How to test speaker ohms?

P

Phil Allison

Jan 1, 1970
0
"Paul the Puke "
** Yes you can.

** That is all you need - then allow 15-20% extra on that number for the
nominal ( usually also the minimum ) AC impedance value.

The DC ohms plus 15-20 % rule applies to any cone loudspeaker ( drivers
only, not systems) - it accounts for the additional resistive losses in
the magnet structure and suspension parts when that speaker is driven with
AC at the frequency of its impedance minima.

As the other poster said, your method is a very rough
guestimate.

** No one here said that - you lying, fucking puke !!

The method is very accurate.

My point,

Dumbshit, was that the impedance of a speaker is
measured with AC, not DC.

** Irrelevant to the Q being asked - fuckwit.

Folk have been using multimeters to test speaker impedances ever since they
both existed.

ASD fucked shit brains like YOU are not about the stop them.

So **** Off and Die.

...... Phil

P

Phil Allison

Jan 1, 1970
0
"Anahata"
It depends on the crossover network, but even a simple 2nd order LC
network has a nominal crossover point independent of load (The frequency
where the impedance magnitudes of L and C are the same).

** The term " nominal crossover point" = meaningless drivel !!

Cos the word "nominal" means " in name only ".

In *reality*, a 2:1 impedance mismatch with a x-over filter has DRAMATIC
effect on its performance and the load impedance seen by the driving
amplifier in the region of the crossover frequency.

The drive unit impedance will have an effect but it will be second order.

** That is utter BOLLOCKS.

Eg An under loaded LC x-over filter turns into a series tuned circuit -
it then has a VERY low input impedance at the resonant frequency and
MULTIPLIES any input signal by many times creating a huge peak in the
response around that frequency. Very bad news.

...... Phil

E

Eeyore

Jan 1, 1970
0
Phil said:
"Eeysore

** Those speakers are 6 ohms AC impedance, as sine wave tests conducted at
250 - 400 Hz demonstrate.

It's ages since I ran a plot, so it's a bugger to remember. Note that the
cabinet will influence actual AC Z too.

The "nominal 8 ohms " value quoted by the makers is NOT derived by
electrical test, but is a *marketing tactic*.

EV started this nonsense in the 1980s, in order to squeeze out a couple of
dB extra sensitivity and so out-spec comparable JBL products - in the eyes
of dim witted customers.

Hi-fi speaker brands often do the same and justify it as "compensation " for
resistive losses in typical passive x-overs.

And now you get home hi-fi and especially 5.1 systems where the speakers are
actually rated at 6 ohms nominal to extract that extra dB or so.

Graham

E

Eeyore

Jan 1, 1970
0
George's Pro Sound Company said:
except when you put a 4 ohm loudspeaker on a passive crossover designed for
a 8 ohm box it doubles the value of the crossover point
so if it was crossing over at 1800 with a 8 ohm speaker it will now be
crossing over ar 3600 with a 4 ohm load

Only with a first order crossover. As the fliter order increases, the
difference will be less, but the filter damping suffers, so the response will
still be affected.

Not to mention a GOOD crossover compensates for the T-S characteristics of the
driver ( especially voice coil inductance ).

Graham

E

Eeyore

Jan 1, 1970
0
GregS said:
Well it probably will not work well, but the nominal Z is not important.
You have to know the exact graph of Z to know what the Z is at for
some desired crossover. The order of the crossover is also very important
to driver damping. You can get some really bad plots from some crossover
using another driver with different stories. Unless you get real lucky,
replacing it will cause some kind of grief. Its highly unlikely that the
level matching will be on or the phase will be slightly off. Many speakers will have
level controls, and sometimes that will be enough to compensate, but level controls
often also change the plot.With the name of the manufacturer in mind, the
crossover probably does not have any impedance compensation or
response compensation. Everything is built into the drivers and simple
crossover. Remember the driver can also cause an added pole depending on
the phase shift.

All the more reason to use active crossovers and bi / tri amping.

Graham

E

Eeyore

Jan 1, 1970
0
Paul said:
As the other poster said, your method is a very rough
guestimate.

My point, Dumbshit, was that the impedance of a speaker is
measured with AC, not DC.

I once did a sweep of a driver without thinking, cone downwards on the bench.
Turning it cone up made a visible difference to the plot. This is because the
speaker is doing mechanical work.

Graham

E

Eeyore

Jan 1, 1970
0
Rich said:
If it's really just a tear, and not a hole, you can repair the cone with a
little fingernail polish and toilet paper.

I tend to use PVA as the glue. More flexible.

Graham

P

Phil Allison

Jan 1, 1970
0
"Eeysore"
I once did a sweep of a driver without thinking, cone downwards on the
bench.
Turning it cone up made a visible difference to the plot. This is because
the
speaker is doing mechanical work.

** Face down, the speaker was being loaded by a ( more or less) sealed
enclosure of LESS than 1 litre volume.

No wonder the impedance curve was NOT the same as for "free-air" !!!

The correct procedure for finding the Fs of a driver involves dangling it
from the roof on a string.

...... Phil

P

Paul

Jan 1, 1970
0
"Paul the Puke "

As the other poster said, your method is a very rough
guestimate.

**  No one here said that   -   you lying, fucking puke !!

The method is very accurate.

Dumbshit, was that the impedance of a speaker is
measured with AC, not DC.

** Irrelevant to the Q being asked  -  fuckwit.

Folk have been using multimeters to test speaker impedances ever since they
both existed.

ASD fucked shit brains like YOU are not about the stop them.

So **** Off and Die.

.....   Phil

The stupider people are, the angrier they get!!

I can see the smoke from here!

BWAHAHA!

P

Phil Allison

Jan 1, 1970
0
"Paul the Retarded PUKE "

** No one here said that - you lying, fucking puke !!

** Irrelevant to the Q being asked - fuckwit.

Folk have been using multimeters to test speaker impedances ever since they
both existed.

And no ASD fucked shit for brains PUKE like YOU is about the stop them.

So **** Off and Die.

..... Phil

P

Paul

Jan 1, 1970
0
"Paul the Retarded PUKE "

** No one here said that - you lying, fucking puke !!

** Irrelevant to the Q being asked - fuckwit.

Folk have been using multimeters to test speaker impedances ever since they
both existed.

And no ASD fucked shit for brains PUKE  like YOU is about the stop them..

So **** Off and Die.

..... Phil

+BWAHAHAHA!

W

William Sommerwerck

Jan 1, 1970
0
Folk have been using multimeters to test speaker
impedances ever since they both existed.

You cannot properly measure impedance with a DC device.

W

William Sommerwerck

Jan 1, 1970
0
Folk have been using multimeters to test speaker
VOM read both ac and dc
here is how to use a VOM to measure impedance of a unknown
but working speaker, it does involve injection of signal

A multimeter (see above) does not provide that signal.

P

Phil Allison

Jan 1, 1970
0
Folk have been using multimeters to test speaker
impedances ever since they both existed.

You cannot properly measure impedance with a DC device.

..... Phil

W

William Sommerwerck

Jan 1, 1970
0
One of the fascinating things about UseNet is coming into contact (even if
only at a distance) with people who, at the very least, need someone to talk
to.

"Phil" (that's a Hitchhiker joke), do you think I'm actually bothered by

P

Phil Allison

Jan 1, 1970
0
"Richard Crowley = yet another PITA wanker "
You have not stated any motivation for this. In the likely opinion of
most people here, you have a speaker that is not worth any effort
to repair.

As others have observed you cannot measure AC impedance with
a device that measures DC resistance.

** Shame how you and the other two fuckwit, autistic pedants are 100% wrong
in the case of cone loudspeakers.

Nobody needs your posturing BULLSHIT shoved down their throats either.

And nobody give a flying **** what idiots like you think.

So piss off.

....... Phil

Replies
1
Views
706
M
Replies
4
Views
843
Phil Allison
P
E
Replies
13
Views
1K
Jeroni Paul
J
Replies
8
Views
1K
Replies
6
Views
663