Oct 27, 2004 8:00 AM, By George Petersen

ELECTROSTATIC NEAR-FIELD STUDIO MONITORS

Electrostatic loudspeakers were first introduced into the home hi-fi market in 1956 by QUAD Electronics and have been the source of lively debate ever since. Though they’re revered by a segment of the audiophile population, a constant complaint about electrostatic speaker designs has been that they are more suitable for classical or jazz music and don’t have adequate punch for rock and other styles. And, despite more than four decades of acceptance of electrostatic speakers in the home stereo community, no one to my knowledge has ever used electrostatic elements in professional studio monitors—until now.

Enter the StudioStat 8.2 from Benson Audio Labs. Rather than employ an expensive all-electrostat design—which also equates to a very large surface area to create the air motion required for low-frequency reproduction—the StudioStat 8.2 uses a hybrid approach, combining a conventional cone woofer crossed over at 1,600 Hz to a single electrostatic panel handling the upper mids and highs. This allows the extended high-end performance (to 25 kHz and beyond) of an electrostatic design while reducing the size of the cabinet (which measures 17.75x11x12 inches), providing punchy bass response and keeping the cost of the system down to an earthly $1,399/pair.

Operating much like a condenser microphone in reverse, the StudioStat 8.2’s 4x4-inch electrostatic element works by charging a large 19.3-square-inch diaphragm surface with a high voltage. Changes in the input signal cause the polarizing potential to vary, and the ultralow-mass (0.1 mil) Mylar diaphragm vibrates to re-create the input.

Physically, the StudioStat 8.2s are a front-ported design. There is no grille, and the front baffle and cabinet edges are smooth to reduce diffraction effects. Centered between the drivers is an “Optimum Listening Plane Indicator,” a blue LED fitted into a custom light pipe that’s designed to help the listener find the center of the listening sweet spot. The LEDs also double as a power-on indicator for the electrostatic panels. Inputs are gold-plated, five-way binding posts, and each StudioStat has an input jack for an external wall-wart DC adapter (two are included with each pair of speakers) that powers the electrostat panel.

I hooked the speakers up to an Australian Monitor power amp, which has excellent specs and delivers about 400 watts per side. Benson says that the speakers can handle 250 watts over long periods, so the 400-watt amp would offer plenty of headroom. The monitors were set up with the speaker centers at ear level and the LED indicators shining brightly.

I began my listening with a B&K test disc that has material ranging from symphonic and chamber ensembles to pop acts such as Little Feat and Jennifer Warnes. Bass was nicely damped and well-defined, and in balance with the vocals and midrange instruments. The top end seemed overly bright, and as I leaned across the console to check the EQ, the HF response dropped off dramatically. By moving my head slightly, I determined the speakers’ sweet spot was about six inches wide due to the beam-like dispersion of the electrostatic tweeters.

On my next session, I was recording an acoustic ensemble with some Earthworks mics, Millennia preamps and dCS 96kHz/24-bit ADCs/DACs storing to a Nagra D. On this session, I really wanted to hear some upper-end response and by re-aiming the StudioStats to about 10 to 12 degrees off-axis, the HF performance became more in balance and I could appreciate the speaker’s ability to go out to 25 kHz. But I was still working within the narrow confines of the sweet spot, which also precludes anyone else being in the listening area at the same time.

This tight sweet spot relegates the StudioStats to applications in which the user stays in place during a session. While problematic for engineers working a big board, this could work in desktop audio, in which the user remains in front of a computer screen or small digital console. In these “cockpit audio” applications, magnetic shielding is often necessary on the drivers; perhaps Benson could add this as an option, as the speakers distorted video screens when placed near a display.

Overall, the Benson StudioStat 8.2s have much to offer, including a frequency response that’s flat (±2 dB) from 80 to 7k Hz—an impressive accomplishment in a critical audio range. The LF response stated in Benson’s specs says the speakers go to 40 Hz, but at that level, they’re -6 dB down. The -3dB down point (which is more realistic in defining usable bass energy) is around 60 Hz—respectable for an 8-inch driver in a compact cabinet. The high-end response is more enigmatic and with a bit of experimentation in placement can yield good results in single-engineer setups.

Benson Audio Labs, www.bensonaudiolabs.com.

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Lab Analysis: Benson StudioStat 8.2
By Mike Klasco
Physical Characteristics
The enclosure is 0.75-inch-thick MDF woodstock construction with thick vinyl wrap on sides and back. The sides have a 1-inch radius curved edge. No grille cloth is provided, although there is a protective screen over the electrostatic tweeter element. The drivers are recessed flush to the front baffle, and the woofer mounting has threaded screw inserts. The bass-reflex port is flared to reduce air turbulence noise. Enclosure packing is 2 inches thick and appears to be polyester fiber.

The woofer appears similar to a popular Vifa model and features a rubber surround and a straight-sided paper cone with a wet-look glossy surface finish that might contribute some humidity resistance and damping of resonances. A flat spider is used, providing more linearity than a cupped spider. The frame is cast and therefore does not drain magnetic flux from the magnetic structure. The magnetic structure (pole piece) is vented, which should help keep the voice coil cool and reduce power compression.

The electrostatic tweeter is a 4x4-inch panel. A 12VAC external power supply is used to bias up each tweeter panel. A rear panel switch toggles +2 dB, 0 and -2 dB. There is no “waveguide” profile or acoustic lens, so the pattern becomes progressively more narrow as frequency increases. This effect is significant, as can be seen with the rising on-axis response and off-axis droop. You’d best have a favorite listening position or you will get largely varying HF impressions of your mixes. An LED at the end of a blind hole lets you see if you are on-axis—far more elegant than a bite bar!

The passive crossover has an air core inductor for the woofer, a large laminate core inductor for the tweeter, and Mylar caps and sand cast resistors, all mounted on a thick copper-clad board.

Acoustic Characteristics
The impulse response measurement is good, but the StudioStat 8.2 woofer and tweeter appear to not be in time-alignment. Frequency response is extended and smooth. For flat frequency response, the ideal listening position is about 15° off-axis. We tested distortion at 90 dB SPL at 1 meter. The woofer measured excellently, and the mid/high range measured very well. Spectral contamination is typically 50 dB down from the signal tones on the woofer and 40 dB-plus on the electrostatic element.