So what is a Magnepan 30.7? It is a four-panel (two panels per side), line-source, ribbon/quasi-ribbon loudspeaker system of considerable width (a little under four feet across per side!), height (about six-and-a-half feet), and just a couple of inches in depth. As the four panels that comprise a stereo pair are completely separate (not hinged to one another, as the panels on each side of the Tympanis once were), you will have considerable latitude in placement, which is both a blessing and a curse. (With great latitude comes great responsibility).
Magnepan’s Marketing Manager Wendell Diller has been taking the new 30.7s on a tour—a road trip to visit dealers all over the U.S. with initial stops in The Pacific Northwest, such as Seattle, Portland and Acoustic Sciences hometown of Eugene, at Bradford’s Home Entertainment. As you might have guessed, this quartet of sizable panels—two per channel comprising a four-way system—requires a rather large room to work their magic, and Bradfords does not have this type of room..
Enter Acoustic Sciences Corporation. Bradford’s Home Entertainment reached out to us as they had concerns in regards to the size of the room vs. the size of the speakers, and how to maintain the beautiful sound that these speakers produce.
Here’s What ASC Did:
Bradford’s Hi Fi store is 70’ long 18’ wide and 10’ tall. Acoustic tile overhead with a lower entry soffit and glass front, street wall and double entry doors. About 33’ into the showroom a storage space was created about 4 1/2‘ wide down the remaining length of the showroom. The showroom is walled off at the back, some 55’ into the room, in with two offices, each 15’ deep. The front desk is L shaped and is composed of two 7’ straight sections, joined together by a ninety-degree turn. One end is at the wall and the other end is out in the showroom with a half round cylinder.
The basic strategy is to rearrange the room. The glass wall will become the front of the listening room. The face of the storage room, 33’ in from the front glass wall, becomes one side of the back wall of the room. A similar wall needs to be created on the other side of the room, opposite the face of the storage room, similar in size and acoustic properties, which will leave an open 6’ wide doorway in the middle of the back wall.
Cabinets and other objects will be arranged to create the effect of a section of back wall that matches the reflectivity of the face of the storage room. The display desk will be rearranged to create the effect of a section of back wall, parallel to the face of the storage room.
The goal is to use the two back walls, one real and one fake to give the impression of a room that is 18’ wide and 33’ long, with a 6’wide opening (a bass vent) in the back of the room which leads to a second reverberant room. The office doors at the very back can be opened or closed to dial in the base modes and reverb level. Acoustic objects will be added to the face of the storage room and on top the front side of the display case to further dial in a similar sonic signature off the two back corners of the listening room.
Dipoles produce a semi flat/cylindrical figure 8 shaped wavefront with the front side being in phase and the back wave being out of phase with the signal but otherwise identical. Early reflections off the side walls are generally discouraged by adding sound absorption, otherwise they mix with the direct and create a foggy direct signal.
In addition to minimal early reflections, time delayed lateral reflections are beneficial. They cause a sense of spaciousness to be developed in the listening area. It is a specific type of signal, low level, -10 to 15 dB down from the direct signal, delayed 25 to 60ms and arrive at the listener’s ears from the sides, as if due to lateral reflections.
A spaciousness type of reflection can be derived from the back wave of the dipole. By splitting the back wave in half and redirecting the splintered fractions of the back wave to either side of the front of the room, a set of side to side multiple reflecting side to side reflections that slowly “walk” down the length of the room to eventually engulf the listener with side to side sounds that are derived from the direct signal, time delayed and amplitude reduced….
Another aspect of dipoles is the strength of the front wall reflection in the bass range, which needs to be minimized. Phase add and cancel effects are one reason to minimize bass wave reflection and another is so that the huge lightweight diaphragm is not pushed around by the reflection off the front wall. TubeTraps along the front wall, with the diffuser panels oriented into the room is the traditional way to manage the back wave bounce. Typically four 6 to 8’ stacks of 16” TubeTraps are more than sufficient to minimize the low frequency reflections and to establish treble range lateral diffusion.
This event happens:
Friday, March 16
4:00pm – 8:00pm