Trying to understand “phase”, Third order and fourth order” low pass filters

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Analogous

Analogous

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Hi,
I have a subwoofer with the following settings that I can’t figure out.
Phase (0-180 - invert or in steps)
Third order low pass filter settings
Fourth order Low pass filter settings.
The Sub is called Dynamo 800X (from Martin Logan). I have been trying to adjust the settings by the ear. (after using Anthem room correction) The company website is very economical with words on the topic. I am feeding the sub full range signal and it’s for two channel music
Can anyone recommend a good article or video that explains these concepts and how to adjust these settings?
Thank you
 
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Analogous said:
Hi,
I have a subwoofer with the following settings that I can’t figure out.
Phase (0-180 - invert or in steps)
Third order low pass filter settings
Fourth order Low pass filter settings.
The Sub is called Dynamo 800X (from Martin Logan). I have been trying to adjust the settings by the ear. (after using Anthem room correction) The company website is very economical with words on the topic. I am feeding the sub full range signal and it’s for two channel music
Can anyone recommend a good article or video that explains these concepts and how to adjust these settings?
Thank you
Click to expand...
Have you downloaded the operating manual for the 800X. All settings are mentioned therein.

 
Analogous said:
Hi,
I have a subwoofer with the following settings that I can’t figure out.
Phase (0-180 - invert or in steps)
Third order low pass filter settings
Fourth order Low pass filter settings.
The Sub is called Dynamo 800X (from Martin Logan). I have been trying to adjust the settings by the ear. (after using Anthem room correction) The company website is very economical with words on the topic. I am feeding the sub full range signal and it’s for two channel music
Can anyone recommend a good article or video that explains these concepts and how to adjust these settings?
Thank you
Click to expand...

The phase is self explanatory, it adjusts the phase in degrees, best to play around with it to see what works for you.

Third and Fourth order defines the slope, meaning 18db for 3rd order or 24db for 4th order. A low pass will filter higher frequencies while sending the lower frequencies unfiltered based on the frequency on which you set it. I would recommend playing around with 50-150Hz to see what suits you, I'd also in general recommend the 4th order.
 
The LPF (and HPF) is just a filter meant to pass frequencies either below or above the set frequencies, it is not a brick wall and comes with a slope and slope type.

Phase is time domain, a fixed time delay in ms will affect different phase shifts at different frequencies. While a fixed phase shift will affect different delay in ms in different frequencies. Out of the gate go with invert first IMO.
 
Decadent_Spectre said:
The LPF (and HPF) is just a filter meant to pass frequencies either below or above the set frequencies, it is not a brick wall and comes with a slope and slope type.

Phase is time domain, a fixed time delay in ms will affect different phase shifts at different frequencies. While a fixed phase shift will affect different delay in ms in different frequencies. Out of the gate go with invert first IMO.
Click to expand...
Thanks for this @Decadent_Spectre.
 
Changing phase is nothing but electrically delaying the subwoofer signal, which helps in time aligning the subwoofer with the mains so that they are in the same phase at the crossover point.
Most subwoofers offer only 2 options (0 or 180). 180 is same as acoustically wiring the +ve and -ve leads of the speaker terminal in reverse (i.e reversing the polarity of the subwoofer).
A continuously variable delay from 0 to 180 offers more control and can be useful if the subwoofer is placed at odd positions from the main speakers or along the opposite wall.

Filter is nothing but a shelf (attenuation) applied at the crossover point. The industry standards are 6db/12db//18db/24db...even 48db.
'Low Pass Filter' of say 150hz on the subwoofer at 12db slope, will attenuate the signal strength by half, i.e 12db per octave above 150hz, but will allow full signal under 150 to play.
An 18db slope will attenuate the signal by 2/3rd or 18db per octave above 150hz.
A 24db will offer total attenuation above 150hz (it is like chopping off the entire frequency beyond 150hz from the subwoofer).

The slope mentioned above is a general standard, but will vary depending on the type (Butterworth, Linkwitz Riley (the common ones) or Bessel or sometimes intermix in complex crossovers).

High Pass Filter is opposite to Low Pass and allows frequencies higher than the crossover point to pass through.
Band Pass Filter has a low pass at one end and a high pass at the other end, especially in a 3-way where you dont want the midrange driver to play between 2 frequencies, like say between 300 hz (high pass) and 3 khz (low pass).

Subsonic filter is common to subwoofers to protect them from playing too low and bottoming out. It is usually provided at around 30/35 hz at 12 or 18 db fixed slope.
 
Kannan the filter are not brick walls, even a 48db filter will "leak" sound.

A 24db LR filter will be about 6db down at the selected frequency so the roll off starts much higher, even an octave above/below there will be slight attenuation.
 
Kannan said:
Changing phase is nothing but electrically delaying the subwoofer signal, which helps in time aligning the subwoofer with the mains so that they are in the same phase at the crossover point.
Most subwoofers offer only 2 options (0 or 180). 180 is same as acoustically wiring the +ve and -ve leads of the speaker terminal in reverse (i.e reversing the polarity of the subwoofer).
A continuously variable delay from 0 to 180 offers more control and can be useful if the subwoofer is placed at odd positions from the main speakers or along the opposite wall.

Filter is nothing but a shelf (attenuation) applied at the crossover point. The industry standards are 6db/12db//18db/24db...even 48db.
'Low Pass Filter' of say 150hz on the subwoofer at 12db slope, will attenuate the signal strength by half, i.e 12db per octave above 150hz, but will allow full signal under 150 to play.
An 18db slope will attenuate the signal by 2/3rd or 18db per octave above 150hz.
A 24db will offer total attenuation above 150hz (it is like chopping off the entire frequency beyond 150hz from the subwoofer).

The slope mentioned above is a general standard, but will vary depending on the type (Butterworth, Linkwitz Riley (the common ones) or Bessel or sometimes intermix in complex crossovers).

High Pass Filter is opposite to Low Pass and allows frequencies higher than the crossover point to pass through.
Band Pass Filter has a low pass at one end and a high pass at the other end, especially in a 3-way where you dont want the midrange driver to play between 2 frequencies, like say between 300 hz (high pass) and 3 khz (low pass).

Subsonic filter is common to subwoofers to protect them from playing too low and bottoming out. It is usually provided at around 30/35 hz at 12 or 18 db fixed slope.
Click to expand...
Thank you @Kannan. This is the clearest explanation of these terms I have read so far.
I am trying to figure out how all these and more (standing waves, latency, volume), come together for good integration and sound. I can understand why setting up a sub well takes patience and effort.
I feel, among all the components in the chain, the sub set up and 20-120 hz are the hardest to get right.
 
Decadent_Spectre said:
Kannan the filter are not brick walls, even a 48db filter will "leak" sound.

A 24db LR filter will be about 6db down at the selected frequency so the roll off starts much higher, even an octave above/below there will be slight attenuation.
Click to expand...
True..there is no 100% attenuation, but it is close to that.
The slope will also impact the electrical phase, a 12db will actually invert the phase and 24db will not.

So it is quite common to see 24db LR as standard in pro audio DSPs
 
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My subwoofer plate amplifier is a generic made in china class D amplifier but very nice. They don't have any variable phase control. So you can play them at 0deg or 180deg phase difference. This caused a deep null of -16db between 80 Hz to 150 Hz - the critical midbass region in my sound stage when played either at 0 deg or 180 deg electrical phase. This was when the subwoofer was in line with the main speakers.

I tried turning my subwoofer physically to change the acoustic phase and got a flat response at around 45deg w.r.t the main speakers. So it's not very important to have electronic delay in subwoofer as you can do that delay by manual positioning the angle of the subwoofer too. But to do all this you will need a good measuring tool like REW.
 
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