Hello ihor,
I would suggest running all three subs in mono and adding a larger 10 or 12 inch sub for your third sub would be the best choices.
There are virtually no current or past music recordings in any format (vinyl, cd or hi-rez files) that contain stereo deep bass, all of the bass below about 80-100 Hz is summed to mono on the recordings since humans are unable to localize (tell exactly where the bass is coming from) on bass tones below about 80-100 Hz.
Even though all three subs are outputting mono bass, you'll perceive the bass as a form of stereo bass, with the sound seeming to come from the proper bass instruments within the soundstage illusion ( for example, the drums are located in the center rear of the soundstage and the upright acoustic bass is located in front of the drums and off to the left.).
This is because, even though the fundamental deep bass tones below about 80-100 Hz coming from the subs will not be able to be localized, the related bass harmonics or overtones of the fundamental bass tones coming from the main speakers are able to be localized (since they extend above the 80-100 Hz limit). Our brains are able to associate the higher frequency bass harmonics/overtones with the much lower frequency bass fundamental tones and thereby determine where the much deeper fundamental bass tones are originating from. This process is one of the principles of he science of psychoacoustics (how our brains process sounds and form perceptions).
Having a larger 10 or 12 inch sub as the third sub also relies on psychoacoustics and will give the perception that the overall in-room deep bass response has been extended a bit deeper.
Proper positioning within your room and the proper setting of the volume, crossover frequency and phase control of each sub are very important for optimizing bass output in your room and integration with your main speakers.
Tim
I would suggest running all three subs in mono and adding a larger 10 or 12 inch sub for your third sub would be the best choices.
There are virtually no current or past music recordings in any format (vinyl, cd or hi-rez files) that contain stereo deep bass, all of the bass below about 80-100 Hz is summed to mono on the recordings since humans are unable to localize (tell exactly where the bass is coming from) on bass tones below about 80-100 Hz.
Even though all three subs are outputting mono bass, you'll perceive the bass as a form of stereo bass, with the sound seeming to come from the proper bass instruments within the soundstage illusion ( for example, the drums are located in the center rear of the soundstage and the upright acoustic bass is located in front of the drums and off to the left.).
This is because, even though the fundamental deep bass tones below about 80-100 Hz coming from the subs will not be able to be localized, the related bass harmonics or overtones of the fundamental bass tones coming from the main speakers are able to be localized (since they extend above the 80-100 Hz limit). Our brains are able to associate the higher frequency bass harmonics/overtones with the much lower frequency bass fundamental tones and thereby determine where the much deeper fundamental bass tones are originating from. This process is one of the principles of he science of psychoacoustics (how our brains process sounds and form perceptions).
Having a larger 10 or 12 inch sub as the third sub also relies on psychoacoustics and will give the perception that the overall in-room deep bass response has been extended a bit deeper.
Proper positioning within your room and the proper setting of the volume, crossover frequency and phase control of each sub are very important for optimizing bass output in your room and integration with your main speakers.
Tim