4 ohm to 8 ohm conversion? - AVS Forum
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post #1 of 6 Old 05-06-2005, 07:18 PM - Thread Starter
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This probably sounds bizarre, but is there anyway to convert a 4 ohm speaker to 8 ohm? I have two Kef c25 bookshelf speakers (about 13 years old that are 4 ohm) that have not been abused by any means. I would like to add them to my HT system, could this be done? Would I be better off just selling them? My receiver is rated at 6-8 ohm.

Thanks.
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post #2 of 6 Old 05-06-2005, 08:35 PM
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The KEF series to which you refer are 8ohm drivers. Although I did see some 6 ohm versions in the "C" series here in Canada. Your receiver should be fine.

"C" series link to KEF:

http://www.kef.com/history/1980/c20.htm

:)
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post #3 of 6 Old 05-06-2005, 08:55 PM
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Other people please feel free to correct me if this is a bad idea, but... When I was in middle school, I bought some car subwoofers at a pawn shop. They were 4 ohm speakers, but I needed them to be 8 ohm (just like you). So I went to RadioShack, bought 8 1-ohm resistors (big ones, they looked like little pencils made of concrete) and wired them inline with the speakers.

The speakers worked. But the speakers were crappy and the receiver was crappy also. There very well may be a reason not to do this, but it seems like it should work. Just make sure they can handle the amperage.

Your mileage may vary.
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post #4 of 6 Old 05-06-2005, 09:18 PM
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I would never put resistors in series because you are just robbing your speakers and turning half the current into heat.

Your reciever will most likely be fine if you listen at moderate levels, or you add an external 2 channel amp for just those speakers.

If you can find an impedance plot or have the know how to do it yourself (and you can do it yourself, it just takes a bit of doing), you might be suprised to know that those 4 ohm speakers are only 4 ohm for maybe 100-200hz, and they rise to 8 ohms for most of the bandwidth, and the 4ohm rating is only a minimum, manufacturers do the rating of resistance in all sorts of ways.

If you turn your speakers down 3 db, you will be needing the same current as if you were using an 8 ohm load, so just consider that, and keep your reciever cooled, and if you really want to be safe you could calculate how much amperage your reciever can put out safely and put a fast blow fuse on your speakers so you know when you've hit that level and not to go that much.

If you must use resistors (and I say this is a very bad idea), do not buy from radioshack, but buy from partsexpress, etc, and look for non-inductive mills resistors, so you don't degrade the audio signal as much, but there really is no reason to do this, because it does the same thing as turning the speaker down 3db, in essence.

If you have any questions about measuring impedance I can point you to some resources, and its a fairly cheap operation just takes some know how, and doing and time.
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post #5 of 6 Old 05-07-2005, 11:36 AM
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... like I said, please correct me if this is a bad idea. Thanks bjackson for the professional opinion.
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post #6 of 6 Old 05-08-2005, 12:51 PM - Thread Starter
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I appreciate your responses. On the back of the speaker near where you hook up the wires is a sticker that says 4 ohms (actualy it is the ohm symbol) followed by 100w. My C25's do not look like the speakers in the link that you provided to me, i.e. (the KEF history link). My other speakers are 8 ohm. I am using a Pioneer 1015 receiver. Would they still work if I play them at a moderate level as I know that they will draw more current. Or am I risking receiver damage?

When I bought these many years ago I used them with a Yamaha receiver (An RX-350, a very low end yamaha receiver back then for sure) that was rated at 6 ohm min imp. They always played fine for me though.

Thanks
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