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Since the merger, the new products have been flowing thick and fast, due to the increased numbers
on the Whatmough-Whise design team and thanks to Colin Whatmough’s now-unfettered access
to all Whise’s technology. This Impulse subwoofer was the first off the drawing board,
but Whatmough has also since re-designed his flagship Paragon loudspeaker system so its sub-bass
unit now uses PAM technology and is in the process of incorporating PAM into all Whatmough-Whise
subwoofers.
The merger has turned out to be good news in terms of both performance and pricing. There’s
no doubt the use of PAM has improved the performance of Whatmough’s sub-bass modules (as
in the Paragon) and subwoofers, but according to Colin Whatmough, the cost efficiencies of building
in your own factory (Whise used an OEM) has enabled him to deliver Whise’s leading edge
technology at far lower prices than ever before. Nowhere is that better evidenced than in the
subwoofer that’s the subject of this review. Previously, the nearly-identical subwoofer
made by Whise (available only in black) retailed for more than three thousand dollars. The RRP
on the Whatmough-Whise Impulse is just under two – and you get a choice of cabinet finishes.
The Equipment
You can tell the Impulse is no ordinary subwoofer as soon as you pick it up – or if you’re
not a weightlifter, when you try to pick it up. I don’t think I’ve ever before run
across a subwoofer so small that was so heavy! Much of this weight is down to the incredibly
ruggedly built 254mm diameter long-throw sub-bass driver inside the cabinet. It has 75 mm diameter
voice-coil and a suspension that permits a full 36mm of linear cone travel.
Then there’s the weight of the power supply for the 200-watt Class A/B (Linear) amplifier
that drives it. But it’s also because of the thickness of the cabinet walls (they’re
25mm thick rather than the usual 19mm), and the fact that the interior of the cabinet is not
largely empty like most other subwoofers but instead contains an arrangement of ducts and baffles
that acoustically filters distortion from the bass driver’s pressure waves before they
have a chance to leave the cabinet as sound waves. It’s this filtering process that’s
known as ‘Parametric Acoustic Modelling’ (PAM) and the theory behind it was first
presented to a conference of the Acoustical Engineering Society (AES) ‘way back in the
1990s.
Unlike all other driver/cabinet alignments (bass reflex, infinite baffle, transmission line,
etc) this complex labyrinth of ducts and baffles physically changes the acoustic frequency
response of the bass driver without affecting its electrical performance, a clever ‘trick’ that
allows Whatmough-Whise to extract the maximum acoustic output from the driver while at the same
time delivering a flat frequency response along with extremely low distortion. The concept is
both unique and patented, but perhaps most importantly for Whatmough-Whise, it’s impossible
to ‘reverse-engineer’ a PAM design in order to copy it, because the labyrinth is
so driver-specific that you not only can’t substitute another driver, you can’t even
substitute a driver with identical Theile/Small parameters. Only the original driver can be used
in the cabinet.
PAM’s only minor limitation is that its upper frequency cut-off depends on the size of
the enclosure and in the case of the Impulse cabinet – which is fairly small as subwoofers
go, at 470mm high, 325mm wide and 420mm deep – that upper cut-off frequency is 100Hz. This
means that your main speakers have to be capable of delivering bass down to 100Hz in they’re
to integrate smoothly with output from the Impulse.
Whatmough is renowned for its finishes (whereas Whise always offered the Henry Ford option:
black or black), so I wasn’t surprised to find the Impulse is available either in Whatmough’s
stunning new and modern ‘Graphite’ finish or in its more traditional Bubinga burled
woodgrain veneer.
The Impulse’s rear terminal plate has line in/line out RCA terminals, speaker level inputs
and outputs, rotary phase (0-180°), crossover (40-160Hz) and volume controls, plus a power
switch (On/Auto/Off).
Listening Sessions
A very good test of a subwoofer is to drive it with a full-range audio signal and listen to
what comes out. The easiest way of doing this is to connect the line output of a CD player
to the
line inputs of the sub, insert a CD and press ‘play’. What you shouldn’t hear
are any muffled higher-frequency sounds, particularly voices. Try this test with the Whatmough-Whise
Impulse and all you hear are low frequencies…and if there are no low-frequency sounds on
the CD, total and complete silence. The high-pass filtering is that good.
The bass I heard from the Impulse was immediately noticeable because it was so free from
distortion that I was able to immediately detect the pitch of every note the instant it was
played. In
a perfect world, this is exactly what should happen, but the fact is that almost all subwoofers
have such high levels of distortion that this is not possible. The mechanism that’s at
work is that when a bass guitarist plays a low ‘G’, for example (49Hz), nearly all
subwoofers will generate not only this ‘G’, but also another ‘G’ an octave
above (at 98Hz, which is the second harmonic) as well as a ‘D’ five notes above that
(at 147Hz, which is the third harmonic). So instead of hearing just the one single note, you’ll
hear three notes, and it’s up to you to decide which one the composer (and musician) intended
you to hear! The ear works this out automatically from the context of the music (the key the
music is in lets you eliminate the false D fairly quickly while the phrasing would be the only
clue to which G to choose). These decisions are made by your subconscious, in just a few moments,
but the more distorted the signal (and thus the harder your ears and brain will have to work)
the less ‘easy to live with’ you’ll find the quality of the bass.
Play a ‘G’ through the Impulse and all you’ll hear is the original ‘G’ at
49Hz. The difference this makes to the clarity of music being played is so unbelievable that
you really have to hear it for yourself to believe it. When you do, you’ll discover it’s
easiest to hear with musical examples, either from a CD or a DVD soundtrack, but the freedom
from distortion is clearly audible even with movie sound effects.
The frequency response is exceptionally flat. I connected a standard synthesiser directly
to the line inputs of the Impulse and played a two-octave chromatic scale starting at the
lowest
note on the synth (a ‘B’ at 30.87Hz) I couldn’t detect any change in volume
level until I reached the ‘G’ at 98Hz. Needless to say, if the Impulse can pass such
an extreme ‘live music’ test, you’ll have no worries playing back recorded
music. The synth also showed the Impulse’s response dropped off very quickly above the ‘G’,
being noticeably softer even just three notes above, at ‘C’ (130.81Hz). For this
reason, I’d recommend using the Impulse only in conjunction with main front speakers that
have a flat response down to at least 87Hz (the ‘F’ immediately below the ‘G’),
to allow the smoothest transition from them to the sub. In practice this will rule out all milk-carton-sized
satellites, but even the smallest conventional bookshelf speakers should be capable of achieving
this level of performance. (And of course you can use larger speakers: simply adjust the crossover
control on the Impulse counterclockwise to suit.)
I started my sessions with the Impulse linked to a pair of relatively small bookshelf speakers – all
of different brands, and none of which were made by Whatmough – until I finished with the
Impulse working in tandem with a pair of large, three-way, five-driver floorstanders. Two things
stood out. One was how easily I was able to integrate the sub’s output with that of the
main speakers: this is an extraordinarily ‘user-friendly’ design. The other stand-out
was the way the Impulse seemed to take on the ‘character’ of the sound of whatever
speakers I was teaming it with, so it seemed as though the main speakers had suddenly found some
bass they didn’t know they had, rather than I’d added a subwoofer. I suspect this
was actually because the Impulse has so little unique tonal ‘character’ of its own
that the ear confuses the tonal character of the main speaker with it, so the two sounds seem
as one. If this is indeed the mechanism at work, it’s a very welcome one.
Conclusion
If you’re in the market for a subwoofer you owe it to yourself to listen to Whatmough-Whise’s
Impulse, either in a home theatre set-up or as the sub in a sub/satellite two-channel system.
It’s easy to position, easy to integrate and chameleon-like in the way it appears to imitate
the tonal character of whatever speakers it’s paired with. Brilliant!
Chris Green
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