Planar Speakers and Diffusors

Hi Ozzy,

I have been using Line source Dipoles (planars) since 1978. I owned Apogee Divas for 6 years. I currently use Sound Labs ESLs. 

You are headed in the right direction, but someone fed you the wrong information. 

Line source dipoles radiate sound in a "flat" figure 8 pattern. By "flat" I mean there is no sound radiated up or down. In your case the lines source characteristic ends at about 250 Hz. Middle C is 256 hz. For the best imaging you need sound absorption behind the speakers. You want to kill the back wave as much as possible. Diffusers are simply going to increase the number of early reflections, confusing the image more. I use 4" acoustic tile behind the speakers. It is very effective above 250 Hz and dirt cheap. It also looks cool if you get the pattern right. You can get it on Amazon.

At first you might think the sound has become duller, less air, whatever. But, if you are paying attention, voices now hang, well defined in space. Any hint if sibilance behind female voices is greatly reduced or gone altogether. Everything is in better focus. The third dimension becomes palpable. The glare is gone. If you take the tile down you will not believe what you had been listening too!

The problem below 250 Hz is much more difficult. As the wavelengths get longer they are harder to stop or deflect. The wavelength of 250 Hz is about 1 meter. 

Another issue with planar speakers, especially full range or two way types is they HATE making bass. They will do it but it distorts everything else the driver is doing and wastes a lot of power. You can lower distortion and increase your head room by as much as 10 dB by adding two subwoofers and a two way crossover with digital bass management. People think it is difficult to match subs to planars. Not true at all if you do it correctly. It is tougher, but it can be done to great effect. You have to cross up around 100 Hz with a very steep slope of at least 8th order and match the launch time of all the drivers. This can only be done digitally. it is like adding a turbocharger to your car. Two Martin Logan Balanced Force 212s and a DEQX Pre 4 processor would be amazing.

@ozzy That is incorrect. The back wall reflection is their one big weakness. The design is so successful because it limits reflection from everywhere else except the back wall. Instead of having to worry about four walls, the floor and the ceiling you only have to worry about the front and rear walls. Line sources also project sound better. 

Sound diffusers are best used to kill echos, but again they only work well at higher frequencies. Bass traps are a total and complete waste of money. Four subwoofers is the best solution for bass problems. 

Analog crossovers, as you noticed are insufficient. The crossover has to be digital to do everything it needs to do. The problem is now you need four DAC channels instead of two. The MiniDSP crossover is excellent except for those DACs. You can use a MiniDSP SHD Studio and two stereo DACs, but that is going to cost $6 K. The DEQX Pre 4 is way more powerful than the MiniDSP, has fabulous room control functions and great digital bass management. It also Streams and has a MM phono stage designed by Dynavector. I own the Pre 8 which is the same unit with a 4 way crossover. You can triamp your speakers and run subwoofers. I just got a pair of step up transformers. Once I build the complete MC transformer I will comment on the phono stage. It will be a bit as I am still waiting for the Permalloy shielding.