Lexicon MC-12HD Manual

Comparing the MC-12HD and RV-5/MV-5 EQ Calibrations
The Automatic Speaker and EQ calibrations are key features in select Lexicon products. While both were
designed to improve the overall listening experience and help expedite setup times, the RV-5/MV-5 and
the MC-12HD automated calibrations perform in very different ways.
In short, the RV-5/MV-5 calibration provides system equalization and bass correction, adjusting the
frequency response of the outputs to provide a balanced overall system. The MC-12HD Room EQ
calibration addresses the problem of room modes, applying specific parametric filters to the outputs and
thus accommodating for the resonances present in the listening space.
In the actual performance of the calibration, the products differ as well. While both are automated, the
RV-5/MV-5 calibration requires the interaction of the user during the procedure. Whereas, once the initial
setup and preparation are complete, the MC-12HD automatically performs the whole calibration without
user interaction.
RV-5/MV-5 Autocal Calibration
The RV-5/MV-5 Autocal Calibration performs system equalization and bass correction using a single
microphone. However, unlike most equalization systems that simply knock down the peaks in the
response, the RV-5/MV-5 calibrates the system more intelligently – compensating for frequency response
aberrations, varied speaker performance, and balancing the entire system for the best overall results.
The main features of the RV-5/MV-5 calibration are:
to reduce the audible differences caused by using low-quality
speakers, or mixed speaker brands within the surround system
to equalize the output of the system to improve stereo imaging
and precision
to reduce timbre differences between the left, right, and center
sound due to placement and reflecting surfaces
to equalize low-frequency response with high resolution within
a reasonably large listening area Calibration Results Below 1 kHz
to set the distance, level, and crossover for each speaker
to provide subwoofer, mid-frequency, and high-frequency adjustments from 20 Hz to 20 kHz using
three distinctively separate calibration routines
In the diagram below, note the consistency between Seat 1 and Seat 2, the much smoother overall
response, and the roll-off as the frequency increases.
Frequency Response at 2 Seats
For surround systems with two subwoofers, the
calibration equalizes the listening area between
two listening positions placed within a 10-foot
area. The calibration measures the response
from each subwoofer to each listening position
and then equalizes the system so that the bass
response between those two locations is flat. This
calibration is very useful since fluctuations in
frequency vary considerably from seat to seat
and adjusting for one position can make the other
much worse. The subwoofer calibration algorithm
guarantees flat responses, consistent over the
entire area, with a defined roll-off at the upper
end providing a transition to the main speakers.
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The calibration has three separate routines – Far Field, Near
Field, and Subwoofer Tests – all performed within the same
calibration procedure. The Far Field test sets the speaker
distances, crossovers, and output levels of each speaker in
relation to the primary listening position and corrects the timbre
of the direct sound field and early reflections between 100 Hz
and 1 kHz. The Near Field test corrects for loudspeaker
deficiencies at frequencies above 1 kHz. The Subwoofer test
suppresses the room response below 100 Hz within an area
between the two Far Field microphone locations.
The end result of the calibration is a balanced system, with
equalized speaker response times, improved stereo imaging
and precision, and reduced sound coloration. Near Field Test Results
MC-12HD Calibration & Room EQ
The MC-12HD has two automatic calibration procedures – one performs speaker output levels and
distance calibrations, while the other performs the Room EQ calibration. The Room EQ calibration, which
is the calibration that this article discusses, uses four microphones to measure the acoustical
characteristics and modal properties of the listening room. In addition, the Room EQ calibration
measures and calibrates for low frequencies - from 19 Hz to 150 Hz – making it very effective at treating
problem resonances.
Using four microphones ensures that potential problem resonances aren’t overlooked, since more than
one listening position is measured, as well as providing additional data for evaluation. This acquired data
then gives the MC-12HD a clearer picture of the room’s acoustical properties, helping to ensure that ALL
of the problem resonances are addressed.
Understanding Room Modes
To understand the MC-12HD Room EQ calibration, you must first understand what room modes are and
why the modal properties of the listening room have a significant impact on the sound quality of any
surround system.
A listening room has surfaces that cause the sound waves
from your loudspeakers to reflect back on themselves and
interfere with each other, creating “room modes”. The result
is peaks and dips in the overall frequency response of the
room, which can often sound unpleasant – too loud at some
frequencies, too quiet at others, and the bass very “boomy”
or even “flabby”. These peaks and dips can also be very
different for each seat in the listening space, adding further
complication to any potential solution.
At high frequencies, these anomalies are difficult to predict
because the wavelength of the sound is so short –
sometimes just turning your head can cause the sound to
change! But low frequency room modes have very long
wavelengths and hence are predictable, and correctable.
Proper speaker placement and acoustic treatment of the
walls, ceiling, and floor can solve some of these problems,
but usually additional equalization is needed to remove the
more troublesome room modes. Frequency Response at 2 seats
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These room modes affect the way you hear in several ways – the most pronounced effect of room modes
is to make certain frequencies too loud, but the most difficult to solve is the tendency of some resonances
to linger in a room after the speaker has stopped reproducing them. A very strong resonance can linger
as long as half a second and, in the worst cases, also has a distinct pitch.
These lingering resonances are not always noticed because the frequencies are so low; but they do
present problems because a lingering sound often obscures the details in the following passages of the
music or soundtrack. For example, the lingering sound from a kick drum could mask details of the
following vocal passage. Trying to fix this problem by tweaking your audio controls doesn’t provide a
satisfactory solution because each can cause detail loss in other areas. The other problem is that each
seat in the listening area potentially has different room modes affecting it.
Correcting Room Modes Using the MC-12HD
The only way to properly correct these lingering resonances is
by applying the appropriate filter to each frequency where a
problem room mode exists. The MC-12HD Room EQ
calibration measures the impulse response of the room at
frequencies between 19 Hz and 150 Hz; anything higher than
150 Hz has too small of a wavelength to accurately predict.
The MC-12HD then analyzes the results and applies the
proper parametric filters to neutralize the problem frequencies.
Unlike the typical solutions to these lingering resonances, such
as using graphic equalizers or filters that are targeted to the
peaks instead of to individual frequencies, the MC-12HD
Room EQ calibration takes a different, innovative approach.
The MC-12HD measures the decay time of the resonant
frequency to within 0.732 Hz to identify the problem
frequencies, and then treats each individual frequency with up
to seven separate parametric filters. 2 Microphone Responses (of 4 total)
The calibration then performs a second pass for each speaker to apply general response smoothing from
25 Hz to 250 Hz and to examine the spectrum for peaks and dips; the result of this second pass is
generally a subtle tweaking of the initial calibration response. In addition, during this second pass, the
calibration applies an additional filter at 120 Hz to provide a bass compensation boost.
The two graphs below demonstrate the effectiveness of the Room EQ calibration.
AFTE
R
BEFORE
4 Microphone Responses for the Left Front Speaker – Before and After the Calibration
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The main advantages of the MC-12HD Room EQ calibration are:
Addresses what is important for the audio – the objective is not to make the numbers better, but to
make the audio sound better.
Resonances are a feature of any room – treating them helps the entire room as well as improving
overall bass uniformity.
The amount of correction can be adjusted by the listener.
It’s reliable and easy to calibrate – you can even use it to screen out external noise sources.
Two Different Systems
There’s really no fair way to compare the two EQ calibration systems. While the overall goal of each is to
improve the audio performance of the system, the actual implementation of those goals is very different,
as explained.
In summary, the RV-5/MV-5 calibration uses an internal sound pressure measurement and calibration
system that automatically balances the speaker channel levels for optimum surround sound enjoyment –
regardless of the speaker type or listening space conditions. In general, the RV-5 calibration is a simpler
system, most useful for the casual listener. The MC-12HD neutralizes the room modes of the listening
space and equalizes the room response to provide an overall smoother, better-sounding audio
experience, regardless of the seating position. The MC-12HD is a more advanced system, specifically
designed for the serious enthusiast.
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