Titanic T1503 MK III Design Comparison

Introduction

As a do-it-yourself speaker builder I was excited to get another kit in hand. With this being a subwoofer kit I decided to take a slightly different approach to the review.  Instead of just putting it together and then listening and measuring, I wanted to take more of a design approach.  First, I used the published driver parameters to design two different types of boxes using WinISD. I have BassBox Pro but WinISD has one significant advantage besides being freeware; it has a section where a parametric equalizer can be used which is precisely what is available with this kit. Next, I compared the published driver parameters with the parameters obtained using the Woofer Tester (WT). Then, I used the WT parameters with the given cabinet size and compared that design with the ideal design. Finally, I measured the completed T1503 kit from Dayton Audio for a final comparison to the two computer designs. What I didn’t do is actually build the ideal design given by WinISD but as you will see it was unnecessary.

Design Comparison

With the published specs from Dayton, two designs were run on WinISD. One is the closed system design of the provided cabinet (yellow) and the other is a vented system (cyan) for comparison. The -3dB cutoff frequency for the closed system is about 40 Hz. I tried applying the equalizer using different frequencies and different boosts and cuts to try and get a better low end cutoff but it really didn’t change the shape of the curve, it just shifted it up or down. That result signifies that the closed box really puts a lot of control on the driver.  The default design that WinISD gives with a flat response is very close to the kit’s cabinet; with only 0.5 ft³ difference the curves are nearly identical. Keep in mind that the amplifier’s volume was subtracted out but not the brace. Also, with the foam provided in the kit a small amount of volume increase will be seen. On the other side of the coin is the vented system and the Titanic Mk III can go either way. The volume for the vented system though, is much larger. WinISD’s recommended volume for a cutoff of 22 Hz was 6.6 ft³ which I believe is just too big. With a volume of 5.2 ft³ the cutoff is 24 Hz which is a fair trade off even though the size is still fairly large. The graph below (cyan) shows this box response.

The frequency cutoff of the design may be of large importance but there are other factors to be considered that are just as important. Namely how the woofer will be placed in the room and its safety performance. Woofer placement can be seen further down in this review. By safety performance I am referring to how the closed system dampens the woofers movement and doesn’t allow it to bottom out. I have some personal experience with vented systems and over driving the woofer beyond its Xmax.  I think it was very wise for Dayton to provide a closed box system especially given a 1000 Watt amp with an equalizer that can give a 6dB boost. I have the same amp in my own subwoofers and have bottomed those out with a 23mm Xmax woofer. Also, most people do not want large cabinet subwoofers.

 Next it was time to get Thiele and Small parameters from the driver. I had some trouble getting my Woofer Tester II working on my new computer so I acquired the Woofer Tester III. The WT3 is leaps and bounds better than the WT2. It is much faster and it plots a lot more data points. If you do a lot of speaker building I highly recommend it and if you already have the WT2 you should consider upgrading. As seen below, the published Thiele and Small parameters have some differences from the measured parameters but they are very close.

In comparing the published spec design with the measured spec design it can be seen that there is virtually no difference. You can also see that the design frequency cutoff is around 37 Hz which doesn’t seem great for a woofer of this size but wait to see how it performs in the room. The dark blue curve is the Woofer Tester specs and the cyan curve is the Dayton published specs. Even though the measured driver parameters are different from the published ones there is virtually no difference in the end result.

Here is a curve to show the cone excursion of the 3.2 ft³ box. The vertical scale is in millimeters and the red line at 20 is the Xmax of the driver.

If the driver is put into a box at almost twice the size, 6.2 ft³, it can be seen how much the cone excursion increases and that the smaller box dampens the woofer.