Really it all depends on how you want them to sound, and to be set up. There really is not specific air space, but there are general air spaces that work, and some times the manufacture will list some specs for different set ups. It also depends on the size of the sub, which you did not specify.
Kicker recommends as follows.
0.4 cubs per sub for a compact box, and 1.8 for an SQ box. SQ stand for sound quality.
So if you want a small box, do .4 per sub. If you want a better sounding box do 1.8.
Rule of thumb and something to think about.
The more air space in the sub, the less power you can run, the less air space, the more power you can run.
For example you can run 200 watts RMS per sub at .4 cubes, but only 140 watts RMS with 1.8.
As well, the smaller box will be louder, But not sound as good.
Answers & Comments
Really it all depends on how you want them to sound, and to be set up. There really is not specific air space, but there are general air spaces that work, and some times the manufacture will list some specs for different set ups. It also depends on the size of the sub, which you did not specify.
Kicker recommends as follows.
0.4 cubs per sub for a compact box, and 1.8 for an SQ box. SQ stand for sound quality.
So if you want a small box, do .4 per sub. If you want a better sounding box do 1.8.
Rule of thumb and something to think about.
The more air space in the sub, the less power you can run, the less air space, the more power you can run.
For example you can run 200 watts RMS per sub at .4 cubes, but only 140 watts RMS with 1.8.
As well, the smaller box will be louder, But not sound as good.
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