Question about Soft Domes and dents, ADS among others

[Tiver]

I have some ADS in the corral. Fortunately all of the domes are clean and dimple free.

I am considering a couple new additions and one of the potential issues is that there is a dimple in each of two midrange drivers.

I haven't really any idea how the dome works, but I would think they started their life in a particular shape for a reason. I have read dimpled domes "don't affect the sound", but that works against what seems logical to me. A little further in the thought, do soft domes and metal domes respond equally to dimples and such?

And, after all of this, is repairing the dimple in the soft dome likely an adequate fix, if a fix is required? I know about the possibility of have the drivers rebuilt, and may look at that as a natural progression, but that will be down the road unless it appears the dimples are irreparable.

 

[Grenadeslio]

Dimples in "dustcaps" have very little affect, but they do have some. So yes, it's my opinion having a dome driver's "diaphragm" out of shape will have an affect on the output, and as the magic is in the midrange.......

That said, I purchased my AR58s knowing one had a dimple in the midrange. Could I hear any degradation of SQ in direct comparison to the other? Absolutely not, but it still bothered me so I used packing tape to pull the dimple out as much as possible and leave the grills installed lol.

The speakers sound fantastic, and I prefer these vintage speakers with the grills anyway.

 

[Tiver]

Dimples in "dustcaps" have very little affect, but they do have some. So yes, it's my opinion having a dome driver's "diaphragm" out of shape will have an affect on the output, and as the magic is in the midrange.......

That said, I purchased my AR58s knowing one had a dimple in the midrange. Could I hear any degradation of SQ in direct comparison to the other? Absolutely not, but it still bothered me so I used packing tape to pull the dimple out as much as possible and leave the grills installed lol.

The speakers sound fantastic, and I prefer these vintage speakers with the grills anyway.

Sure dust caps are not much of anything unless they are something like The Smaller Advent "spit-wad type".

I assume domes are a bit more than a dust cap and I am just trying to get some input on what people have epxerienced. I have a pair of JBL L166 with the 066 titanium dome (dimpled when I got them). That's where I come to wonder whether the dents would be more problematic in soft or hard.

I have read about dispersion and such and realize the domes will still likely sound OK. Just trying to collect thoughts here.

 

[Grenadeslio]

Sure dust caps are not much of anything unless they are something like The Smaller Advent "spit-wad type".

I assume domes are a bit more than a dust cap and I am just trying to get some input on what people have epxerienced. I have a pair of JBL L166 with the 066 titanium dome (dimpled when I got them). That's where I come to wonder whether the dents would be more problematic in soft or hard.

I have read about dispersion and such and realize the domes will still likely sound OK. Just trying to collect thoughts here.

That's why I gave you my experience trying to remove a dimple, and its affect on the SQ.

 

[Tiver]

As I said previously I don't really know much about how these domes work....

With a little time looking into it, I have come up with the following. I would be happy to have anyone add to or correct what I might be missing or misstating.

The dome on this type of driver is the diaphragm, akin to the cone of a what we think of as a conventional speaker. There is still a surround on the dome and is part of the suspension. The voice coil is attached to the dome on the backside I assume, and is continuous through the center and a dust cap is not required. The inner side of the voice coil, front to back orientation, is still attached to some kind of a spider? Something about a front plate and no basket which I guess is possible because these frequencies require limited excursion, so the magnetic assembly is mounted directly to the front plate?

Replacing cone type speaker surrounds is talked about all the time and are promoted as a relatively basic DIY, but tinkering with repairing domes doesn't get much play. Is this because it's more like re-coning? Anyone comment on their experience doing this with domes? I have read about pulling or using a vacuum to remove dents, like @Grenadeslio described, but I don't recall reading about a disassembly and perhaps pushing the dome out from behind. Maybe alignment and attachment of the voice coil is not a manual operation? Maybe the procedure is too difficult and/or parts are too scarce? Can a dome be disassembled and put back together without new suspension parts?

 

[RTally]

As I said previously I don't really know much about how these domes work....

With a little time looking into it, I have come up with the following. I would be happy to have anyone add to or correct what I might be missing or misstating.

The dome on this type of driver is the diaphragm, akin to the cone of a what we think of as a conventional speaker. There is still a surround on the dome and is part of the suspension. The voice coil is attached to the dome on the backside I assume, and is continuous through the center and a dust cap is not required. The inner side of the voice coil, front to back orientation, is still attached to some kind of a spider? Something about a front plate and no basket which I guess is possible because these frequencies require limited excursion, so the magnetic assembly is mounted directly to the front plate?

Replacing cone type speaker surrounds is talked about all the time and are promoted as a relatively basic DIY, but tinkering with repairing domes doesn't get much play. Is this because it's more like re-coning? Anyone comment on their experience doing this with domes? I have read about pulling or using a vacuum to remove dents, like @Grenadeslio described, but I don't recall reading about a disassembly and perhaps pushing the dome out from behind. Maybe alignment and attachment of the voice coil is not a manual operation? Maybe the procedure is too difficult and/or parts are too scarce? Can a dome be disassembled and put back together without new suspension parts?

A tweeter dome is not the same as a woofer dustcap, even though they may look similar. Your description is pretty much right. There is no spider because the diaphragm and VC assembly is rigid and small enough that the VC alignment in the cap is maintained by the surround.

Some tweeter diaphragms are made to be readily replaceable, such as Klipsch tweeters. (See Crites replacement diaphragms for examples). Others, like the ADS tweeters can be rebuilt by an expert, such as Richard So.

As for removing dents in dome tweeters, it depends. Rigid domes like some phenolics probably not. As the dome vibrates, the creases are weaknesses that may not work well when driven. I tried to push out dents on phenolic domes and they sounded terrible. Soft domes, such as coated fabric are likely repairable. I have some Peerless tweeters in some Polks that were crushed and then popped back out. They sound fine to my ears.

 

[Tiver]

@RTally Thank you for the post. I saw that diagram somewhere and it confused me some because the back of the VC looks like it's floating, which you confirmed.

As far as the voice coil attachment to the dome, is this something done by automation in the manufacturing of the part ? IOW would you know if the VC, dome and suspension be a pre-constructed part or are these individual pieces? It seems like alignment would be challenging.

Pretty sure the JBL 066 is vapor deposited titanium. Having these dimpled really bothers me to look at and I always have imagined disassembling them, added some kind of heat to the dome to "soften" the metal as much as that's possible (less brittle at least), and push out the dents. The replacement parts are long gone, but I still imagine it can be done. Further, it's been otherwise posted that there are better replacements for these anyway, but my imaginary scenario costs less.

This video was visually useful to me, but it is about tear down...nothing about reconstruction

Another video was about replacing a voice coil on a car super-tweeter, but seemed a little less relevant. Voice coil assembly just dropped in and no alignment was required. Is this the case with the kind of domes I am posting about?

 

[RTally]

I could not watch the whole video. They guy sounded like a very inexperienced, clueless person who likes to tear things apart and talk before fully investigating and understanding what he is talking about. I feel dumber after watching about half of it. I prefer to learn from people that know more than me, or at least know something about what they are talking about.

As for manufacturing of tweeters, typically jigs are used to align the parts. The jig holds the parts together in alignment as they are secured together. If the VC former is separate from the diaphragm, then the two parts are held in a fixed position by a jig as they are secured together with an adhesive or are welded together.

If you cannot get replacements for the tweeters and they still sound good, leave them be. Put the grills on the speaker so you don't have to look at the dimples.

If you think the dome can be restored to its original shape, I would ensure that replacements are available in case the tweeter is destroyed while being repaired. Keep in mind, many times the dimples can be removed, but a crease will still be visible, particularly for the hard, metal domes. So if you are doing this for cosmetic reasons, you may not be satisfied with the results.

Another alternative is to find a replacement tweeter. Replacing tweeters is easier than replacing a woofer because the cabinet is not a factor. Primarily, you want to match the frequency response, impedance, and sensitivity. Finding one with the same configuration and bolt hole pattern would be nice too, but that can be worked around normally.

 

[Tiver]

Thanks again @RTally . Oh yeah, I understand your comments about the guy in the video, but I found it to be a useful illustration. FYI, further in he discovers the VC had been attached to the dome and the broken bond is quite evident.

Your description of some kind of alignment jig is along the lines of my description of automation in the manufacturing process.

I feel like the construction of the tweeters is much clearer to me. Although I have yet to take one apart, at least I am wary of some of the challenges if I decide to do so. Even with google and youtube and the like for searches, having a real people willing to discuss these things is a much appreciated enhancement.

 

[jdurbin1]

JBL 066 is aluminum vapor-deposited over resin-impregnated linen dome, as the 044. Titanium came later but in solid form, not vapor deposited film like the older tweeters had.

John

@RTally ...

Pretty sure the JBL 066 is vapor deposited titanium. Having these dimpled really bothers me to look at and I always have imagined disassembling them, added some kind of heat to the dome to "soften" the metal as much as that's possible (less brittle at least), and push out the dents. The replacement parts are long gone, but I still imagine it can be done. Further, it's been otherwise posted that there are better replacements for these anyway, but my imaginary scenario costs less.

 

[Fomoco1649]

I have some ADS L780 Version 1 and one of the tweeter has small dimple….maybe 40% not pushed in that much, mild suction has not worked & super sticky tape was able to grip it & pull it forward but it did not just pop out & stay like some materials, this soft dome material reacting like flexible cloth ….should I leave it alone for now or try more suction from a hand pump I have? it sounds fine & probably will send into Richard So eventually….Ive heard the ferrule fluid possibly dried up too?