Home Theatre Subwoofer Build

Greetings friends,

Another little bit of a learning project here. I've been thinking about improving the sound quality for my home "theatre", and a logical step was to get a subwoofer. Unfortunately, any sub of decent quality or with the frequency response I want will cost at least a few kilobucks, so I decided "why not just make one myself?" Well here we go!

As always, I started by scouring the internet for ideas. What shape should it be? How big does it need to be? What drivers produce the right frequencies for a sub? After reading and weighing to pros and cons of various designs, I settled on the SonoSub design. It essentially consists of a simple cylinder into which a driver and vent tube are installed, and blam-o, you've got a sub (at least in principle). Let's dissect the process!

Lucky for me, I got to stand on the shoulders of those who have done this before. Two pieces of software exist to help in designing the sub, SonoSub and WinISD. WinISD allows me to enter the specifications of the driver I select and will calculate the theoretical frequency response for a subwoofer under certain conditions. SonoSub allows me to enter the parameters from WinISD and calculate the dimensions for the actual subwoofer housing.

I decided to get a 12" driver, which seemed a good size without getting ridiculous. This would also fit nicely into an 18" tube, which became one of the independent variables in the calculations. Information for the driver I decided to purchase can be found here. I entered the specs of the driver into WinISD and started playing with the performance specs I wanted from the sub. As a collector of classical music, I have several recordings that play frequencies below 20 Hz, so at the very least I wanted frequency response a few Hz below that. Given the capabilities of the driver, an 18 Hz tuning frequency with a tube volume of roughly 190 litres have me a frequency response I was happy with.

Assuming an amplifier with a low-pass filter, the size and tuned 

vent gave a really nice frequency response.

I entered the parameters from WinISD into the SonoSub software, and played with the numbers until I had an arrangement that I liked. I wanted to keep the dimensions easy to work with, so I decided that a 48" tube length (excluding caps) would be simple.

I started off by buying the 4-foot section of 18" SonoTube - they're cardboard molds used to pour concrete columns. Since it has a lot of rigidity and comes in large diameters, it's perfectly designed to be the casing for a sub. Luckily, the supplier cut the tube to length for me so I didn't need to fuss with trying to make perpendicular cuts on a ridiculously big tube.

To line the tube to provide some sound dampening, I got some 11 mm thick carpet padding from Home Depot, and used spray adhesive to line the inside of the tube. Because caps will go into the ends of the tube eventually, I cut the padding slightly short so the tube can accommodate the caps. Peeking my head inside and singing some low tones showed that the dampening was quite effective.

Onward to cutting the caps, into one of which the driver will be mounted, and into the other the tuning port. I foolishly first tried to cut circles freehand with my router, but was quite unhappy with the result. Simply put, a lot of extra sanding a shaping would have been required, an amount of effort I was looking to avoid. I then fashioned a very simple circle jig using a yard stick. Bolting one end onto the router and using a centered screw as my pivot point, this surprisingly made ridiculously easy work out of cutting circles. Though I unfortunately wasted 2 MDF boards in my freehand attempt and had to get replacements, in the end the simple jig was very worthwhile.

Both caps consisted of two rounds cut out of MDF, the outer round having a diameter of 19" and the inner 18". I cut appropriately-sized holes to accommodate the driver and the 4" port, and rounded over all edges to give it a pleasant look. I glued the pieces together and applied a few coats of shellac to seal the MDF. Below you'll see the cap for the port and the driver sitting in its cap.

The driver nestled neatly into the (bottom) cap and is held in place with 8 screws. Binding posts needed to be installed on the outside to connect speaker wire to the driver within the subwoofer, so I drilled additional holes for these. I didn't bother to make the holes inside look perfect, as they'd never be seen when all is said and done.

The posts were very easy to install, and are tightened into place with a few nuts. From the outside they're quite innocuous and will accommodate either speaker wire or banana plugs. A short length of speaker wire made the interior connection clean and easy!

I pushed the 4" ABS pipe into the port hole on the top cap, and set both caps onto the tube to give it a try... Currently the caps are just pushed in and not glued into place yet, since the exterior of the tube is not yet in its final state.

Wow, this thing really packs a punch. It's almost unbelievable how much sound this can produce for what it cost to build. The sound completely fills the room, and the low frequencies are incredibly rich! An incredibly successful project to say the least! Unfortunately no recording I could post here would do the sound justice, so you'll just have to come hear it for yourselves!

As far as aesthetics, the caps will ultimately be painted and the tube will be covered either with carpet or some other soft dampening material so that the sub will be more inconspicuous. When weather permits, I'll spray paint the caps outside and I'll update this post with some new pictures showing the final look. For now, I'm going to sit back and enjoy it!

UPDATE - 2020.40.15

I finally decided it's time to dress this sub, and my wife had some time to give me a hand with the sewing! Here's how I did it.

I bought a regular moving blanket/pad, that people usually use to protect furniture when moving. Blue on one side, black on the other. We'll be going with black!

To start, we sewed and cut the blanket to rough dimensions to see what we're working with. Another quick stich makes a tube out of the blanket and we're very close to a perfect fit. It only took a few more tweaks to have a decently tight fit, and the overhanging fabric will be tucked into the tube by the caps.

The caps were pretty difficult to press into place. Ultimately I had to take some clamps and gradually tighten while the caps slid into place. At least it won't be coming apart anytime soon!

It looks great, sounds great, and we'll be enjoying it for a long while! The caps will stay light-colored; I think it looks pretty nice!

Thanks for reading,

Juju

Pipe Restoration - Vintage Tyrolean Pipe

Greetings friends,

This is a project from quite a while ago that I've yet to publish. I preemptively took many pictures to document the process, so I'll be able to go into a fair amount of detail!

Seeking an easy restoration project, I searched Ebay and found a decent-looking vintage pipe, which seemed a prime candidate. I really love shape of this pipe, and I think the screw-on bottom cap is a very unique feature. The shank was severely cracked, the mouthpiece was chipped at the tip, and the bowl was nearly filled with years of caked-on tobacco (not pictured).

I started out by disassembling all components that could be removed. The shank, stem, and lid were very easy to get off, but what gave me the most trouble was the cap at the bottom of the bowl. I was convinced that it was meant to come off (whether by screw or tenon was unsure), but it seemed exceedingly difficult to remove. My guess is that not being removed for years allowed tobacco residue to build up and effectively glue it into place. Using thin razor blades, I gently scraped along the seam between the bowl and cap, getting deeper until it was obvious I was hitting wood. After this I used isopropyl alcohol (IPA) to wet the seam and soften the joint. After literally 1-2 hours of this, I was finally able to unscrew the cap. Boy was I right, this thing was nasty inside...

Using q-tips and IPA, I cleaned out the inside of the cap, and scraped out the threads with a razor blade. When everything was nice and clean, the cap was much easier to screw on and off. Moving on to the bowl, I mostly used a small metal scraper to get out the large pieces of burnt tobacco. To finish it used a pipe bowl scraper to even out the walls and get a decently uniform interior surface.

With the interior of the bowl and cap finished, I decided to move along to doing the exterior of the bowl. Whatever finish had been applied originally was looking grimy, so I decided to simply sand through the finish until I reached bare wood. The original maker seemed to have used wood putty to fill any voids that were present in the burl, but I thought it didn't blend in well, so I decided to scrape out the putty as best as I could with a dental scraper. To refill these holes I sprinkled some briar dust into the holes, and dripped some super (CA) glue into the holes. This not only created a durable fill for the hole, but the color will look somewhat better than the putty. I then sanded the super glue flush with the surface.

Left: Wood putty scraped out of voids in the burl. Right: Voids filled with briar 

dust & CA glue, quite dark, but I think better looking than the putty.

The mortise which accepts the shank had a crack in the outer wall, which I wanted to reinforce. I opted to use a collar to both reinforce the wood as well as to create a better looking transition between the bowl and whatever I decided to use for the shank. The collar is made from nickel silver, and had to be ground down on top in order to match the height of the mortise. I used briar dust and super glue to fill the crack and to fill any gaps between the wood and collar singe the cross-section of the mortise isn't perfectly round.

 There wasn't much strength left in the mortise, so there 

was little choice but to slap a collar on there.

 The collar was a pretty snug press-fit, and filling the gap with 

CA glue + briar dust really secured it into place.

After grinding the collar down flush with the 

mortise, it's really starting to look nice!

I decided to stain the briar with some leather dye, which can give very vivid colors with a high tolerance to fading. I opted for Fiebing's Oxblood, since it produces a rich red tone. A few coats of dye followed by two coats of linseed oil brought out the color fantastically.

Dyed with Fiebing's Oxblood.

Two coats of linseed oil on top. The oil makes the burl figuring really pop!

The original shank didn't seem to be made of any special kind of wood, but in any case it was too severely split to hope to recover. I used this as an opportunity to try something different as well as to incorporate using my lathe into this project. I purchased a small piece of buffalo horn from my local woodworking shop, and used it to form a new shank with a more interesting shape. The horn wasn't much different to turn than wood, but it did have a pretty bad smell while I was drilling holes.. 

I fitted the tenon to the mortise on the bowl, and made sure that the bottom tapers so it's flush with the diameter of the collar. Once I reached the shape I wanted, I sanded it gently, and used several polishing wheels to get it to a finish that I was satisfied with. Once polished, I tapped the hole to accommodate the M7 thread that the mouthpiece had.

The mouthpiece needed complete replacement, and I found a fantastic german vendor that specializes in this type of horn mouthpieces. This was by far the easiest part of the restoration as I simply had to order the piece and sit on my ass waiting for it to arrive. This simply threaded into the tapped hole in the shank, and the pipe was essentially finished. I slapped my polishing wheels back on the lathe and gave the bowl lid a final polish. Success!

A final photo, this piece really came together nicely. I love the richness of the color on the bowl, and the new shank really adds something to the pipe. It's fully functional at this point, but I'll likely just hang onto it as a nice collectors piece.

Thanks for reading,

Juju

BMW R65 Restoration - Part 1

Greetings friends,

I've definitely sent myself down a rabbit hole with this project. There's a lot of skill and knowledge needed to undertake this project, but I'm excited to get into it. This will probably be updated over a long period of time, very likely a year at least.

I've done what no wife wants to hear her husband has done... I bought a motorcycle...

Now before you get too worked-up, I'm sure you'll be relieved to hear it has no engine, and in fact has no chance of travelling at any appreciable speed for the foreseeable future! 

This was a lucky find on Craigslist, a previously wrecked frame, which in essence are just parts for the eventual rebuild. A seat was included with the bike, but I removed it for the following pictures.

Pre-cleaning, the bike has a fair amount of grime and dirt on it.

A quick pressure-wash makes quick work of it and leaves it looking nice!
Or at least, a good starting point.

The forks sustained the bulk of the damage, so will need to be rebuilt, or replaced outright. The rear fender is broken, but probably easy to replace. Originally an R65LS, I plan to restore this bike with mostly stock-parts, but I plan to add some light mods, and make it a little more minimalist. I very much enjoy the cafe-racer style, and I think that would suit this project well especially since this will not be an all-weather or highway-driven bike. Ideally, at least to get the bike operational, I'd like to source used parts and do as much dirty work myself as I can. I'll start with the components needed to actually get the bike moving, and focus more on aesthetics later on in the project.

Wheel & Forks Repair

To start things off, I am removing the front wheel. It appears as though the only damage to the rim is the obvious dent... I'll be taking this to a rim repair specialist to see if they can salvage it; I don't trust myself to fix a dent this big. I'm eager to hear whether or not it can be fixed.

With the wheel off, I can really get an idea of how bad the forks are. At the very least, the tubes will need replacing, and it's possible I could salvage the sliders. In any case, I think ordering a used replacement is in order. Will update on the next post what I'm able to find.

Thanks for reading,

Juju