For the last five years I have been working on a new dipole speaker system. I have named it BB(That stands for Big Baffle). It consists of a Raven R2 ribbon tweeter built by ORCA, a Focal Audiom 7K2 midrange, and two Dynaudio 24W75X upper bass drivers. Neither the Focal or the Dynaudios are still being made, but there is a very close replacement for the Focal 7K2 in the 7K 6411. To round out the system and cover the range below 50 Hz, I used my Bipole Sub, affectionately called "The Ugliest Subwoofer Ever Built" which has two Adire Audio Shiva at opposite ends of a Sonotube for several years. After hearing the bass produced by Siegfried Linkwitz' Phoenix Dipole Subs, I just had to have them. I built a version of these using Lambda Acoustics SB-12 drivers and have retired the Ugly Sub. After living with those for a while I decided I needed more and upgraded to the Adire Audio DPL-12 woofers. These are purpose-built for dipole use and have very high excursion and minimum aerodynamic noise. Then to make them real special I got a Stryke 350 watt plate amp, cut it in two and mounted it inside the Phoenix sub enclosure. The fun never ends! The section covering all the iterations of these new subs is at Dipole Subs.
The upper bass/lower midrange Dynaudios use an active crossover. It is dedicated to this driver alone, and has a high-pass at 100 Hz and a low-pass at 700 Hz. This was built using a John Pomann active crossover kit and a power supply I picked up at Alltronics, a local surplus store in San Jose, California. When all the development work is done, I will upgrade this breadboard circuit with a proper circuit board and a low-noise power supply. The Focal midrange uses a passive high-pass and low-pass. It crosses to the Raven at about 2200 Hz.
I originally used a 12 inch Shiva from Adire as a lower midrange/upper Bass. I was always planning to replace the Shiva with one or two of Nicholas McKinney's Lambda Dipole Drivers. When these drivers got delayed for several years, I bought 4 Dynaudio 24W75X woofers. These have a rather high Qt of about 0.9 and seem to make pretty good dipole mid-bass drivers. The upper bass sounds much cleaner with these drivers and I'm really glad I made the switch. The Shiva's really don't work too well above 200 Hz .I ordered some 10 inch sealed box woofers from Lambda to use until the actual Dipole drivers arrived, but once I got them I realized that they were just too big for the baffles I already had made. I ended up using the sealed box woofers in my car (WOW!). I finally received the Lambda Dipole drivers in the Summer of 2002 but had gone down a different path by then. These are the most beautiful drivers I have ever seem and I am planning a new project that will showcase these.
Also apparent in the pictures is the fact that I started out with the Focal T120 tweeter. It was the efficiency of the 7K2 that drove me to opt for the Ravens. I just couldn't see myself padding down a great mid like this to match a tweeter. The Raven is the only tweeter I know of that is as efficient as the 7K2. It sounds wonderful as well.
I decided to wait until the final baffles were complete before completing the crossover development since changes in the baffle really do show up in the crossover. I settled on a baffle design based on a few things I learned during the prototype stage, conversations with lots of people and of course something that would be EXTREMELY difficult to build. With that in mind, I came up with a design that uses MDF quarter-rounds from Anderson International Trading as the edges on a baffle of about 50 inches high and 14 inches wide with one curved edge.
These pictures show a little of the evolution over the five years I have been working on this project.
For another page full of pictures of the completed speaker go to Photos
The Dipole Bass cabinets are featured at Dipole Bass
What follows is a complete story of the development of these speakers. I have attempted to explain how I did the design, why I made some of the choices and the results. First I should include a few construction pictures. I put them on a page called Construction Photos.
After construction was complete I did a whole day of impedance measurements to reduce baffle vibrations. This information can be seen at Vibrations.
Don Maurer and I have done a lot of research to investigate polar response of Dipole speakers. The results of this study can be found at Polar Response Study
Now I will describe the development of the crossover between the Raven and the 7K2. I used Liberty Audiosuite LAud to measure the raw output of the drivers. I imported this data into Calsod 3.1 to develop the crossover. Calsod is a very powerful program that can model complex speaker systems with amazing accuracy. It can do passive and active crossovers and can simulate all manner of loading, reflections, interactions and other things. It can also use actual data obtained from any of the common speaker measurement systems. This is a much more accurate and much simpler method. A trial crossover network is fed into the program, usually calculated from a cookbook formula, and Calsod displays frequency response, phase response and impedance for the raw drivers, the filters, and the driver with filter. These can be combined to get the total system response.
Using a cookbook formula rarely results in an acceptable frequency response, however, and even less often produces a decent phase response. So, then the Calsod optimizer is called up. This is where the real fun begins. Any or all of the filter components can be let loose in the optimizer. A target SPL level, crossover type and slope, as well as the crossover frequency are specified. Then the optimizer is turned on, and a few iterations later Calsod spits out new component values that produce a perfectly flat, phase aligned crossover. Yea Right!!! If only it were that easy. Below I will describe the process I went through to design the crossover for BB (that stands for BB King, one of my favorite guitar players). I'll start with explanations of how the process works using some simple data, then I will get specific and go into the actual data and crossover.
Right now, the actual data section is not quite ready, so only the basics are covered.
Now on to Data Collection.
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This page was last updated on January 20, 2003
Steve Houlihan
sho@starband.net