soft dome versus hard dome tweeters

@asctim DIYaudio is the best place to discuss mods to drivers, but I suggest you want a phase plug instead.  :)

Both metal and soft dome tweeters have improved over the years. But loudspeaker design, possibly more than any other aspect of hi fi, is about system performance. As an example, the Focal inverted dome titanium tweeter sounds radically different in Focal and Wilson speakers (of the relevant era), respectively.

I had speakers with metal drivers for years, seemingly more info than previous soft domes although varied in ringing, glare or sibilant extension.

Even some soft domes were overbearing.

Then I went with Dali Menuet SEs which comparatively subdued but also took out alot of the nuances in music I listened too and I found them way too refined.

Dali Opticon 1s were much better only giving up some resolution and note weight but still decently controlled glare and sibilance, comparatively speaking.

Now have Audel Magika II using a Sartori SB Acoustics tweeter and while it is very revealing, it lacks the glare and controls sibilance better, so it replaced my metal options.  I still have one set of speakers with metal domes, a budget speaker whose attributes are so good overall, I don;t want to sell.  Very melodic on some material, euphonic in spite of the sometimes glare.  Less resolution but plays well with ANY amp, source or genre.  Not neutral, V shaped and good for low level listening.  The titanium tweeter and treated paper woofer work well together.

My other speakers measure better, perform better in the audiophile sense but there it is. 

Also had Martin Logan 15i which were really good with soundtracks re resolution and voice naturalness but didn't like it for music.  I thought it had more to do with the Aluminum woofer than the AMT.  Also, it didn't give nuances like spatial effects like the Dali when I compared but I preferred the 15i with voice in soundtracks.  All else the Dali I thought were better.

If I were to upgrade from here, at higher prices I think I would target something with a good soft dome considering paper variant woofers, even though I am happy with polypropylene as well and avoiding metal infused woofers.  

My last few speakers , Heresy III , Forte IV , Revel M106 , PSB M2, and a few others had metal domes. They all sounded pretty good.

I had a pair of Sonus Faber Concerto that had a silk dome, Igave them to my brother. I replaced them with a single driver "full range" speaker and I missed the sparkle of a conventional 2 or 3 way..

I recently bought a pair of Studio Electric M4, an acoustic suspension compact monitor. They use a 6.5" High excursion mid/woofer and a 1" silk dome tweeter. They sound phenomenal. In terms of sound quality I think they may the best sounding speaker I have ever owned. I can listen for long periods without fatigue, i credit the tweeter for that. . Awesome speaker.

Those who denigrate hard domes and lump them all into the same category haven’t heard any quality ones. A good quality beryllium, diamond or carbon tweeter will outperform nearly any soft dome and sound less fatiguing in the process. Even the $300+ soft domes from Seas and Scanspeak do not sound as extended and realistic as a good beryllium to my ears. And most manufacturers are not employing soft domes near the caliber of a $350 Seas Excel. 

Even the $60 anodized aluminum tweeter from SB Acoustics outperforms a lot of pricier soft domes.