How does adding a second subwoofer improve your systems SQ?


The title pretty much covers my question. Thanks for any insights or comments.   
markj941
With two subs (or more), you often can get more even bass frequency response. You have to be willing to find the best spots for them.
Calling MC. Dont worry it wont be long. 
Search DBA, distributed bass array, Geddes, and study posts of noble100, audiokinesis, and millercarbon. Geddes worked out the relevant science and acoustics that is the basic foundation for using multiple subs. Duke as the only current maker of these type systems has by far the greatest technical knowledge and experience. Tim was a fairly early adopter and has posted extensively on just how well the Swarm works. And I myself used their combined knowledge in building my own DBA. https://systems.audiogon.com/systems/8367 Which is how I know the more, the better.
@erik_squires Another great post! Really well done, and attractive to boot. I’m wondering if you can tell me what the sonic difference might be if I added a second subwoofer? 
The reason that I ask is that in my present set up, my single subwoofer provides enough bass and it is fairly clean and tight. I had to connect the subwoofer to the two mono blocks and that provided a speaker level input into the sub.

 Many people have said that I really need to have a second sub woofer but if I were to get another one what would I notice about the sound (assuming that I could place them correctly)? 
Thank you for the kind words @hilde45

It's hard to tell without measurements, honestly, but before you get to your second subwoofer, the room treatment and EQ could be considered. With 1 sub, and good room treatment, properly set up, it can be magnificent.

A second sub, if you are free to place it anywhere, can certainly compensate for any big nulls, but what if you don't have any, or what if you use an open layout which does not lend itself well to standing waves to begin with?

Best,

E
Please pardon my ignorance, but what is SQ?
markj941 OP
How does adding a second subwoofer improve your systems SQ?

Amazingly so! because bass is done in stereo on more albums than you think.
People that use one subwoofer have no idea that they’re screwing up any stereo imaging that the bass has. You need two subs L & R close to the mains if you are to faithfully reproduce what the studio recording engineer wants you to hear.

I have many albums (CD’s) even from the 80’s 90’s that have <100hz bass notes that come out of either left or right channel. So to mon’ize these recordings into just one mono sub is not what the recording engineer wanted you to hear.

EG: Just listen to the second last track "It’s A Miracle" on Roger Waters "Amused to Death" at the end there is a kettle drum roll that rolls around the room on the ground from right to left and back again. If you had just one sub it would ruin that mesmerizing effect totally.
And the harmonic structure of bass notes like this above go right up into the midrange
Another that comes to mind is Ricky Lee Jones self titled album, it also has tracks where the bass only comes from one channel or alternates

Cheers George
EG: Just listen to the second last track "It’s A Miracle" on Roger Waters "Amused to Death" at the end there is a kettle drum roll that rolls around the room on the ground from right to left and back again. If you had just one sub it would ruin that mesmerizing effect totally.
This statement is misleading. I get exactly that effect using only one sub in my bedroom system.


The issue is that below about 80Hz in most rooms, the ear cannot distinguish where the bass is coming from because it cannot detect a sound until the entire waveform has passed by the ear. In most rooms at about 80Hz, the waveform is so long that it has bounced off of the rear wall and is already passing the ear in the other direction before the waveform has completely passed the ear on its way to that rear wall!

It is harmonics of bass instruments like the string bass, bass drum, tympani and the like that convince you that the sound is emanating from in front of you and whether it is to the left or the right. So a single sub works, 2 subs better, 3 better than that and beyond 4 you're at the point of diminishing return. It is important however to make sure that bass information is coming from both main channels to the sub system!


However this is only true if the sub or subs do not attract attention to themselves and to do that they can't put out anything above about 80Hz. If they do, now the subs have to be time-aligned with your main speakers and its a royal pain in the rear and at that point a DBA doesn't work. So as a general rule, make sure your sub never ever goes over 80Hz.
Let me give you a practical example-

In my 2-channel setup I basically have only two small areas where my left and right subwoofers will fit- so positional flexibility is very limited.

I recently measured the response of each sub during my integration process.  The left sub had a dropoff below 30 Hz and small peaks above 60 Hz.  The right sub was flat down to 20Hz but lacking some impact.  
When both playing together the response is smooth and flat at my listening spot, sounds exciting, deep, dynamic and smooth.  
Having two subs is a great advantage to achieving a balanced sound if you have limited room to position them.     
I get exactly that effect using only one sub in my bedroom system.

You are getting a just sample of what’s going on down there, you are drawing conclusions about the Roger Waters track with regards to hearing it with two L and R subs, it’s obvious. Because if you did you wouldn’t be saying what you just said.

I done the a/b with 1 mono vs 2 in stereo. And my subs are at 50hz 4th order, and the difference is huge.
Anyone who mono’s their bass below 100hz is ruining many albums that have been recorded in stereo down there.
  
It may not matter to the vinyl crew so much because they’re lucky to get 10db of channel separation down that low from their phono cartridges, so they are basically listening to mono anyway.
Good article on speakers  by Floyd Toole, close to the end there’s a section how to get great sound from a single subwoofer. As long as you’re only interested in one listening position.
https://www.harman.com/Documents/AudioScience_0.pdf
Avanti,
Having two subs is a great advantage to achieving a balanced sound if you have limited room to position them.    

This is what I was waiting for. Unless you have a dedicated audio room, I don't, there are definite limitations to most all rooms. My system is in my living room. I simply can't put subwoofers where they might sound best. I'm confined to placing my sub next to one of my main speakers. Avanti, so your thesis is, buy a second sub and place next to the other speaker and enjoy the music. 
I am a huge fan of Floyd Toole, but in general he seems to not consider affordable bass traps as solutions. He kind of alludes to this:

Short of hiring an acoustical consultant, and being willing to rearrange the furniture and possibly rebuild the walls, what can be done?

So his entire solution space is outside of this possibility, which may be a choice based on who they expect their customers to be.

Other, more modern acousticians have written with the presumption that bass traps are an option and they don’t throw up their hands quite as easily to the problem.

Once we allow for bass traps, things get much better for subs and EQs, and it is from this perspective that I often challenge the DBA cultists. A well integrated single sub, in a well treated room, including bass traps performs really amazingly well.  Two subs is better.

Best,
E
My four subs are in my living room and only one is visible.They easily tuck behind furniture,the wiring runs along the baseboards.The one that's visible is going to masquerade as a table supporting a plant soon,when it's safe to shop again.
Yes Erik there are room treatments too;-)
simple answer

1.  2 subs load the room better, in many applications

2.  bass is supposedly non directional, but in reality, subs have crossovers that 'leak' into higher, directional frequencies... stereo subs put these in L&R space where they belong (moreso)
markj941 OP

If members here that are pro one sub, and running it off a HT sub output.
Forget that single HT preamp sub output, get two subs run both subs from the main L & R preamp outputs 
You will find if you have two subs and in the HT programming "set the mains for large" with "no sub" picked, then cross the 2 subs in at where your mains fall off, get the phasing and level right ect.
Your in for a treat from what can come from active proper stereo setup bass bins.
Your mid sized floor standers or large book shelves will have the scale of sound that you only get from big floor standers like Wilson Alexia Max Alex ect.

Cheers George  
@erik_squires , you already posted a link to your blog page where you wrote: " I am no longer a fan of this idea [distributed bass array/muliple subs] due to the fan boys and how cultish they have become. "

And now you post: "... I often challenge the DBA cultists..."

This is starting to look like trolling, Erik. 

Maybe you can advocate for your preferred solution without name-calling? 

Duke
Duke,
You already know where we stand.  I won't be editorialized by you.
Erik
" I won't be editorialized by you." 

I suppose we're both free to call it like we see it. 

Duke

So some of you may be wondering which actually makes the biggest improvement, adding bass traps or adding more subs. Since bass trap advocate Erik Squires is playing the "cultist" card to discredit multi-sub advocates, I’m gonna play one of my cards. It’s an "acoustician" card.

Matt Poes of Poes Acoustics, who doesn’t sell subs but who gets paid to install bass traps, briefly compares his experiences with bass traps vs multiple subs, as far as effectiveness below 80 Hz.

Takes thirty-two seconds to listen to. From 37:37 to 38:09. Click on the link, suffer through the inevitable ad, and it’s already cued up:

https://youtu.be/shHY7EHY4MA?t=2257

I have zero affiliation with Matt.

Duke
distributed multi-sub system manufacturer since 2006 (so take me with as many grains of salt as you need to)
Toole didn't throw up his hands in defeat to him the answer was in equalization. I also agree with his assessment that to much absorption leads to an acoustical dead room like a studio, reflections aren't all bad and the lower 300-500 hz is where most problems are unless your speakers are all over the place in the upper area. Multi sub is easier to get the bass equalized  but for a single position and enough work one can suffice. 
Toole is so great. I especially liked him in Becket. 🤴 
After watching the video posted by @audiokinesis I have to say this mirrors my findings. I have gone down the road with numerous acoustic panels, bass traps, and diffusers. I would say the best I tried were from a long defunct company called Eighth Nerve, and the most effective trap was the triangle placed in the ceiling corners. In my system my DIY DBA made the most significant difference (in a bi-amp or tri-amp set up) and I was able to rid myself of a lot of extra stuff hanging on my walls in the process.
Atmasphere, in general I agree with what you say with point source speakers that are not digitally corrected and time alligned. However when it comes to linear arrays particularly tall ESL dipoles the situation changes somewhat. If the subwoofer system does not want to get loss under the linear array it also has to radiate like a linear array. This requires a driver every 5 feet or so with the line ending at wall boundaries. If the system were on a long wall this might require more than four units. Dipole ESLs just do not do well under 100 Hz. As you mentioned crossing up higher than 80 Hz without digital correction won't work well. You will always know there is a sub woofer down there. But with time and phase alignment you can go up higher. I cross at 125Hz 4th order and unless you open your eyes you would never know there was a separate subwoofer system and because the sub woofers are forming a linear array the relative volume between the subs and satellites does not change with distance. The linear array also minimizes room effects which allows me to do room correction with much less power. The the resulting improvement in performance of the ESLs at volume is imminently noticeable as is the marked improvement in head room. It's like adding a turbocharger to your engine. 

Mike  
I should also note that I have never used digital correction with a point source system. I have to believe that subwoofer integration would be easier and better. Although I thick you could get away with a higher crossover the benefit would be questionable as the woofer in the satellite has a very limited range whereas with a one way ESL the entire frequency band is affected by the long excursions bass requires particularly at volume. When a very low note comes along say 18 Hz at volume you can actually hear the music flutter. 
@markj941,
good sum summary.  i just added two REL t9i to my system and am very happy with the sound.  they integrate very well with my large british monitors compared to two other sub brands i tried. 
an important considesrtion is distance from wall behind them.  closer than 8 inches created strong peaks in the response.
You are getting a just sample of what’s going on down there, you are drawing conclusions about the Roger Waters track with regards to hearing it with two L and R subs, it’s obvious. Because if you did you wouldn’t be saying what you just said.
It acts the same way on my main system, which has bandwidth to 20Hz out of the main speakers (Classic Audio Loudspeakers Project T3.3).

It appears that bass traps have their cultists too. The simple fact is they are not always practical. A local customer of mine has been using them for years; I finally got him to try a DBA and it solved his bass issues which he's been fighting for over 20 years. His room is arguably the most treated room I've seen anywhere. He was pretty adamant about how great they were until the DBA showed up.  At this point he's running only about 1/5th of what he had before. In my room I simply don't have the space to place them at all, but adding a pair of subs (thus creating a DBA) is easy since they can hide under a couple of tables in the space. No way could I get bass traps to do the same job in my room, and the GF won't stand for it anyway. Science works so much better than myth for solving these problems.
Hi markj941,
I added a set of  REL subs to my system with floor standing speakers and It was a great improvement .Most notable was that the overall soundstage was cleaner and there was a much greater sense of depth. The bass was more authoritive, the details were extended especially in the midrange. Drumskins, toetapping, broken guitar strings, etc. all clearly audible. My system is set up in my livingroom, and I do not have any real room treatments to speak of. I dream of having a dedicated room one day, but the addition of the subs definately elivated my system to the next level.  Mark Knopfler's Private Investigations is also a good comprarable. 

Good Luck
In my experience, bass traps do help, but they help mainly by controlling bass overhang at frequencies above 40 Hz -- and that’s the BIG traps. Trying to even bass response significantly with bass traps is a losing proposition. But in a room that retains bass, they can be useful for sure.

Still, rejecting DBAs because some people are tireless boosters is like rejecting vitamins because some think they cure everything. It is not logical to discard a proven approach because some adherents are obnoxious (not that we have any of them here).

I thought Erik’s linked essay was useful except for that tack. In particular, it pointed out that adding subs is not plug-and-play, if one wants to get good results. Good crossovers, some kind of EQ, and phase matching have been indispensable, when I’ve done it.
How is this even a discussion in the audiophile world any more?

- 2 subs is better than 1, due to evening out of peaks and valleys. 4 is better than 2. In a rectangular room, 3 may not be better than 2 (may not be intuitive but trust the math). This works because of inability to localize bass (see below).


- bass traps obviously can help. They also have to be very big to work really well, and the bigger the room, the bigger they need to be due to the frequency of the bass nodes. Small resonant traps also have small bandwidths.

- No matter how much some people will plead, we can't localize bass less than about 120Hz, hence using 80Hz with steep crossovers. There will always be lots of claims this is not true, and in every case this will be a factor of unequal room response between channels, poor sub/main positioning that causes unequal room responses and/or beamed cancellation effects, inadequate slope, or distortion. Don't believe me? You don't have to. There are a plethora of studies done on this (proper ones, not ad-hoc with improper setups). If you choose to ignore them, I can't help you.


- When Toole was talking about the potential for equalization, he was not talking only about frequency, but phase as well (between multiple bass units) for optimization

- If you think massive floor standers with deep bass response are the "ultimate" in reproduction, you either have an acoustically great room with a significant amount of acoustic treatment, and well shaped room at that, or you are misinformed. The position for optimum bass response in a room of two speakers is not going to be the same location for optimum in-room response, imaging, sound-stage, you name it. It sure sells some expensive speakers though, and since the average audio reviewer blathers over anything expensive, from pictures probably has a less than ideal listening room, and almost assuredly knows the bare minimum about acoustics and likely even less about the science of sound, should one be surprised? Most don't even attempt to measure in-room response, let alone direct/reflected energy at the listening position in order to optimize performance and/or provide consistent reviews.


- On the spouse factor, discreet subs are likely to be a better sell than large floor standers in less than optimum locations for bass, SQ, or spouse acceptance.


Whether you believe any of what I wrote or not, does not really matter, people will still pay me to design and implement acoustic spaces and the sound systems in them, and acoustic products that use these and more complex principles (and tools), that are based on science, not conjecture. Many aspects of the perception of sound are subjective. Many aspects are not. You will have an easier time achieving audiophile nirvana when you accept which are which. Reality is a harsh mistress. She's not your mom.
Thanks ggc. I just ordered my second sub. Actually, thanks too all
that contributed to this discussion. It was informative and at times entertaining.
markj941 OP
Thanks ggc. I just ordered my second sub. Actually, thanks too all
that contributed to this discussion. It was informative and at times entertaining.

Good for you, getting the second sub.

I just did an experiment last night with myself my wife and son, where I played an alternating left to right 100hz sine wave for 5 seconds in each channel for a total of a 30sec run only through the L and R active subs, the main speakers amp amp turned off.

All of us with eyes shut could easily detect which side of the room the 100hz sine wave was emitting from within the first left to right change over in 10sec!!!.

This is proof that digital with it’s over 100db of channel separation will be stereo in the bass to your ears if produced by the recording engineer, and you’d be surprised just how many are.

Like I said before, I have many cd’s where you can hear the very low bass from just one side. Another good one is Brian Bromberg’s "Wood" double bass’ist

It’s better to have 2 subwoofers powered individually from left and right channels, "not from the single rca subwoofer output" if using a HT pre or amp.

Cheers George
@mike_in_nc wrote: " I thought Erik’s linked essay was useful except for that tack"

Agreed. Erik contributes a great deal of highly useful information and well thought-out ideas.  When I'm skimming a thread, I'll stop and read each of his posts. 

Duke
I know you have convinced yourself you have easily detected 100Hz bass frequencies in 10 seconds (why not instantly?), but no, you have not proved stereo bass, far more likely is that you proved your system has a room signature that varies from left to right, distortion, vibration, etc., hence why it took you 10 seconds, technically two switch-overs, to detect. Proper experiments for things like this are not as easy as they sound, and most people are not set up to do them.

p.s. If your eyes were closed, how did you know which was left and which was right, as opposed to just noticing a difference?  Didn't you set up the experiment as randomized left/right, record your results, then check after?

What speakers/amplifier?

All of us with eyes shut could easily detect which side of the room the 100hz sine wave was emitting from within the first left to right change over in 10sec!!!.

This is proof that digital with it’s over 100db of channel separation will be stereo in the bass to your ears if produced by the recording engineer, and you’d be surprised just how many are.

you have easily detected 100Hz bass frequencies in 10 seconds (why not instantly?)
Really??
Because the left plays for 5 sec then the right for 5 seconds, keep doubting and "you’ll be the looser" on this one.

If your eyes were closed, how did you know which was left and which was right, as opposed to just noticing a difference?

Same as you can tell left from right with eyes shut for anything heard.

What speakers/amplifier?
Just search for what I have as my main system
It’s the family TV room, HT setup, not my main audio room.
Elac FS-249
Marantz SR5014
2 x Yamaha linear amps, servo controlled, YST-SW305 classic subs xover at 60hz.

I won't be the "looser". 25+ years of acoustics with personal contacts with many of the leading people in the field, a bunch of peer reviewed papers, a deep understanding of the science of sound, psychoacoustics, and enough interaction with the research community, often helping to design experiments, and well beyond the need to prove anything to anyone in my community.

Unfortunately, or fortunately, I care enough about audio that it gets my back up with people who think they know what they are talking about, but have no clue how to even design an experiment, let alone the underlying principles of what they are trying to test, speak with complete conviction and lead other people astray, causing them to waste precious time and hard earned money to achieve inferior results.


While your main seem to be of good quality, the subs are not very good quality. They were inexpensive new, and used are quite low cost. When they say "servo" they don't mean a servo in that their is position feedback on the amplifier, it is just a marketing term essentially for what appears to perhaps be a current feedback output design as opposed to voltage feedback. Odds are the distortion is not insignificant given the cost constraints.

So the left plays for 5 seconds and the right for 5. You still said it took 10 seconds, i.e. one complete cycle. Normally you can tell source location near instantly. You wouldn't have to wait till the switch back to be sure. This is a "really" moment, because it goes back to the difference between actually localizing bass frequencies, and detecting a differential room signature (potentially exacerbated by distortion).

Are you subs placed in close proximity to your mains?
25+ years of acoustics with personal contacts with many of the leading people in the field, a bunch of peer reviewed papers, a deep understanding of the science of sound, psychoacoustics, and enough interaction with the research community, often helping to design experiments, and well beyond the need to prove anything to anyone in my community.
Wow you really like throwing that one around don’t you, a shrink would be itching to get in on this one.
https://forum.audiogon.com/posts/1955883
https://forum.audiogon.com/posts/1955879

Half as many as I have, and I don’t really care what you have sunshine.
Fact is you benefit greatly from having two L & R subs instead of one mono’ed one. And many others hear the same.

So the left plays for 5 seconds and the right for 5. You still said it took 10 seconds, i.e. one complete cycle.
Yes one cycle, and you have a problem with that, "clean up aisle 4", can’t see the forest for the trees.
You have many contacts among the lumberjacks
To get you facts when someone attacks your imagination
But nobody has any respect, anyway they already expect you to all give a check
To tax-deductible charity organizations

Ah, you’ve been with the professors and they’ve all liked your looks
With great lawyers you have discussed lepers and crooks
You’ve been through all of F. Scott Fitzgerald’s books
You’re very well-read, it’s well-known
But something is happening here and you don’t know what it is
Do you, Mr. Jones?
You know when the Pet Audio Rock dude responds to your posts with ad-nauseum posts that have nothing to do with the topic and carry no relevant content that you must be doing something right.

George,

In my professional world, when you do something and get results that differ from people who have spent extensive research time on a topic, the normal inclination is to assume you have done something wrong, or assume there is something in your setup that you are detecting, that was not what you intended to measure. In this case, a low distortion microphone setup could probably reveal what was wrong, but I don't see an indication you have done that. If you are not willing to consider that something is wrong in your setup, then you are unable to fix it.
A new stalker. goodie, goodie! I was getting bored with the last pseudo skeptic anyway. I don’t even remember his name. 😳

”In my professional world....” Thats gold, Jerry, gold! 
Did you write that all by yourself?
By the way, your moniker is eerily similar to roberttcan, another pseudo skeptic here a couple years ago. Any relation? As in the same person! This is too weird! 😩
Maybe I am, maybe I am not, maybe I am just here to trigger the Pet Audio Rock dude. The universe is so complex, perhaps we will never know will we. Just remember, my words are but a conduit to aid you in making yourself look less relevant than I ever could.
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Let’s dance, flyboy! Maybe you’ll do better this time around. 
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