Slightly different advice:
1. A floorstander's low frequency (in this case 35Hz) can be expected to be its -3dB point (unless you're quite close to a wall). The crossover on a sub is its -3dB point. Therefore, a crossover point an octave above the low frequency spec point of your speaker is a good place to start. In your case that is 70Hz.
2. Though there are many design factors in subs, the amount of air moved by a large sub is much larger than a small one, requiring less excursion (often meaning less distortion) to move the same amount of air.
area = 3.1416 * r squared
10 -> 79 sq in
12 -> 113
15 -> 177 (two 10s)
18 -> 254 (two 12s)
3. Finally, a phase control as well as a volume control is useful in getting floorstanders and sub to sinq.
Good luck.
1. A floorstander's low frequency (in this case 35Hz) can be expected to be its -3dB point (unless you're quite close to a wall). The crossover on a sub is its -3dB point. Therefore, a crossover point an octave above the low frequency spec point of your speaker is a good place to start. In your case that is 70Hz.
2. Though there are many design factors in subs, the amount of air moved by a large sub is much larger than a small one, requiring less excursion (often meaning less distortion) to move the same amount of air.
area = 3.1416 * r squared
10 -> 79 sq in
12 -> 113
15 -> 177 (two 10s)
18 -> 254 (two 12s)
3. Finally, a phase control as well as a volume control is useful in getting floorstanders and sub to sinq.
Good luck.