Searching for matching(?) Subwoofer solution

Hello Mike,

    You stated: "Simplifying the situation, what Duke is saying is that placing subs randomly throughout the room creates a situation that smooths out the frequency response throughout the room. I am trying to understand how that happens. "

    Hopefully, Duke will respond, too. But as I understand it, the key to understanding how and why a distributed bass array (DBA) smooths out the bass frequency response is psychoacoustics, how the brain processes bass information in the room delivered through the ears, as well as through other body senses, and creates our perceptions of the bass.  
    The purpose of four independent, well distributed subs launching bass soundwaves into the room, with the full knowledge that these soundwaves can be relied upon to reflect off room boundaries and collide into themselves and one another until they run out of energy, is to create an abundance of bass room modes (bass peaks, dips and nulls) and then depend upon our brains to process, sort and make sense of the abundance of room modes in order to create an overall perception of the bass in the room. In other words and simpler terminology, psychoacoustic principles, which explains how the brain will sum the bass by frequency and average it out which results in our perception of the bass as smoothed out and natural.
    I believe psychoacoustics are the key to understanding why and how the DBA concept works so well. It seems to me that explaining how and why a line source bass array (LSBA?) concept works so well can be done more easily with just physics than the DBA concept can and the LSBA concept seems to rely much less on psychoacoustic dynamics than the DBA concept does.  I think psychoacoustic principles and dynamics are a bit esoteric and counterintuitive.
    I've never experienced the bass response performance of an LSBA system in any room. I know the first time I experienced the bass response performance of a DBA system in my room it was a revelation and uncanny how well it performed.  I'd love to experience a LSBA system some day soon since I believe it could also be a revelation.
     I share your curiosity about whether I would detect any difference in bass performance with my DBA by limiting the distance between subs to under 14 feet.  However, in 2008 I had a stroke and still don't have full mobility of my left arm and leg.  I also had custom length speaker wires made for all four subs and the wiring is all run and hidden in the crawl space below my room.  Due to these factors,unfortunately, I don't think it's practical for me to experiment anytime soon.  Perhaps I could recruit a fellow audio enthusiast friend as an experimental lab assistant and mover but no promises.


Tim  

Tim, in this case I don't think psycho-acoustics is the reason. An example of psycho-acoustics is masking. MP3 compression strategies operate on this principle. The normal undistorted music masks the distortion because or brains can only pay attention to the loudest noise. If you don't want to hear your car rattle, turn on the radio.
Nodes form in rooms below what is called the Schroeder Frequency which depending on the size of the room is somewhere around 130 Hz.
Where the nodes are depend on the frequency, room size and the position of the woofer. By  positioning the woofers at different places in the room you create nodes in different places which overlap at different phases creating what I think Duke is referring to as a minimum phase system. This is a bit of a tough one to explain but I will give it a shot. Draw a sine wave on paper now draw another one 10 degrees out of phase with the first. Keep drawing sine waves 10 degree off from the last one until you come around a full 360 degrees. Now lets say these sine waves represent volume. The very bottom is zero dB and the very top is 20 dB. If you average all of these sine waves what you get is a flat line at 10 db. Or as Duke implies a minimum phase system. Geddes seems to think that just three sine waves is enough to create reasonably flat response and you can do this at any frequency below 80 Hz because below 80 Hz you can not locate the source. I personally think that should be below 60 as I know for a fact me and my audiophile friends can locate a 60 Hz test tone. The problem with this approach is what about the frequency band up to the Schroeder Frequency? By absolute coincidence I cross over at 125 Hz just below the Schroeder point. So my subs have to deal with all the room nodes from 125 Hz down. Above the Schroeder Frequency nodes do not form. My way of dealing with the node problem is to limit the dispersion below 125 Hz by forming a line source that is right up against the front wall. Now there are only reflections off the ceiling and rear wall. In my case the rear wall is broken up or there really is not a rear wall. The nodes that do form are easily managed by room control. I am not sure this approach would work well with point source speakers. Such an array may overwhelm them. 
When a concept is counter intuitive it usually means it was not explained well.

mijostyn: "Tim, in this case I don't think psycho-acoustics is the reason."   "when a concept is counter intuitive it usually means it was not explained well."

  Hello mijostyn/Mike,

    I think we have different ideas concerning what qualifies as psychoacoustics.  Psychoacoustics is the scientific study of sound perception and audiology—how humans perceive various sounds. More specifically, it is the branch of science studying the psychological and physiological responses associated with sound (including noise, speech and music).  I think you're right, masking and volume could be construed as part of that definition, they're just not the primary examples that I usually think of.
    I also believe my explanation of the DBA concept and the psychoacoustic dynamics involved was sufficient.  
    When I stated the DBA concept is counterintuitive I was referring to the method of creating more bass peaks, dips and nulls in the room to eliminate the perception of all of them in the room, with our brains being used as a sort of natural room correction software and hardware.  
     Do you think the DBA concept is intuitive?  
     Don't you think the cognitive dynamics involved with the DBA concept fall within the definition and realm of psychoacoustics? 

     You're correct, Geddes has stated that good in-room bass response can be attained over a wider area using as few as three subs and good at a single listening position using just two.

     Hopefully, Duke will respond to the bass phase issues.  

    You have no rear wall in your room for bass soundwaves to reflect off of? You must have very good bass performance along with very high heating and cooling costs.


Tim

Tim, Once I read Gedde's explanation of how DBAs work it makes absolute sense. My problem was that Duke was using terms that I was not familiar with that were not self explanatory. He was talking in a language I did not understand. Now that I know what is going on it makes perfect sense and is indeed intuitive. However it has limitations the biggest one is that you have to keep the crossover under 60 Hz or it will start messing up your image. This may work well for people with regular point source speakers that get down to 40 Hz ok. I firmly believe that with any dipole speaker, Planar magnetic, ribbon or ESL you have to cross up higher at least at 100 Hz. This disqualifies a DBA. On the other hand my way of doing things may not work well with regular dynamic speakers. Pick your poison:)

My media room is 16 X 25 feet. The back wall is 75% open to the kitchen and then 30% open to the dinning room the back wall of which is 75 feet away. So, the back wall reflection is broken up all over the place. I designed it that way. Between my speakers is a 113" diagonal Stewart screen the idea being that I can either listen to music or watch TV while cooking and having dinner. The projector hangs from the ceiling.  

Mike

Ok. So after researching the wonderful resources about subwoofers, I think I am beginning to understand nodes, evenness, cancellation, etc. and leaning towards going with the Swarm again.

But Swarm or DEBRA?  Not finding much info about the differences.

Anyone have experience comparing them?

Thanks,
Hans