road noise reduction using a fence of some sorts......

[stevev]

I couldn't think of where else to put this thread so I opted for Acoustics. If any of the mods feel that it's too 'off topic' then feel free to delete or move to another spot as you see fit.

so, to the point....

I've been asked to quote on a job for a block of flats that needs some level of noise reduction from a busy road that is quite close, ie: 8 meters away.

At the moment i'm at the 'concept' stage, so trying to come up with ideas for them regarding construction.

As a concept, all I can think of is 'dense' and 'tall'. In the real world i'd be suggesting a double brick wall (or besser/breeze block) approx 2.4 meters high, core filled with concrete (with an engineer's plan for footings and wall etc etc)

My main questions are: has anyone got an alternative to this that they've used with success? and would some kind of MSM construction have a place in this application?

I think 'mass' is probably the only answer but i'd be interested in anyones thoughts.

steve

[Soundman2020]

Interesting project, Steve! Not really my area of expertise at all, but from what I recall, if the barrier is 1m taller than the line-of-sight from the source to the receiver, then you can get about 5 dB of reduction, and another 1 dB for each additional meter in height. The practical limit is about 10 dB reduction, IIRC. In subjective terms, that means a reduction by half: the traffic noise would sound about half as loud as it is now.

So you'd have to make the barrier tall enough that the road would not be visible at all from the flat on the top floor. If the road is visible, then there's no reduction.

As a concept, all I can think of is 'dense' and 'tall'.

Yup! That's about it. And you are limited to something less than mass law here, since there is edge diffraction going on at the top edge of the wall, redirecting sound back down the other side. Also, at those distances atmospheric effects start to play a role...

i'd be suggesting a double brick wall

I wouldn't bother making it double: no pint to MSM unless the entire source or receiver is fully enclosed. Just make it reasonably massive, and plenty high. And also plenty long! I seem to recall reading somewhere that the barrier has to extend much further than the building in both directions, to be effective. something like five or ten times the building length, I think. And of course, there cannot be any breaks in the barrier: no driveways, pathways, etc. It has to be one single long unbroken barrier, from end to end.

would some kind of MSM construction have a place in this application?

Naah. Not unless you can enclose the entire road in an MSM shell!

I think 'mass' is probably the only answer

Yup.

I have seen some transparent noise barriers along highways not far from where I live, and they do seem to be effective. They are very thick plastic, though. I'm guessing polycarbonate, plexiglass, or some such. I haven't gotten up close, but from the road they look to be pretty darn thick! ie, lots of mass, but they don't block the view. That might be an option.

You might want to look around for professional advice on this one: there are companies that specialize in designing and building noise barriers for roads.

- Stuart -

[stevev]

thanks Stuart, you've pretty much confirmed my suspicions that there isn't a whole lot that can be done aside from mass and height.

Just make it reasonably massive, and plenty high. And also plenty long! I seem to recall reading somewhere that the barrier has to extend much further than the building in both directions, to be effective.

I'll be bound by council planning on height, and being a residential block it can only extend to the boundry of the property which is the same size as the flats. Height wise, there's no way we'd be able to build tall enough to shield the second floor.

So all in all it seems I might be able to get some noise reduction for the bottem floor dwellers, but probably not a 'night and day' difference. I like to give clients as much information as I reasonably can about what they can expect from a finished product, so I might suggest getting some professional consultation if the noise issue is their number one priority.

Could be a better option to build a normal fence and invest $'s in double glazing and proper door/window seals for the front facing units perhaps.....

[Soundman2020]

Could be a better option to build a normal fence and invest $'s in double glazing and proper door/window seals for the front facing units perhaps.....

Actually, that makes a LOT more sense! Considerably cheaper, I would imagine. Assuming that the walls are reasonably decent.

- Stuart -

[stevev]

Assuming that the walls are reasonably decent.

yeah, it's a brick construction so I think i'll certainly suggest the glazing and seals as an option.

steve