Electronics > Beginners
Does cable impedance add to source or load impedance?
fonograph:
I have never seen a thread being derailed so hard in my entire life. All I asked is if cable impedance adds up to source or load, a extremly simple question that can be answered in one sentence and somehow this turned into discusion about audio, a topic I foolishly chosen believing it will be obvious to everybody that I used it merely to give a example to help deliver my question and that this topic of audio is in context of this thread and purpose of my question completly irrelevant, and unimportant.
That is like if you had 6 year old son and he came to you asking how many apples does Bob have if he picked 10 from tree, gave away 2 to grandma and 3 to sister, a first grade homework question that any adult not suffering from brain damage should be able to clearly answer in one sentence yet you would then go on hour long rant about pesticides, fructose intolerance, global warming and its impact on apple yields, stupid politicians making retard laws about imported apples, morals of genetical modification of apples, apple pie recipes and your neighbour who steals apples from your tree in garden by reaching over the fence.
Audioguru:
Cheap intercoms and TVs sound very boomy at the resonant frequency of the speaker and its enclosure. I think because its amplifier has a fairly poor damping factor. I think they will sound much better if the amplifier has a high damping factor.
Johnny B Good:
--- Quote from: Audioguru on February 15, 2019, 10:06:56 pm ---Cheap intercoms and TVs sound very boomy at the resonant frequency of the speaker and its enclosure. I think because its amplifier has a fairly poor damping factor. I think they will sound much better if the amplifier has a high damping factor.
--- End quote ---
I'm afraid to say that you're quite wrong in thinking that a low Z output amplifier will have any noticeable effect on the audio quality of such speaker arrangements. The poor quality is essentially down to enclosure resonances with just one significant contribution from the drive's own resonance which can only be damped by the voice coil resistance in series with the amplifier's output impedance which can easily be less than an ohm even with a cheap amplifier meaning an effective DF of just 4 or less regardless of how high a DF is claimed for the amp. The other resonances created by the enclosure will remain unaffected by the DF rating of the amplifier since they're effectively decoupled from the drive unit's voice coil and cone assembly.
To give fonograph the short answer he was seeking, the loop resistance of the cable simply adds to that of the amplifier's impedance and the voice coil resistance since they're all effectively in series across the drive unit's impedance at resonance, typically some three to five times its nominal impedance. It is this resonance impedance that's being damped, not the nominal 4 or 8 or 15 ohm (or whatever) given for the drive unit.
The damping factor figures of merit often quoted in the glossy brochures' advertising copy back in the 1970s were/are simply marketing bullshit designed to emphasise out of all proportion the importance of the ultra low output impedance figures that could be so readily achieved with voltage negative feedback in these new fangled DC coupled solid state amplifiers. The importance of lo-Z was grossly overstated as it relates to any drive unit damping effect, limited as it is by the series resistance of the drive unit's voice coil.
HTH & HAND ;D
JBG
Zero999:
--- Quote from: fonograph on February 15, 2019, 09:23:17 pm ---I have never seen a thread being derailed so hard in my entire life. All I asked is if cable impedance adds up to source or load, a extremly simple question that can be answered in one sentence and somehow this turned into discusion about audio, a topic I foolishly chosen believing it will be obvious to everybody that I used it merely to give a example to help deliver my question and that this topic of audio is in context of this thread and purpose of my question completly irrelevant, and unimportant.
That is like if you had 6 year old son and he came to you asking how many apples does Bob have if he picked 10 from tree, gave away 2 to grandma and 3 to sister, a first grade homework question that any adult not suffering from brain damage should be able to clearly answer in one sentence yet you would then go on hour long rant about pesticides, fructose intolerance, global warming and its impact on apple yields, stupid politicians making retard laws about imported apples, morals of genetical modification of apples, apple pie recipes and your neighbour who steals apples from your tree in garden by reaching over the fence.
--- End quote ---
Don't worry about it. This is fairly common, especially with audio. As I said above, as far as power audio amplifier are concerned resistance = impedance. Although some may find the extra information useful, it can be a pain filtering it.
From the amplifier's perspective, the resistance of the cable adds to the load resistance. If the cable is 1Ω and speaker is 8Ω, then the amplifier sees a 9Ω load.
From the load's perspective, the resistance of the cable adds to the amplifier's resistance. If the speaker is 8Ω, the cable 1Ω and the amplifier has an output impedance of 0.5Ω, then the speaker sees a voltage source with an impedance of 9.5Ω 1.5Ω.
I hope that answers the question.
fonograph:
--- Quote from: Zero999 on February 16, 2019, 10:55:43 am ---
--- Quote from: fonograph on February 15, 2019, 09:23:17 pm ---I have never seen a thread being derailed so hard in my entire life. All I asked is if cable impedance adds up to source or load, a extremly simple question that can be answered in one sentence and somehow this turned into discusion about audio, a topic I foolishly chosen believing it will be obvious to everybody that I used it merely to give a example to help deliver my question and that this topic of audio is in context of this thread and purpose of my question completly irrelevant, and unimportant.
That is like if you had 6 year old son and he came to you asking how many apples does Bob have if he picked 10 from tree, gave away 2 to grandma and 3 to sister, a first grade homework question that any adult not suffering from brain damage should be able to clearly answer in one sentence yet you would then go on hour long rant about pesticides, fructose intolerance, global warming and its impact on apple yields, stupid politicians making retard laws about imported apples, morals of genetical modification of apples, apple pie recipes and your neighbour who steals apples from your tree in garden by reaching over the fence.
--- End quote ---
Don't worry about it. This is fairly common, especially with audio. As I said above, as far as power audio amplifier are concerned resistance = impedance. Although some may find the extra information useful, it can be a pain filtering it.
From the amplifier's perspective, the resistance of the cable adds to the load resistance. If the cable is 1Ω and speaker is 8Ω, then the amplifier sees a 9Ω load.
From the load's perspective, the resistance of the cable adds to the amplifier's resistance. If the speaker is 8Ω, the cable 1Ω and the amplifier has an output impedance of 0.5Ω, then the speaker sees a voltage source with an impedance of 9.5Ω.
I hope that answers the question.
--- End quote ---
This is excellent answer, thank you very much Zero999.
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