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Topic: How to tell if JBL is going bad?? |
Paul Sutherland
From:
Placerville, California
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Posted 17 Oct 2018 9:17 pm |
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I have a couple of cabinets with original cone JBLs. One has a single D120f, and the other has two K120s. Both cabinets are sounding gritty to me. I've played the same steel and used the same heads (a Twin Reverb, and a Milkman Mini) while playing through a third cabinet with a K130, and I don't hear the grit. So I don't think it's all in my head, or in the steel or amp heads I'm using. I'm pretty sure it's those twelve inch JBLs.
So is there a definitive test, or do I just have to wait until a speaker totally fails to know? And is there a danger to the amp to waiting for a speaker to fail?
I've seen apps on the internet for sweeping a speaker. I could run such an app through some PA gear I have (with the power amp turned WAY DOWN) with these JBL cabinets attached. But what should I be listening for?
I hate to give up on original cone JBLs. But if they are going bad the original cones don't mean much.
_________________
It don't mean a thing if it ain't got that swing. |
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Ken Metcalf
From:
San Antonio Texas USA
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Posted 18 Oct 2018 5:08 am
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Old school bonehead method.
With both hands and all fingers gently and carefully push in the cone. If you hear scratching when pushing it in and out it is not a good sign. Coil wire has melted and rubbing the magnet.
_________________
MSA 12 String E9th/B6th Universal.
Little Walter PF-89.
Bunch of stomp boxes |
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Bill A. Moore
From:
Silver City, New Mexico, USA
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Posted 18 Oct 2018 7:09 am
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I recently picked up a JBL that the fellow said "didn't sound right". I haven't had a chance to try it yet, but it passes the movement test easily.
There was a sizeable buildup of dust on the bottom front and rear of the JBLs in the Twin I traded for!I wonder if dirt/dust can enter through the vent opening. (I've only recently owned some JBLs, so I'm not familiar with their characteristics). |
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Michael Butler
From:
California, USA
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Posted 18 Oct 2018 8:59 am
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sounds like possible voice coil rub. i have a set of jbl speakers in their respective cabs. i have them lying down on their side bookshelf style. one was giving a distorted sound. i turned it upside down and it quit. is that a permanent resolution? probably not but it has been two years since i did it. you may want to try pulling the speaker and putting it in the opposite way. also, check the surrounds while you have it out as well as the connections.
play music!
_________________
please see my Snakeskin's Virtual Music Museum below.
http://muscmp.wordpress.com/ |
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Tim Marcus
From:
San Francisco, CA
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John De Maille
From:
On a Mountain in Upstate Halcottsville, N.Y.
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Posted 18 Oct 2018 11:43 am
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| I have an old (20 plus years) 15" E-130 JBL. Is there a way to clean out any dust that probably has accumulated over the years? Don't know where to look for any maintenance videos. |
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Paul Sutherland
From:
Placerville, California
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Posted 18 Oct 2018 4:03 pm
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I just tried a sine wave sweep on the cabinet with the K120s. I didn't hear anything particularly funny. But there did seem to be some noticeable dips in volume as the signal cycled from low to high. Also, there isn't much low end, or high end response.
For comparison, I ran the cabinet with the K130 (that does sound good to me), and there were fewer and slighter dips in volume during the sweep, and there was more low end and high end response.
Finally, I ran the sweep on a QSC K8 that I use as a stage wedge. It had noticeably less in the way of dips in volume, and had more low, and much more high response.
My tentative conclusion is a sine wave sweep won't tell you much with speakers that are heavy on the mid-range.
_________________
It don't mean a thing if it ain't got that swing. |
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Mike Wheeler
From:
Delaware, Ohio, USA
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Posted 18 Oct 2018 4:12 pm
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I'm afraid you can't "clean" JBLs like that, other than dusting off the surfaces. Btw, in case you don't know, those cones are made of paper, so don't get them wet. 
Paul, the dips you were noticing were most likely just standing wave cancellations (due to the room you were in) as you progressed along the sweep. But, since you were primarily looking for scratchiness, or noises, that doesn't really matter.
_________________
Best regards,
Mike
Last edited by Mike Wheeler on 18 Oct 2018 4:24 pm; edited 1 time in total |
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Bill A. Moore
From:
Silver City, New Mexico, USA
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Posted 18 Oct 2018 4:18 pm
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| I have access to compressed air, and I have great success cleaning the dust buildup on speakers. (Low pressure, of course!) |
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Erv Niehaus
From:
Litchfield, MN, USA
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Posted 19 Oct 2018 7:51 am
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I believe the speakers that JBL built for Fender had a little more clearance built into them.
Erv |
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Michael Brebes
From:
Northridge CA
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Posted 20 Oct 2018 6:15 am
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Another thing that can happen to an older speaker is that the voice gets slightly bent with an overexcursion. The following action comes with a disclaimer: If the speaker voice coil rubs when pushing the cone down evenly, then try pushing it down with one or two fingers while moving around the cone. Sometimes you can find a spot where it stops rubbing. SOMETIMES, by pushing down harder opposite of where it stopped rubbing you can straighten out the voice coil so that it no longer rubs.
_________________
Michael Brebes
Instrument/amp/ pickup repair
MSA D10 Classic/Rickenbacher B6/
Dickerson MOTS/Dobro D32 Hawaiian/
Goldtone Paul Beard Reso
Mesa Boogie Studio Pre/Hafler 3000
RP1/MPX100 |
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Godfrey Arthur
From:
3rd Rock
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Posted 21 Oct 2018 2:59 am
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If you want to save them, get them recoiled and reconed. Dirt and rust gets in the gap and the voicecoil rubs.
New voicecoil for JBL D120 8 ohms.
D120F rebuild kit
_________________
ShoBud The Pro 1
YES it's my REAL NAME!
Ezekiel 33:7
Last edited by Godfrey Arthur on 22 Oct 2018 12:09 am; edited 2 times in total |
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Jim Sliff
From:
Lawndale California, USA
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Posted 21 Oct 2018 6:58 pm
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The "bonehead" test - pressing on the cone - is well named. It's a great way to ruin a perfectly good voice coil. NEVER do that. The tolerance of the voice coil gap is very small, and you simply can't physically "feel" that you are applying even pressure to the cone.
If you have compared them to other speakers with the same amp(s) and the same "grit" is noted they need reconing.
_________________
No chops, but great tone
1930's/40's Rickenbacher/Rickenbacker 6&8 string lap steels
1921 Weissenborn Style 2; Hilo&Schireson hollownecks
Appalachian, Regal & Dobro squarenecks
1959 Fender 400 9+2 B6;1960's Fender 800 3+3+2; 1948 Fender Dual-8 Professional |
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