Newsgroups: rec.audio.tech
Subject: Re: 3 ohm speakers with 6-8 ohm receiver ??
References: 
[email protected] (Nataraj Dasgupta) writes:

> Hi,
> 
> I am trying to connect 4 Sony DAV C450 speakers to a Panasonic SA-HE7
> receiver. Now, the receiver specifies a speaker rated impedence of 6-8
> ohms, whereas the speakers are rated at 3 ohms. I found some Wire
> Resistors on www.partsexpress.com of 3 ohms 12W. Will it be alright if
> I connected these in series to the speaker wires ? (Since the rated
> impedence of the speakers is 3 ohms, theoretically, a 3 ohm wire wound
> resistor should make it 6 ohms, and ensure that the speakers do not
> burn out). 

The 3 ohms in series with the speaker element makes the 
element + resistor combination to look like a 6 ohm element to 
the amplifier. This will safe the amplifier not being overloaded
and possibly burning up. 

> While this may limit the speaker max sound potential (that
> I don't think I'll ever need really :) , is it fine to have the 3 ohm
> wire wound resistor in this manner ?

You can use the resistor like this to increase the impedance. 

The downside of the series resistor is the following
(compared to speaker element with no resistor in series):
- half of the power few to the system is lost in the resistor
- the frequency response is much worse
- impulse response and controlling is worse 

> Also, another important question on the power rating for these
> resistors -- they are 3 ohm 12W resistors, ... the receiver can drive
> upto 105 W, and the speakers can handle about 80W. While the
> difference in speaker and receiver power out put rating does not worry
> me, since the 100 W rating is after all only a continuous output
> rating,... how will this affect the resistor, given that they are
> rated 12 W ? Should I be then looking for 3 ohm 100 W rated wire
> resistors ?

If you use 12W resistors, you can nicely okay back audio at 
low volumes. If you turn up the volume to much, you will 
overload those 12W resistor by pushing more power to them that 
they can handle. This will heat them first very much, then overheat 
them (you can usually smell this) and then they will burn out.
When you overload those resistors, it is better that they are 
far wasy from any burning material, or you will soon have a fire 
in your home. Anyway this kind of resistors (if you want to use them) 
shoudl be placed always in such way that when they heat up they 
will not cause any dangers (no fire danger, nobody can touch them
and burn themselves etc.)

-- 
Tomi Engdahl (http://www.iki.fi/then/)
Take a look at my electronics web links and documents at 
http://www.epanorama.net/