Say you have two balconies close to each other, with a sound proof wall between them, will you be able to hear sound from the other side at all?
Assume the building wall is completely straight, the balconies are square in shape, the wall extends out as far as the balconies go, and the distance to other buldings is quite far.
Sound can also diffract around obstacles, go through the floor, the air, etc. So you would hear something, and a better solution is to ask them to turn the music down!
I don’t believe there is such a thing as a sound proof wall and one on a balcony, open on the side, even less so. But there is active noise cancelling, it works great with headphones, but alas! still in the experimental phase for windows, balconies and buildings in general.
I’m reporting this for forum change.
I guess if you magnetically floated a box inside a box with vacuum in between, you might be able to get something perfectly soundproof.
On a balcony, unless you enclose the balcony completely, you’ll get sound from around the open sides, of course. A completely enclosed balcony is what I would call a room, not a balcony.
Moved to GQ (from QZ)
But doesn’t the sound need something to reflect off? It can’t just go out into the air and then go around the wall?
No, sound is a wave that can diffuse throughout the air (or other medium) without needing to reflect. High frequencies are more directional than lower ones, but there’s no (practical) way to prevent sound emanating on one balcony from being audible on all the adjacent ones.
Audible sound has a frequency between 20 and 20kHz. That means a wavelength between 17 metres and 17mm. (aka 56 feet to 2/3 inches.)
This spans a range of dimensions that are from large relative to a human to small relative to a human, over a thousandfold span. This makes reasoning about how sound works less than intuitive. It is also why sound is really hard to manage.
Low frequencies will simply diffract around anything smaller than a wavelength so easily that they barely notice it is there. Watch ripples on a pond pass a small obstruction and reform essentially undisturbed on the other side. This behaviour continues even as the frequencies increase (wavelength smaller) but there will appear a region behind the wall where there is some shadowing. But enough distance behind the wall and the wall will cease to have much effect. Some sound will be reflected by the wall, but energy passing the edge of the wall will diffract and close around the edge again. There will be some of interference effects due to different path lengths, but in terms of general sound energy transmission we can ignore them.
With the OP’s geometry, wall as wide as the balcony, and other buildings far enough away not to matter, sadly the wall is not going to do a great deal for propagation in the air of mid and low frequencies. Losses can occur due to adsorption by the wall, and these do matter. A wall that adsorbed all the energy that hit it would help greatly, but a wall that is simply impervious to sound will just diffract it around. Adsorbing sound is sadly just as affected by the huge range of wavelengths involved. Adsorbing bass frequencies requires space and a lot of clever tricks. Adsorbing high frequencies is easier than appreciated.
Sound waves defract as they pass by edges. Highway engineers have long known this as noise levels behind sound barriers on the highway were not as low as anticipated. The sound going over the barrier “bends” downward. I have seen a proposed solution where the top edge of the barriers is a variable sawtooth shape so defracted sounds tend to cancel each other. This was decades ago and I have still not seen one installed, so…
But it’s common enough for these walls to be covered with ivy or have other shrubbery around them, which I imagine accomplishes much the same thing.
The trouble remains as I outlined earlier - the huge range of wavelengths involved. A feature will typically work for wavelengths close to the feature size. Getting a feature to do anything across more than a couple of octaves is difficult at best. Audible sound covers 10 octaves. Road noise is more limited in range, which is a help.
Vegetation is actually pretty poor at modifying sound energy. Much sound just passes straight past. Diffraction requires that the feature size of the vegetation be similar to the sound wavelength.
Loss of sound energy is proportional to the surface area when considering solid objects, and common macroscopic objects just don’t provide much area. This is why materials like fibreglass, wool, and open cell foams, are used. One of the best is melamine foam (commercially available as Basotec and in small quantities as miracle cleaning erasers.) But the wide range of wavelengths requires a range of different techniques to manage.
Busy roads are particularly evil to cope with because at the important distances they act as closer to a line source than a point source, so intensity drops off closer to proportional to distance, not the square of distance.
Stand back to back with someone in a large field - will you hear them talking at all? (yes)