Specifications

Reference Output Voltage
Voltage Gain
Output Current
Output Source Impedance
Overload Restoring Time
Stability with Capacitive Load
Harmonic Distortion and Noise
Modulation Distortion
Difference-Frequency Distortion
Noise Output Voltage
Phase Response
D.C. Offset at the Output
Hum
Crosstalk
Acoustic Noise Level
Mechanical Noise
Input Sensitivity
Input Impedance
Output Impedance
Load Impedance Range
Voltage Output Capability
Current Output Capability
Transient Output Capability
Transient Overload Recovery Time
Asymmetrical Clipping
Frequency Response
Phase Response
Phase Margin
Time
Total Harmonic Distortion
Intermodulation Distortions
SMPTE IM Distortion
IHF IM Distortion
DIM 30 Distortion
Noise
Hum
Radiated Interference
Conducted Interference
Crosstalk
corresponds to reference level playback. In turning the volume down, the volume level is expressed in
-dB, or how many dB below reference level you are.
Separate Amplifiers and the Amplifiers in Receivers
Metrics Tested on THX Amplifiers:
It's too easy for people, including us here at Secrets, to
say "get as much power as you can", "you should have at
least 100 watts per channel", and so on. While having
more power than you need, even lots more, is not a bad
thing and in fact is much preferred by speaker
manufacturers (in that more speakers are damaged
from underpowered amps driven to clipping, than ones
which were fed too much power), the reality is that
power, REAL power, is expensive. The question is, how
much is needed to drive a reasonably efficient speaker
in a reasonably sized room to reference level and still
have adequate headroom left over?
THX has done something which, to my knowledge, no
one else in the industry has done, at least on the scale
which they have done it: They have logged the
dynamic content of virtually every piece of finished
sound track they can get their hands on (we're talking
hundreds of sound tracks here) and from that
developed a practical "dynamic" requirement for
multi-channel power amplification.
All of the THX amplifier tests use bursts in various
combinations at various frequencies, at various lengths
of time, repeated cycles and combinations of speaker
loads. This enables THX to uniquely qualify an
amplifier, particularly a receiver, as capable of playing
sound tracks to reference level (given of course a
certain speaker efficiency and room size limit).
Make no mistake: THX Ultra power amplifiers tend to
be very powerful. We've never seen one with less than
100 watts/channel continuous RMS, full band, all
channels driven, BUT because of the "practical sum"
THX has defined for themselves, even seemingly modest
receivers under $1,000 can get THX Select2
certification and provide a satisfying experience for a
lot of people who can't afford a stack of THX Ultra
power amps (we'll talk about Select- vs.
Ultra-Certification a little later).
But it's not all about raw power. As we mentioned
when talking about the THX Controller, the input and
output levels and impedances of everything "THX" are within a certain tolerance so that all pieces "talk"
to each other synergistically. One can see from the metrics list above that everything down to the hum
of the power supply transformer must be in check to be THX certified. Yikes!
Speakers and Subwoofers
Back once again to the realties of the consumer market, and once again knowing that a living room will
remain a living room, much of what makes THX speakers unique and special has to do with addressing
this fundamental tenet.