tweeter protection circuit

[SnakeBite]

Hi,

i'm planning to build a speaker crossover and i need to design a proper protection for it. the speaker will be mainly for music or karaokee so i need to protect it from fast overvoltage transiates .
there are many types of protection that exist:

* a series fast acting fuse - some say it create noises because of the small diameter of the fuse wire , it's can be damage by vabriation and it's not resetable.
*a resistor in paralal - can be cheap option but it will always limit the voltage that can apply to the tweeter.
*protection lamp - some say it's the best option and a lot of huge "players" in the audio industry using it by like fuse it's can create noises , in extreme cases can exploide and it's take time to act - not good.
*zener diode or MOV - i think it's THE BEST option ; it's acts fast and it's resetable.
* active protection - using op amp - it's one of the best option avaliable but it's will need a power source to opreate.

the circuit i this is the best for the job it's a mov in series with a resistor and a thermistor (just in case).
this circuit give both voltage protection and amp load protection by the resistor and thermistor.because the mov will clamp the output and create a HUGE load to the amp so you need to put a series resistor to protect both the mov and the amp and i think a thermistor will be a nice addition to protect the over current that can be hurt the amp.

here's the circuit , what do you think? will it works OK ? what are the tradeoffs in this circuit?
(crossover point is 3.5Khz)


Ido

[SeanB]

Just the MOV on it's own, the thermistor and resistor in series with the tweeter instead. The amplifier will not be affected by the MOV clamping, as it will be able to drive it no problem. Adding a series resistor reduces the clamp effectiveness, and this will cook the tweeter.

[SnakeBite]

ok i agree about the thermistor but if i remove the resistor and the clamping will occur the mov will become short circuit and the amplifier will get low resistance so i need something to limit the current and not damage the mov if the transiant will last more than a second (if it will , the mov will not last long and burn out = open circuit and the tweeter will explode) and also when the mov clamp the output to the amp the amp will need to get same load as before (8 ohm) so putting the 8 ohm resistor will do that since the mov effectivly short circuit.

Ido

[SnakeBite]

anyone....??

[c4757p]

You're worried about blowing up the MOV? Fuse the whole thing, so if the MOV starts conducting a lot of current the fuse will trip.

* a series fast acting fuse - some say it create noises because of the small diameter of the fuse wire

Audiophile bullshit. And if you have a beefy MOV you can use a slow-blow. They're thicker.

it's can be damage by vabriation

When was the last time you saw a fuse damaged by vibration?

and it's not resetable.

If it's blowing often enough for that to be a problem, then you need to concentrate more on figuring out why speaker is repeatedly getting overvoltage conditions.

[SeanB]

MOV in clamping is not a short circuit, it is a very poor zener diode, it clamps the voltage peaks to the clamp voltage. A spark gap is a short when conducting ( ignoring the 10V or so drop across it) but needs 300V plus to get it to conduct. If you have 300V across the speakers tweeters are not a problem. Amplifiers are very capable at supplying power into a load that drops some volts across it, a nominal 8R speaker can and will have an impedance curve that is going to be under 2R at some point. The crossover inductor and capacitors will prevent the MOV from loading the amplifier, it will still drive the low driver perfectly happily even if you short out the tweeter completely, with no drama or anything else aside from the lack of treble.

If you are worried about overloading the MOV use a bigger one, or a few in parallel, and use a PTC thermistor polyfuse heatshrunk to the MOV's so the heat will trip it to keep the peace. A 2A polyfuse will do for most sane tweeters, just shrink it to the MOV so it benefits from the heat to trip sooner. Rate the MOV so the tweeter will not die at 2A current through it.

[SnakeBite]

MOV in clamping is not a short circuit, it is a very poor zener diode, it clamps the voltage peaks to the clamp voltage. A spark gap is a short when conducting ( ignoring the 10V or so drop across it) but needs 300V plus to get it to conduct. If you have 300V across the speakers tweeters are not a problem. Amplifiers are very capable at supplying power into a load that drops some volts across it, a nominal 8R speaker can and will have an impedance curve that is going to be under 2R at some point. The crossover inductor and capacitors will prevent the MOV from loading the amplifier, it will still drive the low driver perfectly happily even if you short out the tweeter completely, with no drama or anything else aside from the lack of treble.

If you are worried about overloading the MOV use a bigger one, or a few in parallel, and use a PTC thermistor polyfuse heatshrunk to the MOV's so the heat will trip it to keep the peace. A 2A polyfuse will do for most sane tweeters, just shrink it to the MOV so it benefits from the heat to trip sooner. Rate the MOV so the tweeter will not die at 2A current through it.

thanks for the info , i didn't know all that ... i wanted to protect the amplifier because i building it too...