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2015 SLK250 D
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5 Posts
Discussion Starter · #1 ·
Since getting my 2015 R172 250D AMG Sport in October 2020 I've been less than impressed with the Audio 20 sound quality.

I mainly listen to DAB radio and in order to get anything that's at all listenable to I have to set the Bass to +2 and the treble to -9. Otherwise, the sound is overwhelmingly harsh and tiring to listen to. With these setting though it still doesn't sound quite right.
Being a retired electronic design engineer I decided to investigate further and this is what I found:

There are six speakers, a Bass unit in the front bottom of each door, a Midrange unit in the panel behind each seat where the seatbelts emerge and a Tweeter in the top of each door.

Ideally these speakers should be driven by a passive crossover or a configurable active equalizer in order to route bass frequencies to the Bass units, midrange frequencies to the Midrange units and treble frequencies to the Tweeters. This will result in balanced sound across all frequencies.
Herein lies the problem. The Bass units seem to be driven directly and so receive all frequencies as do the midrange units. The Tweeters do have a capacitor soldered to the back of them (4.6uF) which, in simplified terms, means the Tweeters will only handle frequencies above about 4kHz. This means that far too much midrange and treble sound is being put out by all the speakers combined leading to very harsh sound with the Treble control set to zero.

I have looked for an equalizer when in the Engineering Mode menu but there isn't one so the sound can't be corrected there.

I know many owners have upgraded the amp and speaker system and of course the upgrades either come with an active equalizer in the amp or a passive crossover.

I thought I'd leave the existing speakers in place and add my own passive crossover to the speaker system to see what sort of results I could get and once I've finished I'll post an update.

One easy improvement I found is to disconnect the seatbelt panel midrange speakers temporarily so I've done that for now.

I really can't understand why Mercedes couldn't have done even a half decent job on the standard audio system. Well actually I can - it's to get you to part with a shedload of cash for one of their upgrades!
 

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2011 SLK350
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58 Posts
Hifi is so subjective and depends on what your used to. I came from a none Bose mk1 TT that was terrible with no stereo separation at all so to me the SLK is brilliant! I have noticed that the sound seems to be tuned to be miles better with the roof down than up. Roof up I agree that it does sound harsher but I don't back off the treble as much as you. I haven't heard the HK system so I don't know what I'm missing.
 

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2015 SLK250 D
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5 Posts
Discussion Starter · #3 ·
You're right, sound is very subjective.
I don't listen much with the roof down but with typical UK weather most of my driving is with the roof up so I want the best sound for then. I just find the stock setup, with the treble and bass set at zero, incredibly harsh and I can't stand to listen to it for long.
I've currently disconnected the two rear speakers mounted in the seta belt panel and connected a 3.3 Ohm resistor in series with the two door tweeters and find that gives a much better balanced sound that I can happily live with.
When I can be bothered, I'll remove the door panels and apply some damping materials to the door and panel to try and get rid of some of the bass boominess.
Keeps me out of mischief I suppose!
 

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*Registered
2011 SLK350
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611 Posts
I had these fitted, with dynamat - probably the best investment I’ve made in my car,

 

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*Registered
2011 SLK350
Joined
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58 Posts
You're right, sound is very subjective.
I don't listen much with the roof down but with typical UK weather most of my driving is with the roof up so I want the best sound for then. I just find the stock setup, with the treble and bass set at zero, incredibly harsh and I can't stand to listen to it for long.
I've currently disconnected the two rear speakers mounted in the seta belt panel and connected a 3.3 Ohm resistor in series with the two door tweeters and find that gives a much better balanced sound that I can happily live with.
When I can be bothered, I'll remove the door panels and apply some damping materials to the door and panel to try and get rid of some of the bass boominess.
Keeps me out of mischief I suppose!
Let us know how you get on...I like a good project myself. 👍
 
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