
Home  Forums  Rules  Articles  diyAudio Store  Gallery  Wiki  Blogs  Register  Donations  FAQ  Calendar  Search  Today's Posts  Mark Forums Read  Search 
Everything Else Anything related to audio / video / electronics etc) BUT remember we have many new forums where your thread may now fit! .... Parts, Equipment & Tools, Construction Tips, Software Tools...... 

Please consider donating to help us continue to serve you.
Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving 

Thread Tools  Search this Thread 
24th May 2012, 03:28 PM  #1 
diyAudio Member

3 dB
Like to start this thread to take away a lot of misassumptions about Voltages , Watts and the coupling of those lovely things to our human ears .
I read this forum almost daily and I’m still surprised ( but understanding ) members asking questions , that would be all “answered” under our human ear “3dB” rule . I can explain this Logarithmic stuff , but there must be a teacher out here on this forum that will do much better than me ! so come one , please explain the 10log and 20log stuff ! Cheers , Rens
__________________
If you measure, you know; if you guess, you don't 
25th May 2012, 11:54 AM  #2 
diyAudio Member
Join Date: May 2007

I'm not sure what you mean by the human ear "3dB rule".
Decibels are a way of describing ratios. Because adding and subtracting are easier for humans to do than multiplying and dividing, we make use of the properties of logarithms (which are the inverse of exponentials). The maths is taught in a high school near you. The Bel is simply the base10 log of a ratio. It was found to be inconveniently high a measure, so instead we use a tenth of a Bel  a decibel. To get a ratio in dB you take the log and multiply by 10. In electronics we are mainly interested in power ratios, so take the base10 log of the power ratio and multiply by 10. The result is the power ratio expressed in dB. Power goes like voltage squared. To square a number you double its log, so to get a power ratio in dB from a voltage ratio (e.g. a voltage gain) you take the base10 log of the voltage ratio and multiply by 20. This is only strictly correct if the same impedance is used, but there is a convention in electronics that when we are only interested in voltage gain we use dB anyway and ignore the impedance difference. So 6dB could mean a strict power ratio of 4, or it could mean a voltage ratio of 2. The context should make it clear which is meant. In the case of equal impedance the two ideas are the same. I don't know if this deals with your question, but it is an area where people seem to get confused and sometimes confidently assert wrong ideas which they have picked up. 
25th May 2012, 11:58 AM  #3 
diyAudio Member

I had a column in one of the previous diyaudio newsletters explaining all this in somewhat more detail.
In case you missed it, it should still be on teh forum. Not sure what the '3dB ear rule' is  never heard of it. 3dB of course simply being the point where the voltage level has decreased by 3dB to 0.707 times the starting value. Is that what you mean? jan didden
__________________
Whether we like to think of it this way or not, an audio engineer shares the professional goal of a magician  Richard Heyser Check out Linear Audio! 
25th May 2012, 12:02 PM  #4 
diyAudio Member
Join Date: Mar 2002

I think the ' rule ' is that 3db is the minimum audible
change in level.
__________________
https://www.youtube.com/watch?v=4pBPnds67o0 
25th May 2012, 01:47 PM  #5 
diyAudio Member

That's not correct. There are documented tests that fractional dB differences are audible.
What may be meant is that 3dB difference is perceived as doubling of sound level (not sure it actually is though). Probably need to look up on the FletcherMunson or similar graph. jan
__________________
Whether we like to think of it this way or not, an audio engineer shares the professional goal of a magician  Richard Heyser Check out Linear Audio! 
25th May 2012, 02:01 PM  #6 
Did it Himself
diyAudio Member

10dB is percieved as doubling of sound level.
3dB being the most commonly noticeable change is something I have heard said before. It's kind of a good step.
__________________
www.readresearch.co.uk my website for UK diy audio people  designs, PCBs, modules and more. 
25th May 2012, 03:08 PM  #7 
diyAudio Member
Join Date: May 2007

3dB is half power, but I'm not sure what that has to do with ears.

25th May 2012, 03:27 PM  #8 
diyAudio Member
Join Date: Feb 2008

Phon curves are a better way to describe perceived sound level. 10 phon is a doubling, meaning from 10 to 20 there is a doubling, and from 70 to 80 ... and so on.
As it happens, 10 phon is 10 db @ 1 kHz. But not necessarily 10 dB at other frequencies.... Equalloudness contour  Wikipedia, the free encyclopedia
__________________
dipoles dipoles dipoles dipoles dipoles dipoles dipoles dipoles and dipoles 
25th May 2012, 10:02 PM  #9  
diyAudio Member
Join Date: Mar 2002

Quote:
3db is 'measureable' as doubling of level, but is the (commonly) least perceptable change. Hence the logarithmic scale used.
__________________
https://www.youtube.com/watch?v=4pBPnds67o0 

25th May 2012, 10:07 PM  #10 
diyAudio Member
Join Date: Feb 2008

Wrong. Its easy to hear much smaller changes in level than 3 dB.
__________________
dipoles dipoles dipoles dipoles dipoles dipoles dipoles dipoles and dipoles 
Thread Tools  Search this Thread 


Similar Threads  
Thread  Thread Starter  Forum  Replies  Last Post 
Two versions of Fane's Full Range Model "Studio 5M"  100 db and 92,5 db ??  tiefbassuebertr  Full Range  10  8th December 2015 01:41 PM 
Audax PR170M0 –100 dB or just *94 dB??  rick57  MultiWay  44  22nd December 2013 01:50 AM 
Why 3 dB?  gmphadte  Solid State  6  20th September 2011 11:10 AM 
116 db peak db how loud is that  8cube  MultiWay  21  8th November 2007 07:45 AM 
Coverting dB/2.83w to dB/1w  moving_electron  MultiWay  27  9th March 2004 03:47 PM 
New To Site?  Need Help? 