Impendans question

[hansen]

Hi
The setup is. Xpa-2 gen 3
I conneted my JBL speaker it runs in 6ohm
After some hours the amplifier stopped playing and turnt orange instead of the normal blue when its on.

Now the woofers all 4 of them is silent.
The tweeter and the middle plays.

I have now connected the “Old” speakers that rund in 4 ohm.

No problem at all.
Could it be the crossover in the JBL that is broken?
And why did it happen?
I think it was in the “Old” days that you had to chance the impedans.
I think it automatic swithes ?
Is it a thing if it not get enough power.
Forexamples if there is to many diveses to the same contact.

Hope can help and understand the problem.

[Boomzilla]

Hi hansen -

Your post is somewhat confusing. You first say that you connected your JBL "speaker" (singular) of 6-ohm impedance. You then say that "all 4 woofers are silent."

Does each JBL speaker have two woofers? Or are you connecting two pairs of 6-ohm speakers to the amp (with one woofer per speaker)?

If the latter (two pairs of speakers for a total of four individual six-ohm speakers), then your amplifier may be seeing a load of three ohms. This might put the amp into "protection mode." When multiple speakers are connected to the same amplifier terminals, they are said to be "in parallel." The impedance (as seen by the amplifier) is half what each speaker is.

If, on the other hand, each of your six-ohm speakers has two built-in woofers, then I'm not sure what's going on. While the speakers played (I'm assuming they played briefly before everything stopped?) were you playing them very loudly? Might you have played them so loudly that the woofers burned out? I'm strongly suspecting woofer damage since the midrange and tweeter drivers often have internal protection circuits.

Cordially - Boomzilla

[leonski]

Yet.....Boom......Mids and Tweets ARE the most vulnarable due to lowest power handling and that distortion products end up going 'up' in frequency.....
Some tweeter designs may have a reputation for being fragile....


And Hansen? Impedance of an amp doesn't 'switch'...but is rather a property of the design. Which will usually specify a 'lowest' allowable value or BRAG about some crazy low value the amp is said to be good with.

I'll rely on others, here, but I think the XPA-2 G3 has a lower limit of 4 ohms.......Which if the speakers connected are 2x of your 6ohm JBL per side? Would be mathmatically 3 ohms AND probably lower at some point
since those impedenace numbers are not cast in stone, but rather vary across the audio band. The quoted number is some kind of average and could be higher or lower depending on actual frequency......

[Boomzilla]

Hi leonski -

Your own Magnepan 1.6qr speakers have a fuse for the tweeter, unless I'm mistaken, but the woofer has none? So it is relatively easy to damage the woofers at high volumes without damaging the (midranges or) tweeters. In your case, a blown tweeter fuse would have to be manually replaced before the tweeter would work again, but many speakers use Zener diodes instead. These would shunt excess voltage directly to ground while the volume was high, but the midranges and tweeters (if protected by the diode) would still work fine afterwords. Mr. hansen has not yet answered our questions for more information, so until he does, we're speculating in a vacuum.

[leonski]

Yes.....My panels have a 4 amp fuse for frequencies above the 600hz crossover. But NOT a ribbon. The ribbon is a little more 'fragile', if you will, and might even pop while the fuse is still good!
Maggie 'lore' calls the ribbon a fuse protector.

What it DOES have is a 16ga ferite or iron core inductor on the low end. This will 'saturate' which I suspect puts a lid on power to that 'way'........
Again? Maggie 'lore' calls for any crossover rebuild to use AIRCORE inductors which lack that property.....but take up more wire and space.
People who don't understand use VERY low resistance inductors which changes the crossover and increases relative LF output against the HF.....
My modeling was aimed at an aircore within 5% resistance value OF the stock unit while using 14ga or better. Effective at leaving the crossover
point / balance alone while upping the power limit....

I've put EVERYTHING I've got thru that panel without damage. My PSAudio GCC250 put out 500 into 4ohms....and would go to 'redline' without
audible distress......I eventually SOLD it since I didn't like the high frequency output......just SOMETHING didn't ring true......
Current setup is a PAIR of Parasound A23 which are 200x2 at 4ohms each.......and one per panel, biamped.

I'll look into a Zenar Shunt for 'em......I see such Zenars up to 1kv....so the range I need is probably available.....Shunt to ground thru a 10ohm, 10 watt resistor?

Please Link a sample schematic if you can find one?


Even a speaker MODEL NUMBER would be helpful....JBL makes a lot of 'em.....



I might add....this is the 'edit'.....that my original MG-1 panels from the beginning of the Universe had a similar setup of fuse ONLY for the high frequencies.    In MY case?   It was an AGC of 1 1/2 amps.......And took pretty much ALL of my carver cube to pop.   
Cube was 200x2 @8 but I think 'only' 250 @4....which makes sense because the claimed 'bridged' power was 500 watts...   IIRC?  The MG-1 was a 5 ohm speaker....and oddball.    I can only find the docs for the MG-1c, which IS listed as '5 ohms resistive'......
I may spend some time with a calculator and figure just how much power a 4 amp fuse is good for.....into a 4 ohm load.....