Downward firing speaker port and domestic issues

tenant or your own space below: nix to downward firing bass drivers or ports.

nix to wanting a lot of bass when the space below is used, thus tone controls might help when those spaces are occupied, out of circuit when below is unoccupied.

isolation decoupling speakers from floor probably needed. you could start with a set of 2x2 isoblocks. many swear by townsend iso platforms.

I've installed corporate  fitness centers with occupied space below: add separate  'floating' floor on absorbent blocks, small ramp up.

In my experience, it matters not at all where or if there is a port or a passive or if a sealed box.  Bass goes everywhere, if you have it.  Your best bet is to either luck out with an elderly hearing impaired neighbor, or to get a really nice pair of LF challenged compact monitors and a sweet EL84 amp to drive them.  Black Ice F11 for example, with a pair of LS50s or similar.  Keep the volume down and enjoy.

Not sure whether a down firing port will bother your neighbor more or less than a front or rear facing port or a sealed box—probably makes little difference relative to the overall bass output of the speaker. The more air the speaker moves the more trouble your gonna have with your neighbor. Decoupling from the floor will help so tweaks of this sort are worth exploring. FWIW I have never heard a speaker with a down firing port that provided quality bass—muddy, loose, slow, lots of overhang.

Decoupling your loudspeakers from the floor will help both sound transmission and the sound of your loudspeakers, although you may still need to moderate your volume when your neighbor is home. I recommend the Auralex iso platforms from personal experience. The "Subdude" models will work fine for full range loudspeakers and are not expensive.

I hope this helps!

To address this issue, we need to address the topic of "bass". Your sitting comfortably at home and someone drives by with a rather loud and obnoxious car stereo. The bass overpowers everything in your environment, and large objects start moving aroiund the room. Althought the car is "decoupled" from your space, the bass escapes it’s environment and finds it’s way into yours. The car is relatively "sealed", yet the bass finds a way out. It travels a hundred feet or so, penetrates your siding (or brick, or stone), sheathing, 4"-6" of insulation, 1/2-5/8" of drywall and rattles your brain. Long wavelengths with great intensity are difficult to constrain.

The second issue IS coupling to your room. Sympathic resonances caused by the vibration of your speakers couple with your subfloor, finds their way thru the insulation below, and through the ceiling material of the lower apartment. So, you’re actually dealing with two highly related actions here. YES, coupling will address one issue, but not all issues because high energy, long wavelengths are highly persistent.

The better question(s) are not so much WHERE the bass port is facing, but rather how low the tuned frequency is. Bass penetration is highly relevant to wave lenght. And, how loud you play.

As @ghdprentice suggested, getting to know your neighbors is the key here. You might ask them to help you discover the threshold of pain for them in THEIR apartment via your audio system, and establsh guidelines for behavior. You might discover that your music is not as intrusive as you thought.