SyntripP measurement is hot garbage

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 Hmmm but it's nowhere near as severe in Art's measurements, or am I mistaken? In our measurements it's a ~12db dip, in art's it's only ~6db

The response graph in the post that you linked to seems to be post processing. My comments were regarding a comparison with a raw response. Also note that in the Smaart plot the value of the smooth setting is 9. This averages the amplitude at any frequency with adjacent frequencies. To quote the manual, with smooth set to 3, any given data point will represent the value of that point averaged with the next higher and next lower points on the trace. When smoothing is set to 5, each point is averaged with the next two higher and lower points etc.

This, as its name suggests, smooths out any sharp changes in response.

The below image (from the sameDIY Audio thread) claims to be a raw response.

If you eq the response so that it is flat above 200Hz the notch at 700Hz doesn’t look so bad; especially if the measured graph is smoothed.

The anomaly at about 1.6KHz also shows up in this raw response.

 I actually have the theory that we wired up the hf driver incorrectly. Because there definitely is no inverting happening in the dsp.

When used in isolation, the polarity will have no effect on the frequency response. If the high frequency response was measured with the mids muted, the polarity is irrelevant whether due to wiring or dsp setting. Inverting the signal won’t change a peak in response to a notch. The phase/polarity only becomes relevant when there are multiple sound sources covering the same frequency range. That said, a reflected sound wave also acts as a secondary source, which will combine with the direct wave, either constructively or destructively.

 Hmmmm, would just closing the mid driver horn ports affect the hf measurement so much?

The ports will have some effect, so conversely, eliminating them should too. Just how much, I don’t know. Apart from the coupling between the compression driver and horn, holes in the walls of the horn would seem to be the only other cause.

Tracking down problems is a case of eliminating what is not causing the problem. Covering the ports with duct tape is quick and easy, and will either confirm of eliminate the ports as the problem.