help with impedence

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I have a pair of speakers that are 4 ohms and I need to connect them to an
amp that requires a minumum of 8 ohms. Is there something simple I can do
electronically (add resistors or something like that) to accomplish this. I
really don't know much about it. Help!

rod

Archived from groups: rec.audio.pro (More info?)

Rodney St-Pierre wrote:

> I have a pair of speakers that are 4 ohms and I need to connect them to an
> amp that requires a minumum of 8 ohms. Is there something simple I can do
> electronically (add resistors or something like that) to accomplish this. I
> really don't know much about it. Help!

It's not a great way to go about things, but it is possible.

The simplest thing is to add a 4 ohm resistor in series with each
speaker. However, it won't be very efficient because you'll lose
half your power in the resistor. Also, because half the power is
going into the resistor, it's going to heat up REALLY quick, so
you would need one very heavy-duty resistor to accomplish this.

Another way to do it would be with a transformer that has a
ratio of 2:1. I'm not an electronics expert, so I can't tell you
how well this will work or how hefty transformer you'd need,
but at least you won't lose half your power.

Overall, you're probably better off trading the amp with someone
who has one that can handle a 4 ohm load. Or trading the speakers
for 8 ohm ones. In other words, what you're proposing can be
made to work, but it's about as practical as putting a Chevy
engine in a Ford. (Which is to say, if you know exactly what
you're doing, it can be made to work with some pain and suffering,
but if you don't, it's not something you want to even think about.)

- Logan

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Logan Shaw <lshaw-usenet@austin.rr.com> wrote:
>
>Another way to do it would be with a transformer that has a
>ratio of 2:1. I'm not an electronics expert, so I can't tell you
>how well this will work or how hefty transformer you'd need,
>but at least you won't lose half your power.

It actually works pretty well. EV will sell you a big autotransformer
for a couple hundred bucks which is designed to match to 70V loads but
which also has taps to match 8 to 4 and vice-versa. There will be some
coloration due to the transformer, and it will cost more than an amp
able to drive the load directly, but it might not be bad.

Edcor might make a cheaper version of the same design.
--scott


--
"C'est un Nagra. C'est suisse, et tres, tres precis."

Archived from groups: rec.audio.pro (More info?)

In article <l0sWc.99357$Np3.4807424@ursa-nb00s0.nbnet.nb.ca> rstpierre@ns.sympatico.ca writes:

> I have a pair of speakers that are 4 ohms and I need to connect them to an
> amp that requires a minumum of 8 ohms. Is there something simple I can do
> electronically


Connect them to the amplifier and just don't turn it up so loud that
it distorts.

With more information about the amplifier and the speakers, a more
reliable answer might be forthcoming. But in general, amplifier and
speaker impedance numbers are more guidelines than limits.

Connecting a resistor in series with the speaker will waste power. You
can make less waste simply by not using all the power in the first
place (keeping the volume sensible).

Now if your amplifier is mono and you want to connect the two
speakerse to it, just connect them in series and connect the series
pair to the amplifier. Instant 8 ohms.

--
I'm really Mike Rivers (mrivers@d-and-d.com)
However, until the spam goes away or Hell freezes over,
lots of IP addresses are blocked from this system. If
you e-mail me and it bounces, use your secret decoder ring
and reach me here: double-m-eleven-double-zero at yahoo

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On Mon, 23 Aug 2004 19:59:13 GMT, "Rodney St-Pierre"
<rstpierre@ns.sympatico.ca> wrote:

>I have a pair of speakers that are 4 ohms and I need to connect them to an
>amp that requires a minumum of 8 ohms. Is there something simple I can do
>electronically (add resistors or something like that) to accomplish this. I
>really don't know much about it. Help!


The speakers are 4 ohms each? The amplifier is stereo, rated for 8
ohm speakers?

Just hook them up. If you try to run them too loud either they will
succeed in drawing too much power from the amp and the sound will
distort or (more likely) the amplifier will run out of amps and the
sound will distort. Either way - turn it down a bit :-)


If the amp was made in the last 20 years it almost certainly has
protection circuitry that will cope with a complete short, let alone a
low impendence speaker. If there's a problem you'll know it from
either distorted sound or the cut-out operating.


The impendence figure on speakers is fairly nominal anyway.

CubaseFAQ www.laurencepayne.co.uk/CubaseFAQ.htm
"Possibly the world's least impressive web site": George Perfect

Archived from groups: rec.audio.pro (More info?)

Buy two more speakers just like you have and stack them on each side.
That's the only way to get 4 ohms into each stack of your speakers and get
the power.

Otherwise, look for a new amp that runs 8 ohms.

OTOH, don't sweat the small stuff and decide how it sounds. Just because
the amp is 4 ohm output and the speakers are 8 ohm doesn't mean they won't
work. They just won't work like they were designed to. Maybe you can live
with it, maybe you can't, but it's not likely that you'll kill anything
unless you decide to run maximum volume, and you shouldn't do that on any
system.

Hey, this is supposed to be fun! <g>

--


Roger W. Norman
SirMusic Studio

"Rodney St-Pierre" <rstpierre@ns.sympatico.ca> wrote in message
news:l0sWc.99357$Np3.4807424@ursa-nb00s0.nbnet.nb.ca...
> I have a pair of speakers that are 4 ohms and I need to connect them to an
> amp that requires a minumum of 8 ohms. Is there something simple I can do
> electronically (add resistors or something like that) to accomplish this.
I
> really don't know much about it. Help!
>
> rod
>
>

Archived from groups: rec.audio.pro (More info?)

L David Matheny <ldmnews1@netassoc.net> wrote:
>>
>If the speakers are a "pair" they should have identical impedance curves,
>so wouldn't putting them in series avoid distortion due to nonlinearities?

No, it makes them worse if the speakers are identical!

>Putting one speaker in series with a fixed resistor would divide the
>driving voltage unequally, and that should cause distortion, right?

No, because the impedance isn't constant. Let's say you have a speaker
with a big impedance peak at 100 Hz. As a consequence, the frequency
response at 100 Hz will probably be down a little bit. Now, you put it
in series with another speaker that has a big impedance peak at 100 Hz,
and all of a sudden the frequency response at 100 Hz is down a whole lot.

There are similar time domain problems, but the frequency domain one is a
lot easier to describe and very easy to measure.
--scott


--
"C'est un Nagra. C'est suisse, et tres, tres precis."

Archived from groups: rec.audio.pro (More info?)

> No, it makes them worse if the speakers are identical!

Absolutely wrong. If two speakers have the same impedance curve, the voltage
will always divide exactly 50:50 between them, regardless of frequency. This is
exactly what you want.

It's when they DON'T have the same curve that you get impedance-related response
errors.