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Tom,
I see this as a very good discussion about the pros and cons of the technique.

I am also experimenting with small solid state Class AB amp modules as part of this as they sound very good indeed. That would not be possible with a planar driver like the RD75 as you point out.

It really is a combination of techniques and trade-off's in any project. You have to pick which you accept and reject along the way as part of the system. A key statement, it is a system, designed to work as one.

What I have to wait for is the 16 output channel DSP crossover to really put this all to use with the larger three way system. I need all 16 to do it the way I want. This is in work, and just waiting on the word it is complete. Then need to finish the 38 amp modules to complete the process. All the drivers are on order, speaker cables are cut and terminated. Need the baffles and tweeters to proceed.

Tom,
Probably the most significant thing I have figured out for any project. At some point you have to make tradeoff decisions and get started.

I am going to make a trip next Tuesday to check on the baffles status. Hopefully bring them home to start installing the Neo10's.

What does comb filtering sound like?

For a vertical array, peaks and nulls in the frequency response as you move your head up and down.

Roscoe

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I can explain it to you, but I can’t understand it for you.

for a particular freq, is so how is that determined
how can you tell its just not standing wave peaks or suckouts fron room dimension

If you move your head around at the listening position you would hear variations in the response. It can happen with room acoustics, so hard to separate with that method.

Another way is with speaker measurements that require multiple measurements at different vertical locations and compare responses. The frequency response looks like a comb teeth, hence the term.

Does that help?

Yes thank Tom for a meaningful and simple answer
When I play a single freq tone it easy to hear the level very as I move my head around even very short distances, it always surprises me to hear this effect.

Ummm.. I am not Tom, I am Rich.

It is normal when you move your head around in a room to hear significant amplitude changes at a single frequency especially at higher frequencies. That will occur even with a single driver where comb filtering cannot occur. That is due to room effects. They are sort of like comb filtering but the reinforcing and cancelling waves are caused by reflections not a separate driver. The physics are the same. They call it room nodes when it is the result of a room and comb filtering when it is caused by separate drivers next to each other.

With a multi driver speaker to determine if the problem is the room or speaker the best way is to do quasi-anechoic measurements with a maximum length sequence (MLS) pulse and use a window in the time domain to eliminate reflections. You can then move the mike to different positions to see if the curves are the same. Other than roll off caused by polar response changes the curves should be the same. If you see other anomolies they are most likely caused by interference between the drivers causing peaks and nulls. This is comb filtering because at a fixed inter-driver distance the different frequencies will cause either reinforcement or cancellation depending on the wavelengths vs distance much like room boundaries. If it is comb filtering the differences will be greatest as you move along the the line connecting the two drivers and not along the line perpendicular to that center driver axis. Although not a very simple explanation, hopefully it will give you a better understanding of the mechanism of the problem and how you can identify it.