Date:         Wed, 29 Jan 2003 08:05:27 -0700
Reply-To:     Ben McCafferty <ben@VOLKSCAFE.COM>
Sender:       Vanagon Mailing List <vanagon@gerry.vanagon.com>
From:         Ben McCafferty <ben@VOLKSCAFE.COM>
Subject:      Re: NVC:  measuring impedance of a speaker?
Comments: To: David Beierl <dbeierl@ATTGLOBAL.NET>
In-Reply-To:  <5.1.0.14.2.20030129093010.01b6abd8@pop1.attglobal.net>
Content-type: text/plain; charset="US-ASCII"

OK, here's the scenario.  I found the books on the speakers (had to go
deeeeeep into storage for that), and they are 4 ohm speakers.  The receiver
has a manual switch for 0-4 ohms or 8-16 ohms.  When using A speakers only,
it says to select the range that matches the speakers.  I inherited this
setup about 5-6 years ago, and don't recall ever changing the switch.  It
was set to 8 ohms.

The receiver has intermittently gone into its protection mode over the past
2-3 years.  It now stays in protection mode all the time, i.e. is unusable.
The repair guy thought that running 4 ohm speakers with the receiver set to
8 would cause overheating and eventual damage, as alluded to by David below.

Any other thoughts are welcome, thanks to all who responded.
tx,
bmc  :)
Ben McCafferty
ben@volkscafe.com

Volks Cafe
1823 Soquel Avenue
Santa Cruz, CA  95062
831-426-1244
http://www.volkscafe.com


> From: David Beierl <dbeierl@ATTGLOBAL.NET>
> Reply-To: David Beierl <dbeierl@ATTGLOBAL.NET>
> Date: Wed, 29 Jan 2003 09:43:59 -0500
> To: vanagon@GERRY.VANAGON.COM
> Subject: Re: NVC:  measuring impedance of a speaker?
>
> These are power circuits, and we're talking about a 2:1 ratio of impedance,
> so it's not entirely trivial.  If you're not running at high outputs it no
> doubt doesn't matter -- but if the source and load impedances are not equal
> some of the power will get reflected back into the source, which
> undoubtedly will cause a certain (small) amount of distortion depending
> somewhat on the length of your speaker wires.  Also, if the load impedance
> is lower than the amplifier is rated to handle (and the ratings vary and so
> do the safety margins) the output stage of the amplifier can overheat.  In