Working in the Front Line Page 2

Errors in frequency response of only marginally greater amplitude may impart subjective alterations in timbre or tonal balance. The sense of "immediacy"—the sensation of proximity to the performers—may also be affected. Perspective—the feeling of front-to-back distance in the soundstage—is a related parameter. Other effects include the feeling of transparency in the reproduced sound. Loudspeaker designers become keenly aware of these subjective effects, which may be deliberately or otherwise hidden within the normal tolerances of the amplitude/frequency responses of a nominally well-designed loudspeaker system.

Unscrupulous speaker designers have frequently exploited such subtle changes in energy balance to result in a design with a particular accentuated subjective parameter. Such designs may well be commercially successful for a while; ultimately, however, a consensus develops among listeners indicating that a particular design favors one class of music or type of recording over another, and the trick is exposed, if not fully understood.

Loudspeaker reviewing problems
If hi-fi reviewing in general is considered to be a hazardous undertaking, speaker assessment must rate as a veritable minefield. There is so much potential here for inconsistency of opinion that the test results need to be most carefully balanced before appearing in print.

Factors to take into account include: 1) the listening-room environment and its relationship to the specific design of speaker; 2) the mounting and placement of the speaker; and 3) matching to the associated audio chain, including the amplifier and the maximum available headroom. Ultimately, the good taste and judgment of the critic or critics will remain a dominant factor.

Without going into great detail on the subject of loudspeaker assessment, it is worth noting that a considerable quantity of interesting and revealing laboratory data can be amassed for a particular model. These measurements may indicate that a given design could not possibly be a bad performer, yet conversely, no amount of good measurement results can guarantee that a loudspeaker is really any good and will therefore be the beneficiary of strong reviews and successful sales in a competitive market. The history of high fidelity is littered with superbly engineered models which have measured well but never made it in the real world. How does the reviewer explain to a designer who only believes in graphs and meter readings that his brainchild does not sound involving or interesting?

Good lab technique is a vital part of reviewing and acts as an error trap, identifying common design weaknesses and faults, or the effects of manufacturing tolerances. There is always the temptation, however, for the reviewer to use the lab results as a foundation on which to base his or her arguments. Subjectivity again holds sway, even in the interpretation of such measurements. If the product is not felt to sound good, measured weaknesses may be brought into focus. Conversely, if the unit is favored, the reviewer must then guard against the tendency to ignore or gloss over measured imperfections.

Subjective opinion & sound quality
The assessment of sound quality is the foundation of a good review; without it, the review is almost worthless. Yet how can sound quality, in its broadest sense, be accurately assessed without recourse to the time and expense of fully validated statistical testing? Many members of the audio establishment would prefer not to hear the answer: The ability to assess sound quality is not a gift, nor is it a feature of a hyperactive imagination; it is simply a learned skill. Like any skill, it is acquired by example, by relevant education, and by practice. A basic understanding of music is helpful, not least because much of the subjective characterization is necessarily based on musical terminology and critique. Regular experience of live music-making is exceedingly valuable in order to refresh one's aural memory for natural sound. The latter must form the true foundation of all subjective assessment.

Subjective assessment should be a disciplined process, but should not be so rigorous as to exert undue stress on the assessor. It is a well-observed fact that a person's sensitivity to subtle but worthwhile sound-quality differences reduces to near-invisibility under stressful and trying test conditions.

For example, it is well known to most critics that if you arrive at a situation where differences appear to be small, the harder you try to hear them, then the more impossible the task becomes. On such occasions, a scheduled rest, a change of program, and a conscious effort to relax and distance one's immediate concentration on the matter at hand, generally lead to a recovery in acuity. Paradoxically, the less the critic personally cares about the outcome of a test, the more aware he or she is of the subjective quality differences concerned.

Greatest awareness of the long-term quality of an item is generally obtained by the single presentation method, while maintaining critical control of absolute level and channel balance, combined with an awareness of any relevant response errors. Initially, single presentation techniques were confined to loudspeakers; they later extended to cover RIAA preamplifiers, pickup cartridges, tuners, power amplifiers, and then to preamp line stages and CD players. Finally, the technique has been applied to the reviewing of audio cables and passive components such as resistors, inductors, capacitors, and even printed circuit boards (pcbs) and pcb tracks.

A whole multitude of subjective differences has been identified which relate consistently to engineering differences. At present, however, established measurement has great difficulty in elucidating these differences; as a consequence, most academics tend to regard them as irrelevant. Such skeptics would certainly not like to hear that a number of audio critics can reliably identify the sound of specific kinds of metallic conductor used in audio cables.