Focal Tweeter mods

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Tweaks for systems, rooms and Do It Yourself (DIY) help. FAQ.

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Interesting comment by Thorsten about Focal tweeters, a couple of lines down from this postâ€¦
I havenâ€™t always been happy with Focal tweets, but they have an undeniable â€œyou are thereâ€ quality missing from other tweeters in my experience. Anyway, I've got mine sounding pretty nice now. If you like them, you will like them more after this treatment...
I assume you will start with a titanium dome - no steenkin' kevlar or fibreglass here!
Disassemble tweeter completely. Cover magnet gap with masking tape. Drill a nice big diameter hole thru the pole piece - all the way! (I forget what drill I used, maybe about 10mm). Now use a rat-tail file to taper the hole like a funnel - smoothing the transition from the rear-of-dome cavity into the hole. Glue a piece of tube with the same I.D. as the hole onto the back-plate (you are creating a transmission-line). This tube should be 1/4 wavelength long at the resonant frequency, which is about 90mm, when you take into account the length of the drilled hole. Stuff the tube lightly with wool. Some thin open-cell foam works nicely behind the inverted dome (glue it to whatâ€™s left of the pole-piece). Clean off all the chips and filings (tedious) and carefully re-assemble, taking a great deal of care about centring the voice coil in the gap. Ensure the rear of the dome has good clearance from damping materials.
Make a felt pad shaped like a mushroom-head and about 10mm in diameter (it will be about 4mm thick at itâ€™s thickest point, if it looks like mine). What Iâ€™m describing here is a small felt dome, which is going to sit in the concave dome of the tweeter, facing convex-side into the concave dome. Get it?
Glue this pad onto the existing â€œphase-plugâ€ (the pointy plastic thingy pointing into the centre of the dome on later model Focal tweeters) so that it sits well down into the dome-cavity. You should now have what is effectively a transmission-line-loaded ring-radiator. The felt pad absorbs both spurious noise from the â€œoilcanâ€ break-up of the centre of the dome and also the cavity resonance sound from that acoustic space.
This driver MUST be used in a separate enclosure or free-air, since it is no longer sealed at the rear. It will be less efficient due to these modifications, but still plenty efficient enough for 90dB + speakers. It sounds dynamic, open and very articulate, but much sweeter than the standard Focal. It remains my first choice in conventional tweeters - soft domes just donâ€™t do the job (they just add some tizz to the top of the range, inoffensive, but not real music). Garnish with Hovland Musicaps (serving suggestion only).
Iâ€™d love to try the same mods on an Accuton ceramic concave dome, but theyâ€™re already inefficient, and theyâ€™re too expensive for this little tweaker to mess about with!
No responsibility accepted, thereâ€™s waaay too many opportunities to totally destroy your tweeters messing around in there! If you need more â€œhow-toâ€ advice, then you probably shouldnâ€™t tackle the job.
Andrew.

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Topic - Focal Tweeter mods - AndrewG 23:17:10 06/21/00 (2)

Re: Focal Tweeter mods - Russellc 11:29:25 06/26/00 (0)

Re: Focal Tweeter mods - Philipp 13:13:47 06/23/00 (0)

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