Natural Acoustical Dampening

[K.W. Burnette]

Hello Blue Room,

I didn't think that this would apply to the sound forum, as it has more to do with theatre design more than designing sound itself. I have been looking for some source material on the acoustical profiles of shrubbery and other natural sound barriers to aid in the design and construction of an outdoor ampitheatre. The space is medium to small in size, seating anywhere from 300-400 people at most. We have two buildings near by that act as reflectors and 2 nearby roads, and a close-by highway that can throw off a fair amount of noise. Any help in this area is much appreciated, and though the project is a long way from being done, ill get you guys pictures when, if ever, it is built

in advance, thank you for the help and the time,

K.W. Burnette

[kerry davies]

Interesting!

Have a look at; http://www.etsluk.com/Products/Acoustic%20...ng_brochure.htm which is a trademarked solution, but I don't think there has been too much written source material you will find. Research is a little thin on the ground. (Pun).

From personal experience the best acoustic barrier was a 400 year old yew hedge around a neighbours garden wich was 4 metres tall and 2.5 metres thick. Haave you thought about or will you be allowed to add a wall cover such as Virginia Creeper? That would be an added diffuser.

I believe that hedges are the way to go rather than individual shrubs and bushes but if you come up with any information please post it here so that we too can learn. Good luck

[Robin D]

A row of softwood shiplap fencing with a 1.5 to 2 metre gap and another row of featherboard planted with dense shrubs/hedging in front and between is fairly effective. Height can be a problem though depending on the location. The idea is that the fencing only lasts a decade while the hedge becomes established and takes over. The fences work fairly effectively on their own and having the shiplac horizontal and the featherboard vertical aids the 'disruption' of the sound waves. I also went to one place some years ago where they had a hard wall reflecting sound off a main road. They stuck thick cork floor tiles onto the wall and reported that it made an incredible difference. Cork is of course one of natures best acoustic screening materials but is not cheap.

 

A short term measure is bales of straw.

[Jivemaster]

Have a look at motorwy sound deadening systems -acoustic fences and shrubbery combined. However the cost of the research may mean that it's not freely in the public domain jut for selling the systems and installations. Roads as a line source pose special problems.

[Simon Lewis]

You've had some good pointers in the posts so far. What you should be aware of is that a) vegetation is not very effective as a noise barrier b) its effect can be more aesthetic or can introduce masking through self noise c) the depth or density needed to achieve either noise isolation or sound absorption (two very different issues) is significant and d) the effectiveness of a barrier is dependent upon its height, distance from the noise source and spectral composition of the noise source. Low frequencies are 'harder' to isolate (from the point of view of diffraction effects etc.).

 

Most of the solutions linked to above use some form of fence or absorption material as the core of the barrier, either to act as the noise isolation element, or to provide noise isolation until the planting is dense enough to act on its own.

 

If you are managing this project yourself, I would suggest using a road side barrier system (of which there are many) and then use planting to provide visual softening of the barrier. The barrier provider will be able to give hard data on its effectiveness.

 

Hope this helps,

 

Simon

[ramdram]

Around our "tent" we have a berm:

 

http://en.wikipedia.org/wiki/Berm

 

or perhaps "earthwork" would be a better description, anyway it is a longitudinal mound of earth.

 

If you have the space and the budget of course, perhaps you could engineer an additional earthwork, above your amphitheatre, to deflect the noise upwards; from both external stuff and yourselves.

 

Obviously you can plant the slopes as green as you wish. And, of course the slopes can be used for extra seating, like this for example:

 

http://openairtheatre.org/

 

Apologies for teaching you to suck eggs KW if you knew this already.

[Simon Lewis]

Have a look at lat 53° 1'2.46"N long 1°13'19.70"W on Google Earth.

It's an old Rolls Royce aero engine test site, and there's a substantial earth noise barrier built around the concrete apron. These can be very effective, but take a lot to put in place!

[K.W. Burnette]

Well thank you all for the help!

This being a pre-planning planning session, I can't promise any pictures for a while, but ill get them up when they (hopefully) start construction.

[Richard the chandler]

I once read a fasinating book on straw bale buildings that said that a more and more common use of straw bale walls was to act as a sound barrier. Obviously this would require rendering etc and would be solid but the argument seemed quite logical and convincing as to the effectiveness of this sort of method.

 

 

 

 

 

Well thank you all for the help!

This being a pre-planning planning session, I can't promise any pictures for a while, but ill get them up when they (hopefully) start construction.