Aug 1, 1999 12:00 PM, David Ogilvy


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Poised to conquer another realm of studio products, HHB Professional has entered into the close-field monitor race. Currently HHB offers two two-way systems-the Circle 3 and the Circle 5-each available in passive and active versions. We tested the top-of-the-line Circle 5A, the amplified version of the larger speaker.

The 5A has a 1-inch dome tweeter and 8-inch woofer. The woofer is powered with 140W, while the tweeter receives 70W. Each Circle 5A weighs 28 pounds. Aside from the purple polymer cones on the woofers, I like the look of these monitors: precision construction with smooth curves. The 5A's back panel allows connections through either RCA or XLR jacks, with a switch for balanced vs. unbalanced input. Unfortunately, the master volume knob on each speaker is not stepped, which makes it difficult to match levels left to right. A metal bracket acts as a protective rollbar for the back panel; however, I found each to be bent after shipping.

A pair of Circle 5As has a suggested retail price of $1,399, and an optional Circle 1 subwoofer is $1,399. (Passive Circle 5s retail at $749/pair.) Other models in the HHB Circle Series include the smaller Circle 3A, with an internal amplifier, and the 3P (passive). HHB also offers a 5.1 package, including five Circle 5As and one Circle 1.

CRITICAL LISTENING I set up a pair of Circle 5As about five feet apart, with the tweeters at ear level. Sitting about six feet from each speaker, I played a variety of DATs that I had mixed. Tracks ranged from jazz to country to hip hop, and were all mixed from 24-track 2-inch analog tape. None of these mixes had been through the mastering process.

The thing that impressed me first was the fact that I didn't hear the speakers, I just heard the music. My mixes sounded the same, with all the instruments at the levels I had intended, but with a more detailed midrange. The added depth and clarity around 1 kHz, coupled with a pleasing top end, made me question the flatness of the frequency response curves. (One doesn't want a reference monitor to sound too good; in order for mixes to translate to the majority of stereo systems, the mixing speaker needs to have a flat frequency response curve.) However, when I moved out of the sweet spot, the 5As sounded fairly flat, much flatter than most speakers do off-axis.

The high frequencies from the 5A are accentuated (see sidebar for lab analysis), but I didn't find them overly bright. I've heard many monitors intended for studio mixing that have a much more exaggerated top end. The 5As never exhibited excessive sibilance on the "S"s in the vocal track, or too much brightness from the cymbals. Kick drums translated very well, considering the size of the speaker, but with the master volumes on the speakers all the way up, the bass tended to break up, causing the Circle 5As to distort. Obviously, keeping the speakers within a more reasonable listening level is recommended.

THE NUMBERS, IN BRIEF Although the lab analysis shows that the 5A's frequency response is less than flat, I found these speakers to be very true to mixes done with other speakers (primarily Genelec S30s and Yamaha NS10s). The bump in the 1,200Hz range is apparent, but this peak is so wide that it is smooth on the ears. Although there are narrower peaks at 4 kHz and 9 kHz, I never found the speaker to be edgy or harsh. In fact, long-term listening induced little or no ear fatigue. Eight-hour sessions were relatively painless, even at fairly loud levels.

These speakers seem very useful in a mixing situation where the band and engineer trade places and move around the room. For example, if I sat outside of the sweet spot, I heard a fairly flat response, but sitting in the sweet spot provided a slightly exaggerated focus, so I could move there to check for details like breaths and mouth noises in the vocal tracks. Thus, in a production situation, the band would hear what the mastered song may sound like, while the engineer hears more detail, due to a few well-placed peaks in the response curve. However, an engineer who doesn't move from the sweet spot may not find these speakers flat enough. As long as the engineer is aware of the difference between on- and off-axis listening, mixes produced on Circle 5As should translate well to the outside world. The same is true of many near-field speakers, but I found the 5A more pleasing to listen to, especially for long sessions.

HHB Communications, USA, 1410 Centinela Ave., Los Angeles, CA 90025; 310/319-1111; fax 310/319-1311; www.hhb.co.uk.

PHYSICAL CHARACTERISTICS At first glance, there seems to be a lot of glitz in HHB's Circle 5A powered monitor. The woofer's cone and amp chassis are both a brilliant purple. All cabinet edges are nicely radiused and the woofer and tweeter are mounted on a sculpted, 11/44-inch-thick bezel. The cabinet design appeared to have an elliptically shaped, flared bass reflex port, but closer inspection revealed that the port is a slot, exiting into a reduced-area, elliptically shaped port. Historically, this type of geometry is prone to low-frequency chuffing on loud, bass-heavy program material.

The black painted, textured cabinet is constructed of 0.60-inch- thick MDF. Internally, four sides and the back are lined with [superscript]3 1/44-inch polyester foam. The back piece of foam lies directly on the components of the power amp, so there is no mechanical isolation between the amp and the transducers. The woofer, tweeter and amp are mounted into recessed areas using machine screws and T-nuts.

The 8-inch woofer has a purple, curvilinear, thermally formed polypropylene cone, and a plastic injection-molded vented frame. The cone is terminated on the outside by an inverted half-roll rubber surround. The neck of the cone is mated onto a 1-inch voice coil with a vented aluminum bobbin, and a 4.25-inch-diameter flat spider. The motor structure comprises a 3.95x0.7-inch ceramic magnet, attached to 0.22-inch-thick top and bottom plates. The motor is magnetically shielded with a bucking magnet. Input terminals are dual 0.25-inch male tabs.

The Morel DMS 20 tweeter has a 1-inch-diameter, treated cloth diaphragm mounted on a 4-inch-diameter, semi-horn-loaded plastic faceplate. The coil is cooled with ferrofluid and is on a vented aluminum bobbin. The non-shielded motor also uses a ceramic magnet. The pole piece is vented into a sealed plastic enclosure in order to lower resonance and linearize phase at the crossover. Input terminals are also dual male tabs, 0.11-inch wide.

The Circle 5A is a bi-amped, active-crossover design with 120 watts for the woofer and 70 watts for the tweeter. Bi-amping is more stable than routing the amplifier signal through a passive crossover, and over the course of an extended high-SPL mixing session there should be none of the usual variations in passive component values due to heating, which can cause changes in the crossover characteristics. The amplifier features a toroidal transformer, and a high-grade, glass-epoxy, double-sided circuit board. The ICs are socketed for easier servicing. The faceplate of the amp includes heatsinking fins, but the amp's ability to dissipate heat will be impaired by the glossy purple paint that covers the entire heatsink. There is a continuously adjustable volume control and switchable balanced XLR and unbalanced RCA inputs. A bracket on the rear of the amp helps protect the heatsink, amp and the cables attached to it.

ACOUSTICAL CHARACTERISTICS The on-axis frequency response of this system comprises three broad peaks and adjoining valleys. The first peak is about two octaves wide and more than 3 dB tall, centered near 1,200 Hz. The second peak is over a half-octave wide, 3 dB tall and centered around 4 kHz. The last peak is centered on 9 kHz, almost 4 dB tall and is close to one octave wide. The off-axis response is actually a little flatter than the on-axis response. After a broad (more than one octave) 2dB-tall peak from 5 kHz to 11.5 kHz, the response rolls off rapidly, 8 dB over the last octave.

The impulse response shows us that there might be a slight discontinuity near the crossover point. The multiple transient peaks are signs of unaligned devices. The decay is smooth except for a ripple 1.2 ms after the initial peak, possibly due to an internal cabinet reflection.

The distortion figures for the HHB Circle 5A are fairly low. Above 100 Hz, the THD remains below 1%, and gets lower (0.5% above about 400 Hz). Spectral contamination is a measure of distortion that is not harmonically related ("nonlinear") to the input signal, in this case, 15 tones. Spectral contamination figures correspond to subjective clarity: The larger the difference between the original signal and the distortion products, the better, so in this test a higher number is better. It appears the noise floor is around 45 dB down from the input signals, with a higher concentration of noise at the crossover point and above.

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