British sound with 'unBritish' bass

British brothers: ATC SCM40 (left) and PMC OB1i

When I wanted to upgrade my speakers I was choosing between the PMC OB1 floorstanding speakers and the ATC SCM40. I opted for the ATCs because the bass of the PMC seemed a bit loose and uncontrolled.


So when James Tan of AV Designs asked me if I would like to review the new version - the PMC OB1i - I thought it would be a great chance to compare them with the ATCs again.


The OB1i and the ATC SCM40 floorstanding speakers are like brothers - both are three-way speakers; both have 75mm soft dome midrange units; both are made by companies famed for professional studio monitors and both come from the BBC school of sound.


Even the crossover frequencies are almost the same - the PMC OB1i has crossovers at 380Hz and 3.8kHz while the ATC is at 380Hz and 3.5kHz. This is deliberately done so that the vital mid frequencies emerge from only one speaker unit - the dome mid - without crossover circuits causing phase shifts and distortions.

The PMC OB1i is a three-way speaker.
Note the dome mid.

The only difference is the bass loading - the PMC OB1i uses what PMC calls 'Advanced Transmission Line (ATL)' while the ATC SCM40 is a sealed box design.


There are differences in its frequency response and sensitivity too - the PMC OB1i is rated to go from 28Hz to 25kHz compared to the ATC SCM40's response from 48Hz to 22kHz and the PMC is more sensitive at 87dB, 2dB more than the ATCs.


The ATC SCM40 uses a so-called 'studio' version of its famed SM150s dome mid which has a sticky surface while the PMC's dome mid has a soft outer layer, possibly made of silk, and a hard hemispherical inner layer. The soft dome material is not sticky.


Proprietary to PMC is its ATL enclosure which is touted to be superior to sealed or ported designs. According to PMC's website, the main driver is placed at one end of a long tunnel (i.e. the transmission line) which is heavily damped with absorbent acoustic material specified to absorb upper bass and higher frequencies.


"Low frequencies, which remain in phase, emerge from the vent which essentially acts as a second driver. The advantage of this approach is that the air pressure loading the main driver is maintained which controls the driver over a wide frequency range and reduces distortion.


"The ATL also produces higher SPL and lower bass extension than ported or sealed box of similar size."

The vent of the ATL acts like a second driver.

One thing I have noticed about transmission line designs is that they create a rather big soundstage and seem to handle crescendoes with ease.


The PMC OB1i is not different - its sonic signature is that of a huge soundstage with agile swings in music dynamics. Transparency is also a strong point.


Using the resident system comprising a CEC 3300 CD player used as transport, the Benchmark DAC1 Pre and the Bryston 4B SST power amp with an assortment of cables, the PMC OB1i joyfully created some good music in my home.


Upon close scrutiny with a wide range of music, some differences between the PMC and ATC could be discerned.


The ATC SCM40 seemed to have a bassier tonal balance with a thicker mid and upper bass while the PMC OB1i had a lighter tonal balance with more transparency in the mid to upper bass region.


Paradoxically, the PMC OB1i had a stronger low-bass that went deep and had punch.
I played Lauryn Hill's The Miseducation of Lauryn Hill and it was one of the rare times that hip-hop was delivered with sufficient grunt on a pair of British speakers.


Unlike the older version, the OB1i's bass was not loose or uncontrolled. Its bass was tight and dynamic.


The mids, to be expected of a well-designed British speaker, were natural and voices were rendered well while the highs emerging from the new PMC/SEAS developed Sonolex tweeter were smooth and extended.

The soundstage created by the PMC was also bigger vertically than that created by the ATC. With the PMC, the band and singer seemed to be performing on an elevated stage a couple of feet above my ear level while with the ATC, they were 'grounded' and they seemed to be on the same plane as I was.


Strangely while the PMCs handled crescendoes well, its delivery of fortissimo passages was softer compared with the ATC. Since the ATCs are less sensitive than the PMC, I had to adjust the volume knob to compensate whenever I switched speakers and I noticed that based on more or less the same volume setting, the loud passages sounded louder on the ATCs.


I checked the ATC's specs and found out that the maximum SPL is 112db max but I could not find the corresponding figure for the PMCs. 


The PMC OB1i are pretty large speakers measuring H 102.5cm (40.4"), W 20cm (7.9") and D 32.5cm (12.8"), and weighing 21.5kg. So you would need a pretty large room to house them.


If you are looking for speakers offering a British sound with an 'unBritish' bass, then the PMC OB1i fits the bill. With the weakening of the British pound against the ringgit, the new retail price of the OB1i is RM21,700.


PMC speakers are distributed in Malaysia by AV Designs which is on the mezzanine floor, West Wing of Rohas Perkasa building, Jalan P. Ramlee, Kuala Lumpur. Call them at 03-21712828 or 03-21712825.