Distributed Bass Array configuration

Hello vinylshadow,

      I believe most set their cutoff frequency according to their main speakers bass extension capabilities and personal preference discovered via trial and error experimentation. 
      My opinion is that 80 Hz is too high since that's the generally accepted borderline between bass being directional or nondirectional.  You can't tell where the bass is coming from below about 80 Hz but can begin to tell above this frequency.  
     The goal is to integrate the bass from 1 or more subs as seamlessly as possible with one's main speakers.  The subs should remain completely silent until the source recording contains bass content at or below the low pass crossover frequency setting.  The first step, which you've already done, is to find out the rated bass extension of your main speakers, which you stated is 35 Hz.
     By coincidence, my main speakers (Magnepan 3.7i)also have a rated bass extension of 35 Hz but I utilize an Audio Kinesis Debra 4-sub distributed bass array (DBA) system to supplement the bass performance.  My point is that your optimum crossover frequency is probably going to be a bit different than my setting (currently set at between 40 and 50 Hz) for seamless integration.  But I'll describe the procedure I used in the hope that it'll work similarly as well for your single sub as it has for my 4 subs:

1.  Optimally locate your sub in the room using the "sub crawl" method (you can google it).
2.  Play some music with good and repetitive bass content.
3.  Sit at your listening position, set the crossover frequency control on your sub to 60 Hz, set the phase control to"0".  Then have an assistant slowly turn up the volume control on the sub until the volume of the bass from the sub matches and blends with the volume of your main speakers as closely as possible.
4.  Still seated at your LP, have an assistant slowly lower the sub's crossover frequency as low as possible with the bass still sounding very good to you ( "very good" meaning the bass remains solid, powerful, detailed, dynamic, seamlessly blended with the main speakers and natural sounding). Remember, the goal is to not even hear the bass from the sub until the source material calls for it. 
5.  Still seated at your LP, have an assistant slowly increase the sub's phase control upward from the "0" position to the "180" position until the bass sounds best to you ("best" meaning loudest, most detailed. best blended with the main speakers and most natural).  Note that these changes in phase settings will be subtle and you may need to closely listen through several slow "0" to "180" cycles to discover the optimum setting.  Just do your best since this setting isn't usually critical.

Hope this helped,
      Tim 

@mike_in_nc  - 

Firstly, heed the advice from MC/Noble101/and especially Duke LeJeune.

Secondly, I will divert from phase, crossover frequencies, gain, etc. and instead share my experience regarding subwoofer placement.

I am running four subwoofers (yes, the AudioKinesis Swarm).  Two are mounted up high facing the ceiling.  Their heights vary with one 12 '' and the other 18 '' below the ceiling.

Duke mentioned in an earlier thread that any subwoofers mounted above the room mid height contribute to the vertical plane, thus further reducing standing bass nodes.

My A/B testing (4 on the floor vs. 2 on the floor with 2 up high) in 2 rooms (10 x 12 minus closets and 12 x 16 living room) at my previous house along with over a year at my new house (also A/B testing between a 13 x 16 vs. a 15 x 19 room) all clearly confirm a noticeable all around improvement.

Hope this is helpful to you!

I do like the fact SVS has excellent new subs with great apps 
and even programs you can use with USB Mike and online free programs and setting ,SVS 3000, and Ultra 16 are the only subs I know of with 50 + bitAnalog devices microprocessors and their Dual voice coil on these 2 models is special for when at low volume ,you use the smaller inside of the voice coil to have full control ,and when louder music is player the inner and outer voice coil is utilized .
my brother has 4-Ultra 16s in his Audio ,Home theatre setup .
the sound pressure is so immense when a low Bass note hits you can literally feel it . I have 2-3000s  , buy sealed not ported for best 
tightest Audio . , I will say SVS  tech support is the best I have encountered and I have had the top 4 brands 
and who else gives a 5 year transferrable warranty ,and free shipping ,and 45 day Audition  with even free return shipping !
no one but SVS , Even their latest mini 3000 , and $499 has an app. And I  had a JL Audio 13  before,Rel the SVS is just has much more technologies built in and theApp for phone or tablet is excellent to adjust Bass, or volume on the fly per recording if need be is great👍

Hilde45, very poor choice of experts. Mr McGowan is a businessman with poor hearing. His objective is to make money by any means possible. He is reasonable good at that. I suck at it. 
Most of these people making comments here on this subject are using 3rd if not fourth rate equipment and are running their subwoofers without a high pass filter on the main speakers, people who listen to Yello on Tekton loudspeakers.  There is no way in ---- you can get decent bass out of a system that way. The main weakness of a distributed array system is that there is no way to control time with it. You can not get the impulse from the subwoofers and your main speakers to your ear at exactly the same instant. The result is a mess. But, it really does not matteras none of these people have a way to deal with the problem anyway. They would rather spend their money on cable elevators. 

@mijostyn Both the experts cited have extensive experience in audio, i.e., it’s their profession. Neither are subwoofer salesmen. In both cases, their answers were detailed, and in both cases, they explained pretty carefully -- in Poes’ case, with great detail. In both cases, neither proffered sweeping generalizations about stereo bass, Indeed, the case was pretty well established that in many cases, mono bass was better for room acoustics and might be the only thing hearable, anyway. The information they provided is not susceptible to ad hominem remarks. To be clear, they are not offering arguments that are "pro stereo bass" or "pro mono bass."  They rebut the claim that there is NO such thing as stereo bass and it can NEVER matter. There is, and it can, with all the qualifications provided. I thought that the OP's question was seeking to learn about this topic, so I provided what seemed like good information, rather than just my experience, which is meager.