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  • Details on building the speaker below

    Some expressed interest in building the powered monitors I pictured below. Here is the pic again.



    Start with the Parts Express RS722 kit. You won't use all of the crossover parts. But that's OK, the kit is still cheaper, and the baffle comes precut, it has pretty much everthing you need in it, and who can't use a few parts to put back and have on hand?

    Next pick-up a pair of these 55 Watt biamp plates from MCM (Hey, PE - you guys really need to carry something like this, or a small fullrange amp, or both. Don't make us go to MCM for this stuff :D )

    http://www.mcmelectronics.com/product/50-6277

    Cut your holes to mount the amplifier modules

    OK. Now after measuring the drivers on the baffle and modeling the 4th order active crossover in the plate amp I arrived at the following response shaping circuit that I placed between the amp and speakers.




    The cap on the tweeter was just for protection against any turn-on thumps, but I don't hear any from this amp, so it may not be necessary. I used it anyway though.

    The first notch filter on the woofer combines with the driver's response and impedance to compensate for baffle step, flatten the baffle bump at 1khz and give a little lift at 2kHz, which is needed to get a flat summation at the crossover. The second notch (.20mH and 2.2 uF) suppresses the cone break-up. However, I ended up removing it. I found that the 4th order crossover did a good job here all by itself, and I got a very flat summation without using it, and felt the midrange was at a point where I couldn't improve on it anymore anyway. The reason I left it in the schematic was because I know some people don't like to use these drivers without dealing with this area. I didn't find it necessary though.

    With everthing done I set the tweeter knob to the max and backed the woofer knob off about 2/3 of the way to get a flat response. These speakers have an exceptional midrange quality, and sound very good across the board. The only lack the deepest bass, but would work well in a home theater system with a sub.
    Click here for Jeff Bagby's Loudspeaker Design Software

  • #2
    Re: Very cool!

    Nice step-by-step walkthrough! I never realized making a pair of biamped pair of studio monitors could be so straightforward. Thanks once again for your addition to the collective DIY knowledge!

    -Paul
    Isn't it about time we started answering rhetorical questions?

    Paul Carmody's DIY Audio Projects
    Twitter: @undefinition1

    Comment


    • #3
      Re: Details on building the speaker below

      Jeff,

      Very nice work. That amp module looks decent for the price. You would be hard pressed to DIY the amp for that cost.
      DIY Audio Projects ::: DIY Hi-Fi Audio Blog
      [ DIY K-12 Tube Amp Kit | DIY LM3886 Gainclone | DIY Fostex FE127E Bipole Speaker | DIY Fostex FX120 Bookshelf Speaker ]

      Comment


      • #4
        Re: Very cool!

        Originally posted by undefinition View Post
        Nice step-by-step walkthrough! I never realized making a pair of biamped pair of studio monitors could be so straightforward. Thanks once again for your addition to the collective DIY knowledge!

        -Paul
        All it takes to make almost any two-way work with this amp is the tuning of the parallel notch in series with the woofers, and this is pretty much a must. If you take the response of about any woofer on a baffle and apply a textbook 4th order lowpass to it you will find pretty decent bahavior at the crossover point but a broad peak will exist centered around 800-1kHz due to the baffle diffraction hump lying between the baffle step and the lowpass roll-off. Here's the response with and without the active/passive filters.



        The is the key for about any woofer on a small baffle.

        Jeff
        Click here for Jeff Bagby's Loudspeaker Design Software

        Comment


        • #5
          Re: Details on building the speaker below

          Originally posted by Jeff B. View Post
          ...
          OK. Now after measuring the drivers on the baffle and modeling the 4th order active crossover in the plate amp I arrived at the following response shaping circuit that I placed between the amp and speakers.
          So for modelling you just used a textbook 4th order LR at 3K and went from there to design the notch(es)?

          This looks like a pretty cool project. I'm impressed with how simple the filter/crossover network is.

          Comment


          • #6
            Re: Details on building the speaker below

            You might like the sound even more (and eliminate any question about need for a notch filter) if you spend a couple bucks on the necessary resistors and lower the crossover to 1600-1800 Hz. The RS180 gets quite nasty in HD above 2kHz.. while the RS28 is quite clean in that range.

            Putting the baffle step correction in the box is good if you know where the speaker is going to be placed, but for HT use many receivers have a graphic equalizer built in (I'm thinking particularly almost all the Yamahas) that can do that correction for freestanding or against-the-wall without any additional parts at all.
            "It suggests that there is something that is happening in the real system that is not quite captured in the models."

            Comment


            • #7
              Re: Details on building the speaker below

              Originally posted by gmilitano View Post
              Jeff,

              Very nice work. That amp module looks decent for the price. You would be hard pressed to DIY the amp for that cost.
              It is a great amp for the price. Phil

              Comment


              • #8
                Re: Details on building the speaker below

                Originally posted by philiparcario View Post
                It is a great amp for the price. Phil
                The 3886 makes a great amp at *any* price, with enough power to drive almost any mid or tweeter. Two of them plus a LR4 crossover for less than $90 ? ? ? The result is cleaner than any amp followed by a passive crossover at any price . . .
                "It suggests that there is something that is happening in the real system that is not quite captured in the models."

                Comment


                • #9
                  Re: Details on building the speaker below

                  Originally posted by Deward Hastings View Post
                  The 3886 makes a great amp at *any* price, with enough power to drive almost any mid or tweeter. Two of them plus a LR4 crossover for less than $90 ? ? ? The result is cleaner than any amp followed by a passive crossover at any price . . .
                  But wait there is more a master volume control , a tweeter volume control , a midwoofer volume control ,complete circuit diagram for download and the nicest quality stock two hole plug power cord I have ever seen. That is why I have 5 of them with 1 more for a spare. Phil

                  Comment


                  • #10
                    Re: Details on building the speaker below

                    PE had one of those amps to look at for awhile. They let it go in the tent sale where I swooped it up. A thread like this may be the ticket for them to reconsider.
                    Mongo only pawn in game of life
                    ____
                    Ed

                    Comment


                    • #11
                      Re: Details on building the speaker below

                      Does anyone have a schematic for the filter circuit? And practically speaking, how easy would it be to modify the active filter circuit-anyone have a photo of the pc board/inside of these amps?

                      edit-nevermind. The circuit is posted as a pdf at Jeff's link.
                      audioheuristics isn't around right now...

                      Comment


                      • #12
                        Re: Details on building the speaker below

                        Originally posted by Deward Hastings View Post
                        You might like the sound even more (and eliminate any question about need for a notch filter) if you spend a couple bucks on the necessary resistors and lower the crossover to 1600-1800 Hz. The RS180 gets quite nasty in HD above 2kHz.. while the RS28 is quite clean in that range.

                        Putting the baffle step correction in the box is good if you know where the speaker is going to be placed, but for HT use many receivers have a graphic equalizer built in (I'm thinking particularly almost all the Yamahas) that can do that correction for freestanding or against-the-wall without any additional parts at all.
                        Technically, I agree with you. I also wouldn't normally cross woofers this size in an MTM over at 3khz either. However.........in this case the midrange is as good as anything I have built. I was really quite surprised at how exceptional it was, as well as the overal tonal balance. I also could not detect any audible lobing issues. I had considered the change to a 2kHz crossover, but after listening to this one the customer and myself both agreed to just leave things as they were. By the way, if I model the response with a 2khz active filter you still have to have a notch filter to deal with the peak at 800-1kHz. I don't see any way around it, unless you use an equalizer like you suggested.

                        In the passive crossover I designed for this speaker I ended up with a 1.7khz crossover (I did not go with the RS722 crossover, but came up with my own instead). In my small LS3/5a updates I used the RS28a and cross it at 1.8kHz in it. It sounds fabulous there too.

                        Jeff
                        Click here for Jeff Bagby's Loudspeaker Design Software

                        Comment


                        • #13
                          Nice project.

                          Jeff, thanks for doing this project. This is a perfect example of why several of us have been advocates for this amp module. If someone would work up some mods to allow a few alternative crossover points, this amp could be a real asset to someone that wants a first class system but dosen't want the hassle of building their own crossover. Anyone could build the simple notch you designed. Thanks again.
                          Building it big and playing it loud! Because we all know size really does matter, and a little over compensation never hurt anyone. :eek:

                          Comment


                          • #14
                            Re: Nice project.

                            Originally posted by Todd G. View Post
                            If someone would work up some mods to allow a few alternative crossover points...
                            We already did that--see this post: http://techtalk.parts-express.com/sh...1&postcount=15
                            The Excel version is attached. By changing resistors you can get just about any crossover point you like.
                            50-6277.zip

                            Something that bothered me about that amp is that according to the schematic the crossover isn't really a 4-pole LR filter, unless I made a mistake, which is quite possible. The tweeter filter is OK: two Butterworth filters each with a Q of .71. However, the woofer circuit has two Butterworth filters each with a Q of 1.12. If this is correct, there will be a noticeable peak on the woofer side. The picture shows the textbook LR filter in orange and the response with Q = 1.12 in red.
                            Click image for larger version

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                            A DIY version of this amp is circuit #1 at this page:
                            http://home.comcast.net/~neilrdavis/Plate_amps/
                            You can change the crossover of this amp by swapping in different resistor packs. The parts list has a tab that helps you select the right pack. If you want to build this, just upload the PWB file to ExpressPCB. The parts list is probably out of date because the ROHS requirements forced vendors to change a lot of part numbers (this design is about 5 years old), so you might have to do some cross-referencing.
                            Free Passive Speaker Designer Lite (PSD-Lite) -- http://www.audiodevelopers.com/Softw...Lite/setup.exe

                            Comment


                            • #15
                              Re: Nice project.

                              Originally posted by neildavis View Post
                              We already did that--see this post: http://techtalk.parts-express.com/sh...1&postcount=15
                              The Excel version is attached. By changing resistors you can get just about any crossover point you like.
                              [ATTACH]51[/ATTACH]

                              Something that bothered me about that amp is that according to the schematic the crossover isn't really a 4-pole LR filter, unless I made a mistake, which is quite possible. The tweeter filter is OK: two Butterworth filters each with a Q of .71. However, the woofer circuit has two Butterworth filters each with a Q of 1.12. If this is correct, there will be a noticeable peak on the woofer side. The picture shows the textbook LR filter in orange and the response with Q = 1.12 in red.
                              [ATTACH]52[/ATTACH]


                              A DIY version of this amp is circuit #1 at this page:
                              http://home.comcast.net/~neilrdavis/Plate_amps/
                              You can change the crossover of this amp by swapping in different resistor packs. The parts list has a tab that helps you select the right pack. If you want to build this, just upload the PWB file to ExpressPCB. The parts list is probably out of date because the ROHS requirements forced vendors to change a lot of part numbers (this design is about 5 years old), so you might have to do some cross-referencing.
                              Thank you. I don't know how I missed that before.
                              Building it big and playing it loud! Because we all know size really does matter, and a little over compensation never hurt anyone. :eek:

                              Comment

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