It will be helpful....that's what volume controls are for....
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A simplified answer:
Any deep bass source will produce imperfect in-room frequency response as reflected long bass wavelengths collide in the room. In some cases, the collisions are destructive (resulting in frequecy response dips) in other cases they'll reinforce (creating peaks). The good news is, with subs you can locate the unit to minimize the problem. With full range speakers, the bass generation goes along with kids and highs - to a spot where overall response sound best.
Now, think about potentially "fixing" the bass dips, for a second. The frequencies at which the dips occur are primarily a function of the distance from the sub to the nearest wall (quarter wave effects). Place the first sub wherever it shows smoothest response. It won't be perfect, but it's probably better than you'll get from full range speakers out in the room.
Now, add a second sub. By properly positioning the second sub (probably significantly further from or significantly closer to the nearest wall than the first sub) you can generate a completely different frequency profile of response irregularities. The trick is to position the second sub at a place in which its irregularities will offset the first sub's irregularities.
If you can manage to get it even close to right, the summed response from the two subs is smoother than the response from the single sub. Add a properly positioned third sub and it will be smoother still. A'goner Duke L. sells the four unit swarm subwoofer system which is designed around this idea. This is the primary benefit of multiple subs, IMO.
As a second (completely unrelated) benefit, you will also tend to reduce distortion when you add subs. To generate a given SPL from any sub, you'll require it's driver to travel a given distance (excursion). Add a second sub and the requisite excursion for each of the two drivers to generate the same total SPL is reduced. Distortion in subs increases (usually dramatically at some SPL) with driver excursion, so you get improvement there, too.
Bottom line:. If you have the budget and space to put a second sub where it belongs, it's usually a good idea to do so.
Doing it by ear will usually take time. It's a bit of a PITA, but I've done it successfully several times. Unlike Coli, I've never failed to achieve smoother FR with a second sub. If you use an SPL meter or a RTA, it's much easier.
These days, I use Audyssey. It's certainly not an audiophile approved method, but IME it's a 100% foolproof, no-sweat method of smoothly integrating one or two subs into a system.
I have a 13.5 X 13.5' listening room and decided to bring up my JL Audio e110 sub from the basement HT system to hear what it sounded like. It helped greatly, so I bought a second sub and have no regrets. I do have DIY bass traps in all 4 corners now and the crossovers on the subs turned down, just filling in the bottom octave. The biggest impact in my system so far.
I recently went from a single to stereo pair of subs, wanted to move more air, what I was not prepared for was the startling effect on midrange to high frequencies! More detail, wider stage, no joke it was jaw dropping. The explanation I found was there is a phase shift from summing 2 channels into one sub, or mono, masking information, had I known this years ago would have done a pair right from the start I second meerzistar's advice!
I have 2 Rel G2's integrated with a pair of Sonus Faber stand mounts driven by a pair of McIntosh 601 mono blocks. Tons of power for a treated 11'x 16' listening room. The REL's are crossed over 55 and volume quite low at 8 to 10 on the REL volume setting. Works extremely well....haven't heard many systems I'd trade it for. :) Get a second REL. Jim Smith in "Getting Better Sound" recommends 2 subs, even if inexpensive vs 1 higher priced one.
My 2 cents.
perfectpathtech7 posts04-22-2016 3:08pmForgive perhaps the dumb question. I assume what you heard in the mids and highs are only present when the subs are playing low frequencies which is not all the time. So does that mean for parts of the music when there is no low freq information you do not have the improvement you described? Or is the improvement due to you crossing over your speakers at a higher freq?
I understand the idea the idea that multiple subs can help to smooth out modes but of course subs can only do this when they are outputting sound at and below the crossover point right? If the music I am listening to do not information at and below the cross over point throughout the song then will I hear differences in the mids and highs depending on if my subs are outputting sound?
ptrck8874 posts04-22-2016 7:15pmI have 2 Rel G2's integrated with a pair of Sonus Faber stand mounts driven by a pair of McIntosh 601 mono blocks. Tons of power for a treated 11'x 16' listening room. The REL's are crossed over 55 and volume quite low at 8 to 10 on the REL volume setting.Do you mind if I ask which Sonus Faber monitors you have? I have the Evolutions and cross mine over at around 35hz. At least in my room the Evolutions have a flat response down to about 40hz. BTW, the G2s are crazy!
I find that there is usually a major improvement in the upper bass and much of the mid-range (say the two octaves below middle A and a fair bit of the octave above) when you get the subs integrated properly. "Properly", in this case, includes smoothing frequency response thru the x-over point. That smoothing can be done with more subs, EQ, or room correction (or any combo of the above).
I can't specify exactly why, but I'd speculate that it's probably a matter of cleaning up hash and overhang around/above the crossover point. If not addressed, I believe it may have the impact of muddying response in the area described above. Whatever the reason, the effect is usually very noticeable. If you run Dirac, just a-b (single sub or a pair) with correction engaged and then off-line. My guess is that you'll immediately understand what I'm talking about.
I had 5 subs in operation inside a sealed 10x14 room, I even went so far as to install a solid core door and duct tape any suspected leak points around floor and over the heating duct to keep room as air tight as possible. Not only did it sound great its really nice feeling the pressure waves through your whole body. Base treatments are highly recommended otherwise you will have an impossible time sounding good while getting up to desired SPL.
martykl3,308 posts04-23-2016 8:37amTbooe,Based on your explanation does that mean these improvements to the mid and upper base is only present where the subs are actually outputting sound, assuming I am not using EQ, room correction, or digital Xover? If so, when the subs are not smoothing out the sound with their output, that the improvements to the mid and upper base is not present? Since there is not sub information throughout a song, does that then mean the mid and upper base will have inconsistent sound depending on whether or not the subs are outputting anything?
I'm not sure I'd want to slice my comment that fine. A single subwoofer system that is smoothed with the addition of a second sub, EQ and/or room correction will IME usually produce a sense of cleaner mids than it did prior to such smoothing. As to the conditions required at any specific moment to hear that, I honestly can't say that I've paid enough attention to specify. I can say that the effect has always been pretty evident (and pretty quickly evident) in the systems I've adjusted in this fashion.
Thanks guys. I am just trying to understand the phenomena people describe that subs can help with other areas of the freq response. To me, this can only happen if the sub is outputting something unless you are using an EQ or room correction. Anyway, I am going to buy a usb mic and use REW to measure my room. I am curious to see how the freq response looks. Regardless, I am very happy with the way my room sounds now after re-positioning my speakers and adding 1 sub. I will definitely plan on adding a second one later this year once funds become available. Merry xmas kids!
tbooe, sorry wife has that crappy flu been busy the last few days.
In response to your first question, I am running mine 5' behind
my mains offset in the center.
As for the second question, my speakers are full range, I run the subs off a second set of outputs on my source, my amps and speakers are not connected in any way to the subs, except for ground at the source. The improvement in the upper end is a
constant regardless of whats played.
perfectpathtech8 posts04-26-2016 8:51am ...The improvement in the upper end is aThank you for the reply and I hope the wife feels better.
This last comment is what gets me so confused. I get how a sub can help with smoothing out the sound when playing. But in the absence of a xover or room correction, how can a sub help with other areas of the freq range when it is not outputting sound? I am assuming of course that during a song, the sub is not always playing anything. What am I missing here?
Thanks, she's been throwing up for almost 10 days, really nasty virus.
It is hard for me to wrap my mind around as well, as I understand it
summing 2 inputs L + R into mono creates as phase shift which translates into signal smear if you will, I assume because its low signal its a connection thing the smear happens at the inputs and has no bearing on wether the subs are playing or not. If I leave the subs off or on the improvement is there. Glad to hear you are going to add a second one this year, you will not regret it!