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Background

I live about 350 m from a rail yard. The idling engine are rather noisy. Within my house, only the very low frequencies usually make it through the walls to the living space. I haven't done any measurements, but my guess would be that the peak frequency of this noise is sub- 100 Hz and possibly sub 40 Hz. It is fairly low magnitude (i.e. unless you're sitting in a quiet room trying to work or sleep, it isn't very noticeable)

I am currently doing a renovation of the house, taking the walls down to studs. I would like to reduce the magnitude of this low-frequency noise through the appropriate selection of building materials, wall design, and possibly application-specific technologies (recognizing that these will have added costs).

My question:

What can I do in wall construction to attenuate low-frequency (~40Hz?) noise?

The perfect answer will provide successful, proven examples and explain the theoretical underpinnings.

Existing questions

  • This question is talking about options outside of the house, like an earth berm. This is not an option for me, and the house is 2-storeys so an exterior barrier is not feasible.
  • These questions: (1, 2 3) are looking for solutions that don't involve re-constructing a wall.
alex_danielssen
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    Please don't cross-post to multiple SE sites. Pick one & stick to it, or flag for migration. [Is cross-posting a question on multiple Stack Exchange sites permitted if the question is on-topic for each site?](http://meta.stackexchange.com/questions/64068/) - https://sound.stackexchange.com/questions/51893/reduce-low-frequency-noise-from-nearby-rail-yard-during-home-renovation – Tetsujin Nov 22 '22 at 18:18
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    & to reiterate my comment from Sound Design as an opener here - You won't achieve this in a domestic build, unless you're starting from scratch. You need mass & air-gapping. When you're dealing with such low frequencies & large masses as a building, you need to be floating sections on engineering rubber. Nothing with stud walls can achieve this. You start with concrete. – Tetsujin Nov 22 '22 at 18:21
  • btw, I may only be an amateur when it comes to most DIY projects, but I am a professional sound engineer, have self-built small studios & was responsible for building 7 commercial studios back in the 90s. We had a budget of 1.5 million pounds [for the conversion alone] & started in an old Victorian factory/warehouse with 3ft thick stone walls. – Tetsujin Nov 22 '22 at 18:27
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    @Tetsujin you need to post that comment as THE answer. I am an EE with background in acoustics and agree with the mass & decoupling. Stuffing the walls or adding more sheeting will do nothing except cost $$$ and raise expectations. – P2000 Nov 22 '22 at 18:43

1 Answers1

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After comments:
You won't achieve this in a domestic build, unless you're starting from scratch. You need mass & air-gapping (de-coupling). When you're dealing with such low frequencies & large masses as a building, you need to be floating sections on engineering rubber. Nothing with stud walls can achieve this. You start with concrete or stone.

btw, I may only be an amateur when it comes to most DIY projects, but I am a professional sound engineer, have self-built small studios & was responsible for building 7 commercial studios back in the 90s. We had a budget of 1.5 million pounds [for the conversion alone] & started in an old Victorian factory/warehouse with 3ft thick stone walls. The build/design itself was done by Harris Grant

As also mentioned in comments - stuffing the walls with rockwool etc will just waste money at frequencies below 100Hz & be nothing but an expensive disappointment.

There is some mileage from multi-ply walls on staggered studs [so the boards on one side have no transmission contact with the other side], all floated on heavy neoprene blocks; multiple layers of sheet materials of differing densities - thick drywall/Minerit etc, air-gap, thin drywall or plywood, more air-gap, 'rubber' sheet Revac or engineering neoprene to absorb & energy-disspiate at different frequencies…
…but you will still be expensively disappointed down at 40Hz.

Tetsujin
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    super cool project, wow. – P2000 Nov 22 '22 at 21:16
  • Just to make sure we're on the same page; I'm not looking for 'studio-grade' sound reduction. I'm trying to find out what the best I can do to mitigate, recognizing that I am dealing with stud walls, not concrete. It seems like the answer is: mass, air gaps/decoupling, and heterogeneous densities with the caveat that attenuation decreases at the lower frequencies. Are there any design choices that are marginally better than others? I've found mixed messages online about air gaps for low frequencies because they can introduce resonance. – alex_danielssen Nov 23 '22 at 05:35
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    I'm an entire master's degree short of being an actual acoustician, however, for low frequencies the trick is to find a frequency, find a 'board' of some desity & size that when fastened around the edges resonates at that frequency. You then box that into the middle of your construction leaving it free to vibrate. As it vibrates, it damps that frequency, stopping a lot of the energy from penetrating the next layer. Tiy then need another in front of that at a different frequency, otherwise you get what's known as a coincidence dip which can cause it to 'sing' rather than damp. – Tetsujin Nov 23 '22 at 08:16
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    The trouble with this is the size of sheet you'd need to be resonant at 40Hz - I don't know what it would be, I don't have the math, but at a rough guess, bigger than the house;) I did a bit of hunting & found a company who make [noiseless plywood](https://800nonoise.com/product/noiseless-plywood/) though the performance collapses below 100Hz. – Tetsujin Nov 23 '22 at 08:21
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    I also found a research paper of bamboo absorbers - interesting because they discovered that damping the absorber with rockwool actually did help at some frequencies - but again performance tanked below 100Hz - https://www.euronoise2018.eu/docs/papers/15_Euronoise2018.pdf – Tetsujin Nov 23 '22 at 08:22
  • Long & short of this; you need a professional acoustician to work out your frequencies & materials - but don't hold high hopes down at 40Hz. – Tetsujin Nov 23 '22 at 08:22
  • [sorry, typo, too late to correct… "Tiy then need" == You then need] Also found https://www.extrica.com/article/10418/pdf - again tanks below 100Hz. I don't have the math for any of this, btw. – Tetsujin Nov 23 '22 at 08:24