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  • #1

    curved speaker questions?

    I am thinking/planning/hoping to build the Nat P's in a curved speaker design. These would be similar to yousuredo2's speakers on htguide (a little different size dimensions, though). I do have a few questions (basic questions, I would imagine). I would like to do a 50 liter enclosure size, 28 hertz and 11 inch long 3 inch diameter port as suggested by Evil Twin in his Nat P build.

    One question I have is, I doubt that I would be able to get the 50 liter volume exactly. What with trying to figure out the extra volume of the curves, then subtracting the driver and braces volumes, I am thinking I might be off by 3-4 or 5 liters (maybe more or less)? So, if I use the 11 inch length for the port, but am off 5-10 liters (hopefully not that much) in volume, what differences or problems am I looking at?

    Would I get chuffing? Or a huge difference in sound, etc? I am not too worried about a different tuning number.

    Anything else to consider?

    thx,
    Frank--Still the one
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  • #2
    Re: curved speaker questions?

    Many CAD programs will calculate the area of an object for you. AutoCad and TurboCad are two programs I'm familiar with that have this function. Knowing the area of your curved shape you can calculate volume.

    By teh same method you can calculate the volume of braces. I've recently done two cabinet designs. If you post the original cabinet internal dimensions and any desired curved cabinet dimensions I should be able to work up a CAD file with volume and area.
    If life were fair, Elvis would still be alive today and all the impersonators would be dead.
    ~ Johnny Carson

    Bungelow Ed's Photo Album http://techtalk.parts-express.com/album.php?u=8594

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    • #3
      Re: curved speaker questions?

      Thx, bungalo, for the offer. I will take you up on it, if you don't mind. Only thing right now is, I haven't decided yet on the dimensions exactly as these will be for my daughter and s-i-l and I need to talk to them to get their input. I should see them tomorrow before they go back to Utah.

      I do want the footprint somewhat smaller and not as deep as yousuredo2's as they don't have a whole lot of room. Right now, the front baffle will be 7.5 inches (inside) and I am thinking that the back baffle should be about 3 inches(?) (inside) and about 13.5 deep (inside). Again, these are not set in concrete right now.

      I "think" this would put the height somewhere between 40-45 inches (inside)? I don't know if this height would be OK with them or not. With these dimensions, I won't be able to port in the back. This will be something else I need to speak to them about (where to port, bottom or front?).

      Again, thx, for the offer. I do appreciate it.
      Frank--Still the one

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      • #4
        Re: curved speaker questions?

        Originally posted by gimpy View Post
        Right now, the front baffle will be 7.5 inches (inside) and I am thinking that the back baffle should be about 3 inches(?) (inside) and about 13.5 deep (inside). Again, these are not set in concrete right now.

        I "think" this would put the height somewhere between 40-45 inches (inside)?
        I took your dimensions and did a quick drawing. 13-1/2" x 7-1/2" w/ 3" rear baffle. Area is 86.8 sq inches and at 45" height you end up with a 3600 cu in volume. This gives you a rough idea of the volume and shape. I can do another drawing once you have your final dimensions.

        One nice thing, printing the file so that the dimension lines are full size gives you a template to cut your top and bottom. You can also get internal braces from the shape as well.
        Attached Files
        If life were fair, Elvis would still be alive today and all the impersonators would be dead.
        ~ Johnny Carson

        Bungelow Ed's Photo Album http://techtalk.parts-express.com/album.php?u=8594

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        • #5
          Re: curved speaker questions?

          Thx, for your time and effort. Those numbers are roughly 7 liters more than what I came up with.

          Let me ask you a "what if" question. What if I am 7 liters off in volume and make the length of the port off accordingly, i.e., make a 59-60 liter volume enclosure, but a port length for a 50 liter cab? What kind of difference sonically would I hear?

          thx, again
          Frank--Still the one

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          • #6
            Re: curved speaker questions?

            No offense meant, but there is no reason you can't get the correct volume yourself. Even with no fancy program, you can lay the cross section out on graph paper and count the squares and parts thereof, and get very close to the area of the cross section.

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            • #7
              Re: curved speaker questions?

              No offense taken, djg.
              Frank--Still the one

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              • #8
                Re: curved speaker questions?

                That's how I would do it, as I have no knowledge of any CAD programs.

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                • #9
                  Re: curved speaker questions?

                  Originally posted by gimpy View Post
                  What with trying to figure out the extra volume of the curves, then subtracting the driver and braces volumes, I am thinking I might be off by 3-4 or 5 liters (maybe more or less)?
                  Do you know the inner and outer radius? or the length of the inner and outer curved segments ( arcs length )?
                  "Not a Speaker Designer - Not even on the Internet"
                  “Pride is your greatest enemy, humility is your greatest friend.”
                  "If the freedom of speech is taken away, then dumb and silent we may be led, like sheep to the slaughter."

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                  • #10
                    Re: curved speaker questions?

                    Originally posted by gimpy View Post
                    Thx, for your time and effort. Those numbers are roughly 7 liters more than what I came up with.

                    Let me ask you a "what if" question. What if I am 7 liters off in volume and make the length of the port off accordingly, i.e., make a 59-60 liter volume enclosure, but a port length for a 50 liter cab? What kind of difference sonically would I hear?

                    thx, again
                    Frank,

                    You will need to ask some of the more experienced forum member about the effect of volume on port tuning. Don't forget your internal bracing will take up some or all of the excess volume.

                    My approach is to keep baffle width, driver spacing, internal volume and port the same as original. Maintain the aforementioned parameters and use CAD to quickly visualize proportion, account for braces and determine volume.

                    As mentioned earlier, graph paper will work just fine. I just happen to like documenting my builds in CAD. Easier to share than paper. :D
                    If life were fair, Elvis would still be alive today and all the impersonators would be dead.
                    ~ Johnny Carson

                    Bungelow Ed's Photo Album http://techtalk.parts-express.com/album.php?u=8594

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                    • #11
                      Re: curved speaker questions?

                      Thx, for all the responses. The measurements I gave earlier are what I am going to shoot for and thanks to bungelow, I do have a value I can use. I will keep those design dimensions of the front baffle as designed by Evil.

                      Sorry, Sydney, I do not know the radius. I did read up a little bit on trying to determine the radius mathematically, but it got a little too involved/over my head for me. I will just try to "get close, it's good enough for guv'mint work):o.

                      What I need to decide now is whether to use hardboard or a bendable plywood for the sides. I will do some more looking (research? :rolleyes on the pros/cons of each.

                      As always, money could be the determining factor.:(

                      thx, again.
                      Frank--Still the one

                      Comment

                      • #12
                        Re: curved speaker questions?

                        Originally posted by gimpy View Post
                        ...Let me ask you a "what if" question. What if I am 7 liters off in volume and make the length of the port off accordingly, i.e., make a 59-60 liter volume enclosure, but a port length for a 50 liter cab?....
                        Originally posted by bungelow_ed View Post
                        ...My approach is to keep baffle width, driver spacing, internal volume and port the same as original. ...
                        Don't sweat the small stuff.

                        Box tuning is small stuff in the sense that you have lots of latitude. Any size box will tune to any frequency by changing the port. If your box were a little small, you get the same tune by making the port a little longer, like a fraction of an inch. My NatP's are ~65 liters tuned to 32Hz. I looked at the effect of port length and volume - 1 Hz was ~1/2" port length and 4 liters at 65L. I made my port a little long and never had to trim the length, but then I wanted a lot of extension.

                        While volume and port are in fact, open for alternate optimization, Ed's right that baffle width and driver locations are fixed. They are XO design inputs that the designer used, along with driver FR and impendence, to create a specific design - drivers, placement and XO circuit all go together.

                        Just make sure your "customer" has the space to put these 2-3' from walls, at least for critical listening. Bass will be bloated when placed against a wall unless you use the on-wall/in-wall XO.

                        Speaking of XO's, drivers do change over time, and the RS28's have lost ~1dB of sensitivity. In the XO, consider removing R3 to compensate, and at minimum, test with R3 shorted to see if it brings back the high end. My first NatP's (c. 2008) are flat, near field and on-axis, but my second pair may need this tweak.

                        Have fun,
                        Frank

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                        • #13
                          Re: curved speaker questions?

                          Thx, Frank. No more sweating the small stuff . My rear baffle width will prevent me from porting to the back, so I am considering porting out the front.

                          I don't really understand your last paragraph about the crossover and shorting it, etc, so will probably leave it alone as designed unless something comes on upstairs:rolleyes:.

                          thx,
                          Frank--Still the one

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                          • #14
                            Re: curved speaker questions?

                            Originally posted by gimpy View Post
                            Thx, Frank. No more sweating the small stuff . My rear baffle width will prevent me from porting to the back, so I am considering porting out the front.
                            Have you considered porting out the bottom? I drew up a cabinet using a full half ellipse which would have been ported out the bottom and stood on a short stand to get it off the counter. Just something to think about.....
                            If life were fair, Elvis would still be alive today and all the impersonators would be dead.
                            ~ Johnny Carson

                            Bungelow Ed's Photo Album http://techtalk.parts-express.com/album.php?u=8594

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                            • #15
                              Re: curved speaker questions?

                              I have thought about porting out the bottom, but was not sure how much space would be needed between the port and floor for best sound.
                              Frank--Still the one

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