Is my head unit wearing out or is there another explanation?

[noms78 10+ year member]

Hi all

In recent months the sound in my system has changed for the worse. The bass level/fidelity seems to have dropped off and the treble seems harsher than before (easily fatigues my ears).

I've had the HU (Alpine 9825 cd player) since January 2004 so it is 7.5 years old!

I haven't changed anything in my system. Checked all wires - power/speaker/ground wires - all intact.

I even bought a digital multimeter to check the voltage across my battery and the amps going to the HU. Across the battery it measured 12.73V and upon starting my engine rose to 14.4V so this seems normal. When connecting the MM in line with the HU ( +wire to MM to HU ) the amps range from nearly exactly 1A to 2.X A when I turn up the bass/volume.

The HU is connected directly to the speakers and I am only running two front speakers (6.5" coax). The HU has a parametric EQ - Ive been using +5 2 100 (max is +7) the whole time as I think that sounds best given I'm not using a seperate amp. With these settings do you think the power amplifier component inside the HU would be near the end of its life thus explaining the change in sound?

The other thing I noticed was that very rarely, after disconnecting and reconnecting my HU to the power supply the "megabass" button on the faceplate doesn't work (its ok now) so maybe the faceplate could also be part of the problem.

I am thinking of buying another 9825 HU from ebay and see if that makes a difference.

Jon

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[noms78 10+ year member]

Hi

1) I just tried a second HU and faceplate (same model) which I bought used off ebay. They didn't make a big difference to the bass response.

2) The ground wire coming from the head unit is currently connected to the negative battery terminal, from which another wire runs straight to the chassis. Thinking the problem could be caused by a poor ground I used a digital multimeter (DMM) to measure the resistance from the ground location to the negative battery terminal. To do this I disconnected the positive battery terminal, and connected the DMM (using a 4m wire to extend the range of one probe) in parallel with the ground location (the black ground wire coming out of the car wiring harness) and the negative terminal of the battery (black terminal). The resistance read 0.9 ohms. and the 4m wire had a resistance of 0.4 ohms so I concluded the ground was not the problem.

ie. ground location negative battery terminal

3) I also resealed the MDF baffles using two layers of foam on each side of the baffle. It cut down almost all of the speaker rattle but still no big difference to the bass. The RHS MDF baffle is pretty screwed (water has gotten into it, warping it a bit and causing it to split) so I will have to replace them both and waterproof them. Would one bad MDF baffle cause the overall bass output to drop significantly??

The bass only sounds better when I turn on the megabass of the unit and reduce the bass to +2/+3 (I normally run +5 2 100 and -1 10khz equaliser settings). But I don't like using the megabass as it ruins the fidelity of the sound.

In conclusion, either:

a) speakers are worn out (Alpine DLS-174A) after only 7.5 years of use

b) speakers are ok, current and replacement head units are worn out

c) speakers are ok, warped MDF baffle is causing the large drop in bass output

d) my ears have finally realised that the bass is lacking and I trying to blame the equipment //content.invisioncic.com/y282845/emoticons/smile.gif.1ebc41e1811405b213edfc4622c41e27.gif

Jon