Sound Reinforcement - Forums for Live Sound Professionals - Your Displayed Name Must Be Your Real Full Name To Post In The Live Sound Forums > LAB Lounge

JBL MP418SP popping sound at about 90hz

(1/3) > >>

Jared Bartimus:
A campus ministry program I help out purchased a used MP418SP a few months back and we have been having problems with popping ever since.  When the system is run anywhere near its limit we get a popping sound in the 80-100hz range.  Before I had assumed we were sending out too much in the lower ranges and bottoming out the driver.

The frequency was determined by playing the 80hz warble from the Bink Audio Test CD and then using individual test tones to narrow it down.  Low cut on the channel strip was turned off and the main eq's had, I believe, a 40hz low cut engaged.  Every time the tone would hit the middle of the range the sub started popping.  EQ was set flat for everything below about 120hz and there were no significant changes above that point.

It started popping both when pushed fairly hard at that frequency and when I was moving the fader relatively quickly at a lower level.  I don't know if that part was an issue with the sound board or something to do with the sub.

Is the original assumption that we are doing something wrong and causing it to bottom out probably correct or was the driver maybe somehow already damaged when we got it?  It doesn't seem right that the sub has extreme difficulty keeping up with a pair of JRX115's that are being powered to the same combined wattage.  I know we aren't going to be getting a strong hit from the kick drum with only a single 18" sub in a room as big as we are in but it had trouble getting over stage volume even with just two people singing and an acoustic guitar.

Bennett Prescott:
It sounds like over excursion, but if it's happening with quick fader moves at low levels (or with things that should not be creating sub bass, like an acoustic act) then the problem may lie elsewhere. Check your cable connections, maybe one of them has gotten a little corroded.

Jared Bartimus:
I thought it was overexcursion myself, but shouldn't that get worse at lower frequencies? At 110hz it is fine and at 70hz it is fine but at 80-100hz it isn't.  If I remember correctly pretty much every connector in the sytem has been checked within the past 6-9 months due to other issues we had been having. 

Tim McCulloch:

--- Quote from: Jared Bartimus on April 12, 2011, 03:42:03 pm ---I thought it was overexcursion myself, but shouldn't that get worse at lower frequencies? At 110hz it is fine and at 70hz it is fine but at 80-100hz it isn't.  If I remember correctly pretty much every connector in the sytem has been checked within the past 6-9 months due to other issues we had been having.

--- End quote ---

Can you find another MP418 to compare with?  I don't think it's the loudspeaker itself...

If it were, it would be more likely to bottom out at lower frequencies (particularly at/below the box tuning freq) and that would be at levels below maximum power.

I suspect what you're hearing is a cabinet issue... a broken glue joint, failed fastener, etc that resonates at 70Hz.... or there is something loose in the box that starts moving when the box resonates at 70Hz.

Perhaps Art Welter can share his considerable experience with such things....

Have fun, good luck.

Tim Mc

Jared Bartimus:

--- Quote from: Tim McCulloch on April 12, 2011, 05:46:09 pm ---Can you find another MP418 to compare with?  I don't think it's the loudspeaker itself...

If it were, it would be more likely to bottom out at lower frequencies (particularly at/below the box tuning freq) and that would be at levels below maximum power.

I suspect what you're hearing is a cabinet issue... a broken glue joint, failed fastener, etc that resonates at 70Hz.... or there is something loose in the box that starts moving when the box resonates at 70Hz.

Perhaps Art Welter can share his considerable experience with such things....

Have fun, good luck.

Tim Mc

--- End quote ---

Thanks for the suggestions so far.  It sounds like it is coming from the driver itself but it could still be an issue in the cabinet near the driver. 

Navigation

[0] Message Index

[#] Next page

Go to full version