this is not exactly a tube audio question, but it does concern the old
alnico speakers typically used with tube audio

I recently found some old Jensen alnico speakers that were made in the late
50's how can I tell their impedance? (it is not marked)

I know that speaker impedance is defined as "nominal" impedance and that it
is the minimum? impedance at some point when graphed against frequency, but
what I need to know is whether I can take a simple ohmmeter and figure out
whether an old alnico speaker is 4, 8, or 16 ohms etc.

thanks,

cowboy

arizona cowboy wrote:
this is not exactly a tube audio question, but it does concern the old
alnico speakers typically used with tube audio

I recently found some old Jensen alnico speakers that were made in the late
50's how can I tell their impedance? (it is not marked)

I know that speaker impedance is defined as "nominal" impedance and that it
is the minimum? impedance at some point when graphed against frequency, but
what I need to know is whether I can take a simple ohmmeter and figure out
whether an old alnico speaker is 4, 8, or 16 ohms etc.

thanks,

cowboy

Usually the DC resistance will be only slightly lower than the "nominal"
impedance. For instance, 8 ohm speakers will typically measure 6-7 ohms
on a DC ohm-meter.

Cheers,
Fred
--
+--------------------------------------------+
| Music: http://www3.telus.net/dogstarmusic/ |
| Projects: http://dogstar.dantimax.dk |
+--------------------------------------------+

Fred Nachbaur wrote:

arizona cowboy wrote:
this is not exactly a tube audio question, but it does concern the old
alnico speakers typically used with tube audio

I recently found some old Jensen alnico speakers that were made in the late
50's how can I tell their impedance? (it is not marked)

I know that speaker impedance is defined as "nominal" impedance and that it
is the minimum? impedance at some point when graphed against frequency, but
what I need to know is whether I can take a simple ohmmeter and figure out
whether an old alnico speaker is 4, 8, or 16 ohms etc.

thanks,

cowboy

Usually the DC resistance will be only slightly lower than the "nominal"
impedance. For instance, 8 ohm speakers will typically measure 6-7 ohms
on a DC ohm-meter.

Cheers,
Fred
--
+--------------------------------------------+
| Music: http://www3.telus.net/dogstarmusic/ |
| Projects: http://dogstar.dantimax.dk |
+--------------------------------------------+

I remember reading years ago that the DC resistance of a speaker, is typically
75% of the speaker's impedance. This isn't a hard and fast rule, but it will get
you close in most cases.

It's noth worth being too fussy about the exact value. In real life
it varies widely, particularly close to the crossover frequencies.

http://www.john-a-harper.com/spendor_bc1.html

shows the real-life curve as measured on my Spendor BC1s.
Any speaker will show something similar.

John

"Max Holubitsky" wrote in message
...


Fred Nachbaur wrote:

arizona cowboy wrote:
this is not exactly a tube audio question, but it does concern the old
alnico speakers typically used with tube audio

I recently found some old Jensen alnico speakers that were made in the
late
50's how can I tell their impedance? (it is not marked)

I know that speaker impedance is defined as "nominal" impedance and
that it
is the minimum? impedance at some point when graphed against
frequency, but
what I need to know is whether I can take a simple ohmmeter and figure
out
whether an old alnico speaker is 4, 8, or 16 ohms etc.

thanks,

cowboy

Usually the DC resistance will be only slightly lower than the "nominal"
impedance. For instance, 8 ohm speakers will typically measure 6-7 ohms
on a DC ohm-meter.

Cheers,
Fred
--
+--------------------------------------------+
| Music: http://www3.telus.net/dogstarmusic/ |
| Projects: http://dogstar.dantimax.dk |
+--------------------------------------------+

I remember reading years ago that the DC resistance of a speaker, is
typically
75% of the speaker's impedance. This isn't a hard and fast rule, but it
will get
you close in most cases.

"John Harper

It's noth worth being too fussy about the exact value. In real life
it varies widely, particularly close to the crossover frequencies.

http://www.john-a-harper.com/spendor_bc1.html

shows the real-life curve as measured on my Spendor BC1s.
Any speaker will show something similar.


** The question was about single cone drivers - not a loudspeaker system
as in your example.

Passive crossover networks and enclosures ( particularly ported ones)
dramatically affect the impedance as seen by an amplifier.

The rule of thumb that says add 20% to the DC value for bass drivers is
a very good one - the only issue is that some speaker makers quote phoney
nominal values, ie calling a 6 ohm speaker "nominal 8 ohms " just to fit in
with the standard value.




.............. Phil

Hi RATs!

In the situation of unknown impedence, just try them on the various output taps
and pick the one you like the sound from.

The likelihood that will be the same as the actual Z is high, but, not absolute


Happy Ears!
Al


Alan J. Marcy
Phoenix, AZ

PWC/mystic/Earhead