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Category: BMW Sound System

Harman Kardon vs Hi-Fi vs Aftermarket Upgrade for BMW

Bart Donda

Apr 22, 2021

Harman Kardon vs Hi-Fi vs Aftermarket Upgrade for BMW

Wondering what the difference is between all the audio options and speakers for BMW? We’ve explained everything you need to know right here. In this guide you’ll find a comparison of the four standard factory BMW sound system options, alongside BimmerTech’s Premium Audio System and Alpha One speaker and amplifier upgrades.

If you're up for a BMW audio system and speakers upgrade, you’re in the right place. See what’s the best audio replacement kit for your vehicle.

But first, if you don't know which BMW sound system you have, decode your VIN and we’ll send you the full vehicle specification list.  Relevant option codes to look out for are S674A, S676A, S677A, S688A, S6F1A, S6F2A and S752A.


Base (stereo) sound system

Audio option: N/A

The Base system, as the name suggests, is the most basic audio option for BMWs. In some countries (for example the US and Canada) it’s not available in cars produced after 2012 and is replaced by the HiFi system as the standard option. That should be evidence enough that even casual music fans would be best advised to steer clear of this option.

Equalizer settings here are very limited, with the only options available being:

  • Bass/treble
  • Front/back
  • Left/right

It’s usually composed of 4 mid-range speakers and 2 underseat woofers. Tweeters are nowhere to be found here (which can be observed by the missing mesh tweeter grilles usually located inboard of the side mirrors or on the a-pillar covers), resulting in music that will sound dull.

There is no dedicated amplifier either; instead, the head unit itself with 4 audio output channels is responsible for the amplification, further reducing audio quality and maximum audio output. This may result in a lack of sufficient volume, and wishing you could turn it up more than your BMW allows you. Towards the end of the volume scale you may start experiencing distortion, so you might want to refrain from going all the way up.

What’s more, since the Base woofers can only be powered by the head unit, BMW opted to use 4 Ohm woofers, easier to power by weaker sources like the iDrive system head unit. For comparison, HiFi cars have 2 Ohm woofers, as the amplifier present in these systems is able to cope with the increased load of lower impedance woofers. Apart from the higher, easier to drive impedance, the Base woofers are “lightweights” both literally and figuratively, as they weigh hardly more than the air they take up and don’t produce much bass at all. What they do deliver instead is a rather unimpressive, cardboardishly boomy kind of bass.

Another piece of equipment that may or may not be present in the Base system is an ASD module. If it happens to be featured in the vehicle, it will be located in the trunk between the head unit and speakers. Its purpose is to inject fake engine noises into the cabin through the speakers, so it’s not the most desirable unit in terms of the sound experience. However, it does make the amplifier retrofit process much easier,as the bracket holding the ASD module comes with all the mounting points for an amp, too.

Base sound system

BASE (stereo) system upgrade

The lack of tweeters and a standalone amplifier are the two greatest weaknesses of the Base stereo, meaning owners of these vehicles will benefit most from a complete BMW sound system upgrade. Adding an aftermarket amplifier alongside tweeters* and beefy woofers as part of a replacement speaker kit will make a drastic difference to the audio quality in your vehicle. Starting from the bottom, the bass will become low-reaching, powerful and punchy, while being perfectly integrated into the smooth and detailed mid and high frequencies. Equipping your car with tweeters will extend your audio system's capability to deliver very high, crisp tones – while the Base stereo frequency response rolls off at around 12kHz, your upgraded system including tweeters will go all the way to 20kHz. Although the install of the whole Alpha One speaker kit and Premium Audio System amplifier will take a while due to additional wiring, it will undoubtedly be worth it in the long run.

*Base cars aren’t fully factory prepared when it comes to plugging in additional tweeters. That’s why it’s necessary to equip your car with the trim pieces that will hold the tweeters in your doors or A-pillars – you’ll get the details on necessary parts when ordering with BimmerTech. 

BMW HiFi sound system

Audio option: S676A 

A step above the Base stereo audio system is BMW’s HiFi (S676A) option. As previously stated, in the North American market almost all vehicles have the HiFi system as standard, while the rest of the world has to have it optioned in.

The BMW HiFi sound system is a noticeable upgrade with tweeters (usually 2), an additional midrange in the dashboard (usually found in later cars) and an 8-channel amplifier in the trunk (7 of 8 channels are used to power the speakers). What that means is each speaker or speaker pair (in the case of midrange+tweeter channels) has its own dedicated amplifier channel. This is a great improvement over the Base system, since the amplifier located in the trunk has quite a bit more power than one built into the head unit. Due to that change, the system can play louder with less distortion compared to Base models. Also, thanks to the more powerful amplifier, the woofers used in the BMW HiFi speaker system are more capable than their Base counterparts – they have a 2 Ohm impedance, go lower with the bass and deliver cleaner sound at higher volumes. Nonetheless, they will still be lacking some low end thump driven by the OEM amplifier, which is why it’s so beneficial for the HiFi system to get a powerful Premium Audio System upgrade.

BMW HiFi sound system

BMW HiFi system upgrade

You might ask – why start with upgrading the amp? All thanks to the beauty of DSP processing – we can EQ the decent factory speakers for a smoother frequency response and optimized stereo imaging, which makes listening much more pleasant. The BMW HiFi speaker system is especially well suited to give it that extra bit of power, detail and smoothness. Starting your upgrade with the amplifier will give you the best bang for your buck out of your factory speakers, and once you’re ready for the Alpha One Speakers let us know to supply you with a new tune for your amp that has been optimized specifically for them.

The installation of our amp is a DIY-friendly project that’s based on a straightforward plug & play job. No cutting wires or installing additional mounts and brackets. Just unbolt and take out your stock amplifier, and pop the new one in.

BMW Harman Kardon sound system  

Audio option: S674A

Another small step above the HiFi (S676A) option audio system is the S674A Harman Kardon system. Why only a small one? You might have been under the impression that Harman Kardon systems are pretty high up in BMW’s audio system hierarchy with their heaps of power and unpleasantly loud volume levels. But, here is the caveat - the Harman Kardon system present in 3, 4, 5 and 7 Series, X5 BMWs and others (listed under option S688A) is completely different to the S674A Harman Kardon option system which can be found in MINIs, 2-Series BMWs and i3s.

The amplifier used in S674A Harman Kardon vehicles is more like the one used in option S676A HiFi BMWs, featuring the same power levels and amount of channels. It’s more or less just like the HiFi system, but with slightly different speakers and coding in the head unit. The reason why BMW created such a system was most probably due to space constraints – the big, powerful, digital 10-channel Harman Kardon amplifier would have a hard time fitting in the smaller chassis cars. For many owners this comes as a disappointment. The good news is that S674A Harman Kardon vehicles can easily be upgraded with BimmerTech’s plug & play Premium Audio System and Alpha One Speakers upgrade.

BMW Harman Kardon sound system

BMW Harman Kardon (Top-HiFi) sound system

Audio option: S688A / S677A

Out of all four standard audio options, Harman Kardon (S688A) – with modest changes carried over from the earlier S677A HiFi System Professional – comes top of the pile. Some late E Series and early F Series models were produced with both the S677A HiFi System Professional and the Harman Kardon S688A, depending on model year. They have their differences, but both share a similar layout and amplifiers which have been described below.

With the BMW Harman Kardon surround sound system, you’ll find a surprising amount of speakers in your BMW — usually 16. Two underseat woofers, and 7 mid-ranges along with 7 tweeters placed all around the car as far as the eye can see :)  

When it comes to the woofers used in HiFi System Professional (S677A) and the Harman Kardon (S688A), they are also dissimilar from the ones present in all of the lower systems due to their 8 Ohm nominal impedance. Such high impedance woofers require very powerful low frequency output channels, which the Top Hifi amplifier has. It’s an interesting design choice, because as a rule of thumb you need four times the power that you would to move a 2 Ohm woofer. 

BMW Harman Kardon (Top-HiFi) sound system

The Harman Kardon amplifier has 10 channels, of which 9 are used, and is connected to the head unit by a fiber optic cable that transfers audio signals digitally (considered better than an analogue signal). Again, compared to amps of other systems, this one is undoubtedly the biggest and heaviest-hitting, with plenty of power on tap. In the head unit’s menu, you’ll find its multi-band graphic equalizer, much more useful compared to the bass/treble adjustment sliders available in the lesser systems, as well as a surround sound option which you can toggle thanks to the DSP processor. With these two, it’s possible to extensively customize the sound profile inside your car to your liking. 

BMW Harman Kardon upgrade

As any BMW Harman Kardon sound system review would agree, Top Hi-Fi is a significant improvement over the BMW HiFi speaker system. For anybody looking to upgrade their system at a later date, the fiber optic amplifier connection means most popular aftermarket amplifiers on the market will not be compatible with the system, including ours. Yet, while we don’t offer an amplifier upgrade for HiFi System Professional (S677A) and the Harman Kardon (S688A),  they’d still very much benefit from replacing speakers for our Alpha Ones. Immediately upon installation the mids and highs become smoother and more pleasant, but equally importantly our 7 Ohm woofers created for these cars, offer even lower reaching bass response.

As for the install, we made our speakers to match every bolt and screw of your factory kit, so replacing your speakers is as easy as disconnecting and removing the old set and putting the new one in. Fully plug & play, reversible project that will be manageable even for novice DIY-ers. 

See for yourself.

BimmerTech - Speakers & Amplifier Upgrade

Audio option: N/A

There are still many reasons to upgrade your BMW amplifier or speakers, and for BMW owners that need even better audio, BimmerTech provides an amplifier and speaker upgrade — the Premium Audio System and Alpha One Speakers



The amplifier features 64-bit digital signal processing (DSP), which allows maximum customizability with options such as EQ, crossover, delay, and others. Another benefit of the Premium Audio System BMW amplifier upgrade is an increased signal-to-noise ratio and a much higher output power, meaning more volume and clarity for the listener. 

When it comes to our Alpha One Speakers, they have a much higher quality build compared to the BMW factory speakers. Mid-range and tweeter quantity will vary, and depends on the number of factory speakers in your BMW and additional speaker slots in your model. As a BMW-specific kit, BimmerTech is able to offer kits tailored to your exact vehicle, and with each speaker designed to closely match the factory equivalent, installing your BMW replacement speakers is easy. Kits are fully customizable, letting you opt just for a BMW underseat subwoofer upgrade, or replacing all your car's speakers. If you aren't sure how to upgrade BMW sound system, BimmerTech's plug-and-play upgrade makes it easy.

Alpha One Speakers complete setBMW speaker placement. Please note: The base and Hi-Fi options will not have the full amount (16). The base system does not include an amplifier.

Both the Premium Audio System and the Alpha One speakers stand on their own two feet, but when you combine both of them with a designed DSP tuning file within the BimmerTech amplifier — you’ll be in for a ride.

As a side note, whenever upgrading your amplifier in a BMW equipped with ASD (Active Sound Design), we also recommend adding an ASD deactivation harness. This will get rid of the artificial engine sounds that interfere with your favorite music, and also obstruct the true sound of your engine and drivetrain – especially annoying if you have a powerful engine under the hood. 

Fully customized sound experience

At BimmerTech we’re fully aware that ‘one size fits all’ audio systems are never going to cut it in the long run, as every BMW is different, just like the music taste of its owner. That’s exactly why we’ve decided to equip our amplifier with individually tailored tune sets for specific BMW or MINI chassis and your preferences – the music you're listening to and the way you like listening to it.

Since a jack of all trades is a master of none, we felt it’s important to break the monotonous streak in the audio industry, and started to offer personalized audio systems. 

It’s vital to remember though, that with all the different audio options available, specifications only tell part of the story. You won’t truly know the difference an audio upgrade can make to your car until you hear it for yourself.

Follow the link for more information on the BimmerTech BMW speaker and amplifier upgrade.


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