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We live on a busy street with sound of tires and revving engines. We were wondering if hedges could help reduce the sound that comes into the house? if not, what other alternatives can we try? We already got soundproof curtains but it's still loud. Below is a photo of the front yard and the house.enter image description here

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  • I think that since the road is so low, that a hedge would visibly block traffic from most of the front windows. If that's the case, they will also dampen sound. The dampening is a factor of mu and the frequency, so it would work better on tire noise than engine noise. I would expect 2-3DBs of loss from a thick hedge, much more when it's covered in snow (if you choose an evergreen). Replacing the iron fence with wood could give you several more DBs. It will never be quieter than what you hear in the backyard though, be realistic.
    – dandavis
    Jul 3, 2021 at 7:53

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A hedge can’t reliably decrease the sound pressure level by more than 2 dBA (i.e. barely perceptible), and most of the reduction is in the higher frequencies (i.e. tire noise but not engine noise). This phenomena is well researched:

In the three trials where a significant attenuation of the noise occurred, the porosity of hedges measured less than 4.6% and an average noise reduction of about 2.7 dB(A) (max 7.0 dB(A)) was observed. This effect was particularly relevant in the range of higher frequencies (between 2 and 20 kHz).

Biocca, M., Gallo, P., Di Loreto, G., Imperi, G., Pochi, D., & Fornaciari, L. (2019). Noise attenuation provided by hedges. Journal of Agricultural Engineering, 50(3), 113-119.

Thick dense hedges are found to provide only a small total A-weighted light vehicle noise reduction at low speeds. Measured insertion losses range from 1.1 dBA to 3.6 dBA. The higher noise reductions are found to be associated with an increased ground effect.

Van Renterghem, T., Attenborough, K., Maennel, M. et al. (9 more authors) (2014) Measured light vehicle noise reduction by hedges. Applied Acoustics, 78. 19 - 27. ISSN 0003-682X

There was minimal noise attenuation that could be attributed to the coniferous trees at the 15 study sites examined. Attenuation was not correlated with tree stand age, height, species, or density for these sites.

Highway Noise Reduction Experiment. Virginia Department of Transportation. December 2008

It showed that Pithecolelobium dulce have the highest noise reduction of 10.12% [9.9 dB] at 20 m distance,

U.R.Pudjowati et al. “Estimation of Noise Reduction by Different Vegetation Type as a Noise Barrier : A Survey in Highway along Waru – Sidoarjo in East Java, Indonesia”

Noise is a kind of kinetic energy, and energy is conserved. The only ways to decrease the noise that reaches your home are reflection and absorption. (Increasing the distance to the road is not feasible.)

Reflection alternative

This means a tall solid wall. Here is a white paper that describes the principles of sound walls. In order to be effective, a sound wall must have no holes and be tall enough to prevent diffusion around the top.

Absorption alternative

This means converting the noise energy into heat energy (imperceptible in landscaping situations). Materials that absorb noise energy well tend to have complex internal structures. Examples include mulch, rough lumber, and perforated sound absorbing panels.

Psychological alternatives

Noise perception can be subjective. Noise can be added to mask the road noise:

  • Flowing water features.
  • Tipping bamboo fountain (Shishi-odoshi).
  • Wind chimes.
  • Habitat that attracts chirping birds.
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  • +1 for providing references and not just opinion. Maybe also mention that "A" weighted means that measurements reflect the ear's different perception of high and low frequencies, so these dismissals are not just an air pressure / vibration measurement but take into account what noises we are sensitive to, making the conclusions even more relevant.
    – P2000
    Jul 5, 2021 at 16:57
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    The hedge would be very effective at helping to hide what could turn out to be an ugly sound wall. (I'm thinking the concrete monstrosities along freeways - a wood fence would be much nicer looking.)
    – FreeMan
    Jul 6, 2021 at 14:50
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Adding hedges will not do much to muffle the sound. You would need a totally dense hedge like you see in a garden maze which would be impractical.

You would be better off upgrading your windows to double pane gas filled ones.

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Not really.

I live along a highway, and even a substantial row of mature trees and undergrowth doesn't do much. You need density and you need full obstruction. A hedge provides neither.

Do like I do and look forward to the electric vehicle revolution. Hopefully tire manufacturers have discovered that they'll be the biggest noise culprits and are working to reduce sound output in new models. Also file complaints with the city over juvenile drivers with illegal exhausts.

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    I really hope the tyre manufacturers don't do very well, because on a bike or on foot it can be important to hear cars coming up behind, and tyre noise is better than nothing in the absence of engine noise. They are trying to improve efficiency,and that might make them quieter anyway
    – Chris H
    Jul 5, 2021 at 11:47
  • It's a poor strategy to rely on noise in most environments, as we have so polluted our airwaves that you're as likely to not hear it anyway. The disproven fallacy of loud pipes saving lives is a testament to that. Instead, positional radar will continue to evolve until cars see us nearly 100% of the time and avoid incidents nearly 100% of the time. That's a far better rate than we achieve as humans.
    – isherwood
    Jul 5, 2021 at 16:09
  • in all but the noisiest environments (i.e. even on many urban roads) I can not only hear a car coming up behind and how far but get a good idea of where they are laterally too. ICEs give me cues from engine note, but I can easily hear a tesla coming up behind. It will be a very long time before the majority of cars sold have any radar, never mind the majority of cars driven; even with almost perfect sensing, better than humans, you've still removed some of the vulnerable road users' ability to take defensive action. Then you get to blind people
    – Chris H
    Jul 5, 2021 at 18:47
  • I can hear well, too, but that's not the issue. The issue is attention. It takes a significant sound to draw attention from someone who's mentally elsewhere, and they're the ones getting hit. Also, we don't need a majority of cars to have radar--we need the ones with quiet propulsion and quiet tires to have radar. That's coming along nicely.
    – isherwood
    Jul 6, 2021 at 12:53
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    most cyclists and pedestrians who get hit aren't at fault, but may be able to take evasive action. Cyclists in particular are often clipped from the side while being overtaken and knowing that a close pass is coming has saved me more than once. We need multiple layers of protection. Do all Nissan Leafs (as an example of a particularly quiet EV) have radar? I know not all Priuses do but they're only electric at low speed
    – Chris H
    Jul 6, 2021 at 13:30
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From the photo, it looks like there's not a lot of distance between the road and your house, and worse, you're well above road height.
If there were more space,and local codes allowed it, the best barrier is a berm. Even a 4-or 5- foot high berm will deflect a lot of the sound upwards and away from your house. Add a solid fence on top of that and it'll get even quieter.

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Where a hedge can be useful is screening a fence or wall from view. The wall or fence is then what does most of the noise-blocking.

A dense hedge on the outside of a wall will also, to some extent, reduce the effect of sound reflecting off a masonry wall at your neighbours across the street. To a lesser extent they also help by extending the height of the barrier if the maximum fence height is limited. Hedges also take time to grow to full height/density. Even if you buy fairly tall specimens to start with they need to fill out.

Any structure needs to be solid and heavy; while ordinary close-boarded fencing will help, there are specialist noise fences (UK supplier, but I've seen hits from other countries) which use thicker timbers designed to overlap very well. They're not cheap, and need to be installed properly.

As noise fencing is more specialised than improved windows, the windows might be the first thing to look at. Any draughty gaps or deliberate ventilation let in noise, but if you only have a single layer of glass that's the easiest thing to address. In some places, traditional wooden shutters over the outside of the windows (or more modern UPVC-clad shutters operated from indoors) are used to reduce noise. I've seen these in hotels near airports/main roads in Germany, for example.

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