Can anyone explain why a whistle that sounds perfectly fine in a normal sized room sounds thin and reedy in the upper octave when played in a closed car? I almost trashed a perfectly good Acorn D because it sounded so horrible in the car - then I found out my nice 2-piece Clare sounded just as bad. Both are fine indoors.
It’s just acoustics; please don’t trash the whistle! The car is probably absorbing some of the overtones and bouncing back a reduced set of wavelengths, which sounds thin. Try practicing in the bathroom if you are curious, and you might get the opposite effect–I actually had a music teacher suggest this to me once, so I could better hear myself. All the more reason to keep a whistle in the bathroom…
R.
My sweetone sounds okay in the car, but I have a station wagon so maybe it’s due to more internal space.
It might be out of tune but more likely my cassette tape has stretched 
I’ve noticed that whistles respond to the acoustics on places very well. My shop is located among partially abandoned buildings, at night the whole place just echos so nicely. I’d like to have a group play a session there some summer night.
Most of the sound you here when you play is that which bounces off the objects around you and back to your ears. You hear a little direct from the whistle, and a little through vibrations conducted through your jawbone to your ears.
As you change the setting you are in, the sound you get back changes. For example, on a wide open space, you will tend to hear a very dead sound. Similarly, I have a closet at home full of clothes. If I play in there, any instrument sounds very dead. The reverse of that is to play in the stairwell of a large building, and pretty much anything sounds nice because of the reverb.
It’s for this reason that I always record a whistle before I reject it for me, as the sound I hear can be very different from the sound others around me hear. I’ve been very surprised at times by the results…
If you ever get the chance, and you really want to do your head in, try bribing someone to let you play in an anechoic chamber…
Richard