Most of you know me primarily as a booster of panel speakers, electrostatics and ribbons in particular. So, too, you may know of my love for certain dynamic, ostensibly 'conventional' speakers such as the BBC LS3/5A, Sonus Faber Homages and Wilson's WATT Puppy combination. Indeed, it's easier to list my dislikes - horns, speakers that fire off the walls, etc - than to tell you my preferences. But what I'd drifted away from was a closet love for a speaker topology practiced by fewer and fewer manufacturers: transmission line systems.
We've all heard the same drill, that transmission line systems have one-note bass, although incredibly extended and with plenty of it relative to cabinet size. I never found it to be that way - one-note-y, that is - and I rue the missed opportunities when, due to lack of space and/or money, I passed up buying my personal faves - large IMFs in particular. Throw in a couple of Radford models, and here's a sub-genre awaiting rediscovery. But they were larger examples of the art. Quietly, PMC has been making a genuine transmission line speaker no bigger than an LS3/5A, and it's been upgraded to a level of performance so disproportionate to its price, let alone size, that I couldn't resist a go with them. My adventures ended up with one friend immediately deciding to buy a pair.
How they came to my attention is reason enough to review them: Peter Thomas of PMC worked for many years at the BBC, testing - yup, you guessed it - LS3/5As. So he was a bit puzzled by my failure to include the DB1+ in a recent round-up of wannabes. It fit the size and price profile, but, above all, it was conceived by a company with its roots in the BBC. Red faced am I, or what? My only excuse was that there are a few dozen contenders and our choice was random.
Now the DB1 has been upgraded to DB1+ status, and the metamorphosis is not merely a refinement. The DB1+ is a little monster, a deceptive mini that's able to punch way above its weight. The mods, also applied to the FB1 and TB2, include the use of the high performance 27mm fabric soft dome tweeter found in far more costly PMC passive monitor systems. This tweeter upgrade also inspired improvements to the crossover design, while the TB2 and FB1 also benefit from 're-engineering' of their acoustic damping.
According to PMC, these changes not only improve the acoustic characteristics of the monitors, for lower distortion, better-controlled vertical and off-axis dispersion, better stereo imagery and higher power-handling, they also strengthen the sonic family resemblance to the larger PMC systems. Thus, these more compact, affordable models exhibit 'similar high signal definition, consistent on/off axis dispersion, extended frequency response, and tonal consistency at all volume levels.' If you're wondering why this was desirable, think outside of the stereo box: the greater the sonic resemblance across the range, the easier it is for customers to create a mix-and-match line-up for home cinema packages from within a single catalogue.
There are no free lunches, so PMC made the incorporation of the dearer tweeter possible by increasing economies of scale in the manufacture of the less expensive models. The improvements to the crossover, to match the new tweeter, included lowering the crossover point to 2kHz from 3kHz, 'to provide true second order roll off,' and the use of hand-selected and matched components. Also added was a drive unit impedance compensation network to enhance driver integration and power handling. Frequency response is 50Hz-25kHz and sensitivity remains 87dB. Impedance is nominally 8 ohms, and the speakers proved remarkably easy to drive despite sensitivity considered a bit on the low side by today's standards.Read more about the PMC DB1+ on Page 2.