same door. It has two pinch rollers and extra-long reels, and it allows you to switch tapes without opening the door. Or you can set it on "Continuous Play" so that it will play both tapes sequentially.
This boombox measures 26 inches long and weighs 12.3 lbs without batteries. It is powered by two Toshiba TA7283AP amplifier chips - One for the X-Bass speaker, and one for the remaining 4 speakers. Sharp says there are 3 amps, but I think what they're really saying is that the second one is being used in dual-channel stereo format. Anyway, power output is a total of 16 watts RMS. Half of that goes to the X-Bass speaker.
The service manual for this model can be purchased through this vendor: www.Analogalley.com