The best speaker you ever heard?

Yes, ability to pass a square wave is also a claim to fame for full range walsh drivers like those found in original OHM Fs and As.

That was their strong point. They had other weaknesses, mainly reliability and ability to go loud.

Newer OHm Walsh line speakers address those weaknesses however their 2 way design using the wide and not full range Walsh driver also now compromises ability to pass a square wave to some extent as a tradeoff from what I have read.

Is there a full range speaker that can pass a square wave without other significant compromises available today?

Duntech always touted that the Sovereign and Princess could accurately reproduce a square wave, and had the graphs to back up the claim. I believe they are still in production, though I have not checked their website for a while. Dunlavy as well, as was noted above, though they are no longer in production, sadly. I'd be curious if other speaker manufacturers make this claim.

Dunlavey used to be with Duntech , prior to starting his own speaker brand.

I think it was Duntech as set up in Australia with government support. When that support was lost, John moved to Utah and got government support there, becoming Dunlavey. I do know that Duntech for a while continued the Sovereign under a different name. I don't think either company still exists. John died in 2007.

Sometime in the mid 1990s I met with John Dunlavy at his factory in Colorado Springs. To the best of my knowledge, they were never located in Utah.