Richter Thor Series V DSP Subwoofer

Subwoofer

Richter has rationalised its subwoofer line-up and in the process completely re-designed its mighty Thor, with wonderful results…

I t’s been more than five years since I last experienced Richter’s Thor subwoofer, and much has happened in the interim.

One of the biggest changes came about when John Cornell, a 36-year veteran of the Australian audio industry, purchased Richter back in 2012. After looking at what was a huge range of subwoofers for a small Australian company, he decided to concentrate on building just one model… the Thor (which meant the end for one of the most wonderfully-named subwoofers in the world—the Richter Krakatoa—alas).

As with all the other models in Richter’s range, the Thor has recently been updated to ‘Series V’ status, which has meant a total overhaul of what was one of Richter’s longest-running designs. For starters, gone is the Class A/B amplifier that was a trademark of all Thor models up to and including the MkIV: The Series V uses a thoroughly modern Class-D output stage. It’s also a more powerful than ever before: up from 200-watts to 300-watts. And in a first for any Richter subwoofer, the new Thor Series V has digital signal processing (DSP) on-board, one of the functions of which is to ensure best performance no matter whether the Thor is used in a two-channel hi-fi system, or a 5.1-channel home theatre set-up.

The equipmenT

One thing that hasn’t changed about the Thor Series V is that it’s a physically big subwoofer. Very big! Richter’s head designer, Dr Martin Gosnell B.E. (Hons) PhD, has been around for long enough to know that if you want a subwoofer to deliver the deepest bass frequencies with the lowest distortion at the highest sound pressure levels you need a big bass driver, a big cabinet and a big amplifier. No matter what type of spin the manufacturers of small subwoofers put on their publicity hyperbole, no-one can contradict the laws of physics, which dictate that all reductions in cabinet or driver size and/or amplifier power away from ‘big’ will inevitably compromise on subwoofer performance… there’s just no getting away from it.

But don’t let me give you the impression the Thor Series V is not a manageable size. At 510×430×440mm (HWD) it’s actually even bigger than the Thor IV, but still small enough to be hidden behind a lounge chair.

Given some forethought, you could even manage to put it inside a cupboard or an entertainment unit… ploys made possible by the fact that both the bass driver and the twin bass reflex ports are forward-firing. However, in recent years I’ve started thinking that we all need to get away from this ‘let’s hide the subwoofer’ mentality. It would be better to embrace the concept of subwoofers… even to evangelise them. So, when asked about your subwoofer, you could say ‘ Oh, that’s my subwoofer. I need one that large so I can hear realistic low-frequency sounds when I’m listening to music on my system or watching movies on

my TV.’ Now that would be liberating. After all, you don’t hear people complaining about the size of other people’s cars, houses or TV screens! But I digress…

The front-firing bass driver in the Thor Series V is new for Richter. Although the cone is the same diameter as the one fitted to the previous Thor IV, it’s now driven by a doublemagnet motor system, and the suspension has been upgraded to poly-rubber. Interestingly, Richter rates the ‘EPD’ (Effective Piston Diameter) of the cone (rather than the overall diameter as do most other subwoofer manufacturers). Although the overall diameter dimension always reads best on the specification sheet (and in those glossy full-colour advertisements) it’s actually the EPD that is the important dimension, since this is the one which dictates how much air the cone will actually move. Australian Hi-Fi Magazine prefers to use the term Thiele/Small diameter, but they’re one and the same thing: the dimension that’s used to determine the Sd (cone area) which in turn is the parameter speaker designers plug into their equations when determining cabinet volume and (if applicable) bass reflex port sizing. To see an example of the difference, the Thiele/Small (EPD) diameter of the driver fitted to the Thor Series V is 255mm (which gives it an Sd of 510cm²), whereas the overall diameter of the driver is 310mm. The cone itself is made from a composite of paper and fibre, in order that it has as little mass as possible, so the Thor Series V can be a ‘fast’ subwoofer. The dustcap is inverted, so that it follows the slope of the cone—a better design, to my mind, than the conventional ‘bumped’ dustcap.

It’s still a big cone, however, which is why Richter is using such a powerful ClassD amplifier to move it. Whereas the topic of Class-A/B vs Class-D is still contentious when it comes to building amplifiers that are required to cover a wide bandwidth, no-one I’m aware of has any issue with using a ClassD amplifier to power a subwoofer, because all the issues that affect Class-D designs don’t affect their performance below 1kHz, which is far above the highest frequency they could reasonably be expected to amplify when deployed inside a subwoofer.

As for the inclusion of DSP, Dr Gosnell says that he’s exploited every feature in Analog Devices’ ADAU1701, which is a fully programmable device with on-board 28/56-bit audio DSP, ADCs and DACs that can be programmed (via SigmaStudio) for equalisation, crossover, bass enhancement, multiband dynamics processing, delay correction and driver compensation. In an email to Australian Hi-Fi Magazine’s editor, Greg Borrowman, he advised that the DSP: ‘ not only controls every aspect of the signal, providing much greater control over response and dynamics, but also utilises two completely separate digital control formats for the home theatre and music settings.’ It also has full overload (including input signal clipping detection) and thermal protection circuitry.

The rear of the Thor Series V has the usual large black plate (though actually somewhat larger than usual in this case), and offers both LFE and left/right line-level inputs (via RCA inputs, with the left-channel RCA doubling up as the LFE input) and speaker-level inputs (via multi-way banana-capable speaker terminals). There’s also a speaker-level output terminal pair should you prefer—or need—to use this termination. Volume and crossover frequency (40–140Hz) controls are provided via rotary controls, whereas phase (0°/180°) control is implemented via a slider switch. There’s also a Sub/LFE slider switch which should be set according to whether you’re using the line/LFE inputs or the speaker level connections, plus an On/ Auto-Off switch you use to specify whether you want the subwoofer to stay permanently ‘On’ or to switch automatically in and out of standby mode depending on whether it detects the presence of an audio signal at its inputs. Last, but far from least, is a Music/Theatre slider switch. Set to ‘Music’ the maximum output of the subwoofer is slightly curtailed, but you get bass extension right down to around 12Hz. In the ‘Theatre’ position, an infra-sonic filter is inserted to roll off the very lowest frequencies—the bonus being that this allows you to play it louder than you can if ‘Music’ is selected.

The finish on the Richter Thor Series V is a black oak vinyl veneer… the only finish available for this model, except for the lower part of the front baffle which houses the two 68mm diameter bass reflex ports, which has a matt paint finish.

We all need to get away from this ‘let’s hide the subwoofer’ mentality. It would be better to embrace the concept of subwoofers… even to evangelise them.