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Old 16th February 2002, 02:11 PM   #1
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Question Epoxy covered crossover??

I like to make speakers but must admit I'm not up on every tweak. Does anybody out there cover their XO's with epoxy or know of a commercial builder that does? Is this a common practice? Why? I've been told that it is and I cannot figure out why? I mount mine externally so they can be as easily tweaked as possible.

I've torn apart a number of speakers and have never found this. Am I just out of the loop?

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Old 16th February 2002, 02:18 PM   #2
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Could be to hide the values of the cross-over components, so it's more difficult to reverse engineer. Potted circuits were discussed in another thread. Someone brought up this possibility. Search for potted circuits.
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Old 16th February 2002, 02:27 PM   #3
Helix is offline Helix  United Kingdom
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sometimes on cheaper units, Either
a) the soldering/construction is a bit dodgy so they do it just to prevent the components falling out with transporting etc
b) the production managers sees it necessary in case the soldering is dodgy!
c) it also could be used as 'snake-oil' to reduce microphonic effects!
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Old 16th February 2002, 03:28 PM   #4
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As I remember correctly Wilson Grand Slamm have potted crossovers.
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Old 16th February 2002, 06:33 PM   #5
arnach is offline arnach  United States
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Default Well

It's done in alot of mid-fi speakers.

Mainly as a cheap way of reducing vibration.

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Old 16th February 2002, 07:13 PM   #6
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Angry Epoxy, Snake oil, and vibration

Ah, another learned disscussion...... Potting is not a cheap way of doing anything. Most crossover parts are soldered to a PC board or fiber board and tie-wrapped or glued to the board for the parts mechanical mounting. Mid Fi speaker with potted crossovers? I have yet to see one. Potting would be a GOOD IDEA for inductors since the winding can move under signal forces and from speaker vibration. Get an inductor moving in the stray magnetic field from a driver and you have error signals crossover nework. This is why many high end designers are starting to mount the crossover external to the speaker. By the way I have modified speakers including Theils, Magnaplaners, Duntech, Infinity, and B and W. What have you guys taken apart?

H.H.
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Old 16th February 2002, 07:47 PM   #7
arnach is offline arnach  United States
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Default Thanks

Ah, another learned discussion. I was referring to epoxy coating. It *is* cheap to do. For example, you can find it in almost all of Mirage's <$1000 speakers.

Oh, and HarryHaller, thanks for letting us know just how qualified you are. ;-)
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Old 16th February 2002, 09:13 PM   #8
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Epoxied (or Hot Melt Glue'd) X/overs serve two purposes, one; to keep the components in place and, two; as another post suggested quite rightly, dampen the intrisinic resonances in the inductors and especially caps as Tannoy research about ten to fifteen years ago found to be particularly effective on not just BP caps but also plastic film regardless wether polyprop/polyester etc, construction was used. These resonances however minute build up as the signal passes through the components regardless wether mounted in the box, where physical vibration adds to the problem, or wether mounted seperately outside which is preferable. It has also been suggested (by others) as close as possible to the amp so that the x/over is driven almost directly rather than a long run of cable leading to it... The effect it seems is a bit akin to bi-amping without an extra amp...
Make of this last bit what you will as I have not had the opportunity to try it myself yet so I can not verify it's effectivness, but it seems logical and worth experimenting with as is mounting the x/over in an alloy box to isolate it from stray electromagnetic fields around components and power cables etc...
tomcat
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Old 17th February 2002, 11:24 PM   #9
Helix is offline Helix  United Kingdom
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a few thoughts. having the crossover in the amp isn't like bi-amping, more like bi-wireing. To say that this would be better then the more common form of bi-wireing is up to the reader
Putting the speaker crossover in a alloy box doesn't have much point as induced electromagnetic fields are so small they won't drive the speaker at all! However, if it was a active crossover (ones that x's the signal befour the amp stage) then this would be an entirely diffrent matter.

Also, is putting hot glue on those polyprop/polyester caps O.K? i know polyester caps are quite sensitive to their surroundings
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Old 18th February 2002, 10:26 AM   #10
dice45 is offline dice45  Germany
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Default Re: Epoxy, Snake oil, and vibration

Quote:
Originally posted by HarryHaller

... Potting would be a GOOD IDEA for inductors since the winding can move under signal forces and from speaker vibration. Get an inductor moving in the stray magnetic field from a driver and you have error signals crossover nework. ...


Hello Harry and all,



maybe a bit off-topic .... from a Sound Practices article and later from discussions on the JoeNet i faintly remember that potting of inductors, particularly iron-cored inductors and transformators has heavy pros and cons and some manufacturers refuse to pot, some love it. You named some pros, one i'd like to add is making an inductor with unusual, non-standardized shape like C-cores mountable at all, the cons i remember are unwanted stray capacitancs lowering eventual resonance frequencies and thus limiting the usable bandwidth at the upper end and reducing the stacking factor (the potting compound creeping between windings and laminations) which leads to increased excitation current and decreased inductivity which limits the bandwidth on the lower end.



Dunno how significant these effects are however and maybe i should add that my preferred OPT from Tango all are potted, those from Lundahl are not but impregnated with epoxy. Both are C-cores with ultrathin laminations however.
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