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Change Impedence on a Speaker?


The Geoff

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Without going into too much detail, I have a 16 Ohm and an 8 Ohm speaker which I want to match up to an 8 Ohm amp output. Is there a resistor I can put in series in front of the 8 Ohm to make it 16, then wire the 2 in parallel? Or what about if I took a little 8 Ohm speaker & put it in line and maybe if I took the cone out just to make it a resistance?

 

Anyone done anything like that?

 

Geoff

"When the power of love overcomes the love of power the World will know Peace": Jimi Hendrix

http://www.soundclick.com/bands/default.cfm?bandID=738517&content=music

The Geoff - blame Caevan!!!

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You're in a real mismatch situation here, In parallel, you get a bit above 5 ohms,

and in serie, 24 ohms. Of course a 8 ohms resistor in serie with the 8 ohms spkr, then

both in parallel will give you a total of 8 ohms but some good power is going to be lost

as heat in the resistor (which could have to be physically huge to handle it).

 

Are you sure your amp can't handle 4 ohms? 5 and some ohms will do then but the 8 ohms

spkr will pass 4 times the power the 16 ohms will - that's ohms law...

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"Dummy" loads as they are called, have to absorb a lot of heat. If your speakers are rated for 100W, then so should the dummy load. You'd have to find a 100W resistor.

 

The 8 and 16 speakers in parallel would be 5.3 ohms. It won't "wreck" your amp to try it. Just turn the volume up to increasing levels, slowly, and see how it responds.

 

What kind of amp are you using?

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MMmm. It's a pretty old Maine Musician 150 Watt tranny bass/lead combo. It had a couple of ancient McKenzie 12" speakers which showed round about 12 on the multimeter, so I'm assuming they are 16 Ohms and they were wired in parallel, hence 8 Ohms. They are both blown (long story - no good answer). I've a Fane KT100-12T twin cone bass speaker that's gone in & working great and I can get hold of another 100 or 200watt, but either or both are 8 Ohms.

 

Since the amp is so old I don't really know how it'll handle the mismatch. I'm playing my bass through it in the meantime till I get something more suitable (and lighter) so it's pretty imperative I get it up & running. I have a Celestion G12-65 8 Ohm sitting spare but I don't know if it'd take it. I just wondered if there was a way of rigging a resistor to get round the problem Can you get 100W/8 Ohm resistors? I am illiterate in this area (obviously :confused: ). I appreciate any help here at all.

 

Geoff

"When the power of love overcomes the love of power the World will know Peace": Jimi Hendrix

http://www.soundclick.com/bands/default.cfm?bandID=738517&content=music

The Geoff - blame Caevan!!!

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Never heard of the brand. Is it a tube or transistor amp?

 

Either way, if you did match it up with a 8 ohm dummy load, you will end up turning up to a suitable volume and dissipating a lot of heat.

 

Just try the extra speaker. Start at a low volume. Then, bring it up to a volume you can use. If nothing is distorting, you are fine. No distortion means no problems.

 

Perhaps it would run a little hotter, but no more than if you had 1/4 of the power being dissipated as heat and the rest being used to make up for the volume loss.

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OKDKY - it's an old 1st generation transistor amp - came out about the same time as HH and only sold this side of the Pond, to the best of my knowledge - I have this combo which I bought of eBay for about $100 and I also have a 120 head and 2x12 compact cab (130W/16 Ohm) both of which I bought new in the mid-70s. I may recone the McKenzies for that cab - it'll bring it down to 8 Ohm and let the head give its full power. In the meantime I've my eye on a 200 watt/8 Ohm speaker local to me on eBay which is used but OK and cheap, so I'll try for that in a couple of days. Thanks for the feedback.

 

Geoff

"When the power of love overcomes the love of power the World will know Peace": Jimi Hendrix

http://www.soundclick.com/bands/default.cfm?bandID=738517&content=music

The Geoff - blame Caevan!!!

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