Neil Green wrote:
>> The signal coming out of the deck is AC; the signal
>> phase has to be the same in both speakers. There is
>> no "right" or "wrong" polarity as such, they just
>> have to be the same. A DC meter won't give you a
>> meaningful reading.
>
> The AC bit is news to me, I was under the impression
> that the current to the speakers was DC, but as you
> can probably tell I'm more or less ignorant in these
> matters.
Not really... just a little n00bish. That's okay, it's always good to
learn something new!
If you feel inspired to understand it a little better, take a browse of
http://www.bcae1.com
("Basic Car Audio Electronics"), specifically
section 21 on "Audio Output".
> Anyway, the meter showed a minus sign one way and not
> the other, and I connected the two speakers
> accordingly.
It's not unusual for an amplifier's output to have a slight DC offset,
which is probably what you were measuring, but there's no guarantee it
will be the same offset on both channels and thus not a valid indicator
of phase.
(Hmm, it's strange there's not actually a section on "phase" on BCAE...
it's a little crude, but there's a diagram and brief explanation at
http://www.classictruckshop.com/clubs/earlyburbs/projects/stereo/systems.htm
- scroll down to "speaker phase")
>> That makes it a little easier then, because you can
>> check the polarity of the connections to the deck,
>> then confirm them at the speaker end. If you used
>> the factory speaker wiring, just follow the wiring
>> color codes and make sure the + and - outputs on the
>> deck properly match the terminals on the speakers.
>
> My son actually had them written down (good boy!) and
> they tallied with how we had the speakers wired so
> it's all good as far as that goes.
Excellent!
> The rear seats fold forward so there's nothing to
> mount a sub on, and my son needs the folding seats to
> stow golf clubs..
Ah. Of course, folding the seats down also introduces the acoustic
leakage problem we've been battling thus far, though hopefully not as
severely. He'll have to remember that he'll probably see reduced bass
output from the rear speakers with the seats down, and remember NOT to
try to compensate by cranking the bass control.
> OK, so we make up an MDF parcel shelf and kill a
> little of the bass, that's OK.
> The system sounds fine apart from the bass distortion
> so I'll tell him to go easy.
Turning down the bass control is the actual "fix" for the problem... the
rest of the exercise is intended to improve the speakers' own bass
response, so he doesn't NEED to turn up the knob.
> Once again, thanks very much for your time and
> patience.
No worries!
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