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Some time ago I could hear buzzing sound coming out from one woofer when certain bass notes were played. It'd buzz together with each note.Recently, the buzzing sound has disappeared mysteriously.
Then, I manage to get hold of a track from a Chesky test disc that has someone announcing the frequency as it sweeps downwards. I realise that from 190 Hz onwards, there'd be some kind of noise (something like an aeroplane flying past). It's totally different from the clean, straight tone which I can hear clearly on the other speaker that is working fine.
Now, if I press against the dust-cap as the frequency tone is played, the noise will go away and I'd hear the clean tone.
Is it time to change the driver? It's so difficult to get the 17W75XL, and nobody seems to have the 4-ohm version.
If I were to get the non-XL version (ie. 17W75) BUT 8-ohm, would there be a big difference in the sound? I can get someone to help me to modify the crossover to handle the 8-ohm driver, but I really wonder if sound would be for the worse.
As not to break any posting rules, e-mail me for info regarding a replacement driver.
Much research from '86 through '96 was done by me on the series of Dynaudio 17W75 type woofers, the XL's included.The gule that attaches the cone (dish shaped) to the voice coil has a gap in it and what you are hearing is the voice coil vibrating against the cone. This is a difficult repair. It means getting glue (silicone works) in the affected area via hypo needle. Where the cone ridges are (voice coil attachment..you need to insert silicone (clear my preference) metered to 0.1mL into (16) areas from the front of the cone. Very small holes. It will re-adhere the cone to the voice coil. For balance, you need to do the other good woofer as well. Yor f3 will drop a few HZ (due to the extra 0.9 grams of mass) but this is the fix. If you care to replace, you need to relace both of them. The red sticker on the magnet..is it an L series..as in L41 or something like that? What series? L's and M's had this problem.
Also, if the VC looks crimpled (looking at the aluminium former from outside) damaged from slapping the top plate and back plate..then forget the glue. The glue does harden and become brittle and flake leaving gaps between the VC/Cone. Silicone will not. I suspect this is the problem that the glue will repair. Allow 36 hours to fully cure.
When appliying the glue, use a 1.5 to 3 volt source in correct polarity to force the cone foward via VC..this will assure a firm bond. You will need to change the batteries as the large 3" voice coil will draw about 1.28Amps /3V D'Cell in series of 3 volts. It would be advantagous to use a varible power supply to displace cone with DC..just keep it under 3V, as to not heat the coil too much.
I have done extensive research with the XL. This will work if the VC is not crimped. I use to actually have several prebuilt parts for them during driver modification for a possible production..until dynaudio got "new and improved" and killed the DIY market. Now I use Scan-Speak. I find them even nicer in many ways.
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Actually, I'm still not sure on where the glue should be applied to. Could you please elaborate more? After looking at the driver carefully, I have basically figured out what the VC is (brownish-gold colored coils) which is attached to a cylindrical metallic (bluish color) shell, which is directly attached to a concave dish-like thingie (the dust cap?)I hope I got it right!
ok.. the red label says "B1 45".. or was it "B1 51" ?? damn..forgot to write it down!
Thank you so much! That was extremely useful! I'd have to get the woofer out to check if it's the L series.
Silicone glue is typically too thick to dispense from a syringe. But, supposedly you can thin the stuff. I read about thinning in an older issue of SPEAKER BUILDER magazine. But I'm not sure which solvent works best. I've used Lacquer thinner alright, and then poured the thinned mixture into a disposable monoject.
I personally don't think that silicone glue is strong enough in this application. Better make it epoxy!
Silicone RTV (GE Clear) works fine Æ, never had a problem with the syringe. Warning: Have you ever mixed 2 part epoxy (hobbypoxy) and added it to a 17W75 cone while curing? Thought not. It chemically reacts negatively to the cone..warping it. The epoxy dynaudio uses in their voice coils is fully cured and baked before applying the voice coil to the cone (using LX6B). Epoxy (if it did not melt the cone) will harden to brittle and flake off in the voice coil gap! Silicone RTV is used to glue huge aquariums together. It is much stronger than any force the 17W75 could muster. It stays just plyable enough..will never become brittle. Sticks some RTV to aluminium. It is VERY strong.Tell you what, how many 17W75 cones have you applyed epoxy to? I did one, it ruined it. Reminds me of the sugesstion to use "roofing bull" as a dampning agent inside a loudspeaker enclosure. Watch the cones melt from the chemical reaction.
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Actually I've hardly ever used anything by DYNAUDIO, but have plenty experience fixing all sorts of drivers. There are a wide range and variety of epoxies to use. The trick is using the right one. Of course your experience suggests caution, don't want to melt a cone. The epoxies I use don't "flake" or "brittle". The brittle part probably occurs when exposed to long term UV. I never subject any of my woofers to long term UV exposure from direct sunlight!
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