The Linn Isobarik, nicknamed "Bariks" or "Briks", 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 externalised 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 20 Hz to 20 KHz with the isobaric loading extending usable bass response to below 10 Hz". 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 kabinet 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.