[Aaron Gilbert]

Hey folks! I've had a request or two for creating a build thread of my subwoofer, so here it is! Sorry it's taken so long.

( Originally built for a Dayton Quatro 15", it now uses a Tempest-X 15". )

The Emerald Titan is my first (and thus far only) subwoofer designed specifically for home theater, though I have built several car audio subwoofers in the past. Goals for the Emerald Titan included:

1. Low cost - driver under $100
2. In room response flat to below 20Hz
3. Shallow 4dB/octave rolloff from about 40 to 10Hz
4. An extremely solid cabinet which could withstand upgrades to a more substantial driver in the future
5. Unique style
6. Passive - already had separate amplifier on hand


To satisfy the first criteria, I chose the Dayton Quatro 15", which had just come out (this being spring of 2003). It appeared to be a substantial improvement to the Dayton HD series II, which had been my choice for some time, at minimal increase in price. Being a long time Shiva user, Tempest was my first choice, but price was too high and the Quatro was nearly as good a deal in terms of $$/Xmax.

To meet the second and third requirements, I chose a very large vented box, about 275 liters net (9.7 cubic feet), tuned at roughly half of the Quatro's Fs. I had previously found great success in this method using Peerless 850122 in a very large enclosure, for my Emerald Towers (story for another thread).

For the box, I used oak veneered high-grade plywood, to enable a very easy but relatively nice finish, and relatively light weight. For the front and rear baffle/faces, for cost reasons, I used 3/4" particleboard covered by 1/4" hardboard. Construction followed my standard procedure for large boxes, which includes 2x2 glue battens around front and back of the top, bottom, and side panels. The front and back are then set inside the other panels and screwed and glued onto the battens. This alone makes for a substantially stiff cabinet. However, due to the shape, which is very wide, medium height, and rather shallow, I felt some bracing was in order front-to-back. This was accomplished using six 2x4 braces screwed between the two largest panels. Additional grab for the driver mounting screws was provided by gluing 1x1 blocks of 3/4" thick oak behind the baffle.

The style function was met by applying what's almost a trademark of every speaker design since my Emerald Towers - lots of green! I also added some rather unique cosmetic and design elements, but I'll leave that for the pictures.

Amplifier on hand for the subwoofer is a Kenwood KM-X1000, THX certified before THX split into Ultra/Select. It's from c. 1998, is bridgeable, and is stable into two ohms stereo. I'm running it at four ohms mono - which it handles with aplomb, but unfortunately, Kenwood doesn't give a rating for that. I have a Kill-A-Watt meter now, so one of these days I'll take a reading and see what she's drawing. Kenwood rates it at 270 watts mono into eight ohms. Having a fair amount of experience with Kenwood gear, I have always guesstimated around 400 watts into four ohms, mono.

A final note before moving to the pictures, is the reason for the shape. Initially, it was designed to be a 'sofa table', ie a wide, relatively tall, but narrow table behind the couch, for setting your drink, or magazines, books, what have you. Unfortunately, it sounded rather anemic in that location, so to the corner it went, but the shape was already set. So without further ado, on to the crazy amount of pictures!

Collection of wood all going into the subwoofer, along with 3" vent tubes. Remember cost was a big issue with this build (just bought my first house alone, wasn't making all that much at work), and box tuning is 11Hz, which is why you don't see any Precision Ports:

Here are the bottom, top, and side panels after screwing and gluing the 2x2 battens onto the inside:

Here's what the 'shell' looks like when the top, bottom, and sides have been screwed together. I used 1x2 solid oak on the top edges to conceal the plywood ends, secured by glue and finishing nails (set and filled). In the past I'd used 1x1 for the same purpose, but chose 1x2 in this case to give it a lip and look a bit different, and fit with my initial placement goal of behind the sofa:

First test fitment of the baffle, woofer, and hardboard. The front and rear were purposely designed as 2' x 4', to use ready cut panels from Home Depot for the particle board and hardboard (who also cut my plywood):

Here's the back panel ready to be screwed and glued in place. Only 36 screws and glue around the entire perimeter, do you think it's enough? Notice my miscut of the input terminal hole, had to patch and fill it. It's not a true DIY project if there aren't any mistakes, at least for me :bigsmile: :

Back panel secured and terminal surround painted black (you'll see why later). Also note the four sets of three screws in the back - those hold my 2x4 braces. :

View from the front showing the braces. They ended up about 1/8" shorter than required, so I ended up gluing on some rubber pieces to fill the gap. You can also see the insane amount of caulking. Altogether, I used about 3.3 tubes of caulk for this enclosure:

Front panel ready to be screwed on. I honestly don't remember if I used glue between it and the battens, or caulk. I want to say caulk. Either way, it's not going anywhere. All told, I used about 1.5 pounds of screws for this box. Keep in mind that my only power tools available for this project included a router (used only to round off the 1x2), a jigsaw for cutting holes, two drills for ah, drilling and screwdriving, and a random orbital sander.

The front panel's in place, and you can see the two additional 2x4 braces flanking the woofer hole. Just try and flex the front and rear panels! Second picture shows the oak behind the front panel woofer mounting holes.

This being my most powerful and largest speaker to date, I decided to use some spare 10 gauge wire I had laying around from car audio amplifier installations - not because I believed it would make a difference, but because it was free, and it just seemed apropos to the build!

Despite the plywood carcass and particle board instead of MDF, the total weight still came in at about 130 pounds! I therefore purchased some inexpensive swivel casters to enable easy movement. After five years, one broke, but what can you expect for about $5/four at WalMart?

Ah, finally getting close to finished! Here are the front and rear hardboard trim panels which cover the ugly and screwed-to-death front and rear panels. As with my Emerald Towers, they have lots of green! Need you ask what is my favorite color? :cunning: Plus you can see the monstrous motor structure of the 15" Quatro. :bigsmile:

I chose a Minwax Polyshades finish - supposed to be reddish-tone cherry. However, for whatever reason (temperature or improper stirring?), it came out nothing like it was supposed to. It came out just plain light-ish oak, and didn't dry properly at all. Oh well - still looked ok. You'll see in later pictures, that I finally got it to the proper shade, but here's how it started life. You can see the vent holes cut into the top rear.

So, finally we come to the first completely finished pictures! Here's a front view, with one of my Emerald Towers in the background. Note these are version 2 of the towers - upgraded to Peerless 850122 woofers, but still on original tweeter, crossover, and base design. The towers are approximately 68" tall for reference. The subwoofer is 49.5" wide, 18" deep, and about 27" tall. Note, that's 27" on the surface of the top panel! The ports tend to add a little height.

Here's a close up of my high-tech port sealing. The 3" tubes are a friction fit into the top of the cabinet. As mentioned before, the cabinet is tuned to 11Hz, meaning the tubes are 28" long each - they don't fit inside the cabinet, and I was a bachelor at the time with tons of space in a brand new house - so why not try a bit of a unique design! Also, here you can see a close up of the input terminal.

Here's the full back view. No fancy screw pattern or brass screws here, unlike the front - yes all those front screws are brass, but zinc washers.

Here's a final picture from 2003. Forgive the ugly base for the Emerald Tower. The DVD collection has grown quite a bit since then.

Ok, so fast forward a bit more than five years! The Quatro served me extremely well! It had plenty of output, and in-room response was just what I was expecting. Port noise was not an issue, unless I fed it an 11Hz sine wave and cranked the level up to a few hundred watts. Then those ports chuffed like a steam train. But this was never audible with actual program material. Thanks to a nifty feature of my Kenwood THX receiver called subwoofer peak limiter, I could set the maximum output level to the subwoofer, and it was never overdriven. So yes, it limited the dynamics. But in actual use, operation was very transparent, and despite the meager 10mm Xmax, output was still plenty for my needs.

Unfortunately, it was not to last. The DSP board in my Kenwood took a permanent hiatus, meaning I needed a new receiver. Apparently, subwoofer peak limiters are no longer a popular feature among THX receivers. I got an Onkyo TX-SR805, and promptly discovered that the Quatro was fairly easily overdriven with certain material - for example, THX trailers on The Phantom Menace, or first few minutes of Attack Of The Clones, etc.

So, that lead me to purchase a new subwoofer driver, the Exodus Tempest-X. I just installed it a couple months ago and am loving it. Alas, it required a much larger enclosure than the Quatro, but nevertheless, this one still worked out well. I added a fair amount of stuffing to increase the apparent size, and due to addition of some media shelving, had to make the ports almost completely internal, resulting in them being a touch shorter. I figure the new tuning is about 12Hz. I didn't have to enlarge the driver hole or drill new mounting holes. Everything lined up perfectly, even though the physical specs on the Quatro vs. Tempest-X told me otherwise! So, going from 10mm Xmax to 27mm solved my overexcursion problem. I don't believe my Kenwood amplifier has enough power to overdrive the Tempest-X, even with my low tuning. Anyhow, here are some more recent pictures.

Here's the new subwoofer corner, showing the new media shelving aka why the ports have changed, and also the latest version of the Emerald Towers - Apex JR tweeter and fancy new base design. Also, the subwoofer finish now matches my equipment stand and desk - this is the color I originally purchsed that didn't turn out!

Close up of the new port exit, with more fancy sealing:

I also made a grill when I changed the color:

Here's the amplifiers which drive the subwoofer and front left and right speakers, along with my Onkyo 805, on my DIY equipment rack/TV stand:

And finally, here's the whole front stage! The center speaker is behind the screen on top of the TV, same driver layout and orientation as the front L/R, naturally!

Cheers all, hope you enjoyed my little subwoofer novela! :wave:

 

[tcarcio]

Great job, I love the finish on the sub it looks beautifull. I bet there was a big difference when you changed the driver. Also shorter ports must help with placement.

 

[Mike P.]

What is the length of th 3 inch diameter ports?

 

[thxgoon]

Nice work! I have that exact same screw gun.

 

[Aaron Gilbert]

Great job, I love the finish on the sub it looks beautifull. I bet there was a big difference when you changed the driver. Also shorter ports must help with placement.

Thanks! The difference in overall frequency response wasn't large, but certainly there's significantly more output available now and distortion has been reduced.

 

[Aaron Gilbert]

What is the length of th 3 inch diameter ports?

With the original woofer, the length was 28". Now, they're about 20" plus the length of the elbow on top, which is roughly 6". I'll try to get some updated internal pictures in the near future, showing the ports, stuffing, and back of the driver.

 

[Aaron Gilbert]

So I finally got around to removing the driver and snapping a few pictures of the revised insides. I have been too busy enjoying it, plus I take speakers apart all day at work - don't tend to feel like doing that when I come home.

Here's the venerable Tempest-X, yes, you've all seen it, but seems de rigueur to include uninstalled driver pictures. :yes:

Here's my custom wire harness, well insulated against any rubbing. That's 10 gauge wire just for the of it (I realize it's total overkill at this power and length):

Left side vent:

Right side vent:

 

[bluejay]

I really like your use of pipe insulation to guard the wires. When I take my sub apart again, I want to add some of that for sure. I also did not caulk my glue block joints like you. That might also be an error I will have to rectify. I did caulk some mistakes I made with white silicone.

I still do not totally understand the sealing of a ported box that well? I know it shouldn't look like swiss cheese. I just don't understand how the air would channel through the narrow gap along a glue block, when the box is not sealed. Someone answered this by saying a ported cabinet acts like a sealed cabinet at certain frequencies, that a pressure does build up?

Do you find caulking inside of expensive pro audio speakers? You know something like an Electro Voice or JBL? If so, what does it look like they use? What would you recommend?

 

[Aaron Gilbert]

I really like your use of pipe insulation to guard the wires. When I take my sub apart again, I want to add some of that for sure. I also did not caulk my glue block joints like you. That might also be an error I will have to rectify. I did caulk some mistakes I made with white silicone.

I still do not totally understand the sealing of a ported box that well? I know it shouldn't look like swiss cheese. I just don't understand how the air would channel through the narrow gap along a glue block, when the box is not sealed. Someone answered this by saying a ported cabinet acts like a sealed cabinet at certain frequencies, that a pressure does build up?

Do you find caulking inside of expensive pro audio speakers? You know something like an Electro Voice or JBL? If so, what does it look like they use? What would you recommend?

Thanks. I had the pipe insulation lying around - don't know for what, it wasn't pipes. The caulking of my glue blocks really is overkill, since the entire length of the blocks are glued to their panels. But hey, what's a few $2 tubes of caulking compared to the rest of the box, or the woofer/amplifier?

Indeed, as you say, a vented box does act like a sealed box at some frequencies. The farther you get away from the tuning frequency, the more it behaves like a sealed box. With very low tuned boxes like yours and mine, this happens even sooner than many. It's true that sealing is perhaps not as critical, because a sealed box will be prone to air leakage at all frequencies, whereas a vented box is meant to 'leak' air at the tuning frequency. However, any air leaking out a hole other than the vent, is air which could have contributed to the vent output. And, air leaking out of a tiny hole or crack is far more likely to be audible than air coming out the vent(s). I dealt with a poorly sealed vented box (deteriorating woofer hole) just last week, and it indeed sounded awful until the leaking was remedied.

I don't deal with pro audio speakers such as JBL. I deal mostly in home audio speakers, mostly mid-end, with some high end stuff, too, including subwoofers. Although, compared to most DIY subwoofers, many of the subwoofers I work on could be considered low end. It's extremely rare to find caulking in a commercial speaker. About all I ever see is some glue spread around the interior joints - very thin layer at that. And even that is rare. Even more rare is to see glue blocks. Commercial manufacturers build to a price point, and need to make a profit, so therefore only build to the minimum standards which will get the job done, in most cases. For cabinetry, this is ok as long as the speakers aren't thrown around a lot, and my back thanks them for the low weight. But, I have certainly seen plenty of speakers with air leakage and flexing cabinet walls causing bad resonances. So, sometimes they don't quite build as well as they need to. Usually when you buy the mid-high end speakers, a lot of what you're paying for are much more substantial cabinets, both in construction and appearance.

I just use the cheapest good caulk I can find, which is usually acrylic latex 25 year or 35 year stuff. Sometimes siliconized, sometimes not. I almost never pay more than $2.50 a tube unless I'm desparate.

 

[bluejay]

Commercial manufacturers build to a price point, and need to make a profit, so therefore only build to the minimum standards which will get the job done, in most cases. For cabinetry, this is ok as long as the speakers aren't thrown around a lot, and my back thanks them for the low weight. But, I have certainly seen plenty of speakers with air leakage and flexing cabinet walls causing bad resonances.

Thanks for this. I have been telling my less knowledgeable friends that most normal stores or chains do not carry anything like what we are building here, (for subwoofers). There are only a couple of "high end" audio stores within 3 hours drive of us. I don't really know what they do have in stock for subwoofers, but I am suspecting not much at 10 cu. ft. and zero at my price point. :scared:

All the chain stores have smaller stuff, including plastic subs for the computer. You wanna sub? they're over there, stacked up like cord wood. :yikes:

 

[Aaron Gilbert]

Thanks for this. I have been telling my less knowledgeable friends that most normal stores or chains do not carry anything like what we are building here, (for subwoofers). There are only a couple of "high end" audio stores within 3 hours drive of us. I don't really know what they do have in stock for subwoofers, but I am suspecting not much at 10 cu. ft. and zero at my price point. :scared:
...

Yes, it's rare that I see a commercial unit with the robust construction seen in even the lowliest DIY builds. And I work with many units that are several thousands of dollars retail. Now, most of those are still built well enough that there are not issues - the problems I find are typically on cheaper units, say in the $200-1000 range. True enough, I have yet to see any 10 cubic foot commercial subwoofers, though I have seen some close to half that. Most of what I see are in the 0.5-2.5 cubic foot range.

 

[radman12]

that is crazy looking