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R172 Speaker and Amp Upgrade

14K views 41 replies 11 participants last post by  katiebear00 
#1 ·
I've been searching for a few hours and couldn't find anything specific on replacing speakers/amp in a R172 with HK audio system. I'd like to replace with aftermarket equipment and I expect to do some modding of the stock speaker pods. Some decent info on R171, including door panel removal instructions, but I doubt it's the same for the R172. Can anyone point me in the right direction?
 
#2 ·
I've settled on the addition of a powered subwoofer under the passenger seat as my first mod of the audio system. I'm looking for a wiring diagram of the stock amplifier so I can tap the speaker outputs for high level amp inputs. The BBB wiring diagram doesn't seem to exist, and the WIS link from this thread seems to point to a Japanese link. Can someone point me in the right direction? https://www.slkworld.com/slk-r172-general-discussion/491601-where-can-i-find-purchase-wiring-diagrams.html
 
#4 ·
Thanks for the update.

Keep the pictures coming of the updates.
 
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#5 ·
Ran a 4 Guage power cable to the positive battery terminal. Part of an amp wiring kit that came with an 80 amp circuit breaker. There's a rubber grommet just behind the battery making it easy to pass through the firewall. Subwoofer should be delivered today.
 

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#6 ·
I purchased the WIS EPC and was able to find the amp wiring diagram attached. The diagram shows that each door has 2 woofers in addition to a midrange and a tweeter. Can anyone verify that's correct? It could also be a single woofer with a dual voice coil, but that's less likely. I'm going to tap the output of one of the woofers to feed as input to my new powered sub. My concern is that the amp may be using a crossover to limit the lower frequencies to one of the woofers. It certainly filters the low frequencies send to the smaller speakers - I testing this by temporarily attaching a larger speaker to the rear speaker outputs and go no bass response whatsoever.
 

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#7 ·
Subwoofer has arrived! It's thin profile makes for several mounting options. I'm rethinking my idea to put it behind the passenger seat. I may opt instead for the passenger footwell or the rear bulkhead. Some pics attached.
 

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#8 ·
Done! Pics attached. I ended up mounting the sub directly to the passenger footwell metal plate. The improvement in sound quality is surprising good. For less than $300 total, it takes the HK audio system from average to excellent. I was originally going to replace the door speakers, but it's sounds so good with the sub, I'm just going to keep them This is a pretty easy mod for anyone to tackle, and aside from research it took about 8 hours of my labor and basic tools. If anyone's interested I'll post a materials list and an as-built wiring diagram.
 

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#9 ·
How much space do you lose in the footwell? Bass is the one area that I believe that the HK needs improvement. This might be a great upgrade my system as well. I’m just debating about how “factory” it will look. I always try to make non-cosmetic improvements. Ones that you cannot see.
 
#12 ·
Here is my material list and pricing:


JBL Basspro SL 8" Subwoofer - $250

https://www.crutchfield.com/p_109BASPROS/JBL-BassPro-SL.html


Amp Wiring Kit - $20
https://www.amazon.com/gp/product/B00IYER9QC/ref=ppx_yo_dt_b_asin_title_o05_s00?ie=UTF8&psc=1


Circuit Breaker -$13 (More convenient than the fuse included in the amp wiring kit)
https://www.amazon.com/gp/product/B07CXSZL22/ref=ppx_yo_dt_b_asin_title_o04_s00?ie=UTF8&psc=1


Total : $283


If you're on a budget, there are cheaper subwoofer options with the same form factor like this one for $140:
https://www.crutchfield.com/p_777B8PTD/Sound-Ordnance-B-8PTD.html?search=powered_subwoofer



I may end up replacing the door tweeters, but the powered subwoofer addition is definitely the biggest bang for the buck
 
#15 ·
I think this is actually a low risk project. The only wiring you are cutting into are speaker outputs between the amp and the door speakers. Wiring to the battery is pretty straightforward also and does not require disconnecting the battery. The only potential hazard would be accidentally grounding the new power wire you attach the battery, and I eliminated this possibility by using the circuit breaker in my material list. You effectively switch off the new power wire until everything is hooked up and ready to turn on.
 
#16 ·
Are you not worried that somebody stepping into your passenger seat might break the speaker grille?
Having the seats being so low, and sometimes not being able to fully open my door (due to other nearby cars), I always step really hard into the passenger footwell area, before I am able to sit down.

That foam is there also for this specific reason, and now, being thinner...

The speaker is also now covered with the remaining foam, doesn't that affect the sound quality?

Also, did you consider putting the base into the trunk? Possibly into the spare wheel area?
Not sure how it would behave with the top down, but while the top is up, I think the trunk space would further amplify the sound quality.
I have also previously seen most people add their base system in the trunk for this specific reason.

I have retrofitted OEM Bose system into my previous R170. The placement of the additional speakers were on the back wall, just behind the seats, and the sound faced the driver/passenger.

I am no sound expert, just my 2 cents :)
 
#19 ·
Are you not worried that somebody stepping into your passenger seat might break the speaker grille?
No, it's a very stiff grill. The grill is strong enough that I can stand on top of it.


That foam is there also for this specific reason, and now, being thinner...
It was 3 inches of Styrofoam, presumably for sound dampening. There is additional foam on the firewall that I didn't touch. I haven't noticed a difference in cabin noise. Maybe because I'm cranking my tunes with my new sub. :smile: [/QUOTE]

The speaker is also now covered with the remaining foam, doesn't that affect the sound quality?
Not at all. Bass is non-directional. That's why subwoofers still work in the trunk and it doesn't sound like the sound is coming from behind you.


Also, did you consider putting the base into the trunk?

Possibly into the spare wheel area?
I did, but it seemed more difficult to me because it involves running wires further and removing more panels, trim, carpet, etc. There's another thread in this forum where a guy did a great job mounting it there.



Not sure how it would behave with the top down, but while the top is up, I think the trunk space would further amplify the sound quality.
I have also previously seen most people add their base system in the trunk for this specific reason.
Subs are installed in the trunk because that's usually where it will fit, especially for a traditional type sub, which is large. With the sub in the passenger compartment, the sound quality is likely better. But not by much.
 
#27 ·
Check the volume control and crossover setting on the sub to make sure it's not all the way down. Also check to make sure you tapped into the correct speaker wires, and that those connections are solid. I had to cut and untwist the 4 speaker wires I tapped into because there wasn't much slack to work with.
 
#28 ·
If you have a multimeter you can also measure the voltage across the speaker terminals on the sub. With the stereo off you should read zero volts. With the stereo on you should read a few millivolts, indicating a signal is present. If no signal is present at the sub try measuring the voltage at the tap in point or right at the amp connector. Lastly, keep in mind there are two bass speakers in each door, and my diagram shows tapping the output headed to one of those two speakers. This was an arbitrary choice, so you can also try tapping into the output of the other speaker.
 
#29 ·
I finally finished this project! Lol, I haven’t had any time, then after much anguish and many bad words, I determined the sub was bad which pushed this project back after I got the replacement.

It works and sounds great, @katiebear00 thanks for the tips and instructions! Have you given any thought towards speaker replacement? I’m not terribly interested in louder, but would love more clarity.

This was a pretty easy mod if there’s anyone out there considering it.
 
#30 ·
Great! Glad it worked out for you, and how frustrating to get a DOA sub. I am planning to replace the door speakers, but have a few projects in front of that (oil change, brake flush). My plan is to take off the door panel - there's a good video on YouTube, and then measure the approximate impedence of the existing speakers. I think they are 2 ohm speakers but I'm not sure. If I can't find any reasonably priced 2 ohm replacement speakers, I'll wire two 4-ohm speakers in parallel, which will present a 2 ohm load to the amp. This worked well on my whole-house audio system. I'll also plan to install some dynamat on the door. Surely someone has done this before on an R172??
 
#31 ·
I ended up going full on and upgrading to Dynaudio. Audiinson Bit1 Dac, Audison 6 channel amp and Audison Mononbloc amp for a fully active setup.

Upside: Sounds outstanding.
Downside" it definitely wasn't cheap!
 

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#41 ·
That’s strange! I’ve never heard of an R172 SLK having an amplifier in the trunk before! Here in the UK I think models with Comand but no HK use an amplifier built into the Comand head unit itself. It might be different on US models. Perhaps more audio options were available your side of the pond?

I do know there was an amplified speaker option between Audio 20 and Comand with HK on the R171 models but I’ve never heard of this option on an R172.
 
#42 ·
I'm attaching the wiring diagram for your COMMAND unit. It's showing speaker outputs, but they are boxed off with a note that says "not valid for audio system". This is consistent with a separate amplifier. I'm also attaching the MOST fiber optic wiring diagram for your vehicle, which further corroborates you have a separate amp. This is straight out of the WIS manual for your specific vehicle based on your VIN. Seems an easy task to verify if you have an amp in your trunk. A much more difficult option is to pull out your COMMAND unit and see if the connections match the diagram. My money is on amp in the trunk.
 

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