Photo Courtesy of Laurence Platt
Photo Courtesy of Laurence Platt
After posting my Lowther DX series ML TL project, I started to get e-mails asking about the possibility of designing a ML TQWT style enclosure like the one I had built for the Fostex FE-164 driver. People like the tall TQWT style of enclosures, some favored the rectangular front baffle while others liked the mirror imaged trapezoidal design. I ran some simulations which showed a lot of promise. I provided these simulation results, via e-mail, to a number of interested DIYers. Several people have subsequently made this enclosure and some examples of similar designs can be viewed in my gallery.
Recently Laurence Platt built a pair of his own design, based on the simulation dimensions, and was so enthused about the results I decided to add a second virtual project to the site. I have not built or heard this design. But the feedback received recently was so positive I am comfortable adding this to my list of projects.
The ML TQWT enclosure design can be tricky to build with the angles involved but it is a real eye catcher for anybody visiting your home and seeing your audio set-up. The MathCad ML TQWT simulation for the Lowther DX3 can be viewed in pdf format. Any of the Lowther drivers will work with slight adjustments to the baffle step correction circuit. One of the features I really liked about this enclosure is that it can be built as shown in the drawing for Option 1 or the drawing for Option 2 depending on your style preference. Another option is to design a geometry that satisfies your own tastes, Laurence Platt designed and built his enclosure with double slanted sides. Any of the Lowther eight inch drivers will work allowing an easy upgrade path later to one of the more expensive models.
The final piece in the design is the correction circuit. The correction circuit is required to get a balanced SPL response. Leaving the circuit out of the design will result in recessed bass output and an overpowering midrange response. A range of parallel resistor values can be tried when matching the speaker to the amplifier. If you are using a low damping factor tube amp, then the right resistor value is probably near the low end of the range. If you are using a high damping factor solid state amp, then the right resistor values is probably near the high end of the range. Don't be afraid to experiment with the value of the parallel resistor to tune the system's SPL response to your amp, room, and personal taste.
Again, I have titled this a virtual project because I have not actually built or heard the design. But based on the feedback below, I am comfortable adding this to my list of projects. Hopefully one day I will have the opportunity to hear one of these ML TQWT designs.
The taper quarter wave transmission line with Martin King's baffle step correction circuit is by far the best approach I have had to date.
The step correction circuit can be reduced to a series inductor of 2 mH with a switched damping resistor (8, 10, 12, 15 ohms) in parallel. There is no need for the additional capacitor with the DX4’s, just keep the zobel network and use high quality R’s C’s and L’s, I found the Alpha Core inductors sound the best in this application.
You basically can move the top and bottom cross sections around to get the final shape you need keeping the height relationships the same. So the relationship between the port, driver, top, and bottom remain the same. I did not have to tweak the port size at all.
My first impression was that the bass was very light, this was because I had been used to the DX3’s in a reflex enclosure which gave a very uneven bottom end.
I was able to upgrade to DX4’s this together with changing to a good solid state amplifier made all the difference. The DX4’s are extremely fast and reveal all things upstream. I am very pleased with the results and have no interest in making any other speakers at present. Because of their ability to resolve details I am now able to look much closer at DAC designs etc. Originally I felt that the Lowther’s were quite edgy. Then I tried a different DAC and found that the original DAC was the source of the harshness.
I have tried the different phase plugs and find the original bullet plug gives the best results in my room with my tastes. I have made all sorts of speakers Edgar horns, Kef B139 transmission lines, Ted Jordan units in IB’s. The DX4’s in Martin's design is by far the most accurate approach I have been able to make at home.
Although on paper you would think that the limited amount of travel from the DX4’s would be a great restriction in the amount of bass you can accomplish without horn loading. I have not been able to find their limit.
Hope this is of some help, please remember this is only my limited view of our audible world and as such does not offer any guarantee of audio nirvana.
Enclosure and Correction Circuit :
Conclusion :
Review by Laurence Platt :