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Testing a woofer

J

John Webb

Apr 20, 2006
1,095
554
#1
Beyma12G40

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My Beyma 12G40 farts when I play a particularly resonant note like a B,C,D, on the E string.
Beyma says they tested it 3 times and it is fine.
I want to test it myself. Can I bypass the crossover and try it that way?
I figure if it still farts then it is definitely the spkr and I'll just go ahead and replace it.
Help?!
__________________
Follow your blissters.
Peace
 
#3
John Webb said:
My Beyma 12G40 farts when I play a particularly resonant note like a B,C,D, on the E string.
Click to expand...

Does it still fart when you play those same notes on the A string?

Also try moving the cabinet outdoors and see what happens. I've been fooled before because I heard what I thought was distortion, but it was just something in the room vibrating in sympathy to those frequencies.
 
#5
Having no idea about how this test was conducted, I suggest you try to remove all sources of "noise" around the test object.
Step one would be (as suggested) to bring the complete speaker into a lawn or open space. Is it still rattling?

Step two would be to diassemble the speaker and run the signal into the raw transducer. (It will not hurt it, as long as you do not make it "fart out".) Put the transducer on a pillow or something similar to decouple it from the floor. Does it STILL rattle? In that case you have a suspension or motor assembly damage.)
 
#8
I just tested it in an out of the enclosure and not hooked up to the crossover. I put it on a pilllow when out of the enclosure. It doesn't fart until I play it for a minute or two. Once it starts, it doesn't stop.
I am convinced w/o a shadow of a doubt now that the problem is in the woofer. Beyma says nothing wrong with it so I guess I'm stuck.
I don't know whether to have it repaired or replace it.
I have a 2460 with two Eminence in it and it sounds wonderful.
This cab is a 1260 and I wanted it for small gigs and to go along with the other cab for bigger venues. Seller told me the Beyma was new in Jan. this year.
Well, any advice appreciated. Guess I'll price the repair first.
 
#10
I have seen (heard...) overheated / misaligned voice coils on car stereo woofers behave like that. As they heat up, the VC starts rubbing the walls in the VC gap. Supposedly this can also happen to stamped steel woofers when the transducer frame gets bent from some kind of impact.

It seems you have to recone it.

/Alexander
 
#11
John Webb said:
It doesn't fart until I play it for a minute or two. Once it starts, it doesn't stop.
Click to expand...

And the Beyma guys wouldn't have tested it for that long.

To be honest I'm not 100% sure it's the woofer. But I'm going to assume you've used the process of elimination to rule out everything else i.e tried a different amp, a different bass etc etc).

In my experience woofers either work or don't, or they distort or don't. The one exception was when my crew did some metalworking with the cabs nearby and one of my woofers (also a beyma) ingested some metal filings through the vent hole in the back of the speaker. They ended up in the gap, and that speaker would distort, then be fine, then distort again as the debris in the gap moved around.

You could have something similar going on here. If the debris is non metalic (non magnetic), you could remove it by taking off the dust cap, cleaning it out, then replacing the dust cap. Metalic debris is harder to remove as the magnet tends to hold it in place so you never quite get all of it out, so mine needed a recone.

Hope that helps.
 
#13
billfitzmaurice said:
That's as much a product of the cab as it is the driver. Considering the high quality of the 12G40 I'd be far more inclined to blame the cab.
Click to expand...

Thanks Bill,

I am sure it is the speaker (see my results below).
I wonder if I should replace it with a more affordable Eminence or have the Beyma reconed. I'm a little leery of reconing the speaker but not fixing the problem.

Advice much appreciated.

jpw
 
#15
And there's the rub. As Bill opined, the cabinet could be wrong for the speaker. Dr. Bass is going through some kind of crisis ATM so who knows what he did for your cabinet. Maybe he just dropped an available driver into a box he already had. I would d/l winISD and use it to see if the driver and the cabinet can actually work together.

One comment I would like to make is that you should never ever play through a driver when it is not mounted in an enclosure. I feel that if the box is causing your original problem your driver is toast now.

How much were you expecting from a single 12?? For a practice at home cabinet it would be fine but not for playing with other people IMHO. What amp are you using and how are you setting your EQ?

Paul
 
#16
BassmanPaul said:
d/l winISD ?!?!?
:confused:
Paul
Click to expand...

The 1260 is an excellent cab for small gigs and practice with others. Really.
I will find out what the original woofer was when the cab was built. Excellent point about the driver maybe not matching the cab. I bought it fom a TB'er and he said the Beyma was new in Jan this year.
This is a 500 W driver. I've tried it out with my 800RB, my 2001RB (not bridged) and Dr. Bass's Promethean. Same results with all. My P bass, My PJ and Dr Bass J and some boutique bass I forget the name of that he plays.
 
#18
John Webb said:
Thanks Bill,

I am sure it is the speaker (see my results below).
Click to expand...
I don't see anything that describes your test procedure. With the right software one can measure the driver in the cab and by the distortion percentage versus power tell if the driver is performing correctly or not.
 
#19
billfitzmaurice said:
I don't see anything that describes your test procedure. With the right software one can measure the driver in the cab and by the distortion percentage versus power tell if the driver is performing correctly or not.
Click to expand...

Here is my procedure :rolleyes:

I just tested it in an out of the enclosure and not hooked up to the crossover. I put it on a pilllow when out of the enclosure. It doesn't fart until I play it for a minute or two. Once it starts, it doesn't stop.
I am convinced w/o a shadow of a doubt now that the problem is in the woofer. Beyma says nothing wrong with it so I guess I'm stuck.
I don't know whether to have it repaired or replace it.
Well, any advice appreciated. Guess I'll price the repair first.
__________________

Once you guys start talking test software it is clear to me that I may be in over my head. I will try to see what was in this cabinet originally (what it was designed for) and then either repair/replace the Beyma, or replace it with the propoer original type.
 
#20
Don't know if this helps. The 15-inch driver on my Ashdown was farting like crazy. Took it out and brought it to a tech who sign-off that there was nothing wrong with it. Mounted it on the cab and it would fart like hell. I then tried un-screwing the mounting screws while a looped note was being played through it. The farting noise slowly went away. So I tried something different. I put the cab on its back (with the drivers pointing at the ceiling) and took out all the mounting screws and the driver was playing as clear as ever. Turns out that over-tightening or an uneven tightening of the mounting screws on the cab caused the stamped steel speaker basket to distort, and this caused the farting sound. With the cab on its back, I then mounted the driver and tightened the screws evenly in a criss-crossing (star) pattern (the same way you would tighten the lugs on a wheel as you mount them on your car). This won't cost you a cent and is something you might want to try.
 

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