contrary to the opinions of the above 2 posters, this guy isnt full of BS ;)
Giles <
[email protected]> wrote:
>My question is two fold: why would speakers need breaking in ? Is
>anyone aware of any measurements and tests having being done of before
>and after performance that has shown a measurable difference?
I am aware of at least one person who has done extensive measurements
of this type: me. I have a database of several thousand drivers that I
have measured.
>I have been able to think of only one mechanism attributable to the
>speaker that to me could conceivably be at play if there is indeed an
>effect. It is that the elastomeric materials that form the suspension
>of the cone of a driver are somewhat stiff to start with and become
>more pliant through use, thereby allowing the cones of the drivers to
>move more freely with use.
>I don't believe this though, as an elastomeric material that exhibited
>such a change in properties would surely continue to 'loosen' over
>time so as to go beyond the point of aurally optimum elasticity so
>that there was an eventual degradation in sound quality such as when
>the voice coil made some unwanted high speed excursions into
>stationary bits.
Well, there are, indeed, several mechanism that are, indeed, at work
that cause the operating parameters of drivers to change through use.
However, the notion that once one gets a speaker home it requires
"breaking in" suffers from several problems.
First, as a driver comes off the line, it's actual performance if
fairly far from it's intended performance target. Reasons for this
include the fact that the centering spider, typically manufactured
from a varnish- impregnated linen, is far stiffer than needed. Working
the driver back and forth lossens the spider considerably.
Now, one might say: there's objective proof of the need to "break in"
a loudspeaker! Not so fast. The break-in period for the spider is on
the order of several seconds, and if it takes you several seconds or
minutes or whatever once you get the speakers home to loosen the
centering spdier, it's not proof of the need to break thme in, it's
proof that the speaker you just bought HAS NEVER BEEN TESTED!
But, on to other points.
When I measure a driver, I can see a significant change in a variety
of operating parameters as the speaker is driven. Usually, in woofer,
the resonant frequency drops as the speaker is used, often by as much
as 10-20%. This is due, as you suggest, to a relaxing of the
elastomers used in the suspension.
However. If I turn the stimulus off, within a few minutes most, if not
all, of the change has completely recovered, and we're back to go
again. The elstomer has recovered from it's stresses (this is
especially true of certain polybutadene-styrene surround
formulations).
There are plenty of other, real, physical changes. For example, one
can see a reduction of the electrical Q with time under heavy use,
simply because of the positive temperature coefficient of the
resistance of the voice coil. Allow the speaker to cool down, and it's
completely recoverable.
Get it hot enough, and you might permanently loose some flux density
in the magnet. But you have to get REAL hot to do that. Hotter than
most of the compounds used in making a speaker can endure without
catastrophic failure (damned few glues, varnishes, cones and
insulating materials can withstand the temperatures neede to reach the
Curie points of the typical magnetic materials found in loudspeakers).
>What I really think is at play in all this is the adaptive signal
>processing abilities of the brain. It is not the speakers which get
>broken in, rather it is ones 'ears'.
When this has been suggested, despite the fact there's about a century
of research backing it, it is more often than not greated with jears
and cires. See, you can't sell special "break-in" CD's if the speakers
aren't broken in.
>I would be interested to hear other opinions on this.
Well, there will be loads of opinions. However, actual data on several
thousand drivers don't seem to give two shits about opinions, the
usual claims of "mysterious unmeasurable quantities" notwithstanding.
--
| Dick Pierce |
| Loudspeaker and Software Consulting |
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