[HAL]

Been working with the FPS planar drivers from Parts Express and built a DIY open baffle line array with 6 planars per side.  These mate to the 6x12" servo sub arrays.  The baffle is tall enough for 10 planars per side.

Used my digital crossover to design a time domain beamformer for the array with every driver having it's own power amp.  Pairs of drives receive the time delays to operate as the beamformer. 

So far the listening results have been very good.  Next on to the measurements.

[Jazzman53]

What we can see looks pretty awesome... got any more pics?  closesups?

[HAL]

Here is a closer look at a single channel.

[Jim G]

HAL,

I'll be interested in seeing your measurements and your evaluation of these planars.  Real data and a listening experience will be key to judge their suitability.

On another forum I studied these planars a bit when they came out.  I found their specs have significant limitations that concern me about their capability to yield adequate performance.  Read my comments in this thread: 

http://www.diyaudio.com/forums/planars-exotics/262958-fps-planar-speakers.html

Jim

[HAL]

Jim,
The six element line array with the beamformer working gave this result when measured in front of my listening position.  There is a before and after plot using Math Audio's Room EQ software.  The HF rolloff is at 9.5KHz, so the array without EQ needs a tweeter array.  The Flat EQ needed would reduce the overall level 18dB, and really limit the dynamic range.  If I added a tweeter array, that would help significantly. 

In the line array the cylindrical wavefront will loose 3dB/doubling of distance, so that would give back 6dB of SPL at the listening position of 4 meters as compared to a spherical radiator.

[Jim G]

HAL,

Their limited dynamic range because of inherent low SPL rating, low maximum power capability, and equalization requirements doom these planars in my opinion.   

I like your beamforming ideas and the ability to adjust per individual drivers but these transducers have to overcome a lot of shortcomings. 

Perhaps the Christie (formerly B-G) Neo 8 planars would yield better results but even the Neo 8 needs augmentation for low frequencies and support for the treble range before you have a full range speaker.     

Jim
   

[HAL]

The next version will have BG Neo3-PDR's and Neo10's in a line array.  Already have the Neo10's and waiting on the new baffle to be finished.  Probably will not have the Neo3-PDR's until July.

[HAL]

Will be talking about the new DIY planar line array in this thread for anyone interested:

http://www.audiocircle.com/index.php?topic=142716.0

[Davey]

Why is it even necessary to "curve" the arrays with time delays?  I assume you're just applying more relative delay to the driver pairs as you get nearer the center?
It's much extra complication for an obtuse objective...IMO.  Your ear/brain will "process" the lack of "phase-coherency" and comb-filtering and make good sense of it regardless.  Part of the advantage of line-arrays is that the cylindrical radiation pattern DOESN'T "focus" to a designed measurement point.

Also, I think it's a stretch to label this "beamforming."  (You're talking to an old Sonar guy.) 

Cheers,

Dave.

[HAL]

Davey,
I was sonar as well, and this beamformer was in my Sonar processing 101 class text. 

No curved array, just a line. 

[Davey]

Obviously not physically curved.  That's why I put "curve" in quotation marks.
Maybe you should elaborate on what, exactly, you're doing.  If you're applying time-delays and/or phase changing then it's not "just a line" any longer. 
Your line has height but no width so, by definition, you can't effectively "steer/form" horizontally.

But as Jim Griffin noted, if the drivers themselves are not up to the task, it makes little difference what type of electronic wizardry you through at the project.

Cheers,

Dave.

[HAL]

Davey,
This is time domain beamforming in the vertical direction at the listening position with just time delays on pairs of drivers since the line is symmetrical around the center of the array.  Very simple beamforming to give 13dB down sidelobes on either side of the main lobe axis in free space.  I also applied speaker and room correction to make the response flat at the listening position using Math Audio Room EQ.  This was a trial of both those techniques. 

This was really a test of the ideas to see what would happen with this technique.  The test was a success, as I did not hear any comb filtering problems in the vertical plane or horizontal plane.   The horizontal plane had a wide response pattern as I was hoping.  That specific FPS driver had things I had liked over the years in desktop speakers and was a fun thing to try as a line array.  The array would really need a tweeter array to increase the capability, but since I had already started getting the BG drivers, this was just a test platform. 

This is a very simple baffle on purpose for ease of construction and modification if needed for trials.  Also proved it was sturdy enough for the next drivers.

One thing that was an interesting observation is that the beamformer kept the center image from getting to large as other planar systems I have heard.  That was something I wanted to hear, and it seems to work well.  These went low enough in frequency it was easy to mate them directly to the sub array as well. 

I just look at this as an RDT&E type effort to try ideas.  I am good with the outcome and now off to the next design that should be a large improvement over this. 

[Jim G]

A few comments on your experiment. 

I like planars (or ribbons if you can afford them) arrayed in the vertical plane as they maintain great horizontal dispersion.  They also attain good vertical dispersion (as I explain in my Near Field Line Array White Paper) as you essentially have  continuous vertical coverage.  This 'fill-in' dispersion between the drivers is a good thing for rectangular (or slot drivers such as planar or ribbons) as you do not have the comb-lining which is experienced with circular drivers because of their center-to-center spacing.  Figure 10 in the NFLAWP shows how this fill-in dispersion mitigates the gaps between the  rectangular drivers.

Also I'm with Davey on whether you will have improved performance with beamforming.  If you feed the array with the same power level and no time delays to each driver in the array you should hear that with tall line arrays you have a coherent phase front within the near field region (see the NFLAWP for how to calculate the near field to far field transition distance).   What I find that if you listen (do a knee bend and then rise to standing height a few feet in front of one of the lines) is that you hear constant sound that follows your ears as you move up or down the line because of the precedence effect.  You don't any hear sound that comes from the extremes of the array but only the closest drivers to your ears as you move.   Of course time delays or beam forming will impact your far field experience.  It is all about whether you listen to the array in the near or far field in your listening room.                   

http://www.audioroundtable.com/misc/nflawp.pdf

Good luck!

Jim

[HAL]

Enjoyed the paper!

Looking at the paper, the criteria you use for nearfield-farfield would put me in nearfield listening at 4 meters with a 2.2 meter segmented planar array. 

No impedance issues for series/parallel driver combination, since each planar driver has it's own balanced input Class AB amp module.  Those and the speaker cables are completed. 

The DSP crossover has 8 channels and they are all independent and user definable.  Since the time domain beamforming is an easy thing to do and already implemented, it is easy to try both by setting the time delays to zero for all drivers and then try the time delays for the array.  As long as I get a correction range of 10dB or less, should work well with the Room EQ software with just the BG Neo10 planars.  The new baffle already has a slot for BG Neo3-PDR's if the correction is not successful. 

Thanks!  So far a fun project.

[HAL]

The impulse response of the FPS array with the beamformer running was very clean.  This was with 6 drivers running.

[Speakerbldr7]

Awesome!

[HAL]

Thanks!

At this point all the FPS drivers should be here this week.  The last batch arrived with planar damage from bad packing.  They went back and new ones are on the way.

No longer going to use this FPS array, but these drivers make nice PC stereo speakers from a product that I bought years ago.  They just need a woofer for below the planar rolloff.  Might be good to stack 2 for improved power handling for nearfield use with a small baffle.  The same style as the larger baffle I built, but only 2 high would be interesting to try. 

For another day.