left-side car audio weak

[markthomas]

Hello:

New to this forum, thanks for your patience.

Trying to chase down an odd sort of audio gremlin.

The left-side audio in my S70 seems weaker/tinnier than the audio on the right side; by contrast I would say the right-side sounds more full/"gooey" (I have in fact played with all the settings, e.g., bass/treble, balance/fader, et al., and am detecting the same contrast in every case). The "tinny/gooey" contrast is actually clearest when I have bass and treble turned all the way down, and is most pronounced when fading all to the front (and when I isolate the dashboard tweeters, by disengaging the door speakers, the contrast is absurd, with little but a white-noisey mush coming from the left tweeter).

I seem to have power at the radio connectors where/when I should, have checked both of the relevant fuses, and can't find any bad resistance readings anywhere (though I'm sure I haven't checked absolutely everything/everywhere). When I experiment by swapping left/right front speakers/rear speakers (have even swapped dashboard tweeters), the left/right contrast remains. I've even swapped out the HU (SC-816), as I happened to have a spare on hand; no change.

Might there be a ground loop somewhere that a continuity reading would not reveal? Is there a relay I should be testing (I don't think it's the RSR, as the gremlin is there even when engine off)? Other ideas? At a loss here. Also doubting my sanity at this point!

Thanks in advance for any insight.

[RollingThunder]

Has a speaker cone failed? I had to change my front passenger door speaker on my old S70, and my current 940 also has a failed passenger front door speaker! If the tweeter part is working but the main cone has cracked, you'll only get the high tones.

[Lancee]

I assume this is an older car ?

If so it's possible that the bass driver has failed, either it has seized/stuck, this can be checked by gently pushing the cone in to check for free movement, or the surround foam may have perished with time meaning the bass will be poor or largely missing.

Removal of the door card and physical inspection of the speaker would be the way forward to my mind.

Keep in mind that a mono sound recording would be the best for checking the difference between channels. When testing don't get caught out by stereo recordings that may be light on the left, or any other channel.

[Luxobarge]

Concur with the above 2 posts, failure of a bass speaker or the feed to it was the first thing that came to mind. If you play some music with some heavy bass quite loud, and hold the tip of a pencil against the cone, you should feel the vibration of the bass through the pencil. Each speaker should feel the same as the corresponding one on the other side. This may well enable you to narrow down the fault to a specific speaker, which will help a lot.

[markthomas]

Hello everyone! Thank you for replying!

First of all, apologies for not specifying that this is a 1998 S70. Again, the HU is a SC-816.

From what I can tell, all cones are intact and sound and performing properly. And again, the "weakness" or "tinniness" (I suppose I could also say "fuzziness"?) is affecting all left-hand speakers (front left tweeter, front left cone, rear left cone), and with each on its own circuit of course. Furthermore, if I swap a left/right pair (tweeters, door cones, rear cones), the "junk" sound remains on the left.

I think the problem must be at the head (that is, the wiring at the head, because again, the problem remains even when switching head units). I pulled the HU out of its cage and took some voltage readings today at the SDL female terminal connectors (while they were plugged into the HU, with pins inserted into backs of terminals). I've attempted to attach a diagram for reference. I don't quite understand what I'm looking at; just going to put all the strangeness out there in the hopes someone else might see what's going on.

The only "pattern" I think I am seeing is that voltage across the left-hand speakers seem uniformly higher than the voltage across the right-hand speakers (DMM set to read 12V DC):

B1&2 (front left cone): .049V
B5&6 (front right cone): .035V (not a very large gap)
B3&4 (rear left cone): .101V
B9&10 (rear right cone): .028V (a somewhat larger gap)

A5&6 (front left tweeter): OL (! as in off-the-charts?...)
A13&14 (right front tweeter): 1.9V (but the longer I read, the lower the reading drifts?...i.e., from 1.8V to 1.7V to 1.6V &c.)

Two other things I don't understand: A very slender black/yellow wire at terminal/pin B8 (when the diagram does not indicate a function for that pin) and a pink wire at A11 (judging from the diagram, which labels A10 "Reg-" and A11 "REG+", it seems there should be a companion wire at A10, but there isn't?).

OK that's it. Hoping there's an audio tech in the house?

Thank you to everyone for looking in on my newbie thread...

[markthomas]

Well...... just learning that the DMM has to be set to AC, not DC. (Newb!)

New set of readings soon.

[DaveNP]

Originally Posted by markthomas

Well...... just learning that the DMM has to be set to AC, not DC. (Newb!)

New set of readings soon.

I refuse to admit how many times I've made that error

Unfortunately my audio experience is more as a user then a fixer, and whilst the multimeter can be useful for checking continuity in circuits and very basic tests of things like speakers, what I found was that once one is trying to measure audio frequencies and waveforms the average DMM can be confused.

From your later post you say you've tried swapping the speakers left and right but the problem remains which puts it either in the head unit or the wiring, have you checked the wiring from the head to the speakers? if it has a break in the conductor it could still pass audio signals by capacitative coupling but it probably won't sound as good.

[Luxobarge]

Originally Posted by markthomas

Well...... just learning that the DMM has to be set to AC, not DC. (Newb!)

New set of readings soon.

Indeed. However I'm still not sure how useful this will be, the voltage presented at the speakers will vary depending on what music is being played, you're going to get values that rise and fall rapidly with the rhythm & melody of the music. It might have some value if you have a means of playing a constant tone or chord??? Just a thought.

Also, take care NEVER to short the two loudspeaker feed wires together while you're measuring voltages, it's a sure-fire way to blow the output stage of the amplifier, unless it has short-circuit protection, which is common on decent hi-fi amplifiers but rare on car audio. Just thought I'd mention this in case you didn't know.

[Derek UK]

Use a known good speaker as a tester. Use it on all of the speaker feed wires to see which ones aren't working properly.

[markthomas]

Hello again. Yes, Dave NP, the problem must surely be the wiring (as opposed to the HU itself, because again, I have even swapped HUs, with no change)... but where would be the wiring glitch be that would at once affect all three left-hand speakers (even as each of them is on its own circuit, if I'm not mistaken)?

Not really clear on what capacitative coupling is, but it does indeed seem like the left-hand audio is an insubstantial "shadow" of what is sounding so much sonorously across the right-hand side...