CTC is something I'm experimenting with. I have a TPL-150H in MTM with two 8", so CTC is large and this has been a concern of mine while I was designing and deciding if the 8" would be the right choice. My hopes were to xo at 2kHz which suggested awful lobbing (modelling the TPL as a point source, which is not).
Right now I cross them at 1.6kHz and playing with a number of variables. I went the OB route which is new to me. I use digital xo and currently using Neville-Thiele 2nd order which are super steep so that probably limits the range where combing/nulls happen, hence contributing to me not perceiving much of the nulls. The TPL has narrow 30° vertical dispersion so at places I certainly hear the treble diminished but I think it's because of my head going above 15° above the top edge (the driver's dispersion) more than CTC. Not sure though.
FWIW, my plan was/is to include an inductor to the bottom 8" such that its response starts to drop from around 500Hz so by the time it reaches the xo to TPL one of the mids is significantly reduced. Nulls should be minimized (at least that is my expectation).
A significant learning for me is that I might not be as sensitive to the effect of CTC on combing/nulls as models predict. Still worth winding an inductor and testing that too. But I might not need it. I'm also raising the xo and listening. I might not get to 2kHz, but it's sounding great already.
I'd like to have a question perhaps stupid about ribbon or at least planars mixed with a cone :
untill the step response has been matched between the two units at crossover frequency for an ideal theoric impulse response : does it change as the lobbying with the distance please ?
In other words : is the spl attenuation at 3 meters for illustration the same from a planar driver than a cone ?
Or simply should it be designed with measurement at the listener distance : both in axis and at sweet spot merging ?
Yeah stupid question I know, but I have a doubt on the -6db rule with half of the distance here😱
untill the step response has been matched between the two units at crossover frequency for an ideal theoric impulse response : does it change as the lobbying with the distance please ?
In other words : is the spl attenuation at 3 meters for illustration the same from a planar driver than a cone ?
Or simply should it be designed with measurement at the listener distance : both in axis and at sweet spot merging ?
Yeah stupid question I know, but I have a doubt on the -6db rule with half of the distance here😱
... makes sense ! Thanks. I should have read something wrong, it was about big planars saying with distance they had less spl attenuation than classic cones... assume a 2 cents reviewers working for a print or an e-zine (6moons ?)... I can't remember...
ok sorry for the disgression.
ok sorry for the disgression.
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If you plot the nulls, they may not have an apex at the same location as the driver. Moving out at a fixed angle with respect to the driver may cross those nulls, complicating what is observed.
Maybe don't be too hard on the reviewer, if the size of the planar has it approaching a line source then the attenuation can be -3dB per doubling of distance (at least for the frequencies where it is behaving as a line source).
A TPL size driver is not tall enough to exhibit this behaviour though.
Line-source transition to point-source: page 8, figure 5
https://audioroundtable.com/misc/nflawp.pdf
Note though that the graph only starts at a 1 meter distance from the loudspeaker: as you get closer the line length starts decreasing and increasingly becomes more of a line source relative to freq.. To an extent you hear this when distanced from the loudspeaker - in that you actually hear the gradient all the way to the loudspeaker's drivers (..though you don't detect the gradient itself: it's all integrated into the soundfield). Some people "pick-up" on this more than others the less "matched" the drivers sources on the loudspeaker.
https://audioroundtable.com/misc/nflawp.pdf
Note though that the graph only starts at a 1 meter distance from the loudspeaker: as you get closer the line length starts decreasing and increasingly becomes more of a line source relative to freq.. To an extent you hear this when distanced from the loudspeaker - in that you actually hear the gradient all the way to the loudspeaker's drivers (..though you don't detect the gradient itself: it's all integrated into the soundfield). Some people "pick-up" on this more than others the less "matched" the drivers sources on the loudspeaker.
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