High pass filter - a rather extreme example

[dbsfgyd1]

You mean the singer, right?

i though we only can get rid of the drummer….dang informative this site… LOL!!1

 

[mdlewis]

I think you all know this but I'll repeat anyway - fundamentally (haha) this is why a HPF can clean up your sound. Real air moved at these lower frequencies actually can cause a host of problems as the length of the sound waves are in same order of magnitude as room dimensions. Cancelation, beats, interference etc. can really interfere with your tone and make you sound like crap. Removing these frequencies from the actual audio spectrum may not change the sound you "hear" (although it will change the actual feel since you're no longer moving air) much because most of the information comes from your brain extrapolating from the harmonic series of the overtones. Your brain, well at least mine, is much smaller than the room dimensions, and cancelation and beat frequencies don't seem to be contributing to much of the bass-related problems in there.

 

[makanudo]

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:
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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..

Pardon the hijack but as I'm trying to set the Global EQ settings on my HX Stomp for live use I'm taking into consideration all the HPF and Fletcher Munson curve data I can get and while I think I understand it (with lots of help from your post), I have some doubts.

My understending so far is that as we get louder, the traditional bass/treble boosted settings will end up sounding harsher at around 1.5-5 kHz since they need less SPL to achieve equal loudness to the mids, but also scooping the 200 to 900 Hz area isn't as sacrilegious at many people seem to scream bloody murder at since it needs slightly less SPL to achieve equal loudness to the 1 Khz baseline. If I'm understanding this correctly that is.

My conundrum is with the lows. Namely 60 to a 100 Hz. Normally people advice to cut back on the bass controls when going higher in volume but the graph clearly shows you need to boost them a bit to achieve equal loudness. However, I'd assume you wouldn't want a completely 'equal' percieved loudness to the mids and highs in the bass region when usually that's where the money is to provide the low end and energy we often desire to fill out the spectrum. If anything you'd want it to be maybe like 1-3 dB higher than the adjacent lower mid frequencies to feel some heft and meat. At least I know I would.

I'm using the 90 phon curve for reference.

I recall this Billy Sheehan explanation of his Helix patches where he sets his EQ to fight the Fletcher munson curve by going frowny face i.e. cutting bass and highs because as things go louder bass and treble go louder (in his words).



Around 16:40 in this video.

Does he have it backwards? as I understand this, you'd actually want to boost some 60-100 and pull back 4-5k to keep the flatter response. The fundamental's harmonics in the 100-250 range would take care of the perceived bass no?

Anyway, I'm also curious and learning about this stuff. Greatly appreciate any further discusion here or in private.

Cheers!

 

[Wasnex]

Pardon the hijack but as I'm trying to set the Global EQ settings on my HX Stomp for live use I'm taking into consideration all the HPF and Fletcher Munson curve data I can get and while I think I understand it (with lots of help from your post), I have some doubts.

My understending so far is that as we get louder, the traditional bass/treble boosted settings will end up sounding harsher at around 1.5-5 kHz since they need less SPL to achieve equal loudness to the mids, but also scooping the 200 to 900 Hz area isn't as sacrilegious at many people seem to scream bloody murder at since it needs slightly less SPL to achieve equal loudness to the 1 Khz baseline. If I'm understanding this correctly that is.

My conundrum is with the lows. Namely 60 to a 100 Hz. Normally people advice to cut back on the bass controls when going higher in volume but the graph clearly shows you need to boost them a bit to achieve equal loudness. However, I'd assume you wouldn't want a completely 'equal' percieved loudness to the mids and highs in the bass region when usually that's where the money is to provide the low end and energy we often desire to fill out the spectrum. If anything you'd want it to be maybe like 1-3 dB higher than the adjacent lower mid frequencies to feel some heft and meat. At least I know I would.

I'm using the 90 phon curve for reference.

I recall this Billy Sheehan explanation of his Helix patches where he sets his EQ to fight the Fletcher munson curve by going frowny face i.e. cutting bass and highs because as things go louder bass and treble go louder (in his words).



Around 16:40 in this video.

Does he have it backwards? as I understand this, you'd actually want to boost some 60-100 and pull back 4-5k to keep the flatter response. The fundamental's harmonics in the 100-250 range would take care of the perceived bass no?

Anyway, I'm also curious and learning about this stuff. Greatly appreciate any further discusion here or in private.

Cheers!

I eyeballed the chart and estimate these decibel differences:

120 Phon decibel difference between 1kHz and 60Hz = 7dB
120 Phon decibel difference between 1kHz and 4kHz = 14dB
120 Phon decibel difference between 4kHz and 60Hz = 21dB


90 Phon decibel difference between 1kHz and 60Hz = 8dB
90 Phon decibel difference between 1kHz and 4kHz = 10dB
90 Phon decibel difference between 4kHz and 60Hz = 18dB

90 Phon decibel difference between 1kHz and 60Hz = 15dB
90 Phon decibel difference between 1kHz and 4kHz = 7dB
90 Phon decibel difference between 4kHz and 60Hz = 22dB

This should illustrate that you need to change the contour of your EQ when SPL changes. Also, the rate of change for the lows is not the same as the rate of change for the high mids. So, you need to use different amounts of compensation at different frequencies.