Ohm Walsh F Hope of Resurrection

My opinion on the stiffener on the spider is a no.

Conceptually, stiffening the spider or surround causes the raising of the resonant frequency of the driver. The effect of that may raise the low cutoff frequency for the speaker, among other effects, perhaps changing the Q of the system tuning.

If you do fix the surrounds on the F, your could then try an experiment that I did in the mid-'80s, with a musician friend.

Remove the grilles. Have a friend listen to the same musical selection. Without him knowing or seeing what you do, remove the fuses and replace it with a short wire. Play the music. Go back to the fuse, and play the music. Then go back and forth. Without telling him what you were changing, ask what he heard for the two configurations. Get a good description. For my friend, it was clearly and consistently audibly different, and repeatable in his descriptions.

I agree with mapman. If it is 7-8 grand for new drivers from Dale, I'd have gone for it before. Maybe it's worth a call to Dale even now. I still have the F cabinets.

Doug, depending on how old the F drivers are, your surrounds rotting is expected but quite overdue. I had F’s from 1977, and surrounds rotted in 1995. The spider suspension also sagged from the years under a heavy cone. Both are non-repairable by Ohm Acoustics. Furthermore, the inside of the cone has foam damping on the aluminum section. That also was flaking off on my speakers, but only if I touched those parts.

I first tried to repair the surround by ordering a similar sized surround from a place in Florida, if I remember. Installation was easy, took some patience, working methodically, and carefully scraping the old glue off the paper/cardboard part of the cone periphery. Gluing the replacement surround was about the same, making sure it’s centered so the voice coil doesn’t scrape against the magnet, and the edge of the cone is circular, not oval from the handling. This was the cheapest fix for me.

The completed surround repair will let you play the speaker. Ohm says it won’t sound as intended, due to the specific absorption of their surround to properly mechanically terminate the cone edge, that an aftermarket surround couldn’t do.

The other two options were to trade-in the drivers toward currently available speakers at a discount, or trade-in for the F3 driver to mount on my F cabinets. The F3 was clearly the most value.

I decided to upgrade to another Ohm Walsh speaker, and also take the F3 option. All four are in play, two as stereo, or all four as theater main and surround speakers.

Ohm currently appears to have 5 options for upgrading the F now. Good luck.

Doug, consider asking Ohm whether they are willing to make the speaker omni, by not installing the damping pad on the back side of the cylinder, and turning the supertweeter upward as for the surround speakers, for example. I also preferred a full omni (as in the F) vs. the newer Walsh drivers (thousand series) with controlled directivity design. However, with a full omni the central image does shift when you're not along the centerline between the two speakers (the F), whereas it is remarkably near center with the latest Walsh drivers. The latter is of great advantage in a home theater setting, as well as stereo listening if you're casually listening while sitting off center. I get an enjoyable sound even sitting beyond the left speaker, but not past the 90-degree line from the supertweeter axis.

With true omni designs, your choices are more limited. As mapman wrote, call Dale Harder for his versions of the F and A speakers. Otherwise, it's  either MBL or German Physiks, as far as I know.

When I replaced the surrounds on my Fs, that was the first time I had tried a surround replacement on any driver. To me, it was fairly straightforward. I would not attempt to replace the spider - too much risk of damaging the titanium part of the cone. 

The surprisingly easy, but time consuming part was to carefully clean the paper cone periphery of old glue, without damaging the paper periphery, after removing the old surround from the cone and metal rim of the basket. 

The new surround should fit over the periphery exactly, if you order the right size diameter of the surround. Measure carefully before you order and double check after you receive the new surround. The  surround fits over the outside surface of the paper cone periphery, and also to the upper surface of the metal rim of the basket (like in the existing surround).

I had the driver upside down, put the surround over the cone and slide it below the periphery, applied the glue to the outside of the cone periphery, and pull the surround up over the glue slowly to make it positioned evenly around the cone. At this stage it helps to orient the driver right-side up to achieve a even, planar circular interface between surround and cone. I suggest minimal glue to minimize the mass change at the edge. Let glue set. 

Centering the cone periphery was also fairly easy. I had the driver oriented upside down on a table. While holding the cone near its middle height, tilt the cone left and right while gently sliding it up and down. Do the same fore and aft. Find the center point between where you hear slight scraping and no noise, in four perpendicular tilt directions. mark where the surround edge for each center point. Glue it down to the rim, taking care to not radially stretch the cone either outward or inward. 

If you take this route, you can still opt to do more repair later with someone like Dale Harder, or get his TLS-1 speaker. 

Doug, just saw your post. I was writing my previous response when you posted.

Just to fill in some info, I found a few things that differ from the F vs the W5000 speakers, in my room. The F subjectively seems to go deeper in the bass than the W5000, in the sense of very low bass, the room-shaking kind, despite the low frequency bandwidth specs of 37 Hz vs. 25 Hz, respectively. I speculate that the faster roll-off of the W5000 (a vented design) vs. the more gentle roll-off of the F (a sealed system design) may have something to do with this impression. For music, this makes no difference. For movies, I have subwoofers to cover the lowest frequencies, about equivalent to that of the W5000. 

Both the F and the W5000 drivers can produce an impression of surround sound from only two-channel material. In the movie Flyers, there is a scene where a fighter jet flies from-behind to overhead and then to in-front of another jet. The sound, from inside the second jet, with only two front speakers projects the sound movement matching the video. 

The F requires a power to get to reasonable sound levels; the W5000 takes less power. The latter, with a powerful amp will give added headroom to play live recordings at live SPL levels, not that one needs to do this routinely.

I also seem to recall that the power handling on the modern Ohm drivers is much better than in the F. Another related thing is a review of the Walsh 5 showed a linear tracking of output volume and power input, saying that higher power causes little "power compression" of the sound. I never tried to check this on my system, but that is a good indicator to me for the speaker capability to produce correct musical dynamics.

Doug, I did the surround because I really didn't have much choice. Either fix it or get it fixed so I can use the speakers. Again, it won't be like the original F, because the surround characteristics is different than what Ohm had. It will play, however, as a interim solution until I got new Ohms.

I didn't use tape of any kind, because I was afraid the tape could tear the surround attachment part. The new and old surrounds could have different attachment ring diameters. I just thought of an idea that you could use the painters tape to mark the original edge of the surround attachment to the metal rim say in four perpendicular locations, but not on the surround itself. When you try to attach the new surround, it will either be smaller diameter which makes it easier to center relative to the tape, or larger diameter which you'd have to mark the new diameter with more tape and compare the original and new marked positions for centering. You could also measure the new surround diameter and mark that with additional tape relative to the original surround diameter tape marks.

I don't recall what glue was used for the surrounds. I ordered the surrounds from Stepp Audio Technologies in North Carolina. I supplied them the relevant dimensions and cone angle. I cannot find that company anymore on the web. It was 25 years ago!

The spider sagging is from years of weight on it. It could be permanently deformed. I would doubt that turning the driver over will do much in correcting the position, but it's worth a try to see what you get over a given time. 

If you're talking the internal cabinet wiring and the binding posts on the bottom of the cabinet, that's conceptually easier to do. I would caution on working on the binding posts on the metal struts holding the magnet assembly, as these attach the fragile wires that go to the cone internal wiring.

As for the internal cabinet wiring of the F, I bypassed it by directly attaching the speaker wire to the binding posts on the driver struts, and left the internal wiring unused.

The Ohm F is a acoustic suspension speaker system, which means the cabinet is a sealed box. Because of the sealed cabinet and no crossovers, the system should roll off at 12 dB/octave below the cutoff frequency. I think the foam stuffing so full in the box is there for a specific purpose. You'd have to ask Ohm whether the stuffing is there for the purpose I think is.

In an acoustic suspension speaker box design, lining the internal cabinet walls with absorptive material is one method used to damp the sound wave reflections inside, reducing standing waves. Stuffing the box loosely-full will change the thermodynamics inside the box as well. This makes the box act as if it were bigger than its actual physical internal dimensions. That lowers the resonant frequency, so extends the bass when using a smaller cabinet volume that otherwise would have been bigger. There is a tradeoff with this - lower efficiency, for example. If I remember, this affects the system Q (resonant peak width) too, through damping.

The stiffness of the surround and spider along with the moving mass (plus damping) contributes to defining the resonant frequency of the driver. That in conjunction with the cabinet size and stuffing determines the system resonant frequency in the bass, among other things. Any changes you make to the surround or spider stiffness will affect these things. 

I suspect that in the Ohm F, the internal stuffing plays another role, that of absorbing the acoustic wave emitted by the inside surfaces of the cone. Otherwise, the internal reflections will interfere with the later sound waves travelling down the cone.

Been quietly following this thread, and glad that you got the F's fixed.

There's been a lot of talk about the hair-trigger watt limit to blow up the F speakers. As long as you don't tempt fate, it should be fine. I've run my pair of F's for may years with a 300 W/ch (into 4 ohms) power amp, and really never needed to put more than a few watts to get loud enough in the room. 

Let us know how the speakers sound when you get them fully set-up. Congratulations, again.

Douglas, in the restoration, did they do anything to the 'putty' like stuff that's lining the inside surface of the titanium portion of the cone? I doubt they did that. If nothing was done, as it's difficult to do this, the sound will be audibly different from the original F.  

Douglas, the putty on the inner surface of the titanium section of the Ohm F cone will dry out over time. It is a known issue for older F's. The speakers will play but the treble sound from that part of the cone can be different. As an engineer, this makes perfect sense to me, as follows.

The putty acts like a dampening material for the wave travelling through the upper segment of the cone. To dampen the wave, it has to have just the right 'flexibility'. When the putty turns hard, it is less flexible, and becomes more rigid-like, and the cone can't flex the same way as when the putty was new. 

You are already aware of the foam degradation on the inside of the aluminum section of the cone. 

An important parameter for a wave transmission cone is that the impedance of each interface between sections are designed for passing the wave across the boundary, with minimal reflections back up the cone, interfering with the subsequent waves coming down. The same needs to occur at the surround at the bottom of the paper part of the cone. That is why the surround is not replaceable by just any foam surround that physically fits the dimensions.

Hope that clarifies why the sound may be different, if the putty can't be replaced correctly.

Douglas, certainly you cannot compare your F's to the original F's, as none exist as a new F anymore. No one can be sure of its sound once the putty dries out, or the foam in the cone falls apart, as compared to a just-manufactured F speaker.

There are other ways to check, such waveform output. The F has the ability to output a "reasonable facsimile" of a square wave as one reviewer put it, and as shown in the Ohm literature. If one is able to restore the cone to like-new, it should be able to output this kind of waveform, to validate the restoration. If a speaker could pass this test, that would demonstrate phase accuracy over a wide range of frequencies.  

Since you hear a sound that you find not to your liking, like the treble response you noted, you took some of the foam out of the enclosure, and said that helped ("The rebuild was successful in the end mostly because of my foam removal. The driver was terribly constrained until I half emptied the cabinet to let the driver work more freely.") That action changed the system Q, and could reduce the damping to the driver in the bass frequencies, perhaps increase ripple in the frequency response.  

But as you said in the latter part of your posts, as long as it sounds good enough for you, you really don't care if the fixes approached the original F sound or not. I thought you wanted to preserve the F sound to as close to original as practicable. My comments were directed to assist in that direction. Sorry if I misunderstood your intent.

The HHR speakers use the platforms of the Ohm A and F designs, and take them farther that could be done in a commercial setting. I think Dale sells his speakers on a build-on-order basis. If I get the opportunity, I'd like to hear his speakers, as I've heard the first Ohm A's and later owned F's.