How to test speaker ohms?

[Rich Grise]

On Thu, 09 Apr 2009 17:13:36 -0700, muzician21 wrote:

I want to replace the midrange of a Fisher speaker model ST-440
"Studio Standard Series". No idea what vintage it is - maybe 80's or
90's.

What's on the back is

SB-80521-1

L81TNK

AFAIK it's a factory speaker. Obviously I want to replace it with the
right kind of speaker. I have a multimeter, how do I test it? Only one
is damaged - it's been torn since I got them at a pawn shop - but do
you think I should replace both sides or is it not likely to make an
appreciable difference?

For sizing purposes, is the speaker size generally considered to be
across the speaker frame - about 4 3/4 " or the exposed portion of
the cone inside the speaker frame - right about 4"?

If it's really just a tear, and not a hole, you can repair the cone with a

little fingernail polish and toilet paper.

Good Luck!
Rich

 

[GregS]

In article <pan.2009.04.10.19.39.18.817520@example.net>, Rich Grise <rich@example.net> wrote:

On Thu, 09 Apr 2009 17:13:36 -0700, muzician21 wrote:

I want to replace the midrange of a Fisher speaker model ST-440
"Studio Standard Series". No idea what vintage it is - maybe 80's or
90's.

What's on the back is

SB-80521-1

L81TNK

AFAIK it's a factory speaker. Obviously I want to replace it with the
right kind of speaker. I have a multimeter, how do I test it? Only one
is damaged - it's been torn since I got them at a pawn shop - but do
you think I should replace both sides or is it not likely to make an
appreciable difference?

For sizing purposes, is the speaker size generally considered to be
across the speaker frame - about 4 3/4 " or the exposed portion of
the cone inside the speaker frame - right about 4"?

If it's really just a tear, and not a hole, you can repair the cone with a
little fingernail polish and toilet paper.

Good Luck!
Rich

It was not clear if the speaker made sound, or if it really made any
noticable difference in output in the first place. I assumed it
didn't work at all. Its not really necessary to mend the pieces together.
Often a dab of rtv will be all thats needed.

greg

 

[Paul]

On Apr 10, 12:31 am, "Phil Allison" <philalli...@tpg.com.au> wrote:

"Paul"

You cannot test the AC ohms of a speaker with an multimeter,

** Yes you can.

because the multimeter only measures DC ohms resistance.

** 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.

.....   Phil

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.

 

[Phil Allison]

"Paul the Puke "

You cannot test the AC ohms of a speaker with an multimeter,

** Yes you can.

because the multimeter only measures DC ohms resistance.

** 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,

** You had no point - you stupid cunthead.


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 Fuck Off and Die.



...... Phil

 

[Phil Allison]

"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

 

[Eeyore]

Phil Allison wrote:

"Eeysore
Phil Allison wrote:
"Paul"

You cannot test the AC ohms of a speaker with an multimeter,

** Yes you can.

because the multimeter only measures DC ohms resistance.

** 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.

Many nominal 8 ohm speakers I've seen measure as low as ~ 5 ohms at DC.
Largely SR/PA types though.

** 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

 

[Eeyore]

George's Pro Sound Company wrote:

"GregS" <zekfrivo@zekfrivolous.com> wrote in message
Eeyore <rabbitsfriendsandrelations@hotmail.com> wrote:
Phil Allison wrote:
"Paul"

You cannot test the AC ohms of a speaker with an multimeter,

** Yes you can.

because the multimeter only measures DC ohms resistance.

** 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.

Many nominal 8 ohm speakers I've seen measure as low as ~ 5 ohms at DC.
Largely SR/PA types though.

There are speakers that have that 6 ohm nominal Z. Common in todays
consumer market.

Z is probably the least important spec the guy will need.
Efficiency and resonance, and physical size are more
important. I was loking for some cheap looking units of about 8 ohms.
Here Loook..
http://www.mcmelectronics.com/browse/Midrange/3829617


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

 

[Eeyore]

GregS wrote:

Anahata <anahata@treewind.co.uk> wrote:
On Fri, 10 Apr 2009 12:01:51 -0400, George's Pro Sound Company wrote:

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

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

The fact remains that using a 4 ohm unit where an 8 ohm one is expected
still won't work very well: the balance between them won't be right, and
the impedance/frequency curve of the whole box will be even more wonky
than usual.

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

 

[Eeyore]

Paul wrote:

"Phil Allison" <philalli...@tpg.com.au> wrote:
"Paul"

You cannot test the AC ohms of a speaker with an multimeter,

** Yes you can.

because the multimeter only measures DC ohms resistance.

** 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.

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

 

[Eeyore]

Rich Grise wrote:

On Thu, 09 Apr 2009 17:13:36 -0700, muzician21 wrote:

I want to replace the midrange of a Fisher speaker model ST-440
"Studio Standard Series". No idea what vintage it is - maybe 80's or
90's.

What's on the back is

SB-80521-1

L81TNK

AFAIK it's a factory speaker. Obviously I want to replace it with the
right kind of speaker. I have a multimeter, how do I test it? Only one
is damaged - it's been torn since I got them at a pawn shop - but do
you think I should replace both sides or is it not likely to make an
appreciable difference?

For sizing purposes, is the speaker size generally considered to be
across the speaker frame - about 4 3/4 " or the exposed portion of
the cone inside the speaker frame - right about 4"?

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

 

[Phil Allison]

"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

 

[Phil Allison]

"Paul the Retarded PUKE "


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

** You had no point - you stupid cunthead.

** 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 Fuck Off and Die.




..... Phil

 

[Paul]

On Apr 10, 6:15 pm, "Phil Allison" <philalli...@tpg.com.au> wrote:

"Paul the Puke "



You cannot test the AC ohms of a speaker with an multimeter,

** Yes you can.

because the multimeter only measures DC ohms resistance.

** 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,

**  You had no point  -  you stupid  cunthead.

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 Fuck Off and Die.

.....   Phil

The stupider people are, the angrier they get!!

I can see the smoke from here!

BWAHAHA!

 

[Paul]

On Apr 10, 10:39 pm, "Phil Allison" <philalli...@tpg.com.au> wrote:

"Paul the Retarded PUKE "

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

** You had no point - you stupid cunthead.

 ** 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 Fuck Off and Die.

 ..... Phil

+BWAHAHAHA!

 

[William Sommerwerck]

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

You cannot properly measure impedance with a DC device.

 

[George's Pro Sound Compan]

"William Sommerwerck" <grizzledgeezer@comcast.net> wrote in message
news:grpvt7$9ll$1@news.motzarella.org...

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

You cannot properly measure impedance with a DC device.

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

http://zekfrivolous.com/sub/usenet/pierce/impedometer.html

george

 

[William Sommerwerck]

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

You cannot properly measure impedance with a DC device.

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

http://zekfrivolous.com/sub/usenet/pierce/impedometer.html

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

 

[George's Pro Sound Compan]

"William Sommerwerck" <grizzledgeezer@comcast.net> wrote in message
news:grq46a$cha$1@news.motzarella.org...

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

You cannot properly measure impedance with a DC device.

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

http://zekfrivolous.com/sub/usenet/pierce/impedometer.html

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

the multimeter is doing the measurments.
I am simply showing that a VOM is a useful tool that can be used to measure
impedance

you do not need a fancy occiliscope/signal gen rig a amp passing noise
such as between radio stations is sufficent

I use the Part Express /Dayton WT3 for my impedance measuments but years of
in feild service to commercialsound system required that i understand how to
get the most out of a VOM

link to the WT3
http://www.daytonaudio.com/wt3.html

 

[Phil Allison]

"William Sommerwanker CUNT HEAD "

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

You cannot properly measure impedance with a DC device.

** You made that same fucking asinine remark already.

CUNT HEAD !!





..... Phil

 

[Phil Allison]

"William Sommerwanker CUNT HEAD "

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

You cannot properly measure impedance with a DC device.

** You made that same fucking asinine remark already.

CUNT HEAD !!





..... Phil