SOUND is still the stepchild of television. But recently there have been some attempts to upgrade the latest TV sets. Probably the most promising of these efforts is the audio section announced by Magnavox for its top-line models: a 12-watt amplifier driving a three-way speaker system. For its mid-priced 25-inch screen TV sets, Maganavox is offering built-in 7-watt amplifiers and two-way speakers.

Power levels approaching hi-fi expectations also are available in some of Zenith's large-screen sets. Specifications here indicate a 10-watt amplifier with less than 2 percent distortion over the range from 100 Hz to 10,000 Hz. Separate bass and treble controls are provided and the speaker system uses four drivers -- oval woofers of 9- or 7-inch diameter, and a pair of 2-inch tweeters. Ten-watt amplifiers and four-speaker systems also are found in a new G.E. line of TV sets.

Quasar's top TV sets have an 8-watt audio amplifier with bass and treble controls, with three-speaker systems in most, and a four-speaker system in one of their 25-inch consoles. GTE-Sylvania offers the option of adding more audio power in the form of an add-on speaker-amp unit said to be usable with any TV set or with any video cassette deck that has a normal audio output jack.

"Simulated stereo" in the form of a delay system is featured in some of Sony's 26-inch-screen units; the setup includes speakers in two independent bass-reflex enclosures. And RCA is offering what it calls "dual dimension" sound: apparently an older technique for "simulated stereo" in which the audio range is divided and spread out in more than one speaker.

The "audio output jack" mentioned in connection with the GTE-Sylvania add-on unit can, of course, drive the "aux" input of any external amplifier. This kind of jack was often described in technical literature a few years ago as a good way of getting TV sound away from the minimal audio amplifier and speaker typically used in older sets and piping it instead through one's own hi-fi system. This jack today is showing up on more and more TV sets of all sizes and in all price ranges. Using such a jack, or receiving the sound of TV programs on a special tuner (such as the Pioneer TVX-9500), probably is still the best way to get the sound portion of a television program.

Q. One wall of my new living room contains bookshelves. The opposite wall has large windows with heavy draw draperies. I can place my speakers against either wall and arrange the seating accordingly, but I'm not sure which wall to use. What do you advise?

A. As a general rule, speakers should be placed so as to radiate from the "live" portion of a room. If you plan to draw the draperies over the windows most of the time, the bookshelf wall becomes relatively "live" and would be a good location for the speakers. However, with the draperies pulled back to expose the glass of the windows, that wall becomes "more live" than the bookshelf wall. I think you had better experiment a little -- and I hope your speakers are not too heavy!

Q. If I make a tape recording of a disc that has been dbx-encoded, played through the dbx model 21 decoder, should I use the decoder for playing back that tape?

A. No. The model 21, patched into the system correctly, will register a "decoded" (i.e., expanded) signal onto the tape. Further expansion then is not required.

Q. I can get hold of a big speaker system that formerly was used by a rock group at live concerts. Do you think it would serve well as a speaker for my home hi-fi setup?

A. Probably not. The kind of speaker system you describe is typically built for ruggedness and very loud volume. Unless this is a very unusual music-instrument speaker, chances are the extreme highs and the deepest bass have been slighted in its design in the interest of ruggedness and efficiency. For a home music system, you would do better to use a speaker that was designed in just the opposite way -- that is, it gives up something in the way of "rock level" loudness but it does provide cleaner highs above, say, 10,000 Hz, and well-defined bass below 60 Hz.