I’ve read that these three whistles (Overton, Chieftain, and Harper) are considered to be similar but it didn’t read in which way. Could someone elaborate please? Is it the back pressure? I think I’ve read that the Harper has high back pressure but what does this mean? Is it the higher the back pressure, the less air is needed or is the other way around? Thanks.
Strictly speaking Back pressure is the resistance encountered when blowing into a whistle. Normally back pressure will result in a whistle needing less air, yes. It actually makes it much easier to bend the pitch of a whistle without it jumping ocatves.
Some people on the other hand really like easy blowers. It’s personal preference.
I only played overton of those three but overtons do usually have very good back pressure unless you ask the maker for an easy blower
Overtons, Chieftains, and Harpers have similar designs – they’re aluminum with flat windways – the tubing is squared up at the mouthpiece, and a rectangular cross-section fipple is inserted. This leaves a wide but not tall windway.
I’ve played all three and owned a couple of Harpers. The Harpers are high backpressure, but nothing like the Overtons I’ve played. The Chieftains I played, several, but all in the same shop, had little backpressure and took loads of air. I suspect they were unusual, given what I’ve read here.
The Harper C is one of the few whistles I’ve kept since I got into the flute. It’s absolutely amazing.
The three are similar in mouthpiece/windway design and appearance, all are made of aluminum allloy, though Harpers are supposedly made of “gun metal” by gunsmith Steve Harper in the UK.
Overtons and Harpers have the same type of narrow mouthpiece, but Harpers require much less air than an Overton or Chieftain and you can play quite a bit farther into a tune without taking a breath. Harpers have good volume but aren’t quite as loud as an Overton or Chieftain. Harpers have a flared end. Many Harper owners have complained of intonation and pitch problems but the ones I’ve heard and played were good.
Here are some photos:
Harper:
http://www.thewhistleshop.com/catalog/whistles/highend/harper/plain/plain.htm
Overton:
http://www.thewhistleshop.com/catalog/whistles/highend/overton/sopranod/sopranod.htm
Chieftain:
http://www.hobgoblin.com/local/bigpic.php?ID=GR2230D
Harpers really aren’t a bad looking whistle, are they 
They’re handsome whistles, and the engraved version is even more striking:
http://www.hobgoblin.com/local/bigpic.php?ID=GX2263
Here are a couple Harper high D audio clips:
http://www.tinwhistletunes.com/clipssnip/Audio/05-06/UncleDanosPhilipK.mp3
Phil Hardy has a video on his Kerry Whistles site of him playing an engraved Harper:
http://www.kerrywhistles.com/dl.php?group=19# (scroll down to “Harper High D_Phil”
BTW, this thread has sparked my interest in Harpers again 