How many subs is enough?

Collapse
This topic is closed.
X
X
 
  • Time
  • Show
Clear All
new posts
  • Andrew Pratt
    Moderator Emeritus
    • Aug 2000
    • 16507

    How many subs is enough?

    How Many Subwoofers Is Enough?

    Floyd Toole and Todd Welti may surprise you with their answer.

    In previous columns on subwoofer placement, we’ve discussed the conventional wisdom of adding the ".1" to 5.1-, 6.1-, and 7.1-channel surround sound. That wisdom pretty much comes down to "keep trying until it sounds right," which is a variation on Duke Ellington’s advice: "If it sounds good, it is good."

    You can get good results that way -- after all, most of us end up pretty happy with the sounds of our systems -- but it ain’t easy. And, in a lot of rooms, it ain’t even all that good -- not really. Not measurably.

    The problem isn’t the subwoofer. The problem is the room and where you -- and the guy next to you, and the subwoofer -- are in the room. No wonder we A/V junkies are all a bit crazy. If we didn’t start out that way, trying to balance all those variables would drive us nuts.

    So it came as a relief to discover that even the most knowledgeable experts were as frustrated as I am by this situation. I’m referring to Dr. Floyd E. Toole, Harman International’s vice president of acoustical engineering and one of the most respected people currently working in the audio industry. When I heard that Dr. Toole had some interesting ideas on the subject of subwoofers, I contacted him.

    It turns out that Toole and Harman are about to set the industry on its, er, ear. Before we spoke, however, Toole suggested I read a white paper published by his colleague Todd Welti, "Subwoofers: Optimum Number and Locations," an extremely detailed analysis of Welti’s search for some answers to the hit-or-miss nature of subwoofer placement.

    It’s worth reading, if only for fun: Welti has considered the placement of 5000 subwoofers in a room. He asked, "Can a sufficiently large number of subwoofers cancel out all room modes?" His conclusion: "Theoretically, yes. Practically, NO!"

    That’s when I knew this interview was going to be a hoot.

    Wes Phillips: You guys seem to have had quite a bit of fun with this white paper.

    Floyd Toole: And that’s not the end of it, either. We’ve done more work since that one -- it was just the opening shot, I guess. We started this line of inquiry because trying to provide decent bass for more than one listener with a single subwoofer was seemingly a hopeless cause -- well, it is a hopeless cause. You can’t do it.

    However, if there is only one listener -- or only one listener who matters -- you can provide good results with a single subwoofer, as long as you realize that, in the end, you’re going to have to equalize everything. And we’re not talking about the one-third-octave graphic-equalizer BS that the industry has purveyed for decades.

    That said, no matter how many subwoofers and how many listeners we’re talking about, equalization should be the final step to make it sound right. A single subwoofer can entertain a single listener with equalization -- good sound is possible. But once you have more than one listener, then you need multiple subwoofers.

    At that point, the problem can be divided into two separable categories: one where the room is a regular rectangular shape, and the other where the room is not perfectly rectangular or symmetrical, which is the sort of room most of us live in.

    The problem Todd solved in the white paper we published concerned perfectly rectangular rooms with fairly "normal" middle-of-the-room seating. For that, there are some fairly standardized arrangements of subwoofers that work -- or at least reduce the variations from seat-to-seat performance. Of course, once you reduce the seat-to-seat variations, any equalization you apply will apply, more or less, to all of the seats.

    WP: Todd, is it possible to synopsize the conclusions of your white paper?

    Todd Welti: It was surprising to me that I was able to come to as distinct a conclusion as I did. When I first started working on it, I assumed that I would come up with a solution for a theoretical room but it wouldn’t work for real rooms. But I was pleasantly surprised to find that it worked in real rooms as well. From reports I’ve been getting from the field, it not only works in our room, but most other rooms as well.

    The conclusion I came to was that two subwoofers give you about 90% of the performance that is possible, and that four take you about as far as you can reasonably expect to go. Anything more than four is not going to get you much in the general sense -- and these are general conclusions.

    WP: So the 5000-subwoofer solution just didn’t work out.

    FT: Acoustic wallpaper, as I call it.

    TW: In terms of recognition, it sure got a lot of people’s attention, but no, four subwoofers seems to do the trick -- and we came up with three configurations out of about 100 that we looked at that are the cream of the crop. Actually, there’s a fourth solution -- one that Floyd came up with -- that worked even better than the others, but it involves bringing the subwoofers out from the walls, which I generally didn’t consider.

    FT: It’s not very practical, unless you could put them in the ceiling. It uses four subwoofers located at the 25% points from all four walls.

    TW: In other words, you shrink the whole room by 25% and put the subwoofers at the corners of that virtual room. You get incredible performance, but that’s just not practical in most rooms. But if you use two or four subwoofers in the corners or the wall midpoints, you can get pretty good performance -- and that’s about as succinct as I can get.

    WP: That’s pretty succinct. But you’ve continued to do research, and now you’re trying to crack the conundrum of the irregularly shaped room. How’s that going?

    FT: Oh, it’s done -- but it hasn’t resulted in a product yet, which is the frustrating part. Harman is working on fine-tuning the algorithm and the user interface. It requires some serious computer calculations.

    The way I like to describe what this makes possible is that the customer or installer can basically just walk around a room and identify locations where a subwoofer could be positioned, bearing in mind all of the practical constraints of doors, windows, and visual aesthetics. Once you’ve identified some number of possible locations, you then identify where the listeners’ heads are going to be, and you take one subwoofer and you go in turn to each of these locations and you take measurements, establishing a technical database of transfer functions that will be stored in the setup computer you are using.

    Once the computer has all that data, you sit down and ask the optimizing program to find for you the best locations for some number of subwoofers. In doing so, it will add the time delay, level adjustment, and one band of parametric equalization. Of course, that means you need some additional electronics in the signal paths of each of the subwoofers that you end up with.

    Now the question is, how many subwoofers and which locations will prove to be optimal? You can ask the optimization program to find the best solution for these listening locations in this room using, say, two subwoofers -- or three or four or five -- depending on how many you feel you can afford. We find that plateaus pretty quickly at three or four as the best you’re likely to get. The program will calculate what processing you need for each of the channels for each of those locations. Then you apply global equalization to make it sound good for all of the listeners.

    WP: Is this a technology we’re likely to see in products that will be available any time soon?

    FT: Yes. It’s not something you’re likely to see in mass-market products any time in the foreseeable future, but it is very seriously being worked on in our higher-end offerings from Lexicon, Revel, Mark Levinson, and JBL Synthesis, of course. They’ll have access to it first -- and it still requires human intervention.

    Getting good bass in a room has always been pretty much a trial-and-error business. Some systems work pretty well and some don’t. But now, for the first time, we actually have a handle on the problem -- we’re stunned to discover how well it works. I have this system at home, and without it I was getting 28dB variations among my five principal seats at low frequencies. Now, with it, that’s down to about ±3dB. It’s a staggering, amazing difference! You can literally walk around the room listening to your favorite bass riff and it just basically doesn’t change. The room just disappears -- or at least what we recognize as the negative attributes of the room disappear.

    It’s going to change things around the world. American rooms are bigger and more forgiving of deep bass than the rooms in a lot of other countries -- and people outside of America tend to shy away from systems that deliver intense bass signals because of all the room-interaction problems they cause. They just don’t sound good in hard, small rooms. But if we can solve those interaction problems, it’s going to change everything for an awful lot of listeners.

    WP: That’s a prospect that’s going to make a lot of music -- and movie -- lovers very happy.

    ...Wes Phillips
    wes@onhometheater.com
  • Spearmint
    Senior Member
    • Sep 2004
    • 333

    #2
    Thanks for that Andrew...

    I run 5x subs in my setup and it works great IMO. There are 4x along the front and one located behind the listening position.
    Richard

    "Sometimes it is easier to ask forgiveness than to get permission... "

    Comment

    • Bing Fung
      Ultra Senior Member
      • Aug 2000
      • 6521

      #3
      Spearmint, you have 5 Tumults? :E
      Bing

      Comment

      • Spearmint
        Senior Member
        • Sep 2004
        • 333

        #4
        Originally posted by Bing Fung
        Spearmint, you have 5 Tumults? :E

        Yeah I wish....

        No such luck I'm afraid. Although it would be nice, I do love the sound they produce.
        Richard

        "Sometimes it is easier to ask forgiveness than to get permission... "

        Comment

        • DelRay
          Senior Member
          • Jun 2004
          • 369

          #5
          Originally posted by Spearmint
          Thanks for that Andrew...

          I run 5x subs in my setup and it works great IMO. There are 4x along the front and one located behind the listening position.
          Wow, I also have 4 along the front wall and 1 behind the couch :T
          So if the question is how many subs is enough I would say 5. Unless I get another one then the answer is 6 :E

          Comment

          • Spearmint
            Senior Member
            • Sep 2004
            • 333

            #6
            Originally posted by DelRay
            Wow, I also have 4 along the front wall and 1 behind the couch :T
            So if the question is how many subs is enough I would say 5. Unless I get another one then the answer is 6 :E
            Now you’re talking my language :T
            Last edited by Spearmint; 04 November 2004, 23:37 Thursday.
            Richard

            "Sometimes it is easier to ask forgiveness than to get permission... "

            Comment

            • Elmac
              Member
              • Apr 2004
              • 88

              #7
              My position on this would be 5 subs for 5 channels and 7 subs for 7 channels, I know i know I only have 1 sub but working on 1 more for the back than after that will work on sites.
              Elmac
              All HT Signals Processed by D2 for Ultimate Experience

              Comment

              • ajpoe
                Senior Member
                • Jul 2004
                • 439

                #8
                In a 7.1 system, are the 2 rear channels full range? I don't think they are so you would still only need 5 subs for 5.1, 6.1 or 7.1. I run 4 subs in a 5.1 system and think it is sooooo much better than a single .1 sub. The only channel missing a sub is my center which I still run as large. I don't have room in my living room for any more subs or I would get one for the center as well. LOL... I do have a TST as the only thing running off the LFE channel, does that count as a 5th sub? LOL

                AJ
                AJPoe - - Growing old is inevitable, growing up is optional!

                Comment

                • Spearmint
                  Senior Member
                  • Sep 2004
                  • 333

                  #9
                  I run my 7.1 setup with all speakers set to small. The subs are all run off the LFE channel, to be able to do this you need to use some device to allow the customizing of each subs input. For this I use a Behringer DCX2496, as this allows me to adjust the delay, phase angle, and also xover slope for each sub, as well as Parametric EQ. It also allows me to have 1 input split to 6 outputs, and can be programmed via computer for the adjustments in real time.
                  Richard

                  "Sometimes it is easier to ask forgiveness than to get permission... "

                  Comment

                  Working...
                  😀
                  😂
                  🥰
                  😘
                  🤢
                  😎
                  😞
                  😡
                  👍
                  👎
                  Searching...Please wait.
                  An unexpected error was returned: 'Your submission could not be processed because you have logged in since the previous page was loaded.

                  Please push the back button and reload the previous window.'
                  An unexpected error was returned: 'Your submission could not be processed because the token has expired.

                  Please push the back button and reload the previous window.'
                  An internal error has occurred and the module cannot be displayed.
                  There are no results that meet this criteria.
                  Search Result for "|||"