# Difference between 36 and 42db of noise isolation?

I do want to install various soundproofing improvements in an apartment, but when equipment and materials indicate the level of isolation, I really cannot judge at all the difference between them. I saw many charts of hearing db scale but those are really rough approximations, and If I'm correct, db scale is logarithmic, meaning for me that small differences can have huge impact or, oppositely, huge differences can have small impact when I move toward the biggest numbers or towards 0.

So, for instance, last thing I was looking into was the entry door. Many announce about 36-39db where others, usually more expensive says 42db.

But what is the difference between 36 and 42db ? Can I hear the difference clearly ?

Can I "test" or "emulate" that somehow ?

• 6db............. Commented Jan 27, 2015 at 20:59
• Well.. sure.. But that was the point: 6db from 0 to 6 and from 100 to 106 does not mean the same thing for hearing, right ? Commented Jan 27, 2015 at 21:12
• Find hearing protection with the same ratings? It's going to be difficult to reproduce. You may need to stack earplugs and earmuffs, since most earmuffs top out around high 20's to low 30's dB reduction. Commented Jan 27, 2015 at 21:16
• It supposedly does mean the same thing. It is scaled. This is not like earthquake measurements. Might find a more scientific answer in other stacks but human ear won't notice much from 36 to 42db. Commented Jan 27, 2015 at 21:17
• @Doresoom Why is it not like earthquake measurements (although I don't know anything about earthquake measurments..) ? for instance, on wikipedia I can read A change in power by a factor of 10 corresponds to a 10 dB change in level. A change in power by a factor of two approximately corresponds to a 3 dB change Or there is something stupid I don't get (that may be the case). Commented Jan 27, 2015 at 21:24

Every 3db is double the power of the signal (amplitude), however this is also the point at which most humans report hearing a noticeable difference. Most humans will perceive the volume to double around 9-10dB.

So if you found one door that offered 30dB of noise isolation, and another that offered 40dB, you would say that the 40dB is "twice as quiet as the 30dB", approximately.

In reality, your sensitivity to sound is not linear so it really depends on the frequency of the noise. You are less sensitive at the high/low extremes and most sensitive in the center of the range. Likewise, as you get older, you tend to lose sensitivity to the extreme frequencies first.

• Thank you ! So I guess you answered the root of my question: If I could say 10db is "twice as quiet", I guess that 5 or 6db can be quite noticeable at this level. Commented Jan 27, 2015 at 21:28
• Yes you would definitely notice it. Commented Jan 27, 2015 at 21:48
• You should also note that the reduction rating for anything will be related to frequency, either the reduction at a given frequency (e.g. 1000 Hz) or maybe a weighted average, but in general you can expect the reduction to be much less at low frequencies, such as the bass component of music. This is what will usually end up annoying your neighbors, so it's something to consider. Commented Mar 10, 2015 at 5:52

The best practical option may be to go check the difference between various types of hearing protection. You'll most likely have to stack earmuffs and earplugs, since most earmuffs top out around 30 dB reduction.

For an analytical comparison, say your front door is 10 meters from the street. A passenger car produces about 60-80 dB at this distance.

So for your 36 dB reduction door, your experienced levels immediately behind it would be 24-44 dB. This range corresponds to a "very calm room" to the low end of "normal conversation."

For the 42 dB reduction door, experienced levels immediately behind it would be 18-38 dB, which corresponds to a "very calm room," but doesn't reach levels of "normal conversation."

Note that as your distance increases from immediately behind the door, there's also a further decibel reduction.

Wikipedia sound pressure levels

I can recommend dB meter app for the iPhone. It measures not only the dB level, but shows a live spectrum of noise real time. You can set up a loudspeaker on one side of your barrier (door, wall), measure the speaker directly, and then through your barrier, and that will give you the attenuation for the particular spectrum you are playing from the speaker.