More on acoustic offsets...

[pcusine]

Hi to all! First post here. I've been a long time reader of this forum and I've learned a lot from all of you.

I have two projects on going, a small 2-way with Hivi B4N and Vifa DQ25 and my never ending first project, a 3-way with Focal TC90K, Seas MCA15 and Monacor SPH-200K.


To the point! I've been reading all the posts about measuring the relative acoustic offset, the Jeff B paper using OmniMic, dlr's web site, etc. And still have a few questions.


When entering offsets values on PCD, Lspcad, etc., if all the measurement are taken from a single mic position and exported them with minimum phase, wouldn't make more sense to play with Z axis only and leave Y at 0.00? This way I assume that in the measurement is already recorded the high frequency roll-off produced by the driver's off-axis radiation (think in a woofer in a big 3-way combination)


If the measurements are all on-axis, when you enter Y axis values, the software automatically applies the roll-off I was talking before.

I get better matching of individual responses and the summed one leaving Y at 0, when measuring from a single mic position, than entering Y and Z.

I have to try yet to do on-axis measurements with the drivers, but I was curious on what do you think.


Many thanks to all!



Pablo.

[Jeff B.]

Hi to all! First post here. I've been a long time reader of this forum and I've learned a lot from all of you.

I have two projects on going, a small 2-way with Hivi B4N and Vifa DQ25 and my never ending first project, a 3-way with Focal TC90K, Seas MCA15 and Monacor SPH-200K.


To the point! I've been reading all the posts about measuring the relative acoustic offset, the Jeff B paper using OmniMic, dlr's web site, etc. And still have a few questions.


When entering offsets values on PCD, Lspcad, etc., if all the measurement are taken from a single mic position and exported them with minimum phase, wouldn't make more sense to play with Z axis only and leave Y at 0.00? This way I assume that in the measurement is already recorded the high frequency roll-off produced by the driver's off-axis radiation (think in a woofer in a big 3-way combination)


If the measurements are all on-axis, when you enter Y axis values, the software automatically applies the roll-off I was talking before.

I get better matching of individual responses and the summed one leaving Y at 0, when measuring from a single mic position, than entering Y and Z.

I have to try yet to do on-axis measurements with the drivers, but I was curious on what do you think.


Many thanks to all!



Pablo.

These tools, like PCD, can be used in different ways depending on what your goal is. There is nothing wrong with doing it the way you have described, but you do give up some modeling power in exchange. If, on the other hand you extact the minimum phase from the response and import that data, and you enter the Y and Z dimensions, then PCD can accurately calculate the response changes as you move off-axis vertically. This allows you to see how lobing and nulls develop at different off-axis angles. This can be fairly revealing at times.

Jeff