I also have the SongTowers in my case with the Hiquphon silver dome tweeter (OW4). The OW4 is an extra cost option in place of the standard OW2 but I would not expect this change to have much impact on the sound.
Here's what Oskar says:
OW3 and OW4:
Let me state this first: OW3 or OW4 are NOT just colored versions of the OWII!
This could easily be assumed, having studied the frequency curves. But no, they are not!
The basic construction of the OW3 and OW4 is the same as that of the OWII. So far so good.
Different cone (diaphragm) and other materials inside, but a very different combination of coating substances on the dome!
A different amount of coating too! A bit heavier and in fact more like the coating used with the OWI.
As you may have guessed by now, coating is absolutely essential for the quality of a soft dome tweeter.
In my opinion coating is THE far most important part of a soft dome tweeter (when properly done, that is
.
OW3 and OW4 are coated six times each! Standard OWI and OWII 2 times each.
Each coating is accomplished using unique special selected coating substances added to achieve the important damping in the dome surface and of course to achieve the special colors as well.
The sound picture of the OW3 and OW4 does lean towards a more soft and low distorted output in the lower frequencies than does the OWII.
The right coating and damping is in fact the secret behind the high quality we offer!
It takes most of a life time of experience to understand coating and damping in details.
Consistency really is a major problem, as all involved materials are soft and difficult to "measure" from batch to batch. Temperature, humidity and raw materials differ all the time.
To control production of soft domes at the highest quality level does not come easy.