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Sound Reinforcement - Forums for Live Sound Professionals - Your Displayed Name Must Be Your Real Full Name To Post In The Live Sound Forums => LAB: The Classic Live Audio Board => Topic started by: Nitin Sidhu on March 30, 2013, 01:41:18 pm

Title: STX825 blown HF drivers
Post by: Nitin Sidhu on March 30, 2013, 01:41:18 pm
Hello!

I have been hearing a lot of local reports of the HF driver with the 825 blowing themselves out even on moderate level operation. I always tend not to pay much heed to such reports.

We were contracted to provide SR and engineering services for a small festival in the hills, and I really liked how the 825 sounded when i demoed them, so decided to spec the same for the festival. We don't have any 835's around, and I have an eye on them. The venue does not really more a pair in all, we sent in a pair a side, to be safe.

I made presets for the ITech amplifiers, copied eq setting off the XTI, tansfer compared them with the HD presets, and it sounded great!

To be cautious, I setup a system architect custom panel to monitor all inputs and outputs, and GR meters. the RMS and Peak limiters are set to 1/3 of continuous power, and 3/4th of program power respectively.

My partner is now in the hills engineering, last night, midway, he was very impressed with te rig. Loud and hi-fi, without him hitting a single clip or getting the GR into action. However,
During the last act, he reports one HF driver has gone down.

As of midway today, 2nd and last day, he has lost two more HF drivers, and is now happily running the show of just 1 HF, loud enough to cover the small area. He hopefully will manage though the last act. We have taken some 712's off monitor duty as an SOS.

System :

4 x STX825
2 x ITech 4000
4 x SRX728
2 x ITech 6000

Any ideas ?

Thank you for the time.

Regards,
Sidhu
Title: Re: STX825 blown HF drivers
Post by: Art Welter on March 30, 2013, 02:01:55 pm
Hello!

I have been hearing a lot of local reports of the HF driver with the 825 blowing themselves out even on moderate level operation. I always tend not to pay much heed to such reports.

To be cautious, I setup a system architect custom panel to monitor all inputs and outputs, and GR meters. the RMS and Peak limiters are set to 1/3 of continuous power, and 3/4th of program power respectively.

My partner is now in the hills engineering, last night, midway, he was very impressed with te rig. Loud and hi-fi, without him hitting a single clip or getting the GR into action. However,
During the last act, he reports one HF driver has gone down.

As of midway today, 2nd and last day, he has lost two more HF drivers, and is now happily running the show of just 1 HF, loud enough to cover the small area. He hopefully will manage though the last act. We have taken some 712's off monitor duty as an SOS.

System :

4 x STX825
2 x ITech 4000
4 x SRX728
2 x ITech 6000

Any ideas ?

Thank you for the time.

Regards,
Sidhu
Could be a batch of defective  diaphragms in your local pool of cabinets.
Need to inspect them to tell the exact cause of death.

The 2453H driver used in the STX825 is pretty tough, but with highly compressed music with concentrated HF level above the crossover point it still would be possible to burn them in passive mode with the RMS and Peak limiters set to 1/3 of continuous power, and 3/4th of program.

They should be quite loud before they burn, any idea of what levels were being run "A" scale, at what distance?
Title: Re: STX825 blown HF drivers
Post by: Tim McCulloch on March 30, 2013, 02:16:41 pm
Sidhu, I take it you are bi-amping the 825s?  If so I suspect an error in the entry of the settings into the ITech, barring any product defect.
Title: Re: STX825 blown HF drivers
Post by: Nitin Sidhu on March 30, 2013, 02:22:05 pm
Could be a batch of defective  diaphragms in your local pool of cabinets.
Need to inspect them to tell the exact cause of death.

The 2453H driver used in the STX825 is pretty tough, but with highly compressed music with concentrated HF level above the crossover point it still would be possible to burn them in passive mode with the RMS and Peak limiters set to 1/3 of continuous power, and 3/4th of program.

They should be quite loud before they burn, any idea of what levels were being run "A" scale, at what distance?

Not loud. No compressed music, a mix of folk, blues and fusion.

Cant say bout level, will ask, but I can tell from last year, it was a very melow event.

Regarding the limiters, conservative as they might be, they were not being put into action, so full dynamics.

I would not know what to inspect, and have come to not trust local service centers. Possible for me to send a picture across, any help ?

Thank,
Sidhu
Title: Re: STX825 blown HF drivers
Post by: Nitin Sidhu on March 30, 2013, 02:23:03 pm
Sidhu, I take it you are bi-amping the 825s?  If so I suspect an error in the entry of the settings into the ITech, barring any product defect.

Passive.

4 channels of IT4K running 4 cabinets @ a 4ohms load each.

Sidhu
Title: Re: STX825 blown HF drivers
Post by: Nitin Sidhu on March 30, 2013, 02:25:52 pm
Also, to makeself clear, we dont own this inventory, and it is a cross rent.

Even more embarrassing.

To state that we treat cross rented gear better than our own would be an understatement.


Sidhu
Title: Re: STX825 blown HF drivers
Post by: Nitin Sidhu on March 30, 2013, 02:35:20 pm
Sidhu, I take it you are bi-amping the 825s?  If so I suspect an error in the entry of the settings into the ITech, barring any product defect.

Here the Device file for the ITech if anyone cares to review.

Thanks again!

https://docs.google.com/file/d/0B7sbO0TYr9ryU25OdHVjZzdFd1E/edit?usp=sharing

Preset number 9 was being used.

Sidhu
Title: Re: STX825 blown HF drivers
Post by: David Sturzenbecher on March 30, 2013, 03:29:17 pm

Preset number 9 was being used.

Sidhu

The limiters appear to be set really conservative...but if you weren't touching them...
You did forget to rename your preset...but I am guessing you would be able to tell if you were sending the 4880 SUB signal.

I don't see anything glaringly wrong.
Title: Re: STX825 blown HF drivers
Post by: Bob Leonard on March 30, 2013, 07:09:09 pm
A quick look at file #9 w/ SA shows all devices bypassed or off and a crossover center frequency of 1.2khz. My take on this preset is that it's for a bi-amped cabinet. Also, if you've not done anything with SA and the parameters for this preset then none of the modules are active by default.

Again, this is my take on the subject based on what I see in SA and not seeing any details in your post as to what you have done with these settings.
Title: Re: STX825 blown HF drivers
Post by: David Sturzenbecher on March 30, 2013, 08:08:00 pm
A quick look at file #9 w/ SA shows all devices bypassed or off and a crossover center frequency of 1.2khz.

Bob, I attached a screenshot of what I am seeing. Both channel 1 and 2 appear to be the same.
Title: Re: STX825 blown HF drivers
Post by: Nitin Sidhu on March 30, 2013, 10:11:06 pm
Hello David!

That is correct, did not realize that an offline device file without channel names will not overwrite channel names on the ITech. And as you can tell, these amps were deployed for Vertec v4 duty till the very recent upgrade to HD. but what's in a name ?

I can assure you the presets were working as desired, and sounded very good!

Bob, what you are seeing is not correct.
This device file has no bi-amp settings. And I have tried and find it pointless running any of the JBL portable boxes biamp'd.

Regarding the RMS limiter. The RMS limiters have a very slow attack time, 4seconds. And if the amps see a continuous signal above they engage. So far I have rarely ever seen that happen, maybe with some really loud metal acts belting it out. I think its a safe area to be in, if the programme material is really compressed, then the drivers should be able to handle that at 1/3rd rated power over a much longer time than at their full rated continuous power.
Especially since I don't do EDM or the likes. Mostly.

Regarding the Peak limters, set to 100v in this case, I think its moot.
The ITech 4000 is rated 2000watts into 4ohms, which, by my calculation translates to bout 90volts. So I don't see how setting it at 100volts would ever allow them to engage without the amp clipping first.

Unless of course I am totally off on how these limiters work.

None the less, as mentioned before, the limiters were not being put into action, so that should give us all a very real idea of how easy the mix was.

Regards,
Sidhu
Title: Re: STX825 blown HF drivers
Post by: Greg Cameron on March 30, 2013, 10:56:27 pm
And I have tried and find it pointless running any of the JBL portable boxes biamp'd.

Though you may not find an overall sonic reason to run bi-amp as opposed to passive, there may be another - steeper crossover slope for better HF driver protection. The JBL specs don't specify the filter order, but I suspect their only 2nd order, maybe 3rd order filters. External bi-amping means you'll probably be using a 4th order LR filter which means not working the HF driver as hard in it's lower range and possibly smacking the diaphragm on the phase plug. I'll be curious to know the mode of failure, but I'll submit that bi-amping at minimum will increase HF driver safety & clarity compared to running passive mode. And I'll also submit that if you do tend to push the rig, bi-amp will sound better.
Title: Re: STX825 blown HF drivers
Post by: Bob Leonard on March 31, 2013, 01:10:31 am
Dave, Nitin, thanks. I'll run the settings again tomorrow and see what SA say's again.
Title: Re: STX825 blown HF drivers
Post by: Art Welter on March 31, 2013, 12:21:19 pm
Regarding the RMS limiter. The RMS limiters have a very slow attack time, 4seconds. And if the amps see a continuous signal above they engage. So far I have rarely ever seen that happen, maybe with some really loud metal acts belting it out. I think its a safe area to be in, if the programme material is really compressed, then the drivers should be able to handle that at 1/3rd rated power over a much longer time than at their full rated continuous power.
Especially since I don't do EDM or the likes. Mostly.

Regarding the Peak limters, set to 100v in this case, I think its moot.
The ITech 4000 is rated 2000watts into 4ohms, which, by my calculation translates to bout 90volts. So I don't see how setting it at 100volts would ever allow them to engage without the amp clipping first.

Unless of course I am totally off on how these limiters work.

None the less, as mentioned before, the limiters were not being put into action, so that should give us all a very real idea of how easy the mix was.

Sidhu,
The presets show almost a 6 dB boost up high.
The driver is not padded in the high frequency, and the nominal impedance is 8 ohms, though the DC resistance is quite low (4+ohms IIRC).

30 volts or so of feedback could take out the HF drivers.
Title: Re: STX825 blown HF drivers
Post by: Bob Leonard on March 31, 2013, 12:23:24 pm
Bob, I attached a screenshot of what I am seeing. Both channel 1 and 2 appear to be the same.

I have the correct file now Dave. Quick question would be why no LP filter below 20khz, maybe at 17-18khz, and why the 6db of gain in the upper regions.
Title: Re: STX825 blown HF drivers
Post by: Bob Leonard on March 31, 2013, 12:24:48 pm
Same questions at the same time. Great minds think alike.
Title: Re: STX825 blown HF drivers
Post by: Nitin Sidhu on March 31, 2013, 12:51:33 pm
Same questions at the same time. Great minds think alike.

 :)

As mentioned before, eq presets copied over from the STX tunings as provided by Harman for the XTI boxes.

Image attached.


(https://lh4.googleusercontent.com/-AlGRo3Yl5eU/UVhozPrHNxI/AAAAAAAAADY/Uu_FrvvK9WQ/s800/Screenshot%2520%25288%2529.png)
Title: Re: STX825 blown HF drivers
Post by: Art Welter on March 31, 2013, 01:23:47 pm
:)

As mentioned before, eq presets copied over from the STX tunings as provided by Harman for the XTI boxes.

Image attached.

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.

When you inspect the diaphragms to see if they look burnt, also check to make  sure they were the correct impedance and original JBL equipment, and there are no obvious burnt resistors or blown capacitors in the passive crossover.

Good luck sorting out the problems!

Art
Title: Re: STX825 blown HF drivers
Post by: Nitin Sidhu on March 31, 2013, 01:32:58 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.

When you inspect the diaphragms to see if they look burnt, also check to make  sure they were the correct impedance and original JBL equipment, and there are no obvious burnt resistors or blown capacitors in the passive crossover.

Good luck sorting out the problems!

Art

Hello Welter!

Thank you. I understand what you are saying.

We will inspect the HF drivers and revert. I have been told that drivers were inspected and were found to be dead. So the crossover should be good.

This would however put me in a very peculiar dilemma. We have never in the past longest time blown an HF driver. We have worked with the 725/932 for many years now, and it has always been good.

Sidhu
Title: Re: STX825 blown HF drivers
Post by: Nitin Sidhu on April 01, 2013, 11:53:34 am
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.


(https://rajtiq.bn1.livefilestore.com/y1p1Y6bpOA08BXCUMPVe61waRG8lVOfMXRHIGd1i1mpQU_vXTP9f6KtxqpXRgmkgEcOTVE9oCsDiTTMfDS-TvOkQVBdvXsdHjQe/WP_000267.jpg?psid=1)

(https://qwjtiq.bn1.livefilestore.com/y1pDWy2-TYWdWgzOpQoEuhi6wqMLCh2MUZnWvLDXDDQ-6NFFGeF6rp3WPnjdu210anYlCQ0qa3b27ohAg9VZn6oynTq7ZGb99iy/WP_000266.jpg?psid=1)

(https://pgjtiq.bn1.livefilestore.com/y1pCned4Hw1EuCB_phOewad54Buv1AIcd2E56Z6qMtSpte6QgUY6l3SX4BSII6XbETNGxZqHPTggZtOkkZYM6-UobwkyD_Ucmno/WP_000265.jpg?psid=1)
Title: Re: STX825 blown HF drivers
Post by: Greg Cameron 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.
Title: Re: STX825 blown HF drivers
Post by: Nitin Sidhu 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
Title: Re: STX825 blown HF drivers
Post by: Greg Cameron 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.
Title: Re: STX825 blown HF drivers
Post by: Art Welter 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
Title: Re: STX825 blown HF drivers
Post by: Nitin Sidhu 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
Title: Re: STX825 blown HF drivers
Post by: Chris Hindle 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.
Title: Re: STX825 blown HF drivers
Post by: Raul Suarez 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
Title: Re: STX825 blown HF drivers
Post by: Nitin Sidhu 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
Title: Re: STX825 blown HF drivers
Post by: Art Welter 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
Title: Re: STX825 blown HF drivers
Post by: Nitin Sidhu 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
Title: Re: STX825 blown HF drivers
Post by: Bob Leonard on April 30, 2013, 05:37:40 pm
Nitin,
If you have a chance would you check the serial numbers on those cabinets. I would be interested to know the serial numbers are close or maybe even sequential. I would have to think that, as was pointed out, there may have been a short production run of marginal diaphragms.
Title: Re: STX825 blown HF drivers
Post by: Jim McKeveny on May 02, 2013, 07:53:14 am
Ditto the bad run of diaphragms theorem. Similar issues encountered years ago with B&C 750's in V-DOSC. Finally traced to the location of the diaphragms in the curing tray in an oven.

Personally I would like a more robust mechanical + solder connection, but this likely affects response.

Title: Re: STX825 blown HF drivers
Post by: RYAN LOUDMUSIC JENKINS on May 02, 2013, 09:23:19 am
Ditto the bad run of diaphragms theorem. Similar issues encountered years ago with B&C 750's in V-DOSC. Finally traced to the location of the diaphragms in the curing tray in an oven.

Personally I would like a more robust mechanical + solder connection, but this likely affects response.

I am still resoldering the leads on the voice coil wire once or twice a year from my DE85s.  Absolutely nothing wrong with the diaphragm or voice coil, just a solder connection the comes undone every once in a rare while.
Title: Re: STX825 blown HF drivers
Post by: Jason Phair on May 04, 2013, 11:36:10 pm
This reminds me a lot of the problems we've had with 4886 HF failures, that seemed to happen with no reason.
Title: Re: STX825 blown HF drivers
Post by: Nitin Sidhu on May 06, 2013, 08:38:37 am
This reminds me a lot of the problems we've had with 4886 HF failures, that seemed to happen with no reason.

Ditto. 4886 and the 825.

Replacement drivers on both systems now seem to work well.

Sidhu