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Oil Immersion Lens
Name: Matt
Status: Student
Grade: 9-12
Location: CA
Country: United States
Date: May 2007
Question:
Do speaker magnets "age"? A guitarist was
explaining his preference for older speakers
because he said that the field changes over time
(like 20-30 years) and provides a more compressed,
rolled-off output. He described this as a subtle,
yet noticeable effect. What is the science behind
this?
Replies:
Hi Matt,
The only thing a magnet may do as it ages, is to get a little
weaker. If the speaker sounds better with a slightly weaker
magnet, then all the manufacturer needs to do is to use a
weaker magnet in the first place. There is no magic here!
In a sealed box speaker, "Hoffman's Iron Law" states that
there are only four things that affect the speaker's output.
They are efficiency, "motor strength" (strength of the magnet
and coil assembly), box volume, and low frequency response.
These four things can be played off against each other for a
desired result. For example, you can get good low frequency
response (that is, good bass) in a small volume, but you may
need to sacrifice efficiency and therefore require a lot of
power to drive it. If you want good bass, and high
efficiency, you may need to employ a larger cabinet.
One interesting point is increasing the strength of the
"motor" by using a stronger magnet will certainly increase
mid range and high frequency efficiency (the speaker will, at
these frequencies, be louder for a given power input), but
the low frequency response will in fact suffer as a result of
increased electromagnetic damping.
Conversely, if the magnet becomes weaker, low frequency
damping will be less, and there will be an increase in low
frequency output. Unfortunately this increase is as a result
of reduced damping and a more undamped, undesirable "boomy"
sound will result. For those who like this unnatural sound,
there are faster ways to achieve it than waiting for a magnet
to age, such as using a too-large cabinet than the speaker
requires, or, for a "ported" bass reflex speaker, you can use
an excessively large port. Personally, I prefer a speaker to
be as accurate a reproducer as possible; it should not add
phoney "coloring" to the sound that was not there in the first
place.
Mostly, though, I suspect the supposedly better sound is pure
imagination. Magnets simply do not age all that much.
Regards,
ob Wilson
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