https://solen.ca/wp-content/uploads/d3004604010.pdf
Supposedly a great tweeter ($400), but from between 850 and 1200hz output is down 3db and rises up to normal between 1200 and 1600hz. And from 850-1200hz impedance is up 50% and drops to normal from 1200-1600hz.
This seems completely unrelated to the expected impedance rise at resonance, which in this case is centred at 450hz and spans 200-850hz.
What could be causing this? I've seen a few tweeters with this problem (extended response dips of about 3db with associated impedance rises at the beginnings of their frequency responses).
I immediately look elsewhere because of the practically uncorrectable phase problems that would be encountered trying to cross them over anywhere between 1.8 and 2.5khz (almost impossible passively and still a job actively).
Supposedly a great tweeter ($400), but from between 850 and 1200hz output is down 3db and rises up to normal between 1200 and 1600hz. And from 850-1200hz impedance is up 50% and drops to normal from 1200-1600hz.
This seems completely unrelated to the expected impedance rise at resonance, which in this case is centred at 450hz and spans 200-850hz.
What could be causing this? I've seen a few tweeters with this problem (extended response dips of about 3db with associated impedance rises at the beginnings of their frequency responses).
I immediately look elsewhere because of the practically uncorrectable phase problems that would be encountered trying to cross them over anywhere between 1.8 and 2.5khz (almost impossible passively and still a job actively).
I don't think that could be the reason for at least another octave.
Also doesn't account for the impedance.
Other thoughts?
That dip is the least of your concern as far as these tests show.
Test Bench: Two Beryllium Tweeters from Scan-Speak - D3004-604010 and the D3004-604000 | audioXpress
Test Bench: Two Beryllium Tweeters from Scan-Speak - D3004-604010 and the D3004-604000 | audioXpress
My guess is the 'sonically transparent metal protective grill' isn't that transparent, the dot in the middle an attempt at some sort of correction,
as well as the roll surround acting as a sort of waveguide, leading to some of the peaking
as well as the roll surround acting as a sort of waveguide, leading to some of the peaking
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There are 2 impedance peaks due to an airflow restriction in the VC gap, making both the air space under the dome and chamber behind the VC create its own resonance. An internal reflection can also cause this.
Thats the main reason for the weird response and its likely going to cause elevated odd order HD in that FR range.
Some tweeters show this same anomaly, but don't suffer from the respone issues.
Thats the main reason for the weird response and its likely going to cause elevated odd order HD in that FR range.
Some tweeters show this same anomaly, but don't suffer from the respone issues.
^^ this. The air flow path to the rear chamber is restrictive so you see resonances caused by both the airspace behind the dome as well as the rear chamber. Either the hole in the pole piece is too small, or there isn't one and the air gets to the rear chamber via the voice coil gap.
Looks fine to me. Dip at 3kHz in that test is due to baffle diffraction of their small baffle (edit or perhaps their room). No issue with this if the testing is purely comparative as it affects both drivers under test equally. They suspected the drivers were almost identical, so being a bit lazier in the test method is fine if you're just seeking out differences.
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Distortion plotted in the link is unacceptably high, especially for tweeters $400ea.
Now I know to for sure avoid anything with these problems.
If the frequency response was plotted at 8v, would the 3db dip extend further up in frequency, like to 1700hz/correct from between 1700 and 2100hz?