impedance question

[blueguitar]

Hoping that you all can help me understand a basic impedance question.

In theory, if I had a speaker that was at a lower impedance rating than the ampifyer (eg 4 ohms in an 8 ohm amp), could a resistor be added in series to the speaker to bring the total impedance up? Would a 4 ohm resistor be the appropriate choice?

I do recognize that I'm asking a very very basic question here. Humor me.

Blueguitar.

[Jazz P Bass]

In theory, I would have to say it will work.

In practice, there would most probably be a tonal change, speakerwise.

Being a series circuit, you would want to match the two resistances the best that you can.

[Enzo]

Yes, you could put a 4 ohm resistor in series with a 4 ohm speaker and the amp would see 8 ohms.

I cannot think of a very practical application though. The two would share power equally. SO if we had 100 watts leaving the amp, the speaker would see 50 watts and the resistor would see 50 watts.

[The Dude]

^^^^ What he said. A good chunk of your power will become heat instead of sound. What kind of amp are we talkin' here? If it's a tube amp, most are very forgiving. It would not likely hurt the amp to just plug in and forget about the resistor. Also, the power rating of the resistor will need to be matched to the situation. Without knowing what amp we're talking about, it could be a pretty good sized resistor and will likely need a good heat sink.

[blueguitar]

Thanks for the replies. I'm not really interested in doing this, it was more just a theory question. No real world application intended. I never thought about the heat. That is important to consider as well. The power has to be converted into something I suppose.

Thanks again.

[Jazz P Bass]

Try as we might, you cannot ignore 'Ohm's Law'.

[olddawg]

I used to have to do that all of the time when people were mixing brands of stereos and speakers back in the old days. Many amps didn't like some expensive speakers that would drop below the rated lowest load for some solid state amps of the time. Yamaha and Infinity were famous for it. People would burn the amps up over and over. And .... I had to make what the sales people sold them work no matter what. So I would take the speaker apart and add a 2 ohm 20 watt ceramic resistor in series to the positive terminal inside. No body ever noticed a difference except their amps quit blowing up. And these were the "Golden Ear" crowd.

[KCblues]

Sure you can do that, it will serve as a 3dB (half power) attenuator.

[J M Fahey]

So I would take the speaker apart and add a 2 ohm 20 watt ceramic resistor in series to the positive terminal inside. No body ever noticed a difference except their amps quit blowing up. And these were the "Golden Ear" crowd.

Well, that's funny

Not that I don't believe it, quite the contrary.

[blueguitar]

I used to have to do that all of the time when people were mixing brands of stereos and speakers back in the old days. Many amps didn't like some expensive speakers that would drop below the rated lowest load for some solid state amps of the time. Yamaha and Infinity were famous for it. People would burn the amps up over and over. And .... I had to make what the sales people sold them work no matter what. So I would take the speaker apart and add a 2 ohm 20 watt ceramic resistor in series to the positive terminal inside. No body ever noticed a difference except their amps quit blowing up. And these were the "Golden Ear" crowd.

That is interesting. I guess once you pay for the "best" you assume you are listining to the "best". They didn't notice the drop in volume?

[Enzo]

Only way you'd notice a volume drop would be if you switched it in and out while listening. I am not going to think anything was wrong if my listening volume for some song was 5.63 instead of 5.53 on the volume control.

That is why we should shop for audio gear with our ears, not our eyes.

[J M Fahey]

And those are the guys who claim to hear a 0.1dB difference or polystyrene vs.polypropylene cap dielectric.
Oh well.

[R.G.]

... and claim that any test that shows a conflict with their purely-subjective tests is wrong AND that anyone who believes in such tests is dim-witted, closed-minded, and tone deaf. At best.

[pdf64]

Bear in mind that the impedance rating of a speaker is nominal, for regular guitar speakers it applies over the lower mids and mids.
At the speaker's bass resonance frequency, the impedance may be over ten times above the nominal value and at treble frequencies the impedance rises to around twice the nominal rating.

As an example, see the grey trace in http://www.eminence.com/pdf/Legend_GB128.pdf

That may tend to result in the speaker dissipating more than half the power.
Pete

[Chuck H]

That may tend to result in the speaker dissipating more than half the power.
Pete

I was going to post on the dynamic speaker impedance issue if I didn't find it in the thread. But wouldn't the lower ohmage of the resistor mean that the speaker will actually be dissipating LESS than half the power where it's impedance is higher than the resistor?