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In Reply to: Ohms? posted by vanillaice_378@hotmail.com on April 1, 2007 at 20:34:46:
If you really want to use those speakers with that receiver,you could put a 4 ohm resistor in series with each speaker.Half the power will be wasted across the resistors,but at least the amp will be happier.It's only a 3 db drop in output level,so unless you play them really loud,you probably won't even notice the difference.Since the amp is rated 100 w/ch,you should use a 50 watt resistor,but half that should work fine.
Follow Ups:
Speakers are reactive devices where the impedance magnitude and phase varies with frequency.Putting a 4 Ohm nominal speaker in series with a 4 Ohm resistors looses 6dB (not 3 - adding resistance in series halves both voltage and current) where the impedance is actually 4 Ohms, 7.4dB where they drop below that to 3 Ohms, and just 1.1dB down where they peak at 30 Ohms thus instroducing a response variation of 6.3dB which is hardly high-fi.
You don't want to do that.
Assuming the amplifier is stable into 4 Ohms, you can use the speakers as-is but need to live with a lower maximum volume than you could get with 8 Ohm speakers of lower sensitivity.
Most consumer receivers will go into a thermal protection mode before anything gets damaged.
You are correct that adding resistance will lower the current,but are assuming that the voltage will remain constant.It won't,because in this application,you will turn the volume up to where the level was before.Half the power will be across the resistor,and half across the speaker.Still 3 db. Of course,we're assuming a constant impedance in the speaker,which it isn't.Even without the resistor,the current through the speaker will vary depending on impedance,so it's not really a big deal.
If your room does not change the response of your system more than 6 db,you are far ahead of most of us.
He said the amp was not recommended for use at 4 ohms,so telling him it is OK to use it anyway,and rely on the thermal overload is not doing him any good,and IMO,quite foolish...
So are you saying that since it has thermal protection should I use the Control 1 and not have to worry? I know that my receiver has a overload protection but that's probley the thermal protection. Or should I get a speaker called the Control 1Xtreme since they are like the same speakers but only difference is it's 8 ohms and it has titanium-laminate dome tweeters instead of Polycarbonate dome and 4 ohms. But I know I really like the sound of the Control 1 so if I could I would like to use it. But since the Xtremes are very close to the orginal maybe I should get that. I don't know.
There is a speaker called the JBL Control 1Xtreme and I was thinking to swap crossovers then the Control 1 will be 8 ohms. Both speakers use the same enclosures and crossover and woofer and tweeters size they are just measured differently but they are pretty much same speakers. Do you think this will be the best so I can use the orginal Control 1 on my receiver?
How much does this resistor cost? If it's expensive then I can't afford it.
You can use five 20 ohm 10 watt resistors in parallel to get 4 ohms at 50 watts...98 cents each at Partsexpress.com
Well I see in that site that there is a 4 ohms one but will that be the best to get so I can just buy two resistors?
http://www.partsexpress.com/pe/showdetl.cfm?&Partnumber=004-4
Yes,you could use just one 4 ohm resistor,but it only has a 10 watt power rating...Since average power levels are generally considerably lower than peak,it may be all you need.If you play something loud with lots of bass,however,you may need a bit more.
Using five 20 ohm resistors in parallel will give you 4 ohms,with a 50 watt rating.Or you could use four 16 ohm resistors for a 40 watt rating.Or two 8 ohm resistors for a 20 watt rating.
I wouldn't rely on the thermal overloads on the amp to protect it.Better safe than sorry...At 98 cents per resistor,it's cheap insurance.
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