JBL K140 Speaker Rattle

[Kevin Sheppard]

I bought a reconed K140 and it sounds great and shows the correct resistance with a multimeter however I notice when I increase to a louder volume, the speaker creates a strange rattling noise.

I know it is not the cab, as the speaker made this sound detached from the cab. The interesting is the rattling goes away when I block the vent at the back of the speaker.

Any advice would be much appreciated!

 

[LurkingDrue]

I once had a speaker where the spider (the flexible surround that keeps the coil centered) came loose from the basket. It made a loud low frequency rattle, especially at certain frequencies. By low-freq, I mean like 15ish Hz and it was obvious that something was hitting something else.

 

[agedhorse]

Almost certainly you are driving the speaker beyond it's safe power handling, which is roughly 150 watts RMS, but as the frequency falls the power handling also falls. If the cabinet tuning isn't within an acceptable range the low frequency power handling can fall very quickly.

When you block the vent, the driver sees the acoustic load of a sealed cabinet which can increase mechanical power handling while at the same time decreasing low frequency extension.

My guess is that the ported cabinet's tuning is not good for the driver, combined with too much low frequency power.

 

[Mike Caldwell]

Those speakers had a piece of foam under the name badge on the on the back as a filter for the vent slots.....maybe pieces of the foam are loose inside. if the foam has dried up pieces of it can get into the voice coil.
Blocking the vent would slightly limit the motion of the cone and let heat build up if you drive it hard for very long.
Look and see if the lead wires or too long and are hitting the cone or maybe too short. Check that the spider, dust cap and surround all are glued secure.
Or your just over driving speaker and bottoming out the voice coil.

Keep in mind the recone kit is almost certainly an aftermarket kit!!!

 

[agedhorse]

Those speakers had a piece of foam under the name badge on the on the back as a filter for the vent slots.....maybe pieces of the foam are loose inside. if the foam has dried up pieces of it can get into the voice coil.
Blocking the vent would slightly limit the motion of the cone and let heat build up if you drive it hard for very long.
Look and see if the lead wires or too long and are hitting the cone or maybe too short. Check that the spider, dust cap and surround all are glued secure.
Or your just over driving speaker and bottoming out the voice coil.

Keep in mind the recone kit is almost certainly an aftermarket kit!!!

I was thinking the OP was using it in a rear PORTED speaker... hmmm

 

[Mike Caldwell]

I was thinking the OP was using it in a rear PORTED speaker... hmmm

With this "the speaker made this sound detached from the cab" it made me think he was testing it removed from the cabinet???

 

[Kevin Sheppard]

With this "the speaker made this sound detached from the cab" it made me think he was testing it removed from the cabinet???

That is correct. This is a TL606 style cab. I just removed the speaker at sat it on the floor facing up.

 

[agedhorse]

Free air mechanical power handling at low frequencies is less than 50 watts rms, perhaps as low as 25 watts rms.

 

[Tim Skaggs]

Those speakers had a piece of foam under the name badge on the on the back as a filter for the vent slots.....maybe pieces of the foam are loose inside. if the foam has dried up pieces of it can get into the voice coil.
Blocking the vent would slightly limit the motion of the cone and let heat build up if you drive it hard for very long.
Look and see if the lead wires or too long and are hitting the cone or maybe too short. Check that the spider, dust cap and surround all are glued secure.
Or your just over driving speaker and bottoming out the voice coil.

Keep in mind the recone kit is almost certainly an aftermarket kit!!!

I had exactly this occurrence with a JBL K140 speaker. A friend of mine was moving and asked to leave some of his music gear at my shop. One item was a K140 in an old Peavey 115 cabinet. After the gear had been at my place for over a year, he gave it to me.

I put the K140 in an EV TL606 type cabinet. When I originally tried the speaker in the cabinet I noticed a slight rattle I thought was the cabinet.

I began trying to determine the res freq of the cab. I laid the cabinet on its back, supported between to chairs, to sprinkle some rice on the cone and used a tone oscillator to find the cab tuning. I noticed the rattle was gone when the cab was on its back.

After I got the cab res. freq. figured out, I stood the cabinet back up and the rattle returned. The rattle sounded like it was directly behind the aluminum dust cover. I laid the cab on its back again and the rattle was gone again. I pulled the back off the cab and looked in the vent hole in the magnet. It appeared I was seeing the back side of the dust cover. With the back off the cab, I laid it on its back again with the cab between a couple chairs. I used the tone generator to pass some low end through the speaker; no rattle. With the cab still on its back supported by two chairs, I looked in the vent again and could see “something”. I pulled the screen out of the vent hole and a semi-round chunk of foam rubber the dia. of the vent hole fell out. It was hard as rock, harder than a chunk of Scotchbright pad, not compressible by fingers. I stood the cabinet back up, and the rattle was gone & stayed gone. I put the screen back in the vent hole and the back on the cabinet. It’s one of my speakers for my shop stereo and has been about 10 years.

 

[Kevin Sheppard]

I had exactly this occurrence with a JBL K140 speaker. A friend of mine was moving and asked to leave some of his music gear at my shop. One item was a K140 in an old Peavey 115 cabinet. After the gear had been at my place for over a year, he gave it to me.

I put the K140 in an EV TL606 type cabinet. When I originally tried the speaker in the cabinet I noticed a slight rattle I thought was the cabinet.

I began trying to determine the res freq of the cab. I laid the cabinet on its back, supported between to chairs, to sprinkle some rice on the cone and used a tone oscillator to find the cab tuning. I noticed the rattle was gone when the cab was on its back.

After I got the cab res. freq. figured out, I stood the cabinet back up and the rattle returned. The rattle sounded like it was directly behind the aluminum dust cover. I laid the cab on its back again and the rattle was gone again. I pulled the back off the cab and looked in the vent hole in the magnet. It appeared I was seeing the back side of the dust cover. With the back off the cab, I laid it on its back again with the cab between a couple chairs. I used the tone generator to pass some low end through the speaker; no rattle. With the cab still on its back supported by two chairs, I looked in the vent again and could see “something”. I pulled the screen out of the vent hole and a semi-round chunk of foam rubber the dia. of the vent hole fell out. It was hard as rock, harder than a chunk of Scotchbright pad, not compressible by fingers. I stood the cabinet back up, and the rattle was gone & stayed gone. I put the screen back in the vent hole and the back on the cabinet. It’s one of my speakers for my shop stereo and has been about 10 years.

That’s great to hear I’m not the only one . I probably am going to need to recone mine to get rid of it.