Fig.17 Acoustic excess phase response of time-acoherent loudspeaker.
But, as I said above, the fact that almost no loudspeakers perform in this manner does not stop many of them from getting good…
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By contrast, fig.17 shows the excess-phase response of the speaker whose step response was shown in fig.11. This model uses a sloped front baffle and a crossover with first-order acoustic slopes to give a time-coherent performance on the listening axis. There's a little bit of positive error at high frequencies, meaning that the microphone is just a little high of the optimal axis.
By contrast, fig.19 shows the CSD of a loudspeaker whose on-axis frequency response is severely unflat. The graph is dominated by a severe mode at 3750Hz. In addition to the speaker's timbral problems, this resonance could be heard as adding a hard "zinginess" to the overall sound. However, loudspeakers with such audible resonant problems appear to be very rare these days.
Fig.19 Poor cumulative spectral-decay plot (0.15ms risetime).
To produce a meaningful CSD, the time data need to be free both from noise—it helps to average as many separate impulse response measurements…
It must be a good idea in general to reduce the amplitude of resonant modes, but how audible a high-Q, narrow resonance will be depends not only on its level and the area of the radiating panel, but also its frequency. If the resonance lies in the upper bass, say between 100 and 200Hz, it will likely coincide with specific musical notes as well as being excited most of the time. An octave or so higher, and a narrow-bandwidth, high-Q resonance might well "fall in the cracks" between the discrete frequencies of musical notes. (With equal-temperament Western music, the notes are farther apart…
References
[29] D.D. Rife, J. Vanderkooy, "Transfer Function Measurement Using Maximum-Length Sequences," presented at the 83rd Convention of the Audio Engineering Society (1987 October). Preprint 2502. J. Aud. Eng. Soc. Vol.37, pp.323-348 (1989 June).
[29] D.D. Rife, J. Vanderkooy, "Transfer Function Measurement Using Maximum-Length Sequences," presented at the 83rd Convention of the Audio Engineering Society (1987 October). Preprint 2502. J. Aud. Eng. Soc. Vol.37, pp.323-348 (1989 June).
[30] D.D. Rife, "Introduction, Theory, & Loudspeaker Time Coherence," DRA Labs MLSSA Reference Manual v.10.0A, pp.7-9, pp.145-150, & pp.159-163 (1996).
[31] J. Vanderkooy, "Aspects of MLS Measuring Systems," J. Aud. Eng. Soc. Vol.42, pp.219-231 (1994 April).
[32] F.E. Toole, "Loudspeaker Measurements and their…
Sidebar: The Fast Fourier Transform
As I have implied in this article, a representation of a signal in the time domain has a related representation in the frequency domain. There is a mathematical operation, the Fourier Transform, that can be used to calculate the frequency-domain representation—the signal's spectrum—from its time-domain representation—the signal's impulse response. In practice, a mathematical shortcut is used, leading to the designation of the mathematical operation as the Fast Fourier Transform or FFT (footnote 1).
As I have implied in this article, a representation of a signal in the time domain has a related representation in the frequency domain. There is a mathematical operation, the Fourier Transform, that can be used to calculate the frequency-domain representation—the signal's spectrum—from its time-domain representation—the signal's impulse response. In practice, a mathematical shortcut is used, leading to the designation of the mathematical operation as the Fast Fourier Transform or FFT (footnote 1).
The basic premise behind the application of the…
Nobody Wants a *" Drill Bit!
One of the most thought-provoking insights I've ever heard from anyone came from a marketing teacher. He claimed that, in the entire history of the human race, nearly all of the *" drill bits that have been bought were bought by people who did not want *" drill bits. What happens is, *" drill bits are bought by people who want *" holes in something. Thwack! Ah, enlightenment.
The makers of Stanley tools are more rewardingly thought of as being in the "hole-enabling" business than the "drill-bit" business. The value of this kind of head-thwack for…
This notion of controlled connectedness might be useful in thinking about why we feel compelled to spend serious money on a stereo—money that others might spend on a bass boat or a red convertible or a foreign vacation. I think if we have deeper insights into the valid reasons for doing what we do, perhaps we can do a smarter and better job of doing it. I could brush my teeth for five minutes using the electrons that have arrived here bearing anguished cries for help from people torn between choosing the Coriolis Effect Deluxe Rev.3.2 Power Cord and the Shamelessly Hosing Neither Balanced…
Letters in response appeared in October 2001 (Vol.24 No.10):
A pattern language
Editor: I was delighted to see John Marks' reference to Christopher Alexander's A Pattern Language in the pages of Stereophile ("The Fifth Element," July 2001, pp.37-41). It's a shame that such a seminal book on architecture is so little known, but refreshing to know that, despite observations of American cultural decline in the past century, there are works whose integrity and usefulness will have application and appeal far into the future.
To see A Pattern Language mentioned in your magazine…
An acquaintance in the world of CD distribution recently gave me an astonishing statistic: that the average classical title sells fewer than 2000 copies worldwide in its first year of release; which in turn means that many titles sell only about 500 copies! Given that the cost of producing a classical orchestral album can include up to $100,000 in union-mandated musician fees, such minimal sales guarantee financial disaster.
Another problem is that the big classical bestsellers are almost all "freaks" aimed at the mass market: the notorious Three Tenors album and EMI's Chant, for example…
Larry Archibald expanded on this issue in September 1997 (Vol.20 No.9):
I read in the August 1997 issue of Stereo Review—"the world's #1 A/V magazine" (gee, that's funny, I thought it was about stereo)—that their renowned digital writer, Ken Pohlmann, won't be buying any more music until a new format comes out. He strongly recommends DVD-Video for the quality of the soundtracks, and is holding off on music until there's a DVD-Audio format with 5.1 tracks recorded at 96kHz/24 bits.
Ken admits that "some of our listeners may not immediately hear the improvement in sound quality…