# How to test speaker ohms?

M

#### muzician21

Jan 1, 1970
0
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"?

Thanks

K

#### Kalman Rubinson

Jan 1, 1970
0
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"?

Well, you can measure the "ohms" in several ways but that is quite
inadequate for selecting a suitable replacement.

Kal

S

#### Scott Dorsey

Jan 1, 1970
0
muzician21 said:
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.

I think you want to toss it.
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?

The impedance of the speaker is only one of about a dozen parameters
that you need to measure for the driver. Vance Dickason's Loudspeaker
Cookbook has a whole chapter on measuring T-S parameters of an unknown
driver.
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"?

Sadly most folks are measuring inside the frame, and including the
surround in the cone size.

Really, though... if this is what I think this is, it's a junk speaker
and not worth the labour to haul it to the dumpster.
--scott

P

#### Paul

Jan 1, 1970
0
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"?

Thanks

You cannot test the AC ohms of a speaker with an multimeter,
because the multimeter only measures DC ohms resistance.

P

#### Phil Allison

Jan 1, 1970
0
"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

W

#### WillStG

Jan 1, 1970
0
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"?

Thanks

Well being what they are, they sell for like $25 -$40 a pair
used. So... for cheap and since you already paid for them, you can
try fixing the tear using the paper unwrapped from a couple of teabags
and some rubber cement. After it dries you can color it a bit with
magic marker,

Or just call Fisher Sanyo and ask them
http://sanyoservice.com/partdistributors.htm

Reconing isn't so very hard for DIY, but being what they are you
could just buy another pair on Craigslist for parts - and it would be
better to buy something else, especially for working on music. Modern
speakers are much, much better and 30 year old speakers have to be
dogmeat by now.

Will Miho
NY TV/Audio Post/Music/Live Sound Guy
"The large print giveth and the small print taketh away... Tom Waits

E

#### Eeyore

Jan 1, 1970
0
Phil said:
"Paul"

** 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.

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

Graham

E

#### Eeyore

Jan 1, 1970
0
WillStG said:
Well being what they are, they sell for like $25 -$40 a pair
used. So... for cheap and since you already paid for them, you can
try fixing the tear using the paper unwrapped from a couple of teabags
and some rubber cement. After it dries you can color it a bit with
magic marker,

Or just call Fisher Sanyo and ask them
http://sanyoservice.com/partdistributors.htm

Reconing isn't so very hard for DIY, but being what they are you
could just buy another pair on Craigslist for parts - and it would be
better to buy something else, especially for working on music. Modern
speakers are much, much better and 30 year old speakers have to be
dogmeat by now.

Graham

P

#### Phil Allison

Jan 1, 1970
0
"Eeysore
Phil said:
"Paul"

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.

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.

...... Phil

W

#### WillStG

Jan 1, 1970
0

Graham

If you can find me some for \$25 I'll take them - and recone 'em
myself! <g> A little saran wrap, ....

Will Miho
NY TV/Audio Post/Music/Live Sound Guy
"The large print giveth and the small print taketh away..." Tom Waits

W

#### William Sommerwerck

Jan 1, 1970
0
You cannot test the AC ohms of a speaker with an multimeter,
** 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.

That's a calculated estimate, not a measurement. There is a difference.

P

#### Phil Allison

Jan 1, 1970
0
"William Sommerwanker"
Paul

That's a calculated estimate, not a measurement.

** Paul used the words: " test the AC ohms of a speaker " - but he was
totally clueless.

The OP ( even more clueless than Paul) simply wanted to identify the
impedance of a small speaker for replacement purposes suing a multimeter.

Now, the actual impedance of any cone speaker can only be shown by a graph
or series of graphs, since it is not a single number and depends on many
variables - none of which matter a HOOT when all you want to know is the
impedance rating for replacement purposes.

Then, some ASD fucked **** called Sommerwanker butts his POINTY
anencephalic head in and a spews a pile of vile PEDANTRY all over the
place.

Go drop dead - Wanker !!!

....... Phil

S

#### Scott Dorsey

Jan 1, 1970
0
Paul said:
You cannot test the AC ohms of a speaker with an multimeter,
because the multimeter only measures DC ohms resistance.

No, although you CAN measure the DC resistance and do some handwaving and
say the impedance at 1 KHz is probably more or less about 1.5 times the
DC resistance. This is usually enough to get you into the ballpark if you
know the speaker is rated for a common impedance.

But, sadly, the impedance is only one of a whole lot of things the original
poster needs to know to replace the driver.
--scott

S

#### Scott Dorsey

Jan 1, 1970
0
Eeyore said:
Many nominal 8 ohm speakers I've seen measure as low as ~ 5 ohms at DC.
Largely SR/PA types though.

That's still more or less within range, if you know it's a standard
load. If you see 5 ohms DC, you know it cannot possibly be a 4 ohm
speaker, and it almost certainly isn't a 16 ohm speaker, so it's probably
an 8 ohm speaker.
--scott

G

#### GregS

Jan 1, 1970
0
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

G

#### GregS

Jan 1, 1970
0
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

Whenever I replace something its usually to BOTH sides if not
an identical replacement. Even that, it needs checked for
uniformity.

greg

G

#### GregS

Jan 1, 1970
0
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.

greg

R

#### Rich Grise

Jan 1, 1970
0
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

G

#### GregS

Jan 1, 1970
0
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

P

#### Paul

Jan 1, 1970
0
"Paul"

** 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.

.....   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.

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