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Melting X-overs before blowing speakers VRX
Old 4 weeks ago
  #1
Melting X-overs before blowing speakers VRX

I am (replacing) Melting X-overs before blowing JBL VRX 8" speakers ... makes no frekin sense to me .. must be a design flaw.. I am using LAB amps, and DBX processing, I think I got it to a point where they just heat up really hot , ....just before freking melt down ..but my next step is to ditch the passive crossover ..and hopefully that helps.. unbelievable

just wanted to see if anyone else has had this happen
Old 4 weeks ago
  #2
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you better ditch the passive x-overs (so you cant melt woofers at whatever temperature you like)! :-)

i got no issues with vrx speakers however; i just don't like them very much.
Old 3 weeks ago
  #3
Quote:
Originally Posted by deedeeyeah View Post
you better ditch the passive x-overs (so you cant melt woofers at whatever temperature you like)! :-)

i got no issues with vrx speakers however; i just don't like them very much.
yes these are not my favorite boxes for sure!...do you have the 12's or 8's.. can you do me a favor and feel the back of your crossovers right after a set and tell me its hot?.. I am hitting 85db at 75 feet - and thats max i think for normal use.. what amps and processing are you using ?

thanks for your reply

Old 3 weeks ago
  #4
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Quote:
Originally Posted by RightOnRome View Post
yes these are not my favorite boxes for sure!...do you have the 12's or 8's.. can you do me a favor and feel the back of your crossovers right after a set and tell me its hot?.. I am hitting 85db at 75 feet - and thats max i think for normal use.. what amps and processing are you using ?

thanks for your reply

both - they are not mine though (but belong to a local rental company for which i get to work, so no, i'm not gonna rip them apart, sorry). they get driven by either lake/lab gruppen or armonia/powersoft.
hard to judge what's 'normal', depends on a multitude of factors (and you didn't mention how many you're using, how far apart, o cover what area, what kinda venues, how many subs, what genre etc.) - could be though that you're not having enough rig for the gig or accidentally clipping the signal elsewhere...
Old 3 weeks ago
  #5
Quote:
Originally Posted by deedeeyeah View Post
both - they are not mine though (but belong to a local rental company for which i get to work, so no, i'm not gonna rip them apart, sorry). they get driven by either lake/lab gruppen or armonia/powersoft.
hard to judge what's 'normal', depends on a multitude of factors (and you didn't mention how many you're using, how far apart, o cover what area, what kinda venues, how many subs, what genre etc.) - could be though that you're not having enough rig for the gig or accidentally clipping the signal elsewhere...
i'm not asking you to rip anything apart..just feel the box...not clipping the amps..crossed at the DBX at 100, JBLSRX828's for subs- not a noob btw, we average over 300 shows a year, with 5 rigs .. this is the only VRX rig and the biggest pain in my ass ..we have bigger boxes as well ..i'm just trying to solve a problem here with these

these are small shows -mostly cover bands in small rooms, I have about 17 bands in rotation..the show's that the xover melted was a larger room, and then again ..literally caught fire..lol , so i stopped trying to push them ..scaled down to smaller rooms and now there just hot to the touch..I am using LAB amps and DBX processing for this rig, only 2 per side which is probably the issue, but I have RCFHD12a's and 32a's that will out run these boxes and not hit the limit lights.... any day ..so it just seems that these boxes are just super inefficient ..I just don't understand how the crossovers fail before the drivers...
Old 3 weeks ago
  #6
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could be that they are of a less sophisticated design - i'm using the small ones mostly for front fills; this without issues though but they are indeed never getting pushed or have to go low - next time i get to use them, i'll check for heat and shall report back...
Old 3 weeks ago
  #7
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Quote:
Originally Posted by RightOnRome View Post
i'm not asking you to rip anything apart..just feel the box...not clipping the amps..crossed at the DBX at 100, JBLSRX828's for subs- not a noob btw, we average over 300 shows a year, with 5 rigs .. this is the only VRX rig and the biggest pain in my ass ..we have bigger boxes as well ..i'm just trying to solve a problem here with these

these are small shows -mostly cover bands in small rooms, I have about 17 bands in rotation..the show's that the xover melted was a larger room, and then again ..literally caught fire..lol , so i stopped trying to push them ..scaled down to smaller rooms and now there just hot to the touch..I am using LAB amps and DBX processing for this rig, only 2 per side which is probably the issue, but I have RCFHD12a's and 32a's that will out run these boxes and not hit the limit lights.... any day ..so it just seems that these boxes are just super inefficient ..I just don't understand how the crossovers fail before the drivers...
My guess is that they are getting too much power.
Old 3 weeks ago
  #8
Quote:
Originally Posted by deedeeyeah View Post
could be that they are of a less sophisticated design - i'm using the small ones mostly for front fills; this without issues though but they are indeed never getting pushed or have to go low - next time i get to use them, i'll check for heat and shall report back...
ok righton thank you !
Old 3 weeks ago
  #9
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Quote:
Originally Posted by jfpenkala View Post
My guess is that they are getting too much power.
hardly: 'not enough' power is much more risky than 'too much' power!
Old 3 weeks ago
  #10
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Quote:
Originally Posted by deedeeyeah View Post
hardly: 'not enough' power is much more risky than 'too much' power!
Not in this case!
Old 3 weeks ago
  #11
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Quote:
Originally Posted by jfpenkala View Post
Not in this case!
how do you know? did i miss any specs? lab manufacturers pretty much the whole range of amps, from wimpy to preemptive strike capacity!

could as well have been an issue stemming from a level-mismatch between max. analog output level of the dbx x-over and max. analog input level of a lab amp or the desk in front of them or...
Old 3 weeks ago
  #12
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Quote:
Originally Posted by deedeeyeah View Post
how do you know? did i miss any specs? lab manufacturers pretty much the whole range of amps, from wimpy to preemptive strike capacity!

could as well have been an issue stemming from a level-mismatch between max. analog output level of the dbx x-over and max. analog input level of a lab amp or the desk in front of them or...
I know because he said he's not clipping the amps. If he were underpowered, he would have to clip the amps to melt a crossover.
Old 3 weeks ago
  #13
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Quote:
Originally Posted by jfpenkala View Post
I know because he said he's not clipping the amps. If he were underpowered, he would have to clip the amps to melt a crossover.
could be the op uses some serious amping - but i usually don't take some vague description of a situation such 'not clipping the amps' at face value...

anyway, hard to judge from the distance/possibly easy to find out by doing some measurements.
Old 3 weeks ago
  #14
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Different parts in the crossover dissipate heat depending both on the total program power as well as the frequency characteristics of the input signal . . . so if you really want to figure out the cause of this issue, you’ll need to know/find exactly which components in the crossover are failing. If you do this and the legwork of posting the schematic, we can take a look as to how likely it’s caused by in-band versus out-of-band energy, amplifier clipping or malfunction, etc.etc..
Old 3 weeks ago
  #15
Quote:
Originally Posted by deedeeyeah View Post
could be the op uses some serious amping - but i usually don't take some vague description of a situation such 'not clipping the amps' at face value...

anyway, hard to judge from the distance/possibly easy to find out by doing some measurements.
2 channels of c 48 series bridged per box ( 8 ohm load...2 amps,8 channels, for 4 boxes)- yes, i am overpowering them - my point is the crossovers go before the drivers and that's a design flaw.. IMO ..nothing more, nothing less.. one would think these could hold their own in a small club..

but

I seem to have found a safe spot with the DBX ..

any way..the point of this thread... i was surprised that the boxes got so hot to the touch ..and melted the passive crossovers before the drivers blew .. i'm thinking cheap components ..but it is what it is.. I'm glad I have plenty of other speaker choices
Old 3 weeks ago
  #16
Quote:
Originally Posted by kirkus View Post
Different parts in the crossover dissipate heat depending both on the total program power as well as the frequency characteristics of the input signal . . . so if you really want to figure out the cause of this issue, you’ll need to know/find exactly which components in the crossover are failing. If you do this and the legwork of posting the schematic, we can take a look as to how likely it’s caused by in-band versus out-of-band energy, amplifier clipping or malfunction, etc.etc..
so i pushed the system harder then ever on this day.. yes..i wanted to see if they could keep up.. i knew i was pushing it.. but i did it anyway..

the speakers sounded fine..sounded good..I had just gotten a compliment on the sound...then ..WTF..smoke!.. ..then i look over and see the frekin smoke...

here is the crossover i replaced, the others were not as bad ..they just smell bad..but this one was nuked.. lesson learned


so since then i keep clamping down limiters, on the amps, on the dbx..but still the boxes are hot, on the front, and on the plate..so.. wtf.. i guess these were designed for very low key applications.. and they use crappy low power components ..
Attached Thumbnails
Melting X-overs before blowing speakers VRX-img_1864.jpg  
Old 3 weeks ago
  #17
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A picture of the component side would be helpful . . . also maybe a less-burned board to see the routing . . .

But my guess is that the resistors showing through the holes around the burn marks are part of the shunt elements of the tweeter high-pass . . . so the energy that’s overheating these parts of course won’t blow up the woofer. Continuing with my assumption, the overload is happening in the midrange (esp. the 1-2KHz area) . . . if you’re running the tweeters set to “-3” this will make things worse. The power that’s taken away from the tweeters to lower their level has to go somewhere . . . perhaps run them at “+3” and compensate by shelving down in the DSP’s EQ? This would theoretically be capable of cutting down the heat by something like 50-75%.

There’s always biamp mode . . . I know the VRX is nobody’s favorite box, but I have seen them run reliably and deliver excellent ROI. From what I’ve seen lying around dead at my reconer’s shop, these things aren’t all dropping like flies, at least anecdotally.
Old 3 weeks ago
  #18
Quote:
Originally Posted by kirkus View Post
A picture of the component side would be helpful . . . also maybe a less-burned board to see the routing . . .

But my guess is that the resistors showing through the holes around the burn marks are part of the shunt elements of the tweeter high-pass . . . so the energy that’s overheating these parts of course won’t blow up the woofer. Continuing with my assumption, the overload is happening in the midrange (esp. the 1-2KHz area) . . . if you’re running the tweeters set to “-3” this will make things worse. The power that’s taken away from the tweeters to lower their level has to go somewhere . . . perhaps run them at “+3” and compensate by shelving down in the DSP’s EQ? This would theoretically be capable of cutting down the heat by something like 50-75%.

There’s always biamp mode . . . I know the VRX is nobody’s favorite box, but I have seen them run reliably and deliver excellent ROI. From what I’ve seen lying around dead at my reconer’s shop, these things aren’t all dropping like flies, at least anecdotally.
that is exactly what I did! .. but at the end of the last show they were hot again, not burned, they worked for the situation,no complaints ...but they were hot to the touch

here's a pic of the problem area
Attached Thumbnails
Melting X-overs before blowing speakers VRX-screen-shot-2019-07-23-10.34.41-am.png   Melting X-overs before blowing speakers VRX-screen-shot-2019-07-23-10.34.18-am.png  
Old 3 weeks ago
  #19
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Well from your pictures it seems that I was wrong in my assumption . . . are the resistors that are overheating labelled R1A, R1B, R1C, R1D, and R1E? If so, then referencing the service manual here . . . they're actually in series with the woofer, not the shunt elements for the tweeter as I had suspected. So to increase the power-handling of these boxes through DSP settings . . . your options are to increase the frequency of the HPF and/or use a steeper HPF slope (should be at least 4th-order/24dB-per-octave).

You could do something cute like replacing these resistors with metal-case types bolted to the crossover's mounting plate, and then adding a heatsink on the outside . . . but IMO for all the effort/time/cost to do this it makes more sense to biamp them. But even then . . . I think it's becoming obvious that you're simply not bringing enough rig to do what you want. Whether or not the crossovers "should" fail before the drivers is irrelevant . . . that's kinda like saying that if you push an engine too hard it "should" swallow a valve before it throws a rod.

In any case you're still exceeding the design limits of this speaker as a whole, and it seems like splitting hairs to blame the engineers for not anticipating the exact way in which you happen to be doing it . . . so the product fails in the manner you anticipate that it should. At least JBL specify their power ratings precisely . . . and it's been my experience that their stuff (in both good ways and bad) can be counted on to do what the datasheet says it will.
Old 3 weeks ago
  #20
Quote:
Originally Posted by kirkus View Post
Well from your pictures it seems that I was wrong in my assumption . . . are the resistors that are overheating labelled R1A, R1B, R1C, R1D, and R1E? If so, then referencing the service manual here . . . they're actually in series with the woofer, not the shunt elements for the tweeter as I had suspected. So to increase the power-handling of these boxes through DSP settings . . . your options are to increase the frequency of the HPF and/or use a steeper HPF slope (should be at least 4th-order/24dB-per-octave).

You could do something cute like replacing these resistors with metal-case types bolted to the crossover's mounting plate, and then adding a heatsink on the outside . . . but IMO for all the effort/time/cost to do this it makes more sense to biamp them. But even then . . . I think it's becoming obvious that you're simply not bringing enough rig to do what you want. Whether or not the crossovers "should" fail before the drivers is irrelevant . . . that's kinda like saying that if you push an engine too hard it "should" swallow a valve before it throws a rod.

In any case you're still exceeding the design limits of this speaker as a whole, and it seems like splitting hairs to blame the engineers for not anticipating the exact way in which you happen to be doing it . . . so the product fails in the manner you anticipate that it should. At least JBL specify their power ratings precisely . . . and it's been my experience that their stuff (in both good ways and bad) can be counted on to do what the datasheet says it will.
righton, agreed
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