Funnels and sound attenuation

[shaunnutley]

I know that a a 1ft funnel that is placed to a sound source, such as a small speaker with a continous, same-pitch sound playing will increase the decibel reading substantially at the other end of the funnel.

I wondering about the free-field sound attenuation at the end of the funnel if a longer funnel is used, about 1m.
I know already the decibel reading is increased compared to the speakers sound measurement at the same distance away.
My question is to do with the sound attenuation after the sound leaves the funnel. I am interested in the rule 6dB per doubling of distance. Can the end of the funnel be taken as the start of the sound source, rather than the speaker at the other end of the funnel?

[beso]

The effect of the funnel (known as a horn in this situation) is mostly to do with impedance matching between the high impedance of the driver and the low impedance of the free air. Without the horn the transfer of energy from the driver to the air is very inefficient.

In the free air the source can be taken as the mouth of the funnel.