All Products Modex Module
Problem
Listening and performance rooms often suffer from low frequency modal
problems. Because porous absorption is ineffective at these
frequencies, a high efficiency mechanism is needed to provide modal
control
Solution
RPG® solved this problem by optimizing the absorption
efficiency
using a unique internally damped membrane absorber that provides ideal
absorption in the modal frequency range.
They are also available for floorstanding installation.
Small rooms often exhibit poor low frequency response with significant
emphasis at modal resonances. They also have limited space to make
acoustical improvements. Porous surface absorption is ineffective at
these modal frequencies, because the air motion near walls and in
corners is essentially zero for these long wavelengths. RPG®
research solved this dilemma by developing a unique membrane system
that converts the high sound pressure fluctuations typically found at
wall surfaces and in corners into selective absorption in the modal
frequency range. As the use of sub-woofers becomes more and more
popular, there is a growing need for modal frequency management
Applications
All critical listening rooms, including recording studios,
vocal
booths, home theatres, quality control rooms, CD mastering, film mix
and dubbing stages, and music practice rooms
Performance
Surface or corner applied porous materials lose efficiency at low
frequencies, because the particle velocity or air movement associated
with long wavelengths is low. The sound pressure, conversely, is at its
maximum. The internally damped membrane in Modex™ exploits
this
high pressure by converting the pressure fluctuations into air motion.
As the membrane sympathetically vibrates over a selective low frequency
range (1), determined by its mass and stiffness, it pushes air (2)
through an internal porous layer producing low frequency absorption
(3). This innovative approach makes it possible for Modex™ to
absorb the fundamental and higher harmonic modes that are often
problematic in small rooms.
Resonant Frequency
Simple relationships exist between the design frequency of these
resonant systems and the membrane mass, stiffness and cavity depth. The
chart illustrates the effect of cavity depth on resonant frequency for
two different membranes. Note how the reciprocal square root dependence
on the air cavity distance (and mass) results in progressively smaller
changes as the distance is increased. These equations, however, are
often inexact in predicting the resonant frequency, because the
physical mass of the membrane in the system is different from the
isolated mass. If the resonant system has a high Q, one may be creating
a notch at the wrong frequency, thus aggravating the modal problems.
Absorption Coefficient
Another unknown is the absorption coefficient of the resonant system.
Random Incidence absorption coefficient testing has been standardized
by ASTM using the C423 reverberation room method. The frequency range
is 125 Hz to 4,000 Hz. In the United States, most NVLAP certified
reverberation chambers are not accurate below 100 Hz. Accurate low
frequency measurements can however be made using an impedance tube. To
characterize the Modex™ system, RPG® designed a 2' x
2' x 18'
impedance tube and measures Modex™ in compliance with ASTM
C384.
The graph illustrates the effect of cavity depth on maximum absorption
for a given membrane system. It can be seen that this particular
membrane system has a good absorption between a cavity depth of 4 - 6".
These results indicate that we can provide relatively shallow
Modex™ enclosures
Absorption Bandwidth
While membrane absorbers can be designed for a specific frequency and
offer a high absorption efficiency, their bandwidth or range of
frequencies over which they are effective is limited. One can broaden
the Q of the system by introducing damping in the air cavity, but this
is accompanied by lowering the maximum absorption efficiency.
RPG®
has taken a different approach to provide absorption in the modal
range. By systematic impedance tube testing, RPG® has optimized
the
membrane mass, compliance and cavity depths that offer maximum
absorption efficiency at the third octave centre frequencies of 40, 50,
63 and 80 Hz. To cover the 40-80 Hz frequency range, one can simply
combine Modex modules, thus providing 100% efficiency. Specific modal
problem frequencies can also be addressed with individually tuned
modules.
Installation
Modex™ Module can be free standing, or can be flush mounted
to a wall with the split batten mounting
Benefits
Product Options 
Modex™ modules: 600mm(W) x 600mm (H) x 178mm (D)
Modex™ Plus Modules: 600mm (W) x 600mm (H) x 305mm (D)
Modex™ Wall Modules: 600mm (H) x 1200mm (W) x 178mm or 305mm
(D)
Custom sizes also available
Standard fabric finish is Guilford of Maine FR701 #298. Custom colours
are also available
Shipping weight varies with the membrane (Call for information)
Modex module - MDF finish - also available fully clothed or veneered
finish with choice of fabric face, or scrim finished for concealed
installations.
Features
