#Jet engine decibel how to#

The change in orientation of the aircraft relative to the observer is often more important than the inverse square law. Most of the noise from an airplane is radiated behind it, from the jet engine exhausts. Actual measurements of real cases are much more reliable than calculations because all things are often not equal. There's a lot of information available about the aircraft noise nuisance so, rather than doing your own sums, it's probably best to read a lot (info from both sides). You need to get familiar with that stuff because a factor of 2 in the 'dB you quote' can be very important (it's not just twice the loudness but twice the number of zeros!!!. They often describe sound in terms of Sound Pressure Level (SPL) but, because the Power (intensity) is proportional to SPL 2 so the ratio of SPLs becomesīoth are equally valid but hopping from one to the other can give you a headache. a power ratio of 1,000,000 becomes 60dB and a ratio of 0.000001 becomes -60dB dB are worth while getting familiar with because it avoids having loads of zeros in the numbers you want to quote. Power Ratio (in dB) = 10 log (Power Ratio) and that works for all numbers you care to put in. The way logs work means that a ratio of 4:1 will be 6dB That means the power measured at 2km will be 1/4 the Power at 1km (all other things being equal ) The simplest way to think of the deciBel scale is that if two measured powers have a ratio of 2:1 then that's 3dB. sufficiently high up in the air), the received power will follow the Inverse Square Law. Doubling the distance reduces the sound volume by 6 dB.įor a source that's isolated from any other object (i.e.

#Jet engine decibel how to#

Summary:: How to calculate the reduction in airplane noise as a function of increased distance?įinally, one website about decibels said that they are logarithmic. So, how does the sound of an airplane overhead vary with distance? Or is it not that simple? How much of a reduction is decibels is significant or detectable? And what should the target decibel reading be?

Doubling the distance reduces the sound volume by 6 dB. I could not figure out what they meant by 'pressure'.įinally, one website about decibels said that they are logarithmic. Another one said that the sound 'pressure' has just an inverse relationship with distance (not the square).

One comfirmed what I thought about the inverse square relationship. But I checked a couple of websites and got confusing data.

If the plane is twice as far away, the sound I will hear is 25% (75% less). My foggy memory from my physics classes many years ago tells me that sound decreases as the square of the distance. I'd like to create a spreadsheet that will calculate the reduction in noise if the plane's altitude is increased from 4,000' to 6,000' or if its overhead path changes from 0.5 miles away from my home to 1.0 miles away. I got to wondering how much good that would actually do. I recently attended a meeting where various solutions were discussed, such as changing the flight path or increasing the altitude over residential areas. The city has been working with the airport and the FAA to deal with complaints about the noise the jets make as they come in for a landing. I live close to the (landing) flight path to a major airport.