Is the HPF hype real? I have a question though..and GAS

50hz is a tad high for my taste, but it will give you a good feel for what it does. That is, if you have a speaker that'll even attempt to reproduce that low. My headphones couldn't hear a difference, but my 2x10 and 1x15 would die without a good HPF for how much I like to push them sometimes.

I'm not sure on the additive, but play around and see if you hear the low end start to drop off. Or feed it into a computer and analyze the audio frequencies.

-12db is the 'norm'; it's what a lot of HPF pedals do, including the Boughton pedals. Most of these have sweepable ranges, but 30hz is their lowest setting I believe. The SFX MicroThumpinator is hardset at -24db @ 30hz

 

It might be a bit hard with a graphical EQ, but the advice I was given (and it worked great) when I had an adjustable Broughton HPF was keep rolling UP the frequency until you hear a slight difference, then back it off a hair. Now I just have a microthumpinator as last in my pedal chain.

A good set HPF, you probably wont hear a big difference, but you'll see it in your speaker cones. For me, it's mainly about not wasting power on inaudible frequencies, and better protecting my speakers from pushing those frequencies hard. I can definitely push more power before they fart out.

Sfx has a good video of a 4x10 and the visual difference it makes. [sfx]:micro-thumpinator

 

No need to mimic anything. The low cut switch on your DBX 131 engages a HPF at 50Hz. The 12dB per octave spec is standard for a high pass filter. No need to get a standalone unless you want to dial in the rolloff frequency. But 50Hz is a pretty good setting for general purposes. And with bass you’ll probably be setting a standalone unit’s dial around there anyway.

FWIW I don’t know what “hype” you’re talking about. A HPF is just another tool. If you need one, it does its thing, and “problem solved.”

 

For more info on the topic that has answers to your questions, please see my High Pass and Low Pass Filters TB Wiki.

I'm up to 26 reasons for using an HPF. Plus there are explanatory graphs of HPF/LPF vs. usual eq operation.

 

Your cabs are only capable of reproducing frequencies down to a certain threshold. If you send them frequencies below that (which they aren't capable of reproducing) you get mud. Most bass cabs will only go down to somewhere in the 50s. So cutting everything below that eliminates the garbage in your signal that your speakers can’t reproduce and frees them up to better do their job. End result is a cleaner and tighter sound. In some cases the difference can be like night and day.

 

^Great resource and well worth reading.

 

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I have a Goliath Jr. II cab loaded with PAS 10s. It’s a distinctly full range cab. I’ve found cutting everything from about 45Hz down allows it to really sing with the SM-400 head it mostly gets used with since the SM-400 is capable of going down to something insane like 6Hz and doesn’t have a built in HPF like many modern amps now do. Without a HPF dead last in the series effects loop (which puts it right before the power stage) the amp runs very hot and the sound can get really muddy. But with the HPF engaged it’s a totally different animal and one of the best amps I’ve ever owned. Great sound and runs significantly cooler.

I personally consider the HPF and compressor two of the “secret weapons” in an experienced bass player’s toolkit. You won’t necessarily need (or want) to use either all the time. But I think it’s essential to at least understand what each of those two devices do, how they do it, and when and how to use them correctly. Because these are tools for grownups.

 

HPF is definitely useful for all the reasons mentioned in this thread. I have a DIY fdeck clone. I don't use the frequency knob very often. It's always in the lowest position and does its job.

 

I personally use a steeper HPF set higher for a tonal effect, and to squeeze out more clean headroom from my tube heads. It is something I’ve done for several years and has allowed me to play in loud bands with 125 watts without really missing anything (my cabinet is also not capable of accurately reproducing deep lows anyway, so the focus of my tone is the first few harmonics). Before the 80s, most bass gear had steeper HP filters built in because the speakers at the time couldn’t handle actual lows to any volume, and that tonal range is still what I favor!

 

Many speaker cabinets don't produce frequencies below 30 to 40 hz. Hence the use of Ported Designs that do.

Many amps can produce frequencies to 20hz, so putting low harmonics only tend to over drive and muddy up frequency response of your speaker cabs. I suggest doing your research and see the response of your particular cabinets.

An open E string has a fundamental frequency of 41 hz, a low B String is 31 hz. I'd adjust HPF accordingly. And found it works well on my Berg B|Amp set up.

 

I use a Broughton HPF/LPF..Takes care of Sub Rumble that is part of the Speaker "farting out" problem...

 

It is important to know some differences between a HPF and one band of a graphic EQ. A 50 hz HPF will have it's 3dB down point at 50 hz. Everything below 50hz will be rolled off at the dB per octave rate of the filter. In this case the roll of is 12dB per octave.

The 50hz slider on a 31dB graphic will be in the center of the band. With 31 bands, the filter width is 1/3 octave, which is pretty narrow. If you cut the band 12dB, you dip 12dB at 50hz and the dip is progressively decreased as you approach 1/6 octave above and below 50hz.

50hz is close to the fundamental of G# played on 4th fret of the E string. I believe 1/6 of an octave is approximately 2 semitones/half steps **. So I believe the 50hz slider will dip from about F# to Bb.

** There are 12 semitones in an octave. 12x1/6=2

 

Good point. It’s an argument I get into with graphic EQ owners from time to time. Just because the EQ is centered on the same frequency as the HPF and also has 12dB of boost/cut, its shape will be different and overlap with its immediately adjacent bands. So we’re talking two different circuits that were designed for two different purposes.

 

Many commonly used bass speaker cabinets still don’t respond well even at 40hz, and will tend to fart-out (or worse) if pushed with actual deep bass. The real bass push from most cabs is in the 80hz-120hz harmonic. If you’ve ever owned or backlined an Ampeg fridge you’ve experienced this, but many cabs aren’t much better. So an HPF saves wasted energy from your amp and cuts your speakers a break. Even with high-powered amps paired with well designed subwoofers an HPF can help clean up the tone and protect the speakers from subsonic noise.

 

IMHO an HPF is beneficial for many reasons. The most important is when you are using a ported speaker. In order to understand why it would be helpful if you had some idea how ported cabs work.

With a ported speaker at some low frequency point, the driver will begin to roll off. The port is tuned to start becoming active so that it reinforces and smoothly extends the low frequency response below this point. A benefit here is, as the port becomes more resonant, it suppresses the drivers cone excursion. This continues until the port tuning frequency (Fb). Below Fb, output drops of very quickly and driver excursion increases dramatically. So there really is very little benefit in running a ported cab much below Fb, because it does not efficiently produce sound and, if pushed hard, the driver will exceed its excursion limits and incur damage. This is related to the mechanical power handling limits of the design which is determined by the drivers T/S parameters, the volume of the cab, and the dimensions of the port(s). Often a designs mechanical limits below 100hz are less than the driver's RMS power rating.

If you look at the various charts in the attached documents you should be able see what I am talking about.

Notice the Deltalite 2512 has a 250W RMS rating and Xmas is 4.9mm

Take a look at the first design in the cabinet design doc. The notes say: "Displacement Limited to 125 Watts; F3 of 64 Hz. Use a steep high pass filter set to 35 Hz to protect your woofer."

If you look at the graph on p. 2 labeled "Cone Displacement (mm/Hz) with 125 watts," you should be able to understand why the note makes sense. Port resonance (Fb) for this design is 44hz. Note that driver excursion decreases as the frequency approaches 44 hz and then quickly increases to Xmax of 4.9mm at ~35hz, which is the recommended HPF frequency. Keep in mind the HPF will be 3dB down at 35hz. Without an HPF, the driver's excursion will be almost 8mm if 30hz is applied at 125W.

One reason you can usually get away with using a ported speaker safely with bass guitar is because the instrument does not produce a strong fundamental to begin with. To understand, take a look at this thread. Bass frequency/waterfall plots: what they mean to rigs So if you don't artificially pump up the lows an excessive amount, the electric bass has sort of a natural HPF built in. But you can still get some low frequency crud that is not harmonically related to the notes you are playing. Filtering this crud out can significant improve the sound.

In my experience an HPF is most beneficial when you speakers are trying to reproduce frequencies below their pass band. Preventing the speakers from trying to reproduce frequencies they are not designed to handle allows them to work better in their intended pass band.

Although less critical, an HPF can also tighten up your sound with speakers that are capable of extended low frequency response. Here the benefit is partly related to the type of sound you want and also partly related to limiting the range of the bass to what is necessary to sound good, so it does not cause other problems.

The next part of this post will get into sort of a larger world-view of the benefit of HPFs:

Low frequencies tend to build up and create a reverberant field that causes the low end to sound boomy and undefined. If the decay time is long enough, the resultant sound field will tend to mask the direct sound of low frequency instruments. In other words the audience will hear more of the incoherrent reverberent field than direct sound coming from amps and PA speakers. This problem is compounded because there are usually multiple sound sources, so the sound from each sound source arrives at the listeners position at a slightly different time causing phase and other timing issues. One solution to masking is to put less energy into problem frequencies.

Typically frequency slotting is used in mixing, so for example a choice may be made to reduce the extreme low end of the base guitar to make room for the bass drum. An HPF can be applied to both the bass drum and bass guitar, but of course the knee will be at different frequencies for each instrument. Basically the HPF is rolled up until it start thinning to sound to an undesirable degree, and then you back it down a bit from there.

When I mix, I tend to apply a variable HPF to every channel. If the vocal mics are allowed to run full range, they will pick up and amplify low frequencies. Keep in mind that both the low frequency sound sources and microphones are in different locations, so any low frequencies picked up by the mics will further compound the masking problem by introducing low frequencies with different phase angles and other timing issues. Usually I can run the HPF on a male vocal mic up around 150-180hz, and the HPF on female mics can usually be run even higher. I often run the HPF on guitars up around 180hz as well. I usually start with a 100hz HPF on all monitor wedges.

 

Happiness passes through HPF. Such a simple solution to a bunch of nagging challenges.