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Re: home stereo impedance matching

If you are going to drive the speakers at low power levels compared to
the rated power output of the amplifier, they can be connected to the 8
ohm output without too much of a problem.

If you are going to use more of the rated power of the amplifier, then
the load should be matched to the output impedance to prevent
overheating the output transistors. Adding 4 ohm resistors in series
will work provided that the resistors have an adequate power rating.

Dr. Mark H. Shapiro
Professor of Physics, Emeritus
California State University, Fullerton
Phone: 714 278-3884
FAX: 714 278-5810
travel and family pictures:

-----Original Message-----
From: Forum for Physics Educators [] On
Behalf Of Matt Harding
Sent: Tuesday, February 17, 2004 12:44 PM
Subject: home stereo impedance matching

I have a pair of old (relatively) Bose 501 speakers that are marked a=
s 4
Ohms, that I would like to use with a new receiver that only offers 8=
ohm connections. From what I've been able to establish, higher end
speakers tend to be of the 4 Ohm variety due to greater power associa=
with lower resistance. =20
What types of problems can I expect if I use 4 Ohm speakers with my 8
Ohm system?
If my only problem will be reduced performance, then I'm not terribly
concerned. If I will cause permanent damage to my new receiver I thi=
I'll leave the speakers in storage.
In the past, my father had wired a 4 Ohm resistor (rated at 15 Watts)=
series with the speaker so that the amp would see 8 Ohms. Is it that

"An expert is a man who has made all the mistakes which can be made i=
n a
very narrow field."
- Niels Bohr

-----Original Message-----
=46rom: Forum for Physics Educators [] On
Behalf Of Justin Parke
Sent: Tuesday, February 17, 2004 1:54 PM
Subject: Re: rolling

I just discovered that the latest edition of Halliday, Resnick, and
Walker has the correct answers (i.e. .5 L and L) in the back of the


In a message dated 2/4/2004 8:11:12 AM Eastern Standard Time,
FIZIX29@AOL.COM writes:

I need some help with the following question from Halliday et al
ch. 12 question 5:

"A woman rolls a cylindrical drum, by means of a board on top,
h the
distance L/2, which is half the board's length. The drum rolls
hly, and
the board does not slide over the drum.
a) What length of board has rolled over the top of the drum?
b) How far has the woman walked?"

The answers in the book are L and 1.5 L. I am not sure I underst=
what is
meant by "what length of board has rolled over the top of the dru=
It seems
to me that it should be L/2. If the questions means how
far has the =3D
moved with respect to the ground then I agree it is L.

Answers in algebraic form (plus verbal explanations) are
preferable t=3D
strictly verbal arguments.


Justin Parke
Oakland Mills High School
Columbia, MD