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Shorting speaker terminals

If the speakers are not powered wouldn't that be the same as not shorted? I'm presuming the speakers are not connected to the amplifier's actual outputs if not selected.
 
rothwellaudio said:
No, there's no current flow, or hardly any at all.

No, that isn't correct. Being offset from the rest position isn't what generates the voltage, it's motion through the magnetic field which generates the voltage.

This is how the brake works:
When the speaker's cone is caused to move by soundwaves impinging on it, the motion of the voice coil through the magnetic field produces a voltage at the speaker's terminals. No current can flow if the terminals are open circuit, but there's a voltage there.
If you place a short circuit across the terminals a current can flow when the cone is caused to move, but the flow of current produces a magnetic field around the voice coil which interacts with the permanent magnetic field and opposes the motion of the diaphrgm. The effect is called "back EMF".

If you google "back EMF" you should get plenty of results. An amplifier with a very low output impedance has the same effect as a short circuit across the speaker terminals.


Actually, yes current does flow, but only when something causes the speaker cone to move.
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Okay, so what is that non flowing current? Potential? Does it come into existence with motion or is something already there?
 
Mr Boochie said:
What maybe important in tube amps, is to short out the secondary leads from the OPT, if the speakers are disconnected. Just in case the amp get turned on, without seeing a speaker load
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Are you sure you don't mean an 8 ohm resistor?
 
Superampman said:
Okay, so what is that non flowing current? Potential? Does it come into existence with motion or is something already there?
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Non-flowing current? That's voltage. Just like a 9 volt battery that isn't connected to anything has 9 volts at its terminals but no current is flowing, the speaker has a voltage at its terminals but no current is flowing - until the link is put in place.
Yes, voltage is also known as electrical potential.
Yes, it's the motion of the cone which produces the voltage.
 
rothwellaudio said:
Non-flowing current? That's voltage. Just like a 9 volt battery that isn't connected to anything has 9 volts at its terminals but no current is flowing, the speaker has a voltage at its terminals but no current is flowing - until the link is put in place.
Yes, voltage is also known as electrical potential.
Yes, it's the motion of the cone which produces the voltage.
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But when the terminals are connected together and the brake is in effect, is there movement of electrons in a closed loop?
 
Powertech said:
Remember that there is a major difference between shorting driver terminals and shorting loudspeaker terminals.
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In the majority of speaker systems the difference is going to be the addition of the series resistance of the LF inductor plus a tiny bit of ESR from any caps parallel to the circuit, maybe 1 ohm give or take.

There will be a difference. But, i wouldn't call it major.
 
rothwellaudio said:
Virtual photons? It's just a flow of electrons like any other electric current.
I suggest you google "back EMF" or maybe "loudspeaker back EMF" because I think I've run out of ways to explain this.
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Again, I don't mean to pester. I'm just trying to get my head around what's going on at the quantum level. It's extremely difficult to get answers at this scale by googling, virtually impossible. Google is broken. You would think with the internet and search engines you'd be able to find answers to as specific a question as you present but no, you will still have to read and understand an entire advanced textbook to get a simple answer.
My understanding is magnetic flux consists of virtual photons so I was wondering if electron movement in a wire represents a complimentary particle due to their interaction. I understand what's been presented about back EMF however it does not speak to my query. Are EEs not schooled in this stuff? Not suggesting you are one or should know about this stuff, just another question.
 
Superampman said:
Are these 'virtual photons' travelling essentially at C? Is what is travelling in the coil the same thing as the magnetic flux?
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Electricity speed in wire is nearly C (speed of light). These are electrons, not photons.

Magnetic field and electric fields are at right angles (90°) to each other. Right hand rule thing.

This site may help. :)

https://byjus.com/physics/electromagnetism/
 
Actually, the electrons themselves travel very slowly. It is the bump from electron to electron that moves at near the speed of light.
 
I'm hanging with @rothwellaudio here ..

It's pure physics ..
A coil moving in a magnetic field generates current and vice versa ..
Wiring the terminals together creates the conditions for both ..
Can't spin forwards and backwards simultaneously .. so it remains at rest ..

Essentially using the EMF as a brake ..

It's a mass suspended on a spring inside that coil so a big enough whump could probably still make it hit the stops ... but it isn't going to bounce and hit twice ..
 
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