[VReijs]

Hello all of you,
I am interested in archaeoacoustics and thus hope to find here people who can help me educate in the certain details of acoustics. At this moment I am looking at Neolithic timber circles in Germany (they are of course reconstructed as the wood would not survive some 6800 years;-)
I am doing some benchmarking measurements for that, so I measured the sound pressure level (with an SPL meter) of pink noise (from loudspeakers) in an open field (mowed grass covered, temp around 15C and humidity ~50%). And it looks that the level change for double distance is between -6 and -9dB/dd: (http://www.archaeocosmology.org/eng/woodcircleaoucistictestplan.htm#doubled_distanc ), on average around -7.2dB/dd.
I measured this in an open field twice (between 5 and 40m) and in these cases it is: -8.2dB/dd or -9.1dB/dd. So I can reproduce it.

In open space it is expected to be -6dB/dd and in hemispherical environment (which would be close to my setup) around -4 to -5dB/dd. So why do I see such 'different' values?

Any hint why this is so different from the -4 to -5dB/dd I expect?
Any idea, or is this different just because of statistical error?

Thanks for your help. If I should post this question somewhere else please let me know.

All the best,


Victor

[FullRangeMan]

Welcome VReijs
Seems a most interesting see these results, please keeps us posted.
When in the center of the circles your ears fell some ususual acoustics?

[ArthurDent]

Greetings & Welcome to AC  Victor    

[Guy 13]

A warm welcome to AudioCircle Mr. Victor.

Guy 13

[Phil A]

Welcome to AC!

[brooklyn]

[nickd]

Welcome Victor,

Outdoor sound measurements are tough to repeat, Especially at distance. Air movement, and other envormental factors would be hard to predict and impossible to compensate for. I know an engineer who has done some Loudspeaker measurements outside but always on a quiet, still night and only at close range.

[VReijs]

Hello Nickd,
The measurements I did were also with low amounts of wind (at dawn, lower than 9 km/h).
At a distance of 40m one could indeed see the influence of wind a variation of plus and minus 4 dBSPL. So perhaps I should remove all the measurements that are less than 10 dB away from the noise level (incl. wind). Then the change in level changes between -5.5dB/dd and -8dB/dd, with average =6.7dB/dd.
This is still 'far' away from the -4 to -5dB/dd in hemispherical environment, but closer...

Thanks for the feedback Nickd.

All the best,


Victor

[JLM]

Victor, are you sure you're not over-thinking all this?  I mean, was this a Stonehenge type of concept (where acoustics would be secondary)?  Otherwise it probably had a roof that rotted over time.  (Not trying to tell you how to do your job, just trying to be practical.)

[VReijs]

JLM, I would not say I am overthinking recent measurements, I am just acoustically stimulating the building. If there is any past relation, I don't know. I normally am quite reluctant to say that things were with intend; Intend is very difficult to show (as with many things in the past).
So I am very open to it and just treating what I hear as something modern and try to explain it or acoustically (technology) or aurally (socially). So my question around the draw away is not related to the past, but to recent measurements.

All the best,


Victor