Dear @hleeid : "" I am still a newcomer to this hobby and am beginning to realize just how much there is to learn about these things. """
In audio always there is something to learn and speaking of subwoofer subject a lot to learn/understand.
First is to understand why with passive speakers we need subwoofers, second if we are listening music in HT fashion or just stereo music and third the bass range quality level we want it.
If you mainly listen MUSIC ( stereo system. ) then please read with care this post:
https://forum.audiogon.com/discussions/do-you-think-you-need-a-subwoofer/post?postid=310058#310058 Listening to MUSIC what we need is a good overall quality room/system at one seat position.
As a fact main speakers mid and high frequency ranges can have only one seat position where both frequency ranges are " optimal " and what we want is that the bass range be " optimal " too.
Now, your speakers small woofers handle a frequency range that goes ( -3db. ) from 48hz to 2khz and works down to 32hz.
That frequency range that handle those small woofers is really wide and makes that the Intermodulation Distortion levels in the speakers goes really high ( in that link is the explanation about. ) and this is the main reason why you need subwoofers that at the same time gives you not only a lot better quality room/system reproduction from your speakers ( midrange/high range. ) with lower overall distortions levels but now you will have at your seat position that really elusive and critical bass range, not boom boom but a true quality bass range and for this you need that the subwoofers bass range goes lower than 20hz that is where belongs a true subwoofer ( With all respect the ones in the link that other gentleman posted are not true subwoofers due that goes down only to 24hz but neither the ones that comes in the post speaking of 4 subwoofers. Both advises can’t give you the third characteristic I mentioned before: bass range quality. The kind of bass range at one seat position of those advises are rounded in the mediocrity/average. Perhaps in a dedicated thread I can explain to those gentlemans the real meaning on what I’m posting here. ) and that the subwoofers gives you a lower self distortion levels: you are looking for quality not only bass, at least is my understanding for what you ask. Of course that I can be wrong.
For just MUSIC it’s worth to invest in good quality pair of self powered subs with kigh pass filter. No, not 8k and you can find out true high quality subs in second hand market even here in the Agon list advertasing.
But if you want the subs mainly for HT then things are different because the HT overall need it quality is different too and had several seat positions. HT needs are different from just stereo MUSIC listening.
Regards and enjoy the MUSIC NOT DISTORTIONS,
R.