Pontiac: Replacing rear speaker

I never did like those factory rear deck speakers. Ya know, the ones that
are made of thin cardboard. Anyway, if I remember correctly, you should keep
the ohms matching. If you don't, the speakers will not sound right. If money
is of no importance, try going to www.crutchfield.com they have a wide
selection of brand name speakers for your car. Even though the cost of the
stuff they sell is a little more than say WalMart, Crutchfield is very
knowledgeable about what you exactly need for your specific make and model.
That's where the extra money goes to. Research. Anyway, I would stay away
from anything that doesnt say 8 ohms to be on the safe side.
"John" <com> wrote in message
news:google.com... 

> pair. The rear speakers say they are 8ohms,but all I can find are 

Gee, I'm very surprised that a modern car stereo worth any salt uses 8 ohm
speakers! Where exactly does it say that the speakers are 8 ohms?

There is an inherent power limitation when it comes to car radios, and the
speaker impedance has a direct effect on this. Here's the deal: If you
have a simple sine wave whose top peak reaches 12 volts, and bottom peak
reaches zero volts, you effectively have the strongest wave you can get from
a 12 volt power supply. Any stronger and it will distort. Do the math --
feed this into a 4 ohm speaker and you get about 9 watts RMS (6 watts
practical). With an 8 ohm speaker you only get 3 watts! This is why car
stereo typically goes the 4 ohm route -- and in some cases, 2 ohms.

There are a couple of methods of getting around this power limitation.
First, if you bridge two amps together, you have an effective + 12 volts and
= 12 volts, or a 24 volt spread. Now you can get up to 22 watts per 4 ohm
speaker (25 if you fudge the numbers just a little -- and most modern day
stereos are 25 watts per channel). Of course with stereo, it's easy to
double the wattage to 50. With four channels you get up to 100 watts. With
6, probably 150 watts, assuming each speaker is fed by its own set of
bridged amps.

Yes, you get do more than this, but only by using a high-power chopper power
supply. These are the big amps that mount in the trunk of the car. From a
dash mounted stereo however, the above applies to power. With this in mind,
it's true that you can increase output power by using 2 ohm speakers,
provided the amp is designed to handle it. However if you up the speakers
to 8 ohms, you cut the available power considerably, no matter how the amp
was designed. This is why I'm surprised to see 8 ohm speakers in your car.

It's possible you can get by with 4 ohm speakers, even if the originals are
8. Since the amps are designed for 8, your power output may be slightly
less, and technically there is more load on the output, but it's doubtful
this is enough to create a problem. A 2 or 1 ohm speaker load is a
different matter. As for sound quality, the only difference is that of the
speaker design -- it does not affect your audio signal in any way.


--
Gary E. Tayman/Tayman Electrical
Sound Solutions For Classic Cars
http://www.taymanelectrical.com

Its says they are 8ohms on the speakers themselves. Prior to making my
posting I read several posts/FAQs about OHMs and impedience(?) but
didnt understand them. What did catch my eye was a few posts saying
that going the 4 ohm route draws more power and could fry the radio. I
just wanted to get a clarification before putting in new speakers.
Thanks
John 

"John" <com> wrote in message
news:google.com... 
ohm 

Well, here's the rundown, without getting really technical. Any audio amp
is designed for a certain output impedance, and this is called maximum power
transfer. The output transistors are biased in such a way that the maximum
amount of power can be sent to the speakers if they have an impedance of 8
ohms. Most car stereos are designed for 4 ohms. If you read the spec sheet
of a large home or pro amp, you may see something like "200 watts per
channel into 8 ohms, 400 watts into 4 ohms," etc. What they're saying is
that, while 4 ohms may give you the peak power output, 8 ohms will work but
will give you less power.

More than likely, if your speakers are 8 ohms, the amp is designed to give
you the highest amount of power at 8 ohms. 4 ohms will work, but will give
you less power. Personally I think you'll be fine; if you install 4 ohm
speakers and the amp blows, I'd be looking for a reason other than the
speakers.


--
Gary E. Tayman/Tayman Electrical
Sound Solutions For Classic Cars
http://www.taymanelectrical.com