blown driver issues

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djtrumptight
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Re: blown driver issues

#16 Post by djtrumptight »

I use a Mackie FX12 board.I spent a good 3 hours trying to re-do my gain structure and its no use,i turned the limiter off and read 122 volts on the DMM,i think that would explain such a low reading on the DCX sub outs before the limiter kicks in,i tried to line up the mixer and the DCX so that the DCX would limit if the mixer hits the red but that was no use.Im pretty sure those power outages did those drivers in,limiters are set correctly,hi pass is correct but i did change my hi pass filters from 48LR to 48BW,i will see what happens.
Built:
2 Autotuba's MCM 55 2421
8 T48's 24"wide 3015 LF
2 DR 250's melded Deltalite II 2510
2 DR 250's flat Deltalite II 2510
2 SLA HT systems
1 Table Tuba Dayton DCS 255-4
2 T 39's 20" wide 3012 LF
1 T-18 13" wide MCM 55 2421
2 SLA Pro's

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Seth
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Re: blown driver issues

#17 Post by Seth »

Where did you get that 122 volt reading?
Build in process - 2 WH6, one Alpha 6a loaded, one PRV Audio 6MB250-NDY loaded

Two 2x6 shorty SLA Pro's
One T39, 16", 3012LF loaded
Tall AutoTuba, 20" wide, 2x 8" MCM 55-2421
TruckTuba, 8½" wide, 2x 8" MCM 55-2421

Bruce Weldy
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Location: New Braunfels, TX

Re: blown driver issues

#18 Post by Bruce Weldy »

SethRocksYou wrote: Thu Sep 12, 2019 8:59 am Where did you get that 122 volt reading?
That would be an amp rated at 1860 watts at 8 ohms...... you sure you have your meter set correctly? What model amp is it?

6 - T39 3012LF
4 - OT12 2512
1 - T24
1 - SLA Pro
2 - XF210


"A system with a few knobs set up by someone who knows what they are doing is always better than one with a lot of knobs set up by someone who doesn't."

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Seth
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Re: blown driver issues

#19 Post by Seth »

Bruce Weldy wrote: Thu Sep 12, 2019 11:03 am
SethRocksYou wrote: Thu Sep 12, 2019 8:59 am Where did you get that 122 volt reading?
That would be an amp rated at 1860 watts at 8 ohms...... you sure you have your meter set correctly? What model amp is it?
Exactly.
The QSC GX7 is rated 725wpc. Suppose it may put that out in a bridged configuration. Dunno.
Build in process - 2 WH6, one Alpha 6a loaded, one PRV Audio 6MB250-NDY loaded

Two 2x6 shorty SLA Pro's
One T39, 16", 3012LF loaded
Tall AutoTuba, 20" wide, 2x 8" MCM 55-2421
TruckTuba, 8½" wide, 2x 8" MCM 55-2421

Bruce Weldy
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Location: New Braunfels, TX

Re: blown driver issues

#20 Post by Bruce Weldy »

SethRocksYou wrote: Thu Sep 12, 2019 12:12 pm
Bruce Weldy wrote: Thu Sep 12, 2019 11:03 am
SethRocksYou wrote: Thu Sep 12, 2019 8:59 am Where did you get that 122 volt reading?
That would be an amp rated at 1860 watts at 8 ohms...... you sure you have your meter set correctly? What model amp is it?
Exactly.
The QSC GX7 is rated 725wpc. Suppose it may put that out in a bridged configuration. Dunno.
You can't bridge the GX series amps. So, something is wrong in the process of metering.....

6 - T39 3012LF
4 - OT12 2512
1 - T24
1 - SLA Pro
2 - XF210


"A system with a few knobs set up by someone who knows what they are doing is always better than one with a lot of knobs set up by someone who doesn't."

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Seth
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Re: blown driver issues

#21 Post by Seth »

Bruce Weldy wrote: Thu Sep 12, 2019 1:36 pm
SethRocksYou wrote: Thu Sep 12, 2019 12:12 pm
Bruce Weldy wrote: Thu Sep 12, 2019 11:03 am

That would be an amp rated at 1860 watts at 8 ohms...... you sure you have your meter set correctly? What model amp is it?
Exactly.
The QSC GX7 is rated 725wpc. Suppose it may put that out in a bridged configuration. Dunno.
You can't bridge the GX series amps. So, something is wrong in the process of metering.....
I'm curious what djtrumptight is measuring, should be roughly 75-76 out of that amp, limited down to 60v.
Build in process - 2 WH6, one Alpha 6a loaded, one PRV Audio 6MB250-NDY loaded

Two 2x6 shorty SLA Pro's
One T39, 16", 3012LF loaded
Tall AutoTuba, 20" wide, 2x 8" MCM 55-2421
TruckTuba, 8½" wide, 2x 8" MCM 55-2421

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BrentEvans
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Re: blown driver issues

#22 Post by BrentEvans »

#1. Certain amps without a speaker attached can output far more voltage than they can drive into a load without crapping out. A reading over 100v isn’t uncommon with no load.

#2. LImiters are only a protection against overexcursion. A speaker can fail from thermal damage even if it never reaches its excursion limit. Such thermal damage comes from overpowering. Remember that we measure everything in RMS watts. If you drive a signal into clip anywhere in the signal chain, you are delivering far more than the current which the math would suggest for whatever voltage (below the limiter) you might read with a meter. A DJ running a signal into the red will do this in a heartbeat.

#3. +12 is nothing. Pro digital consoles regularly go to +18 and I’ve seen analog consoles that are clean to +22. DJ mixers are generally crap.
99% of the time, things that aren't already being done aren't being done because they don't work. The other 1% is split evenly between fools and geniuses.

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Seth
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Re: blown driver issues

#23 Post by Seth »

Re: #1. All the amps I've ever tested (granted, only 10 or so) have always been real close to right on the money. Really good to know Brent. Thank you.

Re: #2. I think we've discussed this point before. I'm not too sure it makes sense to me that a limited signal couldn't or wouldn't prevent thermal damage. Would you mind expanding on that a little? Seems to me your suggesting a heavily over-driven guitar would melt a coil before a sine wave would. Which, I have no idea. Is that the case? Or, what about non-sine wave tones? Does more harmonic content equate to more current? Makes sense that it would from the standpoint that 2, 3, 4+ sine waves is more than 1. What about Pink Noise... Speaker fryer under the limiter?

Re: #4. (I know, you didn't have a #4.) What caused the damage shown for the drivers in this thread? Is that throat pressure? Over excursion? Clipped signals? Obviously not a thermal issue
Build in process - 2 WH6, one Alpha 6a loaded, one PRV Audio 6MB250-NDY loaded

Two 2x6 shorty SLA Pro's
One T39, 16", 3012LF loaded
Tall AutoTuba, 20" wide, 2x 8" MCM 55-2421
TruckTuba, 8½" wide, 2x 8" MCM 55-2421

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BrentEvans
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Re: blown driver issues

#24 Post by BrentEvans »

Thermal damage comes from heat. Heat is generated by current, measured in watts. This is why drivers are advertised with a power rating in watts rather than volts.

The excursion limit comes as much from the cabinet as it does from the driver. Excursion is directly correlated to voltage. This is why the same driver can have different excursion limits in different cabinets, and why the voltage limit of some drivers in some cabs doesn't work out to be the same as the thermal limit. For instance, IIRC, the 3012LF is limited to 50v, or 312W (using the DCR of the driver to calculate) in some of the BF cabs, despite having an RMS power rating of 450W. IN that cabinet, At 50V, consuming 312w, the driver reaches its xmax, where in another cabinet, it might not reach xmax until well beyond the RMS power rating.

The thing that is hard for most people to understand is that when you're dealing with the numbers, we have to use Ohm's law to convert between voltage and current, but Ohm's law really only applies to DC circuits and steady state AC circuits When you're dealing with music program content, you have to think deeper about what Ohm's law means. If you calculate the power from voltage with Ohm's law, you are getting getting a result that applies to a sine wave, and on a graph, this result is the area under the curve of the sine wave, as illustrated below.

That's what power in an audio signal is - the area under the waveform. Ohm's law only applies to the voltage at the When you then amplify and clip this signal, you are squaring off the waveform, which means more power. Its easy to see on a graph that the yellow area is larger in the square wave of the same amplitude (voltage).

Bear in mind that on these charts the vertical position of the point on the waveform is correlated to the voltage going to the speaker, and therefore the movement of the speaker. This also speaks to what may have happened to the speaker in question. Because a clipped signal is causing the speaker to move repeatedly and far more quickly from one extreme to the other than a sine or unclipped program signal of equivalent voltage it can cause mechanical stress and tear the cone even if the thermal limits are not technically exceeded. That said, it's extreme damage for something like this, but not impossible.
Attachments
square wave.jpg
sine wave.jpg
99% of the time, things that aren't already being done aren't being done because they don't work. The other 1% is split evenly between fools and geniuses.

djtrumptight
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Joined: Tue Dec 15, 2009 6:08 pm
Location: Detroit,Michigan

Re: blown driver issues

#25 Post by djtrumptight »

Sorry to be missing from the post fella's,i just happened to come back to possibly give some insight into what "might" have happened.I believe the problem was with some reconing i had done.In the past when i had a blown driver i would send it to Simply Speakers and have them do it.I ended up having to recone some of them because i used 8 T48's one day,lowered the hi-pass to 35 but rather than stack them i ran them side by side,4 per side :owned: So rather than send that many out i did the recones myself.I have since reconed the blown drivers,tightened the drivers screws down over a period of 3 days,checked them for leaks and followed the same procedure for the driver access panels.The first time i did the recones i used a caliper to measure the coil left out of the magnet as i didnt have any info on how much coil should be left out of the gap.I believe the measurement i got was taken from a Simply Speakers reconed driver that blew again.Simply Speakers no longer recone 3015LF's,im assuming they have gotten customer complaints about failed recones from them.I found some old literature on my computer about reconing some eminence drivers,the spec they gave for 15" Kappa was for a 12/64" of coil out of the magnet.After gluing up my new spiders to the coil,i cut the blown drivers dustcaps off and compared them and all the blown drivers had alot more than 12/64" of coil out of the magnet so if the coils were too high out of the magnet,wouldnt those drivers reach over excursion sooner ??????
Especially with a properly set limiter and never exceeding 56 volts ?
To whomever asked the question,i am using a QSC GX7 to power the subs,I dont bridge and as was stated,u cant bridge those amps or run a 2 ohm load.Yes,i did measure 122 volts on my Radio Shack voltmeter with a brand new battery installed in it,i have the video on my phone,i will post it.
Built:
2 Autotuba's MCM 55 2421
8 T48's 24"wide 3015 LF
2 DR 250's melded Deltalite II 2510
2 DR 250's flat Deltalite II 2510
2 SLA HT systems
1 Table Tuba Dayton DCS 255-4
2 T 39's 20" wide 3012 LF
1 T-18 13" wide MCM 55 2421
2 SLA Pro's

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Bill Fitzmaurice
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Re: blown driver issues

#26 Post by Bill Fitzmaurice »

To know how much coil extension there should be measure the extension on the cone that was removed. Of course that only works if the cone was original. Otherwise contact Eminence. You mention Kappa 15. That's not the same as a Kappalite 3015LF.
Limiting isn't perfect. If you set the limiter at 56v and then run the driver at a constant 56v you're going to get long term overheating. But that's not what happened to the pictured drivers. Cone shredding can only happen with substantial over voltage and/or inadequate high passing.

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