Reference

As Hans Christian Oersted, the Danish physicist and founder of electrodynamics, discovered in 1819, an electric current passed through a wire generates a magnetic field. Place that wire close to a permanent magnet and the interaction of the two fields will generate a force. That, in two sentences, summarizes the operating principle of the motor that energizes every moving-coil drive-unit in millions of loudspeakers worldwide. It sounds simple, but—like everything in audio—it isn't.

In 1977, just as I was about to take my first faltering steps in hi-fi journalism, the UK's Hi-Fi News ran two articles, translated from French originals by Jean Hiraga, that seemed to me and many others to turn the audio world we knew upside down. The second of them, "Can We Hear Connecting Wires?" was published in the August issue and is the better remembered because it introduced many English-speaking audiophiles to the contention that cables can sound different. The earlier article, published in the March issue, was less earthshaking but still an eyebrow-raiser of considerable force. Simply titled "Amplifier Musicality," it was a response to the word musicality being increasingly used in subjectivist circles to describe the perceived performance of amplifiers and other audio components. It was implicit that musicality was a quality not captured by conventional measurement procedures—a lack of correlation that Hiraga's article sought to address.

The introduction in 1982 of the compact disc ushered in the age of digital audio. Audiophiles now have lots of new digital toys and technologies at their disposal, including SACD, DVD-Audio, MP3 players, hard-drive–based CD players, and digital equalization and room correction, to name a few. Videophiles have similarly benefited from digital technology, with an armamentarium that includes high-definition television, DVD-Video, Blu-ray, HD DVD (the latter two still on the horizon), DLP, LCoS, and D-ILA, among others. Action-based films have also benefited from breathtaking, digitally enhanced special effects. Even those of us who still prefer LPs must acknowledge—reluctantly, perhaps—the incredible impact that digital has had on our hobby (footnote 1).

If you missed Part 1 of this article (Stereophile, January 2005), or it has faded in your memory, here's a résumé. (Readers who recall Part 1 with crystalline clarity, please skip to paragraph four.) The accurate measuring of loudspeakers requires that the measurements be taken in a reflection-free environment. Traditionally, this has meant that the speaker be placed atop a tall pole outdoors or in an anechoic chamber. Both of these options are hedged around with unwelcome implications of cost and practicality. To overcome these and allow quasi-anechoic measurements to be performed in normal, reverberant rooms, time-windowed measurement methods were developed that allow the user to analyze only that portion of the speaker's impulse response that arrives at the microphone ahead of the first room reflection. MLSSA from DRA Labs is the best-known measurement system to work on this principle, and both John Atkinson and I use it in the course of preparing our loudspeaker reviews.

In the world of digital audio, jitter has been a focus of audiophile attention for well over a decade. It is blamed for many of the sonic ills of which CD and other digital media have been accused. But here's a puzzle: The major source of frequency intermodulation distortion in audio systems—the loudspeaker—has largely escaped such withering inquiry. Why?

Looked at from one viewpoint, DVD-Audio and SACD appear to be exercises in sheer profligacy. In the case of DVD-A, why provide a maximum bandwidth almost five times what is conventionally taken to be the audible frequency range, and couple it to a dynamic-range capability far in excess of that achievable by the microphones used to record the sound? In the case of SACD, why provide a potential bandwidth in excess of 1.4MHz, only to fill more than 95% of it with quantization noise?

The fundamental object of the invention is to provide...the listener a realistic impression that the intelligence is being communicated to him over two acoustic paths in the same manner as he experiences in listening to everyday acoustic intercourse....—Blumlein, et al, British Patent #394,325, issued June 14, 1933