MINI Speaker Upgrades
Sound Advice
n By Kevin Bennett, President Integral Audio
MINI Speaker Upgrades:
Why You Can’t Just Swap In New Speakers
A
equalization applied for speaker correction. The front woofer
only gets low frequencies, the rear woofer gets a mix of low and
midrange, and the rear tweeter gets only high frequencies. The
front midrange and tweeter share a signal, however, and get a
mix of mid and high (this is an additional problem, but is beyond
the scope of this article). All of this is a problem since any normal
aftermarket speaker set comes with its own passive crossover to
divide up the frequencies among the speakers. In order for those
crossovers to work they need a flat, full-range input signal. If you
tried to use a passive crossover inline here you’d end up with massive gaps in coverage where the filters overlapped.
So why not just try to replace the speakers without using an
aftermarket crossover? That won’t work either. No two models of
speaker are the same, and every speaker has unique physical and
electrical properties. Some readers may be familiar with Thiele/
Small parameters, which describe and measure these properties.
They include things like resonant frequency—the natural frequency
of a driver; various measures of Q—the strength of the tendency
to resonate; sensitivity—how much volume a driver produces for
a given amount of applied power; impedance—the frequencydependent amount of electrical resistance of the speaker. There
are dozens of these parameters, and the upshot is that speakers
vary dramatically. Two woofers or two midranges of the same size
and general appearance can be tremendously different from one
another,and one can’t be used as a substitute for the other.
The signal from the HiFi and Harmon/Kardon amps in MINIs
will only work with one set of speakers—the ones they came with
from the factory. This applies universally. Despite what you may
have read online you can’t, for example, use the speakers from the
Harmon/Kardon system in a HiFi system. What would happen if
you tried? You’d get less volume from the door speakers for starters—the Harmon/Kardon door and midrange speakers have lower
sensitivity (the Harmon/Kardon amp has more than twice the
power of the HiFi). The Harmon/Kardon midrange isn’t designed to
play as low as the one from the HiFi (note the difference in where
each of the green
curves drop off), and
pushing it lower will
increase distortion.
The tweeters in the
Harmon/Kardon
system, conversely,
have higher sensitivity. This would
deliver too much
brightness up front,
but even worse,
would deliver too
much high frequency from the rear
channels, damaging
the soundstage and
2008 R56 HIFI AM FREQUENCY RESPONSE
2011 R56 HK AMP FREQUENCY RESPONSE
imaging.
But wait, what
about the posts you’ve read online where folks claim to have upIf you’re thinking “yikes!” you’re thinking right. For those of you
graded their HiFi system with the Harmon/Kardon speakers and it
who aren’t sure what you are looking at, what you would want to
sounds great! Google “choice-supportive bias” and “confirmation
see here is a single, flat line. Instead, you can see that the frequency
bias”. As you’ve heard—don’t believe everything you read online!
division is built into the amp (i.e. crossovers), and there is significant
s much as you love your MINI,
you may not love its sound
system, so maybe you’re
thinking about upgrading your
MINI’s sound and replacing the speakers? Given the ease and price point,
this probably seems like a good option;
however, if better sound is what you
want, you’ll need to replace more than
just the speakers.
The first step in understanding
why is to understand the architecture
of the MINI sound systems. MINIs of all years had two options for
sound systems from the factory. Either the base 6-speaker stereo
(the Boost System) included as a standard option on all MINIs, or the
upgraded 10-speaker system (Harmon/Kardon or HiFi, depending on
the model year). In each model year the head unit (that’s mounted
in the dash) is the same regardless of whether you have the base or
upgraded system. The difference is what happens downstream from
the head unit. In the base 6-speaker systems, the head unit output
drives the 6 speakers directly. In the 10-speaker option, the output
of the head unit is fed to a separate 8-channel amplifier that powers the speakers. Why only 8 channels if there are 10 speakers? The
front door midrange and front tweeter share a channel. If you have
tweeters in the base of the A-pillar trim in your 2nd gen MINI, or the
Harmon/Kardon badge on the door woofer of your 1st gen MINI,
then you have the upgraded 10-speaker system.
Simply replacing the speakers just isn’t an option with the
optional 10-speaker systems. The amplifier does not output a flat
signal—there is significant equalization and filtering applied to each
channel. Take a look at the images below.
The first is the electrical output of the 8-channel HiFi amp in a
2008 R56 Hatchback (there are only 4 lines—left and right outputs
are identical), and the second is from a 2011 R56 Harmon/Kardon
amp.
8 | December / January 2014-2015 | MC2 Magazine
drive an aftermarket set of speakers well enough to compete with
The curves above also give clues to the major weaknesses
the high-noise floor of a moving vehicle. Well-researched readers
(and complaints) about the various factory systems. Look at the
differences in the two red curves (the door woofers). In the earlier may note that there are “high-efficiency” aftermarket speaker sets
HiFi systems, MINI tried to compensate for the poor low frequen- available that claim to be designed specifically to work with lowcy response of the factory door speaker by artificially boosting the power factory head units. That is true—sort of. The missing piece is
low frequencies coming out of the amp. This helps at low or very that there is a trade-off between efficiency and frequency response.
Within a given set of constraints you can design a speaker that
moderate volume, but the speaker can’t keep up at anything beplays loudly, or that has good low frequency response, but not
yond moderate volume and begins to distort heavily, resulting in
the muddy bass that so many HiFi owners are all too familiar with. both.
So what does all of this mean? The bottom line is that if you
In the Harmon/Kardon system, the door woofer gets a very
want to upgrade the sound system
large boost, centered around 75Hz.
in any MINI, you’ll need to plan on
The signal falls off rapidly below
replacing (or adding) an amplifier
75Hz. The result is the exaggerated
as well as replacing the speakers.
“boomy” bass that the Harmon/KarThe factory head unit can remain.
don system is known for. The rapid
[There is one notable exception to
drop off below 70Hz avoids the
this: the head unit in the R56 JCW
distortion of the HiFi system, but at
GP2 does not output a flat signal
the expense of having no true low
and must be replaced or equalized
frequencies reproduced.
when upgrading]. Use the head
What about vehicles with the
unit’s output signal to drive the new
base 6-speaker systems? In these
amplifier, and the amplifier to drive
systems, the speakers are driven
your new speakers. It’ll be more
directly from the head unit. As you
expensive and time consuming than
can see below, the head unit outreplacing just the speakers, but it’s
puts a relatively flat signal. There is a
the only way to get results that are
roll-off at the high frequencies that
2008 R56 HU FREQUENCY RESPONSE
better than what you started with.
can only be accounted for with a
custom-designed system, but overall the signal is relatively usable. The problem is a lack of power.
(Ed: We’re delighted to have Kevin Bennett as our audio columThe head unit—made for BMW/MINI by Alpine—only puts out a
nist starting this issue. Kevin is President of Integral Audio, where
little over 5 volts cleanly. This translates to only about 7 watts for
most aftermarket speakers. The passive crossovers in aftermarket he oversees all R&D and engineering of their acoustically-tailored
vehicle-specific audio systems. If you have a question, you can
speaker sets add impedance and increase losses even further.
reach him at: kevin.bennett@integralaudio.com)
While 7 watts is more than you might think, it isn’t enough to
MC2 Magazine | December/January 2014-2015 | 9
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