Frequency response
The graphs below show the frequency response of the MCS1.
The upper graph shows the (normal) on-axis response and
illustrates the very high degree of accuracy; no frequency is
under or over emphasized more than 2 dB.
The second graph shows the on-axis, octave-averaged
response. This curve is representative of the speaker’s tonal
balance and shows that the MCS1 is very accurately balanced,
especially through the midrange where any over or under
emphasis is less than 0.5 dB.
The third graph shows the 30°off-axis, octave averaged
response and illustrates that the speaker’s overall energy
response is well balanced, with no large depressions in any area
of the spectrum. This high degree of uniformity is in part the
result of the MCS1’s first order crossover system.
Step response
This graph shows the MCS1’s response to a step signal.
Notice that the overall triangular shape is very well preserved
with the output remaining smoothly positive until 2.6 ms when it
finally crosses zero due to the fact that the bass response extends
to 50 Hz rather than DC. The irregularities seen in the first few
hundred microseconds are due to the tweeter diaphragm
resonance at the ultrasonic frequency of about 23 KHz.
Waveform accuracy this good can only be achieved with first
order crossovers and time coherent driver positioning.
Time response
The energy-time response of the MCS1 shows that the
speaker’s output quickly decays to -40 dB in less than 1.5
milliseconds, indicating very clean inter-transient silence. Such
performance is the result of metal diaphragms that have no
resonances within their operating frequency range and very
strong cabinet construction.
10K
Frequency
1K
25
20
15
10
5
0
-5
-10
10020 20K
Amplitude — dB
Time – msec
0.5 1.0
Output
1.5 2.0 2.5
Time – msec
0.5
5
0
-5
-10
-15
-20
-25
-30
-35
1.0
Output — dB
1.5 2.0 2.5
Time coherent topology
An important design goal for the MCS1 which is not shared
with our floor-standing products is placement flexibility. The
requirement that the speaker provide time coherence while placed
either vertically or horizontally and at any height poses its own
technical challenge. This requirement necessitates that the
speaker be symmetrical both horizontally and vertically and,
therefore, that it use either coincident or D’Appolito driver
configuration. Since the limited woofer area of a 2-way
coincident system would not satisfy the design goal of very high
output ability, a double woofer D’Appolito configuration is used.
In a D’Appolito configuration, two larger drivers flank a
higher frequency driver. The benefit is that the outputs from the
two drivers blend into a coherent wave as if they were produced
by a virtual driver positioned between the two actual drivers. If a
higher frequency driver is positioned coincident with the virtual
driver the high frequencies will be time coherent with the low
frequencies from the flanking woofers.
However, since the virtual driver operates properly only for
frequencies where the driver spacing is not larger than the
wavelength being reproduced, the commonly used topology of
two woofers with a center mounted tweeter cannot provide
coherent reproduction through the midrange. At these frequencies
an off-axis listener would hear two separate sound sources, the
closer woofer being heard before the farther driver.
To maintain a coherent wavefront through the mid
frequencies the MCS1 utilizes a 3-way configuration which
allows the woofers to operate only below 800 Hz. Coherence of
the high frequencies with the mid (and low) frequencies is
provided by coaxially mounting the tweeter with the mid driver.
So, by utilizing the topology of coaxially mounted tweeter
and mid drivers flanked by a pair of woofers, the MCS1 provides
a time coherent wavefront at all frequencies and in all directions.
In other words, even an off-axis listener will always hear the
sound from
each of the
drivers at the
same time.
To
maintain time
coherence the
coaxially
mounted drivers must be aligned with the woofers. Usual woofers are deep enough that
the coaxial drivers would need to be recessed to a degree that would cause substantial
diffraction and horn loading effects. To avoid this problem woofer diaphragms of a very
shallow shape were developed for the MCS1. The diaphragms use polystyrene
reinforcement to maintain high strength with a very shallow profile.
D’Appolito drivers’ performance at
low frequencies is equivalent to a
center located virtual driver.
At mid frequencies where the driver
spacing is greater than the wavelength
coherence is not maintained.
Virtual
driver
Acoustic
plane Acoustic
plane
Normal
woofer
diaphragm
Recessed
coax
Shallow
MCS1
diaphragm
