JBL SYNTHESIS HDI 5.1-channel speakers

The JBL floorstanders in this group won a Sound+Image 2021 award for their performance in straightforward stereo. So what happens if we place them at the front of a full multichannel speaker package and start kicking out movies?

What happens if we place award-winning floorstanders at the front of a full multichannel speaker package and start kicking out movies?

JBL’s ‘HDI’ models heralded a new direction for the US loudspeaker company. JBL is, of course, active across both the professional and hi-fi speaker markets, and it’s often been the case that its hi-fi designs have the heft of that pro background (see News p12), so that even their loving owners might be pressed to describe them as ‘décor-friendly’.

So the HDI range has been designed to be easier on the eye, with new finishes, and cabinets where the only flat surfaces are their tops and bottoms. Yet all the main speakers in the HDI range also sport JBL’s patented HDI (High Definition Imaging) waveguide technology and its associated high-frequency compression driver, of which more below.

Our first encounter with this range was with the second largest floorstander, the HDI-3600 — and we were so impressed with their smooth fluid midrange sound, lovely imaging, extended highs and great bass that they landed a 2021 Sound+Image Award as our Loudspeakers of the Year $5000-$10,000.

But this is a range built not only for stereo; there’s everything required for a full home cinema set as well. So we figured it was time to hear a whole room full of JBL HDI speakers!

Equipment

JBL’s Australian distributor Convoy International doesn’t group up specific multichannel HDI speaker packages, so you’re free to choose whatever combination from the HDI range best suits your space. We went with a 5.1-channel scenario, and chose the award-winning HDI-3600 floorstanders for the crucial left and right front channels, at $7999 the pair. We could have gone larger, to the flagship $9999 HDI-3800 design, which would add 11cm in height to the neat metre of the HDI-3600s, and more importantly would switch the three bass drivers from the 6.5-inchers of the HDI-3600 up to a trio of 8-inchers. But since we were already enamoured with the performance of the smaller floorstanders, we retained them as part of our surround experience.

Besides, their slightly smaller drivers seemed a better match for the centre-channel speaker of the range, the $3499 HDI-4500, which lines up a full four 130mm (5.25-inch) woofers, of the Advanced Aluminium Matrix cone construction used throughout the range, together with the common high-frequency compression driver which gives the range its name. A compression driver is unique among high-frequency drivers. All conventional ‘tweeters’ — be they cones, domes or ribbons — operate directly into the airspace in the room, where they attempt to move all the air in front of them, which is in effect the entire volume of air in the room. A compression driver, on the other hand, has to compress only the air in a small cavity directly in front of the driver diaphragm. Obviously the air it compresses eventually has to go somewhere, so at the other end of the compression cavity there is a small opening (usually known as a ‘throat’) to an acoustic horn of some type.

In the case of the models in the HDI range, JBL uses the description ‘waveguide’ rather than ‘horn’, but the two share the same purpose, the difference being the way

in which the sound waves are radiated outwards, which in turn is controlled by the shape of the horn/waveguide.

According to JBL, the HDI waveguide was specifically designed to deliver neutral frequency responses both on-axis and off-axis, as well as a seamless transition between it and the driver below that delivers the midrange frequencies (though it’s not a dedicated midrange driver, as we shall soon discover). The aim was to deliver the smoothest in-room response possible by ensuring uniform directivity. The particular compression driver that’s used in the HDI-3600 is a JBL type 2410H-2, which has a 25mm polymer (Teonex) diaphragm with a V-shaped geometry that reduces mass and minimises break-up modes.

In fact we had found during our review of the HDI-3600 that the off-axis performance extended well from side to side, but not vertically. Standing up, above the tweeter, significantly reduced their abilities in the upper frequencies. Remembering this, we set the fairly bulky (28kg) centre speaker firing up slightly, directly to the listening position, ensuring we heard its full effect in concert with the HDI compression drivers from the left and right pair.

The more traditional cone drivers are, as noted, made from what JBL calls ‘an advanced aluminium matrix’, with chassis that are cast, rather than stamped. In the HDI-3600 one of the drivers is used for midrange, with a hybrid 2½-way crossover network where all three cone drivers deliver the bass below 900Hz, while the driver highest on the front baffle continues up to just below 2kHz, where the high-compression driver takes over. The 2½-way design means that you get the full benefit of maximum cone area (and thus maximum bass) at low frequencies, but the midrange frequencies still come from a point source, which is essential to preserve stereo imaging.

It’s less clear exactly how the drivers in the centre speaker are employed, but two crossover points are again quoted (600Hz and 2200Hz), so it seems likely this too is a 2½-way design, with two drivers supporting the midrange, and all four cones delivering bass.

The HDI-1600 standmounts, $3999 the pair, were the obvious choice for rear channels, with identical drivers to those in the HDI-3600, just fewer of them — a single 6.5-inch cone on mid and bass duties, though crossing over at a lower 1900Hz to the Teonex compression driver.

The last member of the team was the $5999 HDI-1200P subwoofer, which is HDI only in name, of course, since it is more bass-focused, with a 12-inch (300mm) Poly-plas cone woofer driven by a 1000W internal amplifier. Unusually the subwoofer is available in all three finishes offered for the other speakers: an attractive grey oak veneer (as on the HDI-3600 we originally reviewed, pictured right), a richer walnut (below), and finally a black (main image, left) which may appeal for home cinema use, though note it has a reflective high gloss finish.

Performance

So the full pack here yields only a few dollars change from $21,500, but the result is a pretty mighty package from a company that knows a thing or two about cinema sound. Immediately notable was how well the floorstanders integrated with the subwoofer under the filtering of our receiver; the overall response of the system was seamless as the HDI-3600 speakers handed over to the subwoofer. Bass was prodigious when required, but also controlled and detailed. We also appreciated the subwoofer’s relative ease of positioning in the room, as although is it a bass reflex design the ports here fire down, with its feet raising the base high enough for the exiting air to clear any carpet (for which you can also add spikes to the feet, as for all speakers in the range).

The movie sound overall was wellbalanced in tone, with plenty of depth to punch for blasts, rumbles and underlying tones of alarm, but also significant slam from those high-frequency compression drivers, with the midrange and treble emerging rich and unharnessed.

We generally prefer a subwoofer, if we’re using just one, to be positioned up the front — it’s often said that bass is nondirectional, but in fact it’s merely less directional, and it’s not hard to feel a pull towards the bass particularly at its higher frequencies. Here, however, there’s an argument for placing the bass at the rear, since we were aware of the rear standmounts’ lesser size as effects passed around the room. With the front speakers so bass-capable in their own right, you might drop your receiver’s crossover frequency for those a little and use the sub more to support the full soundfield. Or heck, you could use two subs, or HDI-3600s at the rear too, and enjoy a magnificently matched system.

Conclusion

What’s impressive here is that the system can kick out movies at high level, yet has the quality to deliver music with passion and accuracy too, whether a surround mix from Blu-ray or stripped back to the pair of HDI-3600s, where you can enjoy what we’ve already established to be award-winning stereo performance. An all-round delivery of music and movies, then, from speakers good-looking enough not to hide away.