> I long ago met a unique ULF sound generator of very high acoustic power
> level.
> I've described it on-list before.
> I only ever heard it and never saw it but this is what I think it was:
>=20
> Two diesel electric locomotives run up together in an engine shed on a co=
ld
> winter morning.
> (Temperature and season optional probably).
> Shed probably corrugated iron. Acoustically somewhat constrictive, but
> flexible at low frequencies.
>=20
> Set engine speed of both locomotives to the same speed with governors.
>=20
> Engines run ALMOST at correct speed and hunt gently around correct speed.
>=20
> Pressure waves from acoustic signals mix in confined space to produce
> difference frequency.
>=20
> SO:
> We lived near what was then probably NZ's largest shunting yard.
> Lie in bed on said cold winter morning at about 4am in house about 100
> metres from engine shed.
> Whump .... whump a whump a whump ..... whump a whump a whump a .........
> Loud softly explosiveish waves repeating at sub-Hz to a few Hz - maybe li=
ke
> somebody hitting house gently with a 10 ton bean bag.
> Lasts for maybe 10 minutes on and offish.
> Then stops suddenly. Until tomorrow.
>=20
> Fun, after the first few times.
>=20
>=20
>=20
>                Russell
>=20

Doesn=92t that damage the house ?  Maybe shake some fasteners loose ? =20
GID
--=20
http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive
View/change your membership options at
http://mailman.mit.edu/mailman/listinfo/piclist
.