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  • BSC and speaker placement

    I've been reading a small bit about baffle step compensation. I understand the issue but I'm curious about BSC in relation to placement of a speaker in a room.

    So placing a small speaker on stands several feet from any walls, I see a need for BSC.

    Take the same speaker and place it nearly snug against a wall, now it would seem the need for BSC is substantially reduced.

    If you were designing a small speaker maybe the size of Minimus 7's, expecting the speaker to be places against a wall, would you use BSC?

    Do any of you design speakers with BSC that can be switched in and out (is that possible?).

    Thanks!

  • #2
    Re: BSC and speaker placement

    This program will tell you:


    But in general terms if the cabinet is deeper than it is wide and you place it up to the wall you are still going to experience most of the baffle step that you would if the speaker was placed out into the room, except at low frequencies, which will be boosted. This type of placement can be more difficult to deal with than if the speaker is placed further into the room. There is also the issue of the wall refection that will create a big dip in the frequency response on axis at a frequency corresponding to the the distance between the wall and the front baffle. A very small speaker like a Minimus 7 will certainly sound more full than when placed in the middle of the room though.

    I never design a speaker with BSC compensation that can be switched in or out for a couple of reasons - first, I design it directly into the lowpass crossover, so there is nothing to switch in or out. Second, it is not correct thinking that switching it out and placing the speaker near the wall will result in a smooth / flat response. The only advantage would be in the lower vocal range which might sound better with no BSC and near wall placement.
    Click here for Jeff Bagby's Loudspeaker Design Software

    Comment


    • #3
      Re: BSC and speaker placement

      Originally posted by philthien View Post
      ...If you were designing a small speaker maybe the size of Minimus 7's, expecting the speaker to be places against a wall, would you use BSC?...
      Honestly before the internet, I never heard of BSC.
      I don't recall the link ( Ethan Winer? ) that showed a "suck-out" that was attributable to the 1/4 distance from the Center of a driver to the wall behind ( creating a 1/2 wave reflection ).
      In olde days the wall behind was often covered with absorbent material to help attenuate.
      Softening the transition from driver plane to back wall helps too.
      For me, going in-wall was the ticket.
      "Not a Speaker Designer - Not even on the Internet"
      “Pride is your greatest enemy, humility is your greatest friend.”
      "If the freedom of speech is taken away, then dumb and silent we may be led, like sheep to the slaughter."

      Comment


      • #4
        Re: BSC and speaker placement

        Originally posted by Sydney View Post
        Honestly before the internet, I never heard of BSC.
        I don't recall the link ( Ethan Winer? ) that showed a "suck-out" that was attributable to the 1/4 distance from the Center of a driver to the wall behind ( creating a 1/2 wave reflection ).
        In olde days the wall behind was often covered with absorbent material to help attenuate.
        Softening the transition from driver plane to back wall helps too.
        For me, going in-wall was the ticket.
        Yeah, I didn't know about BSC until I think I saw it at the Madisound forum, or here.

        And I don't think most of the old-timey speakers I enjoyed (Advent, Genesis, EPI, etc.) had any sort of BSC.

        My current speakers are tiny and use Faital 3fe22 drivers. It would be sorta interesting to make some fiberboard "walls" with a cutout for the cabinets and see how they sound with, and without, these extensions in place. Both in their current position (near wall) and also on stands, pulled out from the wall.

        I'd just sort like to hear the effect with, and without, the BSC.

        Comment


        • #5
          Re: BSC and speaker placement

          AS I recall most bookshelf speakers were actually in bookshelves :p.
          Adjustments on mid and tweeter levels ( l-pads or selector switchs ) were often provided.
          The attenuation curves often implemented with BSC were usually within the capabilities of tone adjustment.
          Simpler times, smaller rooms

          fiberboard "walls" with a cutout
          Should be easy enough to try.
          "Not a Speaker Designer - Not even on the Internet"
          “Pride is your greatest enemy, humility is your greatest friend.”
          "If the freedom of speech is taken away, then dumb and silent we may be led, like sheep to the slaughter."

          Comment


          • #6
            Re: BSC and speaker placement

            Originally posted by Sydney View Post
            AS I recall most bookshelf speakers were actually in bookshelves :p.
            And the bookshelves actually had books in them, so the speaker baffle often lined up with the spines of the books, giving "in-wallish" behavior.

            But "up against the wall" (without the books) there was indeed that nasty half-wave suckout, which led to "stand mount" (with the resultant loss of lows), which led to baffle step correction to address that fundamental defect of monkey coffins (their unfortunate polar response) and led Linkwitz to dipoles, and the rest is history . . . ;)
            "It suggests that there is something that is happening in the real system that is not quite captured in the models."

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            • #7
              Re: BSC and speaker placement

              Originally posted by Sydney View Post
              Honestly before the internet, I never heard of BSC.
              It was going on long before it had a name.

              Comment


              • #8
                Re: BSC and speaker placement

                I've said this before, but I think it bears repeating - A discussion of baffle step compensation is really a moot topic when discussing crossover design. Aside from simply understanding the phenomenon involved acoustically, it is something that shouldn't even be thought of when designing a crossover. Thinking about it can just get in the way.

                This is where Phil and I are miles apart. His statement of building a crossover so it could be switched in or out is completely foreign to me and I wouldn't even know what that means. (OK. I know what he is saying, but I believe the entire premise is flawed). I couldn't switch it in or out on my crossovers because I don't consciously design BSC in there; it doesn't even cross my mind when I design a crossover, so there is nothing that I can switch out.

                Designing with no baffle step compensation, as opposed to what? Having a big peak in the upper midrange? When you design a crossover you should target a flat frequency response, and that should be based on the expected use of the speaker. If I am designing for a wall-mount speaker or a stand mount speaker I would take my measurements in that application and then design for a flat response. I don't think about BSC, I only think about a flat response. The guys that designed those older "classic" speakers did the same thing.

                Designing for a flat response on a stand mounted speaker typically requires using a larger inductor on the woofer in the low pass crossover to level out the rising response. It simply takes what it takes. It seems the only time BSC is discussed is when people are also prone to using textbook crossover values - something else that should not be done, and another flawed way of thinking about speaker design.

                So, my two cents worth is this - don't use or even think about textbook crossover values and don't even think about baffle step compensation. Think about making a speaker with flat response and use whatever values are necessary to achieve that goal. But on a free standing speaker with a 9 inch wide baffle there will be a 9 dB rise in the response through the midrange that will need to be dealt with in some way to achieve flat response. Simply do what needs to be done.

                The Continuum is a little 5" mini-monitor with the 3.0 mH inductor in the lowpass filter - not because I was thinking about baffle step compensation, because I wasn't - but because I had a target frequency response I was shooting for, and this is what it took to hit my target. It's really that simple.

                Jeff B.
                Click here for Jeff Bagby's Loudspeaker Design Software

                Comment


                • #9
                  Re: BSC and speaker placement

                  Originally posted by Deward Hastings View Post
                  And the bookshelves actually had books in them, so the speaker baffle often lined up with the spines of the books, giving "in-wallish" behavior....
                  People ( I knew ) appeared more concerned with getting the low frequency boost from boundary loading ( up to 18db ) and didn't have the luxury of large rooms which allowed speaker placement well away from boundaries.
                  Though unaware of all the Physics involved with room interaction, the difference when a speaker was taken outside for a party was very apparent.
                  "Not a Speaker Designer - Not even on the Internet"
                  “Pride is your greatest enemy, humility is your greatest friend.”
                  "If the freedom of speech is taken away, then dumb and silent we may be led, like sheep to the slaughter."

                  Comment


                  • #10
                    Re: BSC and speaker placement

                    Originally posted by philthien View Post
                    Do any of you design speakers with BSC that can be switched in and out (is that possible?).

                    Thanks!
                    Should be easy enough to do in a 2.5 or 3 way design. In a 2.5 way, simply add an L-pad before the inductor and .5 woofer so you can vary it's level without affecting it's xo frequency. A variable L-pad would allow nearly infinite adjustment of the .5 woofer level. a 2-pole switch could allow switching the pad in or out.

                    On a 3 way, simply cross the woofer to mid at the BSC frequency, then put variable L-pads on the mid and tweet. This is probably what they were doing in the old 3 ways.

                    Seems like you could easily accomplish this on modern equipment via room correction software.

                    I understand what Jeff is saying about designing for flat response, but flat response at the listener position will depend on where the speakers and listener are located relative to each other, and how both interact with the room acoustics.

                    This would seem to make using room correction eq even more likely to succeed, if the speaker does not have any major dips or peaks in it's response. A 6 db dip or peak should be easy to compensate for.

                    Cheers!

                    Stan

                    Comment


                    • #11
                      Re: BSC and speaker placement

                      Originally posted by stan View Post
                      Should be easy enough to do in a 2.5 or 3 way design. In a 2.5 way, simply add an L-pad before the inductor and .5 woofer so you can vary it's level without affecting it's xo frequency. A variable L-pad would allow nearly infinite adjustment of the .5 woofer level. a 2-pole switch could allow switching the pad in or out.

                      On a 3 way, simply cross the woofer to mid at the BSC frequency, then put variable L-pads on the mid and tweet. This is probably what they were doing in the old 3 ways.

                      Seems like you could easily accomplish this on modern equipment via room correction software.

                      I understand what Jeff is saying about designing for flat response, but flat response at the listener position will depend on where the speakers and listener are located relative to each other, and how both interact with the room acoustics.

                      This would seem to make using room correction eq even more likely to succeed, if the speaker does not have any major dips or peaks in it's response. A 6 db dip or peak should be easy to compensate for.

                      Cheers!

                      Stan
                      Two things - I mentioned designing according for the intended use of the loudspeaker. For example, so are intended to be near the wall, others are not.

                      Second, if you're getting a notch due to a wall refection you can't EQ something like that away. You need to make the speaker wider and shallower. It's not something we can correct in the crossover or with external processing, but there are other ways to design it out of there.
                      Click here for Jeff Bagby's Loudspeaker Design Software

                      Comment


                      • #12
                        Re: BSC and speaker placement

                        That "big dip in frequency response" Jeff mentioned when placing close to the wall is not talked about much but easily measured. Whether you design with BSC in mind or not, it's easier than trying to avoid.

                        Comment


                        • #13
                          Re: BSC and speaker placement

                          Originally posted by Jeff B. View Post
                          I've said this before, but I think it bears repeating - A discussion of baffle step compensation is really a moot topic when discussing crossover design.
                          It's hardly "moot" if you want to design a speaker that can be used in a variety of positions in the room. It's difficult to do, perhaps, with passive crossovers (which limits the application of such speakers to the position they're designed for), but many active monitors have switch selectable compensation to allow greater choice of placement for the end user. That's good design, I think . . .
                          "It suggests that there is something that is happening in the real system that is not quite captured in the models."

                          Comment


                          • #14
                            Re: BSC and speaker placement

                            Originally posted by Deward Hastings View Post
                            It's hardly "moot" if you want to design a speaker that can be used in a variety of positions in the room. It's difficult to do, perhaps, with passive crossovers (which limits the application of such speakers to the position they're designed for), but many active monitors have switch selectable compensation to allow greater choice of placement for the end user. That's good design, I think . . .
                            I agree with your post, but you may be missing my point. Understanding the phenomenon is a good thing, but it's a big misconception that placing most speakers near a wall will eliminate baffle step. When the baffle is narrower than the distance between it and the wall behind the speaker most of the baffle step will still be present and the boost will be at lower frequencies. I am just saying we need to think about how that environment affects that speaker and design accordingly. There usually isn't a simple switchable passive feature that will work.
                            Click here for Jeff Bagby's Loudspeaker Design Software

                            Comment


                            • #15
                              Re: BSC and speaker placement

                              Originally posted by Jeff B. View Post
                              This is where Phil and I are miles apart. His statement of building a crossover so it could be switched in or out is completely foreign to me and I wouldn't even know what that means.
                              I was just asking questions, not taking a position.

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