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Simple yet VERY effective BSC crossover adjustment (Illegal in DIY competitions?)

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  • Simple yet VERY effective BSC crossover adjustment (Illegal in DIY competitions?)

    I wouldn't be surprised if other DIY speaker designers have used this "trick" in order to compensate for different room/boundary conditions...



    Consider my Alpheus MkII 3-way speaker design which is configured such that it can be bi-amped (Woofer / Mid+Tweeter). The crossover point between the woofer and the mid/tweeter is 350 Hz with very shallow (2nd order) slopes. The impedance of the mid/tweeter section with the crossover is fairly flat within a few ohms from peak to valley. The speakers were designed with minimal BSC using the stock crossover(s)...



    There are two different ways to adjust the bass/mid+tweeter blend. I'll first explain how to achieve this without having to bi-amp the speakers... All of the parameters discussed above contribute to the effectiveness of this approach.

    In order to increase the amount of BSC (or room blend/balance) simply use a resistor in series with the mid/tweeter section of the speaker. This will effectively boost the bass by attenuating the mid/tweeter section (and since the impedance is fairly tame, there will be minimal peaks/dips due to the interaction of the series resistor). Also since the crossover region is very wide, with a lot of overlap, the blend remains balanced regardless of how large of a resistor is used.

    The second method is to simply "bi-amp" the two sections of the speaker. Then simply adjust the level of the mid/tweeter network until the balance is "right". This is how I currently have my Alpheus MkII speakers set up (4 channels of an Outlaw 750 power amp, using an Alps Pot on the mid/tweeter channels). I've even found that I like to adjust the balance based on the recording, which is extremely handy!

    Both techniques are very effective at adjusting the blend and balance of the speaker, and allow you to adjust them to suit just about any listening room (based on a few tests that I've performed).

    I first discovered this "trick" by using resistors after noticing that these speakers sounded very "thin" when auditioned at my friend's house (much larger room, speakers a few feet away from the rear wall, open floorplan with no room pressure bass gain). I couldn't believe how effective, and simple, this technique was when I started experimenting with different series resistor values! :eek:


    I suppose that this would be "legal" in a speaker competition (using resistors, not bi-amped) and would really allow a 3-way speaker to perform much better in any "new" environment. I've never been to a speaker competition, but I've heard the same thing soooo many times.... My speakers didn't sound as good in the room where the competition was held due to the "unfamiliar" room interactions. I can guarantee that my Alpheus MkII speakers would sound very "thin" with the stock crossover configuration, yet could be easily adjusted using a small series resistor. :D

    Would this be considered "cheating?"

    It seems that most of us DIY'ers tend to optimized the speakers/system for a particular room and then find out that they don't sound as good elsewhere. :(

    Has anybody else out there used this technique in any of your speaker designs???? Any comments about the pros/cons to this technique?

    RJB Audio Projects
    http://www.rjbaudio.com

  • #2
    Re: Simple yet VERY effective BSC crossover adjustment (Illegal in DIY competitions?)

    My experience is that designing "flat" on axis and smooth falling off axis, usually wins the competitions. Using the resistor/s to EQ SPL may create broad frequency response deeps and throw the loudspeaker completely off balance. Of cause it depends on the design, designer and the level of adjustment. But throwing resistors to EQ the speaker 5min before the competition may do more damage then good. Perhaps using a secondary LR with the switch to compensate for the room/back wall placement is a better solution? In any event, I never found a necessity to adjust a "flat" loudspeaker to the room conditions.
    Also, I don't think it's "illegal". On NY DIY people just don't have time to tinker and fine tune for the conditions. We end up with 20 or so pairs to listen and there's only time for short introductions.
    http://www.diy-ny.com/

    Comment


    • #3
      Re: Simple yet VERY effective BSC crossover adjustment (Illegal in DIY competitions?)

      Heck, slap an L-pad on the mid-and tweeter section, slap it on the box and call it "BSC adjustment knobamathing"

      ....lol

      For it to work better in your case, the baffle would have had to be a touch wider IMO. However, it would still work. Competition legal? No clue.

      Regards,
      Eric
      Pro/Fi Cinema Speaker project: "From the Ashes"

      Comment


      • #4
        Re: Simple yet VERY effective BSC crossover adjustment (Illegal in DIY competitions?)

        Originally posted by r-carpenter View Post
        My experience is that designing "flat" on axis and smooth falling off axis, usually wins the competitions. Using the resistor/s to EQ SPL may create broad frequency response deeps and throw the loudspeaker completely off balance. Of cause it depends on the design, designer and the level of adjustment. But throwing resistors to EQ the speaker 5min before the competition may do more damage then good. Perhaps using a secondary LR with the switch to compensate for the room/back wall placement is a better solution? In any event, I never found a necessity to adjust a "flat" loudspeaker to the room conditions.
        Also, I don't think it's "illegal". On NY DIY people just don't have time to tinker and fine tune for the conditions. We end up with 20 or so pairs to listen and there's only time for short introductions.
        I'm going to have to "politely" disagree with your conclusions...

        Simply stated... Take a pair of speakers and first place them against the back wall and listen. Then move those same speakers 3 feet away from that rear wall... Is there a "generic" crossover design that can accomodate both scenarios (without any adjustments/equalization)????
        RJB Audio Projects
        http://www.rjbaudio.com

        Comment


        • #5
          Re: Simple yet VERY effective BSC crossover adjustment (Illegal in DIY competitions?)

          Originally posted by mdocod View Post
          Heck, slap an L-pad on the mid-and tweeter section, slap it on the box and call it "BSC adjustment knobamathing"

          ....lol

          For it to work better in your case, the baffle would have had to be a touch wider IMO. However, it would still work. Competition legal? No clue.

          Regards,
          Eric
          Yeah, I thought of that as well... but some "audiophiles" are not very fond of L-Pads as opposed to a non-inductive resistor (even a 5 way switched resistor network ala. Dynaco A25 tweeter "L-Pad" would work well).

          I can tell you that with these particular speakers, this method is extremely effective!
          RJB Audio Projects
          http://www.rjbaudio.com

          Comment


          • #6
            Re: Simple yet VERY effective BSC crossover adjustment (Illegal in DIY competitions?)

            no doubt speakers will sound and measure differently, depending on the position in relation to boundaries. I just think that a "quick" adjustment without verification, measurements and voicing can do more damage. After all, your subject was about "simple", "Illegality" and "competition".
            Let's say you'd bring your speakers to NY DIY. We usually set loudspeakers roughly in the same position which is about 3ft away from back wall and 6ft away from side wall. My shop is a bit echoic, ringy place with 20ft ceilings.
            What would you be able to do prior to the listening session (without the ability to voice) or in a given 5min introduction window?
            http://www.diy-ny.com/

            Comment


            • #7
              Re: Simple yet VERY effective BSC crossover adjustment (Illegal in DIY competitions?)

              Originally posted by r-carpenter View Post
              no doubt speakers will sound and measure differently, depending on the position in relation to boundaries. I just think that a "quick" adjustment without verification, measurements and voicing can do more damage. After all, your subject was about "simple", "Illegality" and "competition".
              Let's say you'd bring your speakers to NY DIY. We usually set loudspeakers roughly in the same position which is about 3ft away from back wall and 6ft away from side wall. My shop is a bit echoic, ringy place with 20ft ceilings.
              What would you be able to do prior to the listening session (without the ability to voice) or in a given 5min introduction window?
              Simply calibrate the speakers at home for different configurations (relative to the room boundaries) and then choose a subset of resistors to compensate for the extremes. Even if it isn't perfect, it will sound much better...

              I know because these speakers used to sound very balanced with the original crossover in the original (smaller) listening room, yet now I have to adjust the mid/tweeter section so that they don't sound thin and overly "agressive" in the mid/treble region. I suppose that it is tough to describe how effective and how easy it is to adjust.

              Another trick that I just discovered/verified... if you place your speakers at a ~45 degree angle in the corner of a room, the room modes are almost non-existent from the listening position! Just another one of those "duh" moments that took 15+ years for me to discover! I've had these same (Alpheus MkII) speakers for years, and they have never sounded better (by a longshot!)
              RJB Audio Projects
              http://www.rjbaudio.com

              Comment


              • #8
                Re: Simple yet VERY effective BSC crossover adjustment (Illegal in DIY competitions?)

                I believe this is what Magnapan does with their planers, providing jumpers with a known resistance value to attenuate the top octaves.

                Comment


                • #9
                  Re: Simple yet VERY effective BSC crossover adjustment (Illegal in DIY competitions?)

                  I've done exactly that with speakers I've built for others. I get them right in my room. Then I take them to their new home, where I dial them in by fiddling with resistors until the new owners are grinning. Works fine, if XO is about 300-400. I've also left port variants with people so they can tune to their preference.

                  Comment


                  • #10
                    Re: Simple yet VERY effective BSC crossover adjustment (Illegal in DIY competitions?)

                    Originally posted by maynardg View Post
                    I've done exactly that with speakers I've built for others. I get them right in my room. Then I take them to their new home, where I dial them in by fiddling with resistors until the new owners are grinning. Works fine, if XO is about 300-400. I've also left port variants with people so they can tune to their preference.
                    Hmmm... Thanks for the confirmation... Especially the part about the "optimal" crossover frequency for this type of adjustment.

                    It must have been a case of DIY serendipity that I happened to design a speaker that allows you to make this adjustment with minimal "side-effects" considering all of the parameters I mentioned above, as well as the crossover freq/slopes that I chose originally.

                    I'm really hoping that others try this technique (with a 3-way design, of course... although I've also "invented" a circuit which allows you to adjust the amount of BSC in any 2-way speaker design by altering the attenuation of the typical series inductor), even if they have to choose slopes and crossover points that make it a bit more effective.

                    Unless you've tried it yourself, you won't believe how effective it is at making a pair of speakers sound "balanced" regardless of the room!
                    RJB Audio Projects
                    http://www.rjbaudio.com

                    Comment


                    • #11
                      Re: Simple yet VERY effective BSC crossover adjustment (Illegal in DIY competitions?)

                      Wow, you've invented the concept of padding a mid range and tweeter. Unbelievable. You'd have though someone would have figured that out forty ot fifty years ago. Just unbelievable. :D

                      Comment


                      • #12
                        Re: Simple yet VERY effective BSC crossover adjustment (Illegal in DIY competitions?)

                        Roman,

                        I did something similar with an open baffle mid design. I added two different legs for the mid resistor with a switch. One setting attenuated the mids about 1db more. This made it possible to do a fairly subtle adjustment to fit room placement and how far from the front wall you were setting the speakers up.

                        That said, one problem with your suggestion is the ability to decide beforehand how the speaker would need to be adjusted, especially if you hadn't experienced the room before. You don't typically get a chance to listen to your speakers at a competition and then make a change before they are auditioned, so you must decide beforehand how to tweak them. A lot of the ones I have been at actually have some bass or midbass emphasis, often making the bass seem more prominent at the DIY event than at home. You seem to be expecting it to be the other way around, less bass than you hear at home. In my experience, a design with something like 3db bsc seems to sound more balanced in the typical DIY event setup than one with 6db, even though the speakers are often placed quite far from any surrounding boundary walls, much further than in most home environments. In other words, unless you've been to the venue before, it is a bit of a crapshoot.

                        I see nothing wrong with making the output levels adjustable. It makes some sense to incoporate the flexibility to adjust to the room the speakers will end up in and to the taste of the user in terms of music, etc. Seems to be fairly common in the commercial world, or at least it used to be. I don't know why that would be cheating.
                        Dan N.

                        Comment


                        • #13
                          Re: What Dan said...

                          With the exception of the last two pairs of speakers I built that had their woofers mounted low on the baffle to allow the floor-boundary reinforcement to minimize/negate BSC, using a 3-dB BSC works well almost universally IME. My listening setup dictates speakers being close to the wall behind, anywhere from 3" to 8" depending on the cabinets' depth, so only 3 dB of BSC is used. My speakers sound well balanced in my room, yet when I take them to the various DIY venues where they are pulled well out and away from walls, they not only don't sound anemic or weak bass-wise, they also haven't ever sounded boomy (unlike quite a few of the other speakers usually); they sound just as well balanced at these venues as in my home.
                          Paul

                          Originally posted by dlneubec View Post
                          Roman,

                          I did something similar with an open baffle mid design. I added two different legs for the mid resistor with a switch. One setting attenuated the mids about 1db more. This made it possible to do a fairly subtle adjustment to fit room placement and how far from the front wall you were setting the speakers up.

                          That said, one problem with your suggestion is the ability to decide beforehand how the speaker would need to be adjusted, especially if you hadn't experienced the room before. You don't typically get a chance to listen to your speakers at a competition and then make a change before they are auditioned, so you must decide beforehand how to tweak them. A lot of the ones I have been at actually have some bass or midbass emphasis, often making the bass seem more prominent at the DIY event than at home. You seem to be expecting it to be the other way around, less bass than you hear at home. In my experience, a design with something like 3db bsc seems to sound more balanced in the typical DIY event setup than one with 6db, even though the speakers are often placed quite far from any surrounding boundary walls, much further than in most home environments. In other words, unless you've been to the venue before, it is a bit of a crapshoot.

                          I see nothing wrong with making the output levels adjustable. It makes some sense to incoporate the flexibility to adjust to the room the speakers will end up in and to the taste of the user in terms of music, etc. Seems to be fairly common in the commercial world, or at least it used to be. I don't know why that would be cheating.

                          Comment


                          • #14
                            Re: Simple yet VERY effective BSC crossover adjustment (Illegal in DIY competitions?)

                            I have a question about the DIY competitions:

                            If the end result is to have the best possible speaker (many metrics here which room adaptation being one) why isn't / wouldn't an actively managed speaker be permissible?

                            Which brings me to my 2nd question: I have seen speakers with wild impedance plots and wide phase angle that require a pretty stout amp that isn't going to oscillate. They also tend to be really expensive. At that point why wouldn't the manufacturer just go with an actively managed design and put all that to rest. The CBT line arrays come to mind as example.

                            Comment


                            • #15
                              Re: Simple yet VERY effective BSC crossover adjustment (Illegal in DIY competitions?)

                              There is one critical factor that has definitely come into play with my current setup, based on the non-orthogonal placement of my speakers as well as the listening position. As I mentioned briefly above, this configuration has almost no room mode peaks, however....

                              When I adjust the bass balance while standing near the receiver/speakers, I notice that the bass is quite strong. However, when I sit down in my listening position, the bass is very well balanced.

                              I suspect that I am having to "boost the bass" based not only on the location of the speakers relative to the nearby room boundaries, but also based upon the bass response from my listening position which may contain very few room mode "peaks" yet a fairly balanced output overall.

                              This principle is easily proven if you simply walk around your listening room, because you'll find that some locations (in the corners, for example) have way too much bass, in a loud/resonant way that tends to accentuate certain bass notes.


                              With that said, this adjustment and compensation is needed not only to balance the bass due to speaker interactions related to the nearby room boundaries, but also to balance the bass at the listening position.


                              BTW, I do recall the old L-Pads in vintage speakers which were helpful for adjusting the tonal balance... I've used them myself (in my first set of DIY speakers)... Even my Dynaco A25 speakers had a variable 5-way L-pad resistor network on the tweeter (which, coincidentally, always sounded best with the least amount of attenuation... so in effect, this control was essentially useless). However, the technique that I'm using now is much more effective in my opinion.
                              RJB Audio Projects
                              http://www.rjbaudio.com

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