Sound Deadening Hedgerow?

[consciousrobot]

Hi

My girlfriend has a property in the middle of a nice village near the river south of CM.

Although it's a large two rai lot the house is towards the front and I have suggested that there may be a type of tree or plant which might help deaden sound from the fairly busy road outside. I said you may have to allow two or more metres deep and may only get some sound attenuation.

Are there any plants.....preferably as fast growing as possible though the sound issue comes first........that might be good for this?

cheers

ps: if it's a bamboo type plant also interested how one would keep the height restricted to, well, not too high.....

[JohanV]

I would suggest you start thinking of "dampening" rather than "deadening".

As sound waves propagate through air and have the ability to bend around objects - just like sea waves bends around coast lines - there is no way ever you will be able to block the sound from the outside if you don't build a sealed shell over your whole land lot and turn it into a hermetically sealed warehouse..

However, there are some aspects of the sound that you might be able to control;

Let me explain - bare with me if it seems complicated - it is - and you need to understand it if you want to do something useful.

1)

First you will need to understand that the sound from the street is made up of many frequencies - from low bass rumble ( bus & lorry engines etc. ) through mid-range elements up to treble ( high pitched ) elements ( the swooshes from tyres on wet concrete etc. ).

The low frequencies have a long wavelength and the high frequencies a short wavelength. To dampen/absorb sound energy on a certain frequency you will basically need to have a solid object ( an obstacle to the waves ) that is at least about half the wavelength - that means a wall thickness of 1 - 3 meters for low bass absorbtion. And this object needs to have considerable mass AND be able to vibrate in tune with the frequency in order to absorb the energy ( the sound ) well.

I guess you won't be able to find any plants with a thickness of 3 meters and a density of hard wood/concrete that will grow to make an airproof cover of your house.

In short - It means you will have to live with the rumble.

2)

What you CAN do is to shield off some of the high frequencies - mostly the noise from the tyres. This can actually improve your sound environment quite a lot, since most "useful" sounds are in this range - like talk, mobile ringtones etc.

Think of it like putting a blanket over the street or a hand over your mouth when you talk. The sound becomes more muffled.

The hedge will need to be higher than your ear-height. i would suggest about 2.5 to 3 meters. The property that will determine the amount of dampening will be the density of the hedge. The denser, the better. If you can see through it it won't do any good.

So, it still will take quite a hedge to get any noticeable results.

A better idea would be to build a wooden screen/fence - about 2.5 meters high and without gaps. You might have seen similar constructions along the sides of highways in western urban areas if you think about it. You could use any solid material - like boards etc.

Then, plant your hedge on both sides of the wall and let it grow to hide the acoustic screen, as that might feel/look much better.

3)

Anything else than this is doomed to fail due to simple laws of physics, which - even in this country - are impossible to bypass. No bribes will help you there

And, yes, I am an acoustician and have spent many years building recording studios and sound-insulating restaurants, airports etc. so I know what I talk about. In another world I would write this on 4 sheets of paper with a drawing of the screen and send you an invoice, so please take my advice

So, to sum it up: A very dense hedgerow as thick(deep) as possible and higher than you, would - to a certain extent - dampen a part of the sound, or rather - muffle it a bit. Thats about it. Any species will do, as long as it is dense. Many small leaves are possibly better than a few big ones..

I wish you all the best of luck.

and I hope that answers your question.

Cheers

Johan

Edited July 27, 2010 by JohanV

[JohanV]

Hmm.. I forgot to mention that the sound you will manage to "muffle out" bounces quite well on hard surfaces like buildings, windows etc.

So, if you make your hedge and then place a house with two floors or more behind it, the high frequencies will bounce from the street onto your second floor which is above the hedge level and straight down to your little garden between the house and the hedge and all your work will be for nothing anyway.

You could, of course, build a pyramid with walls angled so that the sound bounces upwards or elsewhere...

Or have a sunroof or similar over the area where you like to hang out..

In my opinion Thailand has far too few pyramids, so I would go for that

More cheers

Edited July 27, 2010 by JohanV

[opalhort]

Quote from OP's post:

Are there any plants.....preferably as fast growing as possible though the sound issue comes first........that might be good for this?

For the purpose of sound buffering many Ixora or Hibiscus varieties would be best. Dwarf varieties are best as far as density of foliage is concerned but they don't grow higher than 0.8 - 1.2 mtr.

Normal varieties will do well if planted at high density (space them only 30-50cm) and when young are trimmed frequently to force the plants to grow more branches ---> higher density. You can grow them to about 2 mtr high and make the hedge 80 cm deep.

Behind the hedge grow a row of taller trees to add to the sound barrier.

I think you should post your question in the Pets and Plants forum here on TV, where more experienced people may be able to give you more info.

opalhort

[consciousrobot]

Johan

wow thanx for the great answer. Funny enough I did physics and remember that lower wavelengths are easier to bend around things which probably explains why we don't (normally) see round corners but we can hear round corners.

I think I'm wondering if i can get a WORTHWHILE reduction in sound. The plants would make a better visual barrier than is there now too.

The house is essentially on one level and about 30 metres back from the road, so straight lines drawn from where the traffic actually travels and going over the top of a tall hedge would go way high over the house.....which is why I'm wondering if i might get some worthwhile effect. It's only a country road but gets a fair bit of use.

I think I'm going to look for situations where walls or fences or hedgerows are actually there next to a road and go listen in real life.

Opalhort

thanks also for the good info

I actually had decided to put my post in the housing section as a start I guess it was too late at night and it ended up in business!

Edited July 28, 2010 by consciousrobot

[JohanV]

I think I'm going to look for situations where walls or fences or hedgerows are actually there next to a road and go listen in real life.

Now that's a very good idea. When you're at it, try to make comparisons with a place nearby without walls but with the same background noise, if possible. That way you will better hear the actual effect of the wall.

If the house is as you describe it, it sounds to me that you won't get any big reflections from that. That's very good, indeed.

Concerning the plant advice from opalhort it sounds like a good start, but you won't get any effect with a hedge as low as 1 m. - a rule of thumb is that if you can see the sound source you will always hear it, too.

Maybe you should consider making a wall - sand/soil or something - of about a metre, that you can plant grass on and then put the hedge on the top of that ?

Please post your findings here, it would be very interesting to know what solution you find.

Again - good luck and cheers

Johan

Edited July 28, 2010 by JohanV

[JohanV]

Funny enough I did physics and remember that lower wavelengths are easier to bend around things which probably explains why we don't (normally) see round corners but we can hear round corners.

Actually, it doesn't.

Light waves are electromagnetic waves and sound waves are pressure waves in the air. You can't compare them.

Light bends only by gravity - regardless of its wavelength.

However - it does explain why you hear the bass from the neighbour or the nearby discotheque but not the treble as the short

wavelengths of high-frequency sound are easily blocked by a normal house wall, but the bass isn't.

[xen]

I would also suggest what JohanV suggested about building a earthen mound and then planting it out with a suitable plant / hedge species . I would use a turn back at either end of the mounds to block, to a certain extent ,any sound that enters yr property from parallel or a minor angle to the road .

The plants will not block the sound to ant real extent but will give the " out of sight out of mind effect " and add to the aesthetics of your property . They can also be a dust barrier if that should also be an issue. You could even build a wooden paling fence for example lap and cap , and then cover with climbers or an hedge .

Another trick is to use masking sounds like falling water - a waterfall or fountain so your ear pays more attention to that sound rather than the sound of the traffic. This something you can use closer to your outdoor living areas .

Edited July 28, 2010 by xen

[JohanV]

Another trick is to use masking sounds like falling water - a waterfall or fountain so your ear pays more attention to that sound rather than the sound of the traffic. This something you can use closer to your outdoor living areas .

A very good suggestion, indeed. Masking sound is effective and fountains are always nice

Xen, I guess you're into sound engineering / acoustics as well, are you ??

If so, do you know anything about Thai AES section plans ? It seems to be under discussion to open one here..

And.. "earthen mound".. thanks for adding that to my vocabulary. I knew there was a proper word for it

Cheers

Johan

[xen]

Another trick is to use masking sounds like falling water - a waterfall or fountain so your ear pays more attention to that sound rather than the sound of the traffic. This something you can use closer to your outdoor living areas .

A very good suggestion, indeed. Masking sound is effective and fountains are always nice

Xen, I guess you're into sound engineering / acoustics as well, are you ??

If so, do you know anything about Thai AES section plans ? It seems to be under discussion to open one here..

And.. "earthen mound".. thanks for adding that to my vocabulary. I knew there was a proper word for it

Cheers

Johan

I am qualified as a Landscape Designer but have engaged Sound Engineers as consultants at times. Consquently i don't know anything about Thai AES section plans and i even goggled it and came up with nothing . So please let us know something about it - maybe another post .

[JohanV]

[ am qualified as a Landscape Designer but have engaged Sound Engineers as consultants at times. Consquently i don't know anything about Thai AES section plans and i even goggled it and came up with nothing . So please let us know something about it - maybe another post .

AES = Audio Engineering Society www.aes.org

They have regional sections in almost every country, I'm a UK member.

But, Thailand doesn't have one, probably due to the fact that there are very few professional audio engineers/acousticians around here.

There's a general "SEA section" based in Hong Kong, but they don't have any local activity here.

I had a brief discussion earlier with the SAE ( School of Audio Engineering in BKK ) headmaster about perhaps opening a section here.

I think it would be great if acoustics and sound engineering could be taught on a university level in Thailand.

Currently there's only SAE and that's more music/sound production oriented, not so much acoustics.

That's about it, really. Not worth a separate thread yet, but if something's happening I will post here.

[xen]

It is so obvious now that i know what AES means .

[Crossy]

I actually had decided to put my post in the housing section as a start I guess it was too late at night and it ended up in business!

I'll move it to DIY

[jackr]

Someone mentioned an earthen mound. This is probably the most effective, least hassle, cheapest option, unless, that is, you decided to build a swimming pool out the back to extract said earth. How about getting 100cu of laterite delivered and do a nice escarpment? It seems you have plenty of land between you and road, plus when angled (which it would have to be) most sound from the road would be deflected over the house.

[JohanV]

Someone mentioned an earthen mound. This is probably the most effective, least hassle, cheapest option, unless, that is, you decided to build a swimming pool out the back to extract said earth. How about getting 100cu of laterite delivered and do a nice escarpment? It seems you have plenty of land between you and road, plus when angled (which it would have to be) most sound from the road would be deflected over the house.

NO, just a tiny fragment of the sound, actually.

The only frequencies that could be "angled" away are the high frequency components - approx. above 1 kHz

In energy this represents just a few percent at most.

Furthermore - only hard surfaces can "angle" away sound,

any type of soil-based barrier would rather absorb it.

Having said that, an earthen mound could still be a good idea, as long as it is high enough.

[jackr]

My, we are anal aren't we. If you know laterite at all (which is loaded with iron oxides), after time it goes almost solid on weathering, which would throw off the top end while also absorbing the bottom end. The sheer density of a couple metres of clay would be more effective than most applications one could think of. If you want to extra OTT, install an acoustic fence behind the mound to throw off the upper end, which is what industries in the Western world are made to install when located near residential areas.

... oh and light is also bent by refraction... and don't adjust my post.

[JohanV]

My, we are anal aren't we. If you know laterite at all (which is loaded with iron oxides), after time it goes almost solid on weathering, which would throw off the top end while also absorbing the bottom end. The sheer density of a couple metres of clay would be more effective than most applications one could think of. If you want to extra OTT, install an acoustic fence behind the mound to throw off the upper end, which is what industries in the Western world are made to install when located near residential areas.

... oh and light is also bent by refraction... and don't adjust my post.

Well, jackr, if "anal" is the word then it seems to be rather mutual, I would say

As the OP expressed an interest in understanding how these things works, I just thought getting the terminology right was in line with earlier conversation. You can of course call it what you want, but talking about "angling" sound is generally - although obviously not by you in this case - something most people tend to put far too much effort in without understanding the difference between low and high frequency behaviour. A good example are the egg-boxes nailed on concrete walls found in countless amateur recording studios and rehearsal rooms.

If it insulted you I am sincerely sorry.

"after time it goes almost solid on weathering, which would throw off the top end" - yes of course it would. If there's no grass or such growing on it.

"while also absorbing the bottom end. The sheer density of a couple metres of clay would be more effective than most applications one could think of"

- I think exactly this was pointed out in several earlier posts, and you are again absolutely right - absorption is what you get with an earthen mound.

"If you want to extra OTT, install an acoustic fence behind the mound to throw off the upper end" - which was also suggested in an earlier post

and is - again - perfectly correct.

"... oh and light is also bent by refraction..." - Yes, I forgot that, you are right, and just as "anal" as me I'm sorry. My mistake.

"and don't adjust my post." - I never have. What adjustments do you refer to ?

So, relax jackr, you are giving good advice, you know what you talk about, you were eventually using "angling" instead of "absorbing" which is

totally irrelevant unless you're in a discussion where acoustic terminology is being explained - which this is, to a certain extent...

It's a lovely day. Enjoy it. I will.

Cheers

Edited August 1, 2010 by JohanV

[jackr]

[klikster]

Let me add a bit more to the vocabulary.

As I understand sound:

hard surface (high density + high mass) = "reflect"

"porous" surface = "absorb" (shears pressure wave)

resonant cavaties, i.e. soundblocks = "absorption" of sorts

For any non-containment solution, "flanking sound" must be considered.

Even in containment solutions (rooms and enclosures), low frequency sound is more difficult to contain/attenuate. Many building components are rated STC (Sound Transmission Class). STC can be misleading as it does not consider octave bands. There is no practical sound attenuating wall that will attenuate equally across all octave bands.

A sound wall could typically have a sound reduction of 40 db at 3000 hz and 10 db at 60 hz.