One of the assumptions of a Linkwitz Riley 4th order network is that all of the driver acoustic centers are aligned in the z-axis. This assumption was met in the 4430 from what I remember, and the woofer and midrange appear close to being aligned in the S9800 cutaway drawing. Now it is more clear why the 045 is offset in the S9800.

Is this comb filtering problem something people are willing to accept? I don't think the project would have much appeal if it requried digital delay for the supertweeter. Recessing the 045 into the cabinet would likely cause more problems than it would solve unless someone came up with a really creative solution. Also remember that it is best to keep the woofers as close together as possible in an MTM and that the vertical height of the horn/supertweeter assembly is currently 12.5 inches.

I already attempted to add another 180 degrees of phase delay to the 045 by crossing it with a 6th order acoustic network at 10kHz but it didn't solve the comb filtering problem because of the high frequencies involved.

I listened to the MTM with the newest crossovers today, and the high frequencies sound too bright. However, it wouldn't be a problem to add some downward sloping response when I do the system optimization. Based on conversations with others who have built MTM's, they tend to sound bright if they have ruler flat response, so most people add some downward slope or a dip at 3kHz. Then again it may just be my room.
 

According to JBL's Greg Timbers: "The comb filter effect is normal and cannot be eliminated, even with the use of electronic delay. The wavelength at 10k is an inch or less and even if the 045be were delayed to the z plane of the 435Be, even the slightest movement up, down, left or right of the measurement position would change the relative path length between the 435Be and 045Be to where the interference pattern would return.

What I have done is use a 4th order on the 045Be high pass and adjusted the values using substantial smoothing on the frequency response curve. The polarity does seem to matter in getting the smoothest "smoothed" curve.

I originally had the 045Be coming in where the main 435Be cuts off (15k) which cost less parts, but we could hear the 045Be as a separate location and it was distracting. I found that 8k - 10k minimized this effect. In spite of the curve, we have had no negative comments about the 045Be and the choppy response through the crossover range."
 

If Tim will ship the pair of H9800s and drivers along with the bat slayers (045Be) I will whip up a pair of combined horns that will be suitable for listening tests and basic aesthetic study. They will be machined and carved plastic in an MDF frame. (Trust me they will look pretty close to factory, a bit more time and they would look factory.) If I got them by mid week, I can turn them around by the end of the weekend. I will also incorporate a sub enclosure that will be structural so that the 1500AL enclosures can stack on the mid and high horns.

There is no way I can fabricate a pair of wood combination horns in less than several weeks. I am not willing to make more than one pair of them so we will need the industrial design to be locked in before I begin those.

As for the industrial design, if we could get the dimensions of the front layout, i.e. woofer spacing and height of the centerline of the H9800 from the floor that would be very useful.

Once armed with that info I can go back over all of the previously posted drawings and sketches that have been posted by myself and others and put them together in a more coherent form to aide the design process and get the ball rolling again.