2 + 1, variable state bi-amping VS steep low pass subwoofer


2010-09-28 1:19 am

I am tryng to outline pros and cons of both the approaches.

The stereo speakers will be closed box, playing down to let's say 0db/80hz.
The subwoofer has to handle down to 25/30hz.

I. Variable state
+ common tone control for all the system (bass control at 30hz)
- need to be careful with the bass amplification, amp and speaker power handling
+ I think, it will handle better phase shifting (am I correct).
Argument: The stereo and sub would not overlap that much bellow the crossover point.
+ I will spare the stereo speakers (full range) from some bass.
Not that relevant in closed box design. Also, arguing with the next point:
- I plan to listen to the system with sub-woofer off sometimes. Then, the variable state should be able to go low enough, so that I get decent bass from the system.

II. Steep Low pass filter (4th order)
First, I plan to use such a filter, so that the sub is less audible and there is no overlap in the range about 125 hz (the boomy bass)
- 4 gang pot needed (vs the complexity of stereo variable state)
+ no tone control, predictable power levels at the low frequencies.
Still I will have a seporate vol for the sub, but I can set that the max volume matches max volume of the stereo, in terms of power.

What would you advise me?
1. About phase shifting. Can I go without phase shifter in the variable state design?
2. About group delay
3. About any other concern, regardless for design, construction, any unforseen or misunderstood factors.

Regards :)