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Author Topic: STX825 blown HF drivers  (Read 11495 times)

Greg Cameron

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Re: STX825 blown HF drivers
« Reply #20 on: April 01, 2013, 12:34:45 pm »

And as mentioned before, limiters set to protect a woofer won't protect a HF driver rated for 75 watts IES.
The limiter settings offer no protection to the HF when you are using them in the passive mode.
Remember, you are boosting 6 dB in the high end, and there is no attenuation up real high in the passive crossover.

Once again, more reason to processes the horns separately on that box.
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Cameron Pro Audio

Nitin Sidhu

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Re: STX825 blown HF drivers
« Reply #21 on: April 01, 2013, 12:40:08 pm »

Once again, more reason to processes the horns separately on that box.

Agreed.

In my defence, I know very well the capability of the 725. And am saying that the 825's were being run nowhere near that.

However, suddenly, bi-amping seems like such a good idea! hehe...

Sidhu
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Greg Cameron

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Re: STX825 blown HF drivers
« Reply #22 on: April 01, 2013, 01:36:56 pm »

Agreed.

In my defence, I know very well the capability of the 725. And am saying that the 825's were being run nowhere near that.

However, suddenly, bi-amping seems like such a good idea! hehe...

Sidhu

It could simply be that driver diaphragm model is not as robust as the 2451 used in the 725. They spec the same power handling wise, but they are different physically. It could also be that JBL changed the crossover filter setup so that more is getting to the horn. In any case, bi-amping would remove the question mark as far as what's being delivered to the horn.
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Art Welter

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Re: STX825 blown HF drivers
« Reply #23 on: April 01, 2013, 01:38:30 pm »

Here are some pictures. Thank you.

Strange thing is that the one HF that is left working measures in at 4ohms exactly on the multimeter, instead of 8. The service centre says that's cause it too is damaged.

Am I the only person left that still RTFM's ? I sold my last JBL driver a few years ago, but I still read..
The "service centre" is evidently without a clue, 4 ohms is quite within the specified  +/-8% DC resistance of 4.1 ohms.
Sounds like they will try to make you pay for JBL's manufacturing defect, and their incompetent diagnosis.

Look at the drivers that are open with a magnifying lens, if you don't find burned micro-pits, the diaphragms are defective, and should be replaced under warranty.

Since one survived with no burn discoloration, and you have noted other failures in your area, and you and your crew are not burning diaphragms regularly, looks very likely to be a manufacturing defect.

Whether run passive or active, you can't protect diaphragms from a manufacturing defect, or improper installation- my bet would be a "service centre" that does not know what a diaphragm's DC resistance should be also lacks the knowledge to properly install and align said diaphragm.

If the diaphragms are not properly aligned, the voice coil can scrape on the gap and cause shorts between windings that can cause the coil to burn, as can pieces of trash in the gap if not cleaned properly before the alignment procedure.

And if they tell you the alignment pins center the diaphragm perfectly, tell them they have no idea of what perfection is.

Art
« Last Edit: April 01, 2013, 01:40:48 pm by Art Welter »
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Nitin Sidhu

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Re: STX825 blown HF drivers
« Reply #24 on: April 01, 2013, 02:04:27 pm »

Am I the only person left that still RTFM's ? I sold my last JBL driver a few years ago, but I still read..
The "service centre" is evidently without a clue, 4 ohms is quite within the specified  +/-8% DC resistance of 4.1 ohms.
Sounds like they will try to make you pay for JBL's manufacturing defect, and their incompetent diagnosis.

Look at the drivers that are open with a magnifying lens, if you don't find burned micro-pits, the diaphragms are defective, and should be replaced under warranty.

Since one survived with no burn discoloration, and you have noted other failures in your area, and you and your crew are not burning diaphragms regularly, looks very likely to be a manufacturing defect.

Whether run passive or active, you can't protect diaphragms from a manufacturing defect, or improper installation- my bet would be a "service centre" that does not know what a diaphragm's DC resistance should be also lacks the knowledge to properly install and align said diaphragm.

If the diaphragms are not properly aligned, the voice coil can scrape on the gap and cause shorts between windings that can cause the coil to burn, as can pieces of trash in the gap if not cleaned properly before the alignment procedure.

And if they tell you the alignment pins center the diaphragm perfectly, tell them they have no idea of what perfection is.

Art

Art, Ouch!

I actually do read the manuals.

The diaphragm states an impedance of 8ohms on it. And the manual a DC resistance of 5ohms.
I obviously don't know my physics.

Sidhu
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Chris Hindle

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Re: STX825 blown HF drivers
« Reply #25 on: April 01, 2013, 02:08:02 pm »

Art, Ouch!

I actually do read the manuals.

The diaphragm states an impedance of 8ohms on it. And the manual a DC resistance of 5ohms.
I obviously don't know my physics.

Sidhu
Nitin, don't take it personally. The way I read it, Art was talking about the "Service Center", not you.
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Raul Suarez

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Re: STX825 blown HF drivers
« Reply #26 on: April 01, 2013, 02:43:29 pm »

Sidhu-

From the photos supplied it is impossible to tell, but it does not appear that there any burns or pitting on the parts that are visible.  For the few diaphragms that do have warranty failures, we find that the wire lead just as it enters the voice coil breaks.  This is the usual failure point in such.  If so, that should be a warrantied repair.  It is however, very surprising that you would have 3 such drivers out of 4. 

Raul Suarez
Third Ear Sound
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Nitin Sidhu

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Re: STX825 blown HF drivers
« Reply #27 on: April 01, 2013, 03:15:39 pm »

Sidhu-

From the photos supplied it is impossible to tell, but it does not appear that there any burns or pitting on the parts that are visible.  For the few diaphragms that do have warranty failures, we find that the wire lead just as it enters the voice coil breaks.  This is the usual failure point in such.  If so, that should be a warrantied repair.  It is however, very surprising that you would have 3 such drivers out of 4. 

Raul Suarez
Third Ear Sound

Raul, interesting you said so.

This is what the Distributor/Service centre told the vendor the last time around to. The solder broke, nothing wrong with the speaker.

As I got to know today.

Warranty or not, cant have speakers dying.

Sidhu
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Art Welter

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Re: STX825 blown HF drivers
« Reply #28 on: April 01, 2013, 03:39:35 pm »

Art, Ouch!

I actually do read the manuals.

The diaphragm states an impedance of 8ohms on it. And the manual a DC resistance of 5ohms.
I obviously don't know my physics.

Sidhu
Reading does not require a knowledge of physics  ;).

The nominal 8 ohm HF driver should read around 4.1 ohms DC, the  nominally 8 ohm 2226HPL 15" should measure 5 ohms DC resistance, a parallel pair in the cabinet should read approximately 2.5 ohms.

The IEC standard (IEC60268-3) allows any impedance above the rated value, but limits the impedance below. It does not allow the rated impedance to fall below the 80% of the nominal value at any frequency.

Most ported cabinets have an impedance minima fairly close to the DC resistance, if the 825 also does, it's closer to a 2 ohm cabinet than a 4 ohm.

It would be interesting to see the impedance curves of the drivers, the DC resistance is lower than "old school" JBL 8 ohm drivers.


Regarding Raul Suarez comment:
"It is however, very surprising that you would have 3 such drivers out of 4."

Manufacturing defects such as the wire lead just as it enters the voice coil breaking are probably the result of an out of tolerance assembly detail, a number of drivers of the same "vintage" could succumb to the problem.
The factory may only fix the problem after becoming aware of it later, and if the diaphragm had been replaced by a service center the likes of the one you encountered, they may not be aware of a "bad run".

I had three out of four woofers purchased at once fail from a similar problem, all on different shows, with weeks between, all moderate level shows, no visible voice coil damage.
None of the latter units purchased had any problems, and the good 1 out of 4 is still fine 12 years later.

This type of failure is like Russian Roulette, the fourth HF driver might last forever, or may fail soon.

If the cabinets were mine, I'd be inclined to try to find diaphragms with a latter date code than the ones that failed...

Art
« Last Edit: April 01, 2013, 03:42:29 pm by Art Welter »
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Nitin Sidhu

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Re: STX825 blown HF drivers
« Reply #29 on: April 30, 2013, 04:40:20 pm »

Hello!

I was reminded to post a revert on this thread by another.

The vendor has since has all his HF drivers replaced in warranty from Harman, and we have had a few outings with this STX825 rig since.

The tech from Harman said there is nothing wrong with the presets we were using, he knew nothing about pumping EDM music at zero dynamic range, which were not doing, but I asked.

He also did not tell what was wrong with the HF transducers. I even told him that maybe I hit them too hard. He said he would check and revert. Still no reply.

Ill be happy to say that we have no more dead drivers, we are running the same presets, and have since subjected the speakers to much bigger loads.

Regards,
Sidhu
« Last Edit: April 30, 2013, 04:48:04 pm by Nitin Sidhu »
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