Although it has taken some time, the benefits of THX-compliant receiver specifications have finally arrived in a big way. Marantz’s SR-18 is the second THX-Ultra 5.1 receiver I’ve tested in three months, and I am told by THX that the present trickle is about to become a flood, though most of the new models will be of the lower-power THX-Select variety. If those future models perform half as well as the SR-18, Marantz’s first THX-Ultra receiver, home theater enthusiasts will be inundated with top-performing equipment.
Like earlier THX-Ultra receivers, the SR-18 is a powerhouse. Its 140-watt-per-channel rating means that it can drive an 8-ohm speaker to play 21 dB louder than its rated sound-pressure level (SPL) with a 1-watt input. With a speaker whose sensitivity spec is, say, 89 dB, the SR-18 will generate peak levels of around 110 dB at 1 meter, which is extremely loud.
Of course, as a THX receiver (Ultra or Select), the SR-18 not only delivers equal power to all five speaker-level outputs, but it also contains such trademarked THX processing functions as Timbre Matching, Re-equalization, and Adaptive Decorrelation. Timbre Matching is intended to make the surround speakers sound more like the fronts, and Re-equalization applies a specific treble rolloff to compensate for soundtracks that have been balanced for theatrical playback. The third process, Adaptive Decorrelation, switches on surround-channel phase-scrambling circuitry automatically when the surround channels are fed identical (mono) or near-identical signals in order to increase the diffuseness of the surround-channel sound.
You can switch the THX processing on (all three functions at once) and apply it to decoded Dolby Digital, Pro Logic, or DTS multichannel signals. The SR-18 also has three general-purpose (but nonadjustable) surround modes that add simulated room reflections to any decoded multichannel program or to a stereo recording. Behind the front panel’s flip-down door are bass and treble controls (also accessible via the remote control), a headphone output, and an auxiliary A/V input. The horizontal, weighted Gyro Tuning knob on the front panel is fun to use and simplifies the arduous task of manually entering radio stations into the 50-preset memory (this can be done automatically, too). It can also be used to enter station names for the display of up to eight characters.
The SR-18’s rear panel is unusually well equipped. There are four digital audio inputs (two optical and two coaxial), a rare set of digital outputs (one optical and one coaxial) for feeding a CD or MiniDisc recorder, and a Dolby Digital RF input for connection to suitably equipped laserdisc players. All but the RF digital input can be assigned to any source component (except tuner and aux). Selection between Dolby Digital, Pro Logic, or DTS decoding, or stereo operation, can be automatic according to the nature of the input signal (some of these choices can be overridden)