PDA

View Full Version : Jbl 706g-1 (l1)



jfine
02-01-2017, 08:55 PM
L1, the 706G drivers, these sound OK, but when tapping the cone on one side, something is hitting the cone, also pushing cone in evenly, there's some rubbing. Thing is, they sound fine, and only if I play them a little hard, they rattle a little. Both speakers do this almost exactly.

When pushing the cone in, they seem to have a lot of travel, maybe 1/2 inch, unless these cones are supposed to travel/suspension like this :confused: usually when a speaker is damaged, it distorts, plays quieter, or wont play at all.

I have a set of 708G's (L7) and they barely move at all when you push in the cone.

Chris Brown
02-02-2017, 08:31 AM
L1, the 706G drivers, these sound OK, but when tapping the cone on one side, something is hitting the cone, also pushing cone in evenly, there's some rubbing. Thing is, they sound fine, and only if I play them a little hard, they rattle a little. Both speakers do this almost exactly.

Have you verified that the rubber surround is still fully intact? In some environments the rubber can dry out and begin to crack, usually at the inner border of the rubber surround and the cone. You might also take the woofer out of the cabinet, see if a wire is resting against the cone or if anything else is noticeable.


When pushing the cone in, they seem to have a lot of travel, maybe 1/2 inch, unless these cones are supposed to travel/suspension like this :confused: usually when a speaker is damaged, it distorts, plays quieter, or wont play at all.

I have a set of 708G's (L7) and they barely move at all when you push in the cone.

The 708G woofers in your L7 speakers are only used as mid-bass drivers. It's crossed over at 180hz, so it's not playing much below that. It shouldn't have much cone travel during usage in the L7, but the woofer itself has a pretty decent xmax. Here is a video I made of the 708G in my L5s, where it is responsible for everything below 170hz. The cone can move quite a bit: https://www.youtube.com/watch?v=1ZR12g1WJgw


(https://www.youtube.com/watch?v=1ZR12g1WJgw)

jfine
02-02-2017, 08:44 AM
Have you verified that the rubber surround is still fully intact? In some environments the rubber can dry out and begin to crack, usually at the inner border of the rubber surround and the cone. You might also take the woofer out of the cabinet, see if a wire is resting against the cone or if anything else is noticeable.

Hi, the drivers look perfect, surrounds are fine, had them out and they still exhibit the same issue, if you tap on the cone it's hitting something, but they play fine, really unless you drive them louder with hard bass you may hear a rattle, but that's it.


(https://www.youtube.com/watch?v=1ZR12g1WJgw)

The 708G woofers in your L7 speakers are only used as mid-bass drivers. It's crossed over at 180hz, so it's not playing much below that. It shouldn't have much cone travel during usage in the L7, but the driver itself has a pretty decent xmax. Here is a video I made of the 708G in my L5s, where it is responsible for everything below 170hz. The cone can move quite a bit: https://www.youtube.com/watch?v=1ZR12g1WJgw
(https://www.youtube.com/watch?v=1ZR12g1WJgw)

I think I misspoke, I'm not talking about how much the cone travels during play, rather how much it travels when you manually push the cone down with your hand. The 708G's in the L7's hardly move at all, whereas the 706G's out of the L1's move much more, maybe not a fair comparison, but it is sort of odd since the 708 is larger, same L series, I would think they would be constructed similar.

Anyways, it is an odd behavior in a speaker cone I've not come across before, especially when both of them (both L1's) are behaving the same way.

Chris Brown
02-02-2017, 08:55 AM
I think I misspoke, I'm not talking about how much the cone travels during play, rather how much it travels when you manually push the cone down with your hand. The 708G's in the L7's hardly move at all, whereas the 706G's out of the L1's move much more, maybe not a fair comparison, but it is sort of odd since the 708 is larger, same L series, I would think they would be constructed similar.

In terms of manual cone movement, I believe it is still related to the 708G being used as mid-bass in the L7. In the L7 I believe the 708G is in a sealed chamber (better for mid-bass), which dramatically restricts cone travel because you are working against the air pressure of the sealed chamber. The L1 is ported of course, so the cone can move freely in that situation. Similarly, in the L5, the 706G is used as mid-bass and has a sealed chamber. Similar to how you describe the 708G in the L7, the 706G in the L5 does not move much even when you press it in manually, due to the sealed chamber.

jfine
02-02-2017, 09:41 AM
In terms of manual cone movement, I believe it is still related to the 708G being used as mid-bass in the L7. In the L7 I believe the 708G is in a sealed chamber (better for mid-bass), which dramatically restricts cone travel because you are working against the air pressure of the sealed chamber. The L1 is ported of course, so the cone can move freely in that situation. Similarly, in the L5, the 706G is used as mid-bass and has a sealed chamber. Similar to how you describe the 708G in the L7, the 706G in the L5 does not move much even when you press it in manually, due to the sealed chamber.

Maybe. I'll have to pull the 708G out now to see.

But back to the problem, is it normal for the 706G to have such tight tolerances that moving the cone manually by hand, a little offset, would rub so easily? Also just tapping the cone causes something to hit.

Don C
02-02-2017, 10:32 AM
Its not good to be able to detect rubbing, but it is also possible that rubbing can be felt when pushing by hand, but that there is no rub when being driven. If you can feel it, but can't hear it, I'd leave it alone. Gravity can cause this, the moving parts settle downwards after several years. the suspension stretches. Often, the solution is to mount it with the other side up and let gravity work it the other way for the next ten years. But if the speaker was re-foamed recently, it's more likely that the job wasn't done perfectly. It can usually be re-foamed again.

Chris Brown
02-02-2017, 11:12 AM
I know you said you already had the woofers out of the cabinet and that they looked good, but did you check the spider by chance? Although I have not experienced it, there have been some reports of the spider separating on these woofers (706G, 708G, etc), and that could certainly explain the problems that you are having.

This is an extreme example:
http://www.audioheritage.org/vbulletin/attachment.php?attachmentid=72972&stc=1&d=1470487929

jfine
02-02-2017, 12:45 PM
I know you said you already had the woofers out of the cabinet and that they looked good, but did you check the spider by chance? Although I have not experienced it, there have been some reports of the spider separating on these woofers (706G, 708G, etc), and that could certainly explain the problems that you are having.

This is an extreme example:
http://www.audioheritage.org/vbulletin/attachment.php?attachmentid=72972&stc=1&d=1470487929

Good call, I did check that, seems OK, I can't see anywhere where it has become detached, all the way around.

I wonder if it's just the closer tolerance on this smaller driver, I suppose the right way to check is to press manually near the center, using the edges of the dust cap, equally. If I do that, it seems OK, just never had a driver where the voice coil was so close to the motor.

jfine
02-02-2017, 12:47 PM
Its not good to be able to detect rubbing, but it is also possible that rubbing can be felt when pushing by hand, but that there is no rub when being driven. If you can feel it, but can't hear it, I'd leave it alone. Gravity can cause this, the moving parts settle downwards after several years. the suspension stretches. Often, the solution is to mount it with the other side up and let gravity work it the other way for the next ten years. But if the speaker was re-foamed recently, it's more likely that the job wasn't done perfectly. It can usually be re-foamed again.

Funny you mention re-mounting, most all the pics I see of an L1, I can see that in comparison, both mine have been re-mounted 180 degrees, maybe the previous owner knew exactly what you described.