Diamond Audio Hex S12.4 Shallow Woofer

One of a new breed of super-shallow mounting-depth subwoofer drivers, intended for use in the sides of boots and in places where a regular subwoofer would not fit due to space restrictions. Bass with rumble in Ferraris, MR2s and behind the seats of pickup trucks is the intent then. The subwoofer is a Neodymium magnet design but the magnet is actually placed in the front of the cone rather than behind it. This is still driving the voice coil but with a pull and a push rather than a push and a pull! The chassis is a cast job and the cone is made of Carbon Fibre, with a fat top roll surround composed of Butyl rubber. The holes in the chassis are small (which was a minor gripe with the JL Audio product of similar intent) but like the JL Audio product, I reckon the maker wants you to go source some quality fixings to secure the woofer.
Ours was delivered already installed within a one cubic foot sealed enclosure although the correctly ported version was also supplied as an empty box. I say empty as the box was lined with acoustic absorbent material and so despite being a parallel-sided item, had no boom or unpleasant wooffling due to standing waves when running. The box was coated and had chamfered edges and was fitted with a Neutrik gastight ‘Speakon’ connector. I was also supplied a section of gorgeously meaty 11 Gauge speaker cable with a mating male in-line Speakon connector already affixed. Talk about being spoon fed. When I pointed out that this was the highest quality box I had ever been sent in all my time, the chap at Acoustic Wood who made it (was startled as he is both cabinet-maker grade woodsmith and is also involved with high end home cinema installations and the development of loudspeaker products. He figured this was a base standard. Hardly a surprise, then. You can get custom jobs and he’s interested in super-duty SPL boxes.
– Frequency response: Not Quoted – Power Handling: 250w RMS
– Carbon fibre cone
– Die cast Aluminium chassis
– Large Butyl Rubber top roll suspension
– Diametrically opposed squeeze terminals
– Voice Coil Diameter: 3 inch (75mm) 4 Ohms
– Mounting depth 77mm
– Front mounted Neodymium magnet and motor assembly
– Efficiency: 88.4dB 1w/1M
– Xmax 8.8mm
– Fms: 26.995Hz
– Qes: 0.319
– Qms: 3.586
– Qts: 0.293
– Vas: 73.418 Litres
Review by Adam Rayner
There are crucial differences between this and the JL Audio woofer we looked at immediately prior to this one. The JL Product is a few crucial millimetres thinner, being a madly shallow mounting depth of just two and one half inches as the Yanks would say or 65mm as we would now choose to measure wee distances. The HEX S12.4 is three and one tenths of an inch thick or 77mm.
Fact is, both products are seriously truncated in depth versus the regular designs of speakers but they do the job in very different ways. I could be wrong but I think the front-mounted Neodymium magnet technology used here is technology that has been bought in on license by Diamond Audio from those behind it. This sort of thing happens when a technology is so cool that others want to use it. There’s room for all the manufacturers that might buy into the license as they all make products in different ways to different quality levels. (Like for instance the fact that Organic Electro Luminescent displays are a Pioneer Electronics/TDK collaborative property and the whole world is licensing it as OLED even Sony for a TV set.) Diamond Audio’s manufacturing standards are epic. The front mounted magnet system was one I saw first on midranges. It used to be rare on woofers, even on the back, due to the price of Neodymium. Now there are lots of woofers as well as components with Neo Magnets and they work well. (Particularly the Orion HCC component speakers seen here) The magnet assemblies on these woofers are set in crackly finish finned cooling jackets of cast Aluminium and look cool protruding out the front of the cone as well as feeling solid as a rock.
When it comes to performance we know that bass is directly proportional to surface area of driven cone (up to the limits of SPL sanity then it’s how many gazillion watts you can load each cone with) and it is a fact that a flat piston head will have a lower surface area than a cone shaped surface within the same space. This is true of these two products, as the JL Audio item is truncated to the point where some cone depth has also been sacrificed as part of creating the woofer’s very own piston-face. With this HEX S12.4 we get a regular and in fact quite steep angled pukka woven Carbon Fibre cone that absolutely flings the air around.
So yes, while the JL Audio has this Diamond beat all the way on the ultimate shallowness front, there were some sacrifices made with its design to enable the flexibility of install, like the pistonic rather than conical driven diaphragm.
However, the sound of the Diamond Audio HEX S12.4 presented me with no compromises at all. It sounded very clean and tight indeed, wouldn’t purr on the amplifier power I had to offer it and never seemed to run out of travel. This is due in no small part to the use of real Butyl rubber in the cone suspension top roll surround. It means the Xmax or cone travel is a healthy 8.8mm and yet is less than the 9.7mm of the JL Audio 13TW5.3. But the cone is conical rather than a shallow concavity and this makes a difference.
I played some stuff from the Focal Spirit of Sound #6 disc and also some stuff from the dB Drag CD. The subwoofer tracked the changes in the bass lines and held on a treat to the tight bits. As ‘Are you ready for this?’ filled my semi detached house, the floor rippled and wobbled with great aplomb.
The only vexing thing is that out of sheer self-defence, the Diamond Audio people rate their power handling as pretty low and I can’t measure that here accurately as yet so have to use the maker’s figures when marking. The truth is that the rated 250W RMS is more like a real 500W RMS and that would have meant that I could have slapped an extra power handling point in there and so tipped HEX S12.4 into winning a Talk Audio Best Buy flag. As it is, I do recommend it if you need bass in less space and do not want to compromise on the quality of that bass and can fit this one in, it is the shallow subwoofer of choice.
Not a squashed design but darn clever, I’ll actually let the makers throw in some comments about how they made the thing here, as I am well impressed:
‘Due to the magnet being mounted in the front, the woofer has not been `squashed’ (if you added a conventional magnet on the rear it would be a standard depth woofer), this allows the woofer keep the standard cone shape and therefore its inherent strength which can be sacrificed by making the cone flatter. The standard cone shape gives maximum surface area, maintaining output levels – a 12 inch is a 12inch, basically.
The front mounted magnet still allows a normal amount of excursion, another restriction on `flattened’ woofers. You may have noticed the conservative power ratings. This is due to several things;
Diamond have been very conservative on the ratings, to quote ‘if we put 500w on the side of it, people would be shoving a 1000w up it all the time’. For this reason they only put ‘250w’ as an RMS rating.
The reality – this woofer does not need a lot of power, it has a light and efficient cone and motor assembly and as such does not require a power station to drive it. No need to shell out a fortune on a huge amp with this one.’
A shallow mount woofer with no compromise as to sound quality but sacrificing ultimate skinniness to the cause of SQ. That said, the ten inch model is only two tenths of an inch thicker than the JL and also smaller in diameter so will fit in just about any space you have.
Sound Quality 9.0
Build Quality 10.0
Power Handling 7.0
Efficiency 8.0
Value For Money 9.0
Overall rating 8.6