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RPG Modex Corner

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.


RPG® solved this problem by optimising 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.

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. 

Sound (1) strikes the membrane (2) which sympathetically vibrates, converting the sound pressure to air (3) motion. The air loses velocity (4) as it moves through the internal absorber and air cavity. Now you absorb more bass in less space!  

modc_im1Impedance tube testing
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. Therefore, RPG® also measures its bass traps in compliance with ASTM C384 using a 2' x 2' impedance tube which is accurate down to 20 Hz. The graph illustrates the plane wave impedance tube absorption coefficients for three different samples of the Modex Corner. The random incidence absorption coefficient for 72ft² or 18 Modex Corner Bass Traps in a Type A mounting on the floor of the chamber is also shown. The compliance (reciprocal of stiffness) of each Modex Corner membrane is deliberately made slightly different to randomly distribute the resonance frequency over roughly a 10 Hz frequency range. This is evident in the graph by the fact that Sample 1 is about 7 Hz higher than Samples 2 and 3. The plane wave impedance tube data support the general low frequency absorption characteristic of the random incidence data and also indicate the resonance maximum. RPG® has also developed an in-house transfer function measurement system to verify the resonance maxima of its low frequency membrane absorbers.

Absorption Coefficient
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 the Modex Corner exploits this high pressure by converting the pressure fluctuations into air motion. As the membrane sympathetically vibrates over a selective low frequency range, determined by its mass and stiffness, it pushes air through an internal porous layer producing low frequency absorption. This innovative approach makes it possible for the Modex Corner to absorb the fundamental and higher harmonic modes that are often problematic in small rooms.

Modex™ Corner can be free standing, or can be flush mounted to a wall with the split batten mounting.


  • The proprietary internally damped membrane converts any available corner into a highly absorptive low frequency absorber
  • The Modex Corner provides useful low frequency absorption in wall - wall and wall - ceiling corners that are often unused and available for acoustical treatment
  • Corner mounting means you will not have to sacrifice space for equipment
  • The Modex Corner is modular and more can be added as needed. The modules simply stack on top of one another and offer unlimited opportunity for experimentation and modification
  • If a 90° corner is not available or if the existing corners in the room are not right angles, the Modex Corner can be mounted as a stackable free standing column
  • The lightweight and portable Corner Bass Trap can be shuttled between rooms and venues as needed

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.


  • Pressure zone membrane absorber Shallow 7'' depth offers optimal absorption
  • Stackable
  • Wall or free standing mounting
  • Lightweight
  • Portable
  • Modular

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