Announcement

Collapse
No announcement yet.

The Boxers - a subwoofer and waveguide loaded tweeter based 2-way

Collapse
X
  • Filter
  • Time
  • Show
Clear All
new posts

  • The Boxers - a subwoofer and waveguide loaded tweeter based 2-way

    The Boxers are a 2-way stand-mount/bookshelf design utilizing a subwoofer driver with a very clean midrange and a waveguide-loaded soft dome tweeter. They debuted at InDIYana 2015 and will be entered into the MWAF Dayton category this summer. As I just registered for the competition, I thought I'd just copy and paste the info here in the project gallery. Thus the format you see below.

    DESIGN GOAL

    My goal with this speaker was to create what I would consider a true full-range speaker in a package that can actually fit on a bookshelf. Most bookshelf or stand-mount speakers utilize a 6.5" or smaller driver, and while some of them can dig pretty deep, they all end up being output limited pretty quickly. I wanted something that was smallish, could dig deep and could handle just about anything I could throw at it.

    DRIVER SELECTION

    There are many subwoofer drivers that can get low in a small enclosure, but most of them would require a midrange driver to take over by about 500Hz. This would require a separate chamber, taking away valuable air space in this compact design. The Dayton RSS210HO-4 is clean up past 1000Hz, allowing me to cross to a robust tweeter like the Dayton RS28F-4. The waveguide loading allows a low crossover point while still keeping up with the woofer in the output department. The particular waveguide used is a 3d printed model that is 8.5" in diameter and 2" deep with a 1.625" opening that is a perfect mate for the Dayton RS28 series of tweeters.

    ENCLOSURE DESIGN

    The enclosure is a simple sealed enclosure that is just large enough to hold the woofer and the waveguide, but just small enough to fit on a standard bookshelf laying down. The dimensions are 20" H x 11" W x 7.5" D with 3/4" thick walls for a gross internal volume of just over 17 L. The limited space inside was lined with fiberglass and filled loosely with polyfill. This gives the system a measured Qtc of 0.68 for a nice shallow rolloff (F3 = 45Hz and F10 = 30Hz).

    ENCLOSURE ASSEMBLY

    I used pre-finished 1 x 8 poplar from the big box store, which is actually 3/4" x 7.25". I made the top, bottom and sides from this material and joined them with mitered corners. I then glued 3/4" x 3/4" MDF strips just inside the front and rear perimeters of the poplar carcass to give the baffle and back panel a shelf to be adhered to. The front baffle and the back panel are both painted 3/4" MDF with a slight bevel around the perimeter for visual appeal and set into the poplar frame on the MDF rails so that the panel protrudes from the poplar about 1/8". Both panels are braced near the center using triangular gussets. Poplar doesn't take stain very well, so I just coated it with a few coats of shellac which really brought out the grain and colors of the wood.

    CROSSOVER DESIGN

    In order to get rid of some of the nasty upper frequency artifacts the subwoofer driver suffers from, it needed a 4th order electrical circuit with a tank on the leading inductor. This is pretty aggressive attenuation, but it puts the garbage about 40-50dB below the tweeter level and created a nice smooth rolloff near 1000Hz. The tweeter crossover was a breeze due to the waveguide loading and the flat impedance due to the massive attenuation necessary to match up with the woofer's low sensitivity. A simple 2nd order electrical circuit with some attenuation was all that was necessary to bring the frequency response and phase in line. Overall, the xo frequency ended up being about 1200Hz with 4Ω or higher impedance across its frequency response (except as noted below). This crossover point is low enough to mitigate the potential problems caused by a largish C-T-C distance of just under 9".

    I did add a couple other features to this crossover beyond what is described above:

    1) The waveguide generates an 8-9 dB suckout at about 13kHZ, but only on axis (15 off axis it smoothes right out). Some listening tests led me to add a small capacitor across the series attenuation resistor in the tweeter circuit to raise the top octave a bit. This brings the system impedance down to 2 ohms above 20kHz, which should be fine for most amp/content combinations. I felt it a worthwhile compromise.

    2) Since this speaker can legitimately be put on a bookshelf, I decided to add a switch to raise the tweeter level by 3 or 6 dB to counteract excessive bass reinforcement from this sub-optimal placement. The switch is a DPDT center-off type where the three positions engage or disengage series and shunt attenuation resistor combinations to produce the different levels. It should be noted that this crossover was designed for stand mounting and the switch just makes some other placement options more attractive.

    CONCLUSION

    These speakers offer a unique set of compromises that present a unique listening experience. I don't usually hear a presentation this large from speakers so small, but I think the waveguide dispersion pattern, the 8" midrange and the ability to play deep bass very loud offer such benefits. You don't get anything for free, so these speakers are quite inefficient and need a lot of power to get moving. The good news is, with a legitimate subwoofer as the bottom of this 2-way, they can handle a lot more power than other speakers this size.

    Dan
    Attached Files
    Last edited by DanP; 05-19-2015, 04:10 PM.

  • DanP
    replied
    Re: The Boxers - a subwoofer and waveguide loaded tweeter based 2-way

    Click image for larger version

Name:	2015-07-04 13.59.23.jpg
Views:	1
Size:	120.9 KB
ID:	1167276Click image for larger version

Name:	2015-07-04 14.01.17.jpg
Views:	1
Size:	853.4 KB
ID:	1167277

    Wolf picked up on a resonance on these at InDIYana, so I printed some ribs and glued them on to the back of the waveguides and put some Dynamat on the areas between the ribs. Hopefully this takes care of it - initial listening impressions suggest it has. All ready for MWAF!

    Dan

    Leave a comment:


  • TN Allen
    replied
    Re: The Boxers - a subwoofer and waveguide loaded tweeter based 2-way

    DanP,

    Thank you for posting the cross section. tna

    Leave a comment:


  • Pete Schumacher
    replied
    Re: The Boxers - a subwoofer and waveguide loaded tweeter based 2-way

    Nice job Dan. Great to see you finally implement the guide you sent me for experimentation long ago.

    It's interesting to me that you see that dip on-axis. I didn't see it in the guide you sent me or the subsequent iterations in MDF.

    Leave a comment:


  • JasonP
    replied
    Re: The Boxers - a subwoofer and waveguide loaded tweeter based 2-way

    This was a stunning looking and great sounding build at InDIY, I regret if I didn't tell you so at the event. IIRC you spent much of the time front row and center so I can't recall ever actually talking to you. Good job!

    Leave a comment:


  • Pallas
    replied
    Re: The Boxers - a subwoofer and waveguide loaded tweeter based 2-way

    This idea is really cool, and it looks well implemented too.

    Still...I can't help but think this kind of speaker is the ideal case to ditch passive networks (except for the 1st pole of the tweeter's network, which I prefer to keep passive to provide a measure of protection for the tweeter) and use something like a miniDSP PWR-ICE250 plate amp.

    Leave a comment:


  • DanP
    replied
    Re: The Boxers - a subwoofer and waveguide loaded tweeter based 2-way

    I've attached the off axis response of the Boxers as well as the measured distortion. As you can see, the dip is greatly minimized already at 15 degrees off axis and then the response actually begins to rise above 10kHz further off axis as the dip disappears and the crossover correction starts to show up in its place. As I said above, I added a small cap across the series attenuating resistor to compensate for the dip a little. This was purely a voicing choice that I felt sounded better after some listening sessions.

    For some reason, the graph got chopped up pretty bad when uploading, but the graph lines are 2dB apart.

    Dan
    Attached Files

    Leave a comment:


  • scottsehlin
    replied
    Re: The Boxers - a subwoofer and waveguide loaded tweeter based 2-way

    Cool design Dan! I always like to see outside-the-box thinking in order to have your cake and eat it too. :applause:

    Leave a comment:


  • philthien
    replied
    Re: The Boxers - a subwoofer and waveguide loaded tweeter based 2-way

    Originally posted by Wolf View Post
    Their only real issue is the low sensitivity. High 70's....
    He's addressing the resonance I picked out at InDIYana, likely the waveguide.

    Later,
    Wolf
    I remember when I was a kid, visiting a stereo shop I had frequented. One of the salespeople was a pretty nice guy, and he did an A/B comparison in the demo room once between a pair of bookshelf speakers, and these giant Pioneer speakers. The giant Pioneers were actually hugely inefficient, so when he switched to them, the sound level was cut maybe 10 db instantly. I thought there was something wrong with them but he explained they just needed gobs of power.

    Their patch panel allowed for level matching but he was just trying to teach me something.

    That guy (his name was/is Phil Johnson) was the guy that got me hooked on building speakers. The shop was Sound Stage (recently closed). He went to work for Avid a year or two after that demo, this is the way back machine. Super nice guy.

    Leave a comment:


  • Wolf
    replied
    Re: The Boxers - a subwoofer and waveguide loaded tweeter based 2-way

    Originally posted by philthien View Post
    Those look amazing in every single way.

    So to those that heard them, was the 15k valley noticeable? I can't imagine I'd be able to hear that, it is so high.
    Their only real issue is the low sensitivity. High 70's....
    He's addressing the resonance I picked out at InDIYana, likely the waveguide.

    Later,
    Wolf

    Leave a comment:


  • philthien
    replied
    Re: The Boxers - a subwoofer and waveguide loaded tweeter based 2-way

    Those look amazing in every single way.

    So to those that heard them, was the 15k valley noticeable? I can't imagine I'd be able to hear that, it is so high.

    Leave a comment:


  • henry218
    replied
    Re: The Boxers - a subwoofer and waveguide loaded tweeter based 2-way

    Wow, this is really impressive! I liked the concept [emoji4][emoji106][emoji106]

    Leave a comment:


  • Speed Racer
    replied
    Re: The Boxers - a subwoofer and waveguide loaded tweeter based 2-way

    Very nice Dan! Good Luck!

    They looked and sounded good at InDIYana.

    Leave a comment:


  • DanP
    replied
    Re: The Boxers - a subwoofer and waveguide loaded tweeter based 2-way

    Originally posted by [email protected] View Post
    I would be tempted to spray the backs of the wg with bedliner or brush on Duratex.
    Would this do more than just stiffen and/or add mass? I'm hoping the Dynamat will convert some of the kinetic energy of the WG motion into heat to effectively damp the resonance.

    TN - I've attached a picture of the WG cross-section. It is effectively a 4" radius that transitions smoothly to a 57 degree throat entrance.

    Dan
    Attached Files

    Leave a comment:


  • TN Allen
    replied
    Re: The Boxers - a subwoofer and waveguide loaded tweeter based 2-way

    I'm curious about the WG cross section, is this something you can provide? Thanks

    Leave a comment:

Working...
X