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To use notch filter, or not?

DanielT

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Scenario, three-wave loudspeaker where each driver is powered by its own amplifier. Bass driver should work up to 250-300 Hz. Midrange should work up to around 2500 Hz. Why not plug in some resistors and capacitors? Advantages disadvantages? Note that three different separate amplifiers that power the bass, midrange and tweeter respectively.
Here's a calculation program, I entered some different frequencies and this came up. Now I sat Attenuation Level Desired to 30 dB but I can increase it. Advantages and disadvantages of having, for example, 60 dB vs 30 dB?

This is how the notch filter is constructed:

Wideband-notch-filter.png

250 Hz cut of:
Screenshot_2022-08-22_094600.jpg


2500 Hz cut of:
Screenshot_2022-08-22_094618.jpg




* Does this type of notch filter affect the amplifiers ability to drive the speaker elements BELOW the set cutoff level,
notch filter frequency?

*A few resistors and capacitors can hardly cause any audible distortion to be introduced into the sound chain/solution, can they?

* Does the notch filter in any way affect the FR below the set cutoff level?


From the link above about the filter I now used:

This wideband notch filter calculator calculates the values of the resistors and capacitors based on the notch frequency range entered and the amount of attenuation that is desired at the output.

Unlike the twin-T notch filter, this wideband notch filter can have a much larger range for the bandstop.

To use this calculator, a user enters the lower frequency and the upper frequency. The lower frequency is where the user wants the bandstop to start and the upper frequency is where the user wants the bandstop to end. So, for example, if you want the bandstop to be active from 1KHz to 10KHz, 1KHz is the lower frequency and 10KHz is the upper frequency.

The next important part of this calculator is that you specify the amount of attenuation that is desired at the start and stop points of the bandpass filter. The different attenuation values are -15dB, -20dB, -30dB, -40dB, -50dB, and -60dB.
 

Calleberg

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Don´t! Because it.... "sucks" :) Its a band STOP filter, attenuating everything within this band 30dB, but nothing outside.

But if you really need the Super Steep Characteristics there is a way... And it is indeed a type of notch filter combo...
 
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Tangband

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Edit: This answer is about eq:ing out peaks, nothing else.

You have to try in every case . I have tried this with a bassdriver from jbl, and my HYBRID project , and couldnt hear any advantages with mixing passive components with active dsp crossover. My experience is that mixing passive with active dont bring audible benefits in the tweeter area , either. An active dsp crossover without any passive components between amplifier and tweeter will in most cases give you a clearer, more dynamic sound with more details.

If you dont believe me - try it.:)
Its time consuming, but maybe worth it.

Regarding notch filtering, both active and passive - the all have some sideeffects to the sound. Dont believe otherwise.
Peter Stendl from faktiskt.io is right in this.
If using such drivers that need a notch filter, its much better to :

1. Use drivers that are well behaved and dont need a notch filter In the first place.
2. Do Crossover much steeper with an active dsp crossover . The peak from the driver at maybe 6 kHz will then be inaudible.

This is my experience with the bassdriver from jbl 530, and the Seas er18rnx, and some scanspeak tweeters.
 
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Thomas_A

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Edit: This answer is about eq:ing out peaks, nothing else.

You have to try in every case . I have tried this with a bassdriver from jbl, and my HYBRID project , and couldnt hear any advantages with mixing passive components with active dsp crossover. My experience is that mixing passive with active dont bring audible benefits in the tweeter area , eather. An active dsp crossover without any passive components between amplifier and tweeter will in most cases give you a clearer, more dynamic sound with more details.

If you dont believe me - try it.:)
Its time consuming, but maybe worth it.

Regarding notch filtering, both active and passive - the all have some sideeffects to the sound. Dont believe otherwise.
Peter Stendl from faktiskt.io is right in this.
If using such drivers that need a notch filter, its much better to :

1. Use drivers that are well behaved and dont need a notch filter In the first place.
2. Do Crossover much steeper with an active dsp crossover . The peak from the driver at maybe 6 kHz will then be inaudible.

This is my experience with the bassdriver from jbl 530, and the Seas er18rnx, and some scanspeak tweeters.
A steep active filter may indeed make a 6 kHz resonance inaudible. However a 6 kHz high impedance notch may reduce 3rd harmonic distortion around 2 kHz which may or may not be audible.
 

Tangband

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A steep active filter may indeed make a 6 kHz resonance inaudible. However a 6 kHz high impedance notch may reduce 3rd harmonic distortion around 2 kHz which may or may not be audible.
A big problem with notch filtering, active or passive is that they are never at the same frequency . In my HYBRID the left speaker with Seas er18rnx had a first breakup at 4,3 KHz , and the right was at 4,8 KHz . So one need to measure and see how it looks like. Much easier to use steeper crossovers with a dsp .
In the case of HYBRID , a crossover at 2,3 kHz with 36/dB oct made the breakup resonance inaudible.
 
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Plcamp

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As I understand it, if a driver has a breakup you wish to suppress, it is better for 2nd and 3rd order subharmonics IM distortion performance to suppress that breakup with a series notch filter that inserts high impedance at breakup…because it is only that high impedance which suppresses the sub harmonic distortion mechanism. Ie a steeper earlier pre power amp cross won’t suppress that.
 
OP
DanielT

DanielT

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Okay, but IF the signal below the cut off frequency with a notch filter is not negatively affected, why not lower noise levels by 30-60 dB above the frequencies that the driver should not be used anyway? That together with crossover filter (whichever type you choose, passive, active, digital).

Especially if you have a driver that breaks up unfavorably in frequencies above set crossover point, for example a driver with cone made of aluminum.Check here what Purifi did and their results, I'm pasting all seven pages so you can read that PDF:
Screenshot_2022-08-22_130321.jpg
Screenshot_2022-08-22_130330.jpg
Screenshot_2022-08-22_130338.jpg
Screenshot_2022-08-22_130344.jpg
Screenshot_2022-08-22_130352.jpg
Screenshot_2022-08-22_130359.jpg
Screenshot_2022-08-22_130405.jpg
 
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Tangband

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As I understand it, if a driver has a breakup you wish to suppress, it is better for 2nd and 3rd order subharmonics IM distortion performance to suppress that breakup with a series notch filter that inserts high impedance at breakup…because it is only that high impedance which suppresses the sub harmonic distortion mechanism. Ie a steeper earlier pre power amp cross won’t suppress that.
This is probably a false statement, because if this were true, one could never use a seas DXT tweeter with its enormous breakup mode at 28 KHz .
I think you and ThomasA are wrong on this.

As I wrote earlier, if you never exite the breakup frequency ( with the help of a steep crossover ) there is no problem .
This steep crossover is best done with a dsp.
 
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Plcamp

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if you never exite the breakup frequency
It’s counter intuitive to me as well.

But here’s the thing. I believe exciting the driver at 1/3 the breakup frequency actually does excite the driver at the breakup frequency, and that’s why you get higher IM distortion even if you have crossed out the breakup with a steep dsp?

The driver is looking for an excuse to ring at breakup…provided by subharmonic excite signal?
 

Tangband

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It’s counter intuitive to me as well.

But here’s the thing. I believe exciting the driver at 1/3 the breakup frequency actually does excite the driver at the breakup frequency, and that’s why you get higher IM distortion even if you have crossed out the breakup with a steep dsp?

The driver is looking for an excuse to ring at breakup…provided by subharmonic excite signal?
Again, if it worked like that , noone could use metal drivers …
 

Plcamp

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That’s not what is claimed…the claim is that sub harmonic IM levels will be decreased with series notch…not that it would be unusable without them.

Looking at the driver being a source, one can imagine that the presence of the series notch limiting resistor would cause suppression of the driver’s ability to produce third order distortion vs no limiting resistor at all. The series notch resistor won’t allow the driver to create as much breakup frequency 2nd and 3rd order current as when it is absent?

Edit: I will try it on this woofer at some point. Which raises its own question, given I run two of these in parallel. I think for this to work in the case of two parallel woofers, each woofer might need its own series notch. Gotta think on that more, but you can’t control the notch r value if (thinking of the driver as a source) you have two sources in parallel?
F3D4944D-217D-4B93-862B-8A0AF36FF92A.png
 
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Tangband

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That’s not what is claimed…the claim is that sub harmonic IM levels will be decreased with series notch…not that it would be unusable without them.

Looking at the driver being a source, one can imagine that the presence of the series notch limiting resistor would cause suppression of the driver’s ability to produce third order distortion vs no limiting resistor at all. The series notch resistor won’t allow the driver to create as much breakup frequency 2nd and 3rd order current as when it is absent?
My approach doing ( limited ) passive and active ( extended, many tries ) notch filters is that the sound will become worse, not better . If you dont believe me, try it for yourself.
 

Thomas_A

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This is probably a false statement, because if this were true, one could never use a seas DXT tweeter with its enormous breakup mode at 28 KHz .
I think you and ThomasA are wrong on this.

As I wrote earlier, if you never exite the breakup frequency ( with the help of a steep crossover ) there is no problem .
This steep crossover is best done with a dsp.
You may get third harmonics at f/3. Ie if break-up occurs at 5 kHz you will have harmonics at 1.7 kHz. A steep digital filter at e.g. 3 kHz will not change this. A high impedance seen by the driver will.
 

Tangband

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You may get third harmonics at f/3. Ie if break-up occurs at 5 kHz you will have harmonics at 1.7 kHz. A steep digital filter at e.g. 3 kHz will not change this. A high impedance seen by the driver will.
As I said - people use seas dxt without problems, Kef uses a metal tweeter in their uni Q drivers ( without notchfiltering at the tweeters breakupmode ! ) without problems .

You see also no such problems in monitors from Genelec , and they use metal tweeters and have very low distortion in the audible frequency area, despite the directly coupled amplifiers.

I.Ö investigated this in the beginning of the -90, and the conclusion with metal dometweeters with big breakup modes was that they were less good with high resolution material , but there was no problem at all with CD material using steep filtering , only using the tweeter below the breakup frequency

The same will be true with steep dsp crossovers - if its steep enough, the resonance will not be exited.
 
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Scgorg

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Let's say I have a driver with a breakup/resonance at 27kHz. The driver will move more easily at this frequency, similar to the main resonance frequency of a loudspeaker driver. If I play a tone with this same driver, it will produce some nth-order distortion, because it isn't perfectly linear. Let's say this tone is 9kHz, exactly one-third of the breakup frequency. The driver will now produce a 2nd order 18kHz tone, a 3rd order 27kHz tone, a 4th order 36kHz tone and so on.

As we noted earlier, the driver wants to move at 27kHz. That's smack dab in the middle of the 3rd harmonic, and so it moves a lot more at this frequency than the frequencies immediately next to it (let's say 24kHz and 30kHz), producing higher distortion. The harmonic distortion in itself is harmless, as it is out of the human hearing range in the first place. However in producing this 3rd harmonic 27kHz tone, the driver is in fact moving at that frequency, which can influence intermodulation distortion.

I think it's worthwhile to consider, however, that this 3rd harmonic distortion may still be very low in amplitude (let's be charitable for the sake of example and say 3%, which is -30dB). In addition any music will have considerably lower amplitude at such high frequencies. The audibility of the intermodulation effects introduced by such a breakup not being notched would seem to be low, intuitively. Personally I wouldn't bother notching tweeters.

The story can be a little different for non-tweeters, where the breakup occurs well within the audible band (e.g. the magnesium SEAS midwoofers).
 
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DanielT

DanielT

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Don´t! Because it.... "sucks" :) Its a band STOP filter, attenuating everything within this band 30dB, but nothing outside.

But if you really need the Super Steep Characteristics there is a way... And it is indeed a type of notch filter combo...
Exactly a STOP filter .That's what's interesting.:)

Hmm, I wonder. There must be something I'm missing. Another example. Let's say you have a subwoofer, where you want to set the crossover at 80 Hz. You use some kind of low-pass filter but in addition to it a notch filter with a bandwidth of 80-20 kHz, all frequencies above 80 Hz are attenuated down by 60 dB using two resistors and two capacitors. Where is it that makes it bad? Or hm, do the capacitors cost a lot of money?

With an LP with a slope of at least 24dB, there is probably no need for a notch filter in a subwoofer, but I'm still a little curious.:)

Does the power somehow reduce to frequencies below 80 Hz in this case?



Screenshot_2022-08-22_140623.jpg

 
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Scgorg

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As I said - people use seas dxt without problems, Kef uses metal tweeter in their uni Q drivers ( without notchfiltering at the tweeters breakupmode ! ) without problems .

You see no such problems in monitors from Genelec , and they use metal tweeters and have very low distortion .
Usually people only show 2nd order distortion to 10kHz, 3rd order to 6.7kHz and so on because any distortion beyond that is uninteresting. Amir typically does this too, but if you look at the extended distortion view he did for his 8351B review at 96dB, you'll clearly see the sharp spikes in distortion at 1/2 and 1/3 of the breakup mode. See included image. I maintain that this distortion is unimportant, but it's there.
index.php
 

Thomas_A

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Plcamp

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My approach doing ( limited ) passive and active ( extended, many tries ) notch filters is that the sound will become worse, not better . If you dont believe me, try it for yourself.
It’s not that “I don’t believe you”. This is a mechanism intended to supplement dsp techniques from my point of view.

The one thing low impedance power amps in combination with pre-power amp crossover and eq systems cannot do is raise the impedance seen by the driver at select frequency ranges. If a driver is in any way the source of harmonic voice coil current modulation, then that modulation will see a virtual zero impedance back into a high quality amp. Only a series impedance can change that situation.

It seems plausible to me, and the test results seem to agree.
 

tomtoo

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Hmm, I wonder. There must be something I'm missing. Another example. Let's say you have a subwoofer, where you want to set the crossover at 80 Hz. You use some kind of low-pass filter but in addition to it a notch filter with a bandwidth of 80-20 kHz, all frequencies above 80 Hz are attenuated down by 60 dB using two resistors and two capacitors. Where is it that makes it bad? Or hm, do the capacitors cost a lot of money?

With an LP with a slope of at least 24dB, there is probably no need for a notch filter in a subwoofer, but I'm still a little curious.:)

Does the power somehow reduce to frequencies below 80 Hz in this case?



View attachment 225987

Have fun with resistors that can stand a lot of power. Not to bad in sweden winter time. ;)

Imo there is just no need for.
 
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