Reprinted from Hi-Fi Choice
July 1989
APOGEE
DUETTA SIGNATURE
Launched
with a great fanfare some five years ago, the American Apogee organisation
created a sensation by producing a full sized,
three-way ribbon loudspeaker
simply characterised by the
company name of 'Apogee'. When the dust settled, it became clear that while this
speaker contained elements of a truly stratospheric performance, the operating
principle was not entirely clear; furthermore significant difficulties were
encountered when driving it. Depending on the connection mode, very low
impedances of down to 0.1ohm were present, and to cope with these Krell and
other manufacturers designed experimental amplifiers.
Soon
after this speaker was introduced, its smaller brother the Scintilla appeared. This was closer to a two-way design and offered
a more believable 4ohm impedance. Sensitivity
was very low, requiring a minimum of 200W per channel, Later the Scintilla
was relaunched
with an improved sensitivity rating, but efficiency was still very low and the
impedance now fell to 1ohm - which represents an extremely severe amplifier
load.
For
a year or two in hi-fi circles the main question directed to audiophile
amplifiers was "Can it drive a
Scintilla?" but, since, then further research and development has
resulted in a new range of Apogee speakers which offer more moderate sensitivity
and amplifier loadings, and for their size and performance rather better prices.
These are currently (UK) the Caliper
Signature, Duetta Signature and Diva. Having
tried both the Caliper and Duetta Signature models, the former can genuinely be regarded as a
downsized version of the latter, conceding very little in terms of coloration
and transparency, and only compromised by maximum loudness power handling and
low bass extension. The Caliper is £3,150.
Meanwhile,
the Diva's an awesome 3 way design
which costs an equally awesome £8,600 and requires much dedication in terms of
room and supporting audio system to obtain the best results. The dominant market
position naturally falls to the Duetta reviewed
here now in its third incarnation (MI, MkII and now Signature.) I
did not favour the
first version; the second showed improvement, while the new Signature
version certainly requires serious consideration.
A tall,
modernistic looking free-standing panel, it has provision for leveling
using adjustable spiked feet. The sound-producing sector consists of a large
tensioned membrane covering the bass and low midrange, and a full height
vertical ribbon element offering a wide linear frequency response over the mid
to treble range. A well designed ribbon has almost zero distortion, plus
negligible self resonance and a superb transient response, It is implied by the
literature that the Apogees are all-ribbon designs, but in fact the bass
element, although pleated horizontally, is based on the isodynamic principle, used for example by Infinity and Magneplanar, Behind this
active membrane is an array of bar magnets mounted on a thick steel plate which
is extensively perforated to allow the rear radiation to pass through relatively
unobstructed. This single sided drive method is less linear than a
bi-directional or push-pull system, but given the large driven surface area,
equivalent to several 12-inch bass units, the movement is very small and the
resulting distortion is negligible.
The Duetta
Signature may be bi-wired (strongly recommended) and must be used almost
square on, spaced approximately 0.6 to 1.5 metres
from the back wall. As close as 0.5m from the sidewalls is permissible and helps
to expand stage width, this recommendation dependent on room size.
Measured
in-room, the speaker delivered linear frequency responses on the listening axis,
with good integration shown between the two drivers. No nasty spuriae were found. Driven hard, some distortion was
evident in the bass, mainly doubling, but this was only significant in context
of the rest of the frequency range where the distortion was very low, much lower
than in competing moving coil designs, for example. In fact the ribbon section
has lower distortion than a number of good power amplifiers.
Most
important of all, in my well proportioned listening room the Duetta
Signature delivered a superbly flat computer averaged frequency response
over the listening area, this confirming the subjective findings. The impedance
was quite uniform close to 4ohms - and presented no problems, while the
sensitivity assessed at the listening position was equivalent to an eminently
useable 85-86dB/W. Maximum room sound levels of 104 to 105dB/A were
possible front a stereo pair, enough for thrilling volumes on big classical
works but still not enough for reliable 'disco' duty in large rooms.
SOUND QUALITY
For the listening tests
the main power amplifiers were the Krell KMA-160
(£10,000 a pair) but many others were also tried in order to investigate their
compatibility, these including the ARC D125, Musical Fidelity A470 and A370, and the KSA-200
and the KSA-80. Both MF models were man enough for the job, with the A470
showing world-class slam, while judgment
on its sound quality must be reserved until a final production model is
obtained. Of the less expensive models, the KSA-80 was an unexpected find
and, in the context of its price, power and sound quality proved to be very well
matched to the Duetta Signature, the combination costing £7,200. The bigger
Krell's
were better still, with a sonic reward roughly in proportion to price. At
moderate sound levels the D125 was
very fine but this ARC amplifier was straining to produce higher sound levels
where even the KSA-80 remained quite unperturbed.
Preamplification included a current ARC SP11-II, a Pink Triangle, Pip II, an upgraded MVX
arid a Krell KSP7. Sources were a Goldmund Studio/T4/Koetsu Signature
and a refurbished Cambridge Audio CD1. A veritable high-end feast!
Where
previous Apogee Duetta models sounded
incomplete, brilliant in some respects but flawed in others, the Signature's
balance of qualities proved entirely positive, Once properly aligned, and
noting that vertical setting was quite critical, their performance was wholly believable
on both rock and classical works. While it has often been said before about
exceptional equipment, the effect of this Signature
is simply the removal of a veil from the music. Its transparency and
resolution of detail was extraordinary and was riot just a mid-band phenomenon -
it stretched across the whole audible frequency range.
The
bass was well extended to 25Hz, and can be a mite too powerful in some rooms.
Different to box speakers and partly as a result of the way it drives the room,
the Duetta bass sounded 'right', with
the transient edge, the slam and the weight all occurring in unison and with
excellent pace and rhythm. On other gear bass sounds are often just 'notes',
while the Duetta fully conveys the
character of the instrument playing, and also how it is played, Never sounding
congested, and devoid of compression, the Duetta
Signature managed to separate out the fine strands of complex scoring in a
most satisfying manner, Moreover it achieved all this without hardness or
exaggeration, free from ringing, 'tizz', or 'boom'.
Stereo
images are well focused once you have adjusted to their specific presentation,
with a large-scale soundstage including good height and depth. Listener fatigue
is very low a good sign, this.
CONCLUSIONS
At
a substantial but a believable price, Apogee has demonstrated a remarkable level
of design maturity in the Duetta
Signature. It can be driven well by a number of suitable amplifiers and has
a sensitivity that is sufficient for inputs of 100W per channel upwards. At this
time, I favour bi-amped
connection with a pair of KSA-80s,
though a single amp used bi-wired also gave fine results. KMA-160s
were also first rate.
With a wide
frequency response (no need for sub woofers!) these elegant modern designs can
produce decent sound pressure levels of very high quality and with low
distortion exceedingly low in the mid and treble ranges. In terms of tonal
balance they are neutral, accurate, very low in coloration and their excellent
transient performance gives them the ability to 'drive' on rock, and flow on
classical material.
A
true reference grade loudspeaker, the overall balance of this design is most
successful, marrying theory, technology, build quality and finish to a first
rate sound. As you may already have guessed, I bought a pair!
Typical
price inc VAT £4,250
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