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Price in Poland: 9,429 PLN (per pair)

Manufacturer: PMC Limited

43-45 Crawley Green Road | Luton | LU2 0AA
United Kingdom
tel.: +44 (0) 1582 405694 | fax: +44 (0) 870 4441045



Country of origin: UK

Product provided for testing by: MJ Audio Lab

Text: Wojciech Pacuła
Photos: PMC (1-6, 16) | Wojciech Pacuła
Translation: Andrzej Dziadowiec

Published: 3. December 2012, No. 103

The newest series from PMC that is Professional Monitor Company is the Twenty series. Prepared for the manufacturer’s 20th anniversary it is much more affordable than most other products offered by this British manufacturer based in Luton, north of London. And it seems at the moment to be the apple of PMC eye.
But one needs to keep in mind that in addition to studio behemoths such as the MB2i, the MB2XBDi or the BB5i speakers that really define PMC image we also find speakers with the letters T, G, F, O, P, and E in front of the symbol, belonging to the so-called iSeries. Just as the once reviewed OBi1, speakers with unique looks and sound.
The GB1i speakers I would like to have a closer look at this time is the smallest floorstanding design from the manufacturer. Slim, with a slender front baffle, using only two drivers - a soft dome tweeter and paper coated midbass woofer. The latter is quite small, only 140 mm in diameter. It is, however, loaded into a long labyrinth with a large vent located at the bottom of the front panel. The dome tweeter is from Norwegian SEAS, modified to PMC order. Its dome is made of material called SONOLEX.
The predecessor of the GB1i was the GB1 model developed on the basis of the award-winning FB1 and OB1. It is worth noting that there is also a special version of the reviewed speakers, the GB1i Signature.

Transmission Line

Transmission line is the PMC trademark. The manufacturer’s innovative proprietary version is called ATL for "Advanced Transmission Line". Owing to that the small speaker with a tiny woofer is quoted to have bass extension to 29 Hz. ATL is simply a long tunnel or labyrinth inside the cabinet, suitably shaped and damped – here consisting of three sections – rear-loading the woofer. Normally, the energy from the back of the speaker (which amount is equal to that from the front side) is either suppressed (closed enclosure design), radiated directly to the room (open baffle design) or partially suppressed and partially (at a specific frequency) radiated in ported or bass-reflex designs. Transmission line promises to recover that energy across a full driver bandwidth. These designs used to much more popular and were pioneered in commercial designs by John Wright. He developed them in his own manufacturing company, IMF Electronics. PMC is an immediate successor of these ideas (a very interesting article on that subject appeared in "Hi-Fi News & Record Review": Steve Harris, Landmark loudspeakers, Vol. 59 No. 06, June 2012, pp. 14-18). Let’s add that Wright subsequently founded TDL ("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 rear of the speaker. It was subsequently jointly developed in the 60s by Arthur R. Bailey from Bradford Institute of Technology and Arthur Radford. In 1965 "Wireless World" magazine published Bailey’s article on the subject that remains valid, titled A Non-Resonant Loudspeaker Enclosure Design, in which he showed practical applications of the theoretical work of Radford. Steve Harris writes in the article IMF Pro Monitor that the name “transmission line” was derived from electrical engineering by the way of analogy.

PMC products featured so far in “HIGH FIDELITY”:

  • REVIEW: TWENTY.22 standmount speakers, see HERE
  • REVIEW: OB1i floorstanding speakers, see HERE
  • REVIEW: PMC OB1+ standmount speakers, see HERE



  • 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);
  • Elgar
  • Delius, Cello Concertos, wyk. Jacqueline Du Pré, EMI Classic, 9559052, 2 x SACD/CD (1965/2012).
  • Fauré, Requiem, dyr. Michel Corboz, Erato/Warner Music Japan, WPCS-12545, SACD/CD (1972/2012).
  • Hilary Hann, Hilary Hann Plays Bach, Sony Classical, SK 62793, Super Bit Mapping, 2 x CD (1997).
  • Manuel Göttsching, E2-E4. 30th Anniversary, MG
  • ART, 404, CD (1981/2011).
  • Maria Peszek, Jezus Maria Peszek, Mystic Production, MYSTCD 214, CD (2012).
  • Pink Floyd. The Wall, EMI/EMI Music Japan, Digital Remaster, 2 x CD (1979/2011).
  • Suzanne Vega, Nine Objects of Desire, A&M Records, 540 583 2, CD (1996).
  • The Beatles, Abbey Road, Apple/Toshiba-EMI, TOCP-51122, CD (1969/2000).
  • The Modern Jazz Quartet, European Concert. Volume One + Two, Atlantic/East West Japan, AMCY-1186-7, "Atlantic Jazz Collection, 50 Years", K2HD, 2 x CD (1960/1998).
  • This Mortal Coil, HD-CD Box SET: It’ll End In Tears, Filigree & Shadow, Blood, Dust & Guitars, 4AD [Japan], TMCBOX1, 4 x HDCD, (2011).
  • Tomasz Stańko Quartet, Lontano, ECM, 1980, CD (2006).
  • Vangelis, Blade Runner Trilogy. 25th Anniversary, soundtrack, Universal Music K.K., 550689 4, 3 x CD (1998, 1991/2007).
Japanese editions available from

Humphrey Britton-Johnson in his letter to "Hi-Fi News & Record Review," titled From IMF to PMC writes as follows:
Having thought PMC speakers were for pop, rock and ‘head-bangers’ I was won over by the company’s OB1s a few years ago, after auditioning numerous floorstanders with classical recordings. I’m now appreciating PMC’s PB1i, which has awesome dynamics and insight. It’s the best for ‘mighty Mahler’ symphony recordings and outstanding for modest orchestral forces too. Far too good fo head-bangers!
I don’t know whether it was intentional but the letter’s author very accurately describes the general sonic characteristics of the reviewed GB1i. They are speakers with universal, exceptionally even sound.

The PMC speakers are not large. They are rather kind of "matchsticks" - quite tall and slim. Despite that, they offer considerable sound volume, much larger than standmount speakers for comparable money. What sets them apart from standmounters, some of which can also demonstrate low bass extension - see the Twenty.22 from the same manufacturer or the Callisto III from RLS (reviewed HERE), is a much more natural, unrestrained presentation. To go really low in a small enclosure with a small woofer some compromises had to be made, starting with sensitivity and ending with lower dynamics. Yet the GB1i can "breathe", is alive and does not show noticeable compression. The latter is of course present, after all it’s a small woofer, but we perceive it more on a subliminal level, not directly. I will say more: the reviewed speaker is one of the very few designs – not being a large or a very large box – that easily cope with dynamics differentiation.
It shows, for example, how much compressed dynamics is on the Remixes 2. 81-11 album with new versions of Depeche Mode songs; how radically different the tracks are from one another. I had no problem finding out where the artist had gone too far with compression, where poor sampling choices killed off vitality in the recording leaving a flat “something”. The same is true of The Beatles Abbey Road which only comes "alive" at higher than "background" levels of sound. Apparently, the mix was made at a relatively high sound pressure in the recording engineer’s room and the album begins to sound good at a similar volume level during home audition. The GB1i has no problem with showing these correlations.

It’s almost certainly a result of extraordinarily even frequency response down to low end. I'm not sure whether the 29 Hz quoted by the manufacturer is possible at home. In my opinion it’s rather closer to 39 Hz – the lowest double bass note, about 41 Hz, sounded full but electronic music going lower still was not as full as with the Harbeth M40.1. Nevertheless, it is almost a full range speaker. Many floorstanders could only dream of such a result.
And the reviewed speakers do not sound monotonous, non-differentiated. At first, the speakers may appear totally unattractive. We get very even presentation without sonic fireworks. With a bit of imagination we can imagine the letter M (for ‘monitor) in the company logo in bold – it is indeed a “monitor” sound (not to say “monitoring”). Nothing stands out or steps out of line, and definitely not the bass.

The latter can sound very attractive and fleshy but only when it finds some “ground” for that. As on Maria Peszek’s album Jezus Maria Peszek or on Lontano by Tomasz Stańko Quartet. For it's not that something needs to pump the bass, it's a matter of a well-engineered recording where the sound is natural, with a proper base, breath and volume. It’s not simply “bass” in the sense of a single low frequency generated by keyboard or the lowest string played on bass guitar. Such thinking is simplistic, ignorant – sorry for being blunt… What I mean is the kind of presentation that has depth, is natural and full.
And it was the recordings from Lontano that best showed what I’m saying and that the GB1i coped with without any problems. The title track opening the album develops slowly, calmly, but from the very beginning we get a rendering of a large space, kind of a holographic image with emerging large virtual sources, some closer others further away, all well differentiated and natural in their “presence”. The PMC speakers can’t do it as capably as the Harbeths, my reference speakers, or even – I remember that well – the larger model from the company, the OB1i (reviewed HERE). But for their size and their price they compare very, very favorably.

It is difficult to point out a particular sub-range which would be more or less "important". As I have probably demonstrated it’s not bass that "rules" here, despite that type of connotation associated with transmission line. But treble is not accented, either. It is not bad; the speaker sports quality tweeter, very well "joined" with midrange. It's just that you need to be aware of its limitations. It will not play with dense and full sound. It complements the whole rather than creates it. While dynamic and quite selective, it is not really resolved. And it’s no use deceiving oneself that it’s the “best of the best” among tweeter for it is not.
Its strength lies in a proper level setting, its exemplary “fusing” with the rest of the sound range and – evidently – good phase coherence. The sound reproduced by these speakers shows a trait that I value very highly – calmness. No flicker in sound image. That translates into very good spatial resolution. The speakers correctly show the sounds on both sides of the listener or behind him/her, provided they are in the recording. Soundstage depth is pretty good, although I had much better results with the speakers strongly toed in, with their axes crossing about 50 cm in front of me. That almost always works with smaller monitors and speakers with good phase coherence (not so much with the Harbeths M40.1 as their fronts are too broad for that, acting as open baffles). The GB1i are made for such experiments! With that positioning I had narrower, but much better organized soundstage with close-up foreground and ample depth. Please, try that at home - sound focusing is a few lengths more accurate.


If you think that transmission line in general and PMC speakers in particular are for “rockers”, then think again, sitting in front of the GB1i, preferably with a nice drink in hand. Try to free yourself from stereotypes and prejudices for, in this case especially, they are foolish and make us fools. Play anything classical – first some solo violin, then a large symphony orchestra – and see how they both sound equally “vigilant”. Play some jazz from the 50s and 60s, for example Monk, Coltrane, Armstrong, Ellington, Richie, anything – and see your jaw drop (be careful with your drink). And it's not because it's a perfect speaker. It is not. It’s because it’s so well put together and because all design choices such as transmission line serve a purpose, rather than prove any point.
I’ve already mentioned a couple of weaker points, like the not entirely full and not quite resolute treble. I would add to that one more thing, a shortening of after-sounds. The sound of the GB1i is well controlled and kept in check and in this case (remember, it's one of PMC least expensive speakers) it affects after-sounds – they are quickly suppressed, without full decay. Soundstage is wide and deep but it seems to lack proper sound decay. It's probably partly due to a slight suppression of lower midrange dynamics, something that is not particularly audible in itself but comes out somewhere else.
The speakers are cute, modestly sized and very attractively, solidly made. They do not dominate the interior. They do require a fairly powerful amplifier. Their sensitivity is below average and although their quoted nominal impedance seems high, they need a capable amp. It might be worth thinking of a tube amp; it will saturate treble and upper midrange which is just what’s needed.

Testing methodology

The speakers were tested in A/B comparison with A and B known. The reference point was "High Fidelity" reference speaker, the Harbeth M40.1. Musical samples were 2 minutes long. After the actual test whole tracks were also auditioned. The speakers sat on the accompanying spikes and those in turn on marble slabs. They were aimed at the listener’s ears as well as with axes crossing in front.
Similarly to the Monitor Audio Monitor MR4 reviewed in the same issue of "High Fidelity", the GB1i is one of the nowadays less frequent designs with dual speaker terminals. In this case, the two pairs of speaker terminals for the tweeter and midbass sections accordingly can be coupled by “jumpers” installed between the two sets. As always, they should be discarded immediately after removing the speakers from packaging. In their place one should use short jumpers, preferably from short lengths of one’s speaker cable. As I said in the Audio Monitors review, instead of jumpers I used something else, much better.
I wrote about it once in my editorial: if you I’m forced to do that by certain conditions (length, positioning, etc.) I use during tests the Acoustic Revive SPC-PA speaker cable. It’s a top cable from that manufacturer, made of an oval solid-core wire terminated with proprietary RBN-1 banana plugs (Acoustic Revive does not recommend soldering!). The company also has its own solution to the problem of dual speaker terminals, much better than jumpers. It’s the BWA-4 “Bi-Wire Adapter” featuring two connectors at one end and four at the other. The adapter comes ready with short lengths of cable, the same as the one used in SPC-PA. All we need to do is to install banana plugs (four per channel) and we have an elegant, very “purist” bi-wiring with a classic cable. That’s what I did with the PMC speakers.


The GB1i is a floorstanding speaker from British PMC. It is a two-way design, with transmission line loaded midbass woofer. In this model, the transmission line has a length of 2.4 m and it terminates with a rectangular vent on the bottom of the front baffle, sealed with sponge. It looks very elegant, much better than bass-reflex vents. The transmission line length is calculated in such manner that the air pressure from the back of the speaker is in phase with the front side pressure. The cabinets are finished in real wood veneer, also on the inside, in four different colors. Bottom plinth is made of black lacquered MDF. With it, the spikes protrude beyond the outline of a fairly narrow speaker cabinet. Interestingly, the plinth is not solid featuring two cut out holes, diminishing its weight. It seems that has been done deliberately, as if the speaker sounded better this way.

Speaker drivers come from Norwegian SEAS, after slight modification. The 27 mm SONOLEX soft dome ferro-fluid cooled tweeter is crossed-over at 2 kHz. Its front is covered with metal plate featuring concentric angled slots. The plate reinforces the tweeter front but also somehow seems to help control sound waves propagation.
Below the tweeter is the 140 mm woofer with coated paper cone and cast magnesium basket. The cabinet interior is heavily damped with sponge. Due to the presence of transmission line the cabinets are exceptionally solid.
The speaker has dual gold plated terminals with gold plated jumpers between them. The jumpers should be treated as a "transport" or "exhibition" accessory only serving to prove that the speaker works. They need to be replaced them as soon as possible with real jumpers. The speakers arrive with a very well-written, really helpful user manual.


Frequency Response: 29 Hz-25 kHz
Nominal Impedance: 8 Ω
Sensitivity: 87 dB (1 W / 1 m)
Crossover Frequency: 2 kHz
Recommended Amplifier Power: 40-200 W
Effective length of transmission line: 2.4 m
Dimensions (HxWxD, without stand): 870 x 155 x 234 mm
Weight (each): 10.5 kg
Available veneer: Walnut, Cherry, Oak, Black Ash


MJ Audio Lab

tel.: (22) 397 79 08 | (22) 397 79 07
tel. kom.: +48 888 693 711 | +48 506 063 857



  • Humphrey Britton-Johnson, From IMF to PMC, "Hi-Fi News & Record Review", Vol 57 No. 11, November 2012, s. 106.
  • Steve Harris, Landmark loudspeakers, "Hi-Fi News & Record Review", Vol 57 No. 06, June 2012, s. 14-18.
  • Steve Harris, IMF Pro Monitor,"Hi-Fi News & Record Review", Vol 57 No. 04, April 2012, s. 122-126.
  • Peter Thomas, Transmission lines, materiały firmowe PMC,
  • John Crabbe, The Truth About Transmission Line, "Hi-Fi News & Record Review", 1993.
  • Arthur R. Beiley, A Non-Resonant Loudspeaker Enclosure Design, "Wireless World", October 1965, s. 483-486; available in PDF formatTUTAJ.

  • associated-equipment

    • CD player: Ancient Audio Lektor Air V-edition, review HERE
    • Phono preamplifier: RCM Audio Sensor Prelude IC, review HERE
    • Cartridges: Miyajima Laboratory SHILABE, review HERE), Miyajima Laboratory KANSUI, review HERE
    • Preamplifier: Ayon Audio Polaris III [Signature Version] with Re-generator Power Supply
    • Power amplifier: Soulution 710
    • Integrated amplifier/headphone amplifier: Leben CS300 XS Custom Version, review HERE
    • Loudspeakers: Harbeth M40.1 Domestic, review HERE
    • Headphones: Sennheiser HD800, AKG K701, Ultrasone PROLine 2500, Beyerdynamic DT-990 Pro; 600 Ω version, review HERE, HERE, and HERE
    • Interconnect: CD-preamp: Acrolink Mexcel 7N-DA6300 (article HERE, preamp-power amp: Acrolink 8N-A2080III Evo, review HERE
    • Speaker cable: Tara Labs Omega Onyx, review HERE
    • Power cables AC (all equipment): Acrolink Mexcel 7N-PC9300
    • Power strip: Acoustic Revive RTP-4eu ULTIMATE
    • Stand: Base; under all components
    • Resonance control: Finite Elemente Ceraball under the CD, Audio Revive RAF-48 platform under the CD and preamplifier
    • Pro Audio Bono PAB SE platform under Leben CS300 XS [Custom Version]; review HERE