Similar to the famous sexist tail that women can be only ether pretty or smart the midbass horns unfortunately behave in the very same way: they can be only nicely placed in a room or they can sound good. You want the horn to place in a specific location of your room as it feel good for your house décor and living habits and it turns out to be the worst location for them from the perspective of About speakers Imbedded Macro-Positioning. Sucks!
It looks the acoustically the default location of your horns is not the best in your room.
I would discard the first two images with both horns playing they are irrelevant at this point. Let look at the image 3 and 4 from above: Left wall and Right wall. It is very clear the right wall is much more interesting from upper-bass Macro-Positioning pint of view. You see the response is more dense and with much more significant LF. Those minor differences in decay at the bottom knee are VERY auditable. I would like to be able to see the grid better, the horizontal lines to see detail but it still is very obvious. Still, you alternative wall position might not be the best in the room and you might have even better location. I do not know how the acoustically better locations are better from the perspective of your living objectives.
Anyhow, let see what you have with your upperbass and what you can do. The usable image would be the third from the top (it has no number). That is OK response but you need to set a proper reference level for this channel. This is VERY important. Let me to explain what I mean. If you look at the response of the horn then probably the gray line on my image below would be the channel reference. It means the other channels need to be balanced to the gray line. What you need however to do is discard the response of the channel and to set the reference level that you would it to be. I would propose a few dB lower. Take a look at the yellow line that I feel much be you reference level:
Looking at the yellow reference line you will see that horn overshoot it but do not let it to bother you. If you implement let say 450Hz filter and add 2-3dB of the upperbass out then you virtually increase the output of your m upperbass in the frequencies that you are looking for. Be advised that you will have a LOT of problems to do it as it is very hard to low-pass of this driver with speaker-level crossover as the coil the crossover will talk with inductance of the driver and combined coil will be much lower. You would need to use a coil 3-4 times larger then what calculation would suggest but this overly large coil would talk too much with your MF channel. Multi-amping will kill the problem and the crossover in the amp will not be seeing the driver inductance. Using the speaker level crossover you need to use larger coil.
So, you roll off the upperbass sooner then the channel would like you to do and boost 2-3 dB of the channel’s gain. You might not have those 2-3dB driving the thing from a single amp. To get 3dB more you will need to go to another tap but it would make the output tube to be loaded harder at the frequency of given channel and might make the sound too slow. Also, do not forget that you use first order filets and change of the loading for a given channel will very much affect loading for other channels, the last picture shows it very well, in fact ML2 with feedback handles it much better then other amps would do. So, what you need to do if you need more gain but do not have it? You need to drop the level of your other associated channels. It would not be a good idea to do it for bass channels as adding resistors would affect damping. However for HF channel adding resistors (dividers or juts single resistors) would be fine. Find a non-inductive resistor (very important) of a few watts and use it with your MF driver, driving it for a few dB doe and matching your yellow reference line. Do the same with tweeter and fundamental channel and your will have proper upperbass balance for your system.
I do not know what kind bass your use but add the LB channel to the mix (still using the NEW yellow line as reference). Then you would need to do a very important thing- to fine tune what would be your Yellow Reference Line (YRL). At this point your YRL is purely arbitrary but you need to bind it to you room. Here are some techniques that you might find useful. Shut down your fundamental channel (still ONLY for one left or right channel) and use ONLY MF and Midbass to get the sound that you feel is right. It shell be a proper balance between the violins/violas and cello section in complex (very important) music. I uselessly use Vein or Berlin Philharmonic only for reference balance; use what performance you fine is right for you. After you set up your MF and Midbass and feel that you have attenuated MF good enough to have proper balance then add bass channel. If your MF/Midbass balance is correct then running your bass channel a few dBs lower then YRL or higher YRL shall NOT make you to wish to change the MF/Midbass balance. Do the same with tweeter and then with tweeter and bass. After you do feel confident about your MF/Midbass balance than begin to inject your Fundamental Channel. Start it from 15dB down and begin to add it (check the phase) very slow until you begin to recognize the very first sighs of it auditable contribution. The auditable contribution of Fundamental Channel will be partially from the Channel itself and partially from the fact that the Channel will affect the response of you Midbass Channel. It is not predictable and you need to play with it for a bit. Disregard the measurable date you will be getting at this point. Remember, you MF/Midbass balance is all set and you now need to see if adding of your Fundamental Channel will be able to compromise your feeling about the MF/Midbass balance. This is a bit tricky and you would need to spend time with it. The key in here is to find out HOW the use of Fundamental Channel will revise your view of MF/Midbass balance. You might decide to change the MF/Midbass balance (via the MF resistor) while you are begin to use Fundamental Channel but at this point it will be very minor change, no more then .5dB.
The result of all of it shall be your confidence that your MF/Midbass balance is proper for the given location of your Midbass channel in the room. A pair of Midbass Channels shall be loading the room with thick and “crowded” sound, acting as a virtual pedal point for your MF. The channel shall also to unload it from the room with proper speed but not faster than it has to. You need to have some music that has the “cello crash” and you need to make sure that your room will be “dramatically” loaded but not over-loaded and will very “gracefully” release the load. Ironically, if everything is done poorly then the “drama” and the “grace” will not fluctuate from volume too much.
When you reach the point where you feel you somewhere near the proper MF/Midbass balance you need to think about your sound not as it a playback but as you are conducting a live orchestra and it is your responsibility to shape the balance in a way you feel it need to be. If you feel that your best MF/Midbass balance would be different at different recordings then you do not have proper MF/Midbass balance yet. The MF/Midbass balance of your system shall be more accurate than any random orchestral balance out there. Then your playback system becomes a reference against which all orchestral and recording deviations will be measuring. You personally shall have absolute confidence and supreme believe in your MF/Midbass balance. If you go in future for multi-amping then do not forget regularly check the outputs your amps (tunes are not stable) to make sure that your MF/Midbass balance still hold a reference level.
Rgs, Romy the Cat
"I wish I could score everything for horns." - Richard Wagner. "Our writing equipment takes part in the forming of our thoughts." - Friedrich Nietzsche