My Ohm F's are in great condition except for a couple issues. I'd like to play them for a while as is before they need a restoration. The issue to discuss here is sagging spiders.
To correct the sag, I've read about wetting, pushing the spider to below flat (driver is upside down) and allowing it to dry, or heating it with a hair dryer, hoping that it remembers its new position.
I've also read about these spiders having bakelite varnish in them when made. Perhaps I can paint them with the same varnish, after being in the correct position, in the hope that they will be more stiff. Bakelite varnish is still available here:
https://bakelite.com/industries/coatings-inks-adhesives-sealants/coatings-and-inks/
I've also read about using a fabric stiffener such as:
Aleenes Flexible Stretchable Fabric Glue 4 fl. oz. – Aleene's
https://aleenes.com/products/aleenes-flexible-stretchable-fabric-glue-4-fl-oz
https://aleenes.com/products/aleenes-flexible-stretchable-fabric-glue-4-fl-oz
To push the spider, I'd prefer not doing this mechanically, as it may throw off the voice coil geometry. So, how about applying DC voltage to position the spider? I used a variable DC power supply on one driver to level the spider. It took 1.8V, 0.31A to get there. So I would dope with water, varnish or fabric stiffener, move the spider into position by DC voltage and wait for the dope to dry.
Any thoughts are appreciated. Again, please do not advise to replace them. I'm already aware of that option for way down the road.
1. Pics of the exterior of the drivers:
www.px625.com/ohm-f/index.html
2. Movie of exterior of driver A:
www.px625.com/ohm-f/a-outside.mp4
3. Same for driver B:
www.px625.com/ohm-f/b-outside.mp4
To correct the sag, I've read about wetting, pushing the spider to below flat (driver is upside down) and allowing it to dry, or heating it with a hair dryer, hoping that it remembers its new position.
I've also read about these spiders having bakelite varnish in them when made. Perhaps I can paint them with the same varnish, after being in the correct position, in the hope that they will be more stiff. Bakelite varnish is still available here:
https://bakelite.com/industries/coatings-inks-adhesives-sealants/coatings-and-inks/
I've also read about using a fabric stiffener such as:
Aleenes Flexible Stretchable Fabric Glue 4 fl. oz. – Aleene's
https://aleenes.com/products/aleenes-flexible-stretchable-fabric-glue-4-fl-oz
https://aleenes.com/products/aleenes-flexible-stretchable-fabric-glue-4-fl-oz
To push the spider, I'd prefer not doing this mechanically, as it may throw off the voice coil geometry. So, how about applying DC voltage to position the spider? I used a variable DC power supply on one driver to level the spider. It took 1.8V, 0.31A to get there. So I would dope with water, varnish or fabric stiffener, move the spider into position by DC voltage and wait for the dope to dry.
Any thoughts are appreciated. Again, please do not advise to replace them. I'm already aware of that option for way down the road.
1. Pics of the exterior of the drivers:
www.px625.com/ohm-f/index.html
2. Movie of exterior of driver A:
www.px625.com/ohm-f/a-outside.mp4
3. Same for driver B:
www.px625.com/ohm-f/b-outside.mp4
Having no idea what the answer is, I'd have to ask what proportion of the cone weight load do the spiders actually carry? I always thought it was zero; the cone surround is what bears the cone weight. The spider's purpose is to assure centered alignment of the VC with the magnet pole piece.
Of course, in a speaker designed to be operated at 90 deg from the usual vertical baffle, the Ohm-F design may be different, even though it looks to me like any other spider. Intuitively, I guess I wouldnt count on that little structure holding up that big heavy metal of a speaker cone. Or anything you could do to it, spray-on that would make much of a difference - or by the time it did, the spider would become something else mechanically.
Whelp - <slaps thighs> - you're in a position to design a really quiet unregulated dual 0-2V power supply, and capacitively couple these speakers to your amplifier. You'll have the only speakers running "class A" during those soft passages, where all those wonderful details arent so obscured by...SPL. Perhaps there's some magic there in doing that, perhaps not. Seems like it wouldnt be so hard to rig up to hear.
Of course, in a speaker designed to be operated at 90 deg from the usual vertical baffle, the Ohm-F design may be different, even though it looks to me like any other spider. Intuitively, I guess I wouldnt count on that little structure holding up that big heavy metal of a speaker cone. Or anything you could do to it, spray-on that would make much of a difference - or by the time it did, the spider would become something else mechanically.
Whelp - <slaps thighs> - you're in a position to design a really quiet unregulated dual 0-2V power supply, and capacitively couple these speakers to your amplifier. You'll have the only speakers running "class A" during those soft passages, where all those wonderful details arent so obscured by...SPL. Perhaps there's some magic there in doing that, perhaps not. Seems like it wouldnt be so hard to rig up to hear.
If I would have been the manufacturer I would have centered the construction so that a hanging spider by one or two millimeters just enables the right centering from the beginning.
So you really do not know if the hanging is a deficiency or not?
So you really do not know if the hanging is a deficiency or not?
Thanks for the replies. Note:
1. The majority of the compliance is from the spider, not the surround. Yes, stiffening it will chamge that but not to any detrimental degree. When people rebuild these drivers with new spiders, they are stiffer by design, as they should have been from the factory. Users note no detrimental effect on the sound; just the opposite, the rebuild has excellent results.
2. I could run it upside down for a long length of time, say at 50Hz. It wastes power though but I can do it if there's no other option. I know of one other F user who just left it upside down for a long while, without playing it, and the spider recovered to its correct position. But, that will still slowly sag once inverted, as it's still the same soft spider.
3. No matter how the spider was "optimally" positioned from the factory, gravity will eventually lower it. The deficiency here is that the voice coil is now not centered, in its optimal position. That means more power is required to play the speakers. It also limits the driver travel to the point where it may bottom out.
4. The factory has stopped supporting this model for years. They want nothing to do with it, except to accept it as a trade-in towards their new models - non-Walsh models. Not an option for me. Certainly they won't advise any DIY effort.
1. The majority of the compliance is from the spider, not the surround. Yes, stiffening it will chamge that but not to any detrimental degree. When people rebuild these drivers with new spiders, they are stiffer by design, as they should have been from the factory. Users note no detrimental effect on the sound; just the opposite, the rebuild has excellent results.
2. I could run it upside down for a long length of time, say at 50Hz. It wastes power though but I can do it if there's no other option. I know of one other F user who just left it upside down for a long while, without playing it, and the spider recovered to its correct position. But, that will still slowly sag once inverted, as it's still the same soft spider.
3. No matter how the spider was "optimally" positioned from the factory, gravity will eventually lower it. The deficiency here is that the voice coil is now not centered, in its optimal position. That means more power is required to play the speakers. It also limits the driver travel to the point where it may bottom out.
4. The factory has stopped supporting this model for years. They want nothing to do with it, except to accept it as a trade-in towards their new models - non-Walsh models. Not an option for me. Certainly they won't advise any DIY effort.
I’ve had some luck doing the following on other speakers with sunken spiders. Protecting the cone from overspray moisten the spider with water uniformly then using soft foam rubber shim the cone into the desired position and let it dry. After the water dries remove the foam to see if the position is now where you want it. If yes, lightly spray the spider with spray starch used on clothes to stiffen them when ironing, I think it’s called Niagra spray starch. Remove the protection from the back of the cone after this has dried. It’s worked for me but no promises!
I did it on two pairs of woofer made by Saire in Europe. The were stored face up in the shipping box for years and had sunken badly. After moistening the spiders lightly I shimmed them into proper position with foam rubber and dried the speeders with a hair drier, not a heat gun! Once they were in the position I wanted I lightly used Niagra spray starch and the hair drier again. They are still being used by my friend and maintain their proper position. They are mounted perpendicular to the ground so sagging is not an issue so I can’t say how an Ohm driver will last being as it’s parallel to the ground. Do one and see how it works, it won’t be any worse and you might save yourself a small fortune!
When I do decide to try any option, I'm going to purchase a similar spider and see if I can stiffen it to a new position. I'll put a small weight on it and wait a few weeks to see if it holds its shape.
FYI, as for saving a small fortune: I contacted the expert in F rebuilds, Bill Legall of Miller Sound. He no longer rebuilds them but charged $1350 per pair. I would pay him that easily today if he still did the job.
FYI, as for saving a small fortune: I contacted the expert in F rebuilds, Bill Legall of Miller Sound. He no longer rebuilds them but charged $1350 per pair. I would pay him that easily today if he still did the job.