"Tim Snell" wrote in message
...
Autolycus wrote:


"Tim Snell" wrote in message
...
Evening all,

I was looking to try and reduce the intrusion of road noise into the
back
garden of my house.

snip

It's 30 years since I worked in the Noise Unit of a County Council,
so I
may be a little rusty on the subject, but iirc the two big factors
were
the plan angle obscured by the barrier, and the path difference
between
the direct line of sight from the observer to a point just (0.5m?)
above
the road surface and the distance from the source to the observer via
the top of the barrier.

Wow thanks. I think I understand the path difference but what is the
plan
angle? Is it not the angle that creates the path difference (over the
distance from source to observer?).

Draw a plan of the road, the barrier, and the point in the garden you're
thinking about. If the road were infinitely long and straight, and
there were no barrier, it would subtend an angle of 180 degrees. Now
think of the barrier blocking part of the view of the road. This
reduces the 180 degree "view", depending on the site geometry, such as
the curvature of the road and the length of the barrier. To maximise
the angle obscured, the barrier may need to extend onto your neighbour's
land, or return at a right angle along the boundary. Other houses, etc,
may help to reduce the angle of view, but if the road rises, it may
become visible over the barrier.


--
Kevin Poole
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