Edge Coating

[PeteMcK]

What do you guys think of this? : edge-coating
Troels says "By adding a proper amount of glue with proper elasticity and resilience and in the right place on the inner side of the surround, the energy coming from the cone can better be absorbed and the result is a more linear frequency response". His graphs are convincing, the downside is "They loose some 0.5-1 dB sensitivity"
However, "The source of material and application technique shall not be revealed"
- so time for some idle speculation: 1: what is an appropriate "glue with proper elasticity and resilience", and 2: where exactly is "the right place ". He sort of answers that with a drawing here: W12CY003 where "part of the inner rounding was made thicker"

As for the goop, I've got a can of "Rustoleum Leakseal - flexible rubber coating which I bought some time ago to try as a cone coating. Unfortunately the nozzles on Rustoleum cans in Aus are rubbish & don't give a consistent spray, so it has to be painted on.
I know Planet10 has been painting stuff on cones for Aeons, perhaps you can comment Dave?

 

[planet10]

Yes it can work.

I have used ModPoge (Troll’s description is more a descriptive) on some surrounds — mostly aged accordian surrounds (Philips comes to mind), and ZIG 2-way glue on the Fostex FF & FF series drivers.

dave

 

[Rallyfinnen]

I have seen improvements too. Usually I've seen resonances from the surround in the 1kHz area. Practice on some old/cheap drivers. I sometimes put it on the back, since it does not affect the look of the driver.

I tried various glues used in house construction, some textile glue, and some special glue for replacing surrounds on drivers. I think I like the glue for surrounds best. It is similar to textile glue and contact glue, but seems to stick better than textile glue, and a little bit 'softer' than contact glue, and is elastic/rubbery when dry, but a bit sticky, so it collects dust. That's why I prefer to put it on the back of the cone/surround.

 

[Rallyfinnen]

I just ordered some ModPodge too, to give it a try.

 

[celef]

is it not a well thought feature, and a selling point, that some drivers has a low loss surrounds and some has high loss surrounds, why not pick the right driver in the first place?

 

[Rallyfinnen]

I would guess there are trade-offs with edge coating too, maybe distortion will go up (on high excursion low frequency), and Qms down.. but FR will (hopefully) be more flat.

 

[turk 182]

what's this?? Troels Gravesen is talking about making a loudspeaker more linear aren't speakers supposed to be linear to begin with?

 

[Rallyfinnen]

There are definitions to this I can't remember (in English), but for example a ruler flat frequency response does not mean you have zero distortion.

 

[turk 182]

??

 

[afa]

I use these products for cone and cone edge treatment, both are available in Australia.
Craftsmart Tacky Glue (stays flexible and slightly tacky)
CRAFT SMART ADHESIVESOff'N On Glue 125 ml (stays very tacky and attracts dust, best applied to rear of cone)

Here are some drivers that have been edge treated by the manufacturer,
Tang Band W3-1878 3" Full-Range Driver
SB Acoustics SB12NRXF25-4 4" midrange | HiFiCompass

I have seen also cone edge treatment on drivers made by AR, Vifa, SEAS, Audax (aerogel) and others.

cheers, Arthur

There also was an article in an early edition of Speaker Builder magazine that had more information related to this topic

 

[Rallyfinnen]

turk 182:
Troels is making the frequency response more linear with coating, and it apparently works quite well!
So, why do the manufacturers not do it? COST, consistency, ageing, chemicals used in production etc, and/or maybe some negative effects to other parameters (like the ones I mentioned).
Well, my guess is that it has a lot to do with money..

 

[Scottmoose]

Entirely about money. Development cost (relatively minor), material cost (more significant), production cost of damping the cone edge-resonance (the big one, since applying the correct amount of the desired material in the correct location is at least one more process, ergo one more thing that can go wrong, raising the production QC failure ratio). Not cheap. Especially when it is potentially one element that gives the driver in question its 'character' in the first place. And we all (well, most of us) know that while we frequently talk until the cows come home about being devoted to whatever we might call accuracy on that day of the week, in practice, many gravitate toward a bit of 'euphonic distortion'. 😉

 

[celef]

i can imagine that cheap drivers are very sensitive to costs in production, but i do not think that applies as much to drivers like the satori's. i believe cone edge damping might worsen some parameters that is more important to them then a linear frequency response, hence they do not apply any edge damping

 

[Scottmoose]

Then you are far off the mark if you think that production cost considerations do not apply to drivers such as the Satori range. I work with driver manufacturers and their staff, owners, distributors etc., and I can tell you, it really does, as a matter of commercial necessity. Standard production drivers, even higher price ones, are not 'cost no object' devices. You can believe me or not of course, that's down to you: I'm simply stating what is in my experience to be the case.

 

[planet10]

Craftsmart Tacky Glue

Hard to say without trying it, but on the face of it seems similar to the Zig i use. Stays tacky if left free to air, but dries more if you ar egluing 2 things together.

dave

 

[planet10]

So, why do the manufacturers not do it? COST, consistency, ageing, chemicals used in production etc

+1

And teh all caps “cost” is a real driving force. Few drivers cannot be improved in some way. What we do that costs say a buck would cost you $10 if they did it at the factory.

dave

 

[planet10]

i believe cone edge damping might worsen some parameters that is more important to them then a linear frequency response, hence they do not apply any edge damping

One does indeed need to approach with caution, one can degrade or even effectively ruin a driver.

dave

 

[planet10]

Then you are far off the mark if you think that production cost considerations do not apply to drivers such as the Satori range.

The only drivers where production cost is not a quality factor are typically horridly expensive.

And driver manufacturers tend to be a VERY conservative lot, not willing to stretch themselves too far.

dave

 

[Scottmoose]

Absolutely. As far as current production units go, there's at best a handful of essentially custom units that qualify under the 'cost no object' banner. Feastrex and Maxonic come to mind. Which doesn't mean the performance automatically lives up to the price, just that they build what they want and charge their small number of clients accordingly.

 

[fatmarley]

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