Impedance Mismatch

sushizen · 15th November 2006, 09:13 PM

I am thinking about salvaging some wonderful Fisher bicone 8" fullrangers from an old set of Executive cabinets, but I am running into a minor roadblock. Due to either the manufacturing quirks of voice coils in the early 1960s, or some brilliant passive-component-free impedance matching speaker design by Fisher, The two 8" units have totally different D.C.R.s. One measures 9ohm and one measures 22ohm. Another spare one I have measures 12ohm as well! Frequency response & Fs are nearly identical. They are sweet little alnicos with underdamped magnets and light, fiber impregnated paper cones. Could do fine in a small Q-shifting type enclosure with an acoustic resistance unit or a mesh vent.

Is there any way that I might be able to match some transformers to these speakers to stabilize the loads? If so, how?

Anyone else had much luck with older fullrangers retrofitted in smallish enclosures who might be able to contribute some suggestions?

Geoff H · 16th November 2006, 12:18 PM

Hi sushizen,
I recently purchased some Martin Audio autotransformers, 200W (system) Multi tap 16:8:4:2:1 on eBay. He had a number available at the time.

Another option would be to use high quality PA 100v line transformers as autotransformers. If you get something rated at 25w or higher, there should be enough primary inductance not to limt the bass.

15th November 2006, 09:13 PM	#1
sushizen diyAudio Member Join Date: Mar 2006 Location: chicago	Impedance Mismatch I am thinking about salvaging some wonderful Fisher bicone 8" fullrangers from an old set of Executive cabinets, but I am running into a minor roadblock. Due to either the manufacturing quirks of voice coils in the early 1960s, or some brilliant passive-component-free impedance matching speaker design by Fisher, The two 8" units have totally different D.C.R.s. One measures 9ohm and one measures 22ohm. Another spare one I have measures 12ohm as well! Frequency response & Fs are nearly identical. They are sweet little alnicos with underdamped magnets and light, fiber impregnated paper cones. Could do fine in a small Q-shifting type enclosure with an acoustic resistance unit or a mesh vent. Is there any way that I might be able to match some transformers to these speakers to stabilize the loads? If so, how? Anyone else had much luck with older fullrangers retrofitted in smallish enclosures who might be able to contribute some suggestions?

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16th November 2006, 12:18 PM	#2
Geoff H diyAudio Member Join Date: Oct 2006	Hi sushizen, I recently purchased some Martin Audio autotransformers, 200W (system) Multi tap 16:8:4:2:1 on eBay. He had a number available at the time. Another option would be to use high quality PA 100v line transformers as autotransformers. If you get something rated at 25w or higher, there should be enough primary inductance not to limt the bass.

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