Australian HIFI - - CONTENTS -

So ac­cu­rate, so mu­si­cal and so nat­u­ral-sound­ing that you’ll be cap­ti­vated!

Revel is a ded­i­cated high-end brand founded by Har­man In­ter­na­tional in 1996, and the F-208s were de­signed by Kevin Voeks, who’s been Di­rec­tor of Engi­neer­ing at Revel since that time. Voeks was pre­vi­ously the head de­signer at Snell, hav­ing taken over from founder Peter Snell af­ter his tragic death from heart at­tack, aged just 38, in 1984. Prior to work­ing at Snell, Voeks worked for fa­mous Cana­dian man­u­fac­turer Mi­rage. As a point of in­ter­est, Revel was only the sec­ond com­pany ac­tu­ally started by Har­man (it­self now owned by Sam­sung), be­cause apart from the har­man/kar­don brand, all the other brands owned by Har­man are the re­sult of ac­qui­si­tions and merg­ers.

Some mea­sure of the pop­u­lar­ity of Revel’s F-208 floor-stand­ing loudspeakers can be gauged by the fact that this model has been a best-seller in Revel’s line-up ever since it was first in­tro­duced in 2014. It’s part of Revel’s Per­forma3 Se­ries, which, be­ing po­si­tioned be­tween Revel’s Per­for­maBe Se­ries and its Con­certa2 Se­ries, puts it ex­actly in the mid­dle of Revel’s five dif­fer­ent se­ries (not count­ing its ar­chi­tec­tural speak­ers).

The curvy cab­i­nets in the Per­forma3 Se­ries are sim­i­lar to those used for the com­pany’s flag­ship Ul­tima2 Se­ries, be­ing formed with con­tigu­ous wood lay­ers and fin­ished in high­gloss piano black or gen­uine Amer­i­can wal­nut us­ing a process Revel says: ‘ is de­vel­oped and over­seen by Ital­ian lux­ury cabi­net-mak­ers and ex­ceeds au­to­mo­tive fin­ish qual­ity.’ (The last words of this com­ment are no doubt a dig against speaker man­u­fac­tur­ers who boast of us­ing ‘high-tech au­to­mo­tive paints’ on their cab­i­nets.)


The Revel F-208s are cer­tainly im­pres­sive, as they stand more than one me­tre tall (1.182 me­tres, to be pre­cise) and sport no fewer than four driv­ers on the front baf­fle— two 200mm-di­am­e­ter alu­minium-coned bass driv­ers, a 133mm-di­am­e­ter alu­mini­um­coned midrange driver and a single 25mm alu­minium-domed tweeter.

This means, of course, that the Revel F-208 is a true three-way de­sign, which is my favourite im­ple­men­ta­tion be­cause it means that the all-im­por­tant midrange fre­quen­cies are be­ing re­pro­duced by a single driver that’s ded­i­cated to the task, so you not only get the purest tonal­ity but also pointsource sonic de­liv­ery.

The bass and midrange driv­ers have res­o­nance-free cast alu­minium chas­sis and the voice-coils and mag­nets use a ge­om­e­try that re­sults in a sta­ble flux field even at high vol­ume lev­els, which has the ef­fect of re­duc­ing dis­tor­tion. The alu­minium cones have rib­bing that Voeks says re­sults in more pis­ton-like be­hav­iour which ‘ elim­i­nates a ma­jor source of res­o­nances that are clearly au­di­ble in most other loudspeakers.’ The sur­rounds of the bass driv­ers and midrange driver are made from San­to­prene, which is a ther­mo­plas­tic vul­can­izate made from rub­ber par­ti­cles en­cap­su­lated in polypropy­lene. San­to­prene com­bines the longevity of rub­ber with the flex­i­bil­ity of foam with­out any of the draw­backs of ei­ther ma­te­rial and as a re­sult is one of the very best ma­te­ri­als avail­able for use in loud­speaker sur­rounds.

Rather un­usu­ally for a high-end loud­speaker, the Revel F-208 uses high-or­der cross­over slopes ei­ther side of both cross­over fre­quen­cies (270Hz and 2.2kHz). Al­though it’s not stated in the spec­i­fi­ca­tions, Voeks es­ti­mates the or­der as ap­prox­i­mat­ing that of a 4th-or­der (24dB/oc­tave) Linkwitz-Ri­ley char­ac­ter­is­tic. Voeks says that it’s es­sen­tial to use higher-or­der cross­over slopes in a loud­speaker if you want low dis­tor­tion char­ac­ter­is­tics, min­i­mal com­pres­sion and high dy­namic range. This is be­cause if you use low-or­der cross­over slopes the driv­ers are be­ing fed au­dio sig­nals that are outside the fre­quency range they’re de­signed to han­dle, so most of the au­dio sig­nal volt­age ends up sim­ply heat­ing up the voice-coils. ‘ The heat makes the voice-coil im­ped­ance go up, and as a re­sult of that the fil­ter net­work is mis-ter­mi­nated be­cause it’s not see­ing the ter­mi­na­tion im­ped­ance it ex­pects to see, then the net­work doesn’t work

right any­more and you get peaks and dips in the re­sponse,’ says Voeks. Also, when a voice-coil gets hot, it in­tro­duces dy­namic com­pres­sion, which squashes dy­namic range.

The 25mm alu­minium-domed tweeter in the Revel F-208 has a in­te­grated acous­tic lens wave­guide that Voeks says not only en­sures that its dis­per­sion char­ac­ter­is­tics match that of the midrange trans­ducer in the cross­over re­gion, but also ac­tu­ally in­creases the tweeter’s dis­per­sion at higher fre­quen­cies. ‘ This gives the loud­speaker very smooth sound far off-axis,’ says Voeks, ‘ pro­vid­ing con­sis­tent sound over an ex­cep­tion­ally wide lis­ten­ing area, which is an im­por­tant con­trib­u­tor to over­all sound qual­ity.’

I loved that the tweet­ers on the F-208 are at seated ear-height, which is ideal acous­ti­cally. And of course you don’t have to use any un­gainly (and of­ten very costly!) stands to ac­com­plish this—one of the many ad­van­tages of a good floor-stand­ing de­sign. I also loved that the tweeter dome is alu­minium, be­cause if you’re go­ing to have any chance of mak­ing your speak­ers sound co­he­sive right across the fre­quency range, a very good start­ing point is to make sure that all the driver di­aphragms are made of iden­ti­cal ma­te­rial. De­sign­ers who try to marry paper-coned bass-driv­ers with a metal-coned midrange and a fab­ric dome tweeter are be­hind the eight-ball be­fore they even start!

A bass-re­flex de­sign, the Revel F-208’s port is on the front baf­fle, which sim­pli­fies room po­si­tion­ing, and the cir­cu­lar port is flared at both ends to min­imise port-gen­er­ated noise. You can ‘tune’ the speak­ers by fit­ting the ports with soft foam ‘plugs’. Revel says of th­ese: ‘ If your loudspeakers are lo­cated less than about 611mm from walls or other large ob­jects, in­sert­ing the port plugs into the loud­speaker’s port open­ings can re­duce the overly-ag­gres­sive bass out­put that can be cre­ated by the speaker’s prox­im­ity to large sur­faces that re­flect bass en­ergy. In the F-208 you can ex­per­i­ment with the port plugs in con­junc­tion with the loud­speaker’s Low-Fre­quency Com­pen­sa­tion ad­just­ment to fine­tune the low-fre­quency per­for­mance even fur­ther.’

So what is this Low Fre­quency Com­pen­sa­tion ad­just­ment? It’s a fea­ture of the Revel F-208 that I have not yet got around to men­tion­ing, so now seems as a good a time as any to do so. But be­fore I do, how­ever, we’ll first need to take a quick look at some ba­sic physics, which is that the low-fre­quency out­put of any loud­speaker will be greater when it is lo­cated close to one or more bound­aries (walls, floor, ceil­ing etc) than it is when it’s lo­cated away from such a bound­ary. This is be­cause the bound­ary es­sen­tially acts as a re­flec­tor to con­cen­trate the bass en­ergy. Think about a light bulb. If you just put a single bulb in the mid­dle of the room, its light will shine in all di­rec­tions, light­ing up all parts of the room equally.

If, how­ever, you put a re­flec­tor be­hind the bulb, all the light that would nor­mally have been sent be­hind the bulb will be re­flected for­wards. The re­sult will be that the room in front of the re­flec­tor will be brighter than be­fore, while the area of the room ob­scured by the re­flec­tor will be darker. Yet the bulb it­self is pro­duc­ing ex­actly the same amount of light as pre­vi­ously.

Ex­actly the same ef­fect oc­curs with the low fre­quen­cies pro­duced by a speaker. If you put a speaker in the mid­dle of a room, the low-fre­quen­cies will spread out om­ni­di­rec­tion­ally from the cabi­net, so that the sound will be al­most equally as loud be­hind the speaker as it is at the front of the speaker. If you move the speaker closer to a bound­ary, that bound­ary will re­flect the sound for­ward, in­creas­ing the level com­pared to if the speaker had been in the cen­tre of the room. This ef­fect only oc­curs at low fre­quen­cies, be­cause high fre­quen­cies are more di­rec­tional so, for ex­am­ple, very lit­tle of the sound from a tweeter goes be­hind the cabi­net: some does, but most of it goes for­wards.

All speaker de­sign­ers know all about this of course, but none of them know where you will place your speak­ers, so al­most all of them de­sign their speak­ers to de­liver the max­i­mum bass out­put the driv­ers are ca­pa­ble of de­liv­er­ing and most of them do their mea­sure­ments with their speak­ers el­e­vated from the floor and well clear of any bound­aries… even, some­times, in large ane­choic cham­bers, where there are no bound­ary ef­fects at all.

This means that when you put th­ese speak­ers in your room, you will get more bass than the de­signer’s mea­sure­ments would in­di­cate, be­cause you are putting the speak­ers on the floor. And if you move the speak­ers closer to a room bound­ary such as a wall, you’ll get even more bass. And if you move the speaker close to a side wall as well, yet more bass again!

The tweeter’s acous­tic lens wave­guide en­sures its dis­per­sion char­ac­ter­is­tics match that of the midrange

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