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The crossover is the heart of any high-end speaker design.
The number of crossover topologies and options that are available
to the designer are endless, and development of a successful design
can take years of patient effort - even with the assistance of modern
measuring techniques.
We have concentrated particularly on achieving an exceptionally
flat in-room frequency response, especially off-axis, and superb
phase coherence - especially through the difficult crossover region.
This encourages optimum room response in the majority of listening
spaces. Lenehan Audio loudspeakers have only medium efficiency,
but their smooth and moderate impedance with low capacitive phase
angle response throughout the frequency range presents a relatively
benign electrical load. This enables the use of a wide variety of
partnering amplifiers, either tube or transistor, though those with
output power below 20 watts or thereabouts may well suffer a reduced
maximum volume capability.
Let's first talk about the individual components that make up
a crossover.
Inductors.
- Our experience proves that inductors need to be air-cored, and
as large a gauge as can practically be achieved. We cannot buy
inductors that meet our high standards, so we wind our own - a
time consuming process, as the tension in the wire must be kept
low - and then double-stabilise them in motor winding varnish.
Importantly, it also allows us to tolerance them to a precision
that commercially-produced components could never match. Compared
to the tiny, low cost examples that most manufacturers utilise,
our inductors are vastly more reliable and durable, can handle
enormous amounts of power, and have very low resistance and distortion.
As a general rule, a serious high-end speaker should use a
bass circuit inductor that weighs at least as much as the bass
driver itself. Otherwise, there is insufficient damping of the
bass driver, which reduces the control that the amplifier has
over the cone. Imagine a boxer whose glove is connected to his
elbow with a rubber forearm - he cannot jab with speed or punch
with power, and that's the effect of a typical small-gauge inductor.
In the ML1, the bass driver weighs 1.05 Kg and the bass inductor
1.2 Kg. We would happily acknowledge those rival manufacturers
who also observe this rule of good audio engineering practice
but we don't know of any!
Capacitors.
- Top quality capacitors certainly make an appreciable difference
to the sound of the finished loudspeaker, but they don't come
cheap! Have we made any compromises? Of course not!
We use only audiophile-grade metallised polypropylene capacitors
from Erse.
Resistors.
- Again, resistors are very important items and
you guessed
it
using top quality components is absolutely crucial to
the final result. How can that be?
Simply, normal commercial grade (ie. cheap) resistors compress
dynamic range. Typically, they will have temperature coefficients
in the 250 to 750 ppm (parts per million) range. Imagine that
we have a resistor attenuating the tweeter in a loudspeaker. When
a musical transient suddenly arrives and hits the resistor (as
a sharp electrical pulse), the resistor will momentarily heat
up and increase its resistance until that transient has passed
... at which point it can hopefully cool down again. The increased
resistance, of course, works to compress the transient - just
what we don't want. The higher a resistor's rated temperature
coefficient (in ppm), the greater the temperature increase and
the greater the compression.
At Lenehan Audio, we use only high power wire wound resistors,
all of which have temperature coefficients in the 30 to 40 ppm
range. This represents a tenfold improvement over the components
typically used by our competitors.
Connections.
- The easiest, quickest and most "cost effective" means
of building a crossover is to solder the components to a PCB.
But a soldered connection is far from optimal - solder is convenient
and does the job, but it is a poor conductor, and PCB tracks are
far from ideal for the best signal retention and transmission.
We have no interest in the easiest or cheapest methods; only
in the best. All of our crossover components are hardwired,
component lead to component lead, and crimped at high pressure
to produce a low contact area cold weld. The joint is then sealed
using Eichmann 5% silver solder. Connections thus formed offer
the maximum achievable conductivity and stability, and will
retain those qualities indefinitely.
The completed crossover.
- The end result of our fanatical attention to detail is a crossover
of truly exceptional build integrity, offering the following proven
benefits:
- Consistent, stable, long-term performance
- Enormous power handling
- Superb damping and control of individual drive units
- Complete on- and off-axis frequency integration
- Amplifier friendly impedance and phase characteristics
Tolerancing and pair-matching the crossovers.
- Designing a great loudspeaker is one challenge - producing it
commercially is quite another! The problem is that all of the crossover
components, and particularly the drive units themselves, have
electrical properties that differ from sample to sample … and,
to make things even worse, those values continue to change as the
speaker settles down during its first 50-100 hours of use.
The net effect is that, without careful adjustment of each
individual crossover before and during this break-in period,
some speakers in a production run will have a frequency response
that differs very audibly from the designer's intention.
Furthermore, it is absolutely critical to a stereo system's
ultimate imaging and soundstaging capabilities that the output
of each speaker is matched precisely, within a tolerance of +/-0.75dB.
So, how do our competitors manage to address these concerns?
That's simple - they don't! Magazine reviews have shown in the
past that different samples of even very costly, well-regarded
speakers can measure quite differently; and if you're the customer
who buys a poorly-toleranced pair, then that's just bad luck.
Perhaps we shouldn't be surprised; after all, the time and effort
consumed by burning-in, measuring, disassembling the speaker
(possibly multiple times) and adjusting the crossover is a
punishing and costly overhead for the manufacturer, all for a
difference that the customer will never see. That's right -
you'll never see the result of all that work but, be in no doubt,
it's a difference that you WILL hear! At Lenehan Audio, of course,
we have never spared any effort to ensure that every pair of
speakers leaving our factory meets our design parameters
(and we supply our speakers with an individual response
trace to prove it!) … because we believe that's what our
customers deserve. There was one small detail, though, that
always irked us, as it was the only factor we couldn't control.
Although we burn in our drivers before assembly, and adjust
the completed speaker after the first few hours of use, it
was still possible that the electrical properties of the
crossover could change minutely while it continued to burn-in
at the customer's home.
Now, though, we've come up with an approach that we believe
to be unique in the industry - one that allows us to ensure
perfect tolerancing and pair matching of our speakers, far more
quickly and accurately than before. After being completely assembled,
each speaker is burned-in on the workbench for 100 hours using music signal.
Then, with access to the crossover provided by a tuning bay behind
the Serial Number plate on the cabinet's rear, measurements are
taken and the precise adjustments required are quickly performed -
after which a fully burned-in loudspeaker, with a frequency response
identical to our reference, is ready to be shipped!
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