Surround Dope

[gearhead63]

If you use some of the water-based doping let us know how it it works. I've never used a water-based adhesive on a speaker cone.
Before finding the Springfield doping, I've used rubber glue etc. to repair small puncture wounds etc, even super glue gel to put a small piece of material over a tear.
But I'm interested in what you find out.

[potatofarmer]

Here's a picture of the clump of Super-Tac. The white in the middle is trapped water, I assume. It's pretty stretchy stuff, feels almost like silicone but stiffer and more rubbery. After a few days of me playing with it / stretching it more of the white has become transparent. It's also interesting to note that I started making another one of these, coating the bottom of a canning jar with coats of the 2:1 thinned Super-Tac and the new layers were lifting and dissolving the old layers. It looked a bit like when scrambled eggs first start to firm up, but then the...curds? redissolved. I'd read this was a possibility with some EVA emulsion glues, but who knows if that's what happens when it's absorbed into paper.

I don't think I've mentioned this yet, but hot-glue guns use sticks of EVA, though in different formulations with stiffeners and what not. This definitely is more elastic than what comes out of a hot glue gun.



And here's a shot of ~5-6 coats of the 2:1 thinned Super-Tac (25mL glue, 50mL water). This speaker cone material really soaked it up; I doubt it discolored the other side of the paper but it's definitely more absorbent than the old Utah cone I was testing it on. I tried it briefly last night and compared to an identical un-doped recone it has slightly stiffer bass response, slightly reduced sensitivity, and the un-doped has a little cone cry. Seems like it's doing what doping should, so I'm going to leave it alone and see if it stiffens up with time. These speakers also haven't been broken in yet, so I have no idea what the final sound is going to be or how much doping I should target.

I don't have a reference mic (nor an appropriate space in which to measure frequency response & sensitivity) but I might try to measure T/S specs on both woofers before I dope the other one. These are the things I do for fun. I think I'll save the butyl investigation for after the spring thaw.


Anyway, big summary: Thinned EVA emulsion glues show potential as a DIY water-based surround dope for paper surrounds.

[gearhead63]

Interesting. Hey, you can download TrueRTA and install on your pc. I use it to generate signals for signal tracing if I'm not at my electronics bench.
I have REAL oscilloscopes and Sig Gen's, but this works ok. It has a spectrum analyzer that you could possibly use to see the change in response.
BUT, you have to keep microphone placement EXACTLY the same etc. I don't have a flat response microphone, so the only good it does me is a comparison to another unit. You might check it out. If you want to be sure of the signal generator actual output voltage you need to do the calibration. And you can download Lightshot and use it to capture the screen. It works very well.
Just a thought so you have a semi-real idea of what it's accomplishing.

[gbono]

In the second picture did you coat the cone and surround with the 2:1 mixture? I'm looking for a refresh solution for discolored (sun dried) cones.

As far as acoustic measurements go.... not a trivial undertaking to do correctly. You can do a very close mic measurement for low frequencies (under 200Hz) and then measure broadband "outside" on say a roof top in the morning (use averaging). The trick is stitching the data together without adding artifacts to the data/info. You need a good mic and DPA and B&K have them but they are $$$ - traceability/calibration are necessary to get accurate and repeatable SPL numbers. Then there is the accelerometer method................

[potatofarmer]

Interesting. Hey, you can download TrueRTA and install on your pc. I use it to generate signals for signal tracing if I'm not at my electronics bench.
I have REAL oscilloscopes and Sig Gen's, but this works ok. It has a spectrum analyzer that you could possibly use to see the change in response.
BUT, you have to keep microphone placement EXACTLY the same etc. I don't have a flat response microphone, so the only good it does me is a comparison to another unit. You might check it out. If you want to be sure of the signal generator actual output voltage you need to do the calibration. And you can download Lightshot and use it to capture the screen. It works very well.
Just a thought so you have a semi-real idea of what it's accomplishing.

If I were going to do that, I'd probably just record white noise going through the speaker with an SM-57 and run an FFT on the recordings. It would be terrible in terms of absolute frequency response and sensitivity, but comparing the two might provide some qualitative data.

In the second picture did you coat the cone and surround with the 2:1 mixture? I'm looking for a refresh solution for discolored (sun dried) cones.

Just the surround and down to the first rib. I was debating stopping before the first rib, but the rib distracts from the sloppy glue line. This stuff is basically clear especially for the first coat or two but I'd be worried about adding weight to the cone. It doesn't take much to permanently alter the performance, and generally not for the better.

Personally, I would just leave the cones alone, but Parts Express sells a product called "The Wet Look" for this purpose - it has 0.2% ammonia, which leads me to suspect it's black liquid latex. It has mixed reviews around the web. You can only thin emulsions so much before they separate, so I would suspect that has a good deal of solid load in it.

If you decide to give it a shot, post it! I'd probably try adding some water-based dye and keep the coats to a minimum.

As far as acoustic measurements go.... not a trivial undertaking to do correctly. You can do a very close mic measurement for low frequencies (under 200Hz) and then measure broadband "outside" on say a roof top in the morning (use averaging). The trick is stitching the data together without adding artifacts to the data/info. You need a good mic and DPA and B&K have them but they are $$$ - traceability/calibration are necessary to get accurate and repeatable SPL numbers. Then there is the accelerometer method................

Yeah, I imagine this is why so many "guitar speaker" manufacturers don't bother.

Oh god, why did I have to google "accelerometer speaker measurement"... nope, tempting as that is, I don't quite care to know that badly.

[dai h.]

vaguely remembered discussions about speaker repair glue, saw this:

Jensen Speaker - advice needed

then this:

https://www.youtube.com/watch?v=lxGswEB3O_Q

and FWIW, there is a mention of using black Permatex silicone adhesive sealant (which appears to be this stuff) :

Sealants : Permatex® Black Silicone Adhesive Sealant

(haven't tried this so can't vouch for its usefulness, etc.)