Impedance matching "patch" ?

Hi, this one may seem a little left of centre, but I do like to try and apply what I have learnt elsewhere... hope this is not a simple impedance question :)

In radio you can match the impedance using different lengths of 50/75 ohm cable to make a "balun" allowing a perfect match and avoiding a standing wave....

In PA terms, you can measure Impedance of wires and speakers, but can you "Correct" the impedance by adding a wire /resistor to the circuit :eg:

I want to bridge my amp at 4ohm , but when I check my cabs and the cables I have got, I have 3 ohms..which is not what I want... can I fix this with a simple wiring patch ?

Would I just make a series and parallel patch box to make the Ohms nearer to 8 , thus keeping in the safe operating parameters of the amp ?

Are the other ways I should consider ? ( its all theoretical at present...but better to plan than shell out and find you have the wrong set up )

many thanks in advance as always !

Hey, thanks for the response-
Maybe I have phrased eth question poorly.

the answer to your query is nope- I would buy an Ohm Meter , and I know Impedance is for AC and resistance for DC :) . the terms do get interchanged , but remember I am trying to apply some theory to see if there is similar theory to matching theory in RF

I also get the basic series -parallel usages to keep/ change resistance, matching , but wondered if there were any other ways used to adjust say when we wanted to use 4ohms, but ensure we don't drop too far below this figure for too long. for example you have 2 8 ohm cabs- on the same bridged output, getting 4ohms, but with the cables you get 3 ohms- can you use a breakout box of some type to correct the 1ohm variance, or would you have to use w series & parallel wiring and go with 8ohm ? IE: Is that the only method ?

You need a HELL of a lot of cable to make a 1 ohm change in a speaker system, especially if you’re using a sensible thickness of copper for the cores. I’m talking over 100m of 4mm2.


Speakers are not a fixed impedance device. They have an impedance curve that always varies with frequency, often by large amounts. A multimeter will not show this, you need to plot the impedance curve to see a true value in the pass band of choice. You can do that with REW - read the manual.

I get what you’re trying to do, but don’t understand why. If your cabs are 4R nominal each, why are you trying to make them 8R. What’s the set up you’re looking to achieve?

Danielr wrote: When people are talking about 50ohm and 75 ohm cable, and the use of a ballum to impedance match source and drain, they are looking at output impedance of antenna, incredibly small signals where it is easy to load the source and add noise to the signal... I don't really think it is applicable when talking about the transmission of a signal tens/hundreds/thousands of watts over a relatively short distance.

Cheers for all the feedback, I will say it doesn't feel like low voltage when some armpit has cut your cable, but due swr protection circuit you still get a jolt at 40 m... When the fun stops 😂