How To- Perfect Subwoofer Integration

If you are able to measure with RTA as described, particularly getting the phase adjusted correctly, you can keep the sub in the corner for the best reinforcement and still achieve "centered" bass imaging. The bass in my system sounds like it is originating dead center despite a corner placement. Proper phase adjustment time aligns the woofers to the mains according to your ears- if you measure / put the microphone at the listening spot.
I did this in my car as well, subwoofer in the cargo area, time aligned to the front seat, bass sounds like it's coming from in front of the windshield.

 

That sounds very interesting, thanks. So far I've left my sub's phase knob at zero while I fine tuned the level and crossover point. I'll need to give the phase a try next, but I'm a bit wary about creating cancellation effects in the frequency region where the mains and sub overlap. Doesn't hurt to try it though.

 

Nulls. In the end I managed +\- 3.5db from 30hz-20hz. At that,I was done.

 

Keep in mind, adjusting the phase can only add lag to the timing. It cannot make the sound wave come out before the signal arrives at the sub.
So moving the sub farther away plus diddling with the phase adjustment may line up the wave peaks but it will be out of sync by at least one wave cycle, maybe more. Putting the sub on the same plane as the mains or in front of the mains gives you a better shot at time aligning while syncing phase.

 

After thinking about this a little more, the subwoofer positioned behind the main speakers is still the preferred position. You get corner reinforcement and can still time align with the main speakers even though they are closer to you.
You start with the sub being 180-degrees out of phase by setting the plolarity switch to inverted. Then you adjust the phase knob to time align. Starting from 180 degrees out of phase lets you "back up" the phase to align the peaks at the crossover frequency. Even though the phase adjustment can only lag or delay the timing, starting from 180-degees out of phase allows you to "lag" until the cycles are in sync.
Same principle in mobile audio- even though the subwoofer is farther away from the listener than the door speakers, you start out with inverted polarity phase and then adjust the phase control to dial it in.
In my car, the subwoofer sound is originating from dead center of the windshield despite the fact that it is 8 feet behind me.
In my home system, all of the bass seems to originate from the main soundstage between the speakers.

 

@avanti1960 The pressures and rarefications may be in sync but the time alignment will be off at least one cycle. Throwing out round numbers phase example you suggested is:

Assuming no HP filter used between the mains and the sub, mains playing full frequency.
-180 degrees (phase switch)
-45 degrees (estimating the phase alignment knob in your example)
-10 degrees (estimating the distance from mains to sub)
-125 degrees (estimating the phase shift of the LP filter used in the mains)
-360 degrees = one cycle lag.

If you add a HP filter to the mains to releave their low frequency duty then you add another phase shift moving the mains forward in time.

Which could look something like this.
-180 degrees (phase switch)
-0 degrees (estimating the phase alignment knob in your example)
-10 degrees (estimating the distance from mains to sub)
-125 degrees (estimating the phase shift of the LP filter used in the mains)
-45 degrees (estimated the phase shift for the HP filter used on the mains to crossover)
-360 degrees = one cycle lag.

Notice that the HP filter between the sub and the mains moves the mains forward in time requiring less shift added to the knob.

The reality is that we don't know the values of any of this stuff without measuring. Can we hear the difference of one cycle? I don't know. I do know that I can hear when there is significant timing lag in the sub signal. How much? I don't know so I shoot for as close to time aligned as possible.

For those suggesting integrating by ear is good enough, well, good luck. This is just a time delay example and doesn't even touch room modes, nulls, absorption, or parametric EQing.

 

Just curious as to the procedure described by the OP just using available adjustments on the sub - how many iterations and measurements did it take to get to 'end state'?

It seems to be a process of making an adjustment, then measuring, then observing the result and if not 'better', going back to make another adjustment, measuring...apply, rinse, repeat.

Not saying the by ear approach is any better, but subs or equalizers, like DSpeaker, with auto cal seem to be the lazy mans approach to at least eq'ing and levels.

 

That is correct. It is a lot of tweak, measure, graph, analyze, repeat, until it is set correctly. Once set correctly there is no more fiddling with levels to "fix a mastering". IMO, if you are using the sub to EQ each album then it is not integrated correctly.

The DSpeaker can measure, analyze, and tweak quicker but it does not account for the rest of the issues like ringing from modes and the absorption required to fix them. For that you still need to measure for yourself to see where the trapping needs to be placed.
Yes, it is possible to reduce sub-bass ringing through absorption but it requires feet thick traps of low density fluffy insulation.

Most people start out looking for a quick solution then get discouraged when they find out there is no quick one size fits all answer. Each room and setup is unique. Dropping a sub in a room and fiddling with knobs by ear is one way but it won't get the most out of the situation.

 

But it can come pretty close. Of course measuring everything will yield a more perfect result but it won't make a poor recording sound OK without fiddling with at least the sub's vol knob unless you suscribe to the ¨listening what the producer intended you to¨ approach which I personally find to be bollocks, esp with budget, old rock recordings.

I usually rarely find myself reaching for the vol knob myself . Instead I disengage the SPK 2 button on my receiver (speaker level connection) to temporarily leave the sub without signal and let my bass-capable mains do the job on their own in case the recording has enough bottom end.

Kudos to all of you who go to those tweaking lenghts to perfect things though. I'd die of an OCD attack if I attempted that

 

I cringe when I go to someones house and they have the sub just rumbling. Less is more when it come to subwoofers and music for me, there is a fine line, when crossed you are subtracting from the music, not adding.

 

At CES 2015 I sat in on a REL demo. They played music with and without one of their larger subs. It was amazing how much better the main stereo speakers sounded when played with their sub, which they had dialed in via their software (I think). It was the first time I heard the addition of a sub make the mains so much more detailed with better imaging rather than just adding boom to the sound.

 

It took about 30 to 45 minute to reach the final settings- it helped to have the pink noise track playing on repeat and the laptop in handy view nearby.
If you do it in the sequence mentioned it will be the quickest path because the sequence is important. I did coarse adjustments first (1/3 turns) then a few finer adjustments once I found the zone.
However- I have been listening to it for nearly a week and have not had the urge to adjust it at all! In previous subwoofer lifetimes I constantly fiddled with the controls and was never really content. So ultimately it is a time saver, you just pay it forward!
If you follow this process and have the required adjustment capability you will get there.
The final response curve reads like a well positioned full range speaker- not a sub plopped into a system and calling it good.
It sounds that way too.

 

GET GREAT RESULTS BY EAR for 2.1, simply use online test tones. First off, if your listening area is the very typical confined area of a room (such as my sofa) you need only tune for that area. In this situation it's easy to properly place the sub by ear - the methods being common knowledge by now. Well a single listening area also makes it fairly easy to tune a sub by ear...especially if you use test tones. I'm computer based so I simply go online and play tones. For my recent sub I went here www.audiocheck.net/testtones. I use their tones in a very simple sweep (if you will) up and down of freq while I'm back and forth turning & moving things. The adjusted result is a very acceptable flat response as I perceive it.

In my case my reference standmounters play beautifully at their low end and naturally roll off at around 70hz, I need only serve prime sub range. My route is I first tune by ear with music alone, then I tune with tones - and adjustment (a little) is usually required. And I tune default for hifi audio so after the test tone tuning I then turn down sub volume a tad. That's my default setting. I'm blessed with needing to fill in only a wee bit o bass, but what it adds just amps up the magic in music.

I do like a rattle so of course Jurassic World gets the boost...it's awesome!!!! .

 

I just got a sub last week and am going about it using this approach. This sub is downward firing and is crossed over around 50 so it is not as challenging as it is with speakers where you have to cross over at higher frequencies. However, I am sure that it is going to take another clue weeks playing both music and using these test ties with an SPL meter to really dial it in.

Even after a limited time playing with it, I will say that the improvement is substantial. The music has a presence that it never did before.

 

nice work! i used test tones a few times to set my car system response and sub. they are definitely helpful. i used a notebook and wrote down the perceived level at each frequency and repeated until they were balanced. unfortunately the lowest notes (40 to 100 hz or so) were now too loud during music. i wound up having to adjust multiple times but eventually it sounded good.
i measured it with the RTA setup and the curve looked good as well.
the goal is to have a smooth, relatively flat response of the subwoofer frequencies all the way through the crossover transition and the lowest frequencies of the main speaker- by adjusting the crossover frequency and phase. no peaks and minimal valleys or nulls.
you really can't blend a sub any better than this no matter what brand of sub it is and it passes the ear test. full and seamless integration.
once you have the crossover frequency and phase angle set correctly, you can leave those positions alone and concentrate on adjusting the sub output level to suit your preferences.

 

Hi Avanti,
I found this to be a really worthwhile article, mainly because I am at present struggling to integrate my subwoofer into my stereo system.
The subwoofer is an SVS SB12 NSD ,which I believe to be capable of producing reasonable amounts of good quality bass.
I am using it with an integrated amp that has left and right channel subwoofer out terminals. There is no bass management at all on the integrated amp and so I am using the subwoofers crossover.
For my speakers , which are Q Acoustics Concept 20 standmounts and are said to go down to 64Hz, SVS recommended a crossover of 60Hz. I set the gain to midway initially but found that some tracks seemed a bit thick and so reduced the gain . This helped on music but left film LFE a bit lacking.
Then I read that it was a good idea to use port bungs in my stereo speakers to reduce interaction between the port bass, the main driver's bass and the subwoofer bass. This allowed me to put the gain back to midway and retain clean bass but it detracted from the movie's bass.
I am now in the position of putting port bungs in my mains for music and removing them for movies. I am wondering if I can intergrate my sub better by possibly adjusting the crossover and the phase but am not sure how to use the TrueRTA software properly or even what mic to buy. I have seen one (very cheap ) on ebay that is rated 20Hz to 20KHz but may be of very poor quality. How would I even know ?
I would very much appreciate some guidance through the prodedure as I am sure the way you have outlined is the way to go in order to get the most from my subwoofer.

 

Given that, I would absolutely go with a pair of subs running in stereo.

I had to forgo the dedicated .1 output on my preamp (since I only have one, and didn't want to use a Y adapter to split the cable) and use my secondary front L+R outputs to drive my subs; this works great for music but I do lose the assigned .1 content for movies as a result.

 

Yes , I think you are correct. The only thing that has stopped me so far is that I have very limited floor space to site the second sub and I'm just not sure that I would be able to find a spot that would put it in synergy with the first sub.
As I am only covering a single seat I keep thinking that I should be able to get an acceptable result with just the one but I can't help wondering if I should make the investment in a second and just try to work around the space issues.
Meanwhile I would really like to go through Avanti's sub integration method to see what improvement I can make.

 

Hi Avanti,
I totally agree with your take on this.
I have a 2.1 system with the sub fed from an integrated amp with right and left sub out and so am using the sub's crossover for bass management. There is no bass management on my integrated amp.
I am having trouble settling on the correct gain and crossover and wonder if you would be so kind as to walk me through your method ?
The " by ear"method is just so imprecise and SVS (the makers of my sub) go as far as to say it is not possible. Sure, you may get lucky but it is not reproducible. I would rather depend on the science.

 

I am not familiar with TrueRTA. If you can upload a file to TrueRTA with the frequency correction curve then I'd suggest Cross-Spectrum Labs for a mic with its own calibrated file.

 

Sounds like a plan... lots of folks have great success with a single sub, once they go through the process of positioning and setting up the crossover, etc. I just happen to love having two subs and how that sounds in my room. I put mine right next to my mains (sorry, no pic at the moment).

Perhaps you could borrow a sub (or, better yet, a pair from someone who runs two) just to see if having two sounds good in your room.

 

Get true rta here- free download for the cheapie version- i recommend at least the level 3 option.
Then the mic I use-
Then the mike phantom power supply-
Then you need some XLR cables- male to female for the mic to the power supply, then female XLR to mini phono jack to connect to your computer mic jack.

https://www.trueaudio.com/rta_selection_guide.htm
http://www.amazon.com/Dayton-Audio-EMM-6-Measurement-Microphone/dp/B002KI8X40
http://www.amazon.com/Nady-SMPS-1X-...=1-5&keywords=microphone+phantom+power+supply

 

Also, here is a link with pics- and how to use RTA with an equalizer (which I no longer use) but it has helpful info.
http://forums.stevehoffman.tv/threads/vision-and-sound-results-of-measuring-and-adjusting.345245/

 

Alex - a couple of considerations gleaned from my flailings.

- Caution using port bungs with quality speakers. Plugged ports may reduce upper bass and midrange SQ (sometimes significantly). I'd do a lengthy SQ listening session without the sub to see if I prefered the sound of the mains plugged or open. I've never heard ported mains sound better when plugged. I sense the audiophile (I ain't one but do pay attention now and then) approach if they dare use a sub would be to set their mains first...as in choose the mains, then power them and position them to their best advantage, then after add sub to fill in as required.

- Caution EQ'ing mains in service to a sub - tail wagging the dog to many 2 channel folk (see above). I'd eq my mains only if I thought they need it as standalone speakers. I use my ears when integrating subs, so not only do I play music and test tones at the crossover range I also occasionally play test tones (up to 300hz so) during the tuning so not to lose sense of the overall bass balance of the mains. If I focus too much at crossover I feel I over think what I'm hearing. That said I do have a set of speakers with a serious bass bloom and I'd been wanting to try a pro quality AudioUnit plugins with Audirvana+ so I'm playing with them all now. Play being the operative word as I've little sound processing exp.