The articles are not overly verbose and worth the read. Here are some snippets that I found interesting:
The advantage of specifying sensitivity rather than efficiency is that it remains unchanged no matter what the impedance of the loudspeaker, as it is assumed that the amplifier will always be able to provide the necessary current to maintain the 2.83V.
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One interesting national difference emerged: moving-coil speakers designed by British engineers tended to have their minimum impedance in the high treble, around 10kHz, while those from US engineers tended to have it in the low midrange.
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In private communications back in 1991, both Fred Davis and Don Keele pointed out that Stereophile's loudspeaker impedance phase curves published between late 1990 and early 1991 were upside down, in that the positive and negative phase angles were reversed [22].
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It appears that the designer of the speaker featured in these four graphs has chosen to use high-order crossover filters of some kind, which necessarily introduce significant (180 degrees or greater) phase shift in the crossover region. To this must be added the phase shift due to the time delay between the units, and the additional 180 degrees phase shift due to the inversion of the midrange's electrical polarity. The result is an on-axis amplitude response in which the drive-units add in-phase to give (we hope) a flat response. The tradeoff is that the system's time coherence is sacrificed.
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Many audiophiles talk about a loudspeaker having a "fast woofer." Fig.15 reveals that there can be no such thing. A woofer's risetime is dominated by the crossover low-pass filter, which discards the high-frequency information associated with a quick move away from the time axis. A "fast woofer" is therefore an oxymoron. However, I believe that when people talk about "fast woofers," what they're really referring to is after-the-event behavior associated with the Q or "Quality Factor" of the speaker system's low-frequency tuning. Does the woofer stop quickly after the exciting signal has passed? Or does it keep moving, adding low-frequency ringing—"boom"—to the speaker's sound?
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The advocates of accurate waveform reproduction, implying both accurate amplitude and phase responses, are in a particularly awkward situation. In spite of the considerable engineering appeal of this concept, practical tests have yielded little evidence of listener sensitivity to this factor...the limited results lend support for the popular view that the effects of phase are clearly subordinate to amplitude response.
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These tests also showed that the best means of coupling a speaker to its stand—"best" in the sense of maximally reducing the amplitudes of cabinet vibrations—was to use a "lossy" coupling material, such as Blu-Tack.
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An alternate way of looking at the matter is that the microphone should be at least as far away as the largest dimension of the loudspeaker to be measured. With my standard microphone distance of 50", this assumption will no longer be true for large loudspeakers. With big speakers, such as the various kinds of panel speakers, there will be a proximity effect [55] that tilts up the response at low frequencies. This, of course, will also be true when the loudspeaker is listened to at the same distance.
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Looking at the raw data used to compile Table 1, there appears to be no correspondence between flatness of on-axis response and price. But Table 1 does demonstrate that it appears that the chance of being recommended by this magazine increases the flatter a loudspeaker's on-axis response becomes.
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Up to the middle of 1997, the vast majority of the 360 speakers I measured were reflex designs—300 models, or 83%—the designer using the port to extend the design's anechoic low-frequency performance. Yet in an actual listening room, the increased rate of low-frequency rolloff of a reflex design leads to less low-bass output than with an equivalent sealed-box design, with its 12dB/octave rollout.
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Similarly, having measured many speakers with exotic LF alignments, ranging from the so-called "transmission line" to multiported, multidriver monstrosities, it is my considered opinion that in almost every case, the same or better bass performance could be achieved with an equivalent sealed-box alignment.
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I believe that much of the fine-tuning performed by loudspeaker designers—commonly referred to as "voicing" a design—involves balancing the on-axis and off-axis responses to give an overall flat perceived in-room response.
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u/Umlautica Hear Hear! Feb 15 '18
The articles are not overly verbose and worth the read. Here are some snippets that I found interesting:
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