Originally Posted by siriusproper
perhaps someone can help to clarify my understanding of the benefits of multiple subs. specifically the Cap S2.
1) sealed sub-woofers are designed for for lower extension, but provide less output...?
2) so adding another or more sealed sub-woofers provides more output at the same extension...? lower extension...? or some combination of the two..?
3) is it linear, or at least predictable...? going from 2-3, and 3-4, so on will provide linear results?
4) is there a cut-off where there is nothing more to gain by adding more S-2's?
The S2 is an amazing sub. It's expensive, but worth every penny! I'll try to answer your questions in order:
1) Yes, while this is not a law, if the same driver is compared in a sealed configuration and a ported configuration, the general trend is for sealed subwoofers to have greater output below the tuning frequency of the ported box. There are caveats, though - the sealed sub will often not have as flat a frequency response as the ported (down to the tuning point of the ported box), and will rely upon some combination of EQ and room gain (greater in smaller rooms, generally) to make up the output deficiencies compared to the ported box. In the S2 and most other high-end sealed configurations, this is done through the use of a DSP equalization profile built into the amp (and often not user-customizable).
Plus, tuning a ported or horn design really low (much below 20hz) requires an ENORMOUS box. The tradeoff for efficiency (more output higher up in the range) is box size, generally. TLDR: at 20hz tuning, a ported box will have more ouput than a sealed box, but will drop off significantly faster (by design) below that tuning frequency than a sealed box.
2) & 3) Adding more of the same exact sub with the same exact frequency response and power does nothing to change the response characteristics of the subs themselves. However, every doubling of the exact same subs adds double the output within the coupling range - at all frequencies where the wavelength(s) in question is less than the distance between the speakers. So, 2 subs is double the output of 1 at coupling frequencies. 4 is double 2, etc. Adding multiple subs also will often help smooth out the room cancellation or excitement modes to eliminate big dips/peaks in response within a room. This varies with the amount and placement of subs, so trial and error is important in getting it right with multiple subs.
4) You never stop gaining by doubling the number of subs, but the point of diminishing returns is reached when you meet your required level of output at desired frequency response. This varies by person, but many are happy with two S2s, though some may require 3 or more to hit that sweet spot.
I think this is approximately right, although I'm no authority on the subject. Good luck, and let us know how many you end up going with!