Bipolar Panel Speakers

[SsZERO]

While searching for some ideas to make myself a set of awesome computer speakers, I came across this link:

http://www.decware.com/panels.htm

I wasn't able to find anything else like it, but I am curious as to how these speakers perform...and if they are as good as the guy said they are, I'd like to build myself a set. They look cool, among other things.

Can anyone provide me with some links to sites with info about building that type of speaker -- a bipolar planar speaker?

Thanks!

-= SsZERO =-

[Matt MacBeth]

I built a speaker to these. I used a coffee cup, and a speaker that is a very good fit to the cup. Used some metal tubing as the posts to hold the plastic material. I used a sandwich bag as the diaphragm. It's all sealed together with clear scotch tape. It doesn't sound bad.

[SsZERO]

Cool! So how exactly are these speakers constructed? Any plans/pics I can reference? What do you use for the motor/driver? Is it just a standard speaker driver with metal rods somehow attached? And is there a better material to use for the panel other than that plastic that wrinkles after 6 mos?

-= SsZERO =-

[Matt MacBeth]

I'll try to get some pics up.

I used a cheap 3" full range 4 ohm speaker firing up. It is sealed around the coffee cup.

I covered the front of the speaker with tape, except the opening between the posts (the sound leaves the speaker, goes through this slot, then enters the baggie). Then attached the bag to the poles and sealed it to the slot with tape.

I drilled a small hole in the coffee cup for the speaker wire to exit.

The posts that support the baggie use the speaker mounting holes for spacing.

[Matt MacBeth]

here's the coffee cup speaker.

[SsZERO]

Thanks for the pic and the info! So how does using this planar setup improve performance over using the driver alone? Wouldn't the sound quality of the planar speaker be limited by the quality of the driver you are using? And if you use a driver rated 50W RMS, does that mean you can feed the speaker 50W or does this configuration alter the driver's power rating?

-= SsZERO =-

[SsZERO]

Another question -- do the rods have to be metal? Or could I use wood or lexan rods instead? Do they have to be solid, or can they be like a tube?

I know I got a lot of questions...heh heh...I wouldn't keep asking them, but I just can't find any good info about this type of speaker on the net.

-= SsZERO =-

[Matt MacBeth]

Sound change - The speaker used is a low-distortion intercom speaker. It sounds remarkably well for music (200-7K frequency response). The bag limits the frequency response (looser bag gives better LF response, thinner bag gives better HF response)

The biggest change is the bipolar radiation pattern; it makes a more diffuse sound. It still 'sounds' like the same speaker, though. Sound quality of the driver is better in a direct radiating (normal) configuration, but is acceptable in the planar configuraton. I imagine that it could be quite good with some refinement (more attention to aerodynamics for the slot, and more rigid mounting - see the upright section below)

The 'uprights' can be made of anything; I used the metal, because it was already threaded. I would add a horizontal support across the top (you can see the bowing of my supports).

This is another fun one!

[SsZERO]

Yes, this is going to be an interesting project. I've selected two shielded Audax 3" 'full-range' drivers to be the main drivers. Since I will also be making a sub, I'll tune the speakers for better mid and high frequency performance and leave the lows for the sub to handle.

A few more questions, mostly about dimensions:

- Is it best to have the drivers firing UP or DOWN?

- What size should I make the slot? Should it be equal to the diameter/width of the poles I use?

- Does the size of the enclosure I use affect sound quality, i.e. should I try to "tune" the enclosure to a certain resonant frequency?

- How long should the poles be?

Thanks for all your help!!

-= SsZERO =-

[Matt MacBeth]

I made the speaker firing up, so that the magnet would be out of the way.

I made the poles the same height as the baggie, but there 'should' be some relationship to the displacement of the speaker vs. the panel area. Maybe just to be safe and limit distortion from the bag stretching 'non-linearly', the total displacement of the panel should be 5 (just a guess) times the displacement of the driver.

I made the opening to the panel the same as the width of the poles, but I think a flared opening into the panel would reduce distortion (turbulance).


If we want to put some sort of scientific measurement into this (sometimes that takes some of the fun out), tuning the panel (bag) to the enclosure (cup) and the speaker should be done. I would guess that we'd want to critically damp the speaker/enclosure/panel system.

What are you planning on using for the panel material. I wonder if a balloon would work better?