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Tony Gee's Black Box / Big Cap on woofer in small box

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  • #16
    Originally posted by davidB View Post
    I don't know. Bill.....$15 for a channel of dsp and amplification is hard to reach in non-industrial quantities.
    I can't imagine a $15 1 Farad 100v cap that I'd want to use, nor any capacitor that has 24 or more individual EQ bands. This isn't 1995, or even 2015 where the price of DSP is concerned.
    www.billfitzmaurice.com
    www.billfitzmaurice.info/forum

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    • #17
      Who buys 1 farad caps? 3 330s(or 5 200s, etc) should work fine, if you are enamored of this technique.
      I can't see anyone pushing 1000 watts through a driver appropriate for this trick.

      Comment


      • #18
        Remember to use bipolar caps, or put normal electrolytics in series back-to-back, if somebody intends to do this.
        Francis

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        • #19
          Anyways , I think the 1 F is ( for most purposes ) off .
          Say ( as a reasonable thought experiment ) we have a driver :
          Fs = 50 Hz
          Qts = 0.5
          Re = 7 Ohm
          Then ( using the given formula ) :
          C = 0.5 / ( 3.14 * 7 * 50 )
          C = 0.5 / 1099 ~ 0.000455
          C = 470 uF ( nearest standard value )

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          • #20
            It will be different for each application.

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            • #21
              For sure but even if :
              Fs = 20 Hz
              Qts = 1
              Re = 3 Ohm
              C = 1 / ( 3.14 * 3 * 20)
              C = 1 / 188.4 ~ 0.00531
              C ~ 5000 uF
              A long ways from 1 F ......

              Comment


              • #22
                Originally posted by billfitzmaurice View Post
                With the price of a 1F cap being what it is I'd use DSP instead.
                My mistake - not 1F, but 1mF, e.g. 1000 uF

                This could be achieved with two 500 uF capacitors from PE, cost of US$7,40 each, for a total of just under $15.

                Not many DSP solutions are available for $15

                The PE 500 uF caps are good up to 200W.

                To reduce artifacts, a small poly cap can be used in parallel with them.

                Brian Steele
                www.diysubwoofers.org

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                • #23
                  Originally posted by Brian Steele View Post


                  Not many DSP solutions are available for $15

                  Also, no non-nerd I know wants to deal with another box.

                  DSP is great for what it's good for, but that's not all situations.

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                  • #24
                    So, has anyone built/heard the black boxes or another design with passive aassist? Is this just a "trick" with drawbacks?

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                    • #25
                      Originally posted by perhellion View Post
                      So, has anyone built/heard the black boxes or another design with passive aassist? Is this just a "trick" with drawbacks?
                      It's just a passive form of EQ. No drawbacks other than needing a big cap.
                      Francis

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                      • #26
                        Originally posted by Brian Steele View Post
                        My mistake - not 1F, but 1mF, e.g. 1000 uF
                        If it's a full range speaker I wouldn't use an NPE. Ten of these to reach 1000uf comes to $298:
                        https://www.parts-express.com/dayton...citor--027-447

                        If it's a sub NPE would do, so you could use a pair of these for $15:
                        https://www.parts-express.com/500uf-...citor--027-378

                        I'd still rather use DSP, especially with a sub. A cap can't fix room response issues. DSP used to be expensive, but $60 isn't:
                        https://www.parts-express.com/dayton...oller--230-520


                        www.billfitzmaurice.com
                        www.billfitzmaurice.info/forum

                        Comment


                        • #27
                          Originally posted by billfitzmaurice View Post
                          If it's a full range speaker I wouldn't use an NPE. Ten of these to reach 1000uf comes to $298:
                          https://www.parts-express.com/dayton...citor--027-447

                          If it's a sub NPE would do, so you could use a pair of these for $15:
                          https://www.parts-express.com/500uf-...citor--027-378
                          If it's a full range speaker, I'd use the latter and a small film shunt cap to reduce/eliminate their impact at higher frequencies, and save myself around $280

                          Originally posted by billfitzmaurice View Post
                          I'd still rather use DSP, especially with a sub. A cap can't fix room response issues. DSP used to be expensive, but $60 isn't:
                          https://www.parts-express.com/dayton...oller--230-520
                          Still twice as expensive as two 500 uF caps and you have to a system config that actually supports the insertion of a DSP solution like that.
                          Brian Steele
                          www.diysubwoofers.org

                          Comment


                          • #28
                            Originally posted by perhellion View Post
                            So, has anyone built/heard the black boxes or another design with passive aassist? Is this just a "trick" with drawbacks?
                            I am finishing a design now similar to the "Black Box" with a RS270 woofer. Near-field miking of the woofer shows a bit more bass extension, and the cap will help prevent exceeding xmax.
                            I both measured and listened to it, and definitely like the bass more with the cap inline.
                            Red trace is with about 600uF inline.
                            Click image for larger version

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                            Attached Files

                            I think I hear a difference - wow, it's amazing!" Ethan Winer: audio myths
                            "As God is my witness I'll never be without a good pair of speakers!" Scarlett O'Hara

                            High value, high quality RS150/TB28-537SH bookshelf - TARGAS NLA!
                            SB13/Vifa BC25SC06 MTM DCR Galeons-SB13-MTM
                            My Voxel min sub Yet-another-Voxel-build

                            Tangband W6-sub

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                            • #29
                              Yes !
                              Contrary to the ' D.C. to Light ' school of thought,
                              caps do help with low end musicality.
                              Perceptually anyways : )

                              Comment


                              • #30
                                I had 2 retail speakers, (1990s Athena) one was a small bookshelf monitor 5" woofer, AS-B1 vented box, the other a very small surround that was acoustic suspension, similar woofer but it used the cap boost idea.

                                The surroundClick image for larger version

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ID:	1446119 was half the size of the monitors, very small, but had "Okay bass", for how small it was.

                                But the double sized bass reflex version was just better overall. A nice idea for making a TINY speaker have some bass impact, but if one could do bigger boxes not sure the idea is that great.

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