HHB Circle 5

HHB and Harbeth have collaborated to produce a high quality active studio monitor at an attractive price. Paul White listens in.

HHB's Circle 5 active studio monitor is the result of a collaborative project between HHB and Alan Shaw, the designer behind the well‑respected Harbeth range of monitors. The Circle 5 is based on the Harbeth Xpression DPM1 Pro Active monitors reviewed back in the February 1998 issue of SOS, but with the benefit of updated amplifier packs, providing 120 Watts for the bass/mid driver and 75 Watts for the tweeter. The cosmetics have been changed to make the monitor even more purple, fitting the HHB corporate image, but the essential components and design philosophy remain unchanged.

The Circle 5 is a two‑way, ported monitor housed in an MDF cabinet measuring 420 x 255 x 300mm, with rounded corners to reduce cabinet‑edge diffraction effects. A large, shallow heatsink covers a significant proportion of the rear panel. The audio input, which has a rotary gain trim control, is switchable between balanced XLR and unbalanced phono connectors, and an active crossover operates at 2.6kHz using low‑Q active filters. Two integrated amplifiers (bridge mode) power the bass/mid driver, with a single amplifier driving the tweeter. Regulated power supplies are used to prevent the supply rails sagging at high power levels, and high‑quality capacitors are used throughout. A power‑on delay circuit avoids switch‑on thump, and 'Polyswitch' tweeter overload protection switches off power to the tweeter in the event of a potentially damaging overload. On the front panel, an LED warns when the protection circuit is operating.

The eight‑inch bass/mid driver is custom‑made, utilising a polymer cone in a flexible rubber surround. A high‑temperature, one‑inch aluminium voice coil provides the drive, and a shielding magnet reduces stray magnetic fields, so the Circle 5s may be used close to video equipment. The thickness of the cone isn't constant, as it is with most designs, but instead varies in a precise way over the surface of the cone as a strategy for reducing cone distortion.

A custom‑built 28mm soft‑dome tweeter, featuring ferrofluid cooling, an aluminium voice coil and a shielding magnet, handles the highs. The outcome is a system with a +/‑3dB response from 48Hz to 20kHz.

Constructionally, the Circle 5s seem to be very nicely put together, with a solid but stylish cabinet and nicely built glass‑fibre circuit boards. Both drivers are recessed into the sculpted front panel, the metal bar in front of the tweeter providing a degree of physical protection.

Performance

The original Harbeth active models performed exceptionally well, delivering an accurate and detailed sound without the artificial edge or pumped‑up low‑end flattery of some competing designs. HHB's Circle 5s have the same overall character, but the increased amplifier power prevents the bottom end from running out of headroom, as the original design had a tendency to do. At typical nearfield monitoring positions the Circle 5s are adequately loud, and their sound remains clean up to monitoring levels that are on the high side of comfortable.

...an attractively priced, smartly styled active monitor capable of delivering a neutral, revealing sound with a high degree of accuracy.

Other than the input gain control, there is nothing for the user to tweak — you can't adjust the bass end to match the speaker position, but in practice I didn't find this to be much of a limitation. In an average small studio room, the bass is reasonably well extended without sounding overblown or tubby, and the critical mid‑range comes through surprisingly smoothly for a monitor in this price bracket. Providing the room isn't an acoustic disaster area and that the monitors are set up in the correct geometry, the stereo imaging is also reassuring, with a good spread of sound between the speakers. A better than average off‑axis response gives a sensibly wide sweet spot, but the monitors really should be mounted upright rather than being placed on their sides, as this introduces all kinds of phase problems and narrows the sweet spot enormously. Similarly, stand‑mounting monitors, rather than perching them on a console meter bridge, always gives better results.

Conclusion

I've always had a soft spot for Harbeth‑designed monitors. This latest collaboration with HHB has produced an attractively priced, smartly styled active monitor capable of delivering a neutral, revealing sound with a high degree of accuracy. Of course, there are better speakers if you can afford to pay for them, but in the sub‑£1000 bracket these have to be one of the better active monitor buys. If they have any limitation it's probably that they still don't go loud enough for those who like to mix rock or dance music at very high levels; for private studio, edit suite or general mixing applications, however, they're more than adequately loud. All you have to worry about is whether the purple goes with your studio decor!