Converting from 4 ohm to 8 ohm

[SpinninAgain]

Is it possible to convert 4 ohm speakers to 8 ohm speakers? If I wire in a 4 ohm resistor will it degrade to audio too much?

The reason I ask is that I acquired a set of model twenty speakers. They are 4 ohm, have RCA jacks and are in rough shape.

I was going to install some binding posts to run them off regular speaker wire instead of the RCA jack. While i'm in there I figures I could solder in a resistor and be done with it.

I'm not looking for fabulous sound out of these. I will probably gift them to a family member along with a receiver I'm not using. I don't want to blow anything up in the process.

Thanks for the advice.

 

[SaSi]

That resistor you are refering to would need to consume as much power as the speakers themselves, to have an overall impedance of 8 ohms. That would mean a substantial resistor, 50-100W, with consideration for cooling it. So, in theory it's possible, but there is absolutely no reason to do it.And yes, that resistor would count towards the amplifier's output impedance, making it practically equal to the speakers, giving an overall damping factor of about 1.

Why would you want to raise their impedance? Most amplifiers will be able to drive 4 Ohm speakers.

 

[rothwellaudio]

That resistor you are refering to would need to consume as much power as the speakers themselves, to have an overall impedance of 8 ohms. That would mean a substantial resistor, 50-100W, with consideration for cooling it. So, in theory it's possible, but there is absolutely no reason to do it.And yes, that resistor would count towards the amplifier's output impedance, making it practically equal to the speakers, giving an overall damping factor of about 1.

This is correct. The speakers will also be considerably quieter.
It's not a great idea to add a resistor.
BTW, your speakers may be no closer to 4 ohms than many speakers labelled as 8 ohms. The impedance goes up and down across the frequency spectrum and the nominal impedance figure quoted by manufacturers is really just a kind of average. Some take liberties when deciding what figure to quote.

 

[SpinninAgain]

@SaSi @rothwellaudio You are correct. I wasn't thinking. it was a long day yesterday. I was thinking the resistor would only need to absorb half the power and the rest of the components would do what they normally do. I should know better. Too many projects going right now.

Thanks.

 

[toxcrusadr]

Some receivers/amps won't be happy driving them to high volumes, but most will be just fine.

 

[Bill Ferris]

If possible/practicable, you can have them, or at least the important ones, re-coned to 8 ohms, by a qualified speaker service shop.
Back in 1979 somebody gifted (4) 15"JBL 16 Ohm speakers to the bass player of the band that I was employed as a FOH sound engineer of..
The 16 ohms impedance was not going to draw out of my PA bass amplifier the wattage/ SPL that I wanted, so I had my re-coning employed girlfriend trash them(rip the guts out of perfectly functioning speakers) so as to re-cone them to 8 ohms, so when installed two to a cabinet, the Bose 1800 power amp produced it`s rated power..
And they did their job perfectly..
My girlfriend, employed as a trained speaker re-conner/repair person, was very good at her job.
At parties we(the band) were invited to, I often introduced her as giving "the best cone" in town, she was a good sport about it, and was proud of the quality of her speaker repair/re work..

Just an suggestive option

 

[bowtie427ss]

While it's not practical in terms of cost for the OP's situation, i am surprised that nobody mentioned the obvious, a matching transformer/autoformer.

Specifically, i am referring to high quality audio transformers and autoformers such as those made by the Peerless division of Western Electric/Altec.

The Peerless 15067 is one such example, and a good description can be found here: http://alteclansingunofficial.nlenet.net/publications/techletters/TL_106.pdf

 

[kirk57]

If possible/practicable, you can have them, or at least the important ones, re-coned to 8 ohms, by a qualified speaker service shop.

Or the OP could find a pair of woofers from the KLH Seventeen and drop them in. I have both 17s and 20s and it’s been a while since I was inside them, but I recall that aside from the woofer and terminal plate, they were identical.

But neither of these options are all that cheap.

My advise is to just leave them as they are. Make sure the recipient understands to not use 2 pairs of speakers if one of them are a 4 ohm load.

 

[Keath]

That resistor you are refering to would need to consume as much power as the speakers themselves, to have an overall impedance of 8 ohms. That would mean a substantial resistor, 50-100W, with consideration for cooling it. So, in theory it's possible, but there is absolutely no reason to do it.And yes, that resistor would count towards the amplifier's output impedance, making it practically equal to the speakers, giving an overall damping factor of about 1.

Why would you want to raise their impedance? Most amplifiers will be able to drive 4 Ohm speakers.

I wanted to convert due to thwe fact all my seakers are 8 ohm speakers and i use the a and b all the time at the same time Rockville sent 4 ohm "out of 8ohm" so since i use a and b i cant run both a and B
??

 

[charles 1973]

I wouldn't permanently install a resistor on the speaker. But installing an external 4 ohm resistor in series will have the same effect and can be undone easily. Be sure it is not in contact with flammable material.

You will need one that can handle the heat though. Since heat correlates with continuous rms power, a 10w resistor might be good for 100w amps when clipping. Continuous rms power is about 1/10 the short term peaks for most music.

This is the principle behind those impedance matching speaker switches. While this does effect sound quality, apparently most folks have no complaints. This might be a good option for you.