When comparing amplifier specifications, keep in mind that the amplifier is not the last link. Actual system performance is dependent on how the speaker system performs. An amplifier may have superlative specifications, but what about the speaker system?

Box & cone speaker systems (cone speakers mounted in an enclosure) are prone to deficiencies that introduce distortion.

The typical cone speaker design is a cone suspended in a frame by a flexible membrane from the outer and inner area of the cone to the frame. In the center of the cone is a coil attached to the cone. The coil is held in position within a gap of a fixed magnet by the cone suspension. The amplifier sends a signal to the speaker coil, producing a magnetic field in the coil that interacts with the fixed magnet. This results in the coil and attached cone moving in and out according to the amplifier signal. The cone moves air molecules, producing sound. Although a speaker of this design is driven by an electrical signal, it is by nature a mechanical design.

A speaker cone must stay rigid. To keep the cone rigid, it may be made out of heavy paper or some other stiff material. At lower volume levels, the speaker cone moves with relative ease. As the volume increases with higher amplifier power, the cone suspension, weight of the cone, and momentum work against cone movement.

Momentum is "the force or energy gained by a moving object." The weight of the cone adds to momentum. At higher volume levels, the speaker cone is rapidly pushed and pulled a significant distance as compared to lower volume levels. At the same time, the suspension, attaching the cone to the frame, is trying to keep the cone in the center of travel.

Ideally, a speaker cone should be able to move without any restrictions. Any force placed upon the cone in opposition to its intended motion in effect alters the cones performance, resulting in distortion. At higher volume levels, the amount of opposition to cone travel increases exponentially as momentum and the pull of cone suspension increase.

In addition to mechanical distortion, speaker systems that employ more than one driver using a crossover filter are subject to artifacts such as phasing between drivers. Although crossovers, typically filtering circuits with inductors and capacitors, may be carefully designed there will be some phasing in the crossover region. Multi-speaker system artifacts are fairly consistent at low or high volume. The distortion produced by mechanical artifacts increases at higher volume levels. Distortion caused by the mechanics of cone speakers is seldom, if ever, considered.

The reason for this writing is to point out that it does not matter if amplifiers in the path to the speaker have a couple percent of distortion, especially at higher volume levels where speaker distortion increases. In practice, at lower volume levels, a decent box and cone speaker system should provide a pleasing sound with perhaps one or two percent distortion. Exactly how much distortion is hard to tell, as speaker manufacturers very seldom state distortion figures (although involved, it is possible to measure speaker distortion). An AI search for the question of which speaker manufacturers provide distortion figures returned the following answer. "Most speaker manufacturers do not provide distortion specifications in their product listings, as it is often considered less favorable compared to the low distortion levels typically associated with electronics."

The bottom line is, if you are using a box and cone speaker system, you will have one or two percent of system distortion regardless of how low of a distortion figure an amplifier system has. Regardless of equipment specifications, sound reproduction preference is a matter of the listener's perception. Beyond the realm of equipment test results, it is an area more appropriately left to the field of psychoacoustics.

Electrostatic speakers deserve a mention. In 1971 I visited a coworker that had a pair of electrostatic speakers. At the time, they were the cleanest speakers I ever heard. From a reliability and budget standpoint, they are pricey and prone to overload failure.

Stereophile article
Pros & Cons of electrostatic speakers

Amplifier damping, used to reduce speaker ringing, is not effective in reducing mechanical speaker distortion.
EJ Jurich