# How do I EQ for 2 subs with true stereo bass?



## romnation (Mar 20, 2010)

Each sub will be getting it's own singal (right sub gets the right channel signal, left gets left) What process should I use for EQing? After level matching the subs, should I just EQ them together to get a combined flat response? What I am wondering about though, is if a certain track has the bass on one side of the soundstage, then it will only come out of one sub, wouldn't that make it no longer have a flat response?


----------



## lsiberian (Mar 24, 2009)

romnation said:


> Each sub will be getting it's own singal (right sub gets the right channel signal, left gets left) What process should I use for EQing? After level matching the subs, should I just EQ them together to get a combined flat response? What I am wondering about though, is if a certain track has the bass on one side of the soundstage, then it will only come out of one sub, wouldn't that make it no longer have a flat response?


You should place one sub on the front wall and one on the rear wall. Then eq them together. Bass below 80hz is non directional so placing them at the speakers is unnecessary. But eqing them together is the correct approach in any case.


----------



## romnation (Mar 20, 2010)

anyone have an answer to my bass one side of the soundstage question?


----------



## Moonfly (Aug 1, 2008)

Hi there,

Well you already had that answer. Bass below 80z is omnidirectional, so your ears cant pinpoint its direction as Isiberian pointed out. 

If however you wanted to extend the range of your subs up and beyond 80hz, its a different matter. There are a number of manufacturers that do that kind of thing, and crossover as high as 500hz. It really depends what your goals are. If your building a HT system that is also a music system, and your keeping the 80hz crossover, the the advice in post 2 is sound.

If you plan on something a little different, share your ideas and we can discuss it from there. You should be aware though, that for your left/right channels to work, your highly likely to require high level connections on your subs, unless your processor has true stereo sub LFE outputs, which I highly doubt as its incredibly uncommon.


----------



## bjs (Jun 12, 2008)

Moonfly said:


> ...Well you already had that answer...


I'm not so sure he did...

The answer to the OP's question is that the frequency response will vary depending if one speaker is emitting the sound versus both because room modes will be driven differently. So EQ'ing both together won't work in all cases (e.g. bass one side of soundstage as the OP suspected) but unfortunately neither does EQ'ing separately (for the opposite case). 

One reason for running mono signal to subwoofers. They will then drive the room modes in a consistent fashion that can be EQ'd.

Note: none of this has anything to do with sub bass being omni-directional.


----------



## Moonfly (Aug 1, 2008)

No matter which way you eq'd, either both together, or independently, you would have to accept that there is a possibility that bass may not play as perfectly as it could. If however, the frequency cut off of the sub(s) is 80hz or less, there is simply no point in running them in true stereo. You couldnt tell if only one sub was running, or which one was and wasnt running, except output may be too quiet for a pair of eq'd subs if only one was producing sound.

Once you get to frequencies above 80hz, traditional sub eq starts to become less of an issue as the room has a gradually reduced effect on the frequency response curve in the traditional sense. Over 80hz becomes less about room modes and boundary gain, and more about reflections and echoes.

Personally, I would eq the subs together if the frequency cut off is 80hz. If you run higher frequencies form true stereo connected subs, then you would simply have to pick either together or independently, and accept there is a possibility the response may be slightly inferior to what it theoretically could be for any given set of circumstances.

I think in reality, you would be hard pushed to notice a major difference, especially in music which is more focused in the audible bass range. 

One other point though, in a true stereo setup with higher than typical crossovers, the subs would need to be near your front pair of speakers, and ideally set back slightly and farther apart.

There are a few other issues with the OP idea as well. Most subs wont crossover above 120hz. Most sub eq doesnt go over this either, and LFE eq wont be applied to the subs if they play higher than the standard frequency range. For this to work properly, you would ideally need 2 identical subs that had both high and low level connections. You would connect them using both high and low level methods, and then eq sub 80hz LFE the normal way, and utilise the AVR's speaker eq for the high level connection and any output above 80hz.


----------



## tonyvdb (Sep 5, 2007)

A sub is not a true sub if its crossed over above 120Hz as that puts it in the directional frequency range and even at 120Hz down to about 100Hz is still in my opinion somewhat directional and can be localized This is a Bose trick and is a lousy way to run a so called sub not to mention puts a much heaver load on the driver and amp.. 
There really is no such thing as stereo bass and recordings done properly usually dont separate items like Bass or the Kick on a drum kit. Items like this are usually mixed Mono. 
Music in most cases does not have much information below 30Hz and defiantly not below 20Hz that is useful.

On another note, are these subs identical? If they are not this becomes very complicated if you want them to preform the same.


----------



## Moonfly (Aug 1, 2008)

tonyvdb said:


> A sub is not a true sub if its crossed over above 120Hz


 I would disagree with that. As long as it plays under 80hz and goes down to say 30hz, I would class it as a true subwoofer. Just because it plays over 80 or 120hz wouldnt cause it to no longer be a sub IMO.
I'm not sure Bose is an equal comparison. Bose use small mid/bass drivers that dont go particularly low, but play up into the mid range well, then use some eq and cab trickery to squeeze out evrey last drop of low bass they possibly can from them. Bose themselves dont even call theirs subs, subwoofers, they call them bass modules, and IMO they are a different thing.


----------



## tonyvdb (Sep 5, 2007)

Moonfly said:


> I would disagree with that. As long as it plays under 80hz and goes down to say 30hz, I would class it as a true subwoofer. Just because it plays over 80 or 120hz wouldnt cause it to no longer be a sub IMO.


True, but I dont know of many crossovers that even allow for a higher adjustment than 120Hz


----------



## Moonfly (Aug 1, 2008)

I cant think of any traditional ones either of the top of my head. I know some companies like B&O and Steinway Lyngdorf do, but they are all high end/expense systems that do it their own way so to speak.


----------



## lsiberian (Mar 24, 2009)

If you'd like to keep the channels separate then you can run filters separately on the channels. 

I know some folks really prefer this route regardless of directionality. The beauty in audio is there isn't necessarily a wrong answer.


----------



## Moonfly (Aug 1, 2008)

lsiberian said:


> The beauty in audio is there isn't necessarily a wrong answer.


Amen to that :T


----------



## terry j (Jul 31, 2006)

my experience may-or may not- help.

I don't use subs per se, but my woofers are 18 inch and cover the bandwidth 30-300 hz (ATM anyway),

So not used as true subs a la the original question.

I use a deqx (think lyngdorf etc already mentioned) to control the whole shebang.

Like lyngdorf etc, it performs driver correction on the drivers, and when I calibrate my bass drivers I _do it from the LP_. That way it has the beauty of not only correcting FR as normally done here, but also phase and group delay, from the LP. Ie it takes into account the bass/room interaction.

I measure and correct each driver seperately, and when checked by re-measurement that response is ruler flat (except for true nulls of course).

So far then that is a vote for measuring and correcting individually.

Here is the funny part...when BOTH are measured simultaneously after correction, peaks and dips re-appear in the response! I figure all that means is we have corrected left and room to flat, so handled, right and room to flat, so handled, but when they are run together we have the new sit of left and right interacting (??)

So, I do a final step of simply applying the last bits of correction needed when both are playing together. I find it necessary to do that, as the two together untouched DO produce boom at certain frequencies.

It may not apply to the OP as the first step is missing. 

If you have the ability (and you must be able to do it lest you would not be asking the question) then I would say do it both ways, and _find out for yourself_ what works for you.

Experimenting is cheap and easy, and it is always best to get personal reality on all the data the 'experts' say on the net.

Eg, if I were using a DEQ then it is possible to measure and correct each seperately using the PEQ panel, then correct the two 'on top of that' by using the GEQ panel for example.

Do it both ways and report back!


----------



## Moonfly (Aug 1, 2008)

terry j said:


> Here is the funny part...when BOTH are measured simultaneously after correction, peaks and dips re-appear in the response!


This is not unexpected. A single response is different from different positions. Lets say both subs show a flat response at say 40-50 hz. No eq would be applied to any single sub, but when played together you would get +3db gain in the region. Assuming eq is applied at the rest of the range, the system thinks the individually flat areas need no eq and balance the rest of the response accordingly. The end result would then be a flat response except for the 40-50hz zone, which would show a 3db peak.

EQ'ing them together would be best all round, but then you would have to accept that if material determined only one sub was paying at a certain time, the eq applied to this single sub would be incorrect as the system thinks the other sub is playing a part in the performance, when the source material is forcing this to not be the case.

For this to work perfectly, you would need a pretty advance eq system. It would need to measure the subs individually, and together, combine the results, then apply eq dynamically depending on if both subs were playing, or just the left or right. Then it would need to combine this with the speakers for the very best results.

The crossover point is a big part of the puzzle, but again, if the crossover is the traditional 80hz, there is no point in independently running the sub as left and rights really IMO.


----------



## goyop (May 4, 2010)

As mentioned several times already, bass is not directional. If you were to play a bass guitar in a room you would be able to locate it only by the upper frequencies that are part of the string buzz/slap, overtones, and harmonics. All of these will still be present in your system in the smaller speakers thus giving you "location". There is no stereo bass even if it is offset to one side.

In mixing music the kick drum is always placed in the center as is the bass guitar. On the kick drum engineers will bump it around 400 Hz which is where the whack of the pedal lies. This is what tells your ears that it is a kick drum. That could be offset left to right but is usually left in the middle also.

You are to be commended for seeking to set up a great system. It is worth it. But you will see absolutely no difference by going to the trouble of stereo subs. If you run them mono and do the EQ as mono you will be quite happy.


----------



## Moonfly (Aug 1, 2008)

goyop said:


> But you will see absolutely no difference by going to the trouble of stereo subs.


Unless you use subs that operate above and beyond the 80-120 hz threshold :T.


----------

