Millercarbon has it right: 1. There is no such thing as stereo bass below 80 Hz since it's a fact that humans cannot determine the originating location of any sound deeper than approximately 80 Hz. This is the reason I also configure my Audio Kinesis Debra 4-sub distributed bass array in mono mode. If anyone thinks they're able to distinguish the specific originating location of bass below 80 Hz, I'd suggest testing this for themselves with test tones. These test tones are available on-line via a Google search. 2. I also found the Phase setting is not very important in attaining excellent bass performance in a 4-sub DBA system. Timing and arrival time of deep bass sound waves at an individuals ears are, therefore, also not anything to be overly concerned with since a 20 Hz bass tone sound wave is about 56 feet long, which likely exceeds the dimensions of at least the length or width of most domestic rooms. See the linked sound wave lengths in inches as a reference below: https://www.jdbsound.com/art/frequency%20wave%20length%20chart%202013.pdf Bass sound waves under 80 Hz also emanate outward from the sub driver and are dispersed into the room in an omnidirectional direction, which means these multiple sound waves have likely bounced off at least one room boundary (floor, ceiling and wall) before they reach an individual's ears at the listening position and they perceive a bass tone. The truth is our brains are capable of summing and averaging these bass sound waves by frequency/tone, that arrive within about 10 milliseconds of each other, but we're still not able to determine specifically where these bass sound originated from if they're below about 80 Hz. Finally, even if our brain could locate where these multiple and bouncing sound waves/tones were coming from, there are apparently no examples of commercially available prerecorded music, in any format, that bother to record discrete left and right bass under about 80 Hz. Recording engineers have been routinely summing left and right bass under about 80 Hz as mono, and sometimes even higher, as a standard practice for over 4 decades. Why? Because these recording engineers have known the truth about the myth of stereo deep bass for about the last 100 years, ever since scientists first discovered and formally established this fact through the scientific method. Don't believe me? Try and find any recording, in any format and any date, that has deep bass below 80 Hz recorded in stereo. Perhaps some near future recording engineers will utilize the full capabilities of the latest and greatest hi-resolution direct to digital recording method and introduce the first commercially available music with stereo deep bass. But I wouldn't hold your breath. Later, Tim |
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 |
Hello Duke,
Completely understandable.
Thanks,
Tim |
I completely agree that Duke Lejeune of Audio Kinesis is the most knowledgeable. best and most credible source on these forums about all things concerning 4-sub DBAs. He's always willing to assist and has probably forgotten more about proper 4-sub DBA systems and setup, as well as how bass sound waves behave in domestic sized rooms, than I've ever known. He often chimes in on threads like this but, unfortunately, not this time. I agree with clio09 that you should call or email Duke at Audio Kinesis for the best advice. Best wishes and enjoy, you're going to be amazed once your DBA is setup properly.
Here's a little history on my experiences with the DBA concept for those interested:
I actually first learned of this exceptionally good bass concept by chance. Over 10yrs ago, I was just looking for the best way to supplement the bass performance of my combo music and HT system that utilized Magnepans as mains. I had called Audio Kinesis about another matter, talked to Duke's associate, James Romeyn, and we got talking and emailing about my system goals. He suggested either of their two 4-sub DBA versions (the AK Swarm or Debra) as a very good bass solution for my Magnepans.
This was the first time I'd heard about the 4-sub DBA concept and it really piqued my interest. I dove into reading all I could find on-line about the subject, beginning with Earl Geddess's PHD Thesis on the concept, his subsequent White Papers on it, articles on multiple subs by Floyd Toole and Harman's Todd Welti as well as several others.
At the time, I was planning on buying a pair of high quality subs such as JL Audio, REL or Vandersteen for up to about $6K. But I decided to give the AK Debra a try instead since this whole scientifically tested and proven concept of the 4-sub DBA made so much logical sense to me, I was very interested and curious about its practical performance, I felt a bit adventurous and wanted to try something new, interesting and nonconventional.
Anyway, I was amazed, and still am a decade later, at how well this DBA concept performs in my 23'x16' room. It took half a day to properly set it up but I didn't care once I heard and felt the results. It performs way beyond my expectations on both music and HT and is definitely the single best upgrade I've ever made to my system during my 50+ yrs in this hobby. Hyperbole? Maybe, but this concept is outstanding and I know it will work equally well with any main speakers I care to utilize now or in the future.
Tim |
The following quote was copied from a Stereo Times interview with Duke Lejeune that took place many years ago, There was no date listed on the article that I could find. So, I'm not certain of the exact date but I believe it was published around the year 2000 give or take a few years. I thought the entire interview might be of interest to members and this is a link to the complete interview: http://www.stereotimes.com/comm081710.shtml The interview begins with a fairly lengthy portion about his regular speaker designs. The copied portion below is a portion near the end of the interview, which I thought was more directly relevant to this thread since it is the portion at which "LB", Stereo Times interviewer Larry Borden, first asks Duke, "DL", about his "SWARM" 4-sub distributed bass array system: "LB: Let’s turn now to bass. What is “SWARM,” and how does it work? DL: The concept behind the Swarm arises from a brief conversation with Earl Geddes, as I was driving him to the airport after CES in 2006. I had been trying for years to come up with a subwoofer system that would match up well with Magneplanars and Quads, trying various enclosure types in a quest for very good “pitch definition” in the bass region, along with good impact (good planars excel at the former but not the latter,). Anyway, Earl mentioned that scattering multiple subs asymmetrically around the room resulted in a net smoothing of the in-room bass, as each sub would interact with the room differently so that the sum would be smoother than any one alone. The lightbulb went off in my head, and I asked him for permission to use the idea. He said yes. By the time we got to the airport, I was already designing the Swarm in my head. Let me digress for a minute into acoustics and psychoacoustics. The ear/brain system tends to smooth out peaks and dips that are fairly close to one another, but if they are more than 1/3 octave or so apart then the peaks and dips are usually audible. Now we get room-induced peaks and dips all up and down the spectrum, but only in the bass region are they typically far enough apart (due to the wavelengths involved) that the ear cannot smooth them out. So in the bass region the problem is not too many peaks and dips – the problem is that they are too few and far between! Another factor is that it takes the ear a fair amount of time to hear bass frequencies. The ear cannot even detect the presence of bass energy from less than one full cycle, and it takes several cycles to detect the pitch. So considering the wavelengths and room dimensions, by the time we can hear bass tones the room’s effect is in full swing. Perceptually, in our home listening rooms there is no such thing as “direct sound” in the bass region; by the time we even begin to hear it, it’s all reverberant sound. The Swarm consists of four fairly small subs and a single kilowatt shelf-mounted external amplifier. The subs are “voiced” to have a gentle rolloff over most of the bass region that is the approximate inverse of anticipated room gain (the vented version comes closer to this ideal than the low-Q sealed version does). The amplifier has a steep 24 dB per octave lowpass filter so that the subs can be scattered without betraying their locations by leaking lower midrange energy, along with a single band of parametric EQ in case the scattering alone doesn’t do the trick. To the best of my knowledge, none of my customers are using the parametric EQ because the in-room bass is sufficiently smoothed as it is. Not only does the Swarm result in a smoothing of the in-room peaks and dips, but the peaks and dips that remain are more numerous and closer together, so that the ear’s smoothing mechanism can be effective. Now at first glance it might seem that multiple bass sources with multiple arrival times results in loss of impact and/or mud, but that is not the case in practice. As explained above, we cannot hear the bass wavefront before the room has its say. The ear responds primarily to frequency response (rather than to time-domain behavior) in the bass region, so when we smooth the frequency response we are solving the biggest problem. Because the low fundamentals and first few overtones are present in proper proportion, the pitch definition is very good. The argument for a single large equalized sub can of course be made, and there are some exceptional examples on the market, but equalization is a local rather than a global solution. In other words, the room-induced peak-and-dip pattern varies so much from one location to another within a room that fixing the frequency response at one location via equalization will almost inevitably make it worse elsewhere. In contrast, the multi-sub approach smoothes the bass throughout the room (decreases the spatial variance), ironically making equalization (if needed) even more effective." I thought his statement, "So considering the wavelengths and room dimensions, by the time we can hear bass tones the room’s effect is in full swing. Perceptually, in our home listening rooms there is no such thing as “direct sound” in the bass region; by the time we even begin to hear it, it’s all reverberant sound.", was especially relevant to this thread discussion. He's basically pointing out that the very long and omnidirectional bass sound waves behave very differently in domestic sized rooms than the much shorter and highly directional midrange and treble soundwaves. Which means that sound wave time coherence, the timing of sound waves actually reaching a listener's ears, is very important, necessary and doable for the shorter midrange and treble frequency sound waves for good stereo imaging. But sound wave time coherence is not very important, doable or even necessary for the much longer bass frequency sound waves since there is no such thing as "direct sound" in the bass region, it's all reverberant, or reflected, sound. The fact that humans are poor at locating the source of sounds below 80 Hz and progressively better at locating the source of sounds above about 80 Hz, the fact that we require the detection of a long and full cycle bass sound wave to even perceive bass sound present in the room and several full cycle bass sound waves in succession to perceive pitch, also distinguishes the differences in bass versus mid/treble sound tone perceptions in our rooms. Another interesting fact about bass sounds is that, perceptually, we're much better and more naturally able to perceive them outside or in a very large concert hall because the very long, full cycle bass sound waves, due to the much larger space, have the capability to arrive at our ears as "direct sound" rather than arrive as reverberant sound that has reflected off one or more room boundaries on its path. Just some food for thought, Tim |
soundspectacular:"
Please correct me if any of my comments here are incorrect as I don't claim to have any expertise. I do believe you are misinterpreting the "term" - "stereo subwoofers". It is a "term" not a sonic phenomena or an implementation in any recording process."
Hello soundspectacular,
You are correct, "stereo subwoofers" is just a term, perhaps only used on this audio forum, that does not represent an actual phenomena or an implementation in any recording process.
I consider stereo subs a misnomer since I don't believe stereo bass even exists below about 80 Hz, iwe all perceive it as mono. But others on this forum believe stereo bass below 80 Hz does exist.
The whole stereo bass subject on this forum, unfortunately, only gets more complex and polarized from there, as well as too involved to easily summarize.
Hope this helped,
Tim
|
bdp24, The 4-sub Audio Kinesis Swarm and Debra DBA systems utilize a
Kilowatt class shelf-mount class AB amp/control unit with a 4th order variable lowpass filter that rolls off the bass at 3 dB per octave from 100 Hz down to 20. The 4 sub modules have a gentle roll-off across their passband that is the approximate inverse of typical room gain from boundary reinforcement. Typical room gain from placement near a wall is 3 dB per octave below 100 Hz, and so the Swarm modules roll off at about 3 dB per octave from 100 Hz down to 20 Hz.
Here's a link to the system's description and specs: http://www.audiokinesis.com/the-swarm-subwoofer-system-1.html
When utilizing a 4-sub DBA in mono mode, I think it's important for everyone to understand that one is still able to perceive a deep and wide sound stage illusion in full stereo over the entire, standard and audible 20 Hz-20KHz frequency spectrum. In other words, one is able to perceive stereo deep bass below 80 Hz and localize deep bass instruments in the stereo sound stage illusion. I don't believe this bass perception, however, can accurately be classified as "stereo subwoofers" or "stereo deep bass" since the bass below about 80 Hz is technically being played back in mono. In all the music source material I possess, the bass below about 80 Hz is also summed to mono during the recording process. My theory, about how this mono bass is perceived as stereo bass , is that bass sounds below 80 Hz have harmonics, or overtones, that reach beyond 80 Hz which are able to be localized. These harmonics or overtones are recorded and played back in stereo through the l+r main stereo speakers. Our brains are then capable of associating these over 80 Hz harmonics/overtones, coming from the main l+r speakers in stereo, with the under 80 Hz fundamental tones, coming from the 4 subs in mono, and creating an overall perception of stereo bass that specifically details where in the 3 dimensional stereo sound stage the sound is coming from in a very natural and realistic manner. My opinion is that this type of stereo deep bass perception is unique and deserves its own name or description, other than "stereo subwoofers" or "stereo deep bass". I find a fairly low crossover frequency between 40-50 Hz performs best in my room and system for both music and HT. Even though I know the bass is mono, I definitely perceive the music as high quality, very natural, very realistic and in full range stereo.
Tim
|
Hello lemonhaze,
Thank you for using a very interesting example to confirm this likely principle. I understand your comment about a signal generated 41 Hz fundamental tone not being locatable since it lacks the necessary overtones.
Thanks,
Tim |
soundspectacular,
Yes, I prefer the term omnidirectional, as opposed to non-directional, to describe the dispersion pattern of deep bass sound waves being launched into the room from a bass driver, whether from the main speakers or a sub.
The difference between this and how the midrange and treble sound waves are so much shorter and are dispersed into the room in such a highly directional manner, couldn’t be more stark.
The truth is that bass sound waves behave very differently than midrange and treble sound waves behave in our typical domestic-sized rooms. My experience has been that it’s much more difficult to get the bass sounding right in a room than it is getting the midrange, treble and stereo sound stage imaging sounding right.
Due to the above, my system system building philosophy has evolved to the point that I now consider my system as 2 systems: A Bass System and an Everything Else System.
I like to install the Bass System first in the room, before even bringing in and setting up the main speakers. I use 4 subs positioned in a distributed bass array (DBA) configuration since it provides optimized bass performance and does so throughout the entire room, which is important to me but may not be for others.
If an individual only requires optimum bass performance at the primary listening position, however, very good results can be achieved utilizing just 1-3 subs in the room, provided they are positioned and configured properly in the room and in relation to the LP. In general, the more subs used in the room, the better the bass performance.
Once the bass is sounding very good in the room, the final step is to position the main speakers in the room, and in relation to the LP, to optimize the midrange, treble and stereo imaging performance, which in my experience, is typically much easier to get sounding right in the room than the bass is.
Tim |
mapman: "
What measurements establish the “improved bass”? Improved in what way? Just wondering. Is it just more? More extended? Flatter response ? Different frequency curve? What exactly is different than prior?" Hello mapman, I agree with soundspectacular, that the bass in a room or system does not qualify as improved just because it's louder or there's more of it. I consider more bass an improvement in an audio system only if it manifests itself in the capacity to accurately reproduce large and natural bass dynamics contained on the source material, whether the source material is music or LFE channel information for HT. My goal for my combo system has always been improved bass quality, which I define as bass that is accurate and natural in tone, pitch and intensity as well as powerful, detailed and textured without any exaggeration. I believe a flatter in-room bass response curve and deeper bass frequency extension capacity definitely represent improved system bass performance. However, I've never utilized any in-room bass frequency response measurement equipment, tools or room correction hardware/software. I do believe such gear and tools are generally very convenient and helpful once competent skill at their usage has been attained. Since I bought and installed my AK Debra 4-sub DBA system about a decade ago, my criteria for evaluating and gauging its effectiveness in my room and system has been purely done by ear and subjectively. I'd be interested in measuring its in-room bass performance but, unfortunately, I currently lack the gear and skills to do so But I'm not very concerned about attaining the gear and skills for accurate room measurement since I know without any doubt, based on how it subjectively sounds and feels, that it represents the best bass system I've yet to experience in my room and system. I honestly believe my system, formerly with the AK Debra 4-sub DBA and 2.7 mains and currently with 3.7i mains, has performed so well that I consider it a somewhat miniature version of Magnepan's $30K, 30.7 4-Panel Dipolar Planar Loudspeaker System, click the link attached below for a description and review: http://www.hifiplus.com/articles/magnepan-307-four-panel-dipolar-planar-loudspeaker-system-revisited... About 3-4 years ago or perhaps more, I attended an in-person, Wendell Davis led demonstration of the 30.7 system at Ovation Audio in Indianapolis. Of course, the 30.7 was very impressive being auditioned in about a 30'x20' room with 8' ceilings and being driven by a single, very large ss Anthem amp (I forgot the model). The overall system was very impressive. Natural and powerful sounding with full range and powerful dynamics, very much like how acoustic music played live and unattenuated, sounds and feels when experienced live and in-person. But the most surprising and disappointing impression I heard and felt from the 30.7 demo came from its two very large, 6.5'h x 2.5'w each, what they call bass/ mid bass panels. To be clear, the bass and mid-bass reproduced by these very large dipole speaker panels sounded and felt very powerful, dynamic, natural and seamlessly integrated with the system's two equally large midrange and treble panels. But I could clearly notice that the 4 modestly sized, 2'hx1'wx1'd, subs of my AK Debra DBA system inconspicuously positioned around my 23'x16' living room, roughly equaled the 30.7 system's performance in sounding and feeling powerful, dynamic, natural and seamlessly integrated with my system's two more moderately sized, 6'hx2'w, 3-way and full range 2.7 dipole panels, had a bit deeper and more realistic bass extension. This is proven accurate by the difference in the rated bass extension between the two systems: 20 Hz rated bass extension for the AK Debra system vs 24 Hz rated bass extension for the Magnepan 30.7 system. Not a huge difference but it was obvious to me the AK Debra DBA system. overall, outperformed the 30.7. After the demo during a Q&A session, I described this difference I perceived and asked Wendell if he ever considered just paying a royalty fee per unit sold to Audio Kinesis for adopting their much less obtrusive, and more effective, bass array concept using 4 small subs instead of the two very large and dipole bass/mid-bass panels. Too blunt and pointed a question? Perhaps, but he's a big boy so no big deal, right? He responded with a confused look. a hesitant look around the 20 person audience and a rather quick point for the next question. I like and respect Wendell but everyone could tell he was awkwardly avoiding the question. I still wonder why? Tim |
Hello mapman,
Funny, I have no trouble optimally positioning my subs in the room by ear, when utilizing the sub crawl method on each one sequentially, but I do have trouble optimally setting their phase by ear.
I found it was much easier to optimally set the group phase on my subs once I turned off my main speakers. The proper setting became much more obvious to me once I did this, I just set phase at the position at which the bass is slightly louder, more solid, more detailed and the most natural.
Another tip, which makes setting the proper phase on subs even easier to discern, is to temporarily invert the polarity on the main speakers (simply by reversing the positive and negative connections on each speaker's terminals), optimally set the phase control on the sub(s) and then swap the main speakers' connections back to normal.
This made a lot of sense to me once I learned that the phase and timing of sound waves are almost irrelevant on deep bass frequencies but critically important on midrange and treble frequencies. Humans are much less sensitive to sound wave arrival times on deep bass tones than we are on tones over about 80 Hz.
Later,
Tim |
Here's a good article on the subject of multiple subs that I think is worth reading. https://mehlau.net/audio/multisub_geddes/ My general advice is to also learn as much as you can about how sound waves behave in smaller, domestic-sized rooms and how humans detect sound waves through our body and how our brains interpret/process these inputted senses before creating the perceptions of sound in the room. Spoiler alert: bass sound waves behave quite differently than higher frequency sound waves in our rooms and we perceive them differently based on their frequency range, too. Tim |
Hello audioquest4life,
Congrats and welcome to the DBA Swarm Club, be prepared to be amazed!
I wasn't even aware AK offered a larger Magnum version of their Swarm system.
James Romeyn, of Audio Kinesis, was also the person who convinced me to give their 4-sub Debra DBA system an audition in my room. He and Duke really know their stuff and are very helpful.
Congrats on your humongous and impressive Classic Audio T-5 Reference speakers, too! I wouldn't think those huge things needed any bass help. But that's the amazing thing about the whole 4-sub DBA concept, it'll integrate seamlessly with virtually any pair of main speakers and in any room, when positioned and configured properly.
My only advice is to configure the volume and low pass crossover frequency filter settings as low as possible with the bass still sounding very good to you ("very good" meaning powerful, detailed, dynamic and natural). Oh, and don't forget to make sure your chinstrap is securely buckled.
Tim |
ieales,
I get similar results from my 4-sub DBA as millercarbon, seemingly effortless bass that is seamlessly integrated with my main speakers regardless of volume level, that is as solid, powerful and dynamic as the source content dictates.
Bass smearing and bass masking of midrange frequencies occurs when the deep and mid bass frequencies are accentuated, meaning the lower frequencies are artificially boosted, are not in relative balance in volume intensity with the rest of the frequency spectrum and, therefore, not accurately and faithfully reproducing the recorded source recording.
Of course, this assumes the source material was well recorded with the full frequency spectrum in accurate and natural relative balance without any frequency portions being exaggerated or attenuated.
Whether a 4-sub DBA system over emphasizes the bass frequencies, resulting in smearing or masking of the midrange frequencies, or accurately and proportionally reproduces the bass frequencies, resulting in no smearing or masking of the midrange frequencies, is completely determined by the user’s sound quality preferences and the subsequent sizing, positioning and configuration of the DBA system.
The specific size and bass output capacity of the subs utilized, the specific positioning of the 4 subs in the room, along with the specific volume and low pass crossover frequency settings, allows for a wide range of bass reproduction options which, as a result, allows for a wide range of overall system sound quality permutations. Flexibility and scalability are just another couple of advantages of the DBA concept.
For example, my overall system sound quality preference is accurate, detailed, dynamic, well balanced and natural. My 4-sub DBA system, the Audio Kinesis Debra model, utilizes relatively small, 1’wx1’dx2’h,subs that are rated at 4 ohms and have 10" drivers. My room is 23’x16’ with an 8’ ceiling.
Based on my overall system sound quality preference for high quality, I positioned and configured my DBA system so that the bass would be perceived in the room as being accurate, detailed, solid, powerful, dynamic and well balanced with no portion of the audible frequency spectrum accentuated above another.
I accomplished these goals, of optimum bass quality rather than bass quantity, with the DBA’s bass by positioning 2 of the subs along my front 16’ wall, with each at opposite ends about 1’ in/away from each corner. I positioned the other 2 subs toward the rear of the room, with one placed along each of the 23’ side walls and, again, about 1’ in/away from each rear corner. I also placed 2 stacked GIK Tri-Trap bass traps in all 4 corners of my room.
Avoiding placing any of the 4 subs in corners and utilizing multiple bass traps in all corners is a good start. But my goals also required the proper configuration of the DBA system for my overall system sound quality preferences to be attained. I precisely matched the volume of the DBA to that of my main speakers, running the mains full range down to their rated bass extension of only 35 Hz, and set the low pass bass filter to 40 Hz.
The result? Music and HT reproduction that is accurate, detailed, solid, powerful, dynamic, well integrated and well balanced with no portion of the audible frequency spectrum accentuated above another.
The only exceptions worth mentioning occurs on some HT Blu-Ray discs during LFE channel reproduction when the DBA’s bass can become so decidedly unbalanced and overwhelming that it shakes the seats and walls in the room to very enjoyable and satisfying levels.
Tim |
