Give Oskar a Wedgie and Heil Smooth Out and Won't Be Such a Dip!

[toddalin]

The dip in the Heil that lies in the 5-6K range has now been well documented. I use the Heil in a 3-way system crossed over at ~2,500 Hz and the dip is readily obvious as shown in the included picture. The mic is about 3 feet from the tweeter in direct alighnment.

Certainly this could be handled using eq if one desired. But I run various sets of speakers and the eq for one set would differ from another, and who could remember all of these or want to deal with them when simpling selecting a different pair of speakers? The obvious answer is that we want every set of speakers to be as flat and smooth in the room as possible without the need for electronic modification.

Then perhaps the dip could be handled with the crossovers. I've spent countless hours in various configurations, but anything of value has a volume penalty and when you are trying to match a JBL 2241H 18" woofer, you need as much volume as you can muster.

But what of a "mechanical" solution. I've done extensive work with the JBL 075/2402 placing a slant plate assembly in front of the tweeter. This not only increased the horizontal dispersion, it took the peak (and "in your face") away routing this energy to the sides. It also increased the low end of the tweeter, undoubtedly through the effect of "loading" it.

So why couldn't something like this work with the Heil?

Well, it just so happens that it can! I initially held an engineering scale up to the tweeter and there was a flattening of the frequency response, in a very positive way!

I decided to make a wedge to the size and shape of the ruler (triangular and 1" on each side) by laying two strips of 1" wide brass strip next to each other on a piece of masking tape and folded it to 60 degrees by lying it between two scales that were taped together. I put superglue along the seam and added a piece of lucite to the inside to hold the shape. This was glued to a piece of 3/8" thick acrylic as a stand and to let the wedge protrude ~0.3" into the "void" to test various distances from the Heil diaphragm. The "void" (plastic ledge between the very front and the diaphragm) is 5/16". A piece of foam was glued to the bottom of the acrylic to take up any slop (not shown).





This piece sits in front of the opening. My testing has shown that I am getting the smoothest response with the point of the wedge right at the front edge of the plastic housing.




And of course the proof of the pudding is in the eating.

Without moving the mic from the past photos, this shows the modified frequency response with the wedge in place. Not only does it remove most of the dip, it flattens the response over the entire range.


So, right after I finished testing/photograghing, this arrived. It is pretty clear to me that Oskar is in for a wedgie.

[SEAWOLF97]

I use the Heil in a 3-way system

Every ESS AMT system that I've seen is a 2 way. I wonder if that has a bearing
on things.

[toddalin]

I got over to the workshop today and used the laser to cut the bases for the wedgies. I was suprised that I got it dead on the first time. I also used the chop saw to cut the lucite triangle and it came out better than I could have hoped for.

The JBL 077 won't have anything on these bad boys!



While I was there I also used the laser to cut the grill cloth frames for the 2251Js. The cloth/screen will be sandwiched between the two pieces and the four holes in the "lower" piece locate magnets to attach to the screws that hold the woofer to the baffleboard.

[toddalin]

OOOH that's a tight squeeze!

[10 Watt Street]

How about a wedge on the back side?

[toddalin]

Well that would make sense as that's where wedgies are typically given.

But I have my terminals back there and they would be in the way of the base. Also, when I held the brass wedge back there, I didn't get the flattening of the curve.