What is the expected result of ModPodge cone treatment? - diyAudio
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Old 26th April 2014, 06:44 PM   #1
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Default What is the expected result of ModPodge cone treatment?

I want to try the Mod-podge cone-coating treatment. But, the podge has to diluted with water before use and there isn't a set ratio on how much water to add (someone mentioned to get to the consistence of "auto transmission fluid"....) these is a bit of guess work involved, some kind of "feel" needs to be developed I suppose.

So I bought two Quam 8" full-range from a thrift store, will be practicing coating on those before doing more expensive drivers. (Quam's are 8C10FEPAXB industrial/ceiling speaker with whizzer cone, foam surround, supposedly 40Hz to 18k, Fs=50),

How do I know if I have done the coating right? (what kind of change is to be expected when it is done right?) Is it supposed to kill glare/shout or tighten up bass or enhance details? And what is the symptom of too much podge/not enough dilution?

Last edited by audiocats; 26th April 2014 at 06:48 PM.
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Old 26th April 2014, 06:58 PM   #2
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You want todilute it so that it is thin enuff toapply easily, but not sothin that it warps the paper. This takes a bitof experimentation.

The treatment seals the surface of the paper, locking the paper fibres in place & supplying some damping. This reduces cone self-noise and increases DDR. It also makes the conemoreopaque to stuff coming back thru the cone from inside the box.

Use too much and you will attenuate HF. Don't thin it enuff and it is hard to get an even coat. Be careful but quick, with a big cone it will start to dry before you are done, slightly (and i mean slight) wetting of the brush after initial application can help stetch the time you have to get things even.

You might want to start with paper cone woofers to get a feel, they are less sensitive to too much or not even enuff.

dave
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Old 26th April 2014, 08:38 PM   #3
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All well designed drivers do not/should not need any type of coating/treatment (some already have some type of treatment). The way it sounds is the way the designer designed it to be. Use a filter instead or sell the driver and buy something else.

I've ruined two pair of drivers using modgepodge, the result was a dead sound. A thin coat subtly muted the sound and too much turned the driver into a woofer. So, for a hot peaky driver that you cannot give away than this might be the way...

If the compulsion to mod is overwhelming, you may want to try/experiment with dammar or similar type C-37 (natural not poly) "coating." For those small Fostex drivers use only 2 thin applications (about 70/30 thinned) wait at least two days in between applications. The first application should have gone completely into the paper, the second is barely on the surface almost not a "coating." The change was a subtly clearer sound/less papery sounding treble; not more bass or attenuation of shout. I coat most of my cheap Fostex drivers with this type of varnish to protect from mold, mildew, dirt etc. Otherwise, I would just leave it alone.
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Old 26th April 2014, 09:21 PM   #4
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Quote:
Originally Posted by ultrakaz View Post
All well designed drivers do not/should not need any type of coating/treatment (some already have some type of treatment).
Very few of those. And they all already have a coating, so in the strickest sense not a paper cone driver.

Cost is the major driving force behind most driver.

Quote:
I've ruined two pair of drivers using modgepodge
I've killed a few myself, but had WAY more successful ones (literally 1000s of units).

Quote:
If the compulsion to mod is overwhelming, you may want to try/experiment with dammar or similar type C-37 (natural not poly) "coating."
My experience with dammar was that it is useful for some specific applications, but coating an entire cone was not it. It adds too much stiffness and increases unwanted resonances.

C37 works well on some drivers, but it turned out judicial use of mod-podge was as effective at 100th or so the cost.

Quote:
For those small Fostex drivers use only 2 thin applications (about 70/30 thinned) wait at least two days in between applications.
It is not really possible to give an exact ratio of thinning because how much is needed is dependent on how "stiff" the mod-podge starts out at. Fresh stuff does not need anywhere that much, and stuff that does is probably paste it use-by date and suitable only for cheap woofers.

When i 1st started out with FRs i was coming from 25+ years of doing woofers, and used 2 coats, i now use only 1.

Quote:
The first application should have gone completely into the paper, the second is barely on the surface almost not a "coating."
If you are getting it to soak in it is too thin. It should sit on the surface and hardly penetrate at all. I prefer the glossy stuff and you end up with a sheen with 1 coat, and with the white Fostex clones a change in colour towards a parchment colour.

If this is how you are doing it, it could explain the deadness.

Quote:
The change was a subtly clearer sound/less papery sounding treble; not more bass or attenuation of shout.
Yes, yes, no. I have found it quite helpful in taming shout (ie suppressing resonances). In the case of the FE127 some measures to back that up (treatment more complex than just mod-podge thou)

dave
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Old 26th April 2014, 11:13 PM   #5
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thanks for the inputs.

since the chance of messing up at the beginning seems quite high, I bought 4 more Quam's as back up genie pigs (the "50% off Saturday" deal helped triggered the impulse buy as well.....I suppose I can't lose at $3 per).
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Old 26th April 2014, 11:39 PM   #6
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The first coat is done. I only added a little water to the podge before it felt like transmission fluid (less than 90:10) between my fingers.

Could not get an even coat. I did the whizzer first, the entire front surface plus a 1/4" line on the underside along the lip. Then the main cone.....got tiny white foam came out of the sponge, probably should have use a bristle brush instead. Anyway, the stuff was "sitting on the surface hardly penetrating", and it dried pretty quick, about 5 minutes I got a glassy surface, but it is uneven, I can see my "brush strokes", especially on the main cone.

Does the "brush strokes" suggest I didn't put in enough water?
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Old 27th April 2014, 12:26 AM   #7
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I use a regular artist stranded brush, sounds like the foam brush is generating bubbles

I buy the cheap starter packs of artists brushes at Michaels and give the foam and natural fibre ones to the school.

dave
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Old 27th April 2014, 01:59 AM   #8
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Thanks Dave, are brush strokes visible when done right?

After one hour the coat appears to be completely dry. So I put the driver into the test rig (cardboard open baffle..... 16x21.5" ).

the sound seems
--a little softer, a little less bite,
--a bit less glare,
-- bass might have tightened up a little (can't really tell, since the boom is still there, probably from the cardboard baffle . )
-- no change in detail reproduction.

I guess the coat has smooth out the mid range peaks and reduced the top end. The sound is now boarder line too soft (the Quam is a little soft to start with). I will run the driver a little more, then add another coat tomorrow.(turning it into a woofer is not a problem for me. If I ever have to use it I can glue a tweeter to the pole piece and cross over at 4~5k using a film cap).
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Old 27th April 2014, 02:15 AM   #9
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Quote:
Originally Posted by audiocats View Post
Thanks Dave, are brush strokes visible when done right?
Sometimes.

Quote:
After one hour the coat appears to be completely dry.
It may seem so, but i'd leave longer. At least 4 hrs, 24 is better,

dave
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Old 27th April 2014, 04:51 PM   #10
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Brushed on the second coat late last night, let dry over night...

The difference is more noticeable this time.

The second coat didn't kill more highs. The bit is still about the same as one coat, but the sound is somehow more clear and more "detailed" (even the bass has some details now, instead of the old one-note boom), perhaps because it is a little brighter.

I will run it for a few hours to see if the brightness becomes tiring, then I will add the third coat
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