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"BASS-ND" Mini Subwoofer Project Writeup

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  • tomzarbo
    started a topic "BASS-ND" Mini Subwoofer Project Writeup

    "BASS-ND" Mini Subwoofer Project Writeup

    After I finished up my 'Micro-B' 2.1 amp project, I started thinking about which small subwoofers would be a good match for it. The 'Voxel' designed by Paul Carmody is probably the perfect choice I think, but I wondered what else would fit the bill... it had to be something equally small or smaller... and hopefully a little cheaper.

    That curiosity intersected with another curiosity that has been gnawing at me for an even longer time. For years I've been toying around with the idea of trying to turn a single ND-105-4 into a small subwoofer. I suspected it was too small for real subwoofer duties, but I was still curious. Each time I listen to Chris Roemer's Neo Nano's, I marvel at the bass they are able to put out for their size... If you've heard them, then you know what I mean. So eventually, my curiosity got the best of me. I modeled one in a squared-off tower design I'm calling the "Bass-ND".



    I was shooting for the ability to reproduce around 90 db at 35 Hz as a target... I listen to jazz a lot -- more modern stuff than traditional stuff -- and there is a good amount of low stuff in most of what I listen to, so I went with a longer vent to gain some additional lower bass at the expense of more volume in the 50-70 Hz region. That tradeoff seemed to suit my goals.

    I know the cone excursion is well past X-max at 35 Hz, but I think if you can live with some distortion down there, the cone will survive just fine when pushed within reason. I believe Chris allowed for a generous amount of excursion when modeling his Neo Nano's in part because of its huge X-mech stat, so I felt excursion was going to be outside of the 'damage' region.

    The box is 7" by 7" by 15.5" tall with a long 1.5" by 12" port. I made the sides and top with mitered corners to make it nice and strong and hopefully keep the veneer nice and smooth, I hate it when seams show through the veneer.
    Here are a few shots of the construction of the box:




    I was running out of 1/2" MDF so I had to glue up some scraps for two panels to get enough to make this box with. There are no braces by the way, it doesn't seem like it needs it to me, the box doesn't vibrate at all believe it or not. I was planning on throwing a few dowels in after I fired it up, but it wasn't needed.

    Here are the parts I used to build it: The ND-105, 4 ohm woofer, a binding post terminal, and a few large stainless steel drawer pulls. I thread-locked the mounting screws for the drawer pulls and then cut the heads off. I then epoxied the threaded portion in pre-drilled holes in the bottom of the box. I also lightly stuffed the box with some polyfill, I guess just out of habit.



    I was going for a minimalistic avant guard type of look for this. I chose Mahogany veneer which is kind of boring, but still has enough grain to be somewhat interesting. I couldn't put anything too fancy on it, I thought it would clash with the simple design/lines. It doesn't show in the pics, but it's very glossy, which adds a bit of pizzazz to the piece.



    I made a mistake originally; I always seem to make at least one! I placed the binding post on the bottom without noticing that it would be impossible to plug wires into them for lack of ground clearance. So some dowels were glued in those holes and it was moved to the rear of the box.



    The top and sides received 7 coats of rub-on gloss poly and the bottom was painted with Rustoleum 'painters touch' flat black paint rolled on. That stuff is awesome for a quick cover-up, it covers even MDF end grain, and dries in minutes.
    Here it is in its new home by my chest of drawers in our bedroom.



    It is now the acting subwoofer for my "Micro-B" 2.1 plate amplifier powered set of Jeff Bagby's Quark speakers which set on top of the chest of drawers.
    Here's a better shot:



    So, is it a real subwoofer? Honest opinion: it does a fairly decent job as a small subwoofer if you keep in mind that it's just a 4" driver in there and so it is limited in output down low. It has an F3 of 50.6 Hz, F6 of 38.5 Hz, and the F10 is 30.8 Hz but the slope is kind of shallow until around 30 Hz, then it dives steeply.

    The "Micro-B" 2.1 amp has a knob to control the subwoofer level, so I could tell as I turned down the subwoofer volume that it was really contributing to the overall 'depth' of the music. It didn't get as loud, or as low as the 'Voxel' subwoofer obviously, but it does seem to be efficient enough to keep up with the 'Quarks' volume wise to be a good match for them with this amp setup. Placed next to a wall, the bass filled in nicely in our large bedroom... in a corner with a bit more input power (I was using an old Kindle Fire as a source) I bet it would surprise.

    I suspect that it would probably perform pretty well with the Dayton SA25 25 watt plate amp as well; I like that little bugger also. At 6-5/16" square it would just fit in the cabinet. That amp is kind of pricey though for the time being when not on sale, which kind of negates the 'budget' feel of this project. (one of the factors in designing this was that the ND 105 is only $27 bucks as opposed to the Neo W5, at $59... with the Ferrite version of the W5 running about $40 a pop.)

    That's pretty much it for this project. I was curious like I said and wanted to give the little ND-105 a go just to see how it would do. It was fun to complete a quick project, as well as being a good thought exercise for a few weeks. I played with lots of box sizes, port lengths and various tunings for a long time before settling on what I had. A bigger box would have been better, but after consideration, I went as large as I was willing to go size-wise so that was kind of set in stone near the end...also, the tall shape allowed for an easy time fitting the long vent.

    Well, It was fun to finally 'scratch that itch' so to speak. Thanks for looking.

    TomZ
    Last edited by tomzarbo; 08-15-2015, 06:37 AM.

  • bsl100
    replied
    So, I finished the build with the combo of the ND90-8 and ND20FA-6 doing 2.0 duties and the ND105-8 doing 0.1 sub duties. The ND90-8 are each in a sealed 1 litre enclosure with a 2.0mH coil parallel with a 12 ohm resistor connected in series with a 1st order HPF 150uF cap. The ND20FA-6 has a 1st order HPF 3uF poly cap (9KHz) and is padded down by a 6db L-pad. The presentation is more airy because of the lesser 6db L-Pad instead of a higher 9db L-Pad. The ND105-8 is in a 10 litre ported enclosure (before deducting for speaker, port and crossover etc. volume) tuned to 53Hz with a 2" dia port 7" long with a 40Hz HPF 500uF cap in series. The F3 is 45Hz according to WinISD. The amp crossover (active LPF) is set at around 120Hz. The box dimensions are 10.25" x 11.5" x 10.25" (WxHxD) using 3/4" MDF. I didn't go ahead with the earlier plan for ported enclosures for the ND90-8 because I was advised against doing it to avoid excessive boominess.

    Listening impressions - Clean sound and a very musical presentation. The ND90-8 and ND20FA-6 combine to put out some detailed, airy, non-fatiguing sound.The ND-108 digs deep and puts out clean bass. Though not subwoofer deep, it can still move some air and if you are about 5-6 feet away, you can feel the sound pressure. For smaller spaces of around 300 sq.ft. it would be a good choice for a compact system and would beat the crap out of commercially available bluetooth speakers. I don't do any measurements (other than WinISD), so for the crossovers, everything is done with the help of *online calculators and by listening and tweaking.

    I think if someone did a version of the Nano Neos by merging the two speakers together with an in-built amp for a compact 2.0 system, you would get even better output. The BSC might need to be re-worked though from the originals. I think this has already been tried out with the Overnight Sensations in the Madeleine speaker build.

    Leave a comment:


  • tomzarbo
    replied
    Originally posted by bsl100 View Post
    Tom.... thanks for your reply on the Nano Neo thread and for directing me here.

    As I have mentioned there, I am working on a 2.1 boom box project based on a TPA3118D2 2.1 plate amp with the ND90-8 & ND20FA-6 doing 2.0 duties in 4 litre ported enclosure for each channel and the ND105-8 doing sub duties in a 9 litre ported enclosure. Its roughly a 12" cube. The amp has no HPF for the 2.0 channels and only an active LPF for the sub channel from 30Hz-150Hz.

    I see that you have tuned the ND105 low for doing sub duties. I plan to tune the port to around 53Hz with a 48mm dia flared port, 175mm length and get an F3 of around 46Hz and F10 of 40Hz with a 40Hz 6db HPF (500uF cap). This creates a nice hump from 50Hz-90Hz. Hopefully, the HPF cap will control the excursion of the ND105 and the summed response of the Sprite like bass output from the ND90 pair and the ND105 will create some good low end. It might be quite hot from 45Hz-150Hz because of the summed response.

    Have never tried anything like this. But, I have the parts and plan to give it a go. If for some reason the bass/mid-bass sounds off, then I'll just have to work on another box with the ND90 going in a sealed 1 litre enclosure with a HPF using a 150uF cap.
    It sounds like a fun experiment to try, using the ND 90's and ND105's to both bolster the bass a bit. It's a small enough box to maybe work well.* We're in the range with these box sizes to know that we're giving up a little bass because things are just so small. It's fun to experiment with stuff, though and see what comes of it. Your higher tuning should allow for quite a bit more output, and that 50-90 Hz hump will provide the appearance of a lot more bass.
    I'd love to know how it comes out!
    TomZ

    Leave a comment:


  • bsl100
    replied
    Tom.... thanks for your reply on the Nano Neo thread and for directing me here.

    As I have mentioned there, I am working on a 2.1 boom box project based on a TPA3118D2 2.1 plate amp with the ND90-8 & ND20FA-6 doing 2.0 duties in 4 litre ported enclosure for each channel and the ND105-8 doing sub duties in a 9 litre ported enclosure. Its roughly a 12" cube. The amp has no HPF for the 2.0 channels and only an active LPF for the sub channel from 30Hz-150Hz.

    I see that you have tuned the ND105 low for doing sub duties. I plan to tune the port to around 53Hz with a 48mm dia flared port, 175mm length and get an F3 of around 46Hz and F10 of 40Hz with a 40Hz 6db HPF (500uF cap). This creates a nice hump from 50Hz-90Hz. Hopefully, the HPF cap will control the excursion of the ND105 and the summed response of the Sprite like bass output from the ND90 pair and the ND105 will create some good low end. It might be quite hot from 45Hz-150Hz because of the summed response.

    Have never tried anything like this. But, I have the parts and plan to give it a go. If for some reason the bass/mid-bass sounds off, then I'll just have to work on another box with the ND90 going in a sealed 1 litre enclosure with a HPF using a 150uF cap.

    Leave a comment:


  • greywarden
    replied
    Re: "BASS-ND" Mini Subwoofer Project Writeup

    You can use REW, that's essentially what it was made for, right?

    Leave a comment:


  • Melby Audio
    replied
    Re: "BASS-ND" Mini Subwoofer Project Writeup

    By the look of your measurement, it appears to be ignoring the gate. Some of the FR options in ARTA ignore the gate. Can't remember which ones off the top of my head. If your measurements are correct, I'd say that qualifies as a sub in your room. You are certainly benefiting from room gain, but that's a good thing for a small woofer like that.

    Leave a comment:


  • tomzarbo
    replied
    Re: "BASS-ND" Mini Subwoofer Project Writeup

    Originally posted by Chris Roemer View Post
    Typically a 3.0ms gate's results are only valid down to about 300Hz. To get good data down low, you should really gate to about 30.0ms (or measure no gate at all - but I'm not sure if/how to do that in ARTA). At that long of a gate, you get lots of "late arrivals" - which is why we measure "nearfield" (about 1/4" off the dustcap) where all the extraneous garbage gets suppressed just by nature of its much farther distance from the source.
    Thanks, Chris.
    I'll try to take better measurements tonight or this weekend. I'm curious as to what it can actually do.
    Even though it's a down firing setup. I'll lay it down on it's side and measure as close to the cone as I'm able. Doing that won't demo the benefit of corner loading, but that's pretty much a known thing anyway.

    So do the above measurements yield any useful information or is there just too much "room" in the measurements?

    Thanks for the info,
    TomZ

    Leave a comment:


  • Chris Roemer
    replied
    Re: "BASS-ND" Mini Subwoofer Project Writeup

    Typically a 3.0ms gate's results are only valid down to about 300Hz. To get good data down low, you should really gate to about 30.0ms (or measure no gate at all - but I'm not sure if/how to do that in ARTA). At that long of a gate, you get lots of "late arrivals" - which is why we measure "nearfield" (about 1/4" off the dustcap) where all the extraneous garbage gets suppressed just by nature of its much farther distance from the source.

    Leave a comment:


  • tomzarbo
    replied
    Re: "BASS-ND" Mini Subwoofer Project Writeup

    I finally got a chance to run a few sweeps with this. I had to do this quickly in my hobby room which doesn't have an open corner, but for the corner graphs, it was within a few feet near a kitchen cabinet which was in the corner.

    Here is a short sweep with the cabinet standing upright near the middle of the room with 3 ms. gating and 1/12 octave smoothing. The mic was about 2 feet from the cabinet aiming at the bottom of the cabinet...




    Below is a near-corner sweep with the cabinet standing upright 10 inches from the closest thing I have to a corner in this room, the above mentioned kitchen cabinet, again with 3 ms. gating and 1/12 oct. smoothing. The mic was about 2 feet from the cabinet aiming at the bottom of the cabinet.



    The woofer was capable of a fair amount of additional output here, but those sweeps kind of drive me crazy in my ears so I kept it lower.

    So the graphs show what I was hearing... a much better result in the corner. In our bedroom where the Bass ND lives, corner loading adds quite a bit to the lower range and fills things out much more nicely to my ears. But, that means that I have to get the wire over the doorway, so I've ended up leaving it by my chest of drawers and it still does okay there. If I could have measured this in a real corner about 5-6 inches from each wall, I believe it would have filled in even a bit nicer on the low end. This setup sounds to me more like a mid-sized woofer, and less like an amplified subwoofer when it's playing music...but that's partially due to the higher frequency band it receives from my Micro-B 2.1 plate amp project.

    I powered the sub (not for these measurements) with one of Parts Express's 25 watt plate amps and it did a bit better... but alas, it runs out of steam just when things are starting to sound good... what a tease! With PE's SA25, 25 watt plate amp it sounds like a real subwoofer, and at normal background listening levels, it performs well. Push it though, and it sounds like it's unhappy excursing that far... "whumpa whumpa" noises are present.

    So after messing with it do I think I can call it a real subwoofer? Nope. Is it a good bass module? Yep. Like I said, it sounds like a medium sized woofer; and at moderate volumes, it does fine. Turn it up much past what I would consider 'background level' and it starts to complain.

    But... I like it for it's intended use. As a subwoofer for the Micro-B subwoofer unit, it does really well and matched up with the output of the amp, it stays within it's "safe" range as far as output. Thankfully, although the Micro-B amp lets more upper bass through than I would like, at least this 4" woofer handles it reasonably well, nothing ugly coming out of it to ruin the overall sound... plus it's firing at the carpet which tones that stuff down as well.

    Also, this driver is $27 dollars and if you pair it with my Micro-B 2.1 plate amp, you don't need to worry about additional amplification. The pairing of the Micro-B 2.1 plate amp and this Bass ND subwoofer really makes a good setup for not a lot of dollars. Make it with some scrap wood and add a binding post and a few kitchen cabinet pulls as feet (or bits of wood or whatever) and you have a very cheap bass module.

    So, there you have it, warts and all!

    Sorry it took so long to take a few measurements. September starts a new school year and I have a newly constructed classroom we're trying to outfit, and I haven't had much free time to geek out lately.

    TomZ

    Leave a comment:


  • donradick
    replied
    Re: "BASS-ND" Mini Subwoofer Project Writeup

    I thought I remembered that you liked Minwax wipe on poly - sure is easy to get a good finish.
    I, too, have had many mis-steps with finishing, and like to keep it foolproof and repeatable.

    Oh, my last couple of wipe-on finishes were helped by a white Scotchbrite before the final coat.

    Mitered corners "should" be my next challenge. I just got a biscuit joiner so that should make them easier to assemble.
    I can see some tells through the veneer on my builds - nicer when you don't!

    Love, love, love that mahogany, I'm really going to have to lay in a supply.

    Regards,
    Last edited by donradick; 08-30-2015, 06:34 PM. Reason: spellling

    Leave a comment:


  • tomzarbo
    replied
    Re: "BASS-ND" Mini Subwoofer Project Writeup

    Originally posted by donradick View Post
    Tom, sorry late to the thread.

    As usual, a inventive new design and artistic completion.

    Funny, I've been thinking about mahogany a lot lately.
    Love the color and texture of it on this build!

    OK, questions:
    How did you attach the veneer? Iron on?
    What's the finish? I've got my fav wipe on poiy, always interested in new products.

    Don
    Thanks, Don.

    I used my old standard Iron-on method. I love it, it's therapeutic, and quick.

    I think I got the veneer from PE actually if I'm not mistaken. It may have been Woodcraft though. Packaging was discarded long ago. I have a few black trash bags full of scraps of veneer (so the sunlight doesn't fade it) and these scraps were in there.

    This cabinet is nice and dead, even though it's constructed of 1/2" MDF. I really think the mitered corners contribute to the stiffness somehow, though I can't prove it. I do cut the miters at something like 44 degrees so the corners are tight, maybe the clamping created some tension on the panels, I'm not sure. But it doesn't need any bracing.

    The finish is just 5-6 coats of gloss Minwax rub-on poly with a light sanding in between with 320 grit. Now that I finally figured out how to get a nice finish with rub-on poly, I'm not inclined to try anything else... I've had troubles with finish for years, finally got it dialed in!

    I need to put the PE 25 watt plate amp on it to see what it can do. I've been busy getting ready for the start of school in a day or two, so I've been neglecting my speaker duties.

    TomZ

    Leave a comment:


  • donradick
    replied
    Re: "BASS-ND" Mini Subwoofer Project Writeup

    Tom, sorry late to the thread.

    As usual, a inventive new design and artistic completion.

    Funny, I've been thinking about mahogany a lot lately.
    Love the color and texture of it on this build!

    OK, questions:
    How did you attach the veneer? Iron on?
    What's the finish? I've got my fav wipe on poiy, always interested in new products.

    Don

    Leave a comment:


  • tomzarbo
    replied
    Re: "BASS-ND" Mini Subwoofer Project Writeup

    Originally posted by fastbike1 View Post
    Geez Tom, you're on a serious roll. I would never have thought of handles / towel bars / etc as "feet", but When I saw yours, I literally said "brilliant", why didn't I think of that.

    Kudos.
    I thought the exact same thing when I saw someone else do it before me!

    At least I pick good ideas to steal.

    TomZ

    Leave a comment:


  • fastbike1
    replied
    Re: "BASS-ND" Mini Subwoofer Project Writeup

    Geez Tom, you're on a serious roll. I would never have thought of handles / towel bars / etc as "feet", but When I saw yours, I literally said "brilliant", why didn't I think of that.

    Kudos.

    Leave a comment:


  • greywarden
    replied
    Re: "BASS-ND" Mini Subwoofer Project Writeup

    Hell yeah, I'll be watching for the update

    Leave a comment:

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