BMW i4 Harman Kardon Audio Upgrade

BMW i4 Harman Kardon Audio Upgrade

In this article we will focus on how to make i4 Harman Kardon (S688 option) audio system sound better and last some tips how to upgrade base audio and HiFi 676 systems.

Harman Kardon surround sound is the best option available for i4 and it sounds decent when you boost bass and treble almost to max from iDrive. But in good sound system you don't need to do that. There are few ways to correct that; better speakers, more power and lastly DSP aka digital signal processor to get most out of everything as cars interior is not optimal space for audio even with good speakers and enough power. In this project we start with better front stage speakers and add a proper subwoofer to stock enclosure as sound clearly lacks low end bass. First quick look at what stock sound systems are made of.

BMW i4 stock audio options

Somewhere in 2019 iDrive 7 came as on option to G30 and this is where BMW sound systems changed compared to previous models and same applies to i4 with iDrive 8. Head unit is no longer basic 2DIN that provides 4 analog signals directly to speakers (base audio) or to amp (HiFi 676), or via optical MOST bus to HK/B&O/B&W amp. In iDrive 7/8 head unit is called MGU (Multimedia Graphics Unit) and signal to amp via Ethernet bus. Amplifier is called RAM (Receiver Audio Module) and like name says it has Radio receiver built in so it cannot be replaced.

But as electronics have evolved it seems that speaker quality in not the same anymore most likely because of cost savings.

Base Audio

This option currently exist only on i4 eDrive 35/40. It has 7ch RAM amp which 6ch are used for 6,5" door woofers and 4" midranges in front and back doors so 6 speakers total without tweeters. Impedance of all midrange speakers is 8ohm and door woofers 4ohm. All speakers has ferrite magnets and low quality.

HiFi 676

Hifi speaker system has most likely same 7ch RAM module that includes same speaker setup as in base audio but added low quality fabric dome tweeters at front doors and also there is center speaker with 4" mid and tweeter. In rear there are just 4" midrange speakers without tweeters as in all lower that 5-series BMW's. All fronts are 2-way components with passive crossovers for tweeters, except door woofers that are single speakers and slightly better quality than in base audio and also 2ohm so they get more power. Total 10 speakers. Compared to base audio all speakers have smaller and more powerful magnets.

Harman Kardon

Best stock option for i4 and has 7ch RAM module and 3ch Booster amp for door and trunk woofers. RAM module has better hardware for surround sound with two extra 2-way rear speakers to make that happen. 4" midranges are about same quality as in hifi, but tweeters are metal domes made by Harman Kardon in Hungary, same that BMW has used over 20 years. 8 ohm door woofers are also slightly better and there's classic 8" BMW style 8 ohm woofer in trunk that is used under the front seats in other BMW's. Enclosure is sealed approx. 8L and made of plastic.

Stock trunk subwoofer and RAM + Booster Amp

Harman Kardon sound?

For most people HK system sounds good enough and I don't blame. It's decent but really not in same level as in older ICE cars. Best sound settings are treble/bass 2 steps below max and no need to touch EQ nor surround. Of course that depends of individual "taste" but I think surround is for movies and music should come from front like you are in live concert. Stereo image is rather good for both front seats so BMW/HK has improved this a lot in iDrive 8. Some say that stereo is 2ch left+right but I think this is the best tuned BMW audio system with center speaker.

First notice about overall sound was that door woofers work a lot and panels were shaking. Not much coming from trunk woofer and definitely not much low bass at all so obvious improvement is more power and better woofer. Second notice was harsh sounding tweeters that needed to crank up to get some decent highs, but for longer trips listening of those is hard. Tweeters lacks smoothness and airiness and this has been common issue for these tweeters always.

Upgrading front speakers

First of all you need to replace all 2-way components to front meaning doors and center as they are "connected" to overall tune that Harman Kardon has made rather right. Problem is that there's not many options as space behind 4" door mids is limited under 40mm. There are few brand at least in Europe that will fit to doors, but no option for center speaker as it has narrower bolt pattern. Sure with right adapters everything is possible, but in this upgrade we went plug&play style with german brand Musway. Their 2-way components CSB4.2C has genius idea with different adapters to fit all BMW's and low profile neodiym magnets will fit to i4 doors. Also possible to go with full upgrade including rear speakers.

UPDATE: New DLS Cruise CRPP-BMW1.4 is better sounding option with silk dome tweeters. Half set for center also available -> CRPP-BMW1.4CTR

First and easiest is the center speaker. Just pry the grill off and four T20 torx screws hold the plastic frame where the speakers are attache and replace the speakers.

Musway center speakers.

Next we replace the front door speakers. There are plenty on videos in Youtube how remove G26 door panel for example -> HERE

NOTICE! There are few things differently in i4 compared to ICE 4-series. ICE cars have plastic clips in door panel that goes into holes in door. i4 has metal tabs on door that goes into holes in door panel. So i4 door panels are secured more tightly and you need a lot of force to pry it open. Best start from outer bottom corner and go bottom first towards front. Also one difference is that there is a slider tab on outer top corner that can't be pulled out. So upper rear corner is the last section and need to slide outwards to get the panel out.

Outer slider tab in second pic and door speakers removed.

Tweeter triangles are held by the door panels so you can just pick them up. Then just pull the connectors off and replace the speakers. Musway CSB4.2C components will go into place just like the originals. And while door panels are out it's good to put some sound deadening mat in both the panel and to the door.

In this project we also swap door woofers. As mentioned before most of the low bass is coming from doors and with new subwoofer there is no need for door woofers to go that low. As we cant raise the high pass filter we will use speakers that has naturally higher frequency range. Speakers also need to be 8 ohm and quite sensitive like stock speakers. First of all even finding 8 ohm 6,5" car speakers is difficult as most are 4 ohm. Luckily we came across some GAS Audio PSM68 (currently not available) woofers that has high 95dB sensitivity and frequency range of 100Hz->. That doesn't mean that speakers won't play frequencies under 100Hz it just means they don't play that well and that's the point to just boost midbass little.

Midbass wire colors

Left side: yellow/violet +, black/green -

Right side: black/white +, blue/gray -

Update info! We have tested several 4ohm woofer and there is crackling sound coming from amp so need to be 8ohm. There is one exception AI-Sonic Solo 6 works and sounds great and has maybe slightly bigger resistance as 4ohm. But quite expensive high-end speakers and sold as per speaker -> Solo 6

Cheaper 8ohm upgrade woofers now in stock -> Dayton Audio DC160-8

For install we used modified MDF adapters that are originally meant for BMW E46 compact. Also some STP BiPlast 5 ja 10mm PU-mat for sealing and to top of the speaker so it is pressed tightly to door panel (not yet put in pic). Also some CTK butyl strip for speaker wire hole to make it airtight.

Upgrading trunk subwoofer and adding an amplifier

Rear subwoofer is the most important for good audio in i4 but stock one lacks output. If you take the plug out you almost can't tell any difference. Stock 8" woofer is same kind that are used in other BMW's under the front seats. Only difference is that it's impedance is 8 ohm same as door woofers and aftermarket ones are always 2 or 4 ohms. We tested several aftermarket 4 ohm woofers and stock Booster amp apparently can handle 4 ohm but only in trunk not in doors. Best one was Ground Zero GZCS 200BMW-SW4 and it gave +4dB more SPL measured on top of woofer. We tested it about one week to loosen up suspensions but the difference was so small that it's not worth the money. Easy swap though.

We also tested Gladen RS-X08 subwoofer as we had perfect adapter for that, but the stock amp didn't have enough power to play it any better than stock woofer.

Testing different 4 ohm aftermarket woofers.

So with real subwoofer you need more power so additional amplifier is necessary. Active subwoofer would be a good choice and some have installed for example Audison APBX 10 AS2 that fits to same location where stock enclosure is and sounds amazing. Or even smaller Audison APBX 8 AS2 would beat the stock woofer 100-0.

One important thing you need to take into account is that stock Booster amps speaker signal is 25V+ so in most cases LOC (Line Out Converter) is needed to transform speaker level signal to low level RCA signal. Most amps hi-level inputs take only 8V or some maybe 18V and for example Audison APBX active subs take up to 22V but that's not enough. RAM and Booster amps are regular AB-class amps so amps and LOC's wake up normally seeing DC Offset so no signal sensing is needed, but the main thing is that voltage handling.

But there is one new lineup of amps that can handle voltage up to 32V and work perfectly with i4. We have installed several and one of the best amps we have come up so far. The brand is AI-Sonic and all products are designed in Finland. I personally know the guys behind the brand and every technical aspect has been made perfect. My personal best features besides 32V hi-level inputs are warm and natural sound, more power than promised and really linear bass level knob with clipping led indicator.

For example AI-Sonic S2-A500.1 with 600Wrms @ 12V is plenty of power even for bigger sub. And i4's DC-DC converter gives constant 14,4V so the power output is even more. With just amp you only need to route speaker cable from stock woofers connector to the amp and and back so no need to add LOC in between and power it and remote wire etc.

In this project we wanted to do full Musway audio setup (except door woofers as Musway don't have 8 ohm woofers) and LOC was needed. Good LOC's that can handle 25V+ are for example:

Audio Control LC2i

Connection SLI 2.2

DD Audio SC-2

DD Audio BSI-1

Helix AAC.3 HP

We chose this time DD Audio SC-2 and Connection SLI 2.2 is also good and both are just 49 / 59,9€. DD Audio BSI-1 is also a good choice if amplifier don't have bass level knob (included in BSI) and also it has some EQ properties for boosting bass.

Musway amplifier and connecting to 12V

Like in every electric car there is 12V battery that powers most of the usual stuff like infotaiment systems, lights, seat heaters, wipers etc. 400V battery is just for drivetrain and maybe some EV accessories like heat pumps. So basically everything in EV cars works on 12V like in ICE cars.

12V battery in i4 is located under the hood. But there's no need to tap directly to battery as there's main fuse box behind the right side trunk panel where direct main cable comes from the 12V battery. We don't go into details as there's already a Youtube video about that ->

Amplifier we chose was Musway ONE600. Compact size and good power with bass knob included. Amp also has "pure amplification" button that bypasses internal filters so the signal coming from stock amp is exactly the same as for stock woofer. LOC we installed to the left side just because story continues in the future with DSP amp, so it was convenient to wire power and RCA there. Easier place for LOC would have been right side near the fuse box but as mentioned before more easier is to use AI-Sonic amp.

Power from fuse box and LOC & amp installed.

Amplifiers remote for adjusting bass.

Soundproofing stock enclosure and adding a sub

Sealed stock sub-box has decent ~8 liters or 0,283 cubic foot volume for many 8" aftermarket subwoofers so we decided to try make it better. Box is plastic but seems quite sturdy as there are wavelike shapes and supports all over. But better to be safe than sorry so we added layer of STP Black Gold 2,3mm butyl mat outside and on top of that STP BiPlast 10mm PU soft mat so that there's no resonances.

Subwoofer that we chose was Musway MWS822 8" shallow mount. This is brand new sub from Germany based Musway and price-quality is super good. Good power handling, long 30mm throw and top of the line materials like glass/carbonfiber cone, butyl top surround, big 40oz magnet and 2" copper 2+2 ohm dual voice coil. So with Musway ONE600 we get over 600Wrms to sub that can handle 250Wrms and that's perfect. It's always better to oversize amp output at least slightly rather than trying to drive big woofer with low power. Low power usually means distortion that burns the speaker if pushed too hard too long.

For Musway sub to fit we used plastic bmw speaker adapter between the sub and the enclosure. It's very important to get airtight seal otherwise there will be extra noises and sounds like the sub is not working. But it will and BiPlast mat + CTK butyl cord are good sealing materials. 

And while you are at it it's good to put some butyl mat to the trunk. Not to make the car more silent but to make bass sound more full. We have tested this in many cars and it definitely makes a difference and prevents rattling of panels. And just for looks we wrapped top of the enclosure with carbon fiber vinyl.

So how does it sound?

Sounds Great! The most biggest improvement was adding an amp and better subwoofer. Musway MWS822 works perfectly in small stock enclosure and hits hard and goes deep. Now bass from iDrive can be set to zero/middle and bass level can be adjusted using the knob. Sure 8" has its limits and SPL most likely would be better with bigger wooden box, but we wanted to test if making stock box better works and it does. Even better than we expected. And surely this is not where we stop. Amp is ready so testing different passive subwoofer boxes is easy. Or even making a fit-box with bigger element. We have been in discussion with Poland sub-box manufacturer Basser and they promised to make enclosure to i4 as soon as they get car in their workshop.

Next best improvement was swapping front mid-hi speakers meaning front door and center dash 4" + tweeter components. Now treble boost +2 from iDrive is enough and sound is more balanced. Vocals & highs sounds clearer and overall much easier to listen. There is still slight harshness in Musway tweeters as they are metal domes just like originals, but still way better that stock ones. And because of limited space behind door midrange speakers there isn't really other options to do full front swap including center speaker at the moment.

The last improvement was door woofers that we found hard to find speakers that has 8 ohm impedance. We tested several 4 ohm woofers like Musway, Audison, DD Audio but there was clipping noise in every bass beat so for stock amp those need to be 8 ohm. Even though with sub+amp we could lower bass from iDrive to center, we wanted to have some more punchier midbass coming from the front doors. We had one brand for testing but those ware made in country that is attacking to another so we don't want to mention those. But GAS Audio from Sweden had 6,5" SPL speakers in selection and those did the job. Not much throw and best suited frequencies over 100Hz but that was the point. And those works. Not a huge difference compared to stock woofers as filters are fixed from stock amp, but slightly better midbass kick as we hoped for. So we will definitely keep them.

We have done over 150 audio upgrades for customers cars during 5yrs of business and i4 one of the best cars to enjoy good audio. There is something that Harman Kardon has made right with i4 stock amps. Power output is decent (except trunk sub), stereo image is spot on. It's just that speakers are bad. So with better speakers and trunk subwoofer i4 great car to have good audio experience.

But this is not the end of the story. We already tried to install Match UP 10DSP but there was a problem with Match harness as ICE cars has 2ch Booster amp and i4 has 3ch so it didn't fit. We have been in discussion with Technic PnP and they are looking into it. 

Sub and speaker kits

We have made a ready set for upgrading stock Harman Kardon woofer with Musway MWS822 that includes everything. Amp we chose is AI-Sonic S2-A500.1 with bass-knob. With AI-Sonic there's no need for LOC as it handles signal voltage up to 32V so install is much easier.

Kit can be found ->

And heres kit for Musway front stage that fits all audio options ->

NEW speakers from DLS that fits i4 and are better sounding -> and center:

How to replace rear door and shelf speakers?

Rear door speakers are quite easy. Just two T20 torx screws and panel can be pulled out.

You can check pictures from this Base Audio and HiFi 676 upgrade blog ->

Only difference is that Harman Kardon has tweeters in door panels so those need to be replaces also and attach tweeter crossovers there.

Shelf speakers

These are present only in Harman Kardon option and provides more sound to overall experience than rear door speakers. So if thinking of replacing rear doors or shelf better option is shelf. But replacing those is little bit tricky as grilles won't come out at the top so some panel removal is needed. First it's good to remove trunks upper plastic trims where trunk lid openers come out. Those come off by just pulling out sideways. It also helps if trunks side panels are removed as there are two screws there that hold the inside part where speakers are attached. Here are instructions how to proceed from there:

1. Pull out rear seat side cushion from top. White big plastic fastener usually leaves attached to chassis so that needs to be removed and put back behind side cushion before putting it back. When putting back bottom part first to holes and then top just clicks in.

2. Pry C-pillars plastic airbag tag out and you'll find T20 torx screw under it. Don't worry there is no airbag in there (it's in behind roof liner). Then just pull C-pillar trim out. There are two metal clips holding it at the bottom.

3. Take away upper roof liner plastic trim by pulling downwards. There are two plastic clips and then it just slides out towards forward of the car.

4. Remove two 8mm screwbolts at the front. Then pull out the plastic trim where speaker grille is upwards. It's attached with three metal clips. Now you see midrange + tweeter and mid would be possible to change here, but not tweeter so need to remove the whole plastic part where speakers are attached.

5. That plastic part is held with five black T20 torx screws. Remove those and notice that one is not easily visible from inside as it's behind the tweeter. You can see it by looking outside from the window. Also seatbelts upper U-shaped iron needs to be removed and it's held by two T40 torx bolts.

6. Now the plastic part where speakers are attached is almost loose, except there is one clip in the backside that is tricky to release. You need long screwdriver and push it upwards to release panel and then just pull it out towards front of the car and flip to the side. Last picture shows where to push.

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- Kimmo / Audiokit


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