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This review first appeared in the November 2012 issue of hi-end hifi magazine High Fidelity of Poland. You can also read it in its original Polish version here. We publish its English translation in a mutual syndication arrangement with publisher Wojciech Pacula. As is customary for our own articles, the writer's signature at review's end shows an e-mail address should you have questions or wish to send feedback. All images contained in this review are the property of High Fidelity or PMC. - Ed

Reviewer: Wojciech Pacula
CD player: Ancient Audio Lektor Air V-edition
Phono preamplifier: RCM Audio Sensor Prelude IC
Cartridges: Miyajima Laboratory Shilabe & Kansui
Preamplifier: Ayon Audio Polaris III Signature with Regenerator power supply
Power amplifier: Soulution 710
Integrated amplifier/headphone amplifier: Leben CS300 XS Custom
Loudspeakers: Harbeth M40.1 Domestic + Acoustic Revive custom speaker stand
Headphones: Sennheiser HD800, AKG K701, Beyerdynamic DT-990 Pro 600Ω vintage, HifiMan HE6
Interconnects: CD/preamp Acrolink Mexcel 7N-DA6300, preamp/power amp Acrolink 8N-A2080III Evo
Speaker cable: Tara Labs Omega Onyx
Power cables (all equipment): Acrolink Mexcel 7N-PC9300
Power strip: Acoustic Revive RTP-4eu Ultimate
Stand: Base IV custom under all components
Resonance control: Finite Elemente Ceraball under CD player, Audio Revive RAF-48 platform under CD player and preamplifier, Pro Audio Bono PAB SE platform under Leben CS300 XS
Review component retail in Poland: PLN 9.429/pr

The newest from the Professional Monitor Company or PMC is the Twenty Series. Coinciding strategically with the manufacturer’s 20th anniversary it is much more affordable than most other products offered by this British firm based in Luton north of London. At the moment it seems to be the apple of PMC’s eye. But one needs to keep in mind that in addition to studio behemoths such as the MB2i, MB2XBDi or BB5i which really define PMC’s pro image we also find speakers with the letters T, G, F, O, P and E in their name which belong to the so-called iSeries. Just as the OBi1 I reviewed earlier, these are speakers with unique looks and sound.

The GB1i speakers I take a closer look at today is the company’s smallest floorstander. It’s slim with a slender front baffle and uses only two drivers - a soft-dome tweeter and coated-paper mid/woofer. At 140mm in diameter the latter is quite small. It is however loaded into a long labyrinth with a large vent located at the bottom of the front panel. The tweeter is from Norways’s Seas modified to PMC’s specs and runs a dome made from a textile-derivative Sonolex. The predecessor of the GB1i was the GB1 developed on the basis of the award-winning FB1 and OB1. It is worth noting that there is a special version called the GB1i Signature.


Transmission Line. This design principle is a PMC trademark. The manufacturer’s take on it is called ATL for "Advanced Transmission Line". Owing to this loading a small speaker with a tiny woofer is quoted to have bass extension to 29Hz. ATL refers to a long folded tunnel or labyrinth inside the cabinet suitably shaped and damped (here consisting of three sections) to rear-load the woofer. Normally the energy from the back of the driver whose amount equals the front radiation is either suppressed (closed box), directly radiated into the room (open baffle) or partially suppressed/radiated at a specific frequency in bass-reflex designs. Transmission lines promise to recover that energy across the driver’s full bandwidth. Such designs used to be more popular and were commercially pioneered by John Wright who developed them for his company IMF Electronics. PMC is the successor of these ideas (a very interesting article on the subject appeared in HiFi News & Record Review by Steve Harris as "Landmark loudspeakers" Vol. 59 No. 06, June 2012, pp. 14-18). Let’s add that Wright subsequently founded TLD aka Transmission Line Developments.


The original idea of the transmission line emerged at Stomberg-Carlson which in the 30s patented in the United States the idea of a long tube acoustically loading the back of a driver. In the 60s it was jointly developed by Arthur R. Bailey from the Bradford Institute of Technology and Arthur Radford. In 1965 Wireless World published Bailey’s article on the subject that remains valid today which was entitled "A Non-Resonant Loudspeaker Enclosure Design" in which he showed practical applications for Radford’s theoretical work. Steve Harris in his article IMF Pro Monitor explains that the term ‘transmission line’ derived from electrical engineering by way of an analogy.


Sound – a selection of recordings used during these auditions: A Day at Jazz Spot 'Basie'. Selected by Shoji "Swifty" Sugawara, Stereo Sound Reference Record, SSRR6-7, SACD/CD (2011); Ash Ra Tempel, Ash Ra Tempel, MG; ART/Belle, 101780, SHM-CD (1971/2010); Carol Sloane, Little Girl Blue, Sinatra Society of Japan, XQAM-1036, HQCD (2010); Dead Can Dance, Anastasis, [PIAS] Entertainment Group, PIASR311CDX, "Special Edition Hardbound Box Set", CD+USB drive 24/44,1 WAV (2012); Dire Straits, Brothers in Arms, Vertigo/Universal Music Ltd. Hong Kong, 5483572, XRCD2 (1985/2000)...