Project #2: The 'Tenacious Bass 6' and 'Tenacious Bass 8' Subwoofers

[tomzarbo]

The 'Tenacious Bass 6' and 'Tenacious Bass 8' Subwoofers
I love bass, I admit it. To me it's what makes music sound real. In the past, I've designed mostly larger speakers -- floorstanders and towers -- which were able to produce sufficient bass on their own. However, after designing my first set of truly tiny speakers -- the 'Bantams' as my first Design Team project, I started to see the wisdom in keeping the main speakers small and just using a subwoofer to augment the low end of the sound spectrum.



When thinking of subwoofers, you almost have to consider the drivers from Tang Band. I love how well the Tang Band smaller subwoofers perform; they are almost legendary at this point. The venerable W6-1139 and it's little brother, the W5-1138 subs are just amazing drivers and there are many good designs using them in the DIY community.

The more I considered it, I thought it would be fun to imagine a basic subwoofer cabinet shape in two sizes... or 'strengths' if you will. The smaller design would use the ferrite version of the W6-1139, and the larger version would use one of Tang Bands 8" subwoofer drivers -- both utilizing a slot vent with a front exit design feature. There are a few 8" subwoofer drivers to choose from but the one I originally was looking at became unavailable in small quantities, so Jill, from Parts Express actually recommended modeling another 8" subwoofer driver from Tang Band -- the W8-740P -- It seemed that it would perform perfectly in the box size I was considering... or so I thought.

For those not familiar, a slot vent is usually constructed with a rectangle cross-section and uses standard construction materials (MDF, plywoood, etc.) to make up the small 'box' that is the actual vent. They often can be arranged so that they help 'brace' the cabinet, or add stiffness to the box, which is a good thing. I had never designed one before and thought it would be a good 'learning' experience as a speaker designer. Well, I did learn a great deal with this project, but as many learning experiences go, it came though failure.

The first of these projects I started to build was the larger of the two, the 8" version. I modeled the box several times and came up with what I thought was a sound design. Over several weeks I built the box and got it to the point where it was ready for veneer. I loaded the box with the driver and powered it up... what happened? Well, it did reproduce lots of deep bass, but the air from the vent was moving so fast that it created massive turbulence -- commonly called 'chuffing.' At anything more than around half of the drivers available excursion, I was getting pronounced vent noise -- though my modeling suggested the vent speed would be in the 'safe zone' regarding air speed. As I turned up the volume my shock turned to horror... the amount of vent noise was overpowering... and putting my head in front of the vent opening felt like sticking my head out of a car window at full highway speed.



I wondered what went wrong. I had designed many, many speakers and subwoofers with traditional round vents and had gotten comfortable enough with the results that I felt assured that my simulations would match reality. This time they didn't. Well, I enlisted the help from several of my 'speaker building' friends from Tech Talk and discovered several issues. I used BassBox Pro to design the box with, which is the program I always use to design boxes; it is a good program, and is very intuitive to use. Somehow, the program became corrupted however, and numbers were just not adding up -- a fact discovered later on by Kevin K., another Tech Talk forum member -- when I was seeking a second opinion on the second, smaller subwoofer design. A reinstall restored proper operation. I think I know how it got corrupted... I had recently updated the database, so I'm guessing something probably went wrong during that process.

Another issue was the fact that slot vents behave differently than traditional round vents; the 'ratio' of height to width is obviously different than with a round vent. Although I was aware of this to a degree, I learned that most box modeling programs are not able to account for these changes, nor do they tend to properly predict responses with sharp right- and 180 degree-bends in the vent layout. This is not a 'knock' against BassBox Pro as most box calculators behave similarly... I have used and likely will continue to use it to design boxes -- I'll just probably steer clear of slot vents from now on now that I'm aware of their added complexities.

[tomzarbo]

I tend to use passive radiators when they are a viable option anyway... which brings me to the solution to this problem. A well-known Tech Talk contributor, Chris R. suggested that I consider a passive radiator as a way to maintain a similar box size, and still get the low-end performance that I desired. Turns out I had just received a few of Dayton Audio's brand new RSS265-PR 10" passive radiator, which is based on the sexy aluminum Reference Series drivers.

https://www.parts-express.com/dayton...iator--295-500

After running some box models, it looked like I had a viable solution that would end up being an even better performer than my previous flawed slot vent design. With some help and guidance from my fellow 'Speaker Builder Design Team' members I was confident of the performance of this design.







I had to do a little surgery and cut the top off of the box and add a bit of material, I also needed to remove the 'vent' section of the amp partition, fill the vent opening in the cabinet, and add a second baffle board for the woofer... but the end result is a good performing powerhouse of a subwoofer design with a front view that is 'all ate up' with 10" of pounding Dayton passive radiator.


That's right... the Tang Band 8" subwoofer is actually arranged in a down-firing configuration with the 10" passive radiator facing front. The TB driver with its stiff, double-spider can easily withstand facing down, where the passive radiator with its substantial mass would eventually sag.



It looks mean and nasty, and it's truly entertaining to see the passive radiator moving over an inch at some frequencies -- these new passive radiators from Dayton Audio are amazing performers. Since both the driver and the passive radiator are mere inches from the floor, there is a 'visceral' feel to the bass that is rather impressive. This 8" design creates a lot of bass from not a lot of space, and I think the cabinet design is unique if I do say so myself.

[tomzarbo]

Now that the 'Tenacious Bass 8' design was complete, I turned my attention to the smaller 6" version with some trepidation. I had just experienced a failure with the larger sub, and decided to get a second opinion on this design before cutting any wood. This is the point where Kevin K. noticed that my box modeling program was not calculating some things correctly, and had likely become corrupted. After the reinstall, and realizing that this slot vent was likely going to be noisy as well, I enlarged the height of the vent to 1.25" tall x 6" wide which necessitated an increase the vent length as well. I built the box and the vent assemblies as separate units and used foam gasket tape to temporarily test it with.




So, did I have vent noise with this design as well? Short answer: yes, a little bit -- but not nearly enough to be an issue.

Let me explain: I generally test subwoofers initially with test tones from a test CD, not with actual music. That means that I was testing the sub with the most demanding material possible -- pure sine tones and bass tracks at the deepest frequencies. I do this to make sure that my subwoofer designs can take any punishment they may receive while reproducing movie special effects; but almost no music has bass that low or demanding, and the movies that do also have a non-subwoofer soundtrack playing at high volume along with it, which will tend to mask any minimal vent noise.

But back to the chuffing... I heard minimal chuffing at high volume and was of course a bit worried. However, a few modifications to the internal vent exit along with following some good suggestions from the 'Speaker Building Design Team' took care of any remaining issues.



The end result: I now have a smallish 6.5" powered subwoofer capable of substantial output to the high 20 Hz range at decent volumes. The W6-1139 is kind of a freak... it seems like it has no end to its excursion capabilities, and the Dayton 70 watt subwoofer plate amp is a good match for this driver. At 70 watts, it provides a bit of headroom, and though it got pretty warm at loud levels when played for an extended period of time, it handled it well and has been a known good performer for years.

[tomzarbo]

So here are the design details.

I'll start with the smaller "Tenacious Bass 6" subwoofer.

The box is 11" by 11" by 16" long using 3/4" MDF. The base at the bottom is 1.5" thick and the space between the base and cabinet is 1.25" -- the height of the vent. The vent in total is about 37.5" long measured at the center point, and is 1.25" high and 6" wide. Knowing how much of a beast this little sub driver is, I decided to build a compartment to house the amp in so it wouldn't be subjected to the extreme pressure changes inside the cabinet. The amp is sealed, and designed to deal with being loaded directly into an enclosure, but I went ahead and partitioned it anyway. Since I used the rear of the amp enclosure as part of the vent structure it made sense to do so.



The vent structure was designed as one unit and once completed, was glued in the cabinet and the top glued on to seal it. The vent assembly is made of 1/2" MDF and I rounded over slightly the interior ends of the 1/2" MDF for hopefully better air flow. I also rounded over the internal exit as well and removed excess material from the sides of the vent assembly for smoother air flow.



I highly recommend building the vent assembly in one piece apart from the box to ensure that the proper vent dimensions are maintained.



I made some temporary 1.25" spacer pieces to ensure that the vent remained exactly that thickness during the glue-up procedure.
Before installing the driver, I added a 26" x 26" piece of polyfill batting folded in half, then in thirds to the top of the woofer compartment. This helps calm down vent noise a bit and is specified in the design. You could use an equal amount of loose polyfill pillow stuffing, but the 'batting' has the fibers arranged in a linear fashion which tends to not 'fluff apart' over time, so it will stay put and not come loose.

I used PL Premium construction adhesive for its thicker consistency to glue in the vent assembly and top since I wanted to be sure there would be no gaps. I would normally use Gorilla Glue for something like this, but as it 'foams out' during the curing process, it would likely intrude into the vent area, impeding airflow, and possibly creating noise issues. There is no way to get inside the vent assembly after it is glued in, so any issues inside the vent assembly cannot be addressed after it is glued in.

I also made small 'triangle' shaped blocks in the two front corners of the cabinet since I planned on rounding it over with a 1.25" roundover, which would leave precious little material at that joint.


In order to line up the vent with both the cabinet and the base accurately, I drilled four 1/4" holes in the C-shaped vent that makes the transition between cabinet and base. I inserted four dowel locater pins in those holes, aligned the vent piece carefully, and whacked it with a mallet, marking first the cabinet, then the base with indents which can be used as centers for drilling the holes. I used 3" deck screws to fasten the base to the vent piece and cabinet.






This insured that everything lined up fine during final assembly.

Years of experience has taught me that what you really want to do is create a "Kit" that you will assemble after the veneer and any finish is applied. You don't want to fiddle with figuring out how to mount, attach, or connect anything at that point... you're just asking to scratch the finish or ding a corner if you do that.

Get things 100% ready to assemble BEFORE applying veneer and finish -- then final assembly will be a breeze. You can thank me later.

[tomzarbo]

I covered the smaller subwoofer with Zebra wood veneer, considering how I wanted to orient the grain as I cut out the pieces. The top, front, and bottom are covered with one piece of veneer in one operation. The large roundover allows for bending of the veneer as you apply it, at least using the iron-on Heatlock method that I almost always use.


I screwed a temporary piece of sacrificial MDF to glue the veneer to so getting the veneer to stick to the curve would be easier. I didn't do this on the other cabinet and I had to spend more time fussing with it than I wanted to in order to get it to stay stuck.



If you need some tips on applying veneer around roundovers or dealing with seams and veneer, I have a few videos that may help. Check my signature at the bottom any of my posts and you will see links to several YouTube videos on using iron-on veneer.

I did have a stubborn area at the end of the roundover on the cabinet. I left enough extra on the sides that it ended up causing a problem as I applied the veneer around that part of the curve.



It wanted to stay straight instead of curve. I ended up needing to cut a small triangle out of the veneer to get it to sit flush. This left a bit of a funny looking area in the grain pattern since this is 'reconstituted' veneer (man-made) and the grain sits on an angle depth-wise. Luckily, this area is on the underside of the cabinet and not front-and-center.

I also rounded over the exits of the vent transition pieces between the cabinet and the base. That, combined with the front cabinet and base roundovers allows for a more gradual transition from vent to open air, which reduces vent turbulence.

[tomzarbo]

Now for the "Tenacious Bass 8 Subwoofer"

The box size is 12" wide, 12.5" tall, and 18" deep using 3/4" MDF. This also has a 1/2" thick MDF partition for the amplifier, the Yung SD200, 200 Watt subwoofer plate amplifier in this case. It is remarkably shallow and didn't need a large compartment for mounting. Also, it runs very cool.
.


I used the 'unboosted' version of this amp. The 8" sub driver is centered in the bottom area and I added an additional 3/4" layer of MDF inside the cabinet just where the driver mounts, since the driver needed to be recessed fully, and it has a rather thick mounting flange. The front baffle is 1.5" thick, made with two layers of 3/4" MDF. The recess for the passive radiator is 10.5" and the opening is around 9.25" roughly.

Always measure the drivers when you have them and cut accordingly, of course. I placed the woofer opening in the bottom of the cabinet spaced evenly front-to-back between the inside front and the amp compartment. Placement isn't critical here. There is a single horizontal brace that runs side to side with two smaller braces that connect the horizontal brace to the top of the cabinet.



These were made with 3/4" by 1.5" MDF and I would suggest this as a minimum; there is quite a bit of energy generated in this combination and bracing is required. In fact, on some surfaces, I think some low-profile spikes may be needed to keep this cabinet from moving fore and aft... the loaded passive radiator carries a fair amount of weight around it's middle... sounds a little like me.

I used plywood to glue up four blocks of wood around 1.5" tall to act as spacers between the cabinet and base.



These were then rough-cut on the bandsaw into an oval shape, sanded, drilled out in the centers, then covered with aluminum tape to give it the look of stainless steel or brushed aluminum.



I placed the base on the box and drilled holes through the base into the box using a 1/8" bit. The holes I drilled were 1.5" in from the sides of the box and 3" in from the curved front, and 2.5" in from the back. I drilled out these holes in the base and spacer blocks so the large 3" deck screws I used would easily go through with little friction. I ended up using a 1/2" Fostner bit to drill into the bottom of the base approximately 1" to allow the 3" screws to penetrate into the box sufficiently.



Feel free to use whatever spacer material you want, but I would recommend no less that 1.5" of space between the base and cabinet for the TB driver to 'breathe' and so as to not change the in-cabinet specs too much. I wanted to source some oval aluminum bar stock, but this seemed like a good second-choice option, and I already had all the materials on hand.

[tomzarbo]

I applied the same 1.25" round-over to the front of this cabinet as the smaller one. I realize that 1.25" is a pretty big round over and most won't have such a big round-over bit in their tool box. You could use a smaller round-over if you wanted, I like the bigger round-over myself as it changes the look of the front from merely rounded-over to more of a 'curved' look in my opinion. A round-over isn't necessary on the larger cabinet, but the smaller version would benefit from the added vent exit curving, though it's not absolutely necessary. If you don't have a large round-over bit and like the larger round-over look, you could consider taking visiting a cabinet shop to see if they might do it for you. There are also companies online that sell pre-made round-over blanks that can be glued in if needed. If you go with a more common 3/4" roundover, you may need to orient the grain on the veneer so that the curve is easier to achieve, going with the grain, as opposed to the grain direction as I did.

I went with Walnut for the veneer on the larger 'Tenacious Bass 8' subwoofer cabinet.



As you can see, I was scraping the bottom of the barrel as far as veneer scraps. Nobody will likely see the bottom of this cabinet again, so I just pieced it together as best I could. At least I bothered to orient the grain properly -- I am civilized enough to try to do that.




These can be painted, veneered, or even covered with Parts Express vinyl covering if you like. Either way though, my suggestion would be to sand the seams flat, then wait several weeks and sand the joints again until they are perfectly smooth, in order to minimize the chances for the joints showing up under the finish later on. I ended up with about 10 coats of rub-on poly and it really shines.



In fact, my niece who is a professional photographer had a hard time getting the top to show up in the pics... the light in the room just reflected off the top and made it just disappear or turn into a mirror. She was working with what our family room had to offer, though; which was a lot of beaming light shafts and shadows... she did the best she could with what she had to work with.

I used four of the washers (included) on the passive radiator for a final tuning of around 26 Hz.



I tested several different weights, but when I settled on the final washer amount for my liking, I used the included nylon lock-nut and a little blue thread-lock compound to seal the deal. One of the nice features of the new line of RS-based passives from Dayton is that you can easily try out different tunings by just adding/removing washers from the unit, securing them temporarily with the included wing-nut until you finalize your design.

[tomzarbo]

I have come up with a few tips... there's no reason you can't learn from my mistakes after all.

Use some type of square to level the amp divider so the vent assembly fits snugly with no air gaps.
Also, assemble the vent prior to gluing it into the box -- it will be easier to maintain a true 1.25" cross section this way. If you do use roundovers, it would be best to veneer first, then cut the driver recesses after that. Trying to get veneer to adhere to curved wood where the edge is right at the end of the curve is very difficult.

Another great tip someone at Tech Talk shared with me several years back: It's a great idea to paint the driver recess black. It gives things that 'finished' look that really finishes a project. Great advice!

I just use Rustoleum's Painters Choice flat black paint. It sticks to bare MDF and it dries in 20 minutes.





It just wipes off of polyurethane with a damp cloth also.

I suppose some of my 'miscalculations' and 'mistakes' could be seen as being embarrassing, and I thought of not publishing that part of this journey... but to be honest, I think folks really need to see the 'out-takes' of this process. You never saw Norm Abrams make a mistake on "The New Yankee Workshop," they have video editors for that sort of thing... but did you ever notice the occasional band-aids he sometimes sported? Personally, I think he always wore flannel because it's good for soaking up blood. I know, I'm no Norm Abrams...I usually make a few mistakes on every project I build, though not usually of this magnitude. I make far fewer goofs than I used to though -- and over time, I have gotten much better at dealing with them. They don't throw me quite as much as they used to.

Honestly, things like these happen sometimes when designing and building speakers and subwoofers. We try to plan for everything and anticipate every detail and possible problem. Sometimes we do a pretty decent job of that, sometimes not so much. I was encouraged to put it all out there for others to see and learn from and I have no shame in doing so. It's the end result that matters anyway, right?

[tomzarbo]

I've said it before and I'll say it again... I'm a hack woodworker. I try to find an easy way of doing something that still yields good results and then I perfect it. For instance, I don't like to do woofer recesses... so I figured out how to do one -- like the one in this project for the 8" subwoofer -- in just two passes with the 1/4" bit in the circle jig, and one quick run around with the saber saw. It only works with MDF, but you just run the bit through the outer most range of the driver recess, usually you can get to the proper depth with just two trips around with the router... then drill a single hole and carefully cut the opening for the driver with a jig saw. That round strip of MDF that's still there? Pop it off with a chisel.

What? Yup, get the 1" wide chisel in there from the driver opening and go a bit higher than where the channel your routed out ends. Once you have the bulk of the material removed, you can flip the chisel and clean up the bumpy parts of the MDF and you're done. You'll be surprised at how easy it is... and you'll also be alarmed at how flaky and not-glued-together-very-well MDF is!





Also, has anyone noticed that I usually do a rub-on-polyurethane on ALL of my speakers? I've gotten decent at it... I figured out through experimenting and with some help from fellow Tech Talkers how to get a nice finish with it... I know it works and it's easy so... Even though it's probably considered Low-Tech, I can do it in my basement without stinking up the whole house, and I manage to get a decent finish from it if I do it right.

Thinking logically about what went wrong and seeking some good advice for a solution is how we move past setbacks. I'm personally very proud of these two subwoofer designs. Although the finished products ended up being a bit different then I originally envisioned, they both perform very well and would make a nice 'bottom end' to most bookshelf and small speakers.



Back to the project... The TB-6 has an F3 of around 36 Hz where the bigger TB-8 has an F3 of around 26 Hz. They both sound good, but I really enjoy those last few deep notes on the bigger Tenacious Bass 8 subwoofer. I would pair the TB-6 with the micro two-ways like the Heliums, Quarks, Pico Neo's, my Bantams, etc. The larger TB-8 would probably pair well with the Overnight Sensations, Nano Neos, even up to some larger 6" and 7" stand-mount speakers. I think the TB-8 would even do fine for a small to medium home theater setup, it sure goes low enough!





Well that's it. I've spent a lot of time working on... then reworking these two projects. I like them a lot and I hope you do too.
Thanks for looking, and happy building.

TomZ

[blue934]

Awesome job Tom! Did you use real or 'manufactured' Zebrawood veneer? I'm using the manufactured right now but haven't put a finish on it yet.

[thekorvers]

Wow Tom, another very well done project x2. With a great writeup to boot. Very impressive! I love the way these look. Thank you for sharing this with our community.

[tomzarbo]

Thanks,sir!
I used the reconstituted stuff. It's pretty nice to work with, but it's not as smooth as real wood. Takes a bit more sanding to get smooth.
TomZ

[howard]

Tom,
Very attractive subs! Excellent write ups as well.

[Gordy]

Fantastic work! You stuck with it and had patience. I am not sure most of us have that but do highly respect.

[blue934]

Thanks,sir!
I used the reconstituted stuff. It's pretty nice to work with, but it's not as smooth as real wood. Takes a bit more sanding to get smooth.
TomZ

I too like the product but it has a pinkish hue when raw and I've hesitated to finish it. I've asked here and elsewhere and the general consensus is poly (the 2K automotive preferably) will offset the hue. Yours came out beautiful so that inspires me to move on! Good work sir.