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Author Topic: JBL MP418SP popping sound at about 90hz  (Read 6747 times)

Micky Basiliere

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Re: JBL MP418SP popping sound at about 90hz
« Reply #10 on: April 13, 2011, 02:33:05 pm »

Sounds almost like a 48v problem with the mixer? or dirty faders? or possibly the EQ?  you could try contacting a Crown tech. to see what they say? i dont think JBL would be of any assistance... i have never experienced this issue with my MP418sp's i LOVE these cabs and you just cant find these animals anymore...they were "one of a kind"  and sound great!!!
JBL's biggest mistake was discontinuing them!
The 4ohm output is 660 per channel.

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.
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Chris Davis

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Re: JBL MP418SP popping sound at about 90hz
« Reply #11 on: April 13, 2011, 04:07:45 pm »

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.

Hi, going through this thread and thinking about this box sight unseen, it might seem that you could have two unique problems. 

One being a dirty fader.  Moving it might send out low frequency noise that might make the woofer significantly. 

Then the woofer driver I think might be damaged.  I have replaced ported woofers that did pop around 90 or 100 Hz, exactly as you describe, and at a much lower output than they should have been capable of.  They looked fine and measured fine with an ohmmeter.  It turns out in my case of the speakers I was working on, they had been overdriven and the voice coil formers were damaged.

So, to summarize...  The woofers might be damaged and could be popping like that for any signal that triggers them to move a certain distance.  I had the ones I was working on reconed.

Then there might be one or more dirty/oxidized faders that are sending out enough low frequency rumble to make the woofers to move the distance required to make them "pop".  They probably need cleaning/replacing.
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Jared Bartimus

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Re: JBL MP418SP popping sound at about 90hz
« Reply #12 on: April 13, 2011, 05:44:39 pm »

Hopefully I don't miss any of the suggestions.  This is easier than multiple quotes.

48v problem: phantom is disabled.  Overheads are powered by batteries because we had so much trouble with the snake in the past.  That has since been resolved but it is easier to just stick with the batteries.

Dirty fader: hadn't thought about that being the reason for the problem when actually moving it.  I thought the noise was in sync with the sine wave but I may have been incorrect.  It is doubtful they have ever been cleaned unless there was a specific problem.  The board is a mackie 1604-vlz pro.

EQ: It was flat below I believe 120hz with no significant cuts/boosts anywhere else when I was testing with the tones.  Low cut at, I believe, 40hz (I need to check to verify that).

Driver/cabinet damage: This is the one that seems to be most commonly suggested, and the situation I am hoping is NOT the case.  Reconing would probably be $100 + labor and a new driver would be around $500 + labor from what I have read.  I wish actual potential driver damage had been investigated right when the sub was purchased rather than 6 months later.  Myself and everyone else just assumed it was something to do with how we were running the system and would just keep an eye on it a few times during practice to make sure none of the changes we made at FOH were pushing it past the edge.
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Gordon Brinton

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Re: JBL MP418SP popping sound at about 90hz
« Reply #13 on: April 13, 2011, 05:46:23 pm »

Over excursion is not a function of frequency. It is more directly related to amplitude and velocity. However, frequency can have some effect on amplitude and velocity by means of air damping within the cabinet as mentioned earlier.

It is also possible that this speaker has been reconed by the previous owner. If it was NOT done by a professional, the cone could have been set at an incorrect depth within the magnet gap. Its neutral resting position must be at a depth where, the center of the voice coil (half its depth) aligns with the center of the top plate. In other words, if the voice coil is just a little too deep, it can bottom out frequently. Also, shims must be used to center it side-to-side within the gap to prevent scraping and shorting.

Another possibility is spider and surround fatigue which can result in diminished mechanical damping.

Any one of these things could be wrong and we would never know.

Again, you'll just have to try another speaker cabinet to narrow down the problem by process of elimination.
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Joe Breher

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Re: JBL MP418SP popping sound at about 90hz
« Reply #14 on: April 13, 2011, 06:49:47 pm »

It very well could be overexcursion.

I like the analysis, but not the conclusion. Note OP mentioned this was having a hard time keeping up with JRX115's.

I own an MP418SP/MP418S pair in my C rig. While they aren't VT4880's, one should have no issue keeping up with a pair of JRXanythings.

I'd lean toward the aforementioned structural resonance hypothesis, until shown otherwise.
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Re: JBL MP418SP popping sound at about 90hz
« Reply #14 on: April 13, 2011, 06:49:47 pm »


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