Wednesday, June 15, 2011

The Silly 5 dB Difference

Land Transport Authority plans to install sound barriers near Bishan MRT Station to reduce train induced noise by at least 5 dB. According to the LTA spokesman, the targeted reduced noise level of 75 dB to 80 dB is like listening to someone practising on the piano. What may sound like music to their engineers may drive others to bonkers.

The Singapore environmental quality standards stipulated in Paragraph 1, Article 16 of the Basic Environment Law (Law No. 91 of 1993), determines the following to be "desirable for the preservation of the living environment and (is) conductive to the protection of human health".

Type of areaDaytimeNighttime
AA50 dB or less40
dB or less
A and B55 dB or less45
dB or less
C60 dB or less50
dB or less
  • Category AA is applied to areas where quietness is specially required, such as those where convalescent facilities and welfare institutions are concentrated.
  • Category A is applied to areas used exclusively for residences.
  • Category B is applied to areas used mainly for residences.
  • Category C is applied to areas used for commerce and industry as well as for a significant number of residences.
In any event, space adjacent to a road carrying arterial traffic as an exception has a higher limit of 70 dB or less (Daytime) or 65 dB or less (Nighttime).

Loud noise can be very damaging to hearing. Both the level of noise and the length of time you are exposed to can put you at risk for permanent noise-induced hearing loss. Standards set by OSHA (Occupational Safety and Health Administration) indicate that continued exposure to noise over 85 dB will eventually harm hearing. They list following average decibel levels for everyday sounds.
  • 30 dB = whisper, quiet library (faint)
  • 40 dB = quiet room (moderate)
  • 60 dB = typical conversation, dishwasher, clothes dryer
  • 70 dB = busy traffic, vacuum cleaner, alarm clock (very loud)
  • 80 dB = blow-dryer, kitchen blender, food processor
  • 90 dB = subway, passing motorcycle
  • 100 dB = hand drill, pneumatic drill
  • 110 dB = maximum output of some MP3 players, model airplane, chain saw (extremely loud)
  • 120 dB = jet plane takeoff, siren (painful)
LTA has not pressured SMRT to accelerate the installation of safety barriers that could have spared 14-year-old Nitcharee Peneakchanasak from losing both her legs (they offered her $5,000 as compensation). Instead, they are embarking on an expensive exercise to shave 5 decibels.


  1. As the father of the victim said" $5000 can't even buy her a finger. The cost of their hospital bill came to $46k and a pair of prosthetic legs will cost another $100k." What's a peanut $5k going to help them do? Buy their one way air-tickets for the family back home? They should be sued heavily and be compensated for millions given she will be a handicapped for life. Two pair of good legs are gone for nothing..and she get to live through it. The poor indonesian boy who lost his innocent life (that could have been easily prevented) in the flood..where can his mother go? sigh...

  2. Hey you should be happy SMRT did not ask her to compensate for the economic losses suffered due to train disruption, LOL!

  3. Let me get this straight. My house in a residential area is protected by law to be no noiser than 55 dB or less. Then LTA builds a road nearby, and they are allowed to raise it to 70 dB or less because it's now a "space adjacent to a road carrying arterial traffic"? Who's the law around here?

  4. Well done...keep on pointing out their stupidity to ordinary singaporeans.

  5. So for a mere "5db" reduction, they intend to do a study on 500 blocks, and cited it as a "complex" installation. Waste of taxpayers money and clearly show where their priority lies. But hey, i'm not a resident staying near the tracks, so is unfair for me to deny them the "peace". But at least if you're going to spend millions on improving it, can't you do better than the insignificant 5db? That's like PUB squandering millions on high alert gadget installations but still can't stop the flood for good!

  6. Try going to the Ponggol area: RSAF jets take off so near to the residential areas, turn and fly over the houses at low altitudes: the noise are loud and painful. More residences are being built in this area. If the noise levels are indeed the law, then HDB is breaking them in Ponggol East.

  7. Think that they planning to award the contract to a GLC companies, so that the GDP figures would be "nice".

  8. The perfect solution is to build a tube or sleeve through which the vehicles or train passes through, that would keep all the generated noise within the structure where the road/rail is too near residential areas.

  9. I live across the road from Bishan MRT. The noise of the trains is nothing compared to the noise from the road traffic along Bishan Rd during peak hours. If only the authorities had bothered to consult residents first, rather than spend money on "improvements"...

  10. Limits set out in 1970 by the Ocupational Safety and Health Act for companies working for the US government stipulate that the Limiting Daily Exposure Time is 4 hours for 80 dB, 2 hours for 85 dB. Since LTA says current noise levels are at 80 to 85 dB, those staying in the affected Block 503 should go for a hearing checkup asap.

  11. The dB scale is logarithmic. That is, every 10 dB increases or decreases the sound level by 100%. A 5 db reduction is a 31.6% reduction in noise level.

    For sound level 'adjacent to the road', the intensity drops off by a variable amount as you move away from the road. If you have trees between your block and the road, or just an open area, the sound level drops quite rapidly even if you don't realise it. If you close your windows or use curtains (or both), it drops further. Whatever it is, the engineers aren't measuring sound from inside the flats!

  12. To Trebuchet,
    Increasing 10db means 10 times the power, you got it wrong, not "100%".
    For doubling of power you increase 3dB (log of 2 is 0.3010, muliply it by 10 for Bel to dBel conversion)
    Therefore when the proposal is to decrease the sound level by 5db, it is equivalent to more than halving the sound. TO the layman, 5dB may seem small, but because of the log scale 5dB change is actually rather significant, i think.


  13. Zero: Ah yes, got got it wrong; I meant factor of 10 but had a brain-fart when converting. Thanks.