Wow, this topic seems to be popular & the problem seems appearing over & over.

Back at year 2009, I was introduced to an acosutic technology known as sound masking. One the O&G gweilou wanted to installed the so called sound masking devices it at their new operation office. This sound masking device is a sound generator which generates wide range of sounds at different range of frequencies.

The layman term being used when the qweilou elaborated on how it works was, when 1 or 2 peoples are talking, we can hear their conversations as interrupting because we can understand what they are talking unwillingly, we can't block the sound becasue the sound travels. When we get more & more sounds of talking by making it up via artificiallly generated to 200~300 conversations at on time (using sound masking ), our brain cannot process so many sounds at once go, it actually make us "less intelligent" and the sorrounding sounds appear to be less disturbing.

I believe there should be a similar sound masking technology / devices in the market to cater for the sounds issue for the high rise community.

If you have already tried all methods & still not working , may be give this a try. I personally never tried but the gweilou said very effective.

It is an extra low voltage (ELV) device. ELV have the least risk of fire hazard to my knowledge.