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Compression diaphragm problem


The Dude

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While dialing in the peqs and delays, Chris noticed a drop in high frequency to little or no output. I could still here some high frequency, but it was down 8 db and when increase the gain on that channel I would get no additional output. So today I decided to perform some exploratory surgery and see if I can find something wrong with the diaphragm. For identification purposes, we are working on a BMS 4590. First thing I did was check the resistance which I had confirmed 8 ohms (should be fine on a 16ohm driver). Then I proceeded to remove the driver from the horn and disassemble it. Upon inspection I noticed the leads and ribbon like material have separated. Could this be my problem and if so, what could have caused on a new diaphragm?

 

You may have to zoom in on the picture 89ef48a60c0364d6144a100bbb6565c1.jpg07a91ed8e3b68d8d1b042a433b59c095.jpg9ab51e3b87464c6ff270801cf4c4d6f5.jpg

 

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If you've got a volt-ohm meter (VOM), that would be a quick check of continuity.  Generally, these ring-radiator diaphragms are pretty rugged, so I'd suspect that it was a manufacturing issue if you see an open circuit on the voice coil.  IIRC, this driver is not very old.

 

Chris

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If you've got a volt-ohm meter (VOM), that would be a quick check of continuity.  Generally, these ring-radiator diaphragms are pretty rugged, so I'd suspect that it was a manufacturing issue if you see an open circuit on the voice coil.  IIRC, this driver is not very old.
 
Chris
Showing 8 ohms

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That means the diaphragm is probably good.  Check the output voltage from the amplifier using your VOM.  If you see voltage, then it's either a hung-up diaphragm within the driver (very doubtful), something in the settings of the crossover (most likely). 

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The diaphragms leads have been damaged  by a transient -----but the main diaphragm itself seems to be fine  -------you might have to redo the leads with new wiring to be able to get the diaphragm  working right  -------I  would check both driver' s  diaphragms to verify  if both sides  have identical damages -- 

 

here 's what  the leads should look like

 

https://www.lean-business.co.uk/eshop/images/BMS_M4590_high_Diaphragm.jpgImage result for BMS 4590 diaphragm

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What kind of electronic crossover do you use? Yesterday noticed same for tweeter while measuring and setting. Looked like something hanged on XO, restarted it and it was fine.
Hypex Fushion Fa123,

You saying shut it off and turn it back on?

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That means the diaphragm is probably good.  Check the output voltage from the amplifier using your VOM.  If you see voltage, then it's either a hung-up diaphragm within the driver (very doubtful), something in the settings of the crossover (most likely). 
.030 with fluctuations, seems on point with the other side.

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The diaphragms leads have been damaged  by a transient -----but the main diaphragm itself seems to be fine  -------you might have to redo the leads with new wiring to be able to get the diaphragm  working right  -------I  would check both driver' s  diaphragms to verify  if both sides  have identical damages -- 
 
here 's what  the leads should look like
 
BMS_M4590_high_Diaphragm.jpg25946_0.jpg
Maybe a bad solder on the ring terminal?

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6 minutes ago, The Dude said:

Hypex Fushion Fa123,

You saying shut it off and turn it back on?

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Yes it costs nothing and turn it as last item in chain after amps or what ever you have more (connected computer ex.)

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11 minutes ago, Bacek said:

Yes it costs nothing and turn it as last item in chain after amps or what ever you have more (connected computer ex.)

So going with your advice, I decided to switch through Pre sets and noticed an increase in high frequency as measurement shows has returned.

 

Maybe a setting with preset 3?  Not sure, but does this confirm our diaphragm is working properly?

 

@Chris A not sure if your remember how it looked with first measurement, but this is back to where the spl once was.  However, I now am back to nasty phase and GD measurements.  I think I will add our filters one at a time until I see if something changes this.  

 

image.thumb.png.5559df933c5af35ac2bea3a31c44d1d4.png

 

image.png

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16 minutes ago, The Dude said:

Not sure, but does this confirm our diaphragm is working properly?

Yes. It's working now.   I would try the third round Left Belle-BMS-3.xml, then zoom way in on your SPL response plot within REW.  You're currently zoomed way, way, out. 

 

You might have cleared the issue by dissembling the driver and reassembling it.  It wasn't working beforehand:

 

567767851_LeftBMS-Belle-3PresetSPLandPhaseResponse.jpg.17352c3196be655a49b4295207ba39dd.jpg

 

1041152446_LeftBMS-Belle-3PresetGroupDelay.jpg.3a234c7a1aa6425d4da57485ab7e056c.jpg

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13 hours ago, Chris A said:

Try the right loudspeaker presets on the left. 

Same issue, since all of our work was on preset 3, the amp defaults to preset 3 when the right side config is loaded and then the high frequency drops off.  Weird. 

 

image.png.76c828cad4854f3d5818f18d0c607187.png

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