Sidebar 3: Measurements
Regarding measurements, I use a mixture of nearfield, in-room, and quasi-anechoic FFT techniques (using the MLSSA system from DRA Labs) to investigate objective factors that might explain the sound heard. (Stereophile's measuring microphone is a calibrated B&K/DPA 4006.) The speakers' impedance phase and amplitude were measured using Stereophile's Audio Precision System One.
The plot of the RTA 11t's impedance magnitude and phase against frequency (fig.1) suggests that the two different-mass passive radiators actually act as one, the minimum in…
Love 'em or hate 'em, headphones serve a purpose. My first headphones were Kosses, and they were perfect for use in a college dorm. While I've always owned a pair or more over the years, somehow they never became my primary mode of listening, except in situations where using loudspeakers at satisfying levels risked eviction, bodily harm, or both.
Because of their small size and the low output levels they're required to produce—which, because of the close proximity of the ear, can generate prodigious, even hazardous listening levels—designing a good pair of headphones would seem…
This energizer/amplifier doesn't look like much, but it's full of circuitry. I was able to remove the back but not the top, but that was enough to reveal two small circuit boards crammed with parts, the lower board making up the power supply, the upper the amplifier. According to Koss engineering, the latter produces a whopping 63dB of gain (the specs claim 60dB). This is enough, Koss claims, to provide a maximum 126dB (!) spl at a listener's ears. (Why anyone needs this spl capability is beyond me; coming anywhere near it is an invitation to permanent hearing damage.) This amplifier has an…
The Kosses made their strongest impression in the all-important midrange. The adjective "palpable" is overused, but I don't know of a better term to describe the ESP/950's greatest strength. The human voice is particularly well treated—rich, full-bodied, yet without boxiness, nasality, shout, excess sibilance, or other unpleasant and unnatural colorations. From the close, intimate sound of Rickie Lee Jones's work on Pop Pop (Geffen GEFD-24426)—her first "audiophile" album, and which certainly sounds the part on the Kosses—to Kathleen Battle's gorgeous vocalizing on Baroque Duet (Sony SK…
To prepare for this project, we had scheduled an early October session to select the microphone and its placement. David Manley of VTL/Manley and his wife flew out from California to deliver his Manley Gold Reference Stereo Microphone— a crossed figure-eight design that was one of the prime candidates—and Ed Meitner of Museatex drove down from Canada to bring his FET mike preamps. I felt that this would be a first-rate opportunity to compare the Stax Signature and the Koss ESP/950 with the live event present for immediate comparison. The live event in this instance would not be Robert…
TJN returned to the Koss in February 1994 (Vol.17 No.2):
I was able to compare the Stax Pro Classic with both the Sennheiser HD-580 driven by the matching HeadRoom Supreme headphone amplifier and the Koss ESP/950 electrostatics. When I reviewed the latter last year (Vol.15 No.12, p.158), I was captivated by its midrange performance, but I didn't think its response at the frequency extremes was quite up to the accuracy of the $2000 Stax Lambda Pro Signature. The Pro Signature's balance isn't much different from that of the Pro Classic, save for the Signature's more refined top end.
… Sidebar 1: Specifications
Description: Electrostatic headphones with separate energizer unit. Frequency range: 8Hz–35kHz (no tolerance given). Sensitivity: 104dB at 100Vrms differential input at 1kHz. Diaphragm thickness: 1.5;um. E/90 Energizer/Amplifier. Frequency response: 1.6Hz–50kHz ±3dB at 100Vrms differential output. Input impedance: 100k ohms. Input level: 1Vrms for full output. THD+noise: 0.001% at 1kHz and 100Vrms differential output. Voltage amplification: 60dB. Channel separation: 80dB at 1kHz, 100Vrms differential output. Audio output voltage: 600Vrms differential, 2300Vrms…
Sidebar 2: Review System
The associated equipment used in auditioning the Kosses was simple enough. The primary program source was the MSB Silver CD player (review forthcoming). Some auditioning was also done using the Meridian CD-R recorder reviewed by Robert Harley last month, which, with the Kosses, was used to assemble the compilation CD for use in our latest inexpensive loudspeaker listening-panel survey (scheduled for next month's issue). These players were connected directly to the E/90 energizer/amplifier with Music Metre Silver cable.—Thomas J. Norton
Velodyne introduced their series II subwoofer line in the fall of 1988, and it seems timely to review their largest, most powerful unit, the ULD-18. As the line's flagship, this Velodyne subwoofer represents the most sophisticated and expensive system offered by the company. It is sold as a system, complete with driver, enclosure, amplifier, control unit, electronic crossover, and servo cable and circuitry. Velodyne's unique servo circuitry, manufacturing techniques, and aggressive sales technique emanate from the company's designer, David Hall.
In a short five years, Velodyne has…
Subwoofer THD will mar the performance of a very-high–quality midrange-treble unit, like Quads, Apogees, or Magneplanars. This was the main reason I did not use my earlier subwoofer (an RH Labs SB-1), despite its otherwise high quality, workmanship, and ability to put out huge amounts of deep bass. Hall's studies led him to believe that 0.5% THD is the maximum allowable distortion tolerable in a subwoofer. His "High Gain Servo" (HGS) circuitry is said to reduce distortion by a factor of 30. The ULD-18 is rated at 104dB SPL at 20Hz at 0.5%, well within this limit.
Design features
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