* I'm talking about Organteq 2

However, I'm noticing this problem around the C below middle C or lower, so around as high as 128 Hz (EDIT: the fundamental).

Also brilliance and presence are in the highs - presence around 1 to 4 KHz and brilliance above 4 KHz (EDIT: here I'm referring to the overtones/harmonics).

A lot of virtual instruments lack brilliance compared to real instruments, but the higher notes in Organteq are great. No model is perfect. A lot of sampled instruments lack brilliance, too. I mean by comparison to live instruments, or a good recording of live instruments, especially a high sample rate or DSD.

I was wondering whether the box size, in the model, affects this. I tried changing it and didn't notice much change in the sound.

I'm new to Organteq and I'm not an organist, so I'm just playing it as best I can.

Usually I pull up a few stops and improvise to get a feel for the sound. I'm always playing on the Great keyboard with my one MIDI controller.

I've noticed that no matter what stops I select, the lower notes lack "presence" and "brilliance" compared to the higher notes. So counterpoint, for example, when the hands are more than an octave apart, sounds unbalanced.

Is this inherent to Organteq or is there something I can do to fix it?

The "presence" and "brilliance"  of the low notes depend very much on the speaker system you use. If you test Organteq on a computer with integrated (or small external) speakers, the quality of the bass will be very poor. Note that some Organteq presets have stops whose lowest C plays a fundamental frequency of approximately 16.35 Hz (corresponding to a 32-foot pipe)!  Most Organteq presets have stops with a 16-foot pipe whose fundamental frequency is 32,7 Hz. This is still very low. You need big/powerful speakers with strong low bass to hear these tones.  Our Organteq setup has two front speakers which can go down to 30Hz, and two powerful rear subwoofers which can down to 30 Hz and 20Hz respectively (or even lower).  As you see in the following video, the low notes are quite present, but, in order to see it, you'll need again good speakers:

https://youtu.be/mKgrFxqCdD8

Best regards,
Andrei

Usually I pull up a few stops and improvise to get a feel for the sound. I'm always playing on the Great keyboard with my one MIDI controller.

I've noticed that no matter what stops I select, the lower notes lack "presence" and "brilliance" compared to the higher notes. So counterpoint, for example, when the hands are more than an octave apart, sounds unbalanced.

Is this inherent to Organteq or is there something I can do to fix it?