Puma mystery

Honest John Back Room » Technical matters
View Threaded
Wed 21 Sep 2005 09:39
Puma mystery - Archie
Just getting into the workings of SWMBO's Puma and I wonder if any Backroomers know the purpose of the box that is attached to the underside of the bonnet?
Reply | Report as offensive | Link
Wed 21 Sep 2005 11:21
Puma mystery - Glaikit Wee Scunner {P}
Any brand names visible? Is it wired up to the car?
If not, put it in a bucket of water and call bomb disposal.
Joke.
--
I wasna fu but just had plenty.
Reply | Report as offensive | Link
Wed 21 Sep 2005 14:29
Puma mystery - Chas{P}
It's an acoustic resonance chamber to alter the engine noise.... no really. Read it on some Ford technical notes some time ago when I was working with Ford.

Not sure if it makes any real difference.

HTH
Was Charles {P} but someone c o p i e d my name with spaces.
Reply | Report as offensive | Link
Wed 21 Sep 2005 14:55
Puma mystery - Number_Cruncher
If it is a closed chamber except for the port into the air inlet pipe, it is a Helmholtz resonator. These can be very effective at removing air-borne sound over a narrow frequency range.

The air in the chamber acts as a spring, and the plug of air in the neck acts like a mass. At the resonance frequency (Hz) of the mass/spring system, fn=(1/2*pi)*sqrt(stiffness/mass), the resonator absorbs sound strongly. Big resonators for low notes, small for high notes, just like organ pipes.

These devices are tuned to get rid of any particularly annoying or loud frequencies, but are no good at reducing more broadband sources.

Number_Cruncher
Reply | Report as offensive | Link
Wed 21 Sep 2005 15:10
Puma mystery - Archie
Thanks for the replies. I half thought that's what it was. Now I'll take it off and see if the difference is noticed by the driver!
Reply | Report as offensive | Link