SL500 need advice on capacitors on front speakers. - PeachParts Mercedes-Benz Forum

spinedoc · #1 10-11-2004, 04:34 PM

Hey guys. 1996 SL500 with everything audio stock except a Pioneer AVIC7500 head unit. Anyway I think I am having issues with the differences in resistance between the head unit and the german speakers. I believe I had read somewhere that the speakers accepted a factory resistance of 3ohms, while US head units put out 4ohms. Normally it is not a problem for me, but if I turn up the bass too much the front speakers clip and distort quite badly.

It may even be that I am overpowering the front speakers, I dont know. In any event I wanted to lower the bass coming to the front speakers, without affecting the sub in the rear. It seems like the easiest way to do this (without a lot of digging around for wires) is to add a capacitor to the front speakers to lower out the lowest frequencies. Keep in mind I have not done too much car stereo work since my college days, so if capacitors are not used anymore please let me know.

Can someone please tell me the best solution to lower bass only at my front speaker levels, and if it does involve a capacitor what rating would you suggest? I would assume I would start with cutting out at least 80-100hz, and go from there.

And yeah I know I should get new speakers, but dont have the time this winter to do that. Plus I would lose the factory sub, which is enough bass for me. I just want to be able to put my stereo louder without the front speakers clipping out from too much bass.

spinedoc · #2 10-18-2004, 06:28 PM

Anyone?

Elecmech · #3 10-22-2004, 10:44 PM

Let's say you want to attenuate the power by 50% at your lowest given freq of 80Hz. If the amp's output resistance is 4Ohm, adding another 4Ohm impedance in series at 80Hz will accomplish this. Frequencies below 80Hz will be attenuated even more and above 80Hz less

So Capacitive reactance(Xc) = 1/(2*pi*f*C), where f=Hz, C=Farad

C works out to be about 497uF

Because you need a non-polarized capacitor for audio (which is AC) and non-polarized caps of this value will be expensive if you can get it, you may use 2 electrolytic capacitors each of 1000uF connected in series (back to back), positives to positives or neg's to neg's to create a non-polarized cap. Voltage rating of each cap should be about 25v each. This will be available from your local RadioShack or electronic parts store.

Hope it helps

spinedoc · #4 10-27-2004, 04:53 PM

AWESOME! Thank you so very much. One last question, is my cutoff of 80hz reasonable? What would you suggest?

dieseldiehard · #5 10-27-2004, 05:54 PM

I recommend a non-polarized capacitor over series connected aluminum electrolytics. The car audio people call these bass blockers see:

http://www.electronixwarehouse.com/car/accessories/bass-blockers.htm

Use a 100 to 150 Hz rolloff point, it is a one pole filter so the roll off is gradual

spinedoc · #6 10-28-2004, 10:28 AM

I ordered a pair of these, figured could not go wrong with the price. But I do not want to eliminate all bass from the front speakers, only the lowest end which is causing them to clip.

I guess I just have to experiment, but I still do want some bass from the front.