Sidebar 3: Measurements I estimated the Mahler's B-weighted sensitivity as 87dB(B)/2.83V/m, which is lower than specified. However, I was measuring on the tweeter axis, and a mid-treble suckout on this axis (see later) will reduce the measured figure. The speaker featured a wide variation in impedance magnitude (fig.1), which will make its perceived balance more dependent than usual on the partnering amplifier's source impedance. More important, the impedance drops below 3 ohms throughout the bass, which will mandate using an amplifier with good current delivery.
Fig.1…
RD consistently noted problems with optimizing the Vienna Acoustics' low frequencies in his room. Try as I might, I couldn't find any particular measured problems in the bass. The midrange units hand over to the woofers below 80Hz or so, with the ports covering the range below 40Hz. I suspect that the limited bandpass covered by the woofers, as well as having six radiating areas all contributing to the speaker's output in the upper bass and below, makes its interaction with the room complex. Fig.6 shows the Mahler's horizontal response family 90 degrees to either side of the tweeter axis…
During a recent visit to Canada's National Research Council, I noticed stuck to the wall of the prototype IEC listening room a page of results from one of Floyd Toole's seminal papers on the blind testing of loudspeakers. The scoring system was the one that Floyd developed, and that we adopted for Stereophile's continuing series of blind tests. "0" represents the worst sound that could possibly exist, "10" the perfection of live sound—a telephone, for example, rates a "2." The speakers in Floyd's test pretty much covered the range of possible performance, yet their normalized scoring spread…
Like many Stereophile readers, I have often sped home from a concert to fire up the audio system and then, to the sore vexation of my wife and guests, spent the rest of the evening plunged in the morbid contemplation of what, exactly, was missing. Every lover of music has his pet theories and every theory, it seems, its season. Speaker efficiency and wide frequency response were popular in the 1950s, during the heyday of those hulking Klipschorns and James B. Lansings. The Quad ESLs caught on a few years later, when midrange transparency seemed to be what separated hi-fi from the real…
Secondly, the diffusor breaks up irritating slap and flutter echoes that often plague playback in domestic listening environments. These echoes---artifacts of reflective, parallel room surfaces---overlay the music that follows and obscure its inner details. Thirdly, the diffusor tames comb-filter-type frequency colorations, previously addressed only by laboriously tweaking the physical position of the speakers relative to room boundaries. By decreasing the depth and increasing the density and irregularity of comb-filter notches, the diffusor makes optimum speaker placement decidedly less…
A wide variety of high-grade components was used during more than a full year of listening evaluations, beginning in late 1986. Front-ends included a Goldmund Studietto/T5 'table/arm set-up with Linn Karma or Koetsu Black Gold Line cartridges; a Linn Sondek/Ittok with Grace F9E Super, Linn Troika, or Linn Karma; several Michell Gyrodecs with Zeta, SME, or Eminent Technology tonearms fitted with Madrigal Carnegie, sundry Koetsu, or Grado Signature series cartridges; and The Source turntable from Scotland, fitted with SME V and a Carnegie One. Original master tapes and dubs, played on a Don…
The Particulars
I'll begin with the clearest success story: the KEF 107s. In the untreated soundroom the much-praised 107s betrayed a blare and honk that deepened my appreciation for unalloyed silence. After finding the speakers and the supplied equalizer (the KUBE) to be in proper working order, I got a feeling worse than buyer's remorse: I felt I'd been saddled with a patient with severe personality disorders---and one that was hard to move, took up valuable floor space, and cost me a fair chunk of change into the bargain. When the diffusors were deployed it was as if the patient had…
The Quad '63s have always seduced more than impressed. By enlarging and enlivening the room acoustic, the diffusors rendered the Quads more extroverted, more "commanding" and less reticent. Oh, they're still seducers, these, but they're now seducers of a saucier type. On Chicago Pro Musica's Till Eulenspiegel (Reference Recordings), the effect was one of lusty and infectious merriment, altogether closer in spirit to this ensemble's live performance of the piece. The specificity of acoustic images the speakers suspended in the room (always a forte with Quads) was complemented by a wider,…
But let me give you the good news first. Without the RPGs, the Waveforms had the upfront, grab-you-by-the-glands presence that lifted you from mid-hall to the conductor's platform. Music sounded zesty and sure-footed, an effect like that of a crack orchestra triumphantly returning from a long road trip to play a favorite old lollipop for eager hometown supporters. Bass was generous, lively, yet relatively free of overhang. Up to what I would guess to be 100dB or so, dynamic gradations were first-rate, harking back to those mammoth designs of the JBL era. (It turns out those 15" woofers issue…
I would also like to point out that in order to reduce the variables in the test, I avoided mixing in other acoustical treatments, such as Sonex or ASC Tube Traps, with the diffusors. Yet it is almost a surety that the diffusors will work best as part of an overall listening-room overhaul that would include products like the Tube Traps in corners (for dipolar speakers), and broadband absorbers against the front wall and forward portions of side walls for most forward-firing designs. The diffusors seem to have little or no effect in the sub-150Hz region where Tube Traps can be effective in "…
