Paul Voight has to get the credit for first loading a speaker with a pipe.
After the war, Ralph West and Dr Bailey picked up the mantle.
The reversed tapered aperiodically damped lines grew out of work done at Radford, by Bailey, John Wright, and Irving M Freid.
There were very successful designs from Radford, IMF and especially from TDL as a result of this work.
PMC continues that tradition today.
Unfortunately for reasons I will never understand there is confusion in the minds of many between horns and pipes.
This whole business of mass loaded TLs has confused the situation even more and defeated the whole foundation of the reasons behind the aperiodically damped line, which is critically damped.
The we get the total nonsense, that once the pipe is critically damped, there is no port output.
Well as I posted above, my lines are critically damped as proved by the impedance curve. However drive a tone at reasonable volume in the range at which the line supports the driver and it blows out a propane lighter flame! They really connect to the room.
Mass loaded lines are not critically damped as seen by the impedance curve.
Further a resonant port will not give the driver such wide bandwidth support as a reverse tapered aperiodic line.
Also the mass loaded line flies in the face of the physics of the line.
One of the big advantages of stopped pipe is that pressure is very high towards the closed end and air displacement (air movement) is low. At the closed end air displacement is zero, which is obvious.
At the open end pressure changes are zero, but air displacement is high.
This is exactly what is required. This produces reduced and controlled cone displacement and couples the drivers to the room efficiently with large air displacement. And boy do my lines couple to the room without bloom.
Now when you put a resonant ported chamber at the end of the line, you are converting the end of the line to a high pressure zone.
I will never accept the mass loaded concept as a TL, in the way the original developers conceived it. And some of them I knew, especially those involved in the legendary BBC triamped TL monitors which also came out of that work.