I have been wanting to build a dipole loudspeaker for a long time. There were two articles in Speaker builder that intrigued me a long time ago, one by Michael Allen titled “Flexible Dipole Woofer” (SB 2/1993), and a second dipole design by Ralph Gonzalez titled “A Dual-Baffle Balanced Reverberant Response” (SB 1/1996, AES pre-print). The Michael Allen article was a mad scientist approach; hacking up a woofer and gluing the former to a large mylar foam sandwich, very cool! Gonzalez’s approach utilized a dipole midrange to compensate for loudspeaker radiation pattern issues, the full-space to half-space transition. In 1999, Sigfried Linkwitz (SL) released the Phoenix loudspeaker on his Linkwitz Lab website: http://www.linkwitzlab.com. This really cemented the viability of dipole loudspeaker design for me. Mr. Linkwitz has a compendium of dipole theory and research for which he based the Phoenix’s design upon, and subsequently the Orion.
I’ve listened to the Orion speakers extensively at my friend Corey Lovett’s house, and the first characteristic that jumps out at you is the bass performance. It is very different from what I am used to hearing in a typical loudspeaker with omni polar bass response. Clean and tight is how I would subjectively describe it. There are are two reasons for this subjective sound quality. First, a dipole is a velocity source and not a pressure source like a closed box or vented woofer design, and second, the radiation pattern imparts 4.8dB (66.89%) less power into the listening space (http://www.linkwitzlab.com/images/graphics/beam-dpl.gif
). A dipole, being a velocity source, does not have the distortion issues that are created when a driver excites the resonances of a sealed or vented enclosure. My friend Chris provided me a good example of how a closed boxed system should be constructed to deal with enclosure resonances, and as you can see it’s not an easy task. The second photo is of Chris’ listening room, notice the extensive acoustic treatments needed for top notch sound reproduction from a typical hybrid radiation pattern speaker:
The Orion originally was configured with only one forward firing tweeter. After the Linkwitz Lab Pluto was developed, SL came to the conclusion that the Orion was missing something in it’s sound. The Pluto’s midrange seemed to be subjectively better due to a more even power response one octave higher than the Orion. SL decided to add a rear tweeter to make the polar response more even in the upper octaves, similar to the Pluto. This version is called the Orion+. Personally I think the Orion sounds better than the Orion+. The diffused sound field of the rear tweeter seems to defocus the image. It certainly balances the sound of the system but if I was to purchase the Orion I would not configure it with the rear tweeter.
I know that SL listens to a fair amount of orchestra and chamber music. The Orion seems to excel with this type of music, with rock and pop however, it seems to fall short. I still regard the Orion as an excellent loudspeaker in all regards. Soon my friend Corey and I will be modifying the top end response of the Orions for even better power response. Based on my experiences with the Orion I knew that dipole bass response was the way forward for my design, and dipole midrange/treble response was not optimal in my view.
I wanted to develop a speaker that was unique, compact and of course functional. As you will see, there are few compromises with my design. I selected 4 Acoustic Elegance IB15s to handle the low bass in the W-Frame enclosures. I wanted a driver with plenty of excursion (18.5 mm) and a large surface area, 15", and a high Qts, and since I needed 8 of them, inexpensive. John and AE speakers is known for building high quality inexpensive drivers, $800 for 8 15s is an unreal price. For the mid-basses I picked up four Usher 8848Ps. These drivers feature composite paper cones, a huge machined aluminum phase plug and a very low distortion motor. To keep the off axis response flat through the mid band I had employ the use of a midrange. There seemed to be only one logical choice, the Dayton RS52AN-8. This 2" midrange is unparalleled at this price point. A huge copper capped pole piece, aluminum dome, and a damped rear chamber. The ribbon tweeter is a RAAL 70-10D, this tweeter will be modified to increase the off axis response slightly.
[This is an old design that has never been tested. See tweeter tests for RAAL distortion graphs. Spoiler alert, the RAAL sucks.]
Here are a few 3D renderings of the design (click to enlarge the images):
Heritage Dipole Model
Side & Top Panel Removed