Audio Innovation - by Dan Marx www.danmarx.org

TC Sounds 15" Subwoofer

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First Few Thoughts - Circa 2000 Timeframe

I have begun another subwoofer project. This time I wanted a sub that would top every other sub I had built previously. This would mean I would need some serious raw power and driver that was truly serious about delivering enormous amounts of bass. So I chose the TC-Sounds 15" offered by Rudi at Audio-X-Stream. Lucky for me, when I called Rudi a few weeks ago he said he only had four drivers left from his first batch and wasn't sure when he'd be getting a new batch in. So I went ahead and ordered two of them. But this time this sub isn't going to be for my own sound system. When I met Sterling a few months ago he explained how his company wanted some new subs that would absolutely pound on the competition. He didn't want just another run-of-the-mill subwoofer that anyone can buy at their local stereo shop to plug in to their stereo. He needed something more, something rough, something heavy and most importantly he wanted a sub that would totally rock. That's when I whipped out a design using the TC-Sounds 15" driver. Up until now this has been the best high excursion driver on the market today. With over 2.0 inches of linear throw and a magnet that could reverse the Earth's gravitational pull, I knew this driver would make the ultimate subwoofer.

Checking out the Home Theater

Before making any finalized plans I went up and checked out the home theater that this sub would be installed into. This room is literally a home theater with movie theater seats, huge 100" screen, projector, 5.1 surround, and everything else to boot. The audio system is built into a rack and will only be used for movies. So design goal #1 - sub would be strictly for movies. The size of the room is rectangular about 18' wide by 14' deep with a about an 8' ceiling. So we're looking at having to fill about 2000 cubic feet. Which is about the size of your average family room or living room of a large home. You can see that we will almost be overdoing it by putting a sub this size into a room this small. But then again, since this sub will be for movies only, I see no reason why we can't overdo it just a smidgen to give these new home-theater-movie-goers an experience of a lifetime. Now onto the project plans.

Putting the T/S Parameters to Work

Modeling the TC-Sounds driver is some what of a task. It's difficult to decide on a perfect internal volume and tuning frequency for this subwoofer. There are many tradeoffs to be made by going either one way or the other. One major issue we had to deal with was the size of enclosure. We didn't want the sub so large that it occupied the entire the front-left corner of the room. Yet we didn't want to compromise our sound quality by too much either. We had already decided on going with a 4th order vented alignment and was hoping to stay away from the need to actively EQ the low end. So I wanted a fairly flat response curve knowing that the effects of room gain would also help out. Rudi has on his site a few response plots using LEAP modeling various enclosure volumes from 3.2 ft^3 passive radiator to 5 ft^3 ported/sealed as well as 8 ft^3 ported and sealed all with active high pass filters at 20 Hz. At a glance you can see why this driver appears to model differently than your average speaker. This is not your average speaker. Basically 8 ft^3 was too big and we didn't have the PR's to do the 3.2 ft^3 so it looked as though we'd have to be somewhere in the middle. After running the T/S parameters of the TC-15 through Unibox, I decided on a net enclosure volume of 5.00 ft^3 and a tuning frequency of 24 Hz. The graph to the right and below show the predicted response plot of this particular alignment as modeled by UniBox. Although the tuning is not as low as some designers would shoot for, I chose 24 Hz for a couple of reasons while understanding these tradeoffs: 1. The higher tuning gives a flatter response between 24 and 50 Hz as well as greater output between 24 and 50 Hz. 2. The higher tuning improves group delay by a fairly marginal amount. 3. The higher tuning reduces the need for extremely long ports which take up internal volume making the box bigger. By my experience, boxes with a slightly higher tuning have much more impact, punch and pound-for-the-penny, and therefore work great for movies. It has also been in my experience that the actual tuning frequency versus desired tuning frequency are never the same. The sub will most likely be tuned lower than calculated due to the added insulation for damping which isn't taken into account in the formulas for determining port lengths. So even though I'm shooting for 24 Hz, the resultant box I am sure will sit at 22-23 Hz. Which will still be perfectly acceptable. (Update July10th, 2000-Actual tuning frequency ended up being 23 Hz).

Planning the Aesthetics

Now that I've decided on a box volume and tuning frequency, what in the heck will I want this sub to look like? This is where it's all about aesthetics. I downloaded DeltaCad off the net and started messing around with it whipping up some designs and seeing what I liked. Every design I drew up I sent off to Sterling to get his opinion. After just a few designs, we came up with something we both really liked. Actually a design that is very traditional, nothing fancy. You can see the plans to the right as well as download the DeltaCad files so you can view them or alter them yourself. The box is made of 1" MDF. The dimensions sit at 21"W x 24.5"H x 26.5"D. Gross external volume of this box is 7.9 cubic feet. Meaning this box takes up 7.9 cubic feet of space in the room it will be going into. It is not a small enclosure. Net internal volume minus all bracing, ports, and driver sits at 5.02 ft^3 give or take a little.

The Bracing and Damping

The inside of the enclosure is optimally braced on four sides using 3 shelf braces placed at unequal distances from the front to the back. This is to reduce panel vibration modes at the same frequencies which can cause unwanted colorations in the bass response. By rapping on the cabinet with your knuckles you can hear the tone of the panels at each of the four dividing compartments. It kind of sounds like a tick tick tick tick, tock tock tock tock, dook dook dook dook, dock dock dock dock going from a higher sound to a lower sound. Since the first shelf brace sits back only 6", it will be necessary to cut that brace accordingly to account for the magnet of the driver. Although the magnet of the driver will not sit all the way directly inside this hole, this allows for the air coming from the vented pole piece to flow freely out and around the magnet as it should.

The front baffle has 1" MDF corner blocks all the way around the 14" cutout which support the baffle on the edges where its weakest. Two 11" MDF blocks run between the driver and the ports to support the baffle in that area for strength. The rear baffle has two diagonal braces that run from corner to corner to support the rear baffle. Also notice from the pictures the ample amount of padding on the rear baffle. Three layers of 1" thick egg crate foam were mounted to the rear baffle to help reduce direct front-to-back reflections which can be radiated easily into the cone and out into the listening environment. We want to keep all of the internal reflections inside the box and would like to dampen them as quickly as we can. The bottom of the enclosure has 2" of egg crate and the sides have 1" of egg crate while the front and top have no extra damping. This was mainly because I ran out of egg crate foam. If in the end I decide it needs more foam insulation, I may have to break down and get some more. The final amount of insulation and damping is still pending a good long listening test.

The Ports

There are two 4" ports that extend from the front baffle 20" deep into the enclosure. This is as far back as the ports should go while leaving plenty of clearance from the back panel. There are no elbows or bends to restrict air flow. The front firing ports was a design factor because the sub is intended to be place up against the side wall and back wall. There was no room for the sub to be placed 4-5" away form the back wall, so the front firing ports was a must. The ports are flared slightly at the front to help reduce what little port noise may already exist. The ports do not run directly parallel to the the bottom either. This was because of two reasons: Due to the large grill cover which will go over just the driver, I didn't want the ports to run into the back side of the grill's baffle. So they had to be low on the front baffle, really low. They sit only 1.75" from the bottom. Now on the inside of the enclosure the braces are 2" high which means they sit 1.25" higher than the bottom of the ports. So the ports by default had to be bent upwards by a total of about 2.0". Not only are the ports bent upwards, but inwards as well. This can only be seen by actually looking directly into the ports from the front. You can see that they bend slightly upwards and inwards. I expect no disadvantages in doing this.

Mounting Bolts & T-nuts

I was somewhat disappointed by TC-Sounds' choice of driver mounting holes. I was hoping to fit a large 1/4-20 size bolt through that thing to bolt to to my front baffle with some huge t-nuts. Unfortunately, unless I wanted to drill out the holes larger myself, the biggest bolt I could get through there were #10-32. Which seem rather small to me in order to hold this massive driver in its place. At 40 pounds, it's an absolute monster. Yet amazingly enough, the bolts are holding the driver to the enclosure just fine. One note with regard to t-nuts. Make sure that the t-nuts are securely fastened to your MDF baffle. You need to hammer and glue them in there good. Make sure that all 3 teeth are driven firmly into the MDF and then put lots of glue all around them. If for some reason that t-nut comes lose while your screwing in your speaker, you will NOT be able to get the driver out because that one t-nut will just twirl underneath the screwdriver, inhibiting you from removing that one screw. It's a pain, so just make sure that the t-nuts are securely fastened.

Building and Finishing the Enclosure

The entire enclosure was glued and screwed together using 2.5" drywall screws. I drilled pilot holes and counter sunk each screw and then filled in the holes with putty. The entire enclosure was sealed heavily with Liquid Nails. Including all the bracing and block and ports were covered in Liquid Nails to ensure a strong hold to their respective joints. After a lot of sanding with 120 grit sandpaper, I moved on to 220 and prepared the box for its first coat of primer. I went with Krylon's ruddy-brown sandable primer and put on three even coats while doing a wet-sand between coats with 400 grit. I then painted the box with a satin black polyurethane enamel made by Red Devil. This stuff is impossible to put on nice and even. Even using an expensive brush and the best technique that I know how, there were still a brush strokes that could be seen. I sanded down the first coat with 220 leaving a gray finish on the box and painted the second coat. The second coat turned out a little bit better than the first, but still not as good as I would have liked. So I sanded down both coats lightly with 120 sandpaper which removed most of the brush strokes without removing the paint itself. Then I took a little bit of 220 to the box and made it nice and smooth once again. Then I went the old fashioned route and did 4 coats of a satin black spray paint. As long as I've got the durable enamel underneath, I was hoping to get more of a sprayed-look that was even and flawless. Though spray paint usually isn't the finish of choice, I believe that it it's done properly, it can actually look really quite good. Especially with the enamel as a base coat, it should help provide a lasting and durable finish. So with the 4 coats of spray paint on top of the hard enamel, the box looked absolutely perfect. All the brush stroked were gone and the finish truly did look flawless. There certainly is something amazing about spray paint. Maybe it's because it's so easy and it goes on so evenly. I did use Krylon brand which I feel is the best kind of spray paint you can use. I did a light wetsand between each coat with 400 to remove the grainy feeling that spray paint usually leaves behind. Now that I had a totally black and very smooth finish, I went ahead with the clear satin polyurethane and applied 3 coats sanding with 400 between each one. The final coat looked outstanding. I had read that you can use a sheet of white printer paper to sand down a final top coat for a super smooth finish. So I tried it out and it worked awesome. It didn't take off any of the polyurethane but it did remove all the little tiny bumps that you could feel. So the final finish was very smooth and and looked very good. In the end I counted a total of 12 layers comprised of primer, enamel, spray paint and polyurethane. This finish is on there to last a lifetime.

The First Test Run

I popped the sub in just the other night and did a few frequency response plots and one SPL plot at 600 watts RMS. This sub sounds awesome! I did the measuring in my front yard with no walls and ceilings to affect the response. It's basically as anechoic as I can achieve at this point. And being outside, it's as close as can be measured to an anechoic response without actually using an anechoic chamber. The bass was unreal. It was clean and loud and that sucker was moving some serious amounts of air! The grass below the ports would flutter as far as 6 feet away. The response was very flat except for a small rise above 80 Hz which the low-pass filter will take care of. I figure the 3 dB down point at 19 Hz as indicated by the dotted red reference line. This sub rocks. That's about all I can say. We hooked it up into the home theater it will be used in the other night as well. I still have pictures of all that coming soon. The subs first performance was a few clips from Speedway. It was amazing. The rumble of the engine and intensity and thunderings of the low frequencies. It just shook you to pieces. Then we stuck in Ronin and watched that one part where they blow up the car with that bazooka. Wow! The only way to describe it is to say that all the clothes on your body to the hairs on your head vibrated and shook to the explosion. The whole room filled with a resonance that almost made your ears pop. In fact I think one time my ears did pop. Honestly though, this sub is winner. The bass hits hard and low and very, very loud. The amp pushing it is a THX Certified Parasound 1000 with a conservative 400 watts of power. This baby has no problem pushing the TC-Sounds.

One Down, One to Go

I've finally added the rest of the pictures. The finish on the sub turned out pretty good. It wasn't the easiest or simplest finish to do, but I believe it was well worth the effort. The satin finish matches the main and surround speakers perfectly as they are also a satin black. Finally, sub number one down and one more to go.

Future Modifications

If anyone decides to pursue building a subwoofer similar to this one, please note that if your particular application will accept it, there are a few things that could be done differently or even better. Size was a big factor with this sub. I was shooting for 5 cu.ft. internal while trying to keep the external dimensions down to a minimum. This required a little bit of give in certain areas of the enclosure which occupy space. The first thing I would change is the port size. If you can, use 3 or more 4" ports or even 2-6" ports. This will give the driver much more room to breathe reducing port noise and providing a much more ample and uninhibited bass response. The downside is that larger ports require longer ports which means the volume of your box will need to be much bigger to accommodate - while still shooting for 5 cu.ft internal. The longer ports may also require the need to use elbow pieces (which I wanted to stay away from initially). Three 4" ports would occupy an extra 0.48 cu.ft over just the 2-4" ports for the same volume and tuning. Two 6" ports would occupy an extra 1.45 cu.ft. So if you can spare the extra room, make the box a little bigger and use the larger ports. Another possible alteration would be to tune between 18-20 Hz. The lower tuning once again increases the length of the port and therefore increases the overall box volume, but if you can afford the space, then this might be another worthwhile modification.

February 28th 2001

Just finished sub #2 on this project. Here are two pictures of the almost finished product. Sterling got way too excited to start playing his new sub, that we haven't taken the time to stain it yet. So that will have to come later. From the first few initial runs, this sub sounds fantastic. He's got it connected to a B&K 220 power amp, with a Denon 3801 at the head. A complete Klipsch Reference Series speaker system completes the main channels, center and surrounds. We sat through Gone In 60 Seconds for its first movie debut. The sub pumped out every explosion and every engine with massive stroke and volume. Of course, this sub is going to need some serious break-in. The diaphragm is so incredibly rigid. It's like it doesn't want to move. Once broken in a bit it should open up.

Check out all the pics of the build and thanks for reading.