Mid-range frequencies are no where to skimp on. The mid-range speaker produces the majority of the frequencies that our human hearing is most sensitive to. The heart and soul of any great sounding system will have drivers that can admirably perform at mid-range frequencies. Those being ~300hz-5000hz. It just so happens that planar drivers shine at this frequency range.
A quick lesson.
Planar Transducer- A type of driver in which the diaphragms are flat (singe plane).
These are flat rectangular shaped drivers that radiate in a bipolar behavior. Nestled inside the flat enclosure is a flexible membrane, with a voice coil woven through out the drivers surface (diaphragm). The current in the voice coil interacts with the magnetic field surrounding the diaphram causing the membrane to vibrate, creating a speaker.
The advantages of these drivers are that; when they move, all of the air they move is in phase, because it is all moving forward and backward in the same plane. This is different from the more commonly found conical driver where the diaphrams have some height or depth when they move, due to the geometry of a cone. In turn when the conical driver moves, it compresses air over a distance, this compression corresponds to the cone height of the driver. The compressing of the air by a driver is a behavior commonly referred to as “cone smear” – essentially a disruption in sonic energy.
Another major difference between conical drivers and planar drivers is simply how they are driven. Planar drivers are driven over their entire surface area, where a voice coil is woven throughout its flexible membrane, making up the planar control surface. Conical speakers are typically driven from their perimeter through voice coils. The walls of the conical diaphragm will flex as the force of the voice coil act on the diaphragm. In a planar driver everything is propelled uniformly, in sync across the drivers geometry. Voice coils typically introduce something called “phase shift” over the speakers operating range. Phase shift is due to the inductance of the voice coil. Planar drivers have virtually no induced no phase shift by their drivers because they do not have cylindrical coils.
In summary, geometry, lack of time smear, and minimal phase shift account for the majority of the purity or ” audible image” planar speakers can provide. The rest lies in the dispersion pattern.
Planar speakers have radically different dispersion patterns from round speakers. In particular their off axis response is phenomenal. It is wide and typically remains relatively flat across the desired frequency range.
This wide dispersion along with the traits mentioned above in my opinion, make the planar transducer a superior choice over a conical driver at mid-range frequencies. This is the main reason why I want to use them in my car audio application. In car audio, normally the enthusiast doesn’t have much of a choice as to where his/her speakers can be mounted, unless they do some sort of major modifications, as speakers are rarely where the audiophile wants them to be. In my case some modifications will be necessary as well. Due to the rectangular, flat shape of these speakers, I plan to mount them in the A pillars of my car at about drivers ear level. I will feed them about 80-100 watts, cross them at 700 hz and 8khz.
The speaker I have selected for the job is the
Bohlender Graebener Neo8-PDR Planar Transducer
Dimensions: 7-7/8″ L x 3-1/2″ W x 1/2″ D
“The Neo8PDR does not have heavy voice coils, spiders, glue joints, paper cones and surrounds so there is virtually nothing between the electrical signal and the sound – just an almost weightless diaphragm. Hence these planar transducers do not have cone break-up resonance with associated distortion, phase incoherency or signal smearing that is common for conventional drivers. This allows the Neo8PDR to deliver clean, airy, transparent sound that is inherently natural and musically pleasing.”