High pass filter - a rather extreme example

[lucas303]

One of the attached audio clips is an unprocessed (other than conversion to mp3 so I could post) clip of the open F#0 string on my Dingwall NG2. That note has a fundamental frequency of 21.83 Hz. The other clip is the same other than application of a high pass filter at 34 Hz (and also conversion to mp3, obviously). The slope is extreme to cut out as much of the fundamental as possible. In the high passed clip, there is basically no fundamental and all that's present are the first and higher harmonics. I believe the first harmonic is around 43 Hz.

There's nothing really scientific about this but you might get insight into a few things: the ability of your audio playback gear to reproduce 21.83 Hz; your ability to hear 21.83 Hz (assuming your system can reproduce it, which is no small feat); and how much that fundamental frequency matters to you as compared to just having the higher harmonics.

 

[Cal03]

I'm listening through headphones (Audio Technica ATH-M40x) and I could hardly tell the difference between the two files. To me this shows that the subcontrabass register can still have musical value even if the fundamental isn't actually there.

-Cal.

 

[Passinwind]

One of the attached audio clips is an unprocessed (other than conversion to mp3 so I could post) clip of the open F#0 string on my Dingwall NG2. That note has a fundamental frequency of 21.83 Hz. The other clip is the same other than application of a high pass filter at 34 Hz (and also conversion to mp3, obviously). The slope is extreme to cut out as much of the fundamental as possible. In the high passed clip, there is basically no fundamental and all that's present are the first and higher harmonics. I believe the first harmonic is around 43 Hz.

There's nothing really scientific about this but you might get insight into a few things: the ability of your audio playback gear to reproduce 21.83 Hz; your ability to hear 21.83 Hz (assuming your system can reproduce it, which is no small feat); and how much that fundamental frequency matters to you as compared to just having the higher harmonics.

In the long waterfall plot thread here on TB I tried something similar, but using this plugin: DtBlkFx VST plug-in by Darrell Barrell, a free multi effect FFT VST plugin for Windows and Mac . Unfortunately the files went missing in the 2014 software purge here, like many others in that thread, but IIRC hardly anyone claimed to be able to hear any difference in a casual A/B listening situation. But as usual, this seems like a "just depends" sort of thing IMO and IME.

 

[Sheldon D.]

Very cool. Thanks for posting this. We found that even on the B and E strings, the 2nd harmonic was more present than the fundamental. This led us to conclude that a lot of the useful pitch information was in the harmonics, not the fundamental.

 

[lucas303]

Very cool. Thanks for posting this. We found that even on the B and E strings, the 2nd harmonic was more present than the fundamental. This led us to conclude that a lot of the useful pitch information was in the harmonics, not the fundamental.

I could post similar comparison files for everyone's amusement with the B and E (and even A or D) strings, if anyone is interested in that.

 

[Passinwind]

I could post similar comparison files for everyone's amusement with the B and E (and even A or D) strings, if anyone is interested in that.

Try it on the skinny strings played up the neck too, I think you may find a different outcome up there.

 

[Pings Bass]

Very cool. Thanks for posting this. We found that even on the B and E strings, the 2nd harmonic was more present than the fundamental. This led us to conclude that a lot of the useful pitch information was in the harmonics, not the fundamental.

Yes, the brain is very good at completing the pattern and supplying the missing fundamental. This is well-established and accepted. And yet every few weeks somebody comes on talk bass and insists they want a bass rig that can produce low B fundamentals.

 

[callofcthulhu]

Which one is which? B seems louder so I assume it's hi-passed?

 

[Wasnex]

I think you may understand what's going on a little bit better if you do some experiments with an LPF to see exactly what those super low frequencies sound and feel like. Unfortunately, to really have valid results, you need cabs that are flat to 21.8 hz. Good luck with that!

In large PA systems the subs are often cross at about 80hz. If you listen to the system with everything muted except the subs, I think you will be very surprised what it sounds like. The sound will likely be perceived as sort of an incoherent rumble, sort of like distant thunder. There is very little perception of clear and focused pitch, but that does not necessarily mean subbass is not desirable.

In my experience, strong, well executed subbass does have an impact on the quality of notes, but as you go lower it sort of shift more from an aural sensation to a tactile sensation. An important factor here is the body senses low mids and upper bass better than the lowest frequencies:
Invalid Link Removed

Here's the Fletcher Munson curve . It indicates: For equal perceived loudness the SPL must increase as the frequency drops into sub bass range.

80 phon = 80dB at about 1.2kHz. To get a perceived 80 phon at 20hz the required SPL is about 115dB. The SPL difference for equal perceive loudness is about 35dB.

The final factor is it does not make any sense to send frequencies that are significantly below the port tuning frequency (Fb). Two things occur below Fb:

1. In the typical ported design, the output rolls off at 24dB per octave below Fb. So the output quickly drops off to level that is really not useable.

2. Concurrently, cone excursion increases drastically as the frequency drops below Fb. So not only does the cab become extremely less efficient, power handling also drops off by an massive amount.​

Here is an example.

​

Additional specs:

-Fb for this design is 38hz (port tuning)
-Xmax is 9.6mm (max linear excursion)​

Take a look at the Cone Displacement graph and notice that excursion dips at Fb (38hz). As the frequency approaches Fb, more of the sound comes from the port and driver excursion is suppressed.

Compare to the Maximum Electric input power and note the driver's power handling becomes excursion limited between 50 and 60hz. There is corresponding a peak in cone displacement in this frequency range.

Also notice the trace on the Cone Displacement graph turns gray as the frequency drops below about 32hz. This is where the driver hit's Xmax with 400W. Keep in mind that a 30hz HPF will already have dropped the level by 3dB at 30hz. By 30hz, the Displacement graph shows output is down about 9dB. AFAIK these graphs so response without the HPF.

Finally take a look at the Maximum Acoustic output graph and compare to the others.

AFAIK this design would produce pretty exceptional lows for a bass rig. But it if you try to force it to reproduce 21.83hz, it won't be able to produce significant output, and chances of damage the driver are very high.

My observation is that applying an HPF at the right frequency, not only increases the quality of the lows, but also may increase the perceived volume of the lows. Sending power below the systems bandpass means that power is not available for use in the bandpass. Also if the driver is flopping around like crazy trying to produce sound in a range where it does not work efficiently, it degrades how well the driver works within the system's intended frequency range..

 

[Mechanical]

Which one is which? B seems louder so I assume it's hi-passed?

I believe the same. The point @Wasnex made: "In my experience, strong, well executed subbass does have an impact on the quality of notes, but as you go lower it sort of shift more from an aural sensation to a tactile sensation."

Is how I think A is the non-filtered version.

I'll be happy if I'm wrong.

 

[dbsfgyd1]

I think you may understand what's going on a little bit better if you do some experiments with an LPF to see exactly what those super low frequencies sound and feel like. Unfortunately, to really have valid results, you need cabs that are flat to 21.8 hz. Good luck with that!

In large PA systems the subs are often cross at about 80hz. If you listen to the system with everything muted except the subs, I think you will be very surprised what it sounds like. The sound will likely be perceived as sort of an incoherent rumble, sort of like distant thunder. There is very little perception of clear and focused pitch, but that does not necessarily mean subbass is not desirable.

In my experience, strong, well executed subbass does have an impact on the quality of notes, but as you go lower it sort of shift more from an aural sensation to a tactile sensation. An important factor here is the body senses low mids and upper bass better than the lowest frequencies:
Invalid Link Removed

Here's the Fletcher Munson curve . It indicates: For equal perceived loudness the SPL must increase as the frequency drops into sub bass range.
View attachment 4475878
80 phon = 80dB at about 1.2kHz. To get a perceived 80 phon at 20hz the required SPL is about 115dB. The SPL difference for equal perceive loudness is about 35dB.

The final factor is it does not make any sense to send frequencies that are significantly below the port tuning frequency (Fb). Two things occur below Fb:

1. In the typical ported design, the output rolls off at 24dB per octave below Fb. So the output quickly drops off to level that is really not useable.

2. Concurrently, cone excursion increases drastically as the frequency drops below Fb. So not only does the cab become extremely less efficient, power handling also drops off by an massive amount.​

Here is an example.

View attachment 4475833

​

Additional specs:

-Fb for this design is 38hz (port tuning)
-Xmax is 9.6mm (max linear excursion)​

Take a look at the Cone Displacement graph and notice that excursion dips at Fb (38hz). As the frequency approaches Fb, more of the sound comes from the port and driver excursion is suppressed.

Compare to the Maximum Electric input power and note the driver's power handling becomes excursion limited between 50 and 60hz. There is corresponding a peak in cone displacement in this frequency range.

Also notice the trace on the Cone Displacement graph turns gray as the frequency drops below about 32hz. This is where the driver hit's Xmax with 400W. Keep in mind that a 30hz HPF will already have dropped the level by 3dB at 30hz. By 30hz, the Displacement graph shows output is down about 9dB. AFAIK these graphs so response without the HPF.

Finally take a look at the Maximum Acoustic output graph and compare to the others.

AFAIK this design would produce pretty exceptional lows for a bass rig. But it if you try to force it to reproduce 21.83hz, it won't be able to produce significant output, and chances of damage the driver are very high.

My observation is that applying an HPF at the right frequency, not only increases the quality of the lows, but also may increase the perceived volume of the lows. Sending power below the systems bandpass means that power is not available for use in the bandpass. Also if the driver is flopping around like crazy trying to produce sound in a range where it does not work efficiently, it degrades how well the driver works within the system's intended frequency range..

By gosh, I think I might be understanding some of this. With regard to your conclusion, how does one know how to optimally set an HPF?

For instance, I have 2 Eden 210 cabs. They are ported different and have different speakers specifically designed for each cab. (One is a XLT, the other an XST). The XLT has a mid range bump and rated to about 41hz. The XST does not have the Mid bump, but has an even response and rated down to 32 hz.

When used to together, it's a great combo with the XLT on top (closer to the ear) and the XST on the bottom off axis. Pretty much I can tell when the XLT cab get close to it's limits as it tends to get harsh sounding and the tone of notes below "A" thin out. I haven't found that point on the XST. I also am thinking I may be generating to much unusable tones on stage with this cab.

Any advice here? Thanks in advance.

 

[lucas303]

B seems louder so I assume it's hi-passed?

Is it? I tried to get them to equal volume.

 

[J_Bass]

I'm listening through my smartphone with Sennheiser HD 650 headphones and they sound the same to me.

What does this mean?

 

[Wasnex]

By gosh, I think I might be understanding some of this. With regard to your conclusion, how does one know how to optimally set an HPF?

For instance, I have 2 Eden 210 cabs. They are ported different and have different speakers specifically designed for each cab. (One is a XLT, the other an XST). The XLT has a mid range bump and rated to about 41hz. The XST does not have the Mid bump, but has an even response and rated down to 32 hz.

When used to together, it's a great combo with the XLT on top (closer to the ear) and the XST on the bottom off axis. Pretty much I can tell when the XLT cab get close to it's limits as it tends to get harsh sounding and the tone of notes below "A" thin out. I haven't found that point on the XST. I also am thinking I may be generating to much unusable tones on stage with this cab.

Any advice here? Thanks in advance.

AFAIK, choosing the optimal HPF is part science and part art form, so there is not a single correct answer.

As a end user, you are unlikely to have all the necessary details about the cab's tuning and limits to really make an informed decision. If you are using the HPF for protection, the priority is preventing the driver from exceeding Xmax. But establishing the nominal power limits and frequency where this occurs involves a choice.

In the design I posted, Eminence chose 400W for the power limit. My guess is they set the HPF at 30hz because that is the lowest frequency that prevents the driver from hitting Xmax. You might think it sounds better to run the HPF higher.

Without access to extended technical data, the way you do it is to roll the frequency up until it starts thinning out the sound, and then back the frequency down just a touch. So essentially you are tuning for the best sound and hoping it provides adequate protection.

Unfortunately if you set the HPF for the XST, you are probably not going to provide adequate protection for the XLT. And if you set the HPF to protect the XLT, you will probably loose some of the fat lows you are getting from the XLT.

Priorities can shift depending on the situation. If you need to really hammer the cabs at high SPL, the priority should probably be to protect the XLT. To get the desire results you would set the HPF higher and possibly loose some of the low end you prefer.

But if you are playing at a lower volume where the XLT will remain safe, you can set the HPF for optimal tone.

 

[callofcthulhu]

Is it? I tried to get them to equal volume.

Right and the more you "do" to them (gain, compression, normalization) the louder I'd expect the hi-passed signal to sound.

 

[Iristone]

I often high-pass at 75 Hz when making demo tapes. Looks a bit extreme, but it seems to even out the response between lower and higher notes. With a gradual roll-off it doesn't really remove too much fundamental.

 

[Ggaa]

The second one sounded a little louder on the attack end, through headphones.

 

[lucas303]

I'm listening through my smartphone with Sennheiser HD 650 headphones and they sound the same to me.

What does this mean?

Among other possibilities, it could mean any or all of:

1. Your headphones can't produce 21 Hz so you're not hearing the fundamental whether it's there or not.
2. Your ears can't hear 21 Hz so you're not hearing the fundamental whether it's there or not.
3. When it comes to a fundamental frequency at that extreme low end of the spectrum, the harmonics are much more important than the fundamental frequency itself.

Perhaps most importantly, it would be a sketchy proposition to draw any firm conclusions based on such a small sample size (and one that was admittedly created more for fun than real science).

 

[dbsfgyd1]

AFAIK, choosing the optimal HPF is part science and part art form, so there is not a single correct answer.

As a end user, you are unlikely to have all the necessary details about the cab's tuning and limits to really make an informed decision. If you are using the HPF for protection, the priority is preventing the driver from exceeding Xmax. But establishing the nominal power limits and frequency where this occurs involves a choice.

In the design I posted, Eminence chose 400W for the power limit. My guess is they set the HPF at 30hz because that is the lowest frequency that prevents the driver from hitting Xmax. You might think it sounds better to run the HPF higher.

Without access to extended technical data, the way you do it is to roll the frequency up until it starts thinning out the sound, and then back the frequency down just a touch. So essentially you are tuning for the best sound and hoping it provides adequate protection.

Unfortunately if you set the HPF for the XST, you are probably not going to provide adequate protection for the XLT. And if you set the HPF to protect the XLT, you will probably loose some of the fat lows you are getting from the XLT.

Priorities can shift depending on the situation. If you need to really hammer the cabs at high SPL, the priority should probably be to protect the XLT. To get the desire results you would set the HPF higher and possibly loose some of the low end you prefer.

But if you are playing at a lower volume where the XLT will remain safe, you can set the HPF for optimal tone.

Thanks much for the response. In general, I don't horse my gear. I tend to play with a flat EQ with a little bump at 165hz rolling with the cabs as tuned. i rarely use more than 300 on each cab , although they are rated higher.

So far so good, but for most of the gigs I have FOH support so I don't t want to make a mess for the sound company. Secondly, I have a singer that is saying he's having problems hearing to find his pitches and that my output may be the cause, so I'm interested in getting rid of what is not useful.

thanks again for your response,

 

[lucas303]

I have a singer that is saying he's having problems hearing to find his pitches and that my output may be the cause, so I'm interested in getting rid of what is not useful.

You mean the singer, right?