Subsonic 5i Subwoofer alone
(Reprinted from the Spring 07 Audio Ideas Guide)
Here’s what’s said on the PSB web site: “All units are enclosed in rigid aluminum extrusions which are highly durable and acoustically inert. They use high excursion 4.5″ diameter, wide suspension woofers and a vented system design to get maximum bass from minimum dimensions. A carefully contoured ‘waveguide’ blends seamlessly into the obstruction-free face of the system’s cabinet optimizing the performance of the 1″ dome tweeter.” Too many months ago, Paul talked to me over lunch about his new construction techniques alluded to above. The extruded aluminum casework costs a small fortune to engineer, and to create production dies and other construction needed for manufacturing. But when this effort is over, the consistency and quality can be maintained with manufacturing anywhere in the world, in this case, China. And the overall vision is one of design and tooling sophistication leading to manufacturing simplicity and efficiency.
The tweeter waveguides, and the woofer baskets are all part of the integrated baffle design, which pays off in exceptional immunity to resonance and vibration. The driver elements themselves are intended to offer a level of performance matching the finest mini-monitors, with a single tweeter complemented by several woofer/midrange drivers, providing a line source at low-through-middle frequencies, with a gradual transition to point source above crossover, in order to offer both room filling sound and the precise imaging required by discrete surround program material. I’ll say more about this acoustic concern when discussing the measurements. The SubSonic 5i uses a 10″ driver in a ported enclosure of moderate size, and unlike many similar modestly priced models, has Volume and Crossover slope controls on the front panel, with a Class H amplifier. About this, Paul says in the owner’s manual: “Class H is a special high efficiency amplifier design. Briefly, amplifiers are inherently inefficient because they are designed to have the capability of delivering great output power yet spend most of their life delivering low power. Their output devices must deliver current while withstanding the high power supply rail voltages needed for peak outputs. With a Class H design the rail voltages are not constant. They swing high when the music demands it and stay low during quiet passages. This is achieved by a sophisticated high frequency switching power supply. Power dissipated as heat is greatly reduced and more power is available per dollar of cost. A second benefit is that they tend to have high peak power relative to their steady state power. The SubSonic 5i, for example, has 150 watts continuous but is capable of 450 watt peaks. The result is a subwoofer capable of the great transients required by dynamic music and explosive sound effects.” The SubSonic 5i has inputs on the rear panel for low-level line and speaker level in and passthrough, and a switch to bypass the internal crossover for electronic crossover systems, as well as one for auto or always-on power. Again, simplicity and easy setup and operation are paramount design considerations.
Now we can look at the measurements with a little background behind us. At top are the sub measurements at left, which I’ll get to shortly, and the overlaid Pink Noise Response (PNS) and Summed Axial Response (SAR) for the VS400. The former is the frequency balance of the speaker on axis, while the latter is the added together 0, 15, and 30 degree axial measurements shown individually in the group of traces below. The third group of curves at bottom shows the 3-position frequency contour switch at high, middle, and low positions. All measurements were made at a level of 85 dB at 1 metre.
Let’s start at the bottom, frequency-wise, with the SubSonic 5i (shown in both graphs above). It is measured at the high (150 Hz), mid (roughly 75 Hz), and low (50 Hz) crossover settings, the control offering continuous rotation. At the highest setting (it just accidentally dovetails with the PNS/SAR curves), we see a smooth descent from 100 Hz to just over -3 at 30, pretty respectable for a wide open setting, still down only 5 dB at 25 Hz, more than respectable. But it’s at the middle setting where we see extremely good linearity, +/-1/2 dB between 100 and 30 Hz, and still going strong, just a dB down at 20. Wow! This is a budget sub? The lowest setting pretty much maintains this exceptional performance, appropriately rolling off gently above 50 Hz, as it was designed to do.
The V400 PNS (top) and axial curves (below) show an almost ideal small-room response pattern, especially considering the superb dispersion. By this, I mean that the energy radiated into the room will be closer to flat including reflections off surfaces, but these will sound much the same as direct energy just slightly delayed. Even at 30 degrees off axis, we find very smooth response through the midrange with just a little softness at the very top frequencies. Bass and midrange are very well balanced within a dB or two, with a smooth rolloff below 80 Hz. At bottom, the 3 traces look the pretty much the same as above, but show different stuff: with each flick of the little toggle on the back of the V400 you get a little less energy above 1 kHz in about 1 1/2 dB steps. If the system sounds a little too bright, this is your solution; if it sounds too dull, clean your ears (be careful with a Q-Tip not to push wax up against your eardrum; read John Atkinson’s editorial in a recent Stereophile!), take down a few wall hangings, pull up the rug, or try any appropriate combination of these.
The lower chart (at right) shows the identically derived frequency responses of the V300 in its lateral configuration as a centre channel, where dispersion and midrange smoothness are most important. I’ll explain what I mean by this below.
The subwoofer measurements are shown again, primarily because they’re a little clearer where they cross over with the V300’s response in the bass. The latter’s upper bass is a little more prominent than that of the V400, perhaps enhancing male voice at centre and surround effects not as well bolstered by the sub at front (The LS/35A effect again), but the mids are smooth, with some slope as frequency increases, matching the V400. The V300 also has a single-throw toggle that introduces a slight boost centred at 400 Hz (not measured: ran out of space in the LMS library group), that compensates for a cancellation dip around that frequency introduced by wall mounting, this in place of the 3-position switch for highs on the 400. Its range is about 3 dB, and is quite audible and should work for such applications. The only other thing of note in these curves are the slight dips in the midrange as we measure off axis by 15 and 30 degrees, typical of horizontal placement of speakers with a vertical/linear array of drivers. In this case, the tweeter is placed between two of the bass/midrange drivers. That’s what causes the dips between 2 and 6 kHz, but these are held to a moderate 3 dB or so, likely to be filled in by left and right energy for those sitting at 15 or 30 degrees off the direct axis of the speakers. This phenomenon will not, of course, occur with the speakers mounted vertically, but only when used as centre channel.
And the VS300 can serve very nicely as a front speaker, too, thus being an excellent LCR and surround speaker choice, if you demand true symmetry. The sacrifice in bass response is a relatively small one.
This is a very nicely designed and finished system that delivers true audiophile acoustic performance at an unusually modest price, while dealing with a number of real-world problems faced by wall-mounted and thin tower speakers. It also brings the simple band-pass subwoofer design to a new level of performance in my experience.
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