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Choti HT - A Micro HT speaker using the RS100-4 and ND16FA

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  • Choti HT - A Micro HT speaker using the RS100-4 and ND16FA

    I completed these speakers a while ago but it took me for ever to put a finish on them and then even longer to finally put this thread together. I got the name from another forum member (tc). It is Hindi for "little."

    The intent of this project was to make some very small HT surround speakers for pretty cheap as my first original design project. I decided on the Dayton RS100-4 as the woofer. Modeling showed good low end performance in a failry small box and it had reasonable sensitivity. The Aura NS3 goes a little lower overall and can also be put in a pretty small box, but the RS100 has much lower distortion levels and better sensitivity. at only a roughly $25 difference pair, I chose th RS100. To keep costs down and fit the small form factor I went with the Dayton ND series tweeter. I looked at the ND16FA and ND20FA. The ND16FA was a little cheeper and actually had slightly better distortion performance in its useable range, according to the graphs on Zaph's website.

    After playing around with some different box tunings, I decided on going with a ported 1.7L box that is 6.5"H x 5"Wx 5.5"D made out of 1/2" MDF. It uses a 5" long by 1" diameter port that tunes the box to 75hz. The 1" port is a little smaller than optimal and will just peak above port velocity limits at around 70-75hz. I have these crossed at 80hz and since they are being used solely for surrounds, it is not really an issue for me. A 1-1/8" port will prevent exceeding limits under pretty much all the power the RS100 can take, but needs to be 6.5" long.

    Click image for larger version

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    The crossover is a second order electrical, approximately second order accoustic on the woofer and third order electrical and acoustic on the tweeter crossed around 3.8khz. Based on some advice from Wolf below, I have modified my original crossover a bit. The new schematic is provided below. This actually makes the phase line up even better between the woofer and tweeter, so overall I'd call that a win. The cap in parallel with the inductor on the woofer needs to be 0.15-0.2 uf. If you remove this, the woofer breakup will have a significant impact on the sound.

    Crossover Schematic:
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    Here is the modeled and measured response:
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    Measured response matches the modeled response fairly closely. I't's nice to know that the modeling works pretty well. I wouldn't trust the distortion measurements though. I seem to be having a weird issue with HolmImpulse where increasing the volume is giving me lower distortion numbers.

    When I built these, I used all NPE caps and they cost right at $100 excluding lumber and PVC pipe for the port. The price on the ND16FA went up a little though. A full set of 5 speakers can be built out of one Home Depot handy panel and one 2 ft long 1" PVC pipe.

    And here is a finished speaker:
    Click image for larger version

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    I was not entirely happy with the way the veneer turned out. It had some problems sticking and also split from drying out in a few places. When I put the poly, the spots that didn't stick well bubbled up and caused high high spots, which in turn led to the poly being sanded off on those. This lef some weird looking spots in the finish. Because of this, I didn't try to hard to get the face very smooth and glossy. I think I have learned a few things though, and the next pair should go a little smoother.

    Overall, I am very happy with the way these sound. The soundstage is huge and way more spacious than I expected from such a small speaker. They sound very detailed and airy. Obvouisly they are a little light on the bass by themselves, but I would imagine paired with a small sub, like one of the Tang Band 6.5 inchers, it would make for a great desktop speaker. The top octaves have a bit of a rise in them as seen in the measurements. That was measured on stands out in the middle of the room. They are designed to be placed close to the wall on wall mount stands. This should fill out the lower octaves a bit.

    UPDATE: I wanted to update with listening impressions on the fixed crossover. I didn't get around to finishing my second pair until a few weeks ago. I did a direct head-to-head comparision with the first crossover that I took down and the new crossover which is posted here. The new crossover sounds more coherent and has a smoother overall sound. The old crossover that isn't posted is a little more harsh and nasally sounding. I know I have mentioned in a couple posts in the main forum that there is was some harshness in the midrange when the level gets turned up. This was in reference to the orginal crossover. That no longer exists with the new crossover. So overall, thank Wolf for pointing out the original error and turning this into a better sounding design in the end.
    Last edited by Navy Guy; 02-05-2014, 03:24 PM. Reason: Crossover adjusted based on Wolf's feedback. Updated modeled response.
    -Kerry

  • #2
    Re: Choti HT - A Micro HT speaker using the RS100-4 and ND16FA

    Here are a few pictures for size comparison:

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    -Kerry

    Comment


    • #3
      Re: Choti HT - A Micro HT speaker using the RS100-4 and ND16FA

      Thanks for sharing. I'm considering giving these a shot since i need something small and against the wall.

      I almost ordered the components in the bill-of-materials image in your previous related thread. Luckily i did a sanity check and realized the final design changed a bit (unless i misread something?). Hoping to put together an order soon.

      I'm thinking of venting out the front since these will have to sit against the wall (there is a shelf only about 6 inches deep). They will not be raised (so no botom vent) and top vent might look funny since the top will be visible. Any advice welcome.


      Thanks,
      Joe

      Comment


      • #4
        Re: Choti HT - A Micro HT speaker using the RS100-4 and ND16FA

        Originally posted by lowpolyjoe View Post
        Thanks for sharing. I'm considering giving these a shot since i need something small and against the wall.

        I almost ordered the components in the bill-of-materials image in your previous related thread. Luckily i did a sanity check and realized the final design changed a bit (unless i misread something?). Hoping to put together an order soon.

        I'm thinking of venting out the front since these will have to sit against the wall (there is a shelf only about 6 inches deep). They will not be raised (so no botom vent) and top vent might look funny since the top will be visible. Any advice welcome.


        Thanks,
        Joe
        The bill of materials in the thread is what I bought. I paralleled one of the 5.6 and 2.2 mfd caps to get the 7.8 mfd value. I ordered extra values of resistors to use while voicing the speakers. You can just order the values on the crossover schematic unless you want to adjust the tweeter level.

        As for the port placement, if you put some type of feet like speaker spikes on the bottom to lift it up at least 1/2" you should be ok. You might want to flare the exit of the port and add 0.25-0.5 inches to the length if you do that. Otherwise, the front should be fine, there is just not much space to work with there.
        Last edited by Navy Guy; 10-03-2013, 10:35 AM. Reason: Updated based on Wolf's feedback
        -Kerry

        Comment


        • #5
          Re: Choti HT - A Micro HT speaker using the RS100-4 and ND16FA

          is that 8 ohm resistor across the woofer really needed?

          Comment


          • #6
            Re: Choti HT - A Micro HT speaker using the RS100-4 and ND16FA

            Originally posted by ontariomaximus View Post
            is that 8 ohm resistor across the woofer really needed?
            It softens the knee on the the woofer roll-off. Without the resistor, you end up at with a bit of a boost at around 2kz. The resistors are only $1.25 a piece, so I recommend trying them both and seeing which one you like.
            -Kerry

            Comment


            • #7
              Re: Choti HT - A Micro HT speaker using the RS100-4 and ND16FA

              Originally posted by Navy Guy View Post
              The bill of materials in the thread is what I bought. I paralleled one of the 5.6 and 2.2 mfd caps to get the 7.8 mfd value. I ordered extra values of resistors to use while voicing the speakers. You can just order the values on the crossover schematic unless you want to adjust the tweeter level.

              As for the port placement, if you put some type of feet like speaker spikes on the bottom to lift it up at least 1/2" you should be ok. You might want to flare the exit of the port and add 0.25-0.5 inches to the length if you do that. Otherwise, the front should be fine, there is just not much space to work with there.

              Ah... that makes sense. Thanks for the info.

              Comment


              • #8
                Re: Choti HT - A Micro HT speaker using the RS100-4 and ND16FA

                Originally posted by Navy Guy View Post
                It softens the knee on the the woofer roll-off. Without the resistor, you end up at with a bit of a boost at around 2kz. The resistors are only $1.25 a piece, so I recommend trying them both and seeing which one you like.
                That really isn't the best way to do that. That resistor across the woofer alone will see half the load power when they are the same impedance. It will shunt a lot of current, and likely get rather warm. If the resistor is in series with the cap on the woofer, then it is fine and would still do as you describe the resistor to do to the FR. If this was a 50 ohm resistor, then the effect would be minimal except around Fs.

                Bluntly, I would not advise or recommend the resistor's usage as diagrammed in the pdf above.

                Later,
                Wolf
                "Wolf, you shall now be known as "King of the Zip ties." -Pete00t
                "Wolf and speakers equivalent to Picasso and 'Blue'" -dantheman
                "He is a true ambassador for this forum and speaker DIY in general." -Ed Froste
                "We're all in this together, so keep your stick on the ice!" - Red Green aka Steve Smith

                *InDIYana event website*

                Photobucket pages:
                http://photobucket.com/Wolf-Speakers_and_more

                My blog/writeups/thoughts here at PE:
                http://techtalk.parts-express.com/blog.php?u=4102

                Comment


                • #9
                  Re: Choti HT - A Micro HT speaker using the RS100-4 and ND16FA

                  Originally posted by Wolf View Post
                  That really isn't the best way to do that. That resistor across the woofer alone will see half the load power when they are the same impedance. It will shunt a lot of current, and likely get rather warm. If the resistor is in series with the cap on the woofer, then it is fine and would still do as you describe the resistor to do to the FR. If this was a 50 ohm resistor, then the effect would be minimal except around Fs.

                  Bluntly, I would not advise or recommend the resistor's usage as diagrammed in the pdf above.

                  Later,
                  Wolf
                  Originally posted by Wolf View Post
                  That really isn't the best way to do that. That resistor across the woofer alone will see half the load power when they are the same impedance. It will shunt a lot of current, and likely get rather warm. If the resistor is in series with the cap on the woofer, then it is fine and would still do as you describe the resistor to do to the FR. If this was a 50 ohm resistor, then the effect would be minimal except around Fs.

                  Bluntly, I would not advise or recommend the resistor's usage as diagrammed in the pdf above.

                  Later,
                  Wolf
                  I'm surprised you didn't comment on this early in my other threads in the main forum.

                  I have updated the crossover schematic with a few changes. Putting the 8 Ohm resistor in series with the capacitor causes a less than desirable slope, so a few other minor changes had to be made. The resistor goes to 10 Ohm now and I am also saying that a 0.15-0.20 uF capacitor in parallel with the inductor is necessary. The overall response stays the same, but the phase actually lines up a little better now, so overall I would call it a better design.
                  -Kerry

                  Comment


                  • #10
                    Re: Choti HT - A Micro HT speaker using the RS100-4 and ND16FA

                    These are looking really tempting for in wall in the master bedroom.......
                    Builds - C-Killa - Speedsters - LithMTM - Talking Sticks - Pocket Rockets - Khanspires - Dayton RS Center - RS225/28A - Kairos - Adelphos - SEOS TD12X - Dayton 8 - Needles - 871S - eD6c - Overnight Sensations - Tritrix (ported) - Lineup F4 - Stentorians - The Cheapies - Tub Thumpers - Barbells - Tuba HT - Numerous subwoofers - probably missing a few...... :p

                    Comment


                    • #11
                      Re: Choti HT - A Micro HT speaker using the RS100-4 and ND16FA

                      Originally posted by joeybutts View Post
                      These are looking really tempting for in wall in the master bedroom.......
                      If you do go in-wall, I would play with the padding on the tweeter a bit with lower values of the resistor. The overall shape of the tweeter response on this isn't affected as much by changing the resistor on this one. It almost entirely adjusts level. I would probably try values in the 3-6 Ohm range.
                      -Kerry

                      Comment


                      • #12
                        Re: Choti HT - A Micro HT speaker using the RS100-4 and ND16FA

                        Thanks Kerry! Will keep in mind.
                        Builds - C-Killa - Speedsters - LithMTM - Talking Sticks - Pocket Rockets - Khanspires - Dayton RS Center - RS225/28A - Kairos - Adelphos - SEOS TD12X - Dayton 8 - Needles - 871S - eD6c - Overnight Sensations - Tritrix (ported) - Lineup F4 - Stentorians - The Cheapies - Tub Thumpers - Barbells - Tuba HT - Numerous subwoofers - probably missing a few...... :p

                        Comment


                        • #13
                          Re: Choti HT - A Micro HT speaker using the RS100-4 and ND16FA

                          Glad to hear Wolf speak up. I actually have a significant paranoia that one of my DIY builds will one day start a fire. I have yet to give away any of my builds, partially for this reason. Does this ever/often happen? I imagine it would take an incredibly poor design coupled with a ton of power?

                          I ordered the original BOM listing a day or two ago. I'll review what else I need and order up the extra stuff shortly. I've got a few small sheets of veneer that I was saving for a small project so I hit them with some softner this morning in preparation for the build I think they're crotch mahogany - very brittle and wavy. Hope they flatten out well.

                          Kerry - Did you say you used Zaph's measurements for the mid? I found it reviewed in his small-speaker shootout (http://zaphaudio.com/smalltest/) but didn't know where to look for specs. I played with some modeling in Win ISD yesterday using the Dayton specs sheet but was curious if there was much difference in the T/S values you used. I'm considering making the cabinet a little taller to add volume and maybe try to tune a little lower.

                          I was trying to figure if your dims were inner or outer dims. Inner dims give me 178in^3=2.9l. Outer dims with 1/2" MDF give me 99in^3=1.6l (using WinISD to convert to liters). If your net is ~1.7l I guess you must be giving inner dims and taking out about a liter for port and drivers?

                          Thanks a lot,
                          Joe

                          Comment


                          • #14
                            Re: Choti HT - A Micro HT speaker using the RS100-4 and ND16FA

                            Originally posted by Navy Guy View Post
                            I'm surprised you didn't comment on this early in my other threads in the main forum. .
                            That would be because there aren't any schematics posted in the previous thread. I only recall seeing just the one other thread.
                            Without a schematic, I can't see one thing to say anything.

                            That said- what I see hear is pretty nice.
                            Well done!
                            Wolf
                            "Wolf, you shall now be known as "King of the Zip ties." -Pete00t
                            "Wolf and speakers equivalent to Picasso and 'Blue'" -dantheman
                            "He is a true ambassador for this forum and speaker DIY in general." -Ed Froste
                            "We're all in this together, so keep your stick on the ice!" - Red Green aka Steve Smith

                            *InDIYana event website*

                            Photobucket pages:
                            http://photobucket.com/Wolf-Speakers_and_more

                            My blog/writeups/thoughts here at PE:
                            http://techtalk.parts-express.com/blog.php?u=4102

                            Comment


                            • #15
                              Re: Choti HT - A Micro HT speaker using the RS100-4 and ND16FA

                              Originally posted by lowpolyjoe View Post
                              Glad to hear Wolf speak up. I actually have a significant paranoia that one of my DIY builds will one day start a fire. I have yet to give away any of my builds, partially for this reason. Does this ever/often happen? I imagine it would take an incredibly poor design coupled with a ton of power?

                              I ordered the original BOM listing a day or two ago. I'll review what else I need and order up the extra stuff shortly. I've got a few small sheets of veneer that I was saving for a small project so I hit them with some softner this morning in preparation for the build I think they're crotch mahogany - very brittle and wavy. Hope they flatten out well.

                              Kerry - Did you say you used Zaph's measurements for the mid? I found it reviewed in his small-speaker shootout (http://zaphaudio.com/smalltest/) but didn't know where to look for specs. I played with some modeling in Win ISD yesterday using the Dayton specs sheet but was curious if there was much difference in the T/S values you used. I'm considering making the cabinet a little taller to add volume and maybe try to tune a little lower.

                              I was trying to figure if your dims were inner or outer dims. Inner dims give me 178in^3=2.9l. Outer dims with 1/2" MDF give me 99in^3=1.6l (using WinISD to convert to liters). If your net is ~1.7l I guess you must be giving inner dims and taking out about a liter for port and drivers?

                              Thanks a lot,
                              Joe
                              You have to go into the comparison application on his site. Just before you get to the part on that page where he has the pictures of the drivers with comments, there is a small box outlined in green in the center of the page. There is a link there that takes you to the actual data. He has bubbles at the top of the page to change between frq, imp, spectral decay, and T/S parameters. His specs were a little different than what are published on the PE website, but pretty close overall.

                              As for the box, I used and online speaker box calculator that allows you to input dimensions and port displacement from its size. I got 1.65L for the total volume before the port and driver. I just rounded up to 1.7L. The port volume displaces around 0.08L and with the driver I figured somewhere around ~1.5L for the leftover. I now typically use Jeff Bagby's Woofer Box and Circuit Designer for the box designs, so here is a screenshot from that modeled in a 1.5L box.

                              Click image for larger version

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                              On a side note, another option if you are willing to go taller is to to a sloted vent out the front under the woofer. If you do go taller, try to keep the driver positions the same from the top of the box.

                              On another side note, I feel kind of bad that you ordered parts and for my design already and it ended up having an issue. I have some extra 10 ohm resistors that I could send you if you PM me your address so you don't have to order any. Unfortunately I don't have any spare 0.15 or 0.2 uf capacitors.
                              Last edited by Navy Guy; 10-04-2013, 10:32 AM.
                              -Kerry

                              Comment

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