If you have a speaker with a short in it, sometimes cranking up the volume enough totally overcomes the short, like the more powerful electricty is “jumping the gap”. Is there a term for this?
What you’re probably dealing with here is not a short circuit, but a poor or dirty connection. Turning up the volume increases the voltage across the connection. At some point significant current will start to flow and cause the connection to heat up. When metals heat they expand. The expansion that occurs will temporarily restore good contact and the speaker will play. When the system is turned off for a while, things will cool off and the connection will return to its former state.
A spark?
Seriously, if the speaker sounds distorted at the minimum volume to produce sound, then the signal may be arcing across a gap.
You need to describe the sound being produced, its unlikely to be a short.
If one of the speaker coils were going short, it would be very quiet but you might get some sound from it.
It is possible that one of the coil formers is catching and scraping the magnet.
If the former beomes off centred this can happen, the former is suspended in an air gap in the magnet, the coil is wrapped around the former.
Several reasons it could go off centre, the suspension could have degraded, the speakers could have been overdriven and this can damage suspension.
The symptons would be a scraping noise which might sound like crackling, and low volume, but crank it up and it may have the power to move the speaker cone moreorless correctly.
If its a multi element speaker, there could be a loose connection in the crossover network, this is the circuit that directs signals of range of frequencies to the correct speaker elements.
One very likely cause if we are talking of something like a Ghetto Blaster or a cheap system is that the leads from the terminal and on to the speaker coil have degraded, just from mechanical wear and tear.
These lead go from the underside of the terminal, and go through the cone to the coil, they are a very fine copper woven sleeve, and down the centre of the sleeve there runs a flexible cord, which is supposed to provide mechanical strength.
What happens is that the copper braid over time work hardens and slowly, strand by strand, comes apart.
The amount of copper connecting the reduces, and the remained has to carry the current and gets warmer and warmer, increasing the pace of the work hardening.
The breaks formed by this a small, and intermittant contact usually occurs and leads to the symptons you describe.
Its possible to bridge the breaks by running a little solder onto the damaged braid, but this is a temporary fix and will not last long.
Imaginary?
If the speaker coil has some shorted turns those turns will not contribute to the force that moves the speaker cone in response to the audio signal current. So the force will be less, the cone motion will be less and the sound volume will be reduced.
In addition, the magnetic flux in the iron core of the speaker coil that is produced by those coils that remain unshorted will produce circulating currents in the shorted turns. These currents will, among other bad effects, result in the speaker drive coils getting hot.
Other that that, I really have no explanation for the effects you describe.
The effect is caused by a high wetting current* figure for the set of contacts in question. Oxides build up on old and loose contacts, and can effect a very thin insulator between (say) speaker cable and amp terminal, or between switch contacts, or between signal connectors. A high enough signal voltage will arc through the oxide layer and a current will flow, but at lower voltages the oxide layer will act as a not-very-good intermittent insulator, and will cause low-level signal breakup.
For loudspeaker cables your best bet is to chop off all the cable ends and reterminate with some fresh copper. Do them up nice and tight to get a bit of an airtight seal between the cable strands and the connector, or if you’ve got gold plated amp terminals, silver-solder or crimp on some gold-plated spade connectors, as gold-to-gold makes for a very good contact.
- Wetting current is defined as the minimum current that must flow across a set of electrical contacts in order to make a good connection. As a rule of thumb, for things like switches and relays, the higher the maximum current rating of the contact, the higher the wetting current requirements will be. Sometimes wetting current is defined as “minimum current” in switch and relay datasheets, and even for small signal relays can be as high as 10uA. For switching applications that need to work at very low current levels mercury-wetted contacts are often used.
Hmm, the chances of oxidation of the speaker leads to that extent is pretty unlikely, it can happen, but its rare, and you usually need a hostile environment for it to take place.
The coil leads degrading is very much more likely, I’ve seen it plenty of times and its not at all rare, especially in the budget market.
The air in my house is hostile enough to put an oxidation layer on bare copper, else all my radiator pipes would be gleaming. And a bare wire crush-fit into a terminal will rattle loose with time, what with vibration, thermal expansion and contraction, and the lead occasionally getting yanked. Getting a good long-term reliable contact from connectors, switches and relays isn’t easy, as any owner of a 1980s Citroen will tell you.
The braided leads to the voice coil can break open circuit, or fray and short together. If you’ve got a thin strand of copper making a short, then a high signal level may be enough to burn it away without necessarily blowing a fuse the first time. But, from the symptoms described, I doubt this is what’s happening here - I reckon you’ve got a dodgy contact or a dry solder joint somewhere. Reterminate the cables and swap the speakers around to isolate the cause of the problem (amp/cables/speaker).
If you have a short, then there is no “gap” to jump. A short circuit is when two conductors that aren’t supposed to touch, do. You’re most likely talking about an open circuit, where a connection has “opened”–perhaps between a wire and a terminal. In those cases, there is, indeed, a gap.
In an open circuit, the phenomenon of higher volume (higher current) jumping the gap is called an arc, or as cornflakes said, a spark.
I should not have said short, I should have said bad connection. My pc is connectted to the stereo with wires running under the carpet. If you step on this one spot on the floor you will cut out the right speaker, then you have to jump up and down on the carpet till it comes back on, :smack:
Ah, differant altogether, the leads have probably gone duff.
PC speakers generally have the amplifier built into the body of the unit, unless its the wire that joins the two speakers to each other, one speaker has the amplifer for the pair and a lead connects between the two.
You will be looking at a damaged wire, there will probably be nothing to see on theoutside of the wire, the insulation might well be intact but the copper wire inside will have a break.
I would think at some point you stretched the wires when moving the speakers or something like that.
One way to deal with it is to get the wires out from under and manipulate them as you wrok your way along their length, and see exactly where they cut in and out.
You could then put a join in there, or replace the lead entirely.