The importance of measuring your sub+room response

Discussion in 'Speakers & Subwoofers' started by Ned, May 31, 2004.

  1. Ned

    Ned Supporting Actor

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    I was at a friend's place on Sunday to do some measurements of his SVS 16-46CS+. He has a decent size room, about 15x25 with 8' ceilings. He has 3 rows of seats and currently 6 chairs (1/3/2 from front to back). His SVS is in the back of the theater, in a corner.

    I don't have the spreadsheets we saved (will get later hopefully), but here are my approximations of the results.

    Chair at the front. The approximate db range from the lowest dip to highest peak was 13db. A total rollercoaster response.
    [​IMG]


    Chair in the middle. Virtually perfect, until we hit the 50hz tone and the needle fell 20db! The null began at 40hz and ended at about 63hz. You can imagine how this would sound. Everything outside the null is perfect, then a drumbeat or guitar string hits 50hz and you hear almost nothing.
    [​IMG]


    The third chair I measured was in the 3rd row, right side, nearest of all chairs to the SVS. It didn't have any big dips as I recall but it was peaky at 40-70hz. Didn't sound great subjectively.

    Now imagine this is your room. Depending where you sit the SVS sounds like 3 different subs. None of the spots measured well. You would probably think the SVS "is overrated" and would wonder what all the fuss is about.

    Before we measured, I listened to the first 3 minutes of Toy Story 2 in various chairs. Some spots had no deep bass at all, others were muddy/boomy, the chairs at the back had some nice deep bass but were clouded by the 40-70hz range, the front chair just sounded lousy (see the rollercoaster curve approximation).

    Actually measuring and seeing a plot is invaluable and IMO, absolutely required for anyone with a decent sub. Our next line of attack will be to test different sub placements as well as adding a 2nd 16-46CS+ and a Behringer FD to help smooth out the peaks once we find a good sub position.
     
  2. Ned

    Ned Supporting Actor

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  3. Brian Fellmeth

    Brian Fellmeth Supporting Actor

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    Perfect illustration of why its silly to "calibrate" the sub level to withen 1 or 2 db of the mains using any source of bass noise.
     
  4. ChrisWiggles

    ChrisWiggles Producer

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    No.

    IT's a perfect example of why it's silly to try to do so in an untreated room. This is classic bass response in most rooms. Bass traps will help this a lot, as well as EQ once you've got some good bass absorption going on in the room.

    Know that an EQ won't help the deep nulls. Treat, then EQ.
     
  5. Wayne A. Pflughaupt

    Moderator

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    Likewise, know that not all under-represented areas are nulls. Those can be equalized.

    Regards,
    Wayne A. Pflughaupt
     
  6. ChrisBee

    ChrisBee Stunt Coordinator

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    quote:

    "...as well as adding a 2nd 16-46CS+"

    "Be sure and keep the receipt. A second sub will very likely make things even worse."



    I wouldn't worry unduly. Add another 16-46CS+ and the walls won't be parallel for much longer! [​IMG]

    ChrisBee
     
  7. Kevin C Brown

    Kevin C Brown Producer

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    In my room without an eq, that's about what I got: +/- 7.5 dB. Which sounds huge, until you realize that most rooms are like that (sub in a corner). I have just one filter on my BFD enabled, and I got it down to +/- 5 dB. I can get down to +/- 3.5 dB with 5 filters engaged, but I went with "simpler is better." Good enough for me. [​IMG]

    One thing to think about is that depending on how you measure, there *are* differences between steady state tones (which allow the room nodes to build up), and transients which don't.
     
  8. Mark Seaton

    Mark Seaton Supporting Actor

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    I would point out that there is more evidence to the contrary, but it does require appropriate placement. Random placement of a pair of subwoofers will not necessarily help things, and can certainly make things worse. Both corner and other distributed placements have merit and appropriate applications. It is more important to understand how different options will alter the performance. Likewise, EQ is a great help for low frequency performance, but trying to a single measurement location without checking what is going on elsewhere in the room can yeild very odd or suprising results.
     
  9. Joe Mihok

    Joe Mihok Second Unit

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    I'm curious, what's a bass trap ? I've got some dips in my room as well and plan on buying a BFD. If I can do more to flatten out the response then I would love to know how [​IMG].
     
  10. ChrisWiggles

    ChrisWiggles Producer

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    A well-designed room will have some kind of absorption, and hopefully some diffusion as well for spaciousness.

    Imagine for a moment, a room with bare cement walls, ceiling and floor. You can imagine easily how horrible the echo would be in there. The decay would probably be several seconds. But put in carpet, drapes, furniture, etc, it would be much better. Problem is, what you've just done is put in a bunch of absorption for the high-frequencies, and all the bass is still reflecting like crazy. A bass trap is merely an absorber capable of absorbing bass frequencies. You can use thick fiberglass, and other designs for broadband absorption of some bass frequencies. If you have specific problems in your room, you can also use targeted resonators that will absorb specific frequencies, etc.

    A well-designed room is the primary tweak in ANY audio system. A BFD or other EQ can only do so much to bandage a bad situation. Long bass decay will still be a terrible problem, even if you can get the response perfectly flat in a bad room. This is why good treatment plus more sparing use of EQ is much better for everything.
     
  11. paul clipsel

    paul clipsel Stunt Coordinator

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    That is interesting. Some people are saying an eq is vital. But as you are saying its only really for the prime seat, it's not for all seats. So its no certainty. My VTF-3 sounds great (RAW) right out of the box, so this mixed message eq curiosity is killing the cat.

    PC
     
  12. ChrisWiggles

    ChrisWiggles Producer

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    It really depends on the room. A poor, untreated room will have HUGE swings in reponse almost everywhere, and everywhere will be totally different. The best you can do without getting to the root of the problem(the room), is to try to EQ for one position, and then sit there.
     
  13. Ned

    Ned Supporting Actor

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    Added the real spreadsheet captures at the top.
     
  14. Ronneil Camara

    Ronneil Camara Stunt Coordinator

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    Just for fun, is it possible to connect my svsubwoofer to my pc that has a sound card and use NCH Tone generator utility?

    Thanks.
     
  15. Ned

    Ned Supporting Actor

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    Of course. Connect the line out of your soundcard to your receiver. I use the coax SPDIF from my sblive.

    If you use sinewaves from NCH tonegen, make sure you keep the levels low. Start with the 30 or 40hz tone and adjust the volume on your receiver so it measures 80db on your meter. Then try the other frequencies without touching the receiver volume.
     
  16. Ronneil Camara

    Ronneil Camara Stunt Coordinator

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    Btw, which port on the receiver I should connect the cable?
     
  17. Rick Cohen

    Rick Cohen Agent

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    Ned,

    Thanks for starting this thread. In setting up my PB2+ with my mains I found similar kinds of situations. Say the LFE channel has low output but the mains are not playing low base on the DVD then there is no main to sub interaction. Next sequence could have left and right lows with LFE and there is interaction. Factor in what you found regarding room location and this becomes a situation with far too many variables. I did my EQ with the ART 351 at the sweet spot got reasonably close to flat as described above and then adjusted to improve using my ears and feelings regarding the sound. This is clearly far from exact science given all the variables on location and transient speaker interaction. RICK
     
  18. paul clipsel

    paul clipsel Stunt Coordinator

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    In another thread Craig was hinting that this Eq use for a subwoofer in smaller rooms was not just for the measured spot like it is in Marks big space servodrive installs? I am interested in understanding this problem when using an eq. Is the eq the magical leveler for my listeners?

    PC
     
  19. Wayne A. Pflughaupt

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    I didn’t say the walls needed to slope, Mark.

    The last two places I’ve lived have had the system set up in a living room with cathedral ceilings (15ft. or more at the peak) that opened to other rooms. Since it’s a living area (i.e. not a dedicated room), there is no acoustical treatments other than normal residential furnishings. I’ve had none of the problems Ned’s friend is having – drastically different response curves at locations only a few feet apart.

    My current home, where the living room is open to the dining room and kitchen, I took measurements and equalized for a central sofa. However, bass sounds excellent and uniform pretty much anywhere in the three rooms, except near one of the walls where the subs are cornered, where the bass level intensifies as you get close to it. (Strangely this is not the other case with the other wall.)

    By comparison – a couple of years ago I drug my subs into a rectangular 16’ x 14’ x 8’ bedroom for some tests and measurements, and it was dreadful. With sine-wave test tones, I could hear and measure intensity (SPL level) changes every time I moved one step in any direction. The difference in SPL between dead-center in the room and any given wall was tremendous, although I forget the exact numeric differential.

    Perhaps indeed “a rectangular room is much easier to understand and optomize (sic) with placement and treatment changes,” but any one who has the misfortune of dealing with one has my sympathies.

    Regards,
    Wayne A. Pflughaupt
     
  20. Chu Gai

    Chu Gai Lead Actor

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    Wayne, your lack of problems may have had a bit to do with the fact that the living room opened to other rooms, no? If you 'lose' the reflections then you 'lose' a substantial amount of the reinforcements and cancellations. And what is this drugging of your sub? Are you proud of such behaviour? [​IMG]
     

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