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Crossover cascading
Yahzi
post Apr 12 2013, 20:39
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Hi,

Just wanted confirmation on something. I was having a discussion with someone about crossovers, especially low-pass filters as we were discussing bass management. I told him that he should disable his subwoofer LPF to avoid interaction from his AVR LPF. His response was that the internal passive crossovers in the speakers would still, in effect, cascade if using an active crossover in the AVR.

I'm not sure how this could be. You guys are the experts, just thought I would get your feedback on this.
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Yahzi
post Apr 15 2013, 17:55
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QUOTE ("greynol")
There's a point where you either enroll in a course in electronics or take what people say on faith.


But no one has even attempted to explain anything! If two filters at two completely different frequencies can't interact because they are isolated then how could the filters combine? If one is at 12 dB octave at 80 hz and the other is at 600 Hz then how the effing hell can these filters combine?

Explain that to me? Or must I be an EE to understand something? All I for is an explanation because NONE HAVE BEEN GIVEN.

This post has been edited by Yahzi: Apr 15 2013, 17:55
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julf
post Apr 16 2013, 10:04
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QUOTE (Yahzi @ Apr 15 2013, 18:55) *
But no one has even attempted to explain anything!


We have. And we have answered your question several times. The problem seems to be that you don't understand the answer.

QUOTE
If two filters at two completely different frequencies can't interact because they are isolated then how could the filters combine? If one is at 12 dB octave at 80 hz and the other is at 600 Hz then how the effing hell can these filters combine?


I don't think cursing will help get your message across - it is pretty much like the typical American reaction to someone not speaking English - shout louder.

QUOTE
Explain that to me? Or must I be an EE to understand something? All I for is an explanation because NONE HAVE BEEN GIVEN.


OK, we have said a number of times that the signal will be affected by the transfer functions of both filters. It is pretty clear that you don't understand the answer.

Arnold tried to explain by giving the extremely simple explanation of "Their electrical amplitude responses will be multiplied. Their responses given in dB will add." Seems you didn't understand that one either. So let's try one more time:

You have a 12 dB/oct filter at 600 Hz. Down at 80 Hz that filter will provide approximately 96 dB attenuation. From that point on, your 80 Hz filter will add even more attenuation on the frequencies below 80 Hz, so at 40 Hz the attenuation is 120 dB instead of the 108 dB you would get with only the 600 Hz filter.

Of course that example is simplified and assumes a perfect filter, but you ought to get the idea.

Can we now agree that someone has attempted to explain things to you?
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db1989
post Apr 20 2013, 12:09
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For one, you keep talking about filters that are seemingly highpass filters, whereas the OP has been asking about lowpass filters.

Then there are things like this:
QUOTE (julf @ Apr 16 2013, 10:04) *
You have a 12 dB/oct filter at 600 Hz. Down at 80 Hz that filter will provide approximately 96 dB attenuation.
By my reckoning, the actual figure would be just above –48 dB. The filter should already have cut by 12 dB at the nominal cutoff frequency, and then it attenuates by another 12 dB for every octave below that. So we have three further rounds of 12 dB: one at 300 Hz, one at 150 Hz, and one (just below) at 75 Hz. So, 12 + 36 = 48 dB of attenuation. You should now see that the figures you gave correspond to the response of a filter with a slope of 24 dB/octave.

This is quite basic stuff, so it’s best not to get things like this mixed up whilst attempting to explain things to someone who is greatly confused about similarly elementary concepts… not to mention ever more obstinate as time goes on.
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julf
post Apr 20 2013, 12:40
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QUOTE (db1989 @ Apr 20 2013, 13:09) *
For one, you keep talking about filters that are seemingly highpass filters, whereas the OP has been asking about lowpass filters.

Yes - seems I misread the posts from the OP with regards to the direction of the filters.

QUOTE
You should now see that the figures you gave correspond to the response of a filter with a slope of 24 dB/octave.

Indeed. Not sure why I was off by a factor of 2 - teaches me not to try to do numbers in my head without checking them.

The 25 Hz point was just any random point below the cut-off point of both filters (assuming, erroneously, they were high pass filters).

QUOTE
This is quite basic stuff, so it’s best not to get things like this mixed up whilst attempting to explain things to someone who is greatly confused about similarly elementary concepts… not to mention ever more obstinate as time goes on.

Have to agree. Should not post responses in the "I'll just quickly post something while waiting for the compile to finish" mode. My apologies. Thanks both to you and greynol for pointing out the mistakes.
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Posts in this topic
- Yahzi   Crossover cascading   Apr 12 2013, 20:39
- - Arnold B. Krueger   QUOTE (Yahzi @ Apr 12 2013, 15:39) Hi, J...   Apr 12 2013, 22:16
- - Yahzi   I understand that. But what I am asking is if the ...   Apr 12 2013, 22:31
|- - Arnold B. Krueger   QUOTE (Yahzi @ Apr 12 2013, 17:31) I unde...   Apr 12 2013, 22:39
- - Yahzi   QUOTE ("arnyk")How do you all of a sudde...   Apr 12 2013, 22:48
|- - julf   QUOTE (Yahzi @ Apr 12 2013, 23:48) 2. If ...   Apr 13 2013, 11:35
- - Yahzi   QUOTE ("Arnold B. Krueger")If so why are...   Apr 12 2013, 22:52
|- - Arnold B. Krueger   QUOTE (Yahzi @ Apr 12 2013, 17:52) QUOTE ...   Apr 13 2013, 16:06
- - Yahzi   QUOTE ("Arnold B Krueger")Obviously, you...   Apr 13 2013, 16:58
- - Yahzi   QUOTE ("julf")If you apply one filter, a...   Apr 13 2013, 17:09
|- - Soap   QUOTE (Yahzi @ Apr 13 2013, 11:09) . But ...   Apr 13 2013, 19:29
- - Yahzi   QUOTE ("Soap")Yes. A filter is a filter...   Apr 13 2013, 19:33
|- - Soap   QUOTE (Yahzi @ Apr 13 2013, 13:33) Please...   Apr 13 2013, 19:53
- - Yahzi   Actually just forget about. I said "if a spea...   Apr 13 2013, 20:02
|- - Soap   QUOTE (Yahzi @ Apr 13 2013, 14:02) If you...   Apr 13 2013, 20:11
|- - julf   QUOTE (Yahzi @ Apr 13 2013, 21:02) I...   Apr 15 2013, 09:58
|- - Arnold B. Krueger   QUOTE (Yahzi @ Apr 13 2013, 15:02) Actual...   Apr 15 2013, 15:25
- - Yahzi   QUOTE Their electrical amplitude responses will be...   Apr 15 2013, 16:55
- - greynol   There's a point where you either enroll in a c...   Apr 15 2013, 17:43
- - Yahzi   QUOTE ("greynol")There's a point whe...   Apr 15 2013, 17:55
|- - ktf   QUOTE (Yahzi @ Apr 15 2013, 18:55) If two...   Apr 15 2013, 18:09
|- - julf   QUOTE (Yahzi @ Apr 15 2013, 18:55) But no...   Apr 16 2013, 10:04
|- - Nessuno   QUOTE (julf @ Apr 16 2013, 11:04) You hav...   Apr 16 2013, 11:33
||- - julf   QUOTE (Nessuno @ Apr 16 2013, 12:33) Or t...   Apr 16 2013, 11:58
|- - db1989   For one, you keep talking about filters that are s...   Apr 20 2013, 12:09
|- - julf   QUOTE (db1989 @ Apr 20 2013, 13:09) For o...   Apr 20 2013, 12:40
|- - greynol   QUOTE (julf @ Apr 20 2013, 04:40) The 25 ...   Apr 20 2013, 13:12
|- - julf   QUOTE (greynol @ Apr 20 2013, 14:12) QUOT...   Apr 20 2013, 16:24
|- - db1989   QUOTE (julf @ Apr 20 2013, 16:24) The poi...   Apr 20 2013, 16:59
|- - julf   QUOTE (db1989 @ Apr 20 2013, 17:59) And t...   Apr 20 2013, 17:12
- - Propheticus   The filters add up! The end result will be inp...   Apr 15 2013, 18:46
- - greynol   They add because decibels are logarithmic. So in ...   Apr 15 2013, 19:14
- - dhromed   Even after this thread I'm still not sure what...   Apr 16 2013, 12:36
|- - Nessuno   QUOTE (dhromed @ Apr 16 2013, 13:36) Even...   Apr 16 2013, 13:01
||- - julf   QUOTE (Nessuno @ Apr 16 2013, 14:01) I th...   Apr 16 2013, 13:42
|- - krabapple   QUOTE (dhromed @ Apr 16 2013, 07:36) Even...   Apr 18 2013, 04:37
- - Speedskater   As a side note: Understanding Decibel math is no ...   Apr 16 2013, 15:02
|- - julf   QUOTE (Speedskater @ Apr 16 2013, 16:02) ...   Apr 16 2013, 15:34
- - greynol   We experience much of the world logarithmically. ...   Apr 16 2013, 16:07
- - Yahzi   The question I asked was "can the speaker cro...   Apr 17 2013, 13:47
|- - julf   QUOTE (Yahzi @ Apr 17 2013, 14:47) WHATEV...   Apr 17 2013, 15:14
- - Yahzi   The person I was discussing who claimed the passiv...   Apr 17 2013, 13:49
|- - julf   QUOTE (Yahzi @ Apr 17 2013, 14:49) The pe...   Apr 17 2013, 15:16
- - dhromed   What do you mean by cascade?   Apr 17 2013, 14:38
|- - knutinh   QUOTE (dhromed @ Apr 17 2013, 14:38) What...   Apr 17 2013, 14:53
|- - dhromed   QUOTE (knutinh @ Apr 17 2013, 15:53) I ta...   Apr 17 2013, 15:26
- - Propheticus   If the two slopes are in the same range they will ...   Apr 17 2013, 15:06
- - Yahzi   QUOTE I'm also not entirely sure any more what...   Apr 19 2013, 14:15
|- - julf   QUOTE (Yahzi @ Apr 19 2013, 15:15) I agre...   Apr 19 2013, 16:17
- - greynol   They combine regardless of whether they operate in...   Apr 19 2013, 14:58
- - pdq   How about this explanation: If the crossover freq...   Apr 19 2013, 15:21
- - greynol   That's funny since the original post appears t...   Apr 19 2013, 16:23
- - Yahzi   QUOTE ("julf")So please accept that you ...   Apr 19 2013, 19:58
|- - julf   QUOTE (Yahzi @ Apr 19 2013, 20:58) But I ...   Apr 19 2013, 22:16
|- - greynol   QUOTE (julf @ Apr 19 2013, 14:16) Because...   Apr 19 2013, 22:27
|- - julf   QUOTE (greynol @ Apr 19 2013, 23:27) Plea...   Apr 20 2013, 10:33
- - Yahzi   QUOTE ("julf")And how do they know if th...   Apr 19 2013, 20:03
- - Yahzi   QUOTE ("dhromed")In any case, Arnold sai...   Apr 19 2013, 20:06
- - greynol   http://www.hydrogenaudio.org/forums/index....st...   Apr 19 2013, 20:13
- - pdq   The folks here are an excellent source of informat...   Apr 19 2013, 20:17
- - Yahzi   Perhaps where the confusion is coming from is that...   Apr 19 2013, 20:40
- - Yahzi   QUOTE ("pdq")I think the problem may be ...   Apr 19 2013, 20:46
|- - julf   QUOTE (Yahzi @ Apr 19 2013, 21:46) I am a...   Apr 19 2013, 22:10
- - Yahzi   Read this reply from the member towards the bottom...   Apr 19 2013, 22:25
|- - greynol   QUOTE (Yahzi @ Apr 19 2013, 14:25) Read t...   Apr 19 2013, 22:32
- - Yahzi   Well greynol, what am I supposed to do? The EE is ...   Apr 19 2013, 22:38
- - greynol   I'm an EE (so is Arny and likely others). I r...   Apr 19 2013, 22:48
- - Yahzi   Well thanks for the conflicting information. You r...   Apr 19 2013, 22:50
- - greynol   Just reading your posts you get conflicting inform...   Apr 19 2013, 22:54
- - greynol   Perhaps you can provide either some math or a grap...   Apr 20 2013, 12:21
- - db1989   QUOTE Hopefully the scilab plot explains it better...   Apr 20 2013, 17:35
- - julf   QUOTE (db1989 @ Apr 20 2013, 18:35) A gra...   Apr 20 2013, 17:55


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