damn you. damn you to... New Jersey.
mnem
You’re welcome. -Pat
On the Bench Tonight: INFINITY RS-3000 Driver Refurbhttp://www.hifi-classic.net/review/infinity-rs3000-221.html So all y'alls may remember that I got this far aboot a month ago; well, the surround kit from
Springfield Speaker has been here for a while, so today they finally came back on the bench.
Getting the last little bits of old foam took a little more than IPA; the corner of a towel soaked in
Goo Gone worked, and was then followed by another corner soaked with IPA to get that residue cleaned up.
Here I've propped up the cone with some felt rings and foam tube from my plastic junk drawer; I've applied the cement to the underside of the roll foam and gave it ~30 seconds to tack up.
When I apply the roll foam to the cone, I'll work from the bottom inside the gap as well as the top. This allows me to make certain the roll foam is centered exactly on the edge of the cone. Then I'll go all the way around the cone pinching the roll edge tight between thumb and forefinger of both hands.
I don't usually distort the cone this much when I'm working; it's easy to permanently crease or rip a paper cone doing this. But to show the the work and with the flexible polypropylene cone, for this pic I felt it was okay.
Here I'm getting ready to do the final assembly of the roll foam; the advertised bass resonance of this speaker is 55 Hz, so I'm going to set my old Protek Function Gen to do a sweep from ~30-80 Hz to make sure it passes through the free air resonance frequency of the driver while I'm centering the cone. I've set amplitude so I can clearly hear it when it gets up around the higher end of the sweep; this is applying ~1-2V P-p under load.
Before I actually glue things down, I'll do a reality check on the driver to make sure I actually
can get the cone to center properly using the dynamic method. I do this by holding the roll foam like so to find center where the speaker has normal excursion without the VC rattling.
If I can't find the "sweet spot", or if I do find it and horizontal inspection shows the cone is cocked off at a angle, then I know the voice coil has suffered damage from over-excursion and will need to be repaired.
This requires cutting out and replacing the domed dust cap, which is something I try to avoid doing, as on modern speakers it can really affect the vocal range sound of the speaker.
Here I'm applying cement to the basket of the driver; I'll let it tack up for about 30 seconds before removing my felt and foam blocks and sticking the roll foam down in 4 spots based on how the sound reacts.
This is a very time-critical step; as soon as I have those 4 spots down, I will turn off the sweep gen and deliberately press on the cone unevenly in those same 4 quadrants to see if I can make it deflect and rub the voice coil. If I can, I'll lift the roll foam with curved tweezers and move it towards the side where rubbing does not occur; just a mm or two.
Once I get the foam situated so I cannot make the VC rub by pressing unevenly on the cone, or I if get it so it rubs with about the same deflection in all 4 quadrants, I'll turn the sweep generator back on while I finish stitching the glue down all the way around the basket.
And here the speaker is after the glue is stitched down all the way around. I've turned the amplitude up so I can hear the full 30-80 hz sweep clearly; this has the sweep generator producing ~15V p-p unladen across the entire sweep, with laden signal ~2.5V p-p to a max of ~6.7V p-p at its free-air resonance of ~39 Hz.
Here I've finished gluing down the gasket shims; next up will be the relatively boring part of doing cabinet rehab. I'm knackered, so we'll visit that tomorrow after all the cement has time to cure overnight.
mnem