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DanDan
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#1
26th March 2012
Old 26th March 2012
  #1
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Exploring BIR

I am considering the removal of Thread Starting Posts as a way of speaking to the knee jerk immediate contradiction we have seen repeatedly.
In this case there is a fortuitous coincidence.
Jay has reopened the proper SBIR thread. I will repost the test there.
I will try to clarify the graphics make the test file available to all.
Please remember Ethan has already done this test better, and published it.
He as I, took from it that the rising frequency suggests the Back Wall as the strongest contributor to a large number of nulls.
It could be simply the distance causing Lower Frequency nulls, and their harmonics. The level though....
One could look more carefully for such FWBIR harmonics....

The point regarding all boundaries contributing has been stated and heard and understood. It is simply not a full reality.
One of the later tests will kinda show them blending together to produce a new frequency, all the others seem to show one boundary dominating to the point of rendering others insignificant.
Blocking/absorbing a particular boundary, null gone, seems pretty convincing to me.
As ever it is not necessary for one view to be wrong, for another to be right.

DD
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26th March 2012
Old 26th March 2012
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Great test Dan!

If it's not too much trouble, would you post another graph with about half the amount of sweeps? I'm on my iPhone exclusively for the next week and the graph is a bit busy. (two greens, two purples, etc.)
Thanks
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#3
26th March 2012
Old 26th March 2012
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Great test indeed, thanks

Unfortunately, it's hard to identify which graph is what from the legend format which is very dense, even when using a large 21" display

Could you post the results in a easier readable form, either annotating the graph with arrows/notes, or using much less curves per graph, or whatever is convenient to create ? Thanks
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26th March 2012
Old 26th March 2012
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SBIR
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SBIR

Put simply: that room is simply way too small to be able to study the effect of a single boundary (or a limited selection of lower order reflections) considering the time-bandwidth requirement for a gated frequency response for the lower frequency range.
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26th March 2012
Old 26th March 2012
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Ok it's clear that is the mix of all the boundary that determine the center frequency of the cancellation because in a small room all boudaries are close enough to always play a role in the equation.
But if we move only in one direction, for example: far away from the front wall (so closer to the back wall) is it the relation between these too walls and the test position which will fix the Center Frequency or will the new position in relation to the other walls change that anyway?
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#6
26th March 2012
Old 26th March 2012
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Quote:
Originally Posted by PaulRain View Post
Ok it's clear that is the mix of all the boundary that determine the center frequency of the cancellation because in a small room all boudaries are close enough to always play a role in the equation.
But if we move only in one direction, for example: far away from the front wall (so closer to the back wall) is it the relation between these too walls and the test position which will fix the Center Frequency or will the new position in relation to the other walls change that anyway?
SBIR
SBIR
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26th March 2012
Old 26th March 2012
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+3! Great tests and great reporting. Thank you Dan.

Andre
DanDan
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28th March 2012
Old 28th March 2012
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Tests

Quote:
Ok it's clear that is the mix of all the boundary that determine the center frequency of the cancellation because in a small room all boudaries are close enough to always play a role in the equation.
Well the size of that 'role' seems to vary a lot and not intuitively. IMO certainly enough to warrant separate identities to the boundaries to prioritise treatment.

A Real test in a Real Room shows the Back Wall contributing a lot more BIR than it's distance would suggest. SBIR

On the other hand FWBIR can be pretty much eliminated by moving the speaker very close to wall with an absorbent panel between.
SBIR

I have another test with the speaker in a tricorner, equidistant from all walls.
When moved towards one wall, keeping the others the same, the combined null does appear to shift frequency. So I guess the influences kind of blend together in that close instance.

DD
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