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The main function of the internal
amplifier is to eliminate an additional load
on the system amplifiers—I am aiming at a
“flat” response and have the subwoofer
volume set about 15° from zero gain. The
15EXP has had a long evolution beginning
before DSP became commonplace, and this
acoustical heritage accounts in part for its
ease of system integration. It is not
designed rattle the windows (although it
certainly has that capability); it is
designed to provide an unobtrusive, integral
and natural extension to the frequency range
of the main loudspeakers, and it does this
without dependence on DSP. Mr. Ricketts
writes that, “Without the electronic
contouring of the frequency response most
active subwoofers would be
unlistenable...the 15EXP subwoofer achieves
exemplary, linear frequency response
primarily through the natural and harmonious
mating of its high quality driver and its
sophisticated bandpass cabinet design.”
Controls on the rear include a power switch
(signal-driven auto-on, indicated by a red
LED changing to green), loudness, low-pass
frequency (50-120Hz at 12dB/octave), and
phase (0-180°). Combined with the cabinet
this results in a maximum 24dB/octave slope.
There are two sets of speaker-level
inputs/outputs and two sets of line-level
(RCA) inputs/outputs. The amplifier is
capable of summing right and left channels,
so it is possible to use a single 15EXP,
taking advantage of the diminished ability
of our ears to pinpoint source at low
frequencies. But audiophiles will want two
subs: although we may not be able to
precisely locate a 30Hz primary, the
blending of harmonics by using a single
subwoofer will produce inferior imaging.
Driver. The driver, the heart of the
monitor, is a SEAS H1333: 7½” cast magnesium
basket, 5” TPX (clear polypropylene) film
cone, 39mm diameter voice coil, and a doped
26mm soft dome tweeter. Although I have seen
this driver characterized repeatedly as a
“co-axial” design, it is more accurately
described as a “co-incident” design. The
acoustic center of the woofer is identical
with the acoustic center of the tweeter
(more or less—read on). This configuration
approximates a “point source,” the
theoretical ideal my mentor taught me about
when I was new to the game. To achieve this,
the tweeter is mounted where the woofer
voice coil dust cap would normally be. A
typical coaxial design contains two drivers
on the same axis, but not the same vertical
plane; they are not time aligned; phase
distortions, cancellations and
reinforcements are inevitable. These can be
imperfectly compensated for with an
elaborate, high-order crossover, but doing
so trades one set of problems for another.
The drivers in a coincident array, on the
other hand, lie on the same vertical plane
as well as the same horizontal axis: they
are inherently time and phase coherent.
Coincident drivers do not require elaborate
high-order crossovers and have identical
directivity at the critical crossover
frequency. Mr. Ricketts' first-order
crossover consists of the three components
already mentioned. Unlike higher-order
designs, first-order crossovers introduce no
phase anomalies or group delay.
I stated that the acoustical centers of the
two driver elements are “identical”—this may
be less than accurate in practice. The
tweeter's voice coil linear range of motion
is 0.5mm, whereas the woofer's is 6mm. The
tweeter is mounted to the pole piece of the
woofer magnet structure, it does not move
“with” the woofer voice coil. Even if at
rest their acoustical centers are identical,
when driven they move independently. John
Stone of SEAS USA wrote to me that, “The
tweeter is completely independent,
physically, magnetically and electrically
from the woofer. It has its own neo[dymium]
magnet system. It is very compact and the
motor system is isolated from outside
magnetic influence.The tweeter module is
also field replaceable.”
The SEAS data sheet states that, “The
cone of the woofer acts as a horn loading
for the tweeter, and the chassis of the dome
unit represents the throat of this horn.”
The acoustical relationship between a
moving tweeter dome and a loading horn
that's moving independently of the dome is
complex. There is doppler shift, so at a
given frequency the tweeter may also produce
frequencies slightly higher and slightly
lower. Add to that the different frequency
ranges of the two drivers and you get a
physically relationship in which absolute
coincidence happens but is not continuous.
Moreover the greater excursion of the woofer
voice coil constantly alters the acoustical
environment presented by the tweeter “horn”.
As a practical matter, all this may be
without audible consequence. Mr. Ricketts
notes, “Theoretically it should cause
some Doppler effects at higher volume but in
practice it is not noticeable...” To be
sure, however, if a designer's aim is to
approach a point source, even a
less-than-perfect coincident array is a big
improvement over multiple drivers on
different axes (and, often enough, on
different vertical planes).
Design Issue.
There are a number of different ways to
design and build a loudspeaker. Each has
pros and cons. You might almost say that at
root, the loudspeaker designer's choices
stem from a philosophical underpinning. And
since I've always had an interest in the
why's and wherewithal's of audio design and
execution, I've my share of philosophical
underpinnings too. Simplicity is high on the
list; using high quality, high linearity
drivers rather than relying on elaborate
crossovers. But there are dozens of
parameters and relationships to be
considered in deciding on drivers and
crossovers and baffles. There is no “best”
way to design a loudspeaker, and no matter
what choices are made, there are always
tradeoffs. SEAS makes another coincident
driver, the H1602, that uses an aluminum
cone, which some designers prefer over paper
or polypropylene. It's on-axis response
curve is as smooth as the H1333 up to about
1100Hz; after that it becomes extremely
non-linear. Using this driver instead of the
H1333 would have necessitated a higher order
crossover at a lower frequency, thus a
narrower passband, greater low frequency
demands on the tweeter, more potential phase
issues, and more difficulty getting a smooth
match with the tweeter. Make no mistake, it
can be done; it's just a different approach.
My KEF101's had monstrously complex
fourth-order crossovers with iron-core
inductors, yet they were among the most
neutral loudspeakers of my experience,
comparable to the classic BBC LS3/5a.
The sound.
It is anecdotal that music from another room
can be very convincing. I always assumed
that this had more to do with the casual
nature of listening while otherwise engaged
than with the actual quality of sound
originating from two rooms away, though the
experience is uncanny. But in a web article
on the design of loudspeakers, Siegfried
Linkwitz writes that, “...the uniformity
and flatness of the off-axis frequency
response which we hear via room
reverberation and reflections is rarely a
design goal. You can check the naturalness
of the timbre by listening from another
room. Does it sound like a loudspeaker is
playing?” In the case of the NSMT 20M,
the answer is an unequivocal, ”No”—it sounds
like live music. Maintaining an flat, smooth
off-axis response is precisely one of Mr.
Ricketts' stated design goals. From a
practical standpoint, how a loudspeaker
sounds from another room is of real
importance. If all loudspeakers did it
equally well, mentioning it would be
trivial. If all of us listened to music only
when we're sitting in the sweet spot,
mentioning it would be trivial. But neither
of these is the case. The little 20Ms do it
as well as, or better than, my 75” tall
Newform R645s. The 20Ms can fill the house
with music of extraordinary fidelity and
dynamics. The sense of a real instrument or
a real singer out in the living room can
occasionally be disarming.
The 20Ms are wonderfully clear and fast
transducers with bass performance that
belies their relatively small size. They can
play very loud without distortion or loss of
clarity. I've played music from Mozart to
Clapton, from Cassandra Wilson to Clifford
Jordan, from symphonies to sopranos, and it
has all sounded great. Of course the low
fundamentals are hardly there and a pipe
organ recording with lots of 16' and 32'
stops will be found seriously wanting. Most
music will not. And if I were to rate the
loudspeaker characteristics I value most,
bass extension would be below transparency,
neutrality, imaging, clarity—qualities at
which the 20Ms excel.
Mozart, Die Zauberflöte, Sir Georg
Solti, Weiner Philharmoniker (London 444
210-2). Mozart's last opera, first performed
at Emanuel Schikenaeder's Theater an der
Wien a few months before the composer's
death (the musicologists think from
rheumatic fever). As a matter of fact, the
only operas I own, the only operas I listen
to, are Mozart's. And among these The Magic
Flute is unique, being Masonic (as was
Mozart), its plot centered around a
spiritual quest. But it is the opposite of
somber—it is brimming with delight and
contains perhaps the most enchanting aria
Mozart wrote (Der Hölle Rache kocht...). A
couple of details really caught my
attention. The 20M reproduces the celesta in
this recording with a beauty and solidity
that surprised me. I've heard this CD
countless times. Of course I know what this
particular celesta on this particular
recording sounds like. But the 20M provides
a more palpable and nuanced celesta, one
with the harmonics and resonances of a
actual, present-in-the-room instrument.
Another instrument that stood out in this
listening session was the tympani. I simply
didn't know, couldn't have imagined: the
rich overtones and transients of a real
kettle drum (and this without the
subwoofers). I'd never heard the like. So
complete was the transient and harmonic
information, that without concentration or
effort I literally “saw” the drum in a
precise location with palpable dimension. It
was remarkable how real it seemed.
Subwoofers.
At this point in time I decided to install
and break-in the subwoofers. I ran into a
hookup snag because I couldn't locate a
needed Y-splitter for my bi-amplifier
speaker cables. After repeated phone calls
to parts houses, I finally gave up the quest
and requested a couple of jumpers from Mr.
Ricketts. They were here within a few days.
I adjusted the subwoofer amplifier volume by
ear, as I said, aiming at an flat response,
erring on the side of unobtrusiveness. I
tried the crossover setting at several
positions and left it at around 65Hz, where
it seems to integrate well. Truth is I
hadn't patience to mess about with these
details now: I wanted to play music, I was
about to hear my first full-range
loudspeaker system, ever. I promised myself
I would go back later and adjust the phase,
then recheck to volume and the crossover
point.
The comment I made about the 15EXP—that it
provides a 'natural extension' to the bass
range, that it integrates well with the main
loudspeakers without calling attention to
itself—was based on theory and design and
hearsay: these did not prepare me for the
real thing. And the real thing can be
described in a single word: foundation.
The sound without subwoofers seems lacking
in substance in retrospect, a bit thin and
rickety, a house built on
not-quite-substantial land. If this
far-flung metaphor suggests a subjective,
qualitative change in my experience of the
music with subwoofers, that's just what it
ought to suggest. “More bass extension”
hardly seems an adequate description;
“greater reality” may be hyperbolic, but is
emotionally accurate.
 My
first words after listening for a few
minutes to Bartok's Concerto for
Orchestra (Fritz Reiner conducting the
Chicago Symphony Orchestra, JVC XRCD
JMCXR-0007): “I had absolutely no idea
what I've been missing all these years.”
From a purely objective standpoint, in terms
of measured response, the difference may not
be all that great—essentially an additional
octave. True, a very well-behaved additional
octave, a very flat and uncolored additional
octave. But from an aesthetic standpoint,
the change is phenomenal.
To test my impressions I played the first
couple of minutes of the Bartok Concerto
with the subwoofers switched on, and then I
played them again with the subwoofers
switched off, each time jumping into the
sweet spot and closing my eyes. I did this
several times. Here and there a specific
absence of bass was notable, which is to be
expected when the fundamental is rolled off;
not a big deal in itself. But more
importantly, there was a distinct, continual
sense of something missing with the
subwoofer turned off, an absence...a lack of
foundation: someone had watered the cat's
milk. Although the 20Ms sound good by
themselves and, as I said, do a remarkably
good job of reproducing bass, I think the
20Ms, or any limited-range loudspeaker, will
sound lacking in comparison to a good full
range loudspeaker such as the Armada System.
The absence of “foundation” saps an
important quality from the musical
experience. It was a sonic revelation.
 Mussorgsky,
Pictures at an Exhibition, Rafael
Kebilik, Chicago Symphony Orchestra (Mercury
Living Presence 434 378-2). This recording
was made in 1951 using a single Telefunken
U47 microphone and it remains to this day a
singular example of the recording engineer's
art. I am sitting here shaking my head in
near-disbelief at how clear and dynamic it
sounds through the NSMTs, how solid the bass
is, how detailed the orchestral texture. In
many ways it rivals or surpasses anything in
my collection. In terms of sheer visceral
excitement I know of few equals. Maybe the
Tchaikovsky 1812 in XRCD format. I sometimes
play Pictures for visitors and then
spring on them the remarkable fact that it's
a 60 year old recording. Pictures was
originally written for pianoforte and was
orchestrated by Ravel. Orchestrations can
sometimes digress far afield from the
composer's intention, but I've always felt
Ravel succeeded brilliantly. And this is the
best orchestral version I know of.
 I
next turned to an organ recording J.S. Bach
“Toccata and Fugue,” Lionel Rogg, (Harmonia
Mundi 190771) and played Bach's
Passacaglia and Fugue. This early work
is without doubt one of the supreme
masterpieces for that instrument; it is the
product of a young Bach exalting in his
genius, less introspective and more
exuberant. The variations constituting the
passacaglia have haunted me over a life in
music with their grandeur, power and
astonishing inventiveness. This is where I
first leaned to love the pipe organ. The
nuances that are in the recording, the
reverberation of the venue, the valve action
of the pipes, the mechanical noise of the
pedals, the chirp of the air column as it
first enters the pipes, are not just
present, they are specific in focus and
dynamic value. You might say it is not just
a matter of “hearing” these things, but also
a matter of “seeing” them. The realism of
the instrument is, as might be expected,
extraordinary due to the full frequency
range of the loudspeaker. An acquaintance
who has heard and appreciated the many
changes in my stereo over the past
decade—cables, amplifiers, power cords, DACs,
line filters—was present for the first few
minutes of the passacaglia and left a phone
message later on: “Those speakers are the
closest thing I've ever heard in my life to
the real thing...incredible.” I agree,
the Armada System is extraordinary and in a
class one might not anticipate based on it's
relatively modest cost. It certainly
presents by far the most realistic and the
most exciting music ever to grace our living
room. Even my wife, who has always found
pipe organ music objectionable, was drawn
into the living room: not to complain but to
tell me how much she enjoyed it. Hearing
this CD—from the deep grumble of the big
diapasons to the plangent call of the
bourdons to the crystalline lilt of the
flûtes—was a marvelous experience.
 Cassandra
Wilson, Blue Light 'Til Dawn (Blue
Note CDP 0777 7 81357 2 2). This is a dream
CD, superb sound, superb musicianship,
superb soloist, great songs. Granted, I'm a
jazz lover in a small way only, but when I
hear Ms Wilson's rich, wise voice in this
performance, time and circumstance fall from
me like an old skin, and the world fills
with a graceful radiance. Maybe I should
abandon my Beethoven and my Brahms and
Sibelius more often for a non-contemplative
world where timelessness is measured in the
phrasing of a beautiful woman's haunting
voice singing Children of the Night. This is
one of a handful of CDs I use to test
component performance, and what it reveals
about the Armada System is unmistakable.
Stunning as this CD is with my old ribbons,
it is a more magical with the Armada System.
The bass is tight and clean without a bit of
overhang, the cabinets stone dead, the
treble sparkles without a hint of distortion
or ringing, and the midrange is full and
rich and real as sunshine on your skin. At
these rarefied levels of sound reproduction,
metaphors pale and scamper before the
unalloyed pleasure of the evocation—and in
the back of my mind, appreciation of the
wires and integrated circuits and brilliant
designers that bring this experience about.
The truth.
When one speaks of the sonic qualities of a
loudspeaker, one is primarily speaking of
its truthfulness to the media. But what does
“truthfulness to the media” really mean? The
pat answer is that it means a (relatively)
precise representation of the original data,
be it grooves in vinyl or pits in
polycarbonate, no more, no less.
Far as I know there's no single measurement
called “resolution.” We all know how
changing a component sometimes reveals a
piccolo previously buried in the bassoons
and horns, and how different components seem
more or less transparent relative to one
another. Is it the type of capacitors in the
signal path, is it the construction of the
loudspeaker cables, is it the modulus of the
speaker cone material, the design of the
output stage? Is it all of these and much,
much more? I have no answers. But there is a
clue to resolution, one that has cropped up
in various reviews, including some of my
own: good recordings sound better, poor
recordings sound worse. And if there's
treasure buried deep in an otherwise
mediocre recording, it'll shine through. The
component that further distinguishes such
boundaries could be said to be less
“forgiving,” to be more accurate, more
truthful. Truthfulness to the source is no
guarantee of “musicality,” alas, but it is
the holy grail of our hobby. Although I can
recall reading naïve comments to the effect
that a component or a loudspeaker was “too
revealing,” for a dyed-in-the-wool music
lover and part-time audiophile like myself,
there can be no such thing. Good whiskey
ought to be drunk straight.
The NSMT 20M is a highly evolved design that
from the beginning seems to have aimed at
“truthfulness to the source” and this has
been my experience precisely. If I was
unprepared for any one thing, it is the
degree of contrast between good and poor
recordings. This is a loudspeaker for
someone who really wants to hear what's on
the medium. No wonder sound engineer Kurt
Lundvall wrote, "I purchased a complete
20M Armada system over a year ago which I
use daily for audio mastering. This system
has simply allowed me to get closer to
creating a perfectly balanced master than I
ever thought possible."
And talk about the volume control being like
the focus on a camera—with the 20Ms there is
an unprecedented degree of precision in
balance and image focus. A remarkable
example of this is Wanda Landowska's Well
Tempered Clavier, Book 1 (RCA 6217-2-RC),
where the correct loudness setting snaps the
monaural “image” into proper focus and
dimension. The Pleyel is perhaps my least
favorite harpsichord, but this recording of
music I have loved deeply for a very long
time, played by its supreme interpreter, has
clearly taken on a more natural and balanced
tone. The “Pleyel sound” through the NSMTs
is significantly less strident and more
pleasant to listen to. It is both
interesting—that a more neutral, perhaps
more accurate, loudspeaker would account for
the tonal change; and rewarding—that I can
spend a more amiable time with these
particular CDs which I treasure.
The 20Ms are noteworthy for their effortless
sense of élan and how completely they
disappear while making beautiful music. I
keep harping on those words “neutrality” and
“accuracy.” If there is such a thing as the
“British sound,” these two words are the
twin pole stars in its firmament. Long
experience with KEF 101s—speakers that
exemplify the British tradition—proved to me
the enduring and endearing value of those
qualities. The NSMT 20Ms have those
qualities too, a lot of class, a truthful
portal to the spiritual, sensual, emotional,
exuberant and universal language that music
is.
So much so, I purchased the 20Ms and look
forward to using them as my new reference.
#
Specifications: 20M Ambient Sound Monitor
Dimensions :14 X 9
X 10
Driver array: 7 inch cast frame TPX cone
with one inch soft Dome tweeter
Grill: yes
Inductor: air core
Capacitor type: Film foil
Bi-wireable
Cabinet: eco-friendly
(sealed against emissions)
Cabinet finish: walnut veneer and Peruvian
walnut
Price: 20M Ambient Sound Monitor is
$2995/pair
Specifications:
15EXP Subwoofer:
200 watts high headroom amplifier.
Continuous phase adjustment for the best
possible integration with your speaker
system
:10 inch long-throw paper cone woofer
: Auto-on switch controlled by input signal
: Continuously variable active crossover
switch from 40 Hz to 120 Hz
: Combined bandpass enclosure and crossover
roll off 24dB/octave
: Line level and speaker level inputs
: Line level and speaker level outputs
: Vented band pass design produces extended
flat bass response which is ideal
for music and home theater systems
: Front port allows near wall placement
Price: 15EXP subwoofer is $1295
Price: 27” Sandbag
Stands are $795/pair, all prices include
Free Shipping within the continental USA.
Address: NSMT is located in Research
Triangle Park, North Carolina, phone
919-244-8777
Website:
www.nsmt-loudspeakers.com
Email
nsmt@nsmt-loudspeakers.com.
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