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2 non-idenical subs collocated, different SPL levels?

Discussion in 'Subwoofers' started by nelmr, Dec 13, 2010.

  1. nelmr

    nelmr Active Member

    Okay since the HSU VTF-15H is on it's way I'm trying to figure out what to do with my SVS 20-39PCi. I'm currently running the SVS -5dB relative to the other speakers, as it's limited in the large room I have.

    So I was wondering if collocating the two subs, one at -5dB and one at 0dB would be advantageous? Assuming the same phase, and frequency, the gain by doing this should be just shy of 4 dB*.

    So this would give me the option to run the LFE channel 3-3.5dB hotter for movies, or keep it the same SPL of the other channels with less distortion. However, the subs aren't identical. Would this pose a problem? I realize the boost would be less below 20hz as the SVS drops out at that point. But from 20-80Hz wouldn't this benefit still mostly be there? Even if the SVS were to be -10dB in comparison, I still get a 2.4dB gain by combining the two.

    The other challenge is that I am sitting near the dead center of the room (if ignoring any adjoining areas). I realize this is not optimal for bass. But With the room I'm not sure of any other arrangements that work as this is also our living/dinning area. I'm not sure where the room nulls and modes are mathematically (as it's hard with the open areas). But I do know that 4-5 feet to the right of the listening location, there is about a 6dB gain in bass response using the S&V test tones for the sub.

    Below is a diagram of the room layout. Since I drew the diagram, I have moved the SVS sub to the front right area of the room as the bass response is a couple dBs better there compared to the left. I've also moved the current listening spot and surround speakers about 1/2 a foot closer to the front of the room.


    * Math works out to:
    20Log(1+0.562341) = 3.875518dB
  2. Aaron German

    Aaron German Active Member

    Are you sure you really want to deal with all the potential hassles two subs can bring? Maybe you'd be better off selling me your SVS for a very nice price. If you're still up in Cincinnati, I could pick it up. No need to hassle with shipping.
  3. yromj

    yromj Well-Known Member

    If I were in your shoes, I would sell the SVS and optomize the setup w/ the Hsu. Two non-identical subs aren't going to sound the same, especially with music. I would have a ceremony and let the SVS go.

  4. nelmr

    nelmr Active Member

    I'm not sure I want to sell the SVS at this point, though it is tempting to have extra funds to put towards new main speakers.

    However, I could always use it with my Audioengine A2 speakers for my home office. That would make PC Gaming quite a bit more fun, improve music and sound quality from the A2 speakers since I could cross them over at 80hz, instead of letting them them attempt to play deep and mid bass with the 2.6" Kevlar woofers and internal EQ corrections.

    Those speakers have 9db of EQ boost between 40-100hz. It even has 4dB boost at 10hz, 7dB at 20hz. And when playing anything moderately loud (i.e. 85db) that has bass 60hz or below these speakers go into high excursion. You can see them move and the ports put out a lot of air, blowing papers off my desk. All this comes with the cost of distortion and port noise, which is as high as 5% (third harmonic) at 60hz.

    Basically, I have a use for the sub if I don't use it in the main room. I think it should help the A2's sound quality quite a bit. Nevertheless, I at least want to play with using a second sub to see how it sounds and the effect on overall deep bass output levels for movies. I can always turn the SVS off for music and boost the HSU 4dB.
  5. yromj

    yromj Well-Known Member

    You may find this appealing: set the system up absolutely spot-on w/ the Hsu and use it that way for music. Then if you want some extra oomph for movies, kick on the SVS (with the level set however you want it).

  6. nelmr

    nelmr Active Member

    That's a good idea for the extra oomph as I don't have to worry about level settings. I'll consider that as well.
  7. Maximo

    Maximo Well-Known Member

    How about one for music two for movies?

    Hook up analog outs for two channel plus one sub for music and hook everything else up digitally feeding both subs?
  8. nelmr

    nelmr Active Member

    Measurements. Okay first. I've had some phase issues between the two subs. I have the hsu in the right front corner with facing into the room. The SVS is directly left of the HSU. Ofcourse the port is about 3 feet higher than the Hsu ports and 1 foot left of the left most hsu port. The SVS is also somewhat behind the front right speaker when viewed from the listening position. The SVS has phase nobb. HSU a phase switch. Both the HSU and SVS are set to 0. As you can see the two phases are different below 60hz (the crossover freq of the main speakers). Increasing the SVS only makes the difference even more pronounced:


    Here are FR response differences (by the was the SVS is very heavy at 20 and 50hz at 0 phase. Increasing the phase to 90 smooths it out better but this cuases a more pronounced phase difference between the HSU and SVS). In this graph the SVS and HSU are the same SPL according the S&V disk. But obviously that isn't the most accurate way to calibrate for overall bass level:


    Here is the graph of the SVS set 4dB lower than the HSU according to the S&V disk. Thus combining the two theoretically should produce 4dB more loudness than when the HSU is used by itself. Note the left front speaker is on and active above the 60HZ xover in this diagram:


    When comparing the SVS and HSU together with the S&V disk subwoofer test tones the boost is maybe 0.5dB. IT should be more like 4.25dB. Using pink noise 20-80hz with the front right speaker on as well (but xover set to 200hz since i'm feeding stereo I don't want the speaker to interact much) the output with just the HSU 74dB, with the SVS 64.5dB. With both subs 76dB. I'm not sure why the SVS is reading 64.5dB here when the S&V disk it's 4dB lower. Nevertheless, theoretical combined output with the SVS 9.5dB lower in level than the HSU is 2.5dB. The actual output is 2dB. So I guess collocated subs of different makes will very at different signals/frequencies, etc regarding the extra output gained.

    One cool think is you can see the theoretically 6dB collocation boost at around 18hz in the last chart. This is also where the two subs are best in phase with each other.

    Lastly, if you are curious the HSU is running both ports open, EQ2, and Q0.3.
  9. nelmr

    nelmr Active Member

    Here is a 20hz sine wave with the SVS at -4dB compared to the HSU overall (but remember they have similar level at 20hz). Flint, I know that RS meter isn't accurate for bass and THD, but it is interesting nonetheless.

  10. Aaron German

    Aaron German Active Member

    What software are you using to make these graphs?
  11. nelmr

    nelmr Active Member

  12. Aaron German

    Aaron German Active Member

    Free is better than $100.
  13. PaulyT

    PaulyT Behind the Curtain Staff Member Administrator Moderator Superstar

    Yeah, REQW looks like very good software if it works as advertised. It has a lot of functions (waterfall, rt60, etc.) beyond "just" RTA. And of course free is good! I plan to spend some serious time with this program next time I play around with my system.

    Why haven't we heard much of anything about this software before? Wondering...
  14. Towen7

    Towen7 Well-Known Member Staff Member Moderator

    It's not talked about here because Flint hasn't used it. Lots of people on other forums use RTW... not that I frequent other forums. Just that when I do I see that REW is the tool of choice.
  15. Maximo

    Maximo Well-Known Member

    Don't forget that 3 db gain is doubling the sound output. Although I would have expected more from the two subs as well. I say, throw away that silly old SVS and stick with the HSU. BTW, what day of the week is trash day in your neighborhood?
  16. nelmr

    nelmr Active Member

    Well, the SVS still is a nice sub, don't forget, though it's the old iSD driver version. SVS claims that the NSD driver (if I upgraded it) has better SQ. I'm guessing that means a more balanced response among other things? I think it's odd that two subs next to each other have such a different response. Even when the SVS was where the HSU currently is and with a more appropriate phase setting it still was similar (note that both front speakers where on with this graph, not just the front right):


    So the dip from 25-45 still exists. Thus, this isn't room acoustics causing that dip. This probably explains why the HSU sounds much more balanced in my room. Movies no longer sound weak in the LFE channel (plus the extra output helps as well). I still want to play with the SVS positioned in the opposite corner of the front wall. I'm curious of it's effects on the FR response and how it changes the overall sound.

    Trash day is on Monday morning :laughing: , but you won't find my sub there. It still will have use in my office setup.
  17. malsackj

    malsackj Well-Known Member

    On the room EQ wizard I have a plot of the room decay for the ANS gym and it was well beyond 300 ms.
    This I would atribute to 16 speakers spread out in the gym.

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