More things to tell you about.
I removed the blutack I had around the junction of the mid bass' cone and dust cap. Reason being I decided I couldn't live with the bloody pale yellow of the cone. Decided to lightly spray the whole thing with black plastidip and then put some blacktack in there instead of the blutack - for aesthetic reasons only.
The blutack left a bit of an oily residue and a couple of little blobs on the cone. In my haste I doused a cotton wool bud with alcohol and got it off. Sprayed the cone and dust cap very lightly with black plastidip - just enough to cover the yellow of the kevlar. All looking good until later I went back for a look. Disaster, or so I thought at the time
The glue holding the dust cap on had loosened and it was clearly not adhered anymore .
There is a happy ending to this but at the time my whole system was going in the skip. really. A fair bit of cursing later and I managed to calm down enough to think that maybe all wasn't lost. I could just glue the dust caps back on .....but wait, this might be an opportunity for a bit of experimentation. So I pulled the dust caps off completely which wasn't hard and set them carefully aside for the eventuality that I had to put them back on.
So i could now see the small area of cone below the glue line that was still yellow, the coice coil former and the cavity in the centre of that. The cavity is vented near the bottom of the voice coil former. Anyway, I haven't taken pics but what I was looking at was a bit like this
The voice coil former sticks up a fair bit and the dust cap is glued on part way from the centre of the cone. I obviously didn't want crap being able to get into the voice coil gap but I thought I would have a listen with no dust cap on. It was pretty bad. Bass had diminished and there was a resonance from the open cavity even though it is vented to the rear.
Bass diminished probably due to the enclosure no longer being sealed and I had removed the added weight of the blutack which lowered Fs and increased Qts. the resonance from the exposed cavity was pretty nasty. That got me thinking about putting some open cell foam in there to see what happens. So I did. The resonance was gone but the bass was still a bit under nourished. So the cavity needs to be sealed off to stop any air leak.
That got me thinking. Well I need to add the blacktack at some point to damp the cone breakup and add weight (which brings the sensitivity down to match the 2" tweeter as well). The voice coil former sticks up a bit and there is a volume which could be filled with the blacktack and then a flat dust cap could be pushed in on top of that.
As I don't have any blacktack yet I put the blutack around and on top of the voice coil former. Next I cut a perfect circle of butyl rubber of the correct size to go over the top of all this and join up with cone. I carefully pushed down on the rubber circle with a length of solid brass bar of the same diameter to bed everything in, leave a flat surface and join the rubber and cone neatly all the way around.
Job done. Then I remembered I had left the foam in the cavity inside the voice coil former. Oh well, I can take it out if needs be. There is definitely a resonance from that cavity even when the back is vented in to the enclosure and it must make it's way through what ever dust cap is on. So I left it in. I realise the voice coil won't be able to dissipate heat as well from the area where I added the 10mm thick slice of foam but the cavity is still vented to the rear, my steel spheres are a good thermal conductor and I don't EVER thrash my speakers.
I really don't think power compression will be a problem at the levels I listen to or most hifi scenario's. There is obviously a resonance from the cavity and if the foam helps then it's a winner.
So now the cone is plastidipped, the dust cap is now flat and much thicker material and the blutack is completely hidden from view under the circle of butyl rubber. The cone and new dust cap are still damped by the blutack and the added weight is nearer the voice coil of the driver - it's actually touching it. I now have a much better looking driver but I hadn't listened to it yet
Making even small changes to a driver can have dramatic effects for good or bad.
I fired it up and wasn't disappointed. Not all breakup comes from the dustcap and inner parts of the cone so the very light coating of the cone with plastidip has imo been beneficial. Dust cap removal is very well documented on diyaudio. Some even replace with phase plugs but I'm not going there, seems to be too much of a shot in the dark. The voice coil cavity is a well known cause of resonance which is why venting or filling it with a solid phase plug is done (amongst other things). So I think my foam plug in the cavity and blutack around the outside of the bit of the voice coil former that sticks up will be staying even though there is a reduction in power handling. I reckon the trade off is worth it.
Subjectively I think there is a definite improvement in the FR of the driver. My enjoyment of the speaker is without a doubt increased. I have no before and after measurements to show so it is just my subjective opinion - of limited use I suppose but I only have myself to please after all.
I have nothing that stands out as a problem anymore. It's all good. Am I too fussy ? Probably but I need to get this right as these speakers are going to be with me for the rest of my little, unimportant life (hopefully) and have no measurements to help only my ears (and my family's ears). At least the drivers are much better to look at now as well
As you were. If you hadn't already lost the will to live then you surely will have now. One of my best friend's funeral today