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Old 15th December 2007, 01:52 PM   #1
SikSS is offline SikSS  Canada
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Default 4ohm speakers for 8ohm application?

My first post, so be gentle...

I've got a friend who's selling 2 older Rockford Fosgate 15's but they are single coil 4 ohm, while the 15"s I had in my stereo speakers were 8ohms.

If my speakers were 3 way(3 speakers wired per speaker box: tweeter/mid/sub), each I'll assume 8ohm, then wired to the amp, Is there a way I can wire the pair of these 4 ohmed subwoofers in series or parrallel to make them work as an 8ohm and still have the mids and tweets play as normal?

I've heard that you make the amp work harder if you run them as 4ohm instead of 8ohm, and as my amp only 50watts/channel, probably not a good idea. It's an older AKAI AM-UO1.

Any recommendations...?

If I can't get this to work, I'm going to start a project to build my own new speakers with the new tablesaw I purchased a few weeks ago. Well, I'm going to do that anyway, as I'd like to build some amplified computer speakers...

Your help would be appreciated.
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Old 15th December 2007, 02:12 PM   #2
Did it Himself
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The ohm issue is not so important as long as your amp can drive 4 ohms. The short answer is no you can't increase the ohms without detriment.

If your amp can drive 4 ohms OK then you should be considering the sensitivity differences rather than the ohms differences between drivers.

Are you saying you want to put the Rockford Fosgate speakers into your current box with the other drivers and crossover? That will likely not work as the crossover will be wrong and possibly the box design as well.
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Old 15th December 2007, 03:03 PM   #3
SikSS is offline SikSS  Canada
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Quote:
Originally posted by richie00boy

If your amp can drive 4 ohms OK then you should be considering the sensitivity differences rather than the ohms differences between drivers.

Are you saying you want to put the Rockford Fosgate speakers into your current box with the other drivers and crossover? That will likely not work as the crossover will be wrong and possibly the box design as well.
The amp can run 4ohm, but then what does that do to those already installed 8 ohm speakers....Hmmmm

You nailed it, I'd like to swap the RF's into the same hole.

Now, couldn't I run them in series between each of the 2 stereo speaker boxes. Run positive wire out of the box(crossover) to positive terminal of the sub, then negative not to the negative in the box but run a long length of with to the negative of the other sub in the box, then the power (+ve) wire to the crossover?
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Old 15th December 2007, 03:24 PM   #4
AndrewT is offline AndrewT  Scotland
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Hi,
no, you can't series connect the low pass sections of the two crossovers.

The crossover may be changed to accommodate the lower impedance driver but changing the low pass crossover components is just the start of this fundamental change.

Keep the 4ohm drivers and use them to augment your new speakers if they are suitable.
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Old 15th December 2007, 04:09 PM   #5
SikSS is offline SikSS  Canada
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Think I'll look for a replacement set of 8ohm speakers to make it easier.

Thanks for your help gentlemen.

On to bigger and better things, home-made powered computer speakers..... have to put my tablesaw to use before the wife asks me to start any major indoor projects.
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