Bandpass overlap with High and Low pass |
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JoelDD
Registered User Joined: 20 April 2018 Status: Offline Points: 12 |
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This does bring up another question though, based on what I have heard here. Is driver inductance measured different inside the cabinet vs outside in free air? Currently I just clamp my meter onto the terminals, pass a range of frequencies through the driver and calculate the inductance near the crossover point or between crossover point in the case of bandpass. To my ears this produces good results, but I'm listening if I can be lead in a more accurate direction.
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DMorison
Old Croc Joined: 14 March 2007 Location: Aberdeen Status: Offline Points: 1647 |
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Best thing would be for you to model both and see the difference for yourself - I certainly find I learn things far more thoroughly from doing them than being told :) Or, look for contact info on that website and ask them directly ;)
Inductance should be the same in and out of the cab, but the impedance peak(s) at resonance will be affected by the cabinet. In the case of HF compression drivers, they will also be affected by whatever horn they're on.
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JoelDD
Registered User Joined: 20 April 2018 Status: Offline Points: 12 |
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Honestly, at this point I may just do that. I found that their suggestion for the parallel notch to deal with the bandpass gain was better dealt with by an L-pad a while ago. I suppose you could say that the way I design my crossovers is by selecting the slope and frequencies based on frequency response of the drivers, then tame the characteristics of the drivers and box with post crossover filters like contour networks, notch filters, l-pad's and zobels. It is probably more complex and costly, which is why i'm guessing that manufacturers try to do it with the slope generating circuit instead of post circuits, but I like making things from the foundation up and not modifying the foundation to fit the object. It feels like you should be able to get more accuracy that way. well in my experience so far anyways. I may be totally wrong and have just been getting lucky all this time. Who knows.
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JoelDD
Registered User Joined: 20 April 2018 Status: Offline Points: 12 |
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Just had some insight. I think the reason why specifically that calculator is presenting with overlap in the bandpass is because of their instructions to use the parallel notch to reduce the bandpass gain.
As we know the parallel notch filter lowers output in an arc peaking at the center between the two set frequencies. This would leave peaks at each crossover point, so they are relying on the phase cancellation effect of the crossover to dampen those frequencies that are not effectively covered by the parallel notch filter by extending the bandpass into the pre-crossover point frequencies of the low and high pass filters. Dear god! Just use a driver attenuation circuit! The power drop is not that much! This could "explain" some things I have noticed with this design.....
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gen0me
Young Croc Joined: 20 February 2016 Location: UK Status: Offline Points: 999 |
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Here is driver simmed as pure resistance and as a circuit. Values are off but it shows that hp filter on crossover point is narrower when simmed as circuit.
Edited by gen0me - 21 April 2018 at 5:46pm |
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JoelDD
Registered User Joined: 20 April 2018 Status: Offline Points: 12 |
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Interesting, is this with driver values calculated? There is a difference here, but not as big of a difference that I am seeing in values on other crossovers. This one looks like only +120% on the high pass and even smaller on the low pass.
Edited by JoelDD - 21 April 2018 at 10:34pm |
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JoelDD
Registered User Joined: 20 April 2018 Status: Offline Points: 12 |
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We are officially testing this theory. I just ordered all the caps I need for a recap of my speakers bandpass at the new calculated crossover point and I only had to change one inductor. So this is a fairly easy cheap test.
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gen0me
Young Croc Joined: 20 February 2016 Location: UK Status: Offline Points: 999 |
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No nothing calculated. It should be 8 ohm driver. Values in blue circuit are just guessed reasoneable values looking at some 6,5" PD driver.
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JoelDD
Registered User Joined: 20 April 2018 Status: Offline Points: 12 |
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Just an update, my theory was correct. The crossover points were being drastically padded by the frequency overlap. The crossover is much more balanced now. Take home, overlap will cancel out frequencies and lower dB output near crossover points. Just use an L-pad.
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