strange subwoofer thingie

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LiamSmith

Freshman
Jun 5, 2012
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Ulster, NY
So, last night I thought I lost a sub driver. It somehow, magically, between gigs gave out on me. Today I am testing it to find that it won't produce audio unless fed a more powerful signal. So, a loud tap on a microphone as opposed to a light tap.

I am thinking this is indicative of some kind of a loose connection somewhere in the chain... But, I really don't know. Anybody have an wisdom to impart on me?
 
Re: strange subwoofer thingie

LiamSmith said:
So, last night I thought I lost a sub driver. It somehow, magically, between gigs gave out on me. Today I am testing it to find that it won't produce audio unless fed a more powerful signal. So, a loud tap on a microphone as opposed to a light tap.

I am thinking this is indicative of some kind of a loose connection somewhere in the chain... But, I really don't know. Anybody have an wisdom to impart on me?
Click to expand...

It sounds like there is a broken connection somewhere.

An ohm meter is your friend.

Start at either end (speaker cable to amp-or loudspeaker driver) and measure the resistance between the + and - wires. Depending on the impedance-it will probably be between 3 and 8 ohms. If you read an open-simply keep going down the chain (towards the other end) until you get a low reading (or a high reading_ depending on which way you are going.

That should point you right to the problem-broken wire-lose connection-bad crimp-broken connection and so forth.
 
Re: strange subwoofer thingie

I have probably seen 1/1000 the amount of driver failures Ivan has, but can a driver fail in the manner described? I just can't really imagine, right off the top of my head, how that would happen?

Semi-conductors, on the other hand, are often seen to behave like the OP describes. You are not testing on the same amp channel that was driving it "last night", are you? Just make sure it isn't that.
 
Re: strange subwoofer thingie

Frederik Rosenkjær said:
I have probably seen 1/1000 the amount of driver failures Ivan has, but can a driver fail in the manner described? I just can't really imagine, right off the top of my head, how that would happen?

Semi-conductors, on the other hand, are often seen to behave like the OP describes. You are not testing on the same amp channel that was driving it "last night", are you? Just make sure it isn't that.
Click to expand...

Bad solder joints can often behave like semiconductors...
 
Re: strange subwoofer thingie

Frederik Rosenkjær said:
I have probably seen 1/1000 the amount of driver failures Ivan has, but can a driver fail in the manner described? I just can't really imagine, right off the top of my head, how that would happen?

Semi-conductors, on the other hand, are often seen to behave like the OP describes. You are not testing on the same amp channel that was driving it "last night", are you? Just make sure it isn't that.
Click to expand...
I have seen drivers do this-in a couple of different ways.

One brand has the lead in/tinsel wires that are connected to the voice coil wires via crimps.

In the early runs (can't say about it now-because I am out of the recone business) this crimp would not always be real solid. So it would "kina let lose" a little bit. But when enough voltage was applied it would (jump) back into action-for a little bit anyway. The solution (short fo a full recone) was to scrape away the glue over the connection-spply a little bit of solder and reglue. I would always solder that connection on the recones before assembly-so it did not happen to my jobs.

I have also seen the tinsel wire "wear out" where it attaches to the back side of the cone. This "wire" is not all wire or conductor-so the other parts would hold it in place and the electrical connections were very close-so a high enough voltage would make it work-for a little bit.

Those 2 problems are easy to fix and don't require a full recone.

Other ones include voice coil wires that are bent sharply and burn through-but not completely.

I have seen some speaker that have little fuses behind the input terminals (of the driver) that the fuse element has become "lose" inside the glass-and it floats around making contact sometimes and not other times.

But the problem could be outside the driver-input jacks on the cabinet-wire connected to the input jack-speaker cables and so forth.

It could be anywhere-the only way to tell is to jump in and start measuring to see where the open is. An ohm meter is not gong to supply enough voltage for the connection to "jump".
 
Re: strange subwoofer thingie

If it happened between gigs it could possibly be a shifted magnet causing the voice coil to be rubbing and only makes sound when enough signal applied.

Has the speaker been jarred hard in transportation?

Scott
 
Re: strange subwoofer thingie

I've had a few drivers for whatever reason* the voice coil gets partially jammed in the gap and a strong signal is enough to dislodge it temporarily. Usually when you run a low level signal through it you get nothing but midrange content because of the limited excursion and when it breaks free the bass content comes back but with a lot of other mechanical clicks and pops.


*(in one case it was a JBL driver where the foam vent filter had disintegrated and the particles melted into the voice coil gap melting and became a thick syrupy mess

In another case it was a B&C driver with a cracked magnet that shifted and was pinching the voice coil in place. )
 
Re: strange subwoofer thingie

Scott Abrahamson said:
If it happened between gigs it could possibly be a shifted magnet causing the voice coil to be rubbing and only makes sound when enough signal applied.

Has the speaker been jarred hard in transportation?

Scott
Click to expand...
When you have a shifted magnet-and the voice coil is not cut in half-the voice coils cannot "rub"-since it is pinned. There is no- "a little bit pinned" with a shifted magnet! Just try to move it------------------

The sonic character is no bass. You will still get some upper mids to highs-but it will not be as loud as usual.

The reason is that the voice coil on the opposite side of the "pin" is still free to move (but the pinned side cannot move). So it will vibrate a little bit-which causes the cone to vibrate-but it cannot move back and forth like it normally would. So it cannot reproduce bass.

You cannot apply enough signal to get the voice coil to start to move-other than vibrate on one side.
 
Re: strange subwoofer thingie

Hey thanks for everyone's input. I disassembled everything. I tested the input jacks by switching them out. Tested multiple amp channels and cables.

When I reseated the leads back into the driver everything started working fine. So, I'm assuming it may have been jarred in transport and the leads must have knocked out or something.
 
Re: strange subwoofer thingie

LiamSmith said:
Hey thanks for everyone's input. I disassembled everything. I tested the input jacks by switching them out. Tested multiple amp channels and cables.

When I reseated the leads back into the driver everything started working fine. So, I'm assuming it may have been jarred in transport and the leads must have knocked out or something.
Click to expand...
Don't be so sure.

One other failure I missed-and it is pretty common. Depending on the particular speaker-there there were push terminals that wires go into-often times the screw that holds the ring terminal that the tinsel wires hook to and holds the push terminal to it-can become lose. So there is an intermittant connection at that point.

I would go back and double check that the terminals are tight to the speakers. Check both while you are at it.

It could be that the simple action of pressing the terminal caused it to have a good connection again. If that is the case-it will only get worse.
 
Re: strange subwoofer thingie

Ivan Beaver said:
Don't be so sure.

One other failure I missed-and it is pretty common. Depending on the particular speaker-there there were push terminals that wires go into-often times the screw that holds the ring terminal that the tinsel wires hook to and holds the push terminal to it-can become lose. So there is an intermittant connection at that point.

I would go back and double check that the terminals are tight to the speakers. Check both while you are at it.

It could be that the simple action of pressing the terminal caused it to have a good connection again. If that is the case-it will only get worse.
Click to expand...

They are the push in type of terminal. I will most certainly check those tomorrow. Thanks Ivan! I do also (as a just in case) own a replacement woofer. I might just switch them out to be sure.
 
Re: strange subwoofer thingie

Ivan Beaver said:
When you have a shifted magnet-and the voice coil is not cut in half-the voice coils cannot "rub"-since it is pinned. There is no- "a little bit pinned" with a shifted magnet! Just try to move it------------------

The sonic character is no bass. You will still get some upper mids to highs-but it will not be as loud as usual.

The reason is that the voice coil on the opposite side of the "pin" is still free to move (but the pinned side cannot move). So it will vibrate a little bit-which causes the cone to vibrate-but it cannot move back and forth like it normally would. So it cannot reproduce bass.

You cannot apply enough signal to get the voice coil to start to move-other than vibrate on one side.
Click to expand...

We had a driver in a dj fill sub that still produced some bass, with much reduced output, but would make a loud pop when you ran it moderately hard. When we disassembled it, the magnet was cracked all the way around.
 
Re: strange subwoofer thingie

Tom Manchester said:
We had a driver in a dj fill sub that still produced some bass, with much reduced output, but would make a loud pop when you ran it moderately hard. When we disassembled it, the magnet was cracked all the way around.
Click to expand...
A cracked magnet and a shifted pole piece (often called a shifted magnet-even by me :( -which it could be) are different things.

The shifted pole piece means the center pole (back plate shifts-either from the magnet becoming lose or the back plate becoming lose) is pinned up against the top plate-trapping the voice coil (and cone) from moving.

A cracked magnet will no longer have the strength it used to have-therefore reducing the output level (less magnetic force to interact with the electromagnet of the voice coil.
 
Re: strange subwoofer thingie

Just had a EVX-150A in one of my Rat Traps go bad, it was cutting in and out with some nasty distortion. It was the tinsel wire fraying right where it's soldered to the terminal. The driver is well over 10 years old. With a sine wave sweep, it made and awful racket at 70Hz. Rather than try and repair it, I sent it out for re-cone as it's likely to just go bad again with hard solder down the lead that far. And the tinsel leads in the newer re-cone kits also used for the EVX-155 are more robust.
 
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