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#1
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speaker impedance question
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 |
#2
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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 | +--------------------------------------------+ |
#3
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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. |
#4
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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. |
#5
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"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 |
#6
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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 |
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