Richter Thor Se­ries V DSP Sub­woofer

Sub­woofer

Australian HIFI - - CONTENTS -

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.

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