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Old 4th August 2012, 01:40 AM   #1
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Question Dummy load to change speaker impedance?

Hey all,
I know that this is unconventional, but what are the pros and cons of using a dummy load to change driver impedance? For instance using a 8ohm driver in parallel with an 8ohm dummy load to give a 4ohm load, or in series for a 16ohm load.

Thanks!
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Old 4th August 2012, 02:18 AM   #2
DougL is offline DougL  United States
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Like everything else, it depends.

If your amplifier has lower distortion in either configuration, than its a benefit.
In general, either way you are simply waisting power for the honor of driving the amp harder, which generally has rising distortion.

Either way, half the power is dissipated as heat.
In the series configuration, not only does the speaker only receive half the power, the typical amplifier only is capable of half it's 8 ohm power into 16 ohms. Lowering the damping will change the Q of the base, which could go either way.

Way to go for thinking out of the box.
Just don't see much up side with it.

HTH

Doug
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Old 4th August 2012, 09:46 AM   #3
sreten is offline sreten  United Kingdom
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Hi,

The additional parallel load probably won't do anything useful unless
you have a high impedance amplifier. The additional series load will
make the amplifier act like a high impedance amplifier, which will
either interact well or badly with the speakers, typical multiway
speakers will turn boomy in the bass and peaky at the x/o points.

rgds, sreten.
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Old 6th August 2012, 12:05 AM   #4
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Quote:
Originally Posted by nonsuchpro View Post
Hey all,
I know that this is unconventional, but what are the pros and cons of using a dummy load to change driver impedance? For instance using a 8ohm driver in parallel with an 8ohm dummy load to give a 4ohm load, or in series for a 16ohm load.

Thanks!
An "8 Ohm" speaker can vary from 5 to 50 Ohms. Where it's 5 Ohms 8 Ohms in series will attenuate the output by 4.2dB and where it's 50 the output will be only -1.2dB from if it were directly connected so you'll have a 3dB frequency dependent variation in output level.
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Old 6th August 2012, 12:20 AM   #5
tvrgeek is offline tvrgeek  United States
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Putting an 8 ohm in parallel does two things. It wastes half the power, and it raises the distortion. Putting it in series wastes half the power, but has positive effects on the distortion. In a tweeter circuit, this is the normal way we pad the level in a passive crossover.


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Old 7th August 2012, 12:14 AM   #6
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Thanks for the replies. Mainly I like to use them to make a 4ohm tweeter 8ohms.
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Old 7th August 2012, 02:06 AM   #7
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re: "make a 4ohm tweeter 8ohms" - why?
you can use a 4 ohm tweeter with an 8 ohm mid/bass if crossover values are calculated appropriately, and you'll need an attenuator anyway....
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Old 7th August 2012, 11:56 PM   #8
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Quote:
Originally Posted by PeteMcK View Post
re: "make a 4ohm tweeter 8ohms" - why?
you can use a 4 ohm tweeter with an 8 ohm mid/bass if crossover values are calculated appropriately, and you'll need an attenuator anyway....
Unconventional trials... thats all. Making the 4ohm tweeter 8ohms may not need much padding or none with a 4ohm woofer.
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