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[Nathan Riddle]

Is a current/voltage spike DC?

I thought by definition that a spike would be AC simply because it has a change over time that is very small resulting in high frequency

But I guess a spike could be current flow in one direction only which is the definition of DC...?

To make a long story short, right after I plugged it in and flipped on the phantom power, a DC current spike went up the input cable into the mixer output (which was also not transformer protected) and right into the 18-inch driver in his loudspeaker cabinet. Poof – no more 18.

https://www.prosoundweb.com/channels/live-sound/mojo_rising_apply_those_direct_boxes_correctly/

[TJ (Tom) Cornish]

Is a current/voltage spike DC?

I thought by definition that a spike would be AC simply because it has a change over time that is very small resulting in high frequency

But I guess a spike could be current flow in one direction only which is the definition of DC...?

https://www.prosoundweb.com/channels/live-sound/mojo_rising_apply_those_direct_boxes_correctly/

How long is the spike?  A 0.000001Hz waveform is technically AC, but would sure act like DC.

[John Roberts {JR}]

Is a current/voltage spike DC?

I thought by definition that a spike would be AC simply because it has a change over time that is very small resulting in high frequency

But I guess a spike could be current flow in one direction only which is the definition of DC...?

A voltage spike is neither... it's a spike... 

A voltage transient can have a net DC content, or not.

JR

[Nathan Riddle]

How long is the spike?  A 0.000001Hz waveform is technically AC, but would sure act like DC.

Freq is the inverse of time so wouldn't an extremely short spike be extremely high freq?

Lightning is often considered DC. It represents itself as a high-frequency pulse to surge suppression systems.

[Chris Grimshaw]

Freq is the inverse of time so wouldn't an extremely short spike be extremely high freq?

Lightning is often considered DC. It represents itself as a high-frequency pulse to surge suppression systems.

When you go through the maths, anything less than infinitely prolonged DC is in fact AC with a bunch of frequency components that (through Fourier stuff) describe the "On" and "Off" parts of the DC. In reality, I'd say anything less than 0.1Hz would count as DC being applied - that's one half-cycle in 5 seconds, which can seem like a long time if it's something you weren't expecting.

Short-term DC is just a square wave, and therefore not DC at all.

Chris

[John Roberts {JR}]

When you go through the maths, anything less than infinitely prolonged DC is in fact AC with a bunch of frequency components that (through Fourier stuff) describe the "On" and "Off" parts of the DC. In reality, I'd say anything less than 0.1Hz would count as DC being applied - that's one half-cycle in 5 seconds, which can seem like a long time if it's something you weren't expecting.

Short-term DC is just a square wave, and therefore not DC at all.

Chris

Except Fourier analysis assumes a repeating or continuous waveform...

It is still informative, i,e, a narrower spike will have higher frequency energy.

DC is still meaningful, for example a spike that only goes positive will have a net positive DC content.

JR

[Frank Koenig]

Is a current/voltage spike DC?

In the world of signals and systems DC refers to a theoretical construct that is represented by a non-zero value of the signal at the frequency origin, be it in the Fourier, Laplace, Z, or other frequency domain representation.

In the world of power distribution DC refers to a system where the current always flows in one direction, as supplied by a battery, for example. This is as opposed to alternating current (AC) where the current flows alternately in both directions, as supplied by an alternator, for example.

A pulse or surge, while clearly "AC" in the signals sense, could be considered DC if it occurs in a DC power system, but I would avoid that usage. Better just to describe exactly what you're talking about.

--Frank

[Nathan Riddle]

Except Fourier analysis assumes a repeating or continuous waveform...

It is still informative, i,e, a narrower spike will have higher frequency energy.

DC is still meaningful, for example a spike that only goes positive will have a net positive DC content.

JR

In the world of signals and systems DC refers to a theoretical construct that is represented by a non-zero value of the signal at the frequency origin, be it in the Fourier, Laplace, Z, or other frequency domain representation.

In the world of power distribution DC refers to a system where the current always flows in one direction, as supplied by a battery, for example. This is as opposed to alternating current (AC) where the current flows alternately in both directions, as supplied by an alternator, for example.

A pulse or surge, while clearly "AC" in the signals sense, could be considered DC if it occurs in a DC power system, but I would avoid that usage. Better just to describe exactly what you're talking about.

--Frank

Mkay, yeah this makes sense. Thanks!

Now, as far as why the speaker failed, I don't think it was DC I think it was the spike. Transformer or not wouldn't have protected against that.

[Art Welter]

Now, as far as why the speaker failed, I don't think it was DC I think it was the spike. Transformer or not wouldn't have protected against that.

Nathan,

Back in the "bad old days" there were many woofers with suspensions that would easily allow a voice coil to crush itself on the backplate with a large transient signal ("spike"), instant destruction. Back then Crown had an entire series of "DC" amplifiers, happy to reproduce plenty of DC to cook the coils of drivers even if they survived a backplate (or phasing plug) crash.

Assuming the spike was only DC, a transformer would have eliminated it, as transformers don't pass DC.

Art

[TJ (Tom) Cornish]

Assuming the spike was only DC, a transformer would have eliminated it, as transformers don't pass DC.

Art

The transformer would have eventually stopped passing the DC, but based on some parameters of the transformer and the rest of the circuit, it would have passed the beginning of the DC - maybe the first 100ms or so - and then the amount of the “DC” signal fed through will decrease if the voltage level the transformer is seeing on its primary stays at the same level.

Depending on the DC voltage, it may burn out the primary of the transformer itself, since a transformer being fed with DC isn’t acting as a transformer, it’s a resistor.

[ProSoundWeb Community]