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Hydrogenaudio Forum => General Audio => Topic started by: Yahzi on 2013-04-12 20:39:31

Title: Crossover cascading
Post by: Yahzi on 2013-04-12 20:39:31
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.
Title: Crossover cascading
Post by: Arnold B. Krueger on 2013-04-12 22:16:24
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.



Crossovers need to be designed carefully and intentionally. Because phase relationships in the crossover affect system response everything needs to be considered. Bottom line, crossovers can't be thrown in haphazardly.  Cascade does not mean better.  The crossovers in the AVR are designed to work as they are. Cascading additional crossovers will usually result in undesired dips and roll-offs.
Title: Crossover cascading
Post by: Yahzi on 2013-04-12 22:31:00
I understand that. But what I am asking is if the active AVR crossover could cascade with the passive internal speaker crossover. Wouldn't the slopes combine if both crossovers were operating in the same frequency range? But if my speakers passive crossover for the woofer is 400 Hz and I use a 100 Hz crossover, wouldn't the speakers crossover be well outside the effective range of the AVR's slope?

What is a typical crossover for a 2-way bookshelf? Wouldn't the passive crossover in a speaker be isolated from the AVR crossover? I guess that is the question I'm asking for but I don't know 100% whether it's true or not.
Title: Crossover cascading
Post by: Arnold B. Krueger on 2013-04-12 22:39:59
I understand that.


If so why are you contradicting the answer you were provided with?

Quote
But what I am asking is if the active AVR crossover could cascade with the passive internal speaker crossover. Wouldn't the slopes combine if both crossovers were operating in the same frequency range?


They will combine, but the combination probably won't end up giving you smooth or flat response.

Quote
But if my speakers passive crossover for the woofer is 400 Hz and I use a 100 Hz crossover, wouldn't the speakers crossover be well outside the effective range of the AVR's slope?


How do you all of a sudden know this information, or are you just speculating?

Quote
What is a typical crossover for a 2-way bookshelf?


Probably, a couple of KHz.

Quote
Wouldn't the passive crossover in a speaker be isolated from the AVR crossover? I guess that is the question I'm asking for but I don't know 100% whether it's true or not.


Please post again when you actually have a relevant question based on actual reliable knowledge.
Title: Crossover cascading
Post by: Yahzi on 2013-04-12 22:48:49
Quote
How do you all of a sudden know this information, or are you just speculating?


It's a hypothetical. I'm throwing an example out there to try and make sense of things.

Quote
Please post again when you actually have a relevant question based on actual reliable knowledge.


Why are you behaving like this? You think I would be here if I had "actual reliable knowledge? Don't be silly. I asked a few questions that you did not clearly answer to my satisfaction so clearly asking them again was my only alternative. Your initial reply to my questions did not explain anything.

1. If I use a crossover in my AVR would this cascade with my speakers passive crossover? Yes or no? If yes, then clearly explain why it would. If no, please explain.
2. If crossovers cascade only if they are in the same frequency range then in what scenario would this happen in a conventional speaker set up using an AVR?

Please answer without the aggressive tone.
Title: Crossover cascading
Post by: Yahzi on 2013-04-12 22:52:05
Quote
If so why are you contradicting the answer you were provided with?


I'm not contradicting anything. You said crossovers needed to be carefully designed. That's a truism and it makes sense, but it DOES NOT answer my question to you. If you read what I wrote the answer you supplied did not answer what I asked. I did not ask what the consequences would be of a cascading crossover. I merely asked if and when it would occur.
Title: Crossover cascading
Post by: julf on 2013-04-13 11:35:53
2. If crossovers cascade only if they are in the same frequency range then in what scenario would this happen in a conventional speaker set up using an AVR?


What exactly do you mean with "cascade". If you apply one filter, and then another filter on the filtered signal, the signal will be affected by the transfer functions of both filters. If the crossover frequencies are far apart, the interaction will be small, but it will be there nevertheless.
Title: Crossover cascading
Post by: Arnold B. Krueger on 2013-04-13 16:06:49
Quote
If so why are you contradicting the answer you were provided with?


I'm not contradicting anything. You said crossovers needed to be carefully designed. That's a truism and it makes sense, but it DOES NOT answer my question to you.


Sure it does. Just answer one question: "Am I using this speaker and crossover in a way that fits in with its designers intent?"

What you seem to be suggesting is mixing and matching speakers and crossovers like socks in a drawer.

Quote
If you read what I wrote the answer you supplied did not answer what I asked. I did not ask what the consequences would be of a cascading crossover.


Fooled me.

Quote
I merely asked if and when it would occur.


Obviously, you can cascade crossovers whenever you are able to and actually do so. That is a truism.  Since you don't seem to like truisms, I don't know why you ask questions that have only truisms as logical answers.

Part of your problem seems to be that you don't appear to know enough about your speakers to ask properly formed questions about them.
Title: Crossover cascading
Post by: Yahzi on 2013-04-13 16:58:06
Quote
Obviously, you can cascade crossovers whenever you are able to and actually do so. That is a truism. Since you don't seem to like truisms, I don't know why you ask questions that have only truisms as logical answers.


Do you have a reading comprehension problem? You aren't actually answering my questions ... again! Who cares when you are supposed to cascade crossovers. That is not what I asked. I asked you specific questions and I had hoped you would actually answer them but you sidestep AGAIN with useless babble.

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Obviously, you can cascade crossovers whenever you are able to and actually do so. That is a truism. Since you don't seem to like truisms, I don't know why you ask questions that have only truisms as logical answers.

Part of your problem seems to be that you don't appear to know enough about your speakers to ask properly formed questions about them.


Part of your problem is that you don't seem capable of answering logical questions and instead question the reason why I asked them. I don't need a psychoanalysis from you, I need answers and you have provided none. You just babbled on and gave me useless information for a second time. It boggles the mind why you can't just answer with constructive advice instead of dodging the questions and wasting time.  You've been very unhelpful.
Title: Crossover cascading
Post by: Yahzi on 2013-04-13 17:09:52
Quote
If you apply one filter, and then another filter on the filtered signal, the signal will be affected by the transfer functions of both filters. If the crossover frequencies are far apart, the interaction will be small, but it will be there nevertheless.


Thank you, at least someone who can stick to the topic. So if I use 80 Hz low-pass in my receiver and another 80 Hz low-pass the slopes would combine. But if I use a crossover of 80 Hz and I have a bookshelf speaker, a 2-way, would the crossover of 80 Hz interact with passive crossover in the speaker?
Title: Crossover cascading
Post by: Soap on 2013-04-13 19:29:01
. But if I use a crossover of 80 Hz and I have a bookshelf speaker, a 2-way, would the crossover of 80 Hz interact with passive crossover in the speaker?


Yes.

A filter is a filter is a filter. 

Unless you mean something other than how julf described "interact" ("the transfer functions of both filters").
Title: Crossover cascading
Post by: Yahzi on 2013-04-13 19:33:05
Quote
Yes.

A filter is a filter is a filter.


Please explain how it would interact.
Title: Crossover cascading
Post by: Soap on 2013-04-13 19:53:10
Please explain how it would interact.



Maybe despite his brashness Arnold is right.  I believe I answered how they would interact by quoting julf's description of how they would interact.

You don't seem to understand this answer, and that's cool.  So I'm not dodging the question but we need to step back a second and figure out exactly what you're asking and also what you think julf's answer means.

Please rephrase your original question in a more verbose manner and talk a bit about how you understand julf's answer.
Title: Crossover cascading
Post by: Yahzi on 2013-04-13 20:02:07
Actually just forget about. I said "if a speaker crossover would interact with an AVR crossover" and "julf" said a filter applied to another filter would be effected. Now while that was infinitely more useful than Arnold's babble it still did not answer my question directly.

I'm asking about a speakers passive crossover between the drive units, and the AVR crossover - so if I use an 80 Hz AVR crossover in a 2-way speaker, that has a woofer low-passed at 800 Hz, how the fuck are the filters going to combine or interact? Will the slopes interact and if so, how?

If you understood basic English you would have gathered what I had asked. I'm losing patience when people have fuck all answers to give me and instead question and analyse why I have asked questions that should have been answered. If you can't answer my questions then you have demonstrated your incompetence and I'll go somewhere else.
Title: Crossover cascading
Post by: Soap on 2013-04-13 20:11:10
If you understood basic English you would have gathered what I had asked.


Sorry I can't read minds.

Title: Crossover cascading
Post by: julf on 2013-04-15 09:58:58
I'm asking about a speakers passive crossover between the drive units, and the AVR crossover - so if I use an 80 Hz AVR crossover in a 2-way speaker, that has a woofer low-passed at 800 Hz, how the fuck are the filters going to combine or interact? Will the slopes interact and if so, how?


The problem is that you are using very inexact and ambiguous terminology, so I can understand why people are asking you to explain how you understand our answers.

The filters won't "interact" in the sense that they would somehow change each other's function. But the end result (the frequency and phase response of your speaker) is affected by both filters. That's the "combine" part. Of course their effect combines, because the signal has to pass first one and then the other filter.
Title: Crossover cascading
Post by: Arnold B. Krueger on 2013-04-15 15:25:33
Actually just forget about. I said "if a speaker crossover would interact with an AVR crossover" and "julf" said a filter applied to another filter would be effected. Now while that was infinitely more useful than Arnold's babble it still did not answer my question directly.


I guess that we have an example of the idea that if a person is poorly informed enough, any answer no matter how carefully formed, is undecipherable.

Quote
I'm asking about a speakers passive crossover between the drive units, and the AVR crossover - so if I use an 80 Hz AVR crossover in a 2-way speaker, that has a woofer low-passed at 800 Hz, how the (immature verbiage removed) are the filters going to combine or interact? Will the slopes interact and if so, how?


The filters won't interact because they are electrically isolated from each other.

Their electrical amplitude responses will be multiplied.  Their responses given in dB will add. 

If one filter passes one half of its input at a certain frequency and the other passes one quarter of its input at the same frequency the total response will be 1/8.

If one filter has a loss of 6 dB at a certain frequency and the other has a loss of 12 dB at the same frequency then the total response will show an 18 dB loss.

If one filter has  flat response over a range of frequencies and the other has  flat response over the range of frequencies then the total response will be flat.

If one filter has  flat response over a range of frequencies and the other has sloped response over the same range of frequencies then the total response will be sloped the same as the sloped one..

If both filters have sloped response over a range of frequencies then the total response will have response that sloped by a slope that is the sum of the two slopes.

If one filter has  response sloped up over a range of frequencies and the other has response that is sloped down with the same slope over the same range of frequencies then the total response will be flat.

Title: Crossover cascading
Post by: Yahzi on 2013-04-15 16:55:58
Quote
Their electrical amplitude responses will be multiplied. Their responses given in dB will add.


How?
Title: Crossover cascading
Post by: greynol on 2013-04-15 17:43:06
There's a point where you either enroll in a course in electronics or take what people say on faith.
Title: Crossover cascading
Post by: Yahzi on 2013-04-15 17:55:12
Quote
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.
Title: Crossover cascading
Post by: ktf on 2013-04-15 18:09:37
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?


You asked something different?

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.

Of course crossovers can 'interact' (they'll be around the same frequency) and LPF's can 'interact'. (they'll be around the same frequency) Not really 'interacting' as responses would just be multiplied. 'Interaction' of an LPF with a crossover is a different matter.
Title: Crossover cascading
Post by: Propheticus on 2013-04-15 18:46:21
The filters add up! The end result will be input - filter1 - filter2 = output... Why is that so ffing hard to understand? /agree with Greynol

If the internal (passive) crossover in the subwoofer can be bypassed/disabled, I'd go with the option where the AVreceiver manages the crossover (actively before amplification). If it can't... have faith that the engineers that designed the sub knew what they were doing when calculating the passive crossover.

Some light reading: http://en.wikipedia.org/wiki/Audio_crossover (http://en.wikipedia.org/wiki/Audio_crossover)
Title: Crossover cascading
Post by: greynol on 2013-04-15 19:14:12
They add because decibels are logarithmic.

So in addition to knowing something about electronics, understanding math is also important if you really want to better understand the "how" part.

http://en.wikipedia.org/wiki/Decibel (http://en.wikipedia.org/wiki/Decibel)

I call bullshit on "no one explained anything to me."
Title: Crossover cascading
Post by: julf on 2013-04-16 10:04:17
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?
Title: Crossover cascading
Post by: Nessuno on 2013-04-16 11:33:31
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.

Or the other way around: if (as the OP said) the first one is a low-pass with -3dB @600Hz, it most likely will be flat @80Hz (and add no phase shift).
Title: Crossover cascading
Post by: julf on 2013-04-16 11:58:00
Or the other way around: if (as the OP said) the first one is a low-pass with -3dB @600Hz, it most likely will be flat @80Hz (and add no phase shift).


Ah, yes, my fault - thought the 600 Hz filter was a low-pass too.

Pretty confusing, as the OP was first talking about a 400 Hz and a 100 Hz crossover, then 2 80 Hz crossovers, then an 80 Hz crossover and an unspecified 2-way speaker crossover, and then an 80 Hz unspecified filter and a 600 Hz unspecified filter.

I also notice that the OP hasn't answered our clarifying questions.

I think we have to conclude that either the OP isn't quite sure about what he/she is asking, or isn't interested in finding out the real answer.
Title: Crossover cascading
Post by: dhromed on 2013-04-16 12:36:27
Even after this thread I'm still not sure what is meant in this particular case by "cascading" filters. Does that simply mean "put one filter after another"?
Title: Crossover cascading
Post by: Nessuno on 2013-04-16 13:01:51
Even after this thread I'm still not sure what is meant in this particular case by "cascading" filters. Does that simply mean "put one filter after another"?

I think this was what the OP meant: put them in a series and determine what happens to a full band signal passing through it.
Title: Crossover cascading
Post by: julf on 2013-04-16 13:42:40
I think this was what the OP meant: put them in a series and determine what happens to a full band signal passing through it.


I think that is what we are all assuming, but it would have been helpful if the OP had replied to my request to specify what he/she meant with the term.
Title: Crossover cascading
Post by: Speedskater on 2013-04-16 15:02:07
As a side note:  Understanding Decibel math is no easy matter,  Henry W. Ott in his 850 page very technical book 'Electromagnetic Compatibility Engineering' has a 5 page Appendix on understanding and using the Decibel.

He also has a short overview on his web-page.

http://www.hottconsultants.com/techtips/decibel.html (http://www.hottconsultants.com/techtips/decibel.html)
Title: Crossover cascading
Post by: julf on 2013-04-16 15:34:02
As a side note:  Understanding Decibel math is no easy matter


It is actually pretty easy if you grew up with logarithms and slide rules (we needed those to fend off the dinosaurs, you know).
Title: Crossover cascading
Post by: greynol on 2013-04-16 16:07:47
We experience much of the world logarithmically.  Going at it this way I think it's the multiplication part that is the hard part to understand. The other problem at hand is the use of the word interact in conjunction with the concept of isolation, though this was explained by julf already: if the filters are isolated then they won't interact with one anoher by changing the way in which each other functions. Instead they will act independently and their effects will combine no matter how minuscule or how large.

To insert what will likely be my unwelcome opinion, I hate it when members use our forums to argue by proxy. This is especially shown here when someone is giving advice about a subject he clearly does not understand and then gets annoyed when this is pointed out, likely because it is compromising his credibility.  Google the OP's nick and the relevant terms and you will get hits at two other forums.

Someone please explain how a 12db/octave filter of any variety will attenuate 80 Hz by 96dB when the corner frequency is at 600 Hz. Assuming there is no additional attenuation, the math simply does not add up.
Title: Crossover cascading
Post by: Yahzi on 2013-04-17 13:47:55
The question I asked was "can the speaker crossover be affected by the receiver crossover" and it appears the answer it no, it shouldn't given the crossover frequencies in question are too far apart to interact. The slopes would be too far apart.

I used the examples of 80 Hz or 100 Hz to get my point across. The slope at 80 Hz and the passive crossover of the speaker at 500 hz or 800 Hz or 1 kHz for the woofer - WHATEVER it is, the AVR crossover can't affect it positively or negatively as far as I understand it. Much of what had been posted was sidestepping the questions I posed.
Title: Crossover cascading
Post by: Yahzi on 2013-04-17 13:49:39
The person I was discussing who claimed the passive crossover elements in the speaker still cascade with the receiver crossover, THAT is what I wanted to know. From what I know, this generally can't happen.
Title: Crossover cascading
Post by: dhromed on 2013-04-17 14:38:32
What do you mean by cascade?
Title: Crossover cascading
Post by: knutinh on 2013-04-17 14:53:00
What do you mean by cascade?

I take it to mean "if multiple units are connected in series, will the output be affected by only one component, or all components". The answer is that the output will be affected by all components.

If you AVR has room correction, I would try using it. If it is any good, it should align phase along crossover-points no matter what filtering is applied later on.

Passive loudspeaker crossovers tends to be designed tightly with the loudspeaker - both filters and both drivers (for a 2-way unit). They can be part "ideal, theoretical filtering", and part phase/eq correction adapted to loudspeaker drivers/enclosures.

Active loudspeaker filters should probably be designed by the loudspeaker designer, or based on good measurements and some target response.

-k
Title: Crossover cascading
Post by: Propheticus on 2013-04-17 15:06:12
If the two slopes are in the same range they will add up... the resulting slope will be a product of both (steeper slope). If they are far apart.... either one is useless but won't affect the other.

The way I see it:
If your AVR cuts of from lets say 100Hz and the slope is below -96dB at 150Hz and your sub cuts from 200Hz....there's nothing left to cut. The other way round the AVR would cut of a piece of the range which is then followed by the sub cutting of more. You then might just as well disable the AVR filter, because the result is the same.
Title: Crossover cascading
Post by: julf on 2013-04-17 15:14:09
WHATEVER it is, the AVR crossover can't affect it positively or negatively as far as I understand it.

Then you have totally misunderstood what allmost of us have been saying.
Title: Crossover cascading
Post by: julf on 2013-04-17 15:16:49
The person I was discussing who claimed the passive crossover elements in the speaker still cascade with the receiver crossover, THAT is what I wanted to know. From what I know, this generally can't happen.


Again, can you *please* define what you mean by "cascade"? The output will be affected by both filters.
Title: Crossover cascading
Post by: dhromed on 2013-04-17 15:26:57
I take it to mean "if multiple units are connected in series, will the output be affected by only one component, or all components". The answer is that the output will be affected by all components.


I figured it would mean that in this particular case the two lowpasses will simply superimpose and the final result is always the one with the tightest filter. Therefore, stacking the two LPF's would be harmless as they will "cascade".

But Arnold's usage in his first post clearly means "put the filters in series", which is very different.

I'm also not entirely sure any more what Yahzi's position is. In the OP he warns that the filters will affect eachother, but later he doesn't believe that they will affect eachother anymore.

In any case, Arnold said that stacking the filters will have undesired consequences, so it appears that Yahzi is right and his friend is wrong, but for the wrong reasons.
Title: Crossover cascading
Post by: krabapple on 2013-04-18 04:37:24
Even after this thread I'm still not sure what is meant in this particular case by "cascading" filters. Does that simply mean "put one filter after another"?


Cascading filters is a common enough term in popular audio literature -- it's what happens when you have bass management happening in your AVR (applying a low pass filter with a crossover frequency of X hz to the  signal, and directing the output to the subwoofer channel)  AND your subwoofer applies its own lowpass filter too.  Typically one is advised to turn off the LPF of the sub, or set the  sub's crossover frequency to maximum (which hopefully is well above the crossover frequency used for the AVR's LPF).
Title: Crossover cascading
Post by: Yahzi on 2013-04-19 14:15:06
Quote
I'm also not entirely sure any more what Yahzi's position is. In the OP he warns that the filters will affect eachother, but later he doesn't believe that they will affect eachother anymore.


I agree that two filters will combine or cascade if operating within the same range. If a 80 Hz low pass was operating with a 100 Hz low pass then I imagine there would be a phase shift of some kind. But there should be some interaction of some kind with the filters so close to each other.

What I disagreed with is the idea that a speaker crossover could be affected by the receivers own crossover, which is what my friend was saying. But I do not disagree that filters can combine if operating in the same range.
Title: Crossover cascading
Post by: greynol on 2013-04-19 14:58:08
They combine regardless of whether they operate in the same range, FFS!

Here's a question to ponder:  what if the content creator includes material in the LFE channel that has frequencies well above the x-over in the sub which the AVR doesn't filter out because it isn't part of that AVR's bass management?
Title: Crossover cascading
Post by: pdq on 2013-04-19 15:21:17
How about this explanation:

If the crossover frequencies of the two low pass filters are far apart then one of them will make no audible difference over the effect of the other. Only if they are fairly close together will the addition of the second filter make an audible difference over the other one by itself.

The lack of an audible difference does not mean that the second filter has NO effect.
Title: Crossover cascading
Post by: julf on 2013-04-19 16:17:58
I agree that two filters will combine or cascade if operating within the same range.


And how do they know if they operate in the same range or not? If nobody tells them, they might just not realize they aren't supposed to combine...

Seriously, one more time - they *will* combine in *any* case. That result might not cause an audible difference if their ranges are far enough apart. That doesn't change the fundamental fact that they do combine, even if you don't want them to.

Quote
If a 80 Hz low pass was operating with a 100 Hz low pass then I imagine there would be a phase shift of some kind.


Not only that, but the steepness of the response curve would be pretty much twice the steepness of that of one filter.

Quote
What I disagreed with is the idea that a speaker crossover could be affected by the receivers own crossover, which is what my friend was saying.


So please accept that you were wrong and your friend was right. Can we move on now?
Title: Crossover cascading
Post by: greynol on 2013-04-19 16:23:00
That's funny since the original post appears to say something quite different than what was just quoted.
Title: Crossover cascading
Post by: Yahzi on 2013-04-19 19:58:32
Quote
So please accept that you were wrong and your friend was right. Can we move on now?


But I don't understand how filters can combine if they are operating in two different ranges! How can the slopes combine if one is at 80 Hz, for eg, and another is at 500 Hz? I refuse to believe my friend is right. Speaker crossovers CANNOT cascade with the amplifier crossover. Goodness, I had a discussion with a few EE's in another thread and they agreed that the filters cannot cascade. Now you are saying my friend is correct. WTF?
Title: Crossover cascading
Post by: Yahzi on 2013-04-19 20:03:14
Quote
And how do they know if they operate in the same range or not?


If you set one to 80 Hz in the receiver and the other on the subwoofer to 80 Hz, then they will operate in the same range.

Quote
Seriously, one more time - they *will* combine in *any* case. That result might not cause an audible difference if their ranges are far enough apart.


You keep claiming this, but you aren't EXPLAINING to me how this is so. How do passive crossovers in a speaker combine with a receiver active crossover when the operating range is miles apart? Please explain that FOR ONCE, instead of just making me accept it.
Title: Crossover cascading
Post by: Yahzi on 2013-04-19 20:06:01
Quote
In any case, Arnold said that stacking the filters will have undesired consequences, so it appears that Yahzi is right and his friend is wrong, but for the wrong reasons.


Now you have lost me. I'm right one instance, then I'm wrong in the other. Perhaps this place is just not a good source of information. 
Title: Crossover cascading
Post by: greynol on 2013-04-19 20:13:32
http://www.hydrogenaudio.org/forums/index....st&p=831271 (http://www.hydrogenaudio.org/forums/index.php?s=&showtopic=100384&view=findpost&p=831271)

I won't be surprised when the rest of us simply ignore you after too long.

This has gone beyond silly.
Title: Crossover cascading
Post by: pdq on 2013-04-19 20:17:59
The folks here are an excellent source of information, but we are having a difficult time understanding why this is so difficult for you, so I will try one more time.

I think the problem may be that you are under the impression that an 80 Hz low pass filter passes everything below 80 Hz and removes everything above that. While it is possible to design a filter that approximates that behavior, that is not the kind of filter we are talking about here.

Most likely this would be a filter that passes frequencies below 80 Hz almost 100%, but it also passes higher frequencies to a lesser extent. 160 Hz, for example, might be attenuated to 1/2, 320 Hz to 1/4, 640 Hz to 1/8, etc. Now if you combine that with a 500 Hz low pass filter, that 640 Hz is attenuated even more. It is still not eliminated entirely, and the difference may not be audible, but it is certainly measurable.
Title: Crossover cascading
Post by: Yahzi on 2013-04-19 20:40:35
Perhaps where the confusion is coming from is that when I discussed this with my friend, he told me that in the same way that two crossover filters cascading (combining) if, for example the AVR and subwoofer low-pass filter were both engaged, would apply to speaker crossover and AVR. If the passive crossover in a speaker is isolated from the active crossover in the AVR then I just don't get how there could be any cascading.

When I argued that two LP filters combining would be a bad thing he's argument was that the passive crossovers in a speaker also cascade with an AVR so basically there would also be cancellation going on. I don't see this as the same thing. I wish someone would understand what I'm trying to say. I'm sure the effects are measurable. There will always be a measurable effect, but there is no actual cancellation going on at the kinds of frequencies we are discussing.
Title: Crossover cascading
Post by: Yahzi on 2013-04-19 20:46:12
Quote
I think the problem may be that you are under the impression that an 80 Hz low pass filter passes everything below 80 Hz and removes everything above that. While it is possible to design a filter that approximates that behavior, that is not the kind of filter we are talking about here.


I am aware that a crossover is not a brick wall. It has a slope with a rate of attenuation. With low-pass filters it's usually 4th-order, but if it's 4th-order at 80 Hz, by the time it reaches the kinds of frequencies I'm talking about in a passive speaker crossover, it would be too far down to interact in any meaningful way. So while I agree there may be measurable interaction, however slight, there is no possible way there could be actual cancellation or any audible interaction given how far apart the crossover frequencies are.

In that, I believe my friend is COMPLETELY wrong. I hope I have explained myself more clearly.
Title: Crossover cascading
Post by: julf on 2013-04-19 22:10:27
I am aware that a crossover is not a brick wall. It has a slope with a rate of attenuation. With low-pass filters it's usually 4th-order, but if it's 4th-order at 80 Hz, by the time it reaches the kinds of frequencies I'm talking about in a passive speaker crossover, it would be too far down to interact in any meaningful way. So while I agree there may be measurable interaction, however slight, there is no possible way there could be actual cancellation or any audible interaction given how far apart the crossover frequencies are.


The filters will reinforce each other. It might be measurable, it might be audible - or not. They will still reinforce each other.

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In that, I believe my friend is COMPLETELY wrong. I hope I have explained myself more clearly.


Clearly not, as it seems from the above that you are admitting that your friend is right.
Title: Crossover cascading
Post by: julf on 2013-04-19 22:16:06
But I don't understand how filters can combine if they are operating in two different ranges! How can the slopes combine if one is at 80 Hz, for eg, and another is at 500 Hz?


Because on starts a drop a bit above 500 Hz and goes down, and the other joins in a bit above 80 Hz. They both combine at, let's say, 25 Hz.

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I refuse to believe my friend is right.


I think we get that.

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Speaker crossovers CANNOT cascade with the amplifier crossover.


If you say so...

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Goodness, I had a discussion with a few EE's in another thread and they agreed that the filters cannot cascade. Now you are saying my friend is correct. WTF?


Welcome To Finland.
Title: Crossover cascading
Post by: Yahzi on 2013-04-19 22:25:32
Read this reply from the member towards the bottom.

http://www.avforums.com/forums/speakers/17...r-question.html (http://www.avforums.com/forums/speakers/1763512-crossover-question.html)

He is an EE. What qualifications do you have?
Title: Crossover cascading
Post by: greynol on 2013-04-19 22:27:57
Because on starts a drop a bit above 500 Hz and goes down, and the other joins in a bit above 80 Hz. They both combine at, let's say, 25 Hz.

Please stop with the inaccurate to the point of being nonsensical filter responses!
Title: Crossover cascading
Post by: greynol on 2013-04-19 22:32:20
Read this reply from the member towards the bottom.

http://www.avforums.com/forums/speakers/17...r-question.html (http://www.avforums.com/forums/speakers/1763512-crossover-question.html)

He is an EE. What qualifications do you have?

If you're having a better time saving face over there then by all means...
Title: Crossover cascading
Post by: Yahzi on 2013-04-19 22:38:24
Well greynol, what am I supposed to do? The EE is telling me one thing. You guys are telling me something else. Who am I supposed to trust?
Title: Crossover cascading
Post by: greynol on 2013-04-19 22:48:21
I'm an EE (so is Arny and likely others).  I really don't care who you trust. Go back and read about how I feel about your trying to air your petty laundry over here if I haven't already made myself clear about it.
Title: Crossover cascading
Post by: Yahzi on 2013-04-19 22:50:26
Well thanks for the conflicting information. You really were helpful! I'm done with this thread. At least I know in future where NOT to go for any advice.
Title: Crossover cascading
Post by: greynol on 2013-04-19 22:54:46
Just reading your posts you get conflicting information, so I'm not at all surprised.
Title: Crossover cascading
Post by: julf on 2013-04-20 10:33:32
Please stop with the inaccurate to the point of being nonsensical filter responses!


I think it would be helpful if you could point out in what way my responses are inaccurate and/or nonsensical. Mostly I am just struggling with understanding the conflicting information / questions from the OP.
Title: Crossover cascading
Post by: db1989 on 2013-04-20 12:09:02
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:
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.
Title: Crossover cascading
Post by: greynol on 2013-04-20 12:21:50
Perhaps you can provide either some math or a graphical representation on where you get 25 Hz in this latest example or how you arrived at 96 dB of attenuation in the previous example.  Until you do, I contend that these numbers make no sense (at least to me and most likely to the OP); and as such are not helping. IME these numbers are the only obvious source of contradictory information in the discussion that isn't coming from the OP. Considering everything else you've said was extremely helpful, I'm perplexed by this aspect of your contribution.

EDIT: Beaten by db1989.
Title: Crossover cascading
Post by: julf on 2013-04-20 12:40:42
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.

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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).

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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.
Title: Crossover cascading
Post by: greynol on 2013-04-20 13:12:37
The 25 Hz point was just any random point below the cut-off point of both filters (assuming, erroneously, they were high pass filters).

Assuming they are high-pass filters and assuming that by "combine" you mean the point at which the slope changes, that would occur at 80Hz, not at some random point below 80Hz.
Title: Crossover cascading
Post by: julf on 2013-04-20 16:24:28
The 25 Hz point was just any random point below the cut-off point of both filters (assuming, erroneously, they were high pass filters).

Assuming they are high-pass filters and assuming that by "combine" you mean the point at which the slope changes, that would occur at 80Hz, not at some random point below 80Hz.


The point I was trying to make was that at that random point, below the cut-off point of both filters, the gain would definitely be affected by both filters - so the effects would "combine".

As English is my third language, I might not always manage to express myself as clearly as I would like. Let me try with a graph instead, and hopefully I have now understood the situation the OP described correctly, and got all the numbers right...

So, we have 2 low-pass filters. The one in the AVR has a cut-off frequency at 80 Hz, and the one in the speaker has a cut-off frequency of 500 Hz. I used scilab to plot the resulting frequency response curves - for both filters separately, and for the combination of both in series. Does this help?

(http://www.julfmobile.org/filterplot.png)
Title: Crossover cascading
Post by: db1989 on 2013-04-20 16:59:04
The point I was trying to make was that at that random point, below the cut-off point of both filters, the gain would definitely be affected by both filters - so the effects would "combine".

And the point that various members have being trying to make is that the gain will – equally “definitely” – be affected at any point that is reached by the slopes of both filters. Including yourself! As you said in your first reply, “the signal will be affected by the transfer functions of both filters. If the crossover frequencies are far apart, the interaction will be small, but it will be there nevertheless.”

Your latest invocation of a “random point” seems to refer to some point at which this interaction becomes noteworthy. I don’t wish to speak for greynol or anyone else, but I think that’s what is causing confusion/bemusement. The conversation is about defining the point at which the effects of any two filters combine, not some subjective definition of when that effect is significant. The filters will already be interacting at any frequencies where they are both applying attenuation, which will presumably be some point before the nominal cut-off of the higher LPF, to a degree depending upon the specific way in which it is implemented.

So, the “random point” is either well-defined for any two filters of known implementation, or it’s a subjective marker for when the (always present) interaction becomes worthy of discussion. If the latter, what are your criteria?
Title: Crossover cascading
Post by: julf on 2013-04-20 17:12:25
And the point that various members have being trying to make is that the gain will – equally “definitely” – be affected at any point that is reached by the slopes of both filters. Including yourself!


And I still agree with that.

Quote
Your latest invocation of a “random point” seems to refer to some point at which this interaction becomes noteworthy. I don’t wish to speak for greynol or anyone else, but I think that’s what is causing confusion/bemusement. The conversation is about defining the point at which the effects of any two filters combine, not some subjective definition of when that effect is significant. The filters will already be interacting at any frequencies where they are both applying attenuation, which will presumably be some point before the nominal cut-off of the higher LPF, to a degree depending upon the specific way in which it is implemented.

So, the “random point” is either well-defined for any two filters of known implementation, or it’s a subjective marker for when the (always present) interaction becomes worthy of discussion. If the latter, what are your criteria?


My point was simply to show to the OP that there are some frequencies where the filters *very clearly* interact. Of course they interact to some degree at any frequency.

I think we keep flogging a rather dead horse. I agree with your view about the filters combining, and the 25 Hz point was a failed attempt at explaining the combinatorial effect. Hopefully the scilab plot explains it better.
Title: Crossover cascading
Post by: db1989 on 2013-04-20 17:35:07
Quote
Hopefully the scilab plot explains it better.
Very much so. A graph is worth a thousand words.  Thanks for taking the time to make it!
Title: Crossover cascading
Post by: julf on 2013-04-20 17:55:11
A graph is worth a thousand words.  Thanks for taking the time to make it!


The least I could do after muddling up the thread so badly...