Advertisement
For woofers we also had specific parameters in mind. Cabinet
volume, low frequency cutoff and the number of woofers
defined the "Thiel/Small" parameters needed. These param-
eters differed from the norm in that unusually high mass
and above average motor strength was required. We were
able to achieve these parameters with a special custom-
built aluminum cone woofer. We optimized suspension and
motor parameters to assure that the woofers have low
distortion and are well behaved to very high output levels.
With system configuration and driver choices done the
cabinet design was next. Experience with our .5 systems and
then with our QBx line had demonstrated the importance
of highly damped enclosure walls to control resonance and
preserve midrange purity. These prior designs used two
different techniques to dampen the baffles. Our QBx line
uses a baffle constructed of layers of wood material and a
high loss central layer. With the XA Reference extended this
technique and its benefits to the entire cabinet. The final
cabinet is a multilayer affair with 2 layers for all sidewalls
and the back and 3 layers for the baffle. Each layer is
adhered to the next with a high loss polymer that absorbs
resonant energy. Whereas other manufacturers deal with
mass and rigidity and ignore resonance control, we feel that
this high loss cabinet design is central to the clean bass and
midrange of the XA Reference.
Cabinet styling was important too. At this stage we worked
closely with an industrial designer to give the XA Reference
its sophisticated look without compromising in any way its
performance.
With all of the "raw parts" in place we designed the first
listenable prototype. Computer simulation and optimization
provided a crossover network that would meet the XA
objectives and get the drivers to meld seamlessly into a
high performance system. The computer is a great tool in
this, but takes us only so far. Once objective measurements
show that the system is operating well, response is smooth
and flat on axis and off, our measuring system outlives its
usefulness. At that point we put away the test equipment
and start listening.
Only the human ear can truly evaluate the musical balance
of a loudspeaker system. A great deal of listening and fine
tuning of the system is needed until it has a musical
balance that gives it the purity and invisibility that we
demand.
A secondary requirement of the crossover network for the
XA Reference was that we wanted to give the system a
large degree of subtle tunability. Many years ago there was
a system designed by Henry Kloss, the KLH 12. Its unique
feature was that the crossover parameters that defined its
frequency balance were adjustable via a box with 4
multiposition switches. In every crossover network certain
crossover components will have a dominant effect in
certain frequency ranges. Adjust the values of these
dominant components and you will adjust the response in
one or two octaves, just as you might with a graphic
equalizer. The KLH 12 had three switched values for a
number of these key components to give plus, minus, and
zero positions for 4 frequency ranges. No system since had
offered this feature, but we wanted to incorporate it into
the XA Reference. The goal was to cover most of the
frequency range with subtle adjustability. Why would we
want to offer this if a loudspeaker should ideally be flat? In
short, because the loudspeaker cannot be separated from
the effects of the room and the system it is a part of. A
"flat" speaker in a non-flat room, or which is part of a less
than neutral system, will not sound as good as it could
unless some subtle adjustability is incorporated into the
system. In addition to the network adjustments, the XA
Reference Towers offer bass adjustments through three port
options. Later in the manual we will cover all of these
adjustments, and how to set them, in detail.
Nearly a year after we began the design of the XA Refer-
ence, we are in production and very proud of the end result.
We hope it will give you many years of musical enjoyment
and satisfaction.
David Smith
October 2001
3
Advertisement
