Noise Barrier

Post and discuss acoustic topics, Studio design, construction, and soundproofing here

Postby avare » Mon May 26, 2008 12:14 pm

Trying to get an idea of what is going on here, this thread is an exercise in self knowledge, not for commercial gain.  Correct?

First thing looking at the drawing, the sound sources are spread over 20 m in length and 10 m length, or approximately 300 m^2 and are located 5 m above the monitoring position.  Redo you your sound source calculations taking the area and location of the chillers into account.

Andre
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Postby Mohammad » Mon May 26, 2008 12:20 pm

Thank you Rod,

so, you are looking for a job, to get hired?!!! hahahahhaaha, i am just kidding you.

don't hesitate to say your opinion.

[THIS MESSAGE IS TO YOU AND ALL FRIENDS HERE].

if you go to my profile you will see that i am mechanical engineer, so i don't have any background in acoustics, but because of working with a company that is related to vibration isolation and as you know it is difficult to separate vibration from noise and acoustics. my job here enabled me to be more in touch with acoustics and BELIEVE me i found my self suddenly stuck in love with acoustics science {that's it} and it became my hobby, i know that it is non-sense to get you all busy for only practising my new lovely hobby. but this message for you and all.

[please if you see that my question is stupid and silly, don't waste your time with it].


thank you all,

thank you Rod.
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Postby Mohammad » Mon May 26, 2008 12:23 pm

By the way:


i worked as an average and very general, not per octave band:

and i found the following:

the dBA directly next to the barrier in the pump side is : 53dBA
and in the curved area: 48dBA 10 meteres away from the barrier.

as a first exam for me, i hope it to be correct.
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Postby bert stoltenborg » Mon May 26, 2008 12:45 pm

This tells nothing.
You need to know the wavelengths dominating this dB(A).
A wave of 10 cm will be much easier trapped than a 6 meter wave.
And refelctions can be important.
And you still haven't told how you measured it, or if it is a power level.
This is a waste of time
:?
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Postby Rod Gervais » Mon May 26, 2008 12:56 pm

Mohammad wrote:  

[please if you see that my question is stupid and silly, don't waste your time with it].



Mohammad,

the question is neither stupid nor silly.

My only point was that if this is for a real life application - then your best bet is to have the company hire someone (who can be held responsible) to do the design.

That way the company has recourse if anything should go wrong.

If the question is purely  scientific and for learning purposes - then please continue as if I  said nothing.

Seriously,

Rod
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Postby Bob » Mon May 26, 2008 2:20 pm

Hi Bert

bert stoltenborg wrote:You need to know the wavelengths dominating this dB(A).
And refelctions can be important.
And you still haven't told how you measured it, or if it is a power level.


Did you open the PDF? On page 2 are both pressure and power, broken down by frequencies from 63hz up.

The 'single wall' shown on page 1 has a strange curve. Seems to wrap around some of the machinery, while leaving others completely exposed. It seems to me that if even one of them is exposed, then that wall's maximum sound deflection is around 3dB -- and not the 20dB/30dB mentioned. I'm assuming that the 112 red dots are the machines, and that they are not actually inside that oddly shaped wall.
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Postby Bob » Mon May 26, 2008 2:34 pm

Did a little googling...

The Al Taj Mall is worth about $127.89 Million US (amman jordon).

I think the mall may be surrounded on 3 sides by soon-to-be-built skyscrapers.

Image
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Postby avare » Mon May 26, 2008 2:57 pm

Bob wrote:The 'single wall' shown on page 1 has a strange curve. Seems to wrap around some of the machinery, while leaving others completely exposed. It seems to me that if even one of them is exposed, then that wall's maximum sound deflection is around 3dB -- and not the 20dB/30dB mentioned. I'm assuming that the 112 red dots are the machines, and that they are not actually inside that oddly shaped wall.


The wall seems to be esthetics also, hiding the pumps.

As far as some chillers not screened, they are significantly further away from the listening position.  Bear in mind that the listening position is some 4 - 6 m below the chillers.  If the mall will be surrounded by office towers, I would hate to be 1 or 2 stories up.  For that matter what the effect of the towers will have on the SPL is interesting.

FWIW here is a link to Petra's APS series chiller page.

Andre
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Postby Rod Gervais » Mon May 26, 2008 3:41 pm

avare wrote:
As far as some chillers not screened, they are significantly further away from the listening position.  Bear in mind that the listening position is some 4 - 6 m below the chillers.  


Distance quite often isn't our friend as much as elevation  is - in fact it doesn't always afford us what one might think it should.

An example of this was seen within the last few years with a company I work with extensively -

2 hotels - one sits about 65 to 70' from an 8 lane highway - 4 lanes each direction - the hotel is a 3 story structure with a pitchd roof running parallel to he highway.

The 3rd floor and the highway are roughly the same elevation and the highway is very busy at all hours of the day and night.

No special means were taken to attenuate sound in this building - and it has no issues in that regard.

There has never been a complaint made regarding highway noise.

Building 2 is also a 3 story structure - and it sits about 1/4 mile from an entrance ramp to a 4 lane highway (2 lanes each direction).  The hotel is roughly 100' in elevation higher than the entrance ramp.

No special means were taken to attenuate sound in this building either - but  the hotel was constantly receiving complaints regarding traffic noise from the entrance ramp (apparently a lot of large trucks enter the highway at that location) and was losing a lot of revenue due to the issue.

Sevel hundred thousand dollars (US) were spent to solve the problem.

The great distance didn't help us in the least  due to the elevation of the building in regards to the entrance ramp, while in the first case there was no problem due to the elevation even though you could almost touch the cars as they went by.

If the mall will be surrounded by office towers, I would hate to be 1 or 2 stories up.  For that matter what the effect of the towers will have on the SPL is interesting.


No kidding - perhaps even higher would be worse -

A seperate story about a hotel - 21 stories  - sitting in a nook at the joining of 3 highways  and directly adjacent to 2 entrance ramps with the back of the hotel roughly 400 feet from the nearest highway (which is 8 lanes total).

The highways were roughly level with the 4th floor  and the building runs parallel with one of the highways.

No perceptable levels at the 3rd floor - light readings at 4 - strong readings at 5 (roughly 85 dBC (fast) peaking at roughly the 19th floor with readings of 95dBC.   (Using "C" readings due to my concerns for LF sound from large trucks).  From that point sound levels began to fall off.

Interestingly - the side of the building that was NOT facing the highway was also in need of special treatment - this due to the building across the steet fromthe hotel - which was also a highrise - and which had a glass facade.  

That building reflected enough sound back to our building due to it's exposure from the south of just one of the highways that standard construction would not give the isolation required.

But the problems began around the 8th floor and were slightly lower (around 80 dBC) so we didn't have to dump as much money there as on the near side.

By the time you made the 21st floor of the building there wasn't a problem - apparently  due to the angle of the building in relation to the sound source - with the sound just bouncing off the face of the building.

This probably would have cost a 1/2 to 3/4 of a million dollars to solve as an afterthought - but was only around 250,000 due to buying it out as a part of the bidding process.

Rod
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Postby bert stoltenborg » Mon May 26, 2008 3:43 pm

Didn't look at the bottom, as usual.
Thnx Bob.

Where do they get this 4 dB attenuation with doubling of distance?

If you have these figures, and you know which series is true, and you know where the immission points are, you can roughly calculate the sound attenuation of the screen. The clac is very elaborate, though.
For what's it worth.
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Re: Noise Barrier

Postby abdousony55 » Mon Apr 09, 2018 1:06 pm

I've been considering erecting some form of noise barrier fencing, I originally thought of a concrete fence, the ones with the concrete posts and sections you stack to the right height, but the price is coming back a bit steep! I've found a few more HERE Highway noise barrier
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