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Subwoofer and Mains Filter - Problems?
#1
Hello,

I have a Hifi-System with Devialet 200, Bookshelf-Speakers and a Martin Logan Subwoofer.

I tried to integrate the whole system by using a low-pass filter (2nd Order) on the Subwoofer (mono) and a high-pass filter on the mains. The Problem is, that if I switch between full-range standalone mains and the filtered Subwoofer-Mains system, the standalone version sounds fuller, more bass in the upper registers.

Both filters (low and high) are set to 2nd Order. Phase on the Subwoofer ist 0°. With subwoofer and mains without highpass filter it works well. But my idea was to keep the low frequencies away from the relatively small speakers. The High-Pass filter is set to 25Hz. But it sounds as if this filter decreases the ouput even over 100Hz? Isn't it true that if I set the filter to 25 Hz, everything over 25Hz should be there as if it's unfiltered?

I hope someone can help me out. The ideal thing would be to have the same sound as with Subwoofer + Mains full, but maybe with better mid-quality and less movements on the small chassis of the bookshelfs, so that they could also play louder.

Thanks to all
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#2
I'm by no means an expert on sub-woofer integration, although I have dabbled a bit.  Please forgive me if I'm suggesting things you already know or tried out...

25 Hz seems a very low cross-over frequency to me, especially if your main speakers are bookshelf-sized.  Something in the region of 80 Hz is more normally used.  Maybe that would be worth experimenting with?

I would expect, as you did, that the 25 Hz high-pass filter on the main speakers shouldn't be having any noticeable effect at 100 Hz.  However if the speakers are small I would also expect there's not much output from them anyway at 25 Hz.

Are you sure that the sub-woofer is receiving a low-pass filtered signal both when the mains get a full-range signal and when they're high-pass filtered?  From what you've said it sounds as though maybe the sub is also getting a full-range signal when the mains are.  At least, that's the only way I can understand what you described.

My other thought was to do with time/phase alignment of the sub-woofer with the mains.  Unless you've taken some care to make it so, it's very likely that the sub and mains will not be in phase at the cross-over frequency.  That is generally considered to be a requirement for good integration.  Maybe some tinkering with the phase control on the sub-woofer would be useful.  (Is it continuously variable, or just a 0/180 degrees polarity control?)
Roon (Mac Mini), Wilson Benesch Full Circle, Expert 1000 Pro CI, Kaiser Chiara
Warwickshire, UK
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#3
(27-Oct-2015, 18:58)thumb5 Wrote: I'm by no means an expert on sub-woofer integration, although I have dabbled a bit.  Please forgive me if I'm suggesting things you already know or tried out...

25 Hz seems a very low cross-over frequency to me, especially if your main speakers are bookshelf-sized.  Something in the region of 80 Hz is more normally used.  Maybe that would be worth experimenting with?

I would expect, as you did, that the 25 Hz high-pass filter on the main speakers shouldn't be having any noticeable effect at 100 Hz.  However if the speakers are small I would also expect there's not much output from them anyway at 25 Hz.

Are you sure that the sub-woofer is receiving a low-pass filtered signal both when the mains get a full-range signal and when they're high-pass filtered?  From what you've said it sounds as though maybe the sub is also getting a full-range signal when the mains are.  At least, that's the only way I can understand what you described.

My other thought was to do with time/phase alignment of the sub-woofer with the mains.  Unless you've taken some care to make it so, it's very likely that the sub and mains will not be in phase at the cross-over frequency.  That is generally considered to be a requirement for good integration.  Maybe some tinkering with the phase control on the sub-woofer would be useful.  (Is it continuously variable, or just a 0/180 degrees polarity control?)


One other question on this. Is there any rule how to change the phase when I decide to use 1, 2, 3, 4th order filtering? For Example if I use full range or 2nd order high pass on the speakers. Does that effect the phase of the subwoofer?

Unfortunately I can only choose 0, 90, 180, 270 degree of phase.

Right now, I'm more blending the speakers and subwoofer. The subwoofer crossover is at 90Hz. The speakers was at 25, now at 50hz. Should I have to set both filter at the same value? Or do i need o leave a bigger gab between them?

The subwoofer is not getting a signal when the speakers get full range. I can even turn the subwoofer off and I will notice a big difference between the 25hz filter and the full-range. Sounds like if the filter affects much more than just up to 25Hz.

Thanks for help.
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#4
(27-Oct-2015, 19:19)technikspezi Wrote: One other question on this. Is there any rule how to change the phase when I decide to use 1, 2, 3, 4th order filtering? For Example if I use full range or 2nd order high pass on the speakers. Does that effect the phase of the subwoofer?

Unfortunately I can only choose 0, 90, 180, 270 degree of phase.

There may be a relationship but if so I don't think its one that you can predict.  Typically if the "phase" control on a sub-woofer has more flexibility than just 0/180 degrees, it is in reality a time delay control with the delay expressed in terms of phase at a fixed frequency (normally 80 Hz).  The purpose of this is at least partly to correct for difference in acoustic distance between the sub and main speakers.  At least, that is my understanding.  So there is no a priori way to determine what phase will give the best integration - it's a matter of experimentation, and ideally measurement, in your set-up.  The aim is to get the flattest frequency response around the cross-over point.

(27-Oct-2015, 19:19)technikspezi Wrote: Right now, I'm more blending the speakers and subwoofer. The subwoofer crossover is at 90Hz. The speakers was at 25, now at 50hz. Should I have to set both filter at the same value? Or do i need o leave a bigger gab between them?

From what I've read, the normal recommendation is to set the same cross-over frequency on both mains and sub.

However, in the end it's up to your ears to decide what you prefer.

(27-Oct-2015, 19:19)technikspezi Wrote: The subwoofer is not getting a signal when the speakers get full range. I can even turn the subwoofer off and I will notice a big difference between the 25hz filter and the full-range. Sounds like if the filter affects much more than just up to 25Hz.

OK, that certainly blows up my theory Smile  In that case I'm stumped.  Sorry.
Roon (Mac Mini), Wilson Benesch Full Circle, Expert 1000 Pro CI, Kaiser Chiara
Warwickshire, UK
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#5
you have your main speakers set too low in the frequency range.

on average human hearing only goes down to 20 hz, and not much music really plays that low. so basically you have made your speakers full range bar 20 - 24 hz. what speakers do you have? they have full specifications on the frequency range possible and will give you a better idea of the filters required. generally speaking everyone in here was correct with the 80hz low/high filters. you set them to the exact same number.

Now you also need to realise that the order number of filter actually makes a big big difference! if you select a 80hz high pass filter on your main speakers, it will still play sounds below the cutoff frequency. how much it plays is dependant on the filter order you use.

i have attached a graph here to show you the basic difference

[Image: 2uetkt5.png]

So you can see here that a first order filter will have the most "overflow" into the frequencies you want to cut off while the fourth order filter in the devialet will have the least.

Now the best filter order to use is going to be different for every speaker, enclosure etc but a good place to start is 80 high and low pass with a fourth order filter.
Amp - Devialet 400 Speakers - vivid audio B1 Speaker cable - audioquest oak Power conditioner - furman SPR 16IE Source - audio PC with paul pang audio usb card v3 and paul pang red dual usb cable running through jplay. usb card powered by teddy pardo power supply Source 2 - line in from integra AV receiver (TV)
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#6
(27-Oct-2015, 23:59)completeluxury Wrote: Now the best filter order to use is going to be different for every speaker, enclosure etc but a good place to start is 80 high and low pass with a fourth order filter.

Thanks for your detailed response. Is there any kind of "rule" to choose the filter order? What is it depending on the speaker? Actually I have set the filter to 2nd Order. But I will try 4th order also. Can I try to use different ones for the subwoofer and the mains? So for example using 4th-Order with the mains and 2nd Order for the Subwoofer?

How will the filter order interact with the phase of the sub?

Thanks
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#7
Im on the way to work for the day ill go into the rest later!
Amp - Devialet 400 Speakers - vivid audio B1 Speaker cable - audioquest oak Power conditioner - furman SPR 16IE Source - audio PC with paul pang audio usb card v3 and paul pang red dual usb cable running through jplay. usb card powered by teddy pardo power supply Source 2 - line in from integra AV receiver (TV)
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#8
Just to avoid confusion: the diagram completeluxury posted shows a low-pass filter, which would be applied to/in your sub.  In your case I thought you were worried about loss of output from the mains when they were high-pass filtered.

If you mentally flip the diagram round (left-right) to make it look right for a high-pass filter you can see that the filter order doesn't have much effect on the output level within the pass band, that is above the corner frequency - in other words, in the part of the diagram covered by the light green block.

Put into your context: if you're setting the filter corner frequency to 25 Hz, it shouldn't have any audible effect at 100 Hz whether you use a 2nd or 4th order filter.

I'd suggest you should probably try to work out whether the high-pass filter is working correctly on the mains, and if not, fix it before trying to integrate the sub.  The best way to do that will be to use some audio measurement software such as REW (other programs are available...).  Otherwise I think you'll be chasing your tail.

It will quickly get more complicated once the sub is added and you start worrying about integrating it nicely.  For example, you can read more about it (including a discussion about how to select filter orders) at these links:
What I learned from my reading on this topic is that there is no "one size fits all" set of right answers that you can just apply in all cases because the behaviour of each combination of main speakers, sub-woofer and placement in the room will be different.  To get the best result in your set-up you need to invest time to experiment and listen carefully to (and preferably measure) the result of each changes you make.
Roon (Mac Mini), Wilson Benesch Full Circle, Expert 1000 Pro CI, Kaiser Chiara
Warwickshire, UK
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#9
Removed.
Amp - Devialet 400 Speakers - vivid audio B1 Speaker cable - audioquest oak Power conditioner - furman SPR 16IE Source - audio PC with paul pang audio usb card v3 and paul pang red dual usb cable running through jplay. usb card powered by teddy pardo power supply Source 2 - line in from integra AV receiver (TV)
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#10
Just a question in advace. Can you hear/locate the subwoofer when it's playing alone without any other speakers (the mains).
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