TUNED ACOUSTIC ABSORBERS

Helmholtz Resonators, Quarter Wave Tubes, Perforated Acoustic Liners, and Passive Acoustic Radiators are the tuned acoustic absorbers (band-reject acoustic filters) commonly used in mitigating narrow-band noise.

Examples of such mitigation applications include, but are not limited to quieting the tonal noise at the blade passage frequency of an axial fan and dampening a standing wave of an enclosure (or a duct).

Optimal design of tuned acoustic absorbers for maximum absorption requires a thorough understanding of the effects of geometry variations on their performance. DEICON has developed a finite element analysis (FEA) based tool for optimally designing tuned absorbers. In addition to the synthesis of such absorbers, this in-house numerical tool allows for analysis/evaluation of tuned absorption mechanisms in any acoustic environment. The FEA based design tool uses acoustic impedance boundary conditions to account for damping realized by the acoustic treatment.

[DEICON designs and fabricates tuned acoustic absorbers, of various kinds, for different narrowband sound absorption applications. In addition to analytical and semi-empirical methods for evaluating the surface impedance of acoustic absorbers, this quantity can be measured experimentally.]

In low-frequency applications, the size of passive tuned acoustic absorbers becomes too large. In such applications semi-active and active tuned acoustic absorbers/dampers can be used, instead. In addition to having higher power density than passive devices, active Tuned Acoustic Absorbers can also be re-tuned readily and abate a narrow-band noise with time-varying frequency.

Passive Tuned Acoustic Absorbers

  • Helmholtz Resonators
  • Quarter Wave Tubes
  • Perforated Acoustic Liners
  • Passive Acoustic Radiators

 

Active Tuned Acoustic Absorbers

DEICON’s patented, active acoustic damper/absorber is highly effective in abating undesirable low-frequency tonal noise. Applications of this acoustic treatment include, but not limited to, dampening a resonating standing wave (acoustic mode) in a small room (such as a recording studio or a cabin in a yacht) or mitigating acoustic instability in an industrial combustor (boiler, heater, gas turbine, etc.).

The controller which is realized by either a tunable, op-amp circuit or a high-speed computer (digital signal processor) can be tuned to:

  • one or multiple, low-frequency resonant mode(s) to add damping to that (those) modes and thus abate the boominess and rumble of sound at that (those) resonant frequencies, or
  • frequency(ies) corresponding to a driving perturbation (such as the blade passage frequency of a fan) and absorb sound at that (those) perturbation frequencies.

 

The actuation is provided by a loudspeaker and the sensory information is supplied by either a microphone or a dynamic pressure sensor.

The size of the active tuned acoustic damper/absorber is the size of a loudspeaker which is by far smaller and lighter than comparable passive low-frequency dampers/absorbers targeting the same low frequencies.

The application of this technology in adding modal damping to small rooms (listening rooms, recording studios, home theaters) is licensed to Modular Sound (the reputable manufacturer of Bag End professional grade speakers) which makes electronic bass traps, with the trade name E-trap(TM), based on this technology.

Industrial applications of this technology, due to their uniqueness and need for customization, are being implemented by DEICON.

Learn About Tuned Mass Dampers

RELATED RESOURCES

Vibration Abatement of a Natural Gas Piping System Using Tuned Mass Dampers

Active Boom Noise Damping in Rooms/Cabins

Advanced Air Isolation System for Precision Devices