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bwaslo 10th August 2016 02:39 AM


Thanks, that is a good tip, hadn't thought of that! It would be a bit more confidence inspiring than the plumber's putty for the long-term. I'm not really worried about it falling out (it is in there quite firmly, but I don't like wondering whether the liquid in it might leach out over time into the cones)


Patrick Bateman 11th August 2016 12:51 PM

I'm not sure if bondo is a good idea. I've built a few Synergy horns using the Pyle and QSC waveguides, and I frequently had the following issues:

1) Over time, about half of my midranges died. The reason they died was that I didn't leave enough room for the the woofer's excursion, and the surrounds ripped.

2) The mounting plates for my midranges frequently fell off. This is because the mounting plates would delaminate from the waveguide. This was a problem with the QSC in particular, there's something about the plastic they use, it's very difficult to get anything to bond to it. Eventually I gave up on trying to find a good adhesive, and I simply ran bolts all the way through the mounting plate for the midranges right through the horn walls. But that's ugly and probably causes diffraction.

3) Any type of shrinkage in the adhesives tended to cause issues. This is why I'd stay away from Bondo - it shrinks when curing. IIRC, epoxy doesn't suffer from this as much.

Hope that helps. 3D printed waveguides and wooden waveguides mostly avoid these pitfalls.

nc535 11th August 2016 02:08 PM


Now you tell us :)

Adhesive issues aside, I think Bondo still works for taking up dead air space.

winslow 11th August 2016 03:55 PM

I would never ever ever use Bondo brand body filler...or anything. Horrid stuff.

If you are using body filler, something like Rage Gold Extreme sands like butter. But it won't stick very well to plastic even if you use an adhesion promotor. Though a putty would sand even easier...but not meant to be real thick.

Use some SEM (or similar) Problem Plastic Repair. Can get it or similar at an auto body supply shop. It is made to bond dissimilar plastics of unknown compositions.

Eldam 11th August 2016 05:43 PM

EVA shaped with heat gun, then glued to the horn and a wood plate for the speaker ?

EVA foam from yoga carpets is cheap and can be found in several density easily ?!

There are also a lot of foam tubes for isolation in many several diameters ?!

Good enough for a band path shape for the mids ?

deanznz 11th August 2016 10:16 PM

Winding in a few short screws into the waveguide before applying a filler/epoxy could give the filler some thing to hang on to.

bwaslo 11th August 2016 10:38 PM

On the SEOS15, at least, just scratching up the horn's outside surface with a rough file or rasp gave it good adhesion to the epoxy putty. On earlier ones I did, I also drilled shallow holes into the plastic before adding the epoxy (the walls on the SEOS15 are about 0.35" -- 0.9cm -- thick). I haven't tried prying off the epoxy, but accidentally dropping one of the horns on the floor didn't break the connection between mounting plate and horn. Probably if I were making speakers commercially or for mobile PA work I'd look into something more secure, but for home use I have no fear at all about the bond coming loose.

grec13 13th August 2016 01:09 AM

1 Attachment(s)
I tried fiberglass.
It works for 6.5 woofers, but for 4" perhaps, its too risky.
The cone is too tiny, not gonna to survive the processes.

bwaslo 13th August 2016 01:56 AM

That looks good for phase plugs, but I'm not really doing phase plugs, just filling in the gap between the (not quite flat) horn wall and he cone. The volume in the cone itself is still left empty.

Of course there's always paper mache.

SMathews 13th August 2016 09:55 AM

Side attachment
Hi Bill
Is it possible to attach the mid-ranges to the side of the horn instead of the top? Thanks.

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