Anyone a speaker refoam/rebuild expert? I am curious about voice coil centering technique's during the refoam process?
I recently had my dynaudio woofers refoamed and I spent a great deal of time searching the web for experts. with a conventional woofer, most shops cut the dust cap off and place shims around the voice coil to align it while gluing the foam in place. With Dynaudio woofers you can't do that as the cone/cap is all one piece. one shop told my they just cut the dome out and glue in a felt cap! ugh!
So after much searching It was suggested to me that a certain company had a proprietary method of "electrically" centering the voice coil. this interested me. But by the time i got around to being able to ship the woofers, the shop no longer wanted to do Dynaudio woofers! I ended up using a local shop and well...they work, and i guess that's what counts but i wasn't exactly impressed with there work.
After more web searching and watching many youtube videos on refoaming, it seems that this "proprietary" electrically centering process is probably nothing more than applying a low frequency signal to the woofer while manually manipulating the woofer foam into place so the voice coil doesn't rub. not exactly rocket science. but not exactly perfect either.
SO, I am curious if anyone knows of any special techniques new or old that this company that shall remain nameless, might have been using??
I'm curious how Dynaudio actually does it?? I would love to see how that's done!
Zc
I recently had my dynaudio woofers refoamed and I spent a great deal of time searching the web for experts. with a conventional woofer, most shops cut the dust cap off and place shims around the voice coil to align it while gluing the foam in place. With Dynaudio woofers you can't do that as the cone/cap is all one piece. one shop told my they just cut the dome out and glue in a felt cap! ugh!
So after much searching It was suggested to me that a certain company had a proprietary method of "electrically" centering the voice coil. this interested me. But by the time i got around to being able to ship the woofers, the shop no longer wanted to do Dynaudio woofers! I ended up using a local shop and well...they work, and i guess that's what counts but i wasn't exactly impressed with there work.
After more web searching and watching many youtube videos on refoaming, it seems that this "proprietary" electrically centering process is probably nothing more than applying a low frequency signal to the woofer while manually manipulating the woofer foam into place so the voice coil doesn't rub. not exactly rocket science. but not exactly perfect either.
SO, I am curious if anyone knows of any special techniques new or old that this company that shall remain nameless, might have been using??
I'm curious how Dynaudio actually does it?? I would love to see how that's done!
Zc
Dunno how Dynaudio do it, but my method is by using long shims that protrude past the spider, (which is not glued to the VC, just loose), fixing down the surround firmly, glue the spider to the basket all the way around, then let everything set up. Then you push the spider into place, and tack to the VC in a few spots with superglue. Let that set up, then carefully slide out the shims using long nose pliers and run a bead of glue around the spider and VC, covering all the tacks. It's long winded, fiddly and fussy, and you need to think about how you access everything before you start out, but it can be done.
Sometimes you just have to make things up as you go along!
I missed the bit about refoaming, not something you do a lot of in the pro world.
If the spider's still attached, then that actually does most of the support and spacing. I'd just clean off the old surround and glue with acetone, glue all round to the cone and let it set up, then tack to the basket in a few places, run some 10Hz test tone, and if there's no rubbing, glue it all down. Sometimes you can overthink these things.
AHHH HAAA At 5:51 of this video the secret is revealed!!!
Dynaudio Promotion Video Part 3/3 - YouTube
thin piano wires are put through tiny holes in the cone where the VC attaches to center the VC in the gap. once the glue has dried, they remove the thin wires and glue the tiny holes shut! Magic..or not so much LOL! good old fashion mechanical alignment! no special jigs or tools needed!
Dynaudio Promotion Video Part 3/3 - YouTube
thin piano wires are put through tiny holes in the cone where the VC attaches to center the VC in the gap. once the glue has dried, they remove the thin wires and glue the tiny holes shut! Magic..or not so much LOL! good old fashion mechanical alignment! no special jigs or tools needed!
I've used the LF tone method where removing the dustcap was awkward: Glue the surround to the cone and let it set up a bit. Take care to center it on the cone. Often the old glue line can be a good guide.
Put your bead of glue under the outer surround. Before it starts to firm up, feed an LF tone into the unit that will give a good excursion, say, 1/2" or more peak to peak. Then shift the whole assembly left until it starts to rub, then right until it starts to rub. Note the positions and split the difference. Next shift up to the rub point, down to the opposite rub point and split the difference. Make sure to clamp the surround down so that it will dry with no gaps and make sure it doesn't shift once best centering is found.
Its pretty easy once you try it and I've never had any units that didn't turn out well and play to high excursion without rubs.
David S.
Put your bead of glue under the outer surround. Before it starts to firm up, feed an LF tone into the unit that will give a good excursion, say, 1/2" or more peak to peak. Then shift the whole assembly left until it starts to rub, then right until it starts to rub. Note the positions and split the difference. Next shift up to the rub point, down to the opposite rub point and split the difference. Make sure to clamp the surround down so that it will dry with no gaps and make sure it doesn't shift once best centering is found.
Its pretty easy once you try it and I've never had any units that didn't turn out well and play to high excursion without rubs.
David S.
When I read about this companies "proprietary" process, i had initially assumed it was something like klipple analysis or some way of measuring the voice coil electrically to be able to align the coil in the gap. I was willing to pay the high price the company charged plus shipping if this had been the case. but once they decided they did not want to do Dynaudio woofers anymore and after a bit of discussion i really got the feeling that they were just doing the 30hz tone routine.
Refoaming secrets from a pro.
I do professional reconing and refoaming services. What I use is a variable low voltage DC power supply. The use of this tool is predicated on the existing, glued in spider to do the centering.
With pos. output from the power supply hooked up to the pos on the woofer, the cone pops up, allowing easy attachment of the new foam to either the top or underside of the cone's edge - whichever is required for that particular job. I use an aggressive adhesive that sets up rather quickly vs the white glues provided by foam kit suppliers. With quick set up of the glue at the cone's edge, I can turn off the power supply and let the cone drop after a few minutes. Then I let the glue dry for 1/2 to 1 hour. I then turn on the power supply again. With the surround 'popped up' I can easily apply the same glue to the frame. Working on a LEVEL SURFACE, I can turn off the power supply after I've applied glue all around the frame and let the cone simply drop down (spider keeps VC centered) and the surround's outer edge is then gently pressed into the glue and further adhered by placement of a thick, plastic ring onto the surround's outer rim and clamped with spring clips.
I quicky stroke the cone up and down with my hands, listening for any rubbing. Over 90% of the time this technique works with no rubbing.
However, on some woofers with tight air gaps, rubbing can occur. When this happens, I quickly separate the surround's outer edge from the frame with the power supply on and pushing up from underneath the surround with my fingers. Popsicle sticks inserted and slid around between the surround and frame ensures NONE of the glue threads remain between the surround and frame.
With the power supply still on, I then push down slightly on the cone's center with my hand, feeling for the best centered position where I feel no rubbing. Once I find it, I push a bit harder so the surround contacts the frame and at the same time, turn off the power supply. Voila! no rubbing and the surround is again re-clamped until completely dry.
I do professional reconing and refoaming services. What I use is a variable low voltage DC power supply. The use of this tool is predicated on the existing, glued in spider to do the centering.
With pos. output from the power supply hooked up to the pos on the woofer, the cone pops up, allowing easy attachment of the new foam to either the top or underside of the cone's edge - whichever is required for that particular job. I use an aggressive adhesive that sets up rather quickly vs the white glues provided by foam kit suppliers. With quick set up of the glue at the cone's edge, I can turn off the power supply and let the cone drop after a few minutes. Then I let the glue dry for 1/2 to 1 hour. I then turn on the power supply again. With the surround 'popped up' I can easily apply the same glue to the frame. Working on a LEVEL SURFACE, I can turn off the power supply after I've applied glue all around the frame and let the cone simply drop down (spider keeps VC centered) and the surround's outer edge is then gently pressed into the glue and further adhered by placement of a thick, plastic ring onto the surround's outer rim and clamped with spring clips.
I quicky stroke the cone up and down with my hands, listening for any rubbing. Over 90% of the time this technique works with no rubbing.
However, on some woofers with tight air gaps, rubbing can occur. When this happens, I quickly separate the surround's outer edge from the frame with the power supply on and pushing up from underneath the surround with my fingers. Popsicle sticks inserted and slid around between the surround and frame ensures NONE of the glue threads remain between the surround and frame.
With the power supply still on, I then push down slightly on the cone's center with my hand, feeling for the best centered position where I feel no rubbing. Once I find it, I push a bit harder so the surround contacts the frame and at the same time, turn off the power supply. Voila! no rubbing and the surround is again re-clamped until completely dry.
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It is all very interesting! But so far I haven't heard anyone speak of some magic high tech method! No using lasers or RF or some cutting edge magic specially designed equipment. It's all pretty simple stuff. I have refoamed over 50 woofers myself using the shims supplied in the kits with good success. But if there really was some magic method out there i wanted to learn about it.
Speaker doc and several other post's elsewhere have mentioned using a battery or a power supply. My understanding is that with dc or a LF signal applied that VC will center itself within reason? IE speaker laying facing up on a level surface etc.
I wonder if you applied two tones to a woofer if you could keep the coil centered and control the motion. so for example. apply a HF tone, maybe 1khz or something that will be high enough that it is above the woofers top end roll off. use that tone to keep the VC centered. then use variable DC to raise or lower the cone at the same time. Do like Speaker doc does by using a positive voltage to raise the cone, glue the edge. then lower the voltage so the cone drops into place while the 1khz tone is still keeping the VC centered?
Zc
Speaker doc and several other post's elsewhere have mentioned using a battery or a power supply. My understanding is that with dc or a LF signal applied that VC will center itself within reason? IE speaker laying facing up on a level surface etc.
I wonder if you applied two tones to a woofer if you could keep the coil centered and control the motion. so for example. apply a HF tone, maybe 1khz or something that will be high enough that it is above the woofers top end roll off. use that tone to keep the VC centered. then use variable DC to raise or lower the cone at the same time. Do like Speaker doc does by using a positive voltage to raise the cone, glue the edge. then lower the voltage so the cone drops into place while the 1khz tone is still keeping the VC centered?
Zc
You know, I have one simple request. And that is to have drivers with frickin' laser beams attached to their pole pieces!
The prospect of applying both AC and DC signals to a VC simultaneously doesn't seem feasible to me and isn't necessary, IMO.
I've been doing what I described commecially for years. It works.
I am an ex-test engineer for military electronics and an avid audio freak. I have also often pondered the alignment claims pertaining to voice coils when re-foaming.
Firstly, listen to Speaker Doctor since he knows what he’s talking about. Try not to over-think the process and take your time even without the power supply method. Always glue to the cone first and let dry before alignment and outer edge gluing. This is key and many youtube demo videos are horrifically incorrect. Also use the glue he recommends and good foam edges – I like the latest “Simply Speakers” foams and glue and have had great success and repeatability with their products.
As far as an “electronic method” of alignment goes in theory this would require at least 3 to 4 “sensing coils” built into the manufactured driver or magnet base with test leads. The concept of an externally mounted jig is quite possible and the circuitry would require analyzing a RF or AC sine wave test signals received from each sensing coils in exact calibrated proximity to the voice coil which would transmit the RF or AC signals via a test tone or generator circuit. Phase correction test results could be achieved at each location and converted into distance or direction measurements or indicators for each N-S-E-W position (sensor positions not magnetic poles) around the voice coil gap to aid in manual alignment. I suspect such a test machine may exist in some speaker manufacturer’s lab but I doubt you would see such technology in an audio shop – it would be overkill. My experience, as well as that of other, is there isn’t much ‘extra’ tolerance for centering once free travel without scrapes is achieved. The fact that the voice coil gaps and speaker components are manufactured true and square aids us in achieving a good alignment most of the time using this method. I rarely use shims for alignment when re-foaming but if I do I remove them during the final “manual” alignment of the outer edge and check my work the old fashioned way before the glue sets during the initial 10-20 minutes after application depending on ambient temp. Some tight voice coil gap spaced woofers with weakened spiders may even scrape when tapped or pushed off-axis/center yet work fine when exercised straight inward as when installed. These are the tricky ones that experience and final testing is the only solution for.
If you don’t have the patience or think you may have a problem then have your woofers done professionally. I did for years until I was on the third round needing foam edges for my own 1980’s AR9 tower speakers. I am disappointed in the foam chemistry and manufacturing from previous generations and am appalled by how quickly the Cerwin Vega driver surrounds fail to be specific. I have even had NOS dual wound CV sub-woofers in stock for several years that had surround foam crumbling before they were ever installed or used. Unacceptable - although foam does sound the best in most designs.
Even without using a power supply the manual method works very well. It is the 10 percentile that don’t work that bothers me and after years of experience I conclude that about 5 percent or more of those are usually due to de-formed , defective or damaged voice coils or bobbins or both that indicate woofer replacement or re-coning may be necessary. It seems whenever you re-foam a woofer removed from an “adult owned and operated” cabinet with the dust cap installed the refoam process using the manual method almost always works. Those that are improperly shipped or mis-handled are usually the problematic ones. Some, but not all, that fit this category show the problem during initial inspection. Keep in mind that although the lower spider does a great job of centering the voice coil in the gap it is only part of the equation. Think of the speaker cone as a piston (which it is) and the foam gasket is merely the top alignment to the piston relative to the spider alignment which ideally pushes either up or down (sitting level on your bench that is). Any skew between the cone edge centering and the lower spider centering can cause skew in the alignment which can cause scrapes along the path, sometimes only at extremes of travel and this must be confirmed before your outer foam edge glue is set regardless of your technique. Certain voice coil gaps in many Alnico magnet speakers are very tight and this alignment has only one, sometimes hard to find and align, “sweet spot”. You will find that the “sweet-spot” is so tight that it almost is a mute point to think that there is that much “extra” tolerance or ”free- play” as to be able to align any better using electronics or a high-tech approach other than to have no scrape through the entire cone excursion travel. Usually when you manually clear the circumference in the voice coil gap the speaker is very close to perfect center and this issue has been debated for years as far as “exact” alignment. Proof of this is that when I have performed alignment manually without scrapes the woofers almost always pass the low frequency and listening tests. I suggest a thorough low frequency test only be performed well after the glue has dried and the speaker should always be in a baffle or it’s original cabinet for testing at low frequencies. Contact cement sets in 1 hour but I don’t move it after alignment for 24 hours – patience Grasshoper. Should a woofer scrape because you didn’t do it correctly, order another surround and redo the process for that driver. Don’t make a mess or tear a vintage driver ever. Having patience comes with the territory when performing repairs,etc..
Also, don’t use the contact cement for the manual method without shims in your shop if the ambient temperature is over 75 degrees F or so. That stuff cures way too fast for a beginner. This is why I suspect many parts distributors use the white glue which I find inadequate especially when depending on them for “setting” time to make your alignments and keep the foam edge where you set them. After doing several re-foams one becomes proficient. The trick is to do it correctly the first time and preparation of tools and workplace is a must. Send the wife or girlfriend shopping first!
Firstly, listen to Speaker Doctor since he knows what he’s talking about. Try not to over-think the process and take your time even without the power supply method. Always glue to the cone first and let dry before alignment and outer edge gluing. This is key and many youtube demo videos are horrifically incorrect. Also use the glue he recommends and good foam edges – I like the latest “Simply Speakers” foams and glue and have had great success and repeatability with their products.
As far as an “electronic method” of alignment goes in theory this would require at least 3 to 4 “sensing coils” built into the manufactured driver or magnet base with test leads. The concept of an externally mounted jig is quite possible and the circuitry would require analyzing a RF or AC sine wave test signals received from each sensing coils in exact calibrated proximity to the voice coil which would transmit the RF or AC signals via a test tone or generator circuit. Phase correction test results could be achieved at each location and converted into distance or direction measurements or indicators for each N-S-E-W position (sensor positions not magnetic poles) around the voice coil gap to aid in manual alignment. I suspect such a test machine may exist in some speaker manufacturer’s lab but I doubt you would see such technology in an audio shop – it would be overkill. My experience, as well as that of other, is there isn’t much ‘extra’ tolerance for centering once free travel without scrapes is achieved. The fact that the voice coil gaps and speaker components are manufactured true and square aids us in achieving a good alignment most of the time using this method. I rarely use shims for alignment when re-foaming but if I do I remove them during the final “manual” alignment of the outer edge and check my work the old fashioned way before the glue sets during the initial 10-20 minutes after application depending on ambient temp. Some tight voice coil gap spaced woofers with weakened spiders may even scrape when tapped or pushed off-axis/center yet work fine when exercised straight inward as when installed. These are the tricky ones that experience and final testing is the only solution for.
If you don’t have the patience or think you may have a problem then have your woofers done professionally. I did for years until I was on the third round needing foam edges for my own 1980’s AR9 tower speakers. I am disappointed in the foam chemistry and manufacturing from previous generations and am appalled by how quickly the Cerwin Vega driver surrounds fail to be specific. I have even had NOS dual wound CV sub-woofers in stock for several years that had surround foam crumbling before they were ever installed or used. Unacceptable - although foam does sound the best in most designs.
Even without using a power supply the manual method works very well. It is the 10 percentile that don’t work that bothers me and after years of experience I conclude that about 5 percent or more of those are usually due to de-formed , defective or damaged voice coils or bobbins or both that indicate woofer replacement or re-coning may be necessary. It seems whenever you re-foam a woofer removed from an “adult owned and operated” cabinet with the dust cap installed the refoam process using the manual method almost always works. Those that are improperly shipped or mis-handled are usually the problematic ones. Some, but not all, that fit this category show the problem during initial inspection. Keep in mind that although the lower spider does a great job of centering the voice coil in the gap it is only part of the equation. Think of the speaker cone as a piston (which it is) and the foam gasket is merely the top alignment to the piston relative to the spider alignment which ideally pushes either up or down (sitting level on your bench that is). Any skew between the cone edge centering and the lower spider centering can cause skew in the alignment which can cause scrapes along the path, sometimes only at extremes of travel and this must be confirmed before your outer foam edge glue is set regardless of your technique. Certain voice coil gaps in many Alnico magnet speakers are very tight and this alignment has only one, sometimes hard to find and align, “sweet spot”. You will find that the “sweet-spot” is so tight that it almost is a mute point to think that there is that much “extra” tolerance or ”free- play” as to be able to align any better using electronics or a high-tech approach other than to have no scrape through the entire cone excursion travel. Usually when you manually clear the circumference in the voice coil gap the speaker is very close to perfect center and this issue has been debated for years as far as “exact” alignment. Proof of this is that when I have performed alignment manually without scrapes the woofers almost always pass the low frequency and listening tests. I suggest a thorough low frequency test only be performed well after the glue has dried and the speaker should always be in a baffle or it’s original cabinet for testing at low frequencies. Contact cement sets in 1 hour but I don’t move it after alignment for 24 hours – patience Grasshoper. Should a woofer scrape because you didn’t do it correctly, order another surround and redo the process for that driver. Don’t make a mess or tear a vintage driver ever. Having patience comes with the territory when performing repairs,etc..
Also, don’t use the contact cement for the manual method without shims in your shop if the ambient temperature is over 75 degrees F or so. That stuff cures way too fast for a beginner. This is why I suspect many parts distributors use the white glue which I find inadequate especially when depending on them for “setting” time to make your alignments and keep the foam edge where you set them. After doing several re-foams one becomes proficient. The trick is to do it correctly the first time and preparation of tools and workplace is a must. Send the wife or girlfriend shopping first!
I think I may have replaced a surround on a woofer once. Don't remember. Whatever method used for alignment, it is probably important to realize that unless the spider is shot, you will not be able to force a concentricity change at the voice coil by a concentricity change at the cone edge. You'll only be able to change the angle of the stroke. Because of that, shims at the coil would be very tricky if not lucky to rely upon for coaxial alignment since you're not dealing with a perfect cylinder at the coil and the pole faces at the gap are usually less than 5/16". With original assembly tolerance, cone warpage, and new surround mechanical distortion, you'll probably need the full power of all your senses to get the job right every time. I'd probably be tempted to glue the new surround to the cone as concentrically as possible and after full curing tack the outer edges in tiny spots, maybe even with small neo magnets if steel basket, until I got everything optimized. I've seen brand new Dynaudio woofers with largely non-uniform radius in the surround right out of the box. WIth GRS or Goldwood foam surrounds you can practically depend on seeing that in every driver. If you think about the change in radial position of any surface of the coil that you can force by a concentricity change at the cone edge, you'd have to really botch an originally well constructed woofer re-foam to make it rub, and it's probably going to occur at + Xmax. 0.02 dollar, marked down to .01...
I center and glue up the surround to the cone and let that set overnight. Then I use a 30Hz tone to center the coil and move the outer surround on the frame similar to what Speaker Dave recommends. Hasn't failed me yet and defiantly don't over think it it's a simple centering and alignment procedure to get it right.
Rob
Rob
In my post "you will not be able to force a concentricity change at the voice coil by a concentricity change at the cone edge. You'll only be able to change the angle of the stroke."
is not right. Should be:
you will not be able to force a concentricity change at the spider by a concentricity change at the cone edge. You''ll be changing the angle of the stroke, and the center of an inclined cylinder in the gap.
is not right. Should be:
you will not be able to force a concentricity change at the spider by a concentricity change at the cone edge. You''ll be changing the angle of the stroke, and the center of an inclined cylinder in the gap.