Hello All,
This is my first post here so I guess some basics are in order. I purchased my 2018 SL450 in August from MB of Denver with about 7,000 miles on it. I never thought I would be a "convertible guy" but I drive with the top down at every opportunity. You just never know. I can post more info later but I want to get to the subject of this post.
I am an audiophile and a music lover so the original HK stereo proved to be a BIG disappointment. Really poor tonality no matter the settings chosen. I play almost exclusively from USB full resolution files. The original speakers are 80mm so a 4" driver can be installed with an adapter plate that any decent installer should have no problem with. This allows for better drivers to be installed and save the significant expense of replacing everything including perhaps the front end unit and amplifiers. I chose a set of Focal ES 100K speakers. These have a separate tweeter which should be mounted on the A pillar. This reduces the poor reflections from the original tweeter mounts which are also too low. Please see attached photo of my installed tweeters to see if this would work for you. I painted the body and screen of the unit with Krylon Fusion All-In-One Metallic Aluminum. It was the closest color to the interior covering on the A pillar to my eyes. Available at Lowe's. Your installer can do the painting of course. I just wanted to check the colors for myself.
I may take thing a little further in the future with a new amplifier and a second set of the same speakers, one for the center channel in the dash and one for the center rear. We shall see. The speaker setup is shown on the HK website. A bunch of the 80mm drivers and a pair of subs in the footwells.
In any event, the improvement in sound was well worth the ~$1,300 cost, for me anyway. As a cautionary note though, no speakers can be made to sound really good with both the top up or down. The acoustics are too different to get great sound with both. Most systems will sound pretty thin with the top open. You are almost dealing with an anechoic chamber. YMMV but top up would be the best for musical enjoyment.
This was the best compromise that I could find of sound versus cost. I hope this may help others who have an issue with the sound of the OEM setup.

A Pillar tweeter install.

 

You might want to look in previous posts about upgrading the crummy stereo in the SL. There are hundreds and hundreds of posts as to what some folks went through to get the system better. Welcome to the group!

 

The speaker installation looks great. Any concerns about the airbag that I think is located in the area your A-Pillar speaker is located?

 

Thanks for the info. I had already read all of those posts here and had done a general Google search. I was looking to get the best improvement for the money without getting into the amplifier, the other drivers, or the head unit. This was a relatively easy and moderately priced upgrade that most automotive stereo outfits should be able to handle with less worrying and expense on the owners part. It seems like a large percentage of the owners here use the car as a second or third vehicle in their stable so they might not want to drop a bunch of money on the stereo.
The stereo is one of the very few things that bother me about the car. In fact, it is the only thing I really disliked about it. I really am enjoying this car more than any other I have had in at least 20 years. It is my only vehicle as the weather in the Albuquerque area really is not that bad except for a few days where we might get snow that sticks.