B&W ASW700 / PV1 and Velodyne SMS1 Subwoofers

Double Subs

I never envisaged spending quite as much time as I have over the last few months listening to the effects of sub-woofers. But having looked at the three distinctly different models in the last issue, there seemed to be a number of additional possibilities worthy of further investigation, together with more products to try out. One particular aspect that I was keen to explore was the use of two sub-woofers (identical pairs but of varying sizes) to see what benefits - if any - there might be over a single unit. To that end I had the use of a second Velodyne DD12, along with two similarly priced but highly contrasting products from B&W. The Velodyne was of particular interest due to its integral digital measurement and management system which proved to be a considerable asset when it came to setting up sub-bass units, taking a lot of the guess work out of initial positioning within the room. The company’s SMS 1 standalone unit offers exactly the same facilities in a stand-alone box that is universally applicable to any sub-woofer (or even when it comes to positioning full-range loudspeakers) and also proved both useful and informative in conducting tests over the last few weeks; for a full report on its modus operandi check out the previous issue for more information.

As before, my interest lay in exploring the effects of sub-woofers to augment a system that is used purely for music reproduction; this was an exercise more concerned with integration and ‘hiding’ the sub within the aural palette rather than prodigious amounts of crash, bang and thunder. Its quite possible that this presents a different set of challenges for a sub, a degree of subtlety not always associated with the genre. Ultimately, I guess I want the benefits but I don’t want to hear the thing working. As with the previous sessions, the main speakers were the B&W 805’s, alternating with a pair of the new Acoustic energy AE22 near field monitors, a loudspeaker aimed very much at the professional market. Designed to imitate some of the better aspects of the fabled NS10 it is of infinite baffle construction and has a very dry, well controlled bass roll off that should integrate well into a subwoofer system.

Velodyne’s Digital Drive - Adding a second unit

With the Velodyne SMS1 plugged into the system, I proceeded to again take measurements of the 805’s and in order to regain some perspective, set up a single DD12 bass unit using both the test results and fine adjustments by ear, the results consistent with my earlier sessions. Daisy chaining a second sub necessarily complicates the procedure by requiring not only a parallel signal connection but a serial data feed as well, but this does not transfer any settings, only running commands. Having established basic settings such as phase and crossover on the primary unit, these must then be manually copied across to the slave, whereupon Velodyne suggest doing an EQ set up separately for each box.

In practice, the set up for two subs does become a lot more complicated, with so many more variations in positioning as well as the associated interaction between them. Of course, with the Velodyne subs each individual box can be adjusted comprehensively, whereas the stand alone SMS 1 applies the same correction to both the left and right output. Either way, the ability to repeatedly measure and actually see what was happening alongside listening to the sweeps became invaluable and served to provide a degree of method to what could have become a confusing process. What quickly became clear is that with two subs in play it was possible to even out the room response a lot more effectively with positioning alone than with just a single unit, therefore minimising the amount of correctional EQ needed.

This was strongly reinforced when it came to listening. There are obvious reasons why adding a second sub should be beneficial - doubling the power output and radiating area for a start. Then there’s the fact that our generally rectangular rooms suffer a double bass peak, one for each axis, and that these can be handled more readily by two individually placed units than just one. Each unit will also be working less hard for a given volume. But the response was so much more even and controlled, altogether less obtrusive, that as a consequence I ended up being able to run the bass level a little higher than I had done when using a single unit. The result was a more integrated bass response that was much more consistent with volume and far more natural, tonally and dynamically. There was also less of the rather grey, slightly ‘leaden’ character that I had associated with the single Velodyne sub. Apart from the rather antisocial positioning that I ended up with, my experience suggested that this was definitely the way forward. Moving on…