we hear about decibel all the time when
shopping for I don't know a Bluetooth speaker a wireless antenna or whatever
else but many people I talk to are
shocked to hear that when one thing is rated at twice as many decb as something
else that does not mean it's twice as
strong or twice as loud let's start at
the beginning shall we the base unit in this case is actually the Bell named in
honor of Alexander grambell who achieved Fame and Fortune most notably for filing
a patent for the work of Antonio miuchi the true inventor of the telephone
anyway that's a whole other discussion call me we'll talk about it sometime the
point is one Bell represents a difference in a relative power of 10
with a decibel being on10th of a bell so
if one value is 10 DB higher than another it is an order of magnitude
greater whereas a 20 dcel difference would be two orders of magnitude greater
and so on and so forth well hold on a second lus if it's a unit of relative
rather than AB absolute measure then how can we possibly say something like this
is a 3 D antenna or this fan is rated at
21 DBS you see that a next to the
decibal symbol for that fan that is how
it's all about context decibel have been adapted for many different uses so they
can be expressed more easily by defining standard reference points or a base
value in the case of an antenna's gain reputable companies will rate them in
dbd or relative to a dipole while companies who want to show inflated
numbers will rate in DBI relative to an
imaginary antenna that radiates in all directions and then in the case of noise
the main focus of this video we use sound pressure level a measurement in
decb above a base value approximately equal to the threshold of human hearing
okay cool Linus uh now I know what a deciel is but logarithmic units are a
little hard to compare in your head when you're shopping for a cooling fan or air
conditioner or something so onebody told me that I can just kind of go well a 3
dbel gain is an effective doubling of sound well I heard from someone else
that it's 6 DB which is right ha this is
where things get really fun three DCB equates approximately to a doubling of
the power ratio but when we want an
amplitude ratio let's say to express relative voltage or a field quantity
like sound pressure level we need to square the amplitude which means that a
difference of 6 DB will equate to double
the voltage or double the sound pressure level if you measure it but that doesn't
mean to your ears a vacuum cleaner rated at 6 DB lower than another will actually
sound half as loud as the next leading brand or whatever your ears don't hear
increases in sound pressure in a linear fashion in fact depending on the
frequency of the noise the general rule of thumb is that it takes somewhere
between a 6 to 10 D increase in sound
pressure to achieve a perceived double
of loudness all right lonus I get it now
but why do we need a unit of measurement that appears to have been designed to
confuse people and make comparisons difficult fair question there is the bit
about how human perception of sound and also light actually is more closely
related to the logarithm of intensity rather than the intensity itself but the
main reason is that it allows the use of much smaller numbers in cases where we
need to compare values that can differ by many orders of magnitude instead of
saying these speakers go 10 billion
times louder than your weak human hearing threshold we just say it's 100
DB SPL but if you're sitting there worried about how you're ever going to
remember all of this fear not Wikipedia has a handy dandy chart that you can
reference next time you see a loudness rating in decb so that you have some
context for interpreting the otherwise truthfully pretty confusing numbers
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