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Clearing out my last BF37 pair, feedback on this enclosure/port

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  • Clearing out my last BF37 pair, feedback on this enclosure/port

    Guys, especially Chris Roemer , I'm looking at a small mp3 build for my daughter, being quite young she isn't going to care about how low they will go as long as she can listen to what she wants .I know with my quarenteenee build the sound was pretty decent for a 1.5 inch driver in a 0.01cuft enclosure and a dodgy passive membrane, so I'm thinking the same but with a port

    For a while I've wanted to do a TL or horn, but instead thinking long slot port. I've modeled the 0.01 cuft each enclosure, with a box tuning frq of 90hz, the port is 52mm x 8mm and length of 525mm. The 1st port res is 330Hz

    Total box size is approximately 220mmx100mm x 65mm (external)which is still quite small

    It's not a horn or TL but this is the first rectangular port I've tried, so interested to hear if I'm going to fail or if it is over kill and a 15mm port, 220 long will be just as good.
    ..

    I'll 3d print this so don't care about the size being what is listed above

  • #2
    I think a ~90hz tuned port around 300mm long slows the port velocity down to 17m/s so a larger port beyond that probably won't give noticeable benefits even to a fairly picky listener (and I think going too large starts to make port resonance more of a potential problem).

    It looks like a 15mm x 220mm long port would only push peak velocity up to 22-23m/s....This is still miles better than many store-bought bookshelves/HTIB/computer speakers, so I'm pretty sure your daughter will like them. I imagine the smaller overall size this allows will be a positive thing as well.


    If it makes you feel any better, I'm currently using a pair of PC68's tuned around 65hz....using tiny 10mm diameter ports...on the front. They should easily be hitting over 80m/s port velocity. Their puffing is plenty noticeable with sine-wave sweeps or pure clean bass notes without anything else going on, but with regular full-range music playing it's very rarely noticeable over the rest of the music.
    Not recommending going this small..just saying you'll be way ahead of this and I'm sure they'll sound great.
    My first 2way build

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    • #3
      That driver, in 0.01cf, tuned to 90 (which looks good to me) could probably use a 1/2"dia. by 6" long rear vent.
      That's only 0.20 sq.in. (about 130 mm^2). A slot that's 10mm x 13mm (x15cm long) should do.

      Comment


      • #4
        Originally posted by Chris Roemer View Post
        That driver, in 0.01cf, tuned to 90 (which looks good to me) could probably use a 1/2"dia. by 6" long rear vent.
        That's only 0.20 sq.in. (about 130 mm^2). A slot that's 10mm x 13mm (x15cm long) should do.
        Does the res port freq matter? I was going just a bit silly designing this port the same height as the enclosure, snaking through that 500mm, then I put it in my slicing program and it estimated days, so think the pvc pipe will prevail. I have some 15mm pipe I think that will be perfect

        Comment


        • #5
          Originally posted by 3rutu5 View Post
          Does the res port freq matter?
          With a multi-driver arrangment like a 2way or 3way or subwoofer I think you'd ideally try to aim for the port's 1st resonant frequency to be as high-frequency as possible while balancing that with the port's max airspeed...wider+longer port means lower/better airspeed but also lower/worse 1st resonant frequency, so it's a balancing act between the two. If you can get the port's loudest resonance frequencies far enough above the woofer's crossover point, it can be tamed down enough to not be heard. At least that's what I think the plan is...not sure if it's usually realistic for 2ways since they tend to cross pretty high
          For a fullrange driver, I have no idea if there's anything you can do about the port resonance that's really meaningful. I get the feeling that port resonance is usually pretty far down on the list of things to worry about in speaker building aside from some more niche/specialty designs. I could easily be wrong though.
          My first 2way build

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          • #6
            ok, cheers.

            Here is another question, do i need to separate the two drivers? I'm just tinkering around it CAD and thinking if i dont have to put a divider in, i could install a volume knob in the front center.

            Just spit balling here,

            Got a few interesting ideas, just thinking of culling a couple of them. ALready dropping the snakey port, going with the 15mm pressure pipe. Going to use my previous shell idea for the 2.1ch print job i did a few weeks, it is perfect size, just a bit bigger than required, but will acount for the lost space with the ports and amp etc.

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            • #7
              A 15mm (id) pipe should then be 8" long. I'd exit it out the back (if you can) and add a flair (or roundover) to its exit.
              If you want 2 drivers in 1 box (stereo) they should have a divided space to work in.

              Comment


              • #8
                Originally posted by Chris Roemer View Post
                A 15mm (id) pipe should then be 8" long. I'd exit it out the back (if you can) and add a flair (or roundover) to its exit.
                If you want 2 drivers in 1 box (stereo) they should have a divided space to work in.
                So far the design has an allowance for just shy of 0.03cuft internally, so accounting for ports, components etc I will easily have the minimum 0.01cuft per driver I'm wanting. I don't think these tiny drivers like much more volume than that as the model jumps up at that 80-100 hz range in the transfer graph.

                Wasn't sure if having 2 drivers sharing the same space was a recipe for disaster this being a stereo setup

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                • #9
                  Thinking I might build two now and use some drivers from another project. Got that 2*50w by amp to use and it mentions it can run off 5v which might give me 5-10w per channel at 4ohms. Could be a viable option for a 3.7v battery and step.up module finally, although I have a couple of 2 and 3s cheap BMS ive never tried

                  Any thoughts on a power supply for this based on the above
                  Attached Files

                  Comment


                  • #10
                    guys, having a bit of a hard time thinking what to do here, the overall length of this will be 170mm (plus sides say 10mm per side). so let say 190mm external in total. If im rolling with a port length of 200mm ish, i cannot think of how to put in 2 of them and keep the enclosures separated. Think i may sleep on it, my tired state may be affecting my thought process at the moment.

                    items to refine

                    * central divider
                    * port length and interface
                    * 3d printed knob for amp and interface with body
                    * sides.
                    Attached Files

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                    • #11
                      Ports CAN be shorter, IF smaller (like 12mm?).
                      Since the vent output is omnidirectional, the L side port COULD exit out the R side (& vice versa).

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                      • #12
                        I don't want to unknowingly rehash some huge debate (done that once already) but while it is IDEAL to separate the drivers into their own spaces, it is not mandatory. Theory and feelings aside, just try it. You seem to have stock on these drivers - make two simple boxes, one divided and one mono space and listen to them. Or, if you have some pipe big enough to fit the drivers to, it is easy enough to do this with one length of pipe vs. a pair.

                        I fully agree that people should strive for best practices and maximize opportunities, but sometimes one can cheat a bit and get away with it.

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                        • #13
                          I bought a few of these drivers for the beer cans but realised I just couldn't cram everything into the design without sacrifices, which was mainly the inconsistent amps and putting a 18650 in, so I just stopped. So with this build and one other I'm trouble shooting that will be it using them

                          I'm treading that fine line at the moment where I'm just bigger than my quarenteenee build (out of wood) and was trying to use pipe from the hardware store, which says a nominal diameter of 15mm but is actually 18mm after I measured it with calipers. I can manufacturer bends on the printer but get a bit OCD with port placement being symmetrical. The sky is the limit sometimes with the printer as I have a couple of different ideas for the volume pot, but might come at a sacrifice with internal volume. Also got an idea for the divider
                          .
                          Might be able to print a pipe

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                          • #14
                            Would it be possible to print curved pipes for each side that are part of the sides themselves rather than independant tubes (where the inner sides/top/bottom/back act as one fo the ports' walls...maybe the sides+top/back/bottom acting as two of the port walls if they can fit around the inner corners as they curve around the shape inside the box until reaching the needed length)?
                            They'd be kind of like a pair of ram horns inside the box (that wording makes it sound external..not what I meant though).
                            My first 2way build

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                            • #15
                              Hey LOUT, I've been racking my brain trying to think of how to integrate them and print as one. Maybe if i worked some curves or chamfers i might be able to and come directly off the vertical surface.

                              Just woke up before and printing a 150mm long, 12mm internal tube with a curved end, apparently going to take 35mins. Doesnt use up much filament but interested to see if it is any good, i gave it 2mm thick walls but thinking it may be too think for the application.

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