# Speaker impedance - explain?

Discussion in 'Electronic Basics' started by andrew_h, Feb 19, 2006.

1. ### andrew_hGuest

Can someone explain to me exactly what speaker impedance is?

Also, Why is it only 4, 8, etc. ohm? (such even numbers).

2. ### Phil AllisonGuest

** NO.

** NO.

Do a Google search you lazy piece of shit.

......... Phil

3. ### andrew_hGuest

I have....is confusing.

4. ### andrew_hGuest

Actually I ask is on this board because when an actual person explains
it, it makes alot more sense.

Some of the 'tutorials' and 'faqs' on the net are unneccessarily
complex.

5. ### Phil AllisonGuest

"andrew_h"

** First off - learn to use "googlegroups" correctly.

Do NOT simply hit reply !!!!!!!!!!!!!!

That way we can see who you are replying to and about what.

** Basically, it is the resistance of the coil of copper wire inside.

** Speakers with impedances from 0.5 ohm to 1000 ohms have been made.

The range from 4 to 16 ohms is just *much* easier to make.

In the valve era, 2 ohms was common for radio set speakers and 16 ohms for
early hi-fi speakers.

The most common by far now is 8 ohms, since it suits power transistor
voltage and current abilities best.

Two 16 ohm speakers in parallel gives 8 ohms.

Two 8 ohm speakers in parallel gives 4 ohms.

It is just that simple.

........ Phil

6. ### Pooh BearGuest

How about starting with this response ?

Do you know the difference between resistance and impedance ( of
anything ) before launching into an elaborate discussion of same.
It isn't. 4, 8, 15/16 are simply commonly accepted norms. 6 ohms isn't
uncommon either in some kit. Don't forget that the impedance is simply
'nominal'.

Graham

7. ### Pooh BearGuest

I know. Some ppl like to 'show off' and 'miss the point'.

Graham

8. ### andrew_hGuest

I did search alot on google before - but yeh, alot of people like to
read their own words, and so the descriptions arent as simple as they
can be.

Once something is understood, it then becomes very easy - thats why
people who know about a topic alot will think everything is easy to
understand.

9. ### Bob MastaGuest

First of all, instead of "impedance" think "AC resistance".
It's the value you would use when you are trying to compute
the power the speaker will draw from the amp, via V^2/Z
where V is the RMS output voltage and Z is the impedance.

(Note that the power drawn by the speaker is not the
same as the sound power delivered, since speakers
have a wide range of efficiencies... but 1% is typical.)

In a speaker, impedance is made up of the DC resistance
of the copper wire in the voice coil, plus the AC "reactance"
of the inductive effects from that same wire being in the
form of a coil (with an iron core), plus the mechanical
reactance due to the spring in the suspension and the
mass of the moving cone. The reactance part varies
with frequency, and actual speaker impedance typically
has a big peak around resonance, or two peaks one
on either side for tuned designs (like those with ports
or passive drivers).

So, the numbers like "4 ohms", "8 ohms", etc are
really just nominal values. Their main real use is
in comparing suitability of drivers for use with a
particular amp. Higher impedances demand less
current from the amp to get a certain power, so
amps are typically rated as to the lowest nominal impedance
they are happy to drive. Lower impedance may
draw too much current, but you can always use
a higher impedance speaker... at least with modern
solid state amps. Tube-type amps with output
transformers typically have different taps for driving
different speaker impedances, and there you
should select the matching value.

Best regards,

Bob Masta

D A Q A R T A
Data AcQuisition And Real-Time Analysis
www.daqarta.com
Home of DaqGen, the FREEWARE signal generator

10. ### JamieGuest

its the same as it would be if you were
to calculate DC resistance except with
the term impedance, it normally indicates
that an AC signal is involved and under
these conditions some devices behave differently
giving you a different results of resistance
over what would be Dc ohms.
for example, a speaker coil can be inductive
and thus at high frequencies the impedance of the
circuit may increase. that is one reason among
others that it is good to have a multiple set of
speakers attached to the output that covers all
ranges of audio.
but in most practical mid range type speakers you
will find the impedance matching very close to what

11. ### JamieGuest

P.S.
one more thing.
the lower ohm type speakers are normally used in low voltage
systems where it saves on cost of an amplifier to drive the
voltage up that will thus deliver enough power to satisfy your
needs for volume.
in the case of automobiles for example, 12 volt systems can
only generate a limited amount of Db's from a speaker using lets
say a 8 ohm system how ever, if you were to use a 4 ohm system
you can then get double the output as long as the components can
handle the current.
2 ohms systems even get more current in the speaker coil from a
12 volt amp..
then you have those amps that have power inverters in them so that
the internal power voltage level is actually higher than the supply
line. these normally draw more current depending on how much higher the
increase of voltage is.
these low ohm speakers are great and solves issues of getting more
dbs from a speaker with lower voltage equipment how ever, it also adds
to the cost of larger gauge wire for long runs. this is why higher ohm
speakers are popular in some areas. long runs of small gauge wire with
higher voltage
amplifiers reduces the needs for larger gauge wire.

12. ### Ross MacGuest

Well explained Bob couldn't have done better myself.....that ought to end
.....Ross

13. ### unbiasedGuest

Horrible manners. This IS sci.electronics.basics. People might
actually discuss and help instead of being rude.
<plonk>

14. ### Paul BurridgeGuest

Ignore Phil. He suffers from a form of autism known as Asperger's
Syndrome which means he's incapable of communicating effectively with
the outside world.
Your question's a very good one. If I hadn't drunk a bottle of
Australian wine this afternoon, I'd happily answer it. Hopefully,
however, someone else will.

15. ### Phil AllisonGuest

"Paul Burridge"

** Ignore Paul Buggerage.

The vile pommy cretin suffers from a form of autism known as Asperger's
Syndrome which means he's incapable of communicating effectively with
the outside world.

......... Phil