ESS/Heil's "Power Ring" Tempest
The Equipment: ESS Tempest LS-5 loudspeaker system in wood case. Dimensions: 14 by 24 1/2 inches (front), 14 1/4 inches deep; intended for use vertically as delivered, but tweeter may be realigned for horizontal use.
Price: $219; also available as Performance Series Model 5 in vinyl-finish cabinet and without controls, $205. Warranty: "limited," three years parts and labor. Manufacturer: ESS, Inc., 9613 Oates Dr., Sacramento, Calif. 94827.
Comment: By now, most high fidelity aficionados have heard of, if not heard, the Heil AMT (air-motion transformer). This unique midrange-and-up driver that literally squeezes the air from its pleated diaphragm has been widely acclaimed for its transient response and power-handling capability. A new Heil AMT-dubbed the Power Ring-makes its appearance in the ESS Tempest LS speakers. The Power Ring radiates only to the front hemisphere rather than being "bipolar" like its predecessor.
In the LS-5, the Power Ring is combined with a 10-inch woofer and a rear-mounted. 10-inch passive radiator in a stained oak-veneer cabinet of bookshelf dimensions.
Power input is via a pair of soring-loaded, color-coded connectors mounted in a recess on the rear panel. A continuous control tailors the output of the Heil driver, through a range from 3 dB above "flat" response to totally off.
Measurements taken at the CBS Technology Center re veal a smooth, well-controlled impedance curve over the audio band. The nominal impedance measures 4.4 ohms, while a minimum impedance of 3.6 ohms occurs at about 150 Hz. From there on up the curve stays between 4.8 and 6.4 ohms. If two pairs of LS 5s are to be used, ESS advises a series rather than a parallel connection to most amplifiers.
The LS-5 is just about average in efficiency--80 1/4 dB average sound pressure level from a 0-dBW (1-watt) input measured omni-directionally-and it doesn't flinch when driven hard. No untoward behavior is elicited by a 20-dBW (100-watt) 300-Hz signal, from which the unit delivers 108 dB SPL. On a pulse basis, the lab amp reached its limit (29 dBW) before the LS-5 did, so the peak SPL is above 117 d B.
Above 100 Hz, the second harmonic at a 0-dBW level is well controlled, averaging about 0.3% to 0.4% out to 2 kHz. Above 2 kHz, the distortion averages 1% to 1 1/2% out to 10 kHz. Between 100 and 70 Hz, the second harmonic content increases to 2%. At a drive level equivalent to 100 dB SPL at 300 Hz, the second harmonic distortion in the midband and high end is not much different, but it is slightly greater in the bass, as one might expect. It aver ages about 0.6% above 125 Hz, with a few sharp peaks, and increases to 2% at 100 Hz and 5% at 67 Hz. The third harmonic content is even lower-less than 0.6%, 60 to 2,500 Hz at 0 dBW, and less than 0.8% above 2,500 Hz-although below 60 Hz it increases rapidly. At 100-dB SPL (at 300 Hz), the third harmonic is still mostly below 0.6% from 82 to 2,500 Hz, increasing to 5% in the region of 35 to 70 Hz. If anything, the third harmonic in the high frequency region is even less at the higher level. The high-level THD of the Tempest LS-5 is much better than average in tie treble and midbass regions.
The frequency response in CBS's anechoic chamber is quite smooth. Except for a 6 1/2-dB depression around 5 kHz, the average omnidirectional response is within ±4 dB from 63 Hz to 10 kHz with the region above 1 kHz on average a few dB below the bass. On axis, with pure tones, some interference between the drivers is observable near the crossover frequency (2,400 Hz). This also shows up on the 3-kHz tone-burst test, where it appears that one driver "speaks" before the other.
As ESS points out in the well-written owner's manual, you should experiment with placement of the Tempest LS-5 in your listening room. With its rear-mounted passive radiator, the speaker cannot be placed flat against a wall.
At least an inch of separation is required, and 3 to 5 inches produces the strongest bass response-perhaps excessive bass response for some tastes, with a bit of a tubby sound, although it adds "punch" to a kick drum. A position several feet out into the room appears to tighten the bass a good bit, as does raising the system above the floor and keeping it well out of corners. Thus, bookshelf placement might be a definite advantage. (Since the Power Ring has much better dispersion in one plane than in the other, it should be reoriented if the system is placed horizontally on a shelf; ESS provides an Allen wrench and instructions.) After some experimentation, we set the environmental control three-quarters of the way up, with a slight treble cut in the preamp.
The transient response of the Heil is superb, and this shows up most prominently on high-pitched percussion: cymbals, keys, castanets, etc. The low percussive that are handled by the woofer system are not as well rendered:
The bass tends to be rich, dark, and sonorous, rather than clearly and sharply etched. The stereo imaging is fair but lacks depth and is a bit unstable. We note a slight edge on violins and also on singers, who are made to hiss a bit on sibilants.
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Like most speakers, the Tempest LS-5 has a character of its own: rich, warm, solid bass and sparkling, almost etched treble, qualities that may be designed particularly to please rock and big-band jazz listeners. With its extraordinary ability to make loud music with reasonably low distortion, the LS-5 is ready to take on the type of large, absorbent listening room that simply overwhelms less powerful speakers. And for home disco use, it's a natural.
(High Fidelity, Oct. 1977)
Also see:
Technics SB-6000A floor-standing speaker system (Equip Profile, Oct. 1977)
KLH Model 35 speaker (Equip. Profile, Oct. 1977)
Visonik D-50 loudspeaker system (Equip. Profile, Oct. 1977)
EPI Model 200 loudspeaker system (Equip. Profile, Oct. 1977)