text: linn isobarik the linn isobarik , nicknamed " " or " " , is a loudspeaker designed and manufactured by linn products . the isobarik is known for both its reproduction of low bass frequencies and being very demanding on amplifiers . launched in 1973 , the isobarik dms , linn 's maiden and flagship loudspeaker was based on and named for the isobaric loading principle invented in the 1950s . the speaker exists also as the isobarik pms – destined for the professional market . although discontinued in 1992 , it remains popular among audiophiles . history while other loudspeaker manufacturers sought to outperform each other to produce more quantum bass output from their products , linn was seeking clear undistorted low frequency bass . linn theorised a design whose bass could go all the way to dc and be without fundamental resonance . the quest for that extra octave of " dry and extended bass sound " and more accurate reproduction resulted in the isobarik . linn launched the original isobarik dms loudspeaker in 1973 , the year following the release of its first product , the sondek lp12 . " dms " is the contraction for " domestic monitor system " , and is designed to be driven passively in the home setting – it incorporated a crossover within the loudspeaker cabinet . the isobarik pms ( " professional monitor system " ) loudspeaker launched in 1977 , destined for the professional market is without the internal crossover . this latter configuration opens up more wiring and driving options , in particular active operation and tri - amping . the isobarik is so named as it employs the isobaric loading principle invented by harry olson in the 1950s : two bass units are mounted in a sealed container and driven in parallel so as to effectively double the speaker enclosure volume and extend its bass frequency response beyond what would be possible for otherwise identical speakers . linn used a variant of the isobaric principle and patented the use of two bass drive units ( " woofers " ) facing forward in an isobaric arrangement in early 1974 . in 1988 , linn the crossover of the dms to boards with nominal 4 - ohm impedance designed to lie flat at the base of the stands . upon that change , the original distinction between dms and pms disappeared along with the suffix designation . the " dms " was thus discontinued , although " isobarik pms " remained on price lists until the speaker was discontinued in 1992 . speaker linn brochures dwell little on performance specifications , mentioning somewhat vaguely that the frequency response " varies by only a few db from to with the isobaric loading extending usable bass response to below " . linn also claimed " very low distortion " and " high sound pressure levels " , without quantification . recommended amplifier power rating is in the range of 50 – 500 watts . hi - fi for pleasure noted that the speakers ' impedance , although quoted at 3 ohms nominal , dipped considerably at some parts of the audio spectrum . this made the dms isobarik very hard for amplifiers to drive , potentially causing many amplifiers ' output protection to trip . equally , the two heavy woofers in each isobarik made them twice as power - hungry . such demands happened to make naim amplification the perfect match because of its high current delivery capabilities and its toleration of near short circuits . the isobarik was famously used as the acid test for the budget - priced nad 3020 amplifier at its uk launch . in the 1970s , the dms isobarik , available in a number of veneers , sold for £ 1 , 000 . as part of their corporate philosophy , linn intended significant dealer involvement in customer education and decision - making , and included teaching customers how to listen correctly for musical attributes . the trial and evaluation of the product prior to purchase and dealer 's expert installation are considered by linn to be important parts of the value added of their top - end products . as such , no instructions were supplied with the product . the isobaric pms retailed at £ 2 , 400 including stands in may 1991 , and the 4 - ohm crossover was priced at just under £ 500 . design as a three - way loudspeaker system employing six individual drive units , each isobarik has two tweeters , two midrange drivers and two woofers . one driver of each frequency range faces forward ; a second tweeter and midrange are mounted on the top surface of the enclosure , and one bass unit is hidden from view . while the bass units are isobaric loaded , the midrange is mounted in a terminated transmission line . crossover points are set at 375 hz between the woofer and midrange , and 3 khz between the tweeter and midrange . the upward - firing drivers were designed to aid dispersion and improve the off - axis listening experience . the isobarik , like the sara and kan that were developed in the 1970s and 80s , was designed to work best near room boundaries . manufacturer 's leaflets advise positioning of the speaker close to a rear wall and approximately 2 to 3 feet ( 60 to 90 cm ) from corners . the trade - off is the less than solid stereo image . linn declared forthrightly that loudspeakers that were not designed to work tight against a wall were without merit . according to art dudley of stereophile , linn also maintained provocatively that " anyone who would design , manufacture , buy , sell , or positively review a loudspeaker made to be installed away from room boundaries was a fool " . in early product manuals , linn recommended using the isobarik pms in tri - amped configuration with naim amplifiers . three nap 250 amplifiers , fed by a 3 - way naim electronic crossover , would typically be used , one for each pair of the doubled - up treble , midrange and bass units . from its introduction in 1984 , the monaural nap 135 can be used in a " 6 - pack " configuration . after linn had started manufacturing electronics and upon the release of the isobarik crossover , linn declared that the ' ' system comprises : the source components plus one linn preamplifier , one linn isobarik crossover , three linn power amplifiers , one pair of linn isobarik loudspeakers and the necessary cables . construction the loudspeaker cabinet measures 15 × 15 × 30 inches ( 38 × 38 × 76 cm ) . the extremely rigid 55 - litre cabinet is constructed using 19mm high - density particle board that is strategically damped in places , and extensively braced . according to the manufacturer , there is an array of stressed steel rods inside the enclosure to control energy flows . the techniques employed ensure that energy that would have caused the unwanted motion of the front panel and drivers is cancelled by a similar but opposite energy from the upward facing units , resulting in the minimum amount of resonances . the cabinets were initially made by linn in their own factory , but the manufacturing was later outsourced to furniture - makers leon levin of glasgow . although the speaker uses bought - in drivers , they have been rebuilt using stronger materials . drivers ' metal baskets are treated to reduce the effects of vibration , and the enclosure designed and constructed to control energy . the drive units ( t27 , b110 and ) were sourced from kef in kit form , and two kits were judiciously used for each cabinet . however , linn found the t27 tweeter too fragile and replaced it with the more robust and better - sounding from scan - speak after a very short run ; the scan - speak tweeter was later changed to a linn d20 - lp - 1 , sourced from in denmark . the midrange kef b110 , known for its use in the ls3 / 5a bbc monitor , is a 100mm - diameter unit to which linn applied a layer of doping . the woofer is a kef . each unit of the isobarik cabinet weighs 40 kilograms ( 88 lb ) , and is designed to be placed on stands that are 33 centimetres ( 13 in ) tall so that the tweeter is positioned at the listener 's ear - level . the speaker is supplied with heavy stands made from welded square cross - section tubing , to which top and bottom spikes are fitted prior to positioning the speaker cabinet . input connections are established through 3 - pin xlr connectors . later versions and the pms version have banana sockets ( see image ) . product revisions 1973 isobarik dms launched . 1976 sep revised cabinet style . 1977 isobarik pms launched . 1978 sep damping : midrange enclosure and cabinet damping changed . sn . / 4 1979 the smaller isobarik sara launched . 1979 nov midrange unit : . sn . 10 , 800 / 1 1980 feb treble unit : scan - speak treble unit replaced sn . 10 , 925 / 6 1980 mar : common earth at cannon socket . sn . 11 , 035 / 6 1981 oct treble unit : fitted with t - nuts . sn . / 2 1982 jan cabinet : changed from chipboard to medite and veneered on both sides . sn . 2859 / 60 1983 mar bass / midrange units : sound deadening material painted on bass and midrange units . sn . 3000 / 1 1984 may crossover / treble units : circuit board with wider tracks and improved layout . new treble units with a smoother response . linn logo incorporated on front plate . sn . / 40 1985 dec cabinet : improved internal sealing and damping sn . / 6 1986 apr midrange units : harder rubber used for surround . sn . / 4 1987 cabinet : crossover moved to compartment in bottom of speaker . sn . / 6 1987 sep isobarik sara 9 replaces isobarik sara 1988 crossover : new 4 ohm external crossover fitted in stand . facility for tri - wiring . 1988 dms discontinued – pms can be driven passively ( 4 ohm ) or actively . sn . / 2 1989 isobarik sara 9 discontinued 1991 dec speaker : addition of ku - stone ceramic absorber , sealant changed to gaskets from silicone , improved cabinet bracing ( non - ) sn . / 4 1992 isobarik discontinued . source : linn reception the isobarik loudspeaker has received some polarised opinions , although hi - fi news noted that the speaker kept its promise by managing to " play the lowest bass guitar notes cleanly and give an impression of unlimited bass extension " . the linn / naim active system , using a lp12 source , naim amplification and electronic crossovers together with the isobarik pms , was regarded as the pinnacle of " flat - " hi - fi systems , and the speaker is integral to the general aura of mysticism that went with the linn / naim equipment . other isobarik products the isobarik sara is a product concurrent with the pms for the whole of its life . this 2 - way , 4 - ohm , design was a physically much smaller product – measuring 425 × 332 × 244 mm ( 16 . 7 × 13 . 1 × 9 . 6 in ) – that required tall speaker stands . launched in 1978 , it was linn 's entry - level loudspeaker until the kan ( a non - isobaric bookshelf speaker using the same linn d20 - lp - 1 and kef b110 drive units as its big brother ) was released . the kan was discontinued in 1990 . in the late 1980s , linn worked on a replacement for the isobarik . the project bearing the codename " isobarik " became the . although the final product does not bear the isobarik name , the technology was mentioned in marketing materials and the product manual . other products bearing the trade - marked " isobarik " name include the active isobarik bass and the isobarik ( 2011 – )