Multiple subs increase extension?

[Guiria]

I realize one of the goals for multiple subs in a 5-7.1 setup is to improve the linearity of the in-room response. Will multiple subs produce the lower frequencies better?

If I have a sub that specs to 30 Hz @ -3 db, will adding another sub just like it increase the spl at 30 Hz or will I suffer the same roll off and not receive any gain in extension by adding another sub?

 

[mike c]

adding another sub will only increase SPL, but it will also make it easier for those subwoofers to produce the same SPL. for example, it takes 1 subwoofer to produce 30hz @ 85db SPL with X THD ... 2 subwoofers will produce 30hz @ 85db SPL with < X THD.

 

[j_garcia]

It doesn't make it "easier" per se; it doubles the output at a given frequency. So if each of them only reaches to 30Hz nominal, but still have output down to 25Hz (-10dB), you will lower the total extension with two of them because the output has increased below 25Hz with both playing together.

 

[Matt34]

It doesn't make it "easier" per se; it doubles the output at a given frequency. So if each of them only reaches to 30Hz nominal, but still have output down to 25Hz (-10dB), you will lower the total extension with two of them because the output has increased below 25Hz with both playing together.

Now that is if they are co-located, right?

 

[j_garcia]

I would personally try to collocate or at least keep them fairly close to each other, however I would suspect with both properly calibrated, even with them at opposite sides of the room, you will still benefit from the two working together (calibration will be more complicated though, depending on the room).

 

[Josuah]

It doesn't make it "easier" per se; it doubles the output at a given frequency. So if each of them only reaches to 30Hz nominal, but still have output down to 25Hz (-10dB), you will lower the total extension with two of them because the output has increased below 25Hz with both playing together.

But you are still -10dB at 25Hz, so you haven't increased your extension. Sure, maximum output at 25Hz will increase 6dB if co-located, 3-6dB depending on frequency if not, but that's across the entire band, not only at frequencies below your existing roll off.

The OP got it right: "I suffer the same roll off and not receive any gain in extension".

 

[annunaki]

That is correct. If both subs begin rolling off at 30hz it will not increase extension. Using two identical subs will simply increase output and possibly linearity depending upon placement. Now if you used one sub from 60hz to 30hz and a huge 18" sub for 30hz and down, that would increse extension.

 

[j_garcia]

But you are still -10dB at 25Hz, so you haven't increased your extension. Sure, maximum output at 25Hz will increase 6dB if co-located, 3-6dB depending on frequency if not, but that's across the entire band, not only at frequencies below your existing roll off.

The OP got it right: "I suffer the same roll off and not receive any gain in extension".

That doesn't make sense? If there is more output at 30Hz from using two, then there is more output at 25Hz too, providing they still have some output at that point. It won't give you a LOT more extension, but it will give you more output within their actual output range, say above the -6dB point of the subs, below that it isn't going to make much difference. I'm just theorizing here, so correct me if that is not correct thinking.

 

[Guiria]

It won't give you a LOT more extension, but it will give you more output within their actual output range, say above the -6dB point of the subs, below that it isn't going to make much difference.

My intuition leads me to believe j_garcia's point

and a quick side note, what is co-locate? Like one sub on top of the other?

 

[jazzisnumberone]

I dont understand all the electrical nuances of components but in my theater(posted in member systems) i have 5 subwoofers( 3 Definitive Tech Pro Sub 80's. 1 each for LCR and 2 Energy subs for LFE). The sound is very scary. Clean, tight and fast. Great for live DVD's and CD's. This is just my honest opinion

 

[j_garcia]

and a quick side note, what is co-locate? Like one sub on top of the other?

Basically, yes, or at the very least, side by side -as near to the same spot as possible.

 

[Nuglets]

That doesn't make sense? If there is more output at 30Hz from using two, then there is more output at 25Hz too, providing they still have some output at that point. It won't give you a LOT more extension, but it will give you more output within their actual output range, say above the -6dB point of the subs, below that it isn't going to make much difference. I'm just theorizing here, so correct me if that is not correct thinking.

I see what you are saying j_garcia, but I'm thinking that two subs together will give you greater gain throughout every frequency so the roll-off would still be identical but at a higher dB level. So if you get 3-4 more dB at 25Hz you will be getting 3-4 more dB at every other frequency so the difference is still the same, -10dB at 25Hz.

 

[Ron Temple]

Rolloff will be the same, but audibility of perceived extention may change. Your ears may hear a difference. It also depends on the sub. Some produce little or no output at the bottom, for example, the Cadence XSub reached a brick wall ~ 25hz while the Velo DPS10, rated to 28hz, still had good output at 20hz (30% THD).

 

[Jack Hammer]

I don't know about the technicalities but I can tell you that 2 subs sound and feel better than one. When I added my second sub I recalibrated and level matched to the same spl as before, yet there is a definate difference. when things blow up in movies you feel it much more than with a single sub. There is also a 'envelopingness' to the bass that i didn't notice before. FTR I'm using two subs, one in the corner, the other behind my couch.

Jack

 

[Seth=L]

That doesn't make sense? If there is more output at 30Hz from using two, then there is more output at 25Hz too, providing they still have some output at that point. It won't give you a LOT more extension, but it will give you more output within their actual output range, say above the -6dB point of the subs, below that it isn't going to make much difference. I'm just theorizing here, so correct me if that is not correct thinking.

Having two subs properly calibrated, or co-located is only the equivalent of turning up one of the subs gain by 3 dB correct? So how would you get extension, all frequencies are boosted right?

 

[Seth=L]

I don't know about the technicalities but I can tell you that 2 subs sound and feel better than one. When I added my second sub I recalibrated and level matched to the same spl as before, yet there is a definate difference. when things blow up in movies you feel it much more than with a single sub. There is also a 'envelopingness' to the bass that i didn't notice before. FTR I'm using two subs, one in the corner, the other behind my couch.

Jack

Having that sub directly behind your couch could cause the effect you described. I once used a small room with an Athena 10" "port noise king special" subwoofer and placed it behind my couch. I could feel the bass a lot more than if it was located on the front wall.

 

[j_garcia]

Having two subs properly calibrated, or co-located is only the equivalent of turning up one of the subs gain by 3 dB correct? So how would you get extension, all frequencies are boosted right?

Because the lower frequencies that were less audible with one are now more audible due to greater output, that would equate to greater in room response... So the way I see it, they don't physically go lower than they did before, but they DO have more output lower than they did before.

I think I am going to send this one over to the guys at SVS and see what they have to say.

 

[j_garcia]

That was quick. Here is my question:

The question is, does adding a second, identical sub increase in room extension? The way I see it, the output should increase at all frequencies, so while not exactly lowering the extension of the subs, the two do play louder at lower frequencies. Is that thinking correct?

and here is their response:

You are correct. Assuming optimal acoustical coupling (subs near one
another) you'll gain 6dB of system headroom at all frequencies. This
also assumes the second subwoofer is identical to the first of course.

The true extension of the bass won't change, but the added headroom can
offer flexibility in that regard. For example, you can add an EQ and by
lowering the rest of the frequency range a bit, achieve "quasi" lower
extension of sorts..

In the end though, if you are after deeper extension than your current
subwoofer offers you'll be best served upgrading the subwoofer to a
model that is designed for that imo.

So adding +6dB at the lowest frequencies the sub was capable of does, in effect, increase the usable in room response of the two subs, so there is a definite benefit.

 

[Guiria]

That's an awesome explanation. I'm totally convinced from j_garcia's arguments that it does increase audible in room response within the capability of the subwoofers themselves.

 

[annunaki]

That doesn't make sense? If there is more output at 30Hz from using two, then there is more output at 25Hz too, providing they still have some output at that point. It won't give you a LOT more extension, but it will give you more output within their actual output range, say above the -6dB point of the subs, below that it isn't going to make much difference. I'm just theorizing here, so correct me if that is not correct thinking.

The relationship or ratio is still the same. You will still be down by x amount of db at 25hz depending upon the rolloff of the sub. Say you are down -6db at 25hz from 30hz with one sub. If you add an additional, identical woofer, the response will still be down -6db at 25hz. Your overall volume will have increased some but it will not have increased the extension. To the ear, yes everything will be louder, but the system will still lack the depth one may be after. It may imrove a little to the ear as Jackhammer explained but it will not cure the true problem.


Basically if a sub's reponse is down by -6db from 30hz with one sub and you are at 100 db, the sub would be at 94db at 25hz. If you add another sub and it increases output by 6db you will now be at 106db at 30hz and 100db at 25hz. One did not improve the extension, they just made it (the problem) louder, and potentially more noticeable? Maybe not, but, I don't think you can go wrong by adding a second sub if it is done properly.