All floor standing Zu loudspeakers that do not have a powered subwoofer need a bit of gap between the bottom of the loudspeaker and the floor. While they are not a ported design (bass reflex) the finger port detail on the bottom needs to see the acoustic impedance of the room to correctly function. Setting the gap height is relative to your amp matchup, your room and your tastes—it’s tunable. Yes, optimum gap height will change from amp to amp and person to person.
Start with 1/4” [6mm]
Min. 1/32” [1 mm]
Max. 5/8” [16 mm]
Increasing the gap height, depending on amplifier, usually results in increased bass weight in kick drum and wood timbre, but it nearly always results in less output in deep bass. More gap height usually increases bass noise as well, causing the timbre to be a bit thick or wooly sounding. Less then 1/4” [6mm] will increase bass articulation / attack, increases bottom octave amplitude, but does reduce overall bass amplitude a bit. Typically, most arrive at gap height to be just about 3/16” [5mm], which is the size of those skinny half-hight CD jewel cases, perfect for a quick and easy gauge. But again, each amp will respond differently as the gap height influences the load impedance, a good thing because you can now better match amp and speaker and room, a bad thing because there’s one more thing you can fiddle with. Here is a great time saving idea regarding adjusting your gap height....
How to make adjusting gap height simple.
Zu knows you have music to listen to and that you really hate fiddling with the gap height—getting down on your knees, looking up at the bubble level, checking to make sure all four spikes are solid... it gets old fast. So, once you get your speakers where you like ‘em—making sure the left and right channels are spaced the same distance from the listeners center line, that they have the same toe-in, that they are both level, and that the spikes are equally weighted, with no cabinet wobble—set the gap height to roughly 1/4”. Likely they will sound great, but still, you should mess around with the gap height, with some amps it makes a huge difference. The easy, and best way to do this is shimming the gap with standard letter sized paper. The paper will be placed on the floor centered under the loudspeaker between all four spikes—don’t lift the speaker up you don’t want your spikes on the paper you want them firmly coupled to the floor. Best place to start is with a stack of paper that will take up roughly half the gap space, listen and go from there. You might want to take sheets out, increasing the gap height a bit, or add to reduce the gap height, experiment. Do the gap height shimming with just your left channel connected (or right) it reduces the work to half. After you get the left side sounding the way you want, mirror the changes on the right channel. You might find the difference to be huge, we usually do. It’s easy and free, mess with it.