You are correct about impedance. It may be a dampened situation if the
matching is not proper, causing harmonics to propagate from the load to the
source and vice versa. At the frequency and power levels we are dealing with
here (audio electronics) the effects are not as damaging as say, a power grid
on a city.
If you are concerned about a 4 ohm mismatch due to a speaker upgrade, I
recommend making an impedance matching network consisting of the followng
resistors:
2 100 ohm resistors
1 2 ohm resistor
Connect them in a "pi" configuration such that the 100 ohm resistors are in
parallel, and the 2 ohm is in series.
This will give you an impedance match with only 1 dB of loss through the
network.
If you want to get more adventurous and have a ccess to more parts you can make
a reactive network out of the following parts:
2 2-3 uF capacitors
1 68-70 uH inductor
Chris Middlebrook
62 Custom Southampton
--- On Sat 04/03, W Bell < cbody67tx@xxxxxxxxxxxxx > wrote:
From: W Bell [mailto: cbody67tx@xxxxxxxxxxxxx]
To: mailing-list@xxxxxxxxxxxxxxxx
Date: Sat, 3 Apr 2004 20:13:29 -0800 (PST)
Subject: IML: Chrysler speakers, etc.
<DIV>I believe that most of those middle-'60s and later Chrysler speakers might
be stamped to indicate 8 ohms impedance. Ideally, the ohms should match the
system's other speakers. Using 4 ohm speakers in place of 8 ohm can result in
greater volume levels for the same power setting with no long term damage, from
what I've seen. For many years, GM used "oddball" 10 ohm speakers and one of
the accepted upgrades at the time was the Jensen dual cones (which were not 10
ohm speakers). Currently, it seems that most aftermarket speakers are of the 4
ohm rating.</DIV>
<DIV> </DIV>
<DIV>Somewhere in the folds of my brain, it seems that I recall that impedance
is more of a damping situation which might also be related to magnetic
properties? Not really resistance as ohms is, per se. On the electrical side
of things, resistance is something we can read with a meter, though. Impedance
is calculated?</DIV>
<DIV> </DIV>
<DIV>Magnet size? That whole deal started in the later '60s. A bigger magnet
can make for more forceful bass notes as it takes a large excursion of the
voice coil to make those frequencies happen. Also takes more power to make
forceful bass frequencies happen than the middle and higher end frequencies
too--hence the need for greater power in later times as music tastes seemed to
change.</DIV>
<DIV> </DIV>
<DIV>Many of the modern big magnet/high power handling speakers have a minimum
power requirement of sorts to effectively drive them. In earlier times, the
magnets were small so the bass response was similarly weaker. The stiffness of
the paper is also a factor, which is why the outer edge is pleated or has a
rolled foam interface, to allow less resistance to the actions of the voice
coil as the magnet does its thing. Lots of little, interrelated design items
that make a speaker do what it does. </DIV>
<DIV> </DIV>
<DIV>Physical magnet size? It might take some restraint, but probably buying
the least expensive speaker (6x9, for example) dual cone speaker would be
fine. Best Buy had some Pioneer dual cones for about $20.00/pair a few years
ago. Not a huge magnet, but better frequency response than most factory
speakers too--just no grill cloth on them. They are also 4 ohm speakers. If
you find some front speakers to match the size you need, they'll most probably
be 4 ohm speakers too as that's what's out there these days--UNLESS you can
find some older Chrysler factory speakers of the size you need (if you find one
of the old NOS accessory installation kits, it'll have wiring and many other
things you might need too).</DIV>
<DIV> </DIV>
<DIV>Some radio amps are more critical to open circuits than others, but ALL do
not like direct shorts--period. Highly intolerant of them too! OUCH! Some
"old school" techs would do the "spark test" to see if the radio amp was
working. Even that might cause problems.</DIV>
<DIV> </DIV>
<DIV>As for "phasing" the terminals? The old way to do that is with a C or D
cell battery. The polarity with respect to the terminals will make the voice
coil move a particular direction. Matching that movement with the color coded
wiring will put things in phase. This will mean that both voice coils will
move in unison and will tend to help bass response as the actions of the voice
coils are the same instead of basically 180 degrees out.</DIV>
<DIV> </DIV>
<DIV>Many modern replacement aftermarket speakers use terminals that have one
wider than the other one. If the front side of the cables is not altered at
the amp, no need to phase them. Many Chrysler speakers used a plastic terminal
connector body to do the same thing (especially the stereo outer 3.5" speakers
on the instrument panel). Some speakers also have a dot by the "+" terminal
too, in some cases I've seen.</DIV>
<DIV> </DIV>
<DIV>One reason the perceived imbalance between front/rear speakers might exist
is the sheer spatial relationship of your ear to the speaker location. Being
closer to the front speaker, it'll be louder at the middle of the fader
travel. If you set the balance control to the middle on a modern vehicle
stereo radio, all you hear is the front speakers (especially since they're door
speakers). I usually have to move the balance control more toward the rear
speakers, typically, to make the sound at my ear seem to be "in the middle of
things" or to not loose the backside sounds. Just depends on the environment .
. .and if you're using a "zonal" approach. Personally, I like to hear all of
the speakers with some front/rear balance making for a better musical
experience, unless there's someone in the back seat--then things would need to
be more electronically even f/r.</DIV>
<DIV> </DIV>
<DIV>Just some thoughts,</DIV>
<DIV>W Bell</DIV>
<DIV> </DIV>
<DIV> </DIV><p>
_______________________________________________
Join Excite! - http://www.excite.com
The most personalized portal on the Web!
Back to the Home of the Forward Look Network