I recently purchased a 1999 SLK. Having owned several convertibles in the past, I’ve gotten used to turning the stereo volume up and down as I go from city to highway speeds. I think my SLK’s speed adjustable volume feature will be really useful when warm weather returns, but for now (with the hard top up) it is almost overkill. I wanted to turn the speed-sensitive volume boost down a little bit when the top is up. I suspect I may want to do the opposite – adjust the response up a bit – when the top is down (I like my music LOUD).

Always one to tinker, I decided to take a crack at this.

I‘ve designed a little electronic device that sits in between the SLK’s speed sensor and the head unit. I connect this device to a switch that indicates when the top is up or down. When the top is up, my box modifies the speed signal to the radio downward, so that the increase in volume with speed is not that great. When the top is up, my box modifies the speed signal upward, to add a little more volume boost at speed. The amount of volume adjustment is – well – adjustable.

Details are on my web site at
http://frontiernet.net/~dbipes/SLK/volume/index.htm
if you are interested.

 

I really like to tinker as well and I agree that the stock MB system pretty much leaves everything to be desired. Sensing the top up/down is a major improvement. I've thought about a system like that which you have described. But I came to the conlclusion that a system based only on vehicle speed (top up or down) will never really track correctly as the ambient noise level (which establishes the effective S/N level that your ear is working with) can vary quite indepdently of vehicle speed - the interstate is a lot noisier than a back country road at the same speed. And what about windows up/down? I also don't like the way the radio head unit steps the volume up in discrete jumps. Too obvious to me.

So being a "manual" kind of person (my SLK is a 5-speed manual), this spring (car is currently hiding from the snow) I'm just going to remove pin 1 in the radio hardness connector to disable the SCV completely and adjust the volume by hand. I'll plug the pin back it when when it's time for a new SLK (a new owner may not be so utilitarian).

I'm curious if the head unit itself could be "re-programmed" through the StarDiagnose system to have a different SCV response curve (smoother steps, different gains, etc). Everything else on the car seems to be flash updatable.

Thanks for your post,.

 

I don't know about programmability of the radio, but I used a programmable microcontroller in my add-on box. Right now I'm just using a linear translation, but it would not be hard to change this. I too thought about changing the response from linear, but to what? Top up, I'm pretty happy with the linear response, but I guess I need some experience with top down driving to figure out what a better curve would be.

I thought about using a microphone to measure ambient noise and adjust radio volume accordingly, rather than just using the VSS (speed signal). From an engineering standpoint this gets complicated quickly, because you need to cancel the audio signal from the stereo itself to make this work. It's not so easy, because the signal from the microphone will be out of phase from the signal from the head unit. Bose does the reverse and makes headphones to cancel background noise, but these cost several hundred dollars and I'm sure employ a digital signal processor and lots of software.