Noise level & distance issue

[AO1958]

Hello everybody,

hope all is fine !
I looked in old post but I have not found similar topics.

Please, I'd like to ask you some help since I am stuck in an issue that is puzzling me !

I am facing in following topic: I have a Sound pressure level declared at a certain distance of a long dimension of a unit and @3 m from the ground, according to an hemispherical surface. No reference standard is quoted.

The unit is a sort of parallelepiped with a ratio long/width 6: 1

What makes me confused is what follows:

1 - according to sound theory in case of hemisphere I shall consider the unit as a point, therefore why considering distance from the long dimension ?
2 - which is the influence of the ground distance ? According to theory the ground is in any case a surface that reflects energy

Hope somebody can help me

Thanks in advance !

 

[GregLocock]

I think you are referring to an old standard for testing engines?



Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376

http://eng-tips.com/market.cfm?

 

[AO1958]

Many thanks.

As a matter of fact I cannot find any reference standard as per my introduction.

Would you be so kind and quoting this standard ?

Many thanks

 

[GregLocock]

Sorry, I just know it a sthe MIRA method, as opposed to the hemispherical one which is an ISO.

The distance from the ground has an enormous effect on narrowband noise due to cancellation and reinforcement. Are you in an open field, a semi anechoic chamber, or a reverberant room?

Hopefully not the latter.

Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376

http://eng-tips.com/market.cfm?