Can you help me figure the diffraction angle of sound coming over my sound barrier wall?

Question

Given: Road noise 300 feet away from sound barrier wall, House 20 feet from sound barrier wall.

Purpose: How high will wall need to be to stop boom box sounds (from the street) from reaching my house?

Dear "devilsad" - thanks for that info.

I have researched it no avail, .. except some folks say to make the wall 2 feet higher than the "line of sight" of the noisy source. --- rather arbitrary it seems?

currently my (castle) wall is 8 feet high and I plan to make it 12 feet high. But I could go as high as 15 feet it needs that heighth. (maybe I could go even higher, my foundation (and rebar) is for a 3 story house.

Dear Raji, Thanks for that input. I have spent the last 14 months researching the points you covered (Canada and England seem to do the best jobs in their research labs on those subjects)

I am pretty sure I am well covered (my wall is a double wall tied together with steel and the middle filled with sand, yes sand is one cool sound stopper) -- my big problem now is to stop the sound from diffracting over the wall. --

like I said in my e-mail to you, R/S has some smart folks, so maybe a few of them could help me too.

Answer 1

Shrubbery or a row of thick trees would be the most effective...don't know your climate, so see a landscape expert for the proper trees for your area...

Answer 2

Hey thanks for the Canadian compliment....

Actually, I have a visual for you - since I'm not mathematical.

In my city, there is a very busy expressway that cuts the city in half. They actually tore down neighbourhoods to build it in the 70's.

In the 80's, they found the money to build the sound barriers for the benefit of the people who are still living next to it. In this one section, which I drive by frequently, the houses are about 80 feet or so from the wall, with the expressway butt up against it on the other side. The expressway is 6 lanes at that point.
The wall is at least 16 feet high. If I get out of my car at that point, I can barely hear the traffic on the other side.
Conversely, (and I don't understand this), my mother lives very near the expressway. She has a very deep lot with city owned property behind that. It's all dense bush which you would think would be somewhat of a barrier, but no. If the wind is in the right direction, you practically have to yell when you are in her backyard to be heard.

:)))
(((((uunnccllee) - please be careful when building your wall.....

Answer 3

In addition to Devilsadvocate's answer, you have to take into consideration the sound absorption and re-transmission of the low frequency sounds that would emenate from the wall itself. The Wall would tend to act as it's OWN speaker and be virbrating and giving off it's OWN low frequecny noises as well. The wall would have to be 100% sound absorbing with ZERO re-transmission from sympathetic vibrations. At SOME frequencies, the wall not ONLY fails to serve as a noise reduction but tends to AMPLIFY the noise at certain low frequencies. The wal would have to be made of something like fiberglass insulation and about 100 feet tall to totally eliminate all the low frequency sound from the sub-woofers of todays BOOM boxes on wheels. LOL and then you would still have to deal with ground vibrations being conducted through the ground itself.

Raji the Green Witch

Answer 4

You won't be able to stop all of it this way; the low frequencies (and long wavelengths) mean the boom box noise diffracts readily around such obstacles and is not readily absorbed. That is one reason it is so annoying. You also can't make use of any nulls unless you can count on the boom box's output having a specific frequency, which you can't. The best you can do is to attenuate the noise, not stop it completely.

To answer a question like this, someone would need to know how much to attenuate the noise and at what frequency.

Answer 5

The answer to this question is simple. The density of your human body is close to one gram per cm cubed, that of water. Now, you have clothes, etc. that catches wind or air. These tend to add resistance to your falling human body, and thus slow the jumper down. The sky diver jumps at about the level of clouds at around 2 km. The maximum velocity reached is around 140 kmph, and after that air resistance keeps the speed constant, while the diver does acrobatic displays in the sky. A carbon nanofiber frame work with wings attatched to the human will one day allow man to fly like an Eagle. In India, we have tried this with hang gliders that drop off from cliffs on the Himalayan Mountains. They are very exciting. Above the clouds, the air is thin, so speeds go extremely high. This causes overheating of the falling body, and it is burned and charred black. A very dense body, like lead, when dropped from a high cliff will drop much faster than a human body, and the slowest is cotton or feather, which tends to float in air. Many a sky diver has fallen from the sky becos the parachute did not open. They reach about 140 kmph and fall. Those that fall in a soft place like snow tend to live with some injuries, and they are thus saved, since their speed does not cross 140 kmph.

Answer 6

12 feet is sweet. The most important thing is to plant trees if room allows all along the wall. Trees absorb noise. I have a small woods between the interstate and my house. They buffer the noise beautifully. Wish I could help. I like these kind of projects. I'm a carpenter btw. I know a little about landscaping also. We have a frame company and that's what we do when the economy isn't so sucky like it is now.Ha

Answer 7

UW, I live in the city, and my limited engineering background is electrical, specifically embedded hardware, so I'm of no help.

If I wanted to keep the sounds out of my neighborhood (sirens, gun play, dogs, street revelry, police radios, car stereos, loud mufflers, construction, encroaching raccoons from the local park fighting local feral cats for territory, my neighbors, etc) out of my castle (the place I share with my roommates share), I'd have to live in big sound proof box, lol.

But then what fun would it be living in the city. I can't sleep in silence. I get too suspicious.

I'll keep an eye open and drop you an email if I do dig up info, though.

Answer 8

I would think 12 feet of wall would be good topped with 3 feet of bran muffins. The bran muffins are the total trick! You bet get Aunt Carolyn baking!

Answer 9

I think you might have better luck with noise cancellation using inverse waveform. They make headsets like this for helicopter pilots and this was being toyed with for auto exhaust systems. I don't know if there is something like this for a home system or not. Other than this, have you looked into moving?

Answer 10

First you will have to work out decibel level then follow chart on link.

http://www.fhwa.dot.gov/environment/keepdown.htm