In the first part of this blog, we talked about PSB’s Paul Barton taking a hand-picked group of audio journalists on a guided tour of the anechoic test chamber and control room at the NRC—a facility where many, many great loudspeaker designs have been put through their paces. Click here to read Part 1 of this blog. In the latter part of the day of our visit, Paul had something really special planned, in the form of an official NRC-style blind listening session/listening test.
The NRC maintains IEC-certified listening facilities whose dimensions and reverberant characteristics are a matter of public record, partly so that other listeners/designers could, if they wished to do so, construct similar listening rooms of their own. The room is rectangular in shape, with no dimensions that are multiples of one another (which would cause resonance problems), has a carpeted floor, with storage cabinet/bookshelves down one side, simple acoustic treatment panels down the other side, and provides an specific area to the front of the room where loudspeakers under test are to be placed. The wall behind the test speakers features damping materials, and the left and right corners of the wall behind the speakers are covered in absorptive curtains, which extend several feet out along the sidewalls of the room (all of these features are part of the IEC documentation for the room).
In front of the loudspeaker test area is an acoustically transparent, but optically opaque screen, which contains a removable center section to give researchers access to the speaker test area—making it easier to swap test speakers in and out. Behind the center section of the screen is an illuminated display that shows the (randomly chosen) ID numbers for each of the speaker systems under test. Under NRC practice, there are typically no more than four speakers systems under test in any one listening session, so that as the tests progress the listener simply sees a glowing “1”, “2”, “3”, or “4” to indicate which speaker is playing at any given moment.
The night before the listening sessions, Paul Barton announced that he had some “homework” for us—in the form of detailed instructions for listener/participants in the blind listening tests. Listeners were told they would be listening to several loudspeaker systems with various program materials, and would be rating the speakers in several performance areas, as noted below.
• Clarity/Definition (the scale runs from “Very unclear, poorly defined” to “Very clear, well defined).
• Softness (the scale runs from “Hard, shrill, very sharp” to “Very soft, mild, subdued”).
• Fullness (the scale runs from “Very thin” to “Very full”).
• Brightness (the scale runs from “Dark, very dull” to “Very bright”).
• Spaciousness, Openness (the scale runs from “Dry, very closed” to “Very open, spacious, airy”).
• Nearness/Presence (the scale runs from “Very distant” to “Very near”)
• Hiss, Noise, Distortions (the scale runs from “Very little” to “Very much”)
• Loudness (the scale runs from “Very soft” to “Very loud”)
• Pleasantness (the scale runs from “Very unpleasant” to “Very pleasant”)
• Fidelity (the scale runs from “0”, which roughly means “the worst speaker imaginable”, to “10”, which roughly means “no further improvement can be imagined; for obvious reason, most listeners rate speakers somewhere “1”, meaning “Bad” on up to “9”, meaning “Excellent”).
Finally, listeners are given a blank frequency response chart on which they can attempt to sketch perceived response curves, if they wish.
Conceptually, I stumbled on three of the NRC rating parameters: “Hiss, Noise, Distortions;” “Loudness;” and “Pleasantness.” Here’s why. To me, “Hiss, Noise, and Distortions” are as much, if not more, a function of source components as they are of speakers (for example, a speaker simply can’t produce hiss unless it is fed hiss). “Loudness”, in turn, is more a function of available amplifier power and the manner in which that power is applied; obviously one loudspeaker can be more sensitive than another, but it can’t and doesn’t “turn itself up in order to play louder.” “Pleasantness,” finally, is something I think of more as a property of music than of the speaker; for example, if you feed an accurate, high fidelity speaker obnoxious and abrasive-sounding material, it’s going to sound, well, obnoxious and abrasive (as well it should under the circumstances). Ideally, a speaker wouldn’t have a pleasant or unpleasant style of its own; it would simply reproduce what’s on the recording, whether for good or ill. But despite these conceptual misgivings, the good news is that, as the instructions explained, the main rating—the one that trumps all others—is the “Fidelity” rating (a concept that both objective measurement folks and observational listeners should be able to support).