MartinLogan Subwoofers- Don't Overlook Them!

avanti1960:"@noble100 I agree about the directional cues when at the listener spot but while moving about the room, the sound of a single sub can change dramatically. I had a single sub previously and the sound was so defined and powerful when standing at a certain spot about 10 feet from the front of the sub and lost those qualities as you moved away from that spot. With the two subwoofers it is true- the room is equally balanced.  
With respect to stereo sub-bass it can come off as directional when the higher frequencies of a given note can be localized to a certain direction. Although the corresponding sub bass "hit" is not directional within the room, the fact that the higher frequencies are directional tricks the ear into believing that the sub-bass is also coming from the same spot- e.g powerful stereo drum work."

Hello avanti1960,
     Yes, a single sub is capable of giving good bass response at a single designated listening seat but this also results in poor bass response at numerous other spots in the room.  The traditional "crawl" method of optimally positioning a single sub in a given room results in it being placed at a specific spot in the room at which it will not cause any bass modes (bass peaks, dips and cancellations) at the designated listening position.  
     This very process, however, literally guarantees that there will be an abundance of bass room modes at numerous other specific spots in the room away from the designated listening position.  The relationship between the exact location of the sub in the room and the exact location of the designated listening position in the room is a very unique and precise one with a small margin of error.  In fact, it's very likely that there are bass modes very near to the designated listening position but not exactly at this position, so the bass response precisely at the listening position is still unaffected. 
     The above explains why you experienced poor bass performance as you moved away from a spot about 10 feet away from the front of the sub.   But I wanted to point out that adding a 2nd sub didn't exactly equally balance out the bass response in your room.  The actual dynamics are more complex and I'll try to explain it in another post when I have more time.
       It seems like you have a very good understanding about the fact that there's no such thing as true stereo sub-bass (below 100 Hz).   And you gave a fairly good explanation of the fact that we can perceive a form of stereo sub-bass with the assistance of sub-bass harmonics or overtones that reach into higher frequencies that we can localize (tell where the sounds are coming from) and our brains are able to associate these higher frequency sub-bass harmonics/overtones  with the much lower frequencies of sub-bass fundamental tones and thereby localize the instruments producing them.  This is one principle of what's termed psychoacoustics.  

Later,
 Tim

"But I wanted to point out that adding a 2nd sub didn’t exactly equally balance out the bass response in your room. The actual dynamics are more complex and I’ll try to explain it in another post when I have more time."

     Here’s my promised further explanation of how adding a 2nd sub, and additional subs beyond two, can improve in-room bass performance.

     Two properly positioned and configured subs in a given room typically provides bass response at a designated listening seat that’s approximately twice the quality level of utilizing a single sub. Two subs provide increased bass output capacity and impact as well as increased bass dynamics due to the sharing of total bass requirements between two subs operating well within their limits and stress free with ample power reserves for sudden bass output dynamic demands.
     Psychoacoustic principles also begin to be applied beginning with the use of two subs in any given room that results in the bass being perceived as smoother, more detailed and better integrated with the main speakers.
To understand how this psycho acoustic process works, it’s important to understand how bass soundwaves behave in a room with a single sub. Soundwaves increase in length as the frequency decreases and deep bass tone soundwaves are very long. A full cycle soundwave of a 20 Hz deep bass tone is 56’ long, a 30 Hz is 36’, a 40 Hz is 28’ and a 50 Hz is 23’. It’s also important to know three facts:

1. Our brains can’t even process the presence of a deep bass tone until the full cycle soundwave exists in the room and our ears have inputted this information into the brain.
2. Our brains require the input of at least three full cycle bass soundwaves before we are able to recognize a change in pitch or volume.
3. Our brains cannot localize deep bass tones (detect where the sounds are coming from) with frequencies below 100 Hz.

     With the deep bass soundwaves being longer than any room dimension in many individuals’ rooms, this means the soundwave will leave the single sub and need to travel as far as it can in the room and then reflect off the first room boundary (floor, ceiling or wall) it meets then keep traveling in the reflected direction until it meets the next room boundary. This process continues until the soundwave runs out of energy and with each subsequent bass tone launched into the room by the single sub.
     These numerous bass soundwaves of various frequencies launched into the room by the single sub, and reflecting off room boundaries, inevitably run into each other at various angles causing what are called a Bass Room Mode at each specific room location at which they meet or collide. Depending on the specific angle at which the soundwaves meet, we perceive these bass room modes at specific spots in the room as either a bass overemphasis (bass peak), a bass attenuation (bass dip) or even a bass cancelation (bass null). The result is an overall perception of the bass from a single sub as uneven or ’lumpy’, less detailed and somewhat disconnected, lagging behind and not as well blended with the main speakers. especially with faster planar-magnetic and electrostatic panel speakers.
     However, when a second sub is properly deployed and positioned in the room, the very interesting and useful principles of psychoacoustics (how our brains process sound and our perceptions of it) begin to come into play, which results in a perception that the bass is smoother, more detailed, better integrated with the main speakers and more natural or realistic.
     Unexpectedly, this is accomplished through the second sub actually significantly increasing the number of bass room modes (bass peaks, dips and nulls) in the room. Our brains naturally process the presence of multiple bass soundwaves below 100 Hz, by adding them together by frequency and averaging them out. This results in fewer bass modes being perceived in the room and a perception overall that the bass is smoother, more detailed, better blended with the main speakers and more natural.

     Acoustical experts, such as Dr. Earl Geddes, Dr. Floyd Toole and others, have proven scientifically that in-room bass performance perception improves as more subs are added to virtually any given room, beginning with two subs and with improvements continuing up to the theoretical limits. Of course, there’s a practical limit to the acceptable number of subs in a domestic room.
I’m fairly certain the exact number of subs considered acceptable in a domestic room is higher for most men than most women but, interestingly, the scientists found significant bass performance gains were attained with each additional sub up to four but smaller more marginal gains were attained with each additional sub beyond four.

     Three properly positioned and configured subs in a given room typically provides bass response at a designated listening seat that’s approaching the optimum quality level attainable at a single listening position. Three subs provide even further increased bass output capacity and impact as well as further increased bass dynamics due to the sharing of total bass requirements between three subs operating well within their limits and stress free with very large power reserves for sudden bass output dynamic demands.
Psychoacoustic principles are more strongly applied with the use of three subs, as opposed to two subs, in any given room that results in the bass being perceived as even smoother, more detailed and better integrated with the main speakers. 

     Four properly positioned and configured subs in a given room is the preferred method of achieving the optimum bass response performance quality level at the designated listening position.  The Audio Kinesis 4-sub Swarm distributed bass array(DBA) system for about $2,800 is a very good example of this concept.  This is a complete kit that includes four 4 ohm unamplified subs that are each 1’ x 1’ x 28", weigh 44lbs and have a 10" aluminum long-throw driver and a 1,000 watt class AB amplifier/controller that powers all four subs and controls the volume, crossover frequency and phase of all as a group.
     The use of a 4-sub DBA system will provide near state of the art bass performance not only at a single listening position but throughout the entire room. This is very useful if you have multiple seating positions in your room and prefer having very good audio at each position for both music and HT.
     Of course, only the designated listening position will be optimized for both bass response and midrange, treble response and stereo imaging but very good full-range audio will still be provided at each seating position.
Another benefit of the 4-sub DBA system is that absolutely no bass room treatments are necessary. You’d just need to incorporate room treatments for the midrange and treble response on your main speakers (first reflection points on each side wall and possibly some treatment on the front and rear walls).
It’s also possible to create a custom 4-sub DBA system, rather than using the complete Swarm system, by utilizing any four subs an individual prefers. The only down side is that there’s a need to configure the volume, crossover frequency and phase settings individually for each of the four subs rather than once for all four subs as a group on the Swarm system. Here’s a link to an Absolute Sound review of the A K Swarm system that is very accurate (I use this system in a 23’x16’x8’ room with Magnepan main speakers and it works like a charm).


www.theabsolutesound.com/articles/audiokinesis-swarm-subwoofer-system/

Tim

To clarify and I apologize for my ignorance, you’re running speaker wire from your amp to the sub then from the sub to your mains via the high level inputs/outputs?

@

noble,

" I’m fairly certain the exact number of subs considered acceptable in a domestic room is higher for most men than most women" 
we definitely agree on that point !  I would like to hear the 4-subwoofer swarm system one day, possibly at AXPONA next year? As of now my 2-subwoofer system has been carefully dialed in and sounds excellent,  integrated, dynamic and with balanced, well defined notes.  One key I have found to avoid smearing my main speakers is to use the higher order crossover option on these subwoofers.  The 4th order crossover (24db per octave) set at 65Hz sounds excellent and does a great job at eliminating the directional energy since 130Hz would be 24db down from the main signal.  Doing this saves the need for any kind of high pass filter for the main speakers. 

@gochurchgo2
I am running my main speakers full range.  I connect the subwoofers in parallel connecting at the amplifier speaker terminals.  The high impedance of the subwoofer creates minimal load on the amplifier and draws a very small amount current- just enough to let the subwoofer amplifier do its job.  

Another stupid question but can you link me to a diagram of how you wired this? 

Im not savvy.

Thanks @avanti1960