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Positive Feedback ISSUE 48
march/april 2010



GB1i loudspeakers

as reviewed by Kent Johnson







Magneplanar MG1.6

Dodd Audio Midline tube preamplifier. Rogue 90 Stereo tube amplifier.

Sony SCD-C333ES SACD/CD player for SACD. The Sony feeds a Cullen Circuits DL3 Stage III modded PS Audio DAC for CD replay.

DH Labs Revelation interconnect cables. Alpha Core Goertz MI2 speaker cables. My digital cable is two meters of Belden 1694A video cable terminated with Eichmann Bullet Plugs. It works great. Here is the article that the information for making it came from: PFO Issue 14, "Why longer is generally better for an S/PDIF Digital Cable," by Steve Nugent.

Monster HTS 3600 MKII line conditioner on the source components. I have four dedicated circuits available to me, three twenty amp and one fifteen amp. The Rogue and Hafler are each on their own twenty amp circuits. The front-end equipment is on another. The fifteen amp circuit is not in use at the moment. I have a pair of AKG K240 headphones.


The Professional Monitor Company (PMC) GB1i loudspeaker is the floor standing version of the DB1i monitor speaker that I found so impressive at the 2009 Rocky Mountain Audio Fest. It is also the smallest floor-stander made by PMC and, like the DB1i, uses a transmission line bass alignment.

I had not heard the GB1i speakers previously so when PMC-USA offered me the opportunity to hear them in my own systems, I was pleased to do so.

While I was impressed by the DB1i monitors, my personal prejudice really lies in favor of floor-standing speakers. The major reason for this is the improved bass depth that results from their larger internal volume. These two PMC speakers illustrate this volumetric advantage pretty dramatically. Utilizing identical drivers, the bass of the GB1i extends to 29Hz, that of the DB1i to 50Hz, according to PMC (no tolerances given). The cabinet of the GB1i adds a substantial 21Hz of additional bass response! To me, this is a considerable benefit.

A floor-stander also places the drivers at a height determined by the manufacturer. There is less chance of listening on the wrong axis thanks to using stands that are not at the height assumed by the speaker designer.

There is, of course, more to any speaker than the size of its cabinet—in the case of the GB1i, quite a lot more.

The series "i" Upgrades

While it has been several years since the "i" upgrades were introduced by PMC, it is worth noting what those changes were for the benefit of everyone, myself included, who is not familiar with the original GB1 speakers and is going to wonder what the little italics "i" means.

Three major technical upgrades were made. The first was the SOLONEX 27mm dome tweeter developed in cooperation with SEAS. It is said to offer better detail, power handling, and off-axis response than the tweeter it replaced. The mid/woofer was also upgraded with a new PMC-designed unit with both higher power-handling and a flatter, lower-distortion midrange. The third improvement involved revisions to the hand-wired high-order crossovers. These now use French-made Solen capacitors. The sum of these improvements, according to PMC, can be heard in better driver integration resulting in more realistic vocals and faster, cleaner bass.


The Professional Monitor Company GB1i is a small, relatively narrow speaker. Its cabinet measures 6 by 9.25 by 34.25 inches (WDH). Sitting on its spiked plinth, the height extends to about 36 inches. The front baffle is just wider than the 140mm cast magnesium chassis woofer/midrange. The 27mm SONOLEX® domed tweeter is located at the top of the baffle. PMC specifies the frequency response for the GB1i as 29-25KHz with nominal 8 Ohm impedance and an efficiency of 87db @1W1m. The GB1i sells for $3249 per pair and is made in the UK.

The speaker cabinet is very skillfully veneered on all sides. I found the low-sheen cherry finish of the review pair quite attractive. The cabinet is also noticeably light, 23 pounds, since virtually its entire interior is devoted to the transmission-line loading of the bass/mid driver. This transmission line, described by PMC as ATL—Advanced Transmission Line, is what allows the GB1i to operate all the way down to 29Hz. The vent at the bottom of the speaker acts as an additional driver as it utilizes the sound waves off of the back of the mid/bass unit to energize the transmission line. PMC offers this fuller explanation of ATL from their web site:

"The main driver is placed at one end of a long tunnel (the transmission line), which is heavily damped with absorbent acoustic material. This material is specified to absorb the upper bass and higher frequencies that radiate from the rear of the main driver. The lowest frequencies, which remain in phase, then emerge from the large vent at the end of the line, which essentially acts as a second driver.

One advantage to this approach is that the air pressure loading the main driver is maintained, thus controlling the driver over a wide frequency range, which in turn significantly reduces distortion. A spin-off from the lack of distortion is that the upper bass and midrange is not masked by harmonic distortion residing in the very low frequencies.

The result is PMC characteristic transparent midrange and fast, attacking bass notes, all with outstanding clarity."

Initial Listening

Two things were on my mind when I began listening to these speakers. The first was: these are small speakers. How well do they realize their specified bass performance? The second was: these are small speakers. How well do they justify the price being asked for them?

In the Living Room

I began listening to the GB1is in my living room system. The pair I received had been demos and were fully broken-in. I did my listening with the GB1i's grills off; they were slightly toed-in and located about 6 feet apart. These PMC speakers are designed for bi-wiring and that is how I did all my listening.

Electronics consisted of my Sony SCD-C333ES SACD player, a Rotel RC-1070 preamp and VTL 50-50 tube amplifier. Interconnect cables were DH Labs Revelations; speaker cables were Alpha Core MI2s.

Highs were extended and fast through the GB1is without drawing attention to themselves. "Guitar Concerto No. 1, Op.99" by Mario Castelnuovo-Tedesco (RCA 60355-2-RC) demonstrated the excellent treble extension of the GB1i as well as their inherent speed. I did not hear any blurring or overhang in the higher registers of the guitar. There was also impressively good reproduction of the woodwinds' higher frequencies within the orchestra itself, particularly in the second movement of this concerto.

The GB1i's mids were lovely, especially as they reproduced female vocals. All thirteen female vocalists on The New Jazz Divas (NPR/Shout 836663-11695) were reproduced with clear cut individuality. I was so impressed with "Worrisome Heart" by Melody Gardot that I bought her CD, My One and Only Thrill.

Diana Krall's sultry version of "Temptation" pushed all the indispensable audiophile buttons for me. Soundstaging was excellent; there was lots of vocal nuance present; and piano reproduction came through realistically, especially in the lower ranges where is had credible weight. The guitar sounded harmonically complete with exceptional clarity.

Jane Monheit's rendition of "Over the Rainbow" is perhaps the loveliest that I have heard. The clarity of her voice and the way it effortlessly raises in frequency were reproduced beautifully by the GB1is.

Underlying all this vocal loveliness was a supportive low frequency foundation. This was very evident on Tierney Sutton's "Happy Days Are Here Again" where the acoustic bass sits somewhat back in center stage and comes across deep, solid, and very tight.

Soundstaging was excellent, as would be expected from what are, at heart, monitor speakers. Jazz at Midnight, Volume 2 (RCA 09026-63149-2) is one of those compilation CDs that, based on its cover photo, does not generate very high expectations. It turns out to be a terrific jazz CD, however, with excellent sound and exceptional performances. Track 11 features Sonny Rollins playing "My Ship" by Kurt Weill. He is backed, quite literally, by Herbie Hancock on piano and Ron Carter on bass, who are located center stage behind him. Jim Hall is in the left channel and Roy McCurdy on drums is in the right. Rollins is more forward in the soundstage and plays slowly and melodically. The rest of the performers support his playing with fairly low-key performances. Despite the lower volume levels, the GB1is provided good dynamics and excellent clarity for these performers. The playing may have been subtle but it wasn't lacking in detail or obscured by the presence of Rollins' tenor sax. Just a lovely performance.

Despite their excellent top-to-bottom performance and soundstaging, I still felt a need to explore the GB1i's bass capabilities more directly. So I got some CDs together that I thought would give the GB1is low end a bit of a workout.

Ron Carter's Stardust (Blue Note 72435 37813 2 3) is more of an ensemble recording than showcase for Ron Carter. While Ron does play "Stardust" almost solo—there is some nice emphasis provided by the piano—this recording highlights the talents of the other performers just as fully as his own. Benny Golson brings a relaxed quality to his tenor saxophone playing which comes through as airy, spitty, and about the music, not the performing. Track 6, "Blues in the Closet" demands that a speaker go very deep for the low registers of the bass, which Ron uses to support a drum solo by Lenny White. Then it must deal with drums that are fast and full of dynamic impact with cymbals that are sparkling and reverberant. When the vibes played by Joe Locke come in, they contribute extended resonances and high frequencies as they fill the soundstage from speaker to speaker. Sir Roland Hannah's piano also goes speaker to speaker while all of this happens. Through all of this action, the GB1is keep every musical line well separated and easy to follow. I had to listen to this CD a number of times because I just kept getting too distracted by how well it was being reproduced to take useful notes.

I think the melody John Williams wrote for Schindler's List is one of the loveliest that I have ever heard. Listening to this CD with the PMC speakers was extremely satisfying. The orchestra filled my living room, dynamics were excellent as the orchestra moved between loud and quiet passages, and the ability to follow and locate solo instruments was effortless. The tracks with choral music—the children's choir on Track 6 is gorgeous—were room-filling with good definition of the individual voices. Moreover, there was a solid, physical presence to the singers. This music also has some very low end substance via the bass violins and tympani and this musical massiveness came through the GB1i's with excellent weight and low frequency energy.

I followed up the Schindler CD with Compositions for Virtuoso Double Bass by Paul Ramsier (Albany Troy237). On track 11, the bowed bass hits one of the lowest frequency points on the recording. I felt that this was pushing the low end capabilities of the GB1i pretty hard but they responded with bass that not only sounded realistic and well-defined but felt realistic as well. The ATL technology of the GB1i really does offer remarkable low frequency performance from such a modest cabinet.

To summarize my living room experience, the Gb1is provided excellent soundstage width and depth with exceptional top to bottom frequency response. While there is very substantial bass present, it by no means overpowers the rest of the performance nor does it ever degenerate into amorphous booms. In addition, the GB1is are efficient enough that the approximately 40W output of my VTL amp was able to drive them as loudly as I would ever need in my medium-sized room.

The GB1is proved very compatible with what I would consider entry level high-end equipment and got the most from it. It was time to hear what they could do in my main listening room.

Listening Downstairs

I set the GB1is up in a configuration similar to what I had had in my living room. The speakers were about 6 feet apart and toed-in slightly. They were about 8 feet from my listening position and about 6 feet from the wall behind them. In this free-standing set up, the rear and side walls offered no reinforcement for the bass frequencies.

The source component was my Sony SCD-XA5400ES SACD player; cabling was all Zentara Reference. The GB1is were powered by an STI-500 integrated amp from Wyred 4 Sound. The W4S amp outputs 250 WPC into an 8 Ohm load. This power made its presence immediately felt.

I returned to the Paul Ramsier recording to see how the additional power affected the bass performance of the GB1is. The music now exhibited a noticeably more relaxed and effortless quality throughout the low frequency range. Returning to Track 11, "The Vine Covered Cottage," part of Ramsier's composition, "Silent Movie," the same bowed low notes that sounded quite good in the living room, but not effortless, were now reproduced with ease. There was no sense that the GB1i was having any difficulty at all reproducing these low frequencies. A re-listen to the Schindler's List soundtrack offered the same ease throughout the lower ranges as well. The children's chorus opened up even further within the larger volume of this listening space.

While the GB1is had done very well with modest power, they clearly upped their bass performance when given access to more substantial power reserves and a larger room.

At this point, I decided that I was done singling out the low-end performance of the GB1is for analysis and would just listen to them as small, very impressive full-range speakers. The speaker had proven to me that its claimed low frequency response was the real thing and I felt that I had explored it enough that it would be irritating to keep harping on it as a separate entity of every performance.

Haydn: The Last Three String Quartets by L'Archibudelli (Sony Classical SK 62731) was gorgeously reproduced by the GB1i/STI-500 combination. The strings were smooth, extended, and of luminous clarity. There was genuine weight and body to the entire performance, which filled the area behind the speakers and extended to their sides as well. There was a real sense of actual musicians playing in the room itself.

This sense did not diminish as I moved to VH1 Storytellers—Billy Idol (Capitol 72435-36919-2-9). The GB1is offered a tangible atmosphere that cloaked the performers within a realistic and intimate soundstage. The tracks all exhibited a propulsive beat that was undoubtedly a product of the combined quickness and good timing of the GB1is and W4S amp. "Rebel Yell" comprises Steve Steven's stunning solo guitar and Idol's voice and was spectacular through the PMC speakers. The guitar playing is truly amazing and the sound quality is virtually reference. I am going to have to remember this track for future use as a test track. I am actually surprised by how much I enjoy this CD. True, the intelligibility could have been better but that was hardly the fault of the GB1is.

Ali and Toumani is the last recording made by Ali Farka Toure (World Circuit/Nonesuch 522937-2). According to the liner notes by Toumani Diabate, Ali was in a lot of pain during these recording sessions. He passed away on March 2, 2006. This last CD was released in 2010. Toumani described the recording session this way:

"When you're listening to this album it's like you're reading a book about Ali. The album was going to be a summing up of all the albums that Ali had done in the past. It wasn't about covering old songs just because there weren't any new one, no not at all. It was about revealing all the different possibilities once again. It was the very last album he made."

Most of the songs on this CD consist of Ali on guitar and Toumani on koru, with bass accompaniment. The GB1i's clearly placed the three instruments in space and made each individual instrument easy to recognize and follow. I have never heard a koru live but on the recording it comes across as having a sharp quality to its sound that would be easy to mess up. The GB1i's excellent tweeter did the sharp, fast, metallic quality of the koru's strings in a way that kept its sound interesting and connected to what the guitar and bass were doing, while never crossing over the line into stridency.

The Moscow Virtuosi are a chamber orchestra conducted by violinist Vladimir Spivakov. Their performance of Schubert's "Symphony No. 5", as well as his "5 German Dances" and "5 Minuets", is gorgeously played and very well recorded. (RCA 09026-60452-2) I was particularly impressed with how the PMC speakers filled the room with the orchestra and reproduced the dynamics of the performance effortlessly. They also exposed the only real flaw in this performance—doubtless a product of their being made by a company with "monitor" in its name. During the 5th Symphony the flute can be heard playing somewhat too loudly. Its overtones also come across as slightly edgy. It is when you can hear the keys clicking that you realize that this instrument is being separately miked and somewhat too closely at that. The GB1is are not speakers that editorialize; they present the facts whatever they might be. Even with this added information, the coherence of the overall performance was never lost. Just keep in mind that you will hear what is on your recordings through the GB1is, like it or not.

I recently received Eric Clapton's 461 Ocean Boulevard SACD as a gift. (Polydor B0003638-36) This recording sounded wonderful with the GB1is. Drumbeats were reproduced with terrific speed, sharpness, and impact. They truly sounded real, a quality that I am attributing to the lack of overhang from these speakers in reproducing them. The ability of the GB1is to start and stop is very impressive. The soundstage extended well to the outsides of the GB1is and had good depth where the recording offered it.

I listened to a great deal more music than mentioned here and the positives noted were evident everywhere. Beyond that, the GB1i were a constant pleasure to listen to. They routinely disappeared into a large soundstage that literally engulfed them. Their top to bottom coherence was exceptional. If there is a flaw in their actual reproduction of audible frequencies, I never heard it.

What at first might seem to be a fairly expensive price for two fairly diminutive speakers becomes, after extended listening, a more than fair price for the sound quality that you get. Much of this perception is the result of their exceptionally good bass performance.

I was never able to catch the GB1i's bass performance out on any "normal" recordings whether classical, jazz, or those recordings that I would refer to as "rock." The only recording that I played that demonstrated a weakness in the bass capabilities of the GB1is was Ray Brown's SuperBass 2 (Telarc CD-83483). While the PMC speakers did a remarkably good job of reproducing the three acoustic basses, they simply could not do that and keep the soundstage intact at the same time. So if that sort of recording is all that you listen to, you will probably need one of the larger PMC speakers.

My only criticism of these speakers relates to their lack of actual weight. They just do not weigh enough to really anchor themselves to the floor when placed on carpeting. I did get excellent results with the GB1is but if they were mine, I would explore ways to add weight to the plinth or put them on some sort of base that could itself be connected more positively to the subfloor. I suspect that there might be even more performance to be had from them if this were done. 


The Professional Monitor Company's GB1i speaker does everything that you expect a monitor speaker of its size to do and more. It reproduces the human voice with superb realism, it soundstages terrifically, and its treble performance is clean and extended. What is remarkable, given its size, is that it truly offers full-range bass performance as well. The use of a transmission line bass alignment allows a five-inch mid/woofer to go as deep as any audio system needs to for realistic musical reproduction. This performance comes in very nicely finished cabinetry and at a realistic price. All of which leaves us to ponder the disquieting question: if this is the entry level PMC floor-stander, what do the big boys sound like? Kent Johnson

GB1i loudspeakers
Retail: $3249 per pair

17952 Sky Park Circle
Building 45, Suite A
Irvine, CA 92614
TEL: 949-861-3350
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