Hi,
I got a pair of vintage full range speakers. I haven't tested them sonic-wise as I want to build cabinets first to have a thorough evaluation of the sound.
The units are visually in good conditions, but the Ohm meter reads 5.2÷5.3, while they are rated for 8 Ohm.
Shall I expect any quality degradation from this lower impedance?
Thanks,
gm
I got a pair of vintage full range speakers. I haven't tested them sonic-wise as I want to build cabinets first to have a thorough evaluation of the sound.
The units are visually in good conditions, but the Ohm meter reads 5.2÷5.3, while they are rated for 8 Ohm.
Shall I expect any quality degradation from this lower impedance?
Thanks,
gm
You did measure DC-resistance, not impedance. Impedance is measured with 1kHz sine wave. The measured DC-resistance is within the expectation window,so there is nothing to worry about
8ohm is simply a nominal rating / bracket within which they are classed, not the actual impedance load of the drive unit, which also varies significantly with frequency. Units classed in the 8ohm bracket will typically have a DC coil resistance at the usual 1KHz point of anything from about 5ohms to the nominal.
What you have measured is the speaker's resistance, i.e., its opposition to the flow of direct current.
A speaker's impedance is its opposition to alternating current, which tends to be greater than its opposition to direct current.
A speaker's impedance is its opposition to alternating current, which tends to be greater than its opposition to direct current.
Thanks for the answers and sorry for the late reply, I was traveling.
Right, my question was a bit confusing (however, lower resistance = lower impedance, right?)
They are a pair of Coral 8F-60, which I had been hunting down for quite some time. As you can see, the back of one of the magnets has some stains and I thought that they may have been stored in a humid environment, and that the voice coil may be affected, hence the lower resistance. But if that's fine as you say, the speakers look in great condition otherwise. I just don't have a pair of the same model to do a comparison.
I also see sellers of vintage speakers post images of ohm meter values in their ads, so I thought it would be a key factor for assessing the quality.
Right, my question was a bit confusing (however, lower resistance = lower impedance, right?)
They are a pair of Coral 8F-60, which I had been hunting down for quite some time. As you can see, the back of one of the magnets has some stains and I thought that they may have been stored in a humid environment, and that the voice coil may be affected, hence the lower resistance. But if that's fine as you say, the speakers look in great condition otherwise. I just don't have a pair of the same model to do a comparison.
I also see sellers of vintage speakers post images of ohm meter values in their ads, so I thought it would be a key factor for assessing the quality.
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No, its just an indication that a voice coil is intact, i.e., not open circuit.
As a rule of thumb, if you measure the DC resistance of a voice coil then add on one third of the reading, you will have a good estimate of the nominal impedance of the loudspeaker.
Suppose a DC reading of 6 ohm as an example. Add on 6/3 = 2 ohm and you arrive at a nominal impedance of 8 ohm.
However, remember that the impedance of the speaker varies with the frequency of the AC signal, as the attached graph illustrates (the DC resistance being around 4 ohm for each of the two loudspeakers shown superimposed on the graph).
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The mild steel forming the back plate of the magnet assembly is vulnerable to corrosion, so may be protected by a a surface treatment, e.g., a coating of zinc.
Such a coating is intended to gradually corrode, providing what is known as "sacrificial" corrosion protection of the mild steel.
It may be evidence of this protection in action that you see on one of your magnet assemblies, but it is light enough not to cause concern in regard to the operation of the loudspeaker.
To be sure of the condition of the full range drivers, I would test them on music before committing to building enclosures.