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The crossover circuitry is mainly carried on a printed circuit board attached to the rear of the terminal panel, with the exception of the series air-cored inductor in the woofer feed, which is wound on a circular molding integral with the panel. The low-pass filter for the woofer is second-order, a polarized electrolytic capacitor shunting the drivers, while the tweeter high-pass also appears to be basically second-order. However, a resistor in series with the shunt air-cored inductor and another in parallel with one of two series capacitors give a hybrid response, where the filter's…
The one thing the Polks did well was to achieve good levels of low bass. Bass drum had satisfactory weight. Double basses may have been too boomy in their upper registers, but their sound was sufficiently nourished lower down in frequency. Organ recordings came over well as a result, and as the transient-free sound typical of the organ is only slightly affected by midrange colorations, the music communicated more successfully than with voice, piano, or orchestral program material.
Listening to the Peter Mitchell organ recording on the Stereophile Test CD, however, which was recorded in…
Sidebar 1: Specifications
Description: Two-way, floor-standing loudspeaker with two passive bass radiators. Drive-units: 1" "silver-coil" soft-dome (polyamide) tweeter, two 6.5" doped-pulp—"Trilaminate Polymer"—cone woofers with butyl surrounds, two 8" passive bass radiators ("fluid-coupled subwoofers"). Crossover frequency: 3kHz. Crossover slopes: 12dB/octave (low-pass), 6dB/octave (high-pass) but see text. Frequency response: 29Hz–20kHz ±3dB. Sensitivity: 90dB/W/m. Nominal impedance: 6 ohms. Amplifier requirements: 30–250W.
Dimensions: 39" H by 10.5" W by 14.5" D. Weight: 58 lbs…
Sidebar 2: Review Context
The speakers were positioned for the best sound (with only one pair of loudspeakers in the listening room at a time). Source components consisted of a Revox A77 to play my own and others' 15ips master tapes, a Linn Sondek/Ekos/Troika setup sitting on a Sound Organisation table to play LPs, and Kinergetics KCD-40 and Meridian 206 CD players. Amplification consisted of a Mark Levinson No.26/25 preamplifier combination driving a pair of Mark Levinson No.20.5 monoblocks via 15' lengths of AudioQuest LiveWire Lapis balanced interconnect. Speaker cable was 5' lengths…
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.
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