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  • #16
    Haha, I just need a marketable name for it, how about an Acoustic Mass-Wave Resonator!

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    • #17
      A 50cm port is awful long to be used in a speaker that is not a dedicated subwoofer. The port resonance may be difficult to deal with... It looks cool though.

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      • #18
        Originally posted by 1100xxben View Post
        A 50cm port is awful long to be used in a speaker that is not a dedicated subwoofer. The port resonance may be difficult to deal with... It looks cool though.
        I hope with the crossover at ~200Hz the port resonance won't be a problem. Do you think there could still be a problem?

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        • #19
          I made it in the form of a doghouse which can sit on the back of an existing test box I have. If I have time, I'll give it a shot this evening.
          Attached Files

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          • LOUT
            LOUT commented
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            That's a cool way to test.

        • #20
          Originally posted by zx82net View Post

          I hope with the crossover at ~200Hz the port resonance won't be a problem. Do you think there could still be a problem?
          Crossing that low will certainly help, but it will also depend on how steep your filter is. Your first resonance will be around 340 Hz. Some people use the rule of thumb to keep the resonance at least one octave above the crossover frequency. Another thing to consider is that even though you're going to have an active filter to try an eliminate exciting the port resonance, the transducer will have harmonic distortion that could possibly excite it. It looks like you're far enough along you can try it.

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          • #21
            Deleted (duplicate post)
            Last edited by 1100xxben; 01-20-2021, 02:20 PM. Reason: Deleted (duplicate post)

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            • #22
              Originally posted by 1100xxben View Post

              Crossing that low will certainly help, but it will also depend on how steep your filter is. Your first resonance will be around 340 Hz. Some people use the rule of thumb to keep the resonance at least one octave above the crossover frequency. Another thing to consider is that even though you're going to have an active filter to try an eliminate exciting the port resonance, the transducer will have harmonic distortion that could possibly excite it. It looks like you're far enough along you can try it.
              I recall seeing something in the past about placing lossy patches in the wall of a port, at the nodal points for port resonances, (I think it may have been in the context of a Bose product). Do you know whether that has been proven to be effective.

              Sigma Studio, which I'll be using to program the DSP, supports up to 48dB/octave filters, I don't know whether they have any acoustic disadvantages over shallower filters. I could also notch out the response at the port resonance modes, but that feels like a nasty hack.

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              • #23
                So, I put it together, with a bit of length adjustment and impedance measurements, I have it tuned to 46Hz with a final length of 53cm. Running without a crossover, and using a tone generator, I can find a fairly mild response peak at around 320Hz, and covering the back of the port modulates the volume, so pretty much as expected for the first port resonance. With the 200Hz cross-over in place there seems to be no excitation of the port resonance. I tried taking the test tone down to 160Hz and cranking the volume up to see if the 2nd harmonic would tickle the port. Nothing sounds untoward, and covering and uncovering the port doesn't produce any change in sound. I think I got away with it!

                It this point in time, it is one butt-ugly cabinet and the stub of port coming out of the back makes it look like a camcorder. The TEBM35 is blue-tacked to the top in a separate satellite enclosure I already had. The sound is sweet though. Time to listen to some tunes and contemplate what I can do about the looks.

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                • #24
                  Some photos:
                  Attached Files

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                  • #25
                    Sweet!

                    Now stuff that contraption inside a traditional looking enclosure with lots of sound absorbing material and call it done?

                    Love the work you have done, man.



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                    • #26
                      Thank you. I'm going to think a while on how to style the finished design. I think they deserve something not 100% traditional.

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                      • #27
                        OK, then think about a big pair of potted plastic cactus plants in each corner of the room?

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                        • #28
                          I've read that that the peerless PR doesn't work with the W3-1876, this is what I get using published specs. Seems good to me? This is in a 1.7ltr box.

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                          • #29
                            Originally posted by Misch View Post
                            I've read that that the peerless PR doesn't work with the W3-1876, this is what I get using published specs. Seems good to me? This is in a 1.7ltr box.
                            Interesting, that does work. Where did you get the Qms of 10? I think that is what I was missing. Maybe I'm blind but I couldn't see it on the spec sheet or the parts express page.

                            The port seems to give a fair bit more bass extension, slightly larger box size at 1.9l. (Also looked at cone excursion at 20W input, there's no clawing the difference back with equalization.) No argument the PR saves on size.

                            (For what it's worth, the response comparison is about the same with the W3-1878 measured parameters Hexibase reported in his youtube video)
                            Attached Files

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                            • #30
                              This is the spec sheet I use for the passive radiator (see attached) ​​​​​, though I did notice my PR specs were a little off before. Was going by memory

                              I measured the two W3-1876S I have and the FS is about 10-15 hz higher than published. But in 1.1ltr I get more output beacuse the below 40hz is less pronounced.

                              But as you said, it's tradeoffs, I'm aiming for a small as possible and still get an enjoyable sound.


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