Need Advice/Help: IMF Midrange Refoam

[captouch]

Hi,

I'm in the process of refoaming the midrange of my IMF TLS 50 Mk II's and need some advice.

I've removed the old foams and the driver is shown below. The critical dimensions are:
Basket cavity diameter: 100mm
Width of basket lip (where I'll glue new surround): ~3mm
Cone diameter: 77mm
Previous foam inner diameter: 67mm

I have two foam choices I can go with (assuming at least one is suitable). The left one has a bigger lip (raised portion), slightly larger outer diameter (~97mm), but because of the bigger/wider lip, the inner dimensions are smaller (58-59mm foam inner diameter and 67mm inner diameter to when lip starts).

The right one has a smaller lip, slightly smaller outer diameter (96mm), but larger inner dimensions (62mm foam inner diameter and 72mm inner diameter to when lip starts), due to the smaller/narrower raised lip.

In both cases, I won't be gluing to the exact same part of the cone.

In the case of the left foam, I will be gluing over more of the sticky part of the cone and will likely not make contact with any of the previously glued area (since lip starts at 67mm and previous foam only started at 67mm). And the edge of the cone will not be glued to anything (since the lip will be there).

In the case of the right foam, I will be gluing mostly on the sticky part of the cone, but will have some overlap with the area that was previously glued. But still, the edge of the cone will likely still not be glued to anything because even the smaller lip would have started by this point.

Purely on the basis of the above, I'd tend to opt for the right foam, except for the fact that it's outer diameter is smaller (only measures 1mm less when foams are laying flat, but seems like more than 1mm difference when I rest the foams on the cones themselves). With the small basket lip (~3mm) and the fact that both foam outer diameters are already smaller than the basket cavity, I'm afraid I'm going to have problems making sufficient contact to glue the foam to the basket, which seems a bigger potential risk than not gluing over the same area as the original surround.

So my big question is:
1) Which foam would you go with, or is neither acceptable and I should hunt for another?

Secondary question is whether I need to clean the cone better than shown (do I need to get all the way down to the polyprop cone or is it OK if I glue over the residual old foam?)

Thanks a lot, hope my dilemma makes sense with the pictures.

 

[canuckaudiog]

How do they fit over top doing a mock fit? Try placing the foam ring on top of the driver and just see how it looks. If it looks off, then I wouldn't use it. Maybe do that and post a picture so we can see.

I would clean off the edge of that cone better. Get as much gunk off as you can, at least 90% of it. Just be careful as you remove it. I'd use a q-tip with rubbing alcohol to soften it up, then it should rub off fairly easy.

 

[captouch]

How do they fit over top doing a mock fit? Try placing the foam ring on top of the driver and just see how it looks. If it looks off, then I wouldn't use it. Maybe do that and post a picture so we can see.

I would clean off the edge of that cone better. Get as much gunk off as you can, at least 90% of it. Just be careful as you remove it. I'd use a q-tip with rubbing alcohol to soften it up, then it should rub off fairly easy.

Thanks for the response, Canucker. I can always count on your staying close to AK and having your IMF radar up. :yes:

OK, here's a mock fit. But I didn't add the foam ring, because it obscures the difference in overlap between foam and basket edge that I'm concerned about. If you'd like to see it with the foam ring, I can do that as well.

First, here's the small lip foam:

Now, here's the big lip foam:

Heavily leaning toward using the bigger lip foam because it provides more margin for gluing to the basket. Just wondering if there's any sonic impact to having the foam glued on to a different part of the driver cone. :scratch2:

If I do go with the big lip foam, I'm thinking cleaning the gunk off becomes less important since I'm not gluing to it anymore. But I will try the alcohol next anyway - if it's easy to do, cleaner is always better.

 

[canuckaudiog]

Second one looks great for fit.

The reason you want to clean the gunk off is to make for a better seal, and to have the foam glue to the cone itself and not the old foam material. It will also look much better.