Speaker Dimple

One of my soft dome tweeters has a dimple in it, doesn't really effect the sound as fas as I can tell, but still I wonder if there is a safe way to pop the dimple out?
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The purpose of the dome is dispersion.

It is very possible that your defect is inaudible.
I just used the vacuum method on a pair of Totem Mites I picked up in a thrift store for $35.00. I put two fingers in front of the hose to prevent a perfect seal should the nozzle come in contact with the dimple. Worked perfectly and after running them in for a while any sign of a crease was gone.
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Not true in my system. Imaging is spot-on.

It would indeed be more subtle than that.The dimple is a weak point that will succumb to flexure. The other issue will be dispersion. Think of how a phase plug or a waveguide changes the off axis response of a driver - same thing with a tweeter.

It is easy to show there will be a difference. For example, if your dimple is 1 cm deep right in the center of the tweeter then you will have quarter wavelength cancellation and a dip in the on axis response centered around 8500 Hz. This is probably not as bad as increased breakup or flexure though - as it may simply resonate/flex rather than behave as a piston and lose high frequency output/efficiency.

Remember that ring radiators do behave differently - so a dimpled tweeter will too.

Once you fix a soft dome then provided there is no permanent damage or crease then it should be as good as new (not unfortunately the case for a metal dome which will be toast)