On cabs with good low end response vs HPFs….

[agedhorse]

Wouldn't a behavior/benefit of an external HPF be that it reduces the selected frequencies before they hit the amplifier, resulting in more available headroom? Depending on pedal order and signal chain, a HPF would potentially alter the behaviors of drive and compression pedals after it in the chain. Using the speaker cab as the "filter" for deep lows wouldn't produce similar results. That of course begs the question - are those the results you want?

Yes.

 

[monsterthompson]

…I'm not familiar with the frequency responses of available HPF so I'm hoping some more experienced members can comment on this. Is there a significant difference in the curves produced by HPF pedals vs the roll off of a speaker or is it too varied a landscape to make general assumptions? Do either commonly have resonant peaks at the cutoff/rolloff frequencies?

 

[Wasnex]

…I'm not familiar with the frequency responses of available HPF so I'm hoping some more experienced members can comment on this. Is there a significant difference in the curves produced by HPF pedals vs the roll off of a speaker or is it too varied a landscape to make general assumptions? Do either commonly have resonant peaks at the cutoff/rolloff frequencies?

The frequency of an HPF is the point where response is down 3dB. How fast the filter rolls of from there depends on the slope of the filter. For example is the filter 6dB/octave, 12dB/octave, 24dB/octave, etc. If it's not clear 6dB/octave means the attenuation is 6dB per octave.

HPFs can also have a compound slope. For example I believe the F-deck has a fixed HPF set to 35hz with a 12dB/octave slope. It also has a variable HPF that is adjustable from 35hz to 140hz.

 

[jw23mind]

I'd argue the combination of an HPF with a cab with extended low end has the advantage of creating a steeper roll off slope at the desired frequency, thus keeping more of what you want (say 60 hz) and less of what you don't (like 30 hz). With no HPF, relying on the roll off of a cab alone will yield a less steep curve and less separation of said frequencies. And as monsterthompson pointed out, there's also advantage to rolling off at an earlier stage, conserving headroom in the circuits that follow.

 

[logdrum]

S

…I'm not familiar with the frequency responses of available HPF so I'm hoping some more experienced members can comment on this. Is there a significant difference in the curves produced by HPF pedals vs the roll off of a speaker or is it too varied a landscape to make general assumptions? Do either commonly have resonant peaks at the cutoff/rolloff frequencies?

The speaker will fart or knock when it reaches it's limits.

Seriously. Here is a Kappalite 3015 model response curve. From 100 Hz to 50. The reduction is only 9Db Db. The Mackie board HPF is 18Db per octave. That's 9Db more (just eye balling the graph) and is more or less 4 times (if my math is right) more cut than the speakers natural roll off.

All the mechanical and thermal issues also occur at those low frequencies.

I know - we can argue about HPF all day long by saying let the cab do it or just cut the bass knob. It's not the same. I'll let agedhorse and wasnex explain this further.

 

[agedhorse]

…I'm not familiar with the frequency responses of available HPF so I'm hoping some more experienced members can comment on this. Is there a significant difference in the curves produced by HPF pedals vs the roll off of a speaker or is it too varied a landscape to make general assumptions? Do either commonly have resonant peaks at the cutoff/rolloff frequencies?

There are several fundamentally different implementations of HPF's, different topologies and coefficients have different strengths and weaknesses.

 

[monsterthompson]

Thanks.
I was mainly thinking with my synth brain about filters and resonant peaks. I also have a DSM OmniCab Sim which has one control for the filter cutoff used to simulate a speaker rolloff, and another control to add a resonant peak to the cutoff.

I can't wait for the streams and downloads to explode for my next release now that I have this gem of insight

 

[logdrum]

The AI cabs are inefficient . That's how they manage to put 2 10 + 5 drivers in the size of a 12X8 tom drum enclosure and still have an acceptable LF response (40 Hz to 16 khz) albeit for not very loud gigs and even at those volumes you need 300 - 400 watts head. All their amps come with an HPF as well and I use them all the time

 

[Hollowway]

It's making sense that a good low end response plus HPF will give the best efficiency and reproduction of the freqs you do want. A lot of good information here, and I appreciate everyone chiming in!

 

[Element Zero]

My Mesa Subway 112 sounds great on the bottom end once you really push it

 

[agedhorse]

You have to have acceptable low frequency extension first, then trim it up with the HPF.

 

[WRM]

Don't forget that many/most(?) Amps have a "built-in" HPF, and it's user adjustable on many of the "better" ones....

 

[N. Kentucky Bass]

Don't forget that many/most(?) Amps have a "built-in" HPF, and it's user adjustable on many of the "better" ones....

Indeed. My Phil Jones BG-150 has a built-in HPF that is fixed at 24dB/Octave at 40Hz. My variable Fdeck provides additional/more flexibility on top of that, especially in terms of goosing extra volume. This works very well into the effects loop for a surprisingly beefy tone from such a small combo.

 

[paulraphael]

Here's an interesting listening test to download. 2 recordings of a plucked low E string. One of them unfiltered; the other filtered with a brick wall HPF just above 50 hz. Nothing at 40hz is getting through, but the 2nd harmonic at 80hz is untouched.

Compare and see if it fits your expectations.

I'm guessing that the HPF on a pedal or amp wouldn't have a similar slope, so would sound different. I just did this comparison to see what, exactly, the fundamental contributes to bass sound.

 

[agedhorse]

Here's an interesting listening test to download. 2 recordings of a plucked low E string. One of them unfiltered; the other filtered with a brick wall HPF just above 50 hz. Nothing at 40hz is getting through, but the 2nd harmonic at 80hz is untouched.

Compare and see if it fits your expectations.

I'm guessing that the HPF on a pedal or amp wouldn't have a similar slope, so would sound different. I just did this comparison to see what, exactly, the fundamental contributes to bass sound.

The results will very much depend on the speaker cabinet being used.

 

[paulraphael]

The results will very much depend on the speaker cabinet being used.

I'm listening with headphones that are down just 2db at 40 hz, eq'd flat (relative to Harman curve). I struggle to hear a difference between the files. Maybe with full-range speakers you could feel the difference?

I'd like to try, but neither my bas cab nor stereo speakers have much deep bass extension.

 

[agedhorse]

I'm listening with headphones that are down just 2db at 40 hz, eq'd flat (relative to Harman curve). I struggle to hear a difference between the files. Maybe with full-range speakers you could feel the difference?

I'd like to try, but neither my bas cab nor stereo speakers have much deep bass extension.

The lack of extension is why the HPF can really improve the low end reproduction of most bass cabinets. By limiting the extension to a cabinet that can't reproduce it, there are fewer non-musical artifacts generated.

 

[Fishheadjoe]

I used the HPF on my stereo system in the 80's, the vinyl days. It had a 20hz and 40hz switch that worked really well at stopping record warp from hitting my speakers. You could see the drivers immediately stop flapping flipping that switch.
I use a HPF in my bass chain. I adjust to the room, then adjust eq to fatten up the tone (or not) and my woofers aren't flappling around. Saves power from the amp, takes away the mud.
Fishheadjoe

 

[lug]

The lack of extension is why the HPF can really improve the low end reproduction of most bass cabinets. By limiting the extension to a cabinet that can't reproduce it, there are fewer non-musical artifacts generated.

If I eliminate my amp's output of non-musical artifacts, I'm afraid we would just hear the sounds of silence.

 

[stingray69]

I used the HPF on my stereo system in the 80's, the vinyl days. It had a 20hz and 40hz switch that worked really well at stopping record warp from hitting my speakers. You could see the drivers immediately stop flapping flipping that switch.
I use a HPF in my bass chain. I adjust to the room, then adjust eq to fatten up the tone (or not) and my woofers aren't flappling around. Saves power from the amp, takes away the mud.
Fishheadjoe

Here's a video showing exactly this - a nice visual representation of an HPF stopping excessive & potentially damaging speaker excursion.