Mounting tweeter behind baffle

[Saurav]

I had a crazy idea today. Open baffle, ribbon tweeter (Fountek JP3.0). This mainly arose from wondering how to flush mount a tweeter with a circular faceplate and a rectabgular cutout without buying a router. And then I had the idea of mounting the tweeter behind the baffle. That way I could keep the opening to the size of the ribbon. Maybe angle/roundover the sides of the 'slot' too. If I measured it right, I could get the baffle cutout to follow the angled sides of the faceplate where it meets the grille.

Is there any value to that at all? Or are there strong reasons why I do not want to do this? Could/would any potential resonance issues swamp any improvements in directivity?

[ThomasW]

You'd be making a 'horn' or waveguide'. If that's what you want fine.

Maybe it's time to buy a router since your horn or waveguide would benefit from having smooth and symetrical transition......:wink:

[Saurav]

Yeah, I thought about that too. It's not easy doing a roundover with a router attachment on a dremel

And yes, it would be a shallow waveguide. This is purely handwaving, but I think that might help with dispersion control, especially since the midrange is on the same open baffle, and will probably have narrower dispersion than the tweeter by the time it reaches the crossover frequency.

[Amphiprion]

DREMEL??? Egads. Go get that big Hitachi or the equivalent Porter Cable

I've used the Morel MDT-37 before, and it has an odd rounded-over short horn / dispersion control faceplate. Never any diffraction effects no matter where you drop it on the baffle, and they've done very well to eliminate any "horn" sound. It did have a tad bit of bite on some stuff, but a little crossover tweaking and response contouring took care of that (or maybe I just stopped noticing it).

[jonathanb3478]

Yeah, I thought about that too. It's not easy doing a roundover with a router attachment on a dremel

Seriously, if you are building pairs of speakers (not just a single pair, never to DIY again), you can live with out some tools. A router is not one of those tools, however.

The Hitachi that Mark references may be the M12V. It is a "3.25HP" (read: 15amp on 120VAC) pluge router, that is periodicaly available for <$150, even down to $120 on occaision. That is so worth it it is scary. "Penny wise, pound foolish" seems appropriate regarding not investing in a router for speaker making. How much is your time/sanity worth?

I got my Dewalt DW625 (basically the same specs, 15amp, as the Hatachi) for $213, and I am very satisfied with that purchase. If I could have gotten the M12V for $118 off Amazon a while back, I would be well beyond "very satisfied".

EDIT: Looks like Amazon has the M12V for $144, and mine is down to $213 again, due to the SAVTENPTJUNE coupon code availale through July 4th.

[Saurav]

Well, this is most likely going to be my last pair of speakers for a while. But... I've said that before

If I do get a router... how does one make a cutout like this?



(The tweeter cutout on the right photo).

[ThomasW]

Make a template out of masonite.

Then use either a pattern cutting bit, it has a bearing that follows the masonite,



Or buy a set of template inserts and use a regular bit. I find using these a pain...

[Amphiprion]

I used the template method to make the woofer cutout on this baffle:

http://www.hayenga.com/mark/speakers/hds/newHDSbaffle.jpg

It worked pretty well.

[Saurav]

Or maybe I'll just surface mount the tweeter

So the template ensures that the bit follows the outer edge of the cutout, and the central part where I need to remove all that wood, I just freehand that, and the bit takes care of removing what it needs to remove? I'm not concerned about the rectangular portion, I can jigsaw that if necessary. What I don't know how to do is the flat top part where the material has been 'shaved' of (for want of a better word).

[ThomasW]

Each different cut requires a template or freehand cut. If you just want to recess drivers grab a Jasper Jig or other similar circle cutting jig.

[Saurav]

And then make multiple passes with the router, reducing the radius each time? On the sides, there's a pretty large width where material has to be removed.

[ThomasW]

Yes use a wide flat bottom bit 3/4" or so, and decreasing radi

[Saurav]

Thanks.

[PMazz]

Another alternative is to surface mount the driver and add an 1/8" or 1/4" piece of masonite with the hole cut out to the face of the baffle.

Pete