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DP Tool Club 26
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1992-04-25
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ACOUSTICS is a discussion of some basic acoustics
fundamentals.
1. Most people can hear sound over frequencies of 20 Hz to
20,000 Hz. A piano will reproduce sound from about 50
Hz to over 10,000 Hz in the harmonics.
2. We can hear sound over a huge range in loudness. Most
people with good hearing can recognize sound as low as
0 db, the threshold of hearing. At about 120 db perm-
anent hearing loss occurs ( many rock concerts average
this level in the front rows ). The 120 db range of
loudness represents a difference of 1,000,000,000,000
times a noise at 0 db!
3. Technically speaking, a doubling of amplifier power is
3 db, but the human ear often needs volume differences
of nearly 10 db to qualify a sound as "twice" as loud.
( 1 db is the smallest audible increment in loudness ).
4. Our ear requires significantly more bass for low
frequencies to sound as loud as mids and highs at low
listening levels. This need originated the term
"Loudness" for the little circuits providing bass
boost at low levels.
5. Our hearing has a different frequency response for
different angles of listening. Our hearing is most
sensitive to high frequencies at the sides of our head.
We also listen in real time noticing timing differences
as small as 1/1000 of a second. This is why the direct
sound from a dash speaker, and early reflections off
the windshield, are often heard as a "smearing" of the
overall tonal quality. ( Another reason to keep
tweeters away from glass ).
6. Tremendous low frequency SPL's are possible inside a
car due to "small room" compression effects. It's like
sticking your head inside the woofer box!
More information and examples on this subject are in the
BLAUBOX user's manual.