Down Firing Voxel with SA70 Amp

[KEtheredge87]

Hi Everyone,

While searching for a set of designs I could build to replace an old 5.1 home theater in a box, I was directed to Scott Sehlin's Helium design as a satellite speaker and Paul Carmody's Voxel subwoofer designs. A big THANK YOU to both of you for sharing your designs with us!

With respect to these gentlemen, here are their original design threads:

• Scott's Heliums: http://techtalk.parts-express.com/fo...itor#post64062
• Paul's Voxel: http://techtalk.parts-express.com/fo...-sub#post58008

The more I dug into the Voxel design, I realized I was modifying it enough to warrant a build thread, so here it is. My two design goals for this modified Voxel subwoofer are pretty simple. First, I wanted to change the driver arrangement to allow a down firing subwoofer since this will live near a high traffic corner of the living room (no feet accidentally kicking the driver!) Second, I wanted to incorporate the Dayton Audio SA70 plate amplifier into the rear of the cabinet for simplicity of powering the sub, as well as aesthetics. I'll be using the same Tang Band W5-1138SMF subwoofer that Paul used, and doing my best to keep the same ported chamber volume and tuning. We'll see how this turns out!

Build Photos:
I'm spending more time working and building rather than documenting, so if anyone wants to follow along, here's the shared google photos album for this build

https://goo.gl/photos/uQrhuf5t5ysGm1c59

[KEtheredge87]

Hello Everyone!

Here are the drawings I generated in the design process. Full drawings for each piece are in the attached PDF.

Final edits to this design were posted on Jan 28th 2017.

[KEtheredge87]

Driver Measurements, Performance Modeling, and Port Tuning

At this point, I need to extend a special thanks to forum member Kevin K! Kevin encouraged me to pick up a DATS V2 system in support of this project to make sure I was achieving the same design goals that Paul Carmody set out in his original design. I've learned a lot through a lengthy discussion with Kevin, and I am really appreciative of his support.

Driver Measurements

Initial measurements of the TangBand W5-1138SMF subwoofer obtained from DATS V2 after a break-in (30 minutes of reference level sine wave at 50 Hz amplified with Dayton Audio SA70 amplifier, gain turned up until just before audible distortion) Note: The values reported by DATS would change a little bit from run to run, which is why the text output and the graph don't match 100%. The values are still fairly close to the manufacturer's reported specs.

This data was exported from DATS the Dayton Audio Test System
Manufacturer: Tang Band
Model: W5-1138SMF
Piston Diameter = 104.1 mm
f(s)= 46.43 Hz
R(e)= 3.501 Ohms
Z(max)= 24.21 Ohms
Q(ms)= 3.95
Q(es)= 0.6679
Q(ts)= 0.5713
V(as)= 4.661 liters (0.1646 cubic feet)
L(e)= 1.33 mH
n(0)= 0.06661 %
SPL= 80.33 1W/1m
M(ms)= 25.69 grams
C(ms)= 0.457 mm/N
BL= 6.268
K(r)= 0.0531
X(r)= 0.543
K(i)= 0.01999
X(i)= 0.6686



Performance Modeling

Kevin and I did a back to back comparison of BassBox Pro 6 and the latest version of WinISD to model the subwoofer enclosure and see where our port length needed to be. The target tuning frequency was in the low 40s (we went for Vb = 41 hz), which allowed us to have the same F3 of 35 hz on the system. Ultimately there were some differences between BassBox and WinISD, and we had to trust the data from DATS when we measured an impedance sweep.

Final Port Tuning

Using DATS V2, I measured an impedance sweep after constructing the port to the first length that was suggested by the programs. I ended up with a Vb of ~38 Hz, which was a bit low of my initial target of 41. After discussing with Kevin, I removed the second straight piece I originally had in my port and remeasuring, which bumped my Vb up to 40.37 Hz. At this point we called it good. Unfortunately this left me with some unpleasant chuffing noises during the testing phase. We redesigned the port length and flares to what is documented today and achieved better results... not 100% perfect, but certainly good enough for my use.

Using BassBox, I made one final sim of this design as it was finished out. The Vb reads higher than my design, but the net Vb is correct based on subtracting internal driver volume, port volume, and Dayton SA70 volume.

[KEtheredge87]

The Final Product!

[craigk]

Very nice work, as always.

[KEtheredge87]

Thanks Craig! This little sub has been in service for 3 years now and still going strong!

[Kevin K.]

Is this on hold until you finish the Heliums or do you need some help??

[KEtheredge87]

Is this on hold until you finish the Heliums or do you need some help??

Hey Kevin, this isn't on hold. I actually plan to cut all the materials to build the Heliums and this Voxel at the same time. I've been trying to build a cross cut sled for my table saw for the past few days, but I can't get the accuracy where it ought to be. I'm beginning to think I should have used MDF instead of 3/4 ply since I keep finding little places where the surface isn't as flat as I think it is!

I'm pretty anxious to get cutting on the speaker cabinets, just gotta get all the tools lined up. I hate it when a project takes a lot longer to set up than expected.

[Kevin K.]

Was just curious. Good luck getting the sled worked out. Looking forward to your build.

[Kevin K.]

Just opened your edit to the first post that includes all of the build pics so far. Looks great! I really like the shape of the sub enclosure and it looks really good with all of the round over treatments. Have you decided on a color? Yea, most guys go with traditional black but you mentioned these were for your Mom. I've seen some pretty good looking cabinets done in white. Food for thought. Keep up the good work!

[KEtheredge87]

Hi Everyone,

Just throwing this out there. I've finally documented my down firing version of Paul Carmody's Voxel subwoofer design. I still need to update my pictures thread for the final few steps I took, but the design details are done. I was very impressed by the amount of bass this thing puts out! I paired it with the Dayton SA70 plate amplifier, which drives this subwoofer well. This was the first ported design I've worked on, as well as the first design I ever simulated for design outcomes. I've learned a good deal from this project, so I'd like to thank those guys who helped me along the way. Special thanks to Paul C. for sharing his Voxel design with us!

A word on chuffing... I feel like I am pushing the limits of port size HARD in this small enclosure (BassBox says I'm getting ~25 m/s velocity at 34 Hz). I had to spend significant effort to get a functional design that didn't chuff audibly in bass heavy songs. It handled rock music well, but heavy bass from some electro / techno music wasn't going to happen. Adding some length and an internal flare helped cure most of my issue, but it can still show up given the right material.

Having said all that, This little guy is providing the oomph for a 5.1 setup with Helium speakers. He'll be used for casual listening, not attempting to shake down the house. He'll do a great job in that regard! If someone wants to try this design with a different port arrangement, or maybe a passive radiator or two... I'm all for it. There's just not enough room in a tiny box for a port that's well matched to the air this guy is moving at higher power levels!

[Evan Steeves]

man, I LOVE your worksmanship. Getting me inspired to push my woodworking skills to the next level when I get to building my sub (currently finishing my Sunflower center channel). Will be buying myself a good Rabbetting bit next :D

Nice work and thank you for sharing! Love the paint job as well!

[KEtheredge87]

man, I LOVE your worksmanship. Getting me inspired to push my woodworking skills to the next level when I get to building my sub (currently finishing my Sunflower center channel). Will be buying myself a good Rabbetting bit next :D

Nice work and thank you for sharing! Love the paint job as well!

Thanks Evan, In many ways I find that woodworking is it's own form of therapy. There's always something new to try, and always something new to learn! Painting however... I do NOT find theraputic. The Heliums I was building at the same time as this Voxel kept having some baffle cracking issues due to an undersized press fit tweeter hole, so I had to sand all the finish down to bare wood and repaint... 3 TIMES!!!!

Enjoy your subwoofer build!

[Evan Steeves]

Thanks Evan, In many ways I find that woodworking is it's own form of therapy. There's always something new to try, and always something new to learn! Painting however... I do NOT find theraputic. The Heliums I was building at the same time as this Voxel kept having some baffle cracking issues due to an undersized press fit tweeter hole, so I had to sand all the finish down to bare wood and repaint... 3 TIMES!!!!

Enjoy your subwoofer build!

Yeah, I have to agree with you there. The woodworking, you can mess up and fix fairly easily. Or, find alternate and creative solutions around it. But painting, from my experience with cars, rims, car parts especially, is a big pain. Of course with painting, it's all in the prep work, which means LOTS of time, and if you do mess up and get to the later stages, all the work is scrapped!

[SV Impunity]

I've been following this sub build with a deal of interest. I sold a pair of my column full range speakers to a friend who now wants a small sub to compliment them. They have a small apartment and I think this will be ideal. I especially like the down firing aspect. Your sub looks very neat and compact. Well done!
Regards John L.

[KEtheredge87]

I've been following this sub build with a deal of interest. I sold a pair of my column full range speakers to a friend who now wants a small sub to compliment them. They have a small apartment and I think this will be ideal. I especially like the down firing aspect. Your sub looks very neat and compact. Well done!
Regards John L.

Thanks John! Like I mentioned a few posts up, the only thing to consider very closely if you wanted to use the sub as I did is to check your port velocities. If your buddy wants to pump some serious bass, there may be some port noise to deal with too. I made this for my mom (decidedly NOT a bass-head) so no worries on my use case!

[9sheng]

My Speaker received , I want to build my own VOXEL SUB.