weird phenomenon with sub

[luvinthebass 5,000+ posts]

i got a LA 12" sub single 4 ohm voice coil, powered by a RF 400.2 to it, gain at 3/4, set it for 150 rms) was playin west coast rap songs at the time and i started smellin the voice coil smell then it got worse and the sub got less and less bass then i pull over and the sub is sounding scratchy and when i tapped it it was a dull sound like a thud, lpf was at 50 hz, why the hell does the sub still keep playing? is 50 hz and down shot? i've never had this happen to me before.

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[DaveT 10+ year member]

You have the amp bridged? Did you shoot for 25 volts on the multimeter? Sounds like you pretty well fried the coil, I suggest taking it out and testing the coil with a multimeter.

 

[Haunz 10+ year member]

you have basically burned the windings without completely blowing the sub... output has been reduced because the resistance of the windings has been increased, and now the sub is getting less power from your amp....

oxidized copper will not carry current, hence the resistance of the coil goes up..... //content.invisioncic.com/y282845/emoticons/wink.gif.608e3ea05f1a9f98611af0861652f8fb.gif

 

[luvinthebass 5,000+ posts]

You have the amp bridged? Did you shoot for 25 volts on the multimeter? Sounds like you pretty well fried the coil, I suggest taking it out and testing the coil with a multimeter.

yeah it was bridged, yes, i set it for 24.5 0 db 50 hz tone. did that part today

dmm reading on coils AFTER it was sounding scratchy...

 

[DaveT 10+ year member]

yeah it was bridged, yes, i set it for 24.5 0 db 50 hz tone. did that part today
dmm reading on coils AFTER it was sounding scratchy...

Did you happen to test it before installing? From the looks of it I'm leaning towards they sent you the wrong coil config or it was mis marked, I'm guessing it was single 2ohm and you were really giving it 300 watts, 24.5v @ 2ohms= 300watts. And now that the coil has been toasted the resistance went up to 3.3ohms, but then again I could be wrong.

 

[luvinthebass 5,000+ posts]

Did you happen to test it before installing? From the looks of it I'm leaning towards they sent you the wrong coil config or it was mis marked, I'm guessing it was single 2ohm and you were really giving it 300 watts, 24.5v @ 2ohms= 300watts. And now that the coil has been toasted the resistance went up to 3.3ohms, but then again I could be wrong.

was 3.8 to 3.4 when i first got it. the amp i had before this one was cheap walmart VR3 prolly never even hit 2 ohms, had that amp bridged but i think this RF one just killed it since it doubled it's power from 4 ohm to 2 ohms.

 

[DaveT 10+ year member]

could be. sub was $40 from walmart so idk, they coulda lied.

Well it could have been mis marked, stranger things have happened. But then again I may be way off so take it with a grain of salt, but IMHO it would make sense.

 

[Etac 10+ year member]

3.3 doesnt sound like a bad dcr rating for a 4 ohmn nomial sub...

 

[Immacomputer 10+ year member]

Wait, your LPF was set at 50hz and you used a 50hz tone to set your gains?

What sub was this?

 

[DaveT 10+ year member]

3.3 doesnt sound like a bad dcr rating for a 4 ohmn nomial sub...

I was assuming that they coil to get pretty well cooked and the resistance went up.

Wait, your LPF was set at 50hz and you used a 50hz tone to set your gains?
What sub was this?

I didn't notice that before.//content.invisioncic.com/y282845/emoticons/eek.gif.771b7a90cf45cabdc554ff1121c21c4a.gif

 

[luvinthebass 5,000+ posts]

Wait, your LPF was set at 50hz and you used a 50hz tone to set your gains?
What sub was this?

this one sir...

http://www.lightningaudio.com/products/product_details.asp?cat_id=1&series_id=6&family_id=14&item_id=107720&locale=en_US&p_status=

 

[ultimate157 5,000+ posts]

Smelling coil, scratching noise... sounds like a burnt coil that probably lost a single winding and is now in the gap.

 

[Haunz 10+ year member]

3.3 ohms is a normal reading for a 4ohm sub.... but taking a reading with a DMM isn't necassarilly going to tell you anything....

A DMM will only send a few mV to the coil and a charred portion may still pass the small amount of resulting current without adding any significant amount of resistance to the coil.... Test the working resistance while giving the sub something like 10v DC, and you will probably get very different results......

I've been reconing for a long time, and have ran into exactly what you are talking about with dying PA speakers more times then I can count....... trust me, charred windings and additional resistance is the only explination for an audible drop in output....... //content.invisioncic.com/y282845/emoticons/crap.gif.7f4dd41e3e9b23fbd170a1ee6f65cecc.gif