Feasibility and Methods for Attenuating Low-Frequency Noise (0.5–500 Hz)

Hi all,

I am exploring methods to significantly attenuate or ideally almost completely eliminate noise within the following frequency ranges:

• 0.5 to 20 Hz

• 25 to 90 Hz

• 100 to 500 Hz

From my current understanding, two main approaches could be considered:
Multi frequency Helmholtz Resonators, similar to the design described in this publication: MDPI Materials, Multifrequency Helmholtz Resonator.
Active Noise Cancellation (ANC) using subwoofer based systems capable of reproducing ultra low frequencies.
Regarding ANC, I am aware of products such as the Eminent Technology TRW 17 rotary subwoofer, which can operate down to 1 Hz. However, this solution is costly. I would like to know whether commissioning a professional to build a similar system together with an appropriate amplifier could be done at a lower cost without compromising reliability.

Alternatively, would it be more effective and practical to implement an array of multi frequency Helmholtz resonators to target these ranges?

My questions are:

• Is it technically possible to achieve full absorption or near complete attenuation of the above frequency ranges?

• If so, what are the most effective methods, whether passive resonators or active ANC, for achieving this goal?

• Are there design or implementation considerations that may make one approach preferable over the other for long term performance?

Any guidance, technical insights, or references to relevant designs would be greatly appreciated.

Thanks, Tim.

Cheap, fast and DIY. Helmholtz resonator by example: How to build a Helmholtz Resonator DIY .

All dependent on the size of the room (amount of resonator space) you want to attenuate in, as you will probably need to make several for different ranges of these frequencies.

However, given the overall low cost when it comes to making your own, compared to off-the-shelf ANC solutions where the amount goes into thousands of $ or Euros, it's worth a try.

You can also consider "mass-air-mass" constructions and the use of mineral wool, but it really depends on what you want to achieve and for what purpose (building a recording studio, a small workshop with machines/equipment, a gaming room, etc.).

I understand that this is about attenuating sound and infrasound (air vibrations at acoustic frequencies and below), not filtering electrical signals?

Firstly, the resonator needs to be larger the lower the frequency. A typical bottle is a Helmholtz resonator at around 100Hz. To get a lower frequency, you need to increase the dimensions proportionally - for 1Hz they come out close to the size of the Parthenon. Secondly, achieving attenuation requires proper coupling of the resonator to the space to be attenuated - it will make little difference to add a resonator inlet on the wall, which will be much smaller than the surface area of the wall - meaning there would have to be many such Helmholtz resonators. Thirdly, the bandwidth from 0.5 Hz to 20 Hz is very wide for achieving resonance - 1:40. So I guess any design of mechanical resonators for this band is out - at most you could build a wall that would not reflect infrasound. In ancient Rome, for example, Vitruvius designed a theatre with damping of unwanted sounds, but that was a sizable building, and acoustic frequencies.

I think that if it is not to be a bigger structure than the Acropolis, then at least for these lowest frequencies it would be advisable to use an active system - microphones, amplifier, loudspeakers - and probably with some DSP to filter the signal so as to match the signal fed to the amplifier to the infrasound to be suppressed.