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Do I need a protection capacitor for a full range?

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  • Do I need a protection capacitor for a full range?

    I've been looking at the Tectonic TEBM65C20F-8 for some simple satellite surrounds and front heights. Should I get a 200uF capacitor for protection or will my AVR appropriately filter the signal to ensure safe levels and that no LF content is sent that could damage them. Ideally I'd rather not spend the additional 15$ for the capacitors since I wanted this to be a very low cost build.

  • #2
    I'm running it in a 4L speaker down to the 50's and it doesn't care. You don't need the cap. You will probably want a couple shaping filters to shape the response just before the issue at 1.7Khz and in the top octave. I think someone on here has already done that. You can take a look at my build and see what the lower filter looks like.

    I sort of ...abused... these things to push them past their limits, and they are really polite when they distort. I played both a telarc recording of Bach's Toccata and Fugue (because it made me laugh to hear pipe organs coming out of those things) and a 34Hz test tone fairly loudly. They were going way past their linear Xmax. Neither damaged it.

    http://techtalk.parts-express.com/fo...eaker-bmr-sb19

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    • #3
      As long as you have them set to small in your AVR speaker setup settings, you don't need the cap. However, if you have them set to large (no highpass filter), then you probably should have a protection cap.
      -Bob

      The PEDS 2.1 mini system
      My A7 Project - another small desktop speaker
      The B3 Hybrid Dipole - thread incomplete and outdated

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      • #4
        If you haven't seen these.

        http://techtalk.parts-express.com/fo...fa-hibm65c20-8

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        • #5
          It was Jhollander who posted the full range design. Look at post 6 of this thread. http://techtalk.parts-express.com/fo...speaker-please

          His 2-way speaker with that driver also received rave reviews (I've never heard it though).

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          • #6
            Good, it turns out that the Tectonic TEBM65C20F-8 are a little too large for the piece of wood I intent to use and have to switch it to the Tectonic TEBM46C20N these drivers have a strange 300-400 Hz dip not sure if it's worth correcting?

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            • #7
              It would depend on if it goes away off axis - which given the power response - it might. There's lots of things with fundamentals in that range, and attenuating them that much could be problematic - and I wouldn't use it that low. Most places I've seen that driver used are as midranges (take for example Dennis Murphy's BMR) and I suspect the driver is crossed before that becomes problematic. I'm not sure there'd be anything satisfying about the bass coming out of that speaker, even for HT surround or height channel duty.

              Could you just use a different piece of wood?

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              • #8
                I might have to reconsider, I was really hoping for a 4" cube design, but that won't fit the Tectonic TEBM65C20F-8 but it does fit the Tectonic TEBM46C20N, which look to have severe attenuation in ~300 Hz.

                I might be able to do a 5 1/2 " x 5 1/2 " x 3 1/2" design to fit the Tectonic TEBM65C20F-8.

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                • #9
                  Were you planning sealed or ported? Assuming 1/2" walls, the 5.5x5.5x3.5 looks like it'll have a couple DB of peak at about 160Hz (which can sound good, but this is a little more than I'd like) with an F3 around 95Hz. If you stuff the box with a stuffing with a lot of absorbativity (is that a word?? probably something denser than polyfill) you could tame that. I don't see a ported alignment I like in that size box.

                  The through hole for that driver is about 3.25" so if you can get the internal dimensions a little bigger than that, it should be ok. The driver is REALLY shallow, so if you could make something that's not very deep but bigger to get you to the 4-4.5 liter internal volume range and port it, I think you'll get a lot better bass response. You'd end up with something that mounts flush on the wall and is maybe only 3.5-4" off of the wall. Paint it wall/ceiling color, and you'll barely see it. If you want to be brave and use a thin back - like 1/4" - you could reduce that a little more.

                  To my ears, it NEEDS a crossover too. THe top end is really harsh and the midrange sounds wrong without it.

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                  • #10
                    I was planning to seal it and stuff it with poly and no passive filters, in a 1-2 liter box. I don't think such a small dimension permits porting? Plus I really want to keep these tiny.


                    The drivers look like they already have "built-in" compensation for the BSC.


                    Click image for larger version

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                    • #11
                      I've been looking at http://techtalk.parts-express.com/fo...speaker-please and http://projectgallery.parts-express....ojects/bmr-3l/

                      I don't understand why people are adding a notch filter in a region where there's already a dip?

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                      • #12
                        The notch filter is just a filter for the BSC then a filter to roll off the woofer highs. It works around the dip where a single inductor can't
                        John H

                        Synergy Horn, SLS-85, BMR-3L, Mini-TL, BR-2, Titan OB, B452, Udique, Vultus, Latus1, Seriatim, Aperivox,Pencil Tower

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                        • #13
                          ​​I picked up the pine lumber for this small and inexpensive project. The pine is 1/2" thick.

                          Here's the design I'm going with. It's approximately 1.6L internal volume






                          Click image for larger version

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                          • #14
                            I ran experiments with the filter proposed in the other thread and it really doesn't make sense to. Is my analysis wrong ? ( I don't think so). The purpose of the notch in the design seems off. I understand the inductor is used to roll off the highs, but I also think this is not necessary unless you are listening to the drivers directly at 0degree angle. In the listening window the response flattens and the inductor, I believe, is not necessary.

                            What I did: I simulated the diffraction response based on the baffle dimensions and combined them with the frequency response of the drivers. Here's the circuit proposed in that thread



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                            Response with circuit (and baffle)

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                            Response with no circuit (and baffle)

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                            As you can see in the listening window with a small baffle, this driver is very flat. The baffle step boost corrects the dip in the drivers raw response:

                            Raw driver FR response
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                            Here's the box response. It's a sealed 1.6L enclosure

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                            I have polyfill and will stuff it inside. Does anyone know how polyfill modifies the box response?


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                            • #15
                              I also don't see substantial difference between the TEBM65C20F-8 and TEBM65C20F-4. I'm going to go with the TEBM65C20F-8 version for no other reason that it's more popular. My AVR is already driving nominally 4 ohm speakers, and I figure using 8 Ohm for surrounds and Atmos, should work the AVR less so it's probably best to go with them.

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