Hi all, I need to remove the dustcap from a subwoofer driver so I can mount a motional feedback sensor in the voice coil.
I found a rather drastic way here https://www.diyaudio.com/community/threads/how-to-remove-a-dustcap.397165/ .
But I really would like to salvage the dustcap to put back after the surgery.
Any idea how to best do that? Soften the glue with a heat blower, or will that damage things?
Jan
I found a rather drastic way here https://www.diyaudio.com/community/threads/how-to-remove-a-dustcap.397165/ .
But I really would like to salvage the dustcap to put back after the surgery.
Any idea how to best do that? Soften the glue with a heat blower, or will that damage things?
Jan
What about this thread? https://www.diyaudio.com/community/threads/least-destructive-dust-cap-removal-replacement.404731/
' The most common loudspeaker glue is black and made by C P Moyen. It is easily remove by applying lacquer thinner or MEK. Apply it with a small brush directly to the dust cap edge at the glue line. Use lots of ventilation. There are some white glues used and they dissolve in water with a small amount of chlorine bleach. Some folks do use a two part adhesive that cures and cannot be partially dissolved and easily removed. Fortunately this is the least common adhesive and is typically used on the spider and rim where the stress is the highest.'
' The most common loudspeaker glue is black and made by C P Moyen. It is easily remove by applying lacquer thinner or MEK. Apply it with a small brush directly to the dust cap edge at the glue line. Use lots of ventilation. There are some white glues used and they dissolve in water with a small amount of chlorine bleach. Some folks do use a two part adhesive that cures and cannot be partially dissolved and easily removed. Fortunately this is the least common adhesive and is typically used on the spider and rim where the stress is the highest.'
If you could find a suitable solvent that softened the glue, without dissolving the dye or wrecking the cone that may do it. I think I've seen somebody doing something similar here, applying the solvent with a fine tip brush, but don't have a link I'm afraid. It's hard to know which solvent to go for though. Will require some trial and error. If it were me, I'd start gentle with some kind of hydrocarbon first and work up from there. Depends on your cone material etc though.
Just seen the other replies. If the glue is epoxy then solvent will obviously not work. If it's a different glue then may be OK.
Once the glue is softened, you can cautiously fit the open circular tube end of a vacuum cleaner onto the dome's apex. The vacuum will tightly fix the dustcap to the tube, so that you can pull it away from the cone by simultaneously applying more or less the same force on it's periphery. This may avoid any asymmetrical stress or, worst-case, even deformations.
Same trick with an adapted shape of the duct's opening neatly applies to popped-in-by-kids-fingers tweeter domes. In many cases, you can perform a full functional and even aestetically perfect vacuum reposition of the dome with this procedure. This is where soft domes really shine, and this could be a point to pragmatically consider within the domes materials discussion: Kids < 10 years -->> Soft domes only.
Same trick with an adapted shape of the duct's opening neatly applies to popped-in-by-kids-fingers tweeter domes. In many cases, you can perform a full functional and even aestetically perfect vacuum reposition of the dome with this procedure. This is where soft domes really shine, and this could be a point to pragmatically consider within the domes materials discussion: Kids < 10 years -->> Soft domes only.
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if its a paper dustcap take a sharp cutter and cut a hole into the dustcap without touching the edge.
Do the operation and glue the fitting part of the dustcap back in.
Repaint the dustcap if the look is ugly or put a layer of aluminium foil on it stabilizing the dustcap again
In this video below, he is using a lipless dustcap and "re-using" the old lip which is trimmed very close to cone.
P.S ok if you need to reuse old one, then probably have to use glue removers. It works on most glues including rubber surrounds but I have not tried it on dust cap glue.
P.S ok if you need to reuse old one, then probably have to use glue removers. It works on most glues including rubber surrounds but I have not tried it on dust cap glue.
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With cones not made from plastic, a hot air gun always worked for me, combined with a variable speed vacuum cleaner. You can adjust the power electronically and, on most better ones, have a mechanical slider to bleed in air. You don't want the dustcap to be inhaled the second it comes loose...
If there is a center hole in the magnet assembly, you can even push the dustcap out from the inside when the glue get's soft.
If hot air is no option, use acetone or one of the other mentioned solvents. Some of them that work great are really not good for your health.
I have done such quite often to repair dustcaps. Once removed from the cone, you can get them back to shape and stabilize the paper type by applying clear varnish, then glue them back on after drying.
Are you using a Pirate Logic kit?
If there is a center hole in the magnet assembly, you can even push the dustcap out from the inside when the glue get's soft.
If hot air is no option, use acetone or one of the other mentioned solvents. Some of them that work great are really not good for your health.
I have done such quite often to repair dustcaps. Once removed from the cone, you can get them back to shape and stabilize the paper type by applying clear varnish, then glue them back on after drying.
Are you using a Pirate Logic kit?
With a really sharp skalpell you can cut through the glue below the dustcap not damaging the dustcap nor the driver.
I would be careful of solvents trying to soften dissolve the glue .... you might soften the cone also, especially if it is paper which most are.
I'm not an expert and have only done the procedure on a Cerwin Vega 12", I cut it away much as shown by fredom666 and glued in a new one after
You can buy a new similar dust cap of the net at different stores.
Pleas show pictures of your process and let's hear you learnings.
Also want plan to experiment with mfb ..... when I get time ...
I'm not an expert and have only done the procedure on a Cerwin Vega 12", I cut it away much as shown by fredom666 and glued in a new one after
You can buy a new similar dust cap of the net at different stores.
Pleas show pictures of your process and let's hear you learnings.
Also want plan to experiment with mfb ..... when I get time ...
Yes that's the plan.
BTW I found out that there are numurous places that offer replacement dust caps for a couple of bucks. Maybe I should not worry about reuse, just cut it out and get a replacement one.
Edit @Baldin made a similar point I now see.
Jan
Slightly OT, Jan, are you going to use the piratelogic kit with their electronics or roll your own?
I read somewhere that the Murata accelerometers they use are very noisy. Bummer, I bought a roll before I knew that.
Their whole electronics appear to be very close to the original Philips MFB design. The manual for their EVE board seems to imply that they treat the acceloremeter signal just like the worst and most common way to get a signal from an electret microphone: with a FET in common source configuration. I don't really see that the cascode input and current mirror are really the best way to get the signal from the FET on the sensor board into the EVE circuit. The TL074 is also hardly state of the art. And all in all, I'd like to see the MFB used with current drive in the best of all worlds. Wonder what your thoughts are.
Eric (?) Yes that was the plan. I believe they use several of those sensors in parallel to reduce the noise. One alternative is de audiochiemgau set but that is integrated with a 75w chip amp but I will use 250w nCore class D. Open to suggestions!
Jan
Jan
Iirc the audiochiemgau uses current drive.
They also use the acceleration signal to cancel doppler distortion in DSP - as far as I know this is unique!
Jan
They also use the acceleration signal to cancel doppler distortion in DSP - as far as I know this is unique!
Jan
If your woofer is one if those alu coned Dayton subs, then simply forget it.
But Chris C. sells sensors that can be mounted at the back (cone-vc-neck) of the sub, avoiding dustcap surgery.
But Chris C. sells sensors that can be mounted at the back (cone-vc-neck) of the sub, avoiding dustcap surgery.
Yes I am talking to Chris, these are the Pirate logic units.
My drivers are alu coned SEAS drivers that Linkwitz recommended.
Jan
My drivers are alu coned SEAS drivers that Linkwitz recommended.
Jan
I forgot to mention, that the most simple way to repair a dustcap is to get a new one, a little larger and glue it in so you do not see the vandalized part of the cone. If you fit the Pirate Logic sensor, a larger dustcap would be needed anyway for covering wires to the electronics. Don't forget to ground the basket, or you may get a lot of noise.
Hey Jan, thanks, I am beginning to discover their pages. One learning for me already: while current drive reduces H2 by 20 and H3 by 25 dB in an undemodulated driver from about 2.5x fB, at and around resonance, both are actually massively higher than with voltage drive (+26 dB H2). Part of this is owed to the +15 dB higher excursion at fB with current drive because Qes becomes infinite.
However, the second picture shows current drive insertion of a zero in the preamp which pulls FR flat down to 50 Hz. Excursion at fB is reduced by 12 dB at fB, i.e. now only 3 dB higher than with voltage drive. However, H2 is reduced by only 8 dB, i.e. still about 18 dB higher than with voltage drive.
I am guessing this is due to mechanical nonlinearities from spider, surround, air spring which are normally attenuated by Qes (some vindication for damping factor freaks here). So current drive is best combined with MFB. Absent MFB, a passive compensation (RLC in parallel to the VC) is probably the best option, or mixed voltage / current drive depending on frequency.
https://audiochiemgau.com/nichtlinearitaeten-wirkung-loesungen
Oh, about those Seas drivers, if they are the ones recommended for the LX521.4, I had them and returned them due to excessive air noise and clicking when driven open air near resonance - exactly what you don't want in an open baffle driver. Peerless XLS and XXLS are much quieter in the same application. If you are using some kind of box, it probably does not matter. It is also possible mine were from a poorly made batch. I know someone who uses them in a damped long U-frame and has no such issues (different year of manufacture, though).