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Romy

I had a SG370 mid apart only yesterday.I should have taken a photograph.I have also seen the inside of the tweeter.They are very similar,so I have no reason to suppose the low mid SG 505 will be much different.

I'll try to explain.I think they are in basic structure close to the WW 555. Taking your default JBL 375 for comparison:

The Gotos are of course "Burpers" as opposed to "Farters" like JBL.i.e they use the front (convex) output of the dome for radiation.They come apart as the magnet on one and the dome + phase plug on the other side .They have a very similar appearance to a standard metal dome tweeter.The phase plug appears to be a simple "bullet".

A few observations.The dome on the mid is about 4cm diameter and very beautifully made.It is obviously very thin and delicate compared to the JBL.It has no metal surround but is bonded to a FEP film that is glued to the flat surface surrounding the phase plug.This film is surprisingly big and really very thin and covers a big area.According to Goto this is one of the secrets as conventional compression drivers resonate in the surround(cf the different resonance patterns -frequency response in the otherwise identical JBL 2440 and 2441).

The rear of the dome sees no damping. The only rear chamber would be the minute area formed between the rear of the dome and the front of the magnet assembly.There seems to be a tiny pin prick hole in the magnet assembly,but I have no idea if that acts as a  kind of vent.-I doubt it.

All in all it appears exceptionally simple ,but exquisitely engineered.I have no idea how that membrane can be accurately glued-certainly not a field job!.There are no guiding pins,but 2 dimples in the front magnet face where the terminal screws go. I suspect that these may act as alignment guides as the front screws are tightened to match up.I opened mine because I thought it was scraping.The scrape seems to have originated from the front screws working slightly loose durng shipping-gentle tigtening immediatel solved this.

I was very disappointed in your tweeter battles that you never tried a Goto tweeter.Like you I really loved the Celestion SL6/600 tweeter's tone,but ultimately found them a bit slow.The Gotos I feel has that tone,but also speed and of course efficiency.All in all I think the best highs for me- I come from a tradition of "British "sound so you may not relate,but I think you will.

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