High Pass Filter (HPF) and Low Pass Filter (LPF) Mega Thread

[Stumbo]

v

I figured out for myself though, that I really dig sealed cabs

Ironically, I don't own one atm, but the db410 I do own has a pretty cool tuned port that does not go very deep, afaik it rolls at slightly above 40hz which aaalmost makes it sound like a sealed cab but a tad deeper. In other words, it sounds tight.

v

An Eq with a 20-30hz centre should vasically do the same thing.

I agree that the hpf does it better, but chances are you are going to have tough luck actually getting one.

v

FWIW, here's a model I made of the difference between a ten band graphic EQ pedal with the low fader (32Hz IIRC) all the way down (-10dB), vs. a 4th order HPF with a -3dB point at 32Hz.

View attachment 3118727

View attachment 3118728[/QUOTE]

v

It doesn't do the same thing, dropping this 30Hz band down 12dB would mean that the signal is ~6dB down at 60Hz and maybe 3dB down at 100hz (depending on the topology of the eq circuit).

A 4th order HPF set at 30Hz will be 3dB down at 30Hz, almost 0dB down at 40Hz and 24dB down at 15Hz.

>You guys are awesome as always! :thumbsup;​

 

[Stumbo]

v

Never said that before but I like that you like me. I like you too!!

I figured out for myself though, that I really dig sealed cabs

Ironically, I don't own one atm, but the db410 I do own has a pretty cool tuned port that does not go very deep, afaik it rolls at slightly above 40hz which aaalmost makes it sound like a sealed cab but a tad deeper. In other words, it sounds tight.

v

An Eq with a 20-30hz centre should basically do the same thing.

I agree that the hpf does it better, but chances are you are going to have tough luck actually getting one.

>Check out the always-on fixed-frequency Thumpinator/MicroThumpinator HPF from England based [Invalid or Expired Link Removed]

>They can also make you a sweepable hpf in their custom shop.​

 

[two fingers]

OK.... well.... I'm a believer.

I ordered a Broughton always on HPF a week or so ago and it came in today.

I understood the rationale behind all of the fans of these things. And I have used an HPF on a mixing board live with good results.

But, I have to admit, when it comes to bass rigs, I was a skeptic.

I stand corrected.

The timing could not have been better. I recently acquired a late St.Louis era Ampeg 6-10 cab. The top four speakers are sealed and the bottom two are ported. (Edit: JimmyM corrected me a few posts down. The whole cab is ported.)

@JimmyM was exactly right. It was more beefy than I thought it would be. The bottom end was a bit more "loose" than a standard 8-10 all-sealed cab.

Tonight I went to the jam room to cram for a gig this weekend. I had my little Broughton carboard box in my hand. I was tuning up literally thinking "There's no way these things can be all that."

I was wrong.

Here's the thing that blows my mind. There's a bell curve to them. I started with it all the way down. It sounded virtually no different than before I put it in the chain. Then I started slowly adjusting upward. That's when my mind got blown.

The low end not only got tighter, but it got BIGGER. What??? I just chopped off the lowest frequencies of my signal and the bass got more beef. But it was controlled, and tighter.

Now, the bell curve comes in when you keep going up in frequency. Of course, you can go so high that it thins everything out and makes your tone all nasally.

So, with the knob all the way down, my tone was pillowy. Sure, it had heft but it was mushy. Dial up a little, and things tighten up but kick like a mule.

I'm a convert. @Stumbo , @JimmyM and all the rest of you guys hit the nail on the head.

There's a reason these little boxes are trending right now. Used correctly, they just work.

 

[JimmyM]

I recently acquired a late St.Louis era Ampeg 6-10 cab. The top four speakers are sealed and the bottom two are ported.

Very glad you're finding the Broughton pedal to your liking. However, I must correct something...all the speakers are ported. The speakers are compartmentalized in groups of two kinda sorta similar to the 810e, but there are holes cut in each panel to allow the standing waves in each compartment to escape, where they go out the bottom three ports.

 

[Passinwind]

The low end not only got tighter, but it got BIGGER. What??? I just chopped off the lowest frequencies of my signal and the bass got more beef. But it was controlled, and tighter.

Now, the bell curve comes in when you keep going up in frequency. Of course, you can go so high that it thins everything out and makes your tone all nasally.

And now for the real revelatory fun: go to that bell curve point and then start turning up your bass control. It's now more like a low mid control, and leveraging the HPF against the bass control over various settings buys you a nice wide range of frequencies that the low mids peak at. This is probably my favorite aspect of having an onboard variable HPF built into my amps.

 

[Stumbo]

OK.... well.... I'm a believer.

I ordered a Broughton always on HPF a week or so ago and it came in today.

I understood the rationale behind all of the fans of these things. And I have used an HPF on a mixing board live with good results.

But, I have to admit, when it comes to bass rigs, I was a skeptic.

I stand corrected.

The timing could not have been better. I recently acquired a late St.Louis era Ampeg 6-10 cab. The top four speakers are sealed and the bottom two are ported.

@JimmyM was exactly right. It was more beefy than I thought it would be. The bottom end was a bit more "loose" than a standard 8-10 all-sealed cab.

Tonight I went to the jam room to cram for a gig this weekend. I had my little Broughton carboard box in my hand. I was tuning up literally thinking "There's no way these things can be all that."

I was wrong.

Here's the thing that blows my mind. There's a bell curve to them. I started with it all the way down. It sounded virtually no different than before I put it in the chain. Then I started slowly adjusting upward. That's when my mind got blown.

The low end not only got tighter, but it got BIGGER. What??? I just chopped off the lowest frequencies of my signal and the bass got more beef. But it was controlled, and tighter.

Now, the bell curve comes in when you keep going up in frequency. Of course, you can go so high that it thins everything out and makes your tone all nasally.

So, with the knob all the way down, my tone was pillowy. Sure, it had heft but it was mushy. Dial up a little, and things tighten up but kick like a mule.

I'm a convert. @Stumbo , @JimmyM and all the rest of you guys hit the nail on the head.

There's a reason these little boxes are trending right now. Used correctly, they just work.

Cool!

Looking forward to a gig report!

 

[fcajr]

I have a Radial Bassbone OD with fixed HPF at 80Hz and 150Hz. I have searched and can't find what the slope is on the HPF. Does anyone know what the slope is?

 

[dabis]

Hi! I've benn reading this post the lasts months, and now it's time to try. I've seen the Von-Filterung kit. Does anyone built and played that?

VONG-Filterung – Schalltechnik_04

The VONG-Filterung features:

• adjustable HighPass-Filter (30-140Hz)
  • 4th Order-Filter -> -24dB/Oct.
    • -12dB/Oct. fixed at 30Hz
    • -12dB/Oct. adjustable
• adjustable LowPass-Filter (.250-22kHz)
  • 2nd Order-Filter
    • -12dB/Okt. adjustable
• DI-Out
  • with Ground-Lift-Switch
• adjustable Boost (up to +16dB) for the 1/4″-Output
• Polarity-Switch (180°-Phase) for the 1/4″-Output

 

[JimChjones]

Got a few questions. I was testing doing some testing with speaker porting, and I made a little impedance measuring circuit, and fed the amp tones from a mobile phone sig gen. To give a baseline I started off by measuring the impedance against a 8 ohm resistor instead of a speaker, expecting a flat baseline. What I got was this (frequency along the bottom, vertical is just measured voltage which AIUI is a measurement of impedance, I didn't bother to do the sums to turn it into quantitative numbers).

First, am I right in thinking this indicates the amp I was using, a Fender BXR300, has a LPF in the 60hz region? The 25hz hook in the curve is an artifact caused by inability to read the needle accurately at low numbers.

Secondly is this a viable way of checking for a LPF? I have a new amp now, a Class D Markbass blackline. Is it safe enough to do an impedance test like this, and will it show up the presence or absence of a LPF?

Thirdly, if it doesn't have adequate LPF built in I'd like to add the capability. I really badly don't want to have a powered (battery or mains) box in front of the amp, I don't use any FX. If I do need a LPF I would much rather build a passive circuit into the speaker cabinet. I appreciate its the wrong way to do it, in that the subsonics would consume power in the amp that is just lost in heat, but I have more volume than I need, and the convenience of no extra external gear is rather compelling in my circumstances.

 

[TheBass]

Hi! I've benn reading this post the lasts months, and now it's time to try. I've seen the Von-Filterung kit. Does anyone built and played that?

VONG-Filterung – Schalltechnik_04

The VONG-Filterung features:

• adjustable HighPass-Filter (30-140Hz)
  • 4th Order-Filter -> -24dB/Oct.
    • -12dB/Oct. fixed at 30Hz
    • -12dB/Oct. adjustable
• adjustable LowPass-Filter (.250-22kHz)
  • 2nd Order-Filter
    • -12dB/Okt. adjustable
• DI-Out
  • with Ground-Lift-Switch
• adjustable Boost (up to +16dB) for the 1/4″-Output
• Polarity-Switch (180°-Phase) for the 1/4″-Output

View attachment 3123470

I did, and posted my experience in this thread. I have it since about a month now and used it on a few gigs. When I am rehearsing with headphones the effect is not so noticeable but the HPF is a real live saver in difficult acoustic situations to kill boomy room resonances. But it also serves well as a sound shaping unit. I mainly play 2 band EQ Stingrays which can sometimes sound a bit harsh at the top end. The LPF can tame that quite well.

I highly recommend this stomp box and Julian offers great and quick service with any problem to assemble the box.

 

[two fingers]

Very glad you're finding the Broughton pedal to your liking. However, I must correct something...all the speakers are ported. The speakers are compartmentalized in groups of two kinda sorta similar to the 810e, but there are holes cut in each panel to allow the standing waves in each compartment to escape, where they go out the bottom three ports.

View attachment 3123463

Ah. That makes even more sense. I was going by the not-so-complete diagram in the manual. Thanks!

 

[Stumbo]

Hi! I've benn reading this post the lasts months, and now it's time to try. I've seen the Von-Filterung kit. Does anyone built and played that?

VONG-Filterung – Schalltechnik_04

The VONG-Filterung features:

• adjustable HighPass-Filter (30-140Hz)
  • 4th Order-Filter -> -24dB/Oct.
    • -12dB/Oct. fixed at 30Hz
    • -12dB/Oct. adjustable
• adjustable LowPass-Filter (.250-22kHz)
  • 2nd Order-Filter
    • -12dB/Okt. adjustable
• DI-Out
  • with Ground-Lift-Switch
• adjustable Boost (up to +16dB) for the 1/4″-Output
• Polarity-Switch (180°-Phase) for the 1/4″-Output

View attachment 3123470

FYI, According to the website, it's out of stock right now.

 

[dabis]

Great to hear it @TheBass . I'll check your review. Also, I build a Guma Drive pedal fron Julian last year, he helped me alot.

Unfirtunately like @Stumbo said, it's out of stock. I'll wait till could be served again. Thanks folks!

 

[agedhorse]

Got a few questions. I was testing doing some testing with speaker porting, and I made a little impedance measuring circuit, and fed the amp tones from a mobile phone sig gen. To give a baseline I started off by measuring the impedance against a 8 ohm resistor instead of a speaker, expecting a flat baseline. What I got was this (frequency along the bottom, vertical is just measured voltage which AIUI is a measurement of impedance, I didn't bother to do the sums to turn it into quantitative numbers).
View attachment 3123522

First, am I right in thinking this indicates the amp I was using, a Fender BXR300, has a LPF in the 60hz region? The 25hz hook in the curve is an artifact caused by inability to read the needle accurately at low numbers.

Secondly is this a viable way of checking for a LPF? I have a new amp now, a Class D Markbass blackline. Is it safe enough to do an impedance test like this, and will it show up the presence or absence of a LPF?

Thirdly, if it doesn't have adequate LPF built in I'd like to add the capability. I really badly don't want to have a powered (battery or mains) box in front of the amp, I don't use any FX. If I do need a LPF I would much rather build a passive circuit into the speaker cabinet. I appreciate its the wrong way to do it, in that the subsonics would consume power in the amp that is just lost in heat, but I have more volume than I need, and the convenience of no extra external gear is rather compelling in my circumstances.

Yes there is a HPF (not a LPF) in that amp. That's what you are seeing.

I would suggest doing this at 10V RMS or less (with an appropriate size power resistor).

Be careful not to short the outputs to anything (including the minus output to anything connected to ground) because you do not know the internal topology of the amp. On a class D amp this fault could be fatal.

 

[JimChjones]

Many thanks. Don't know what sort of brainfade I was suffering from to keep typing LPF instead of HPF, but I'd better fix it before I start some serious testing...

I made myself a little plastic box with jack connections with the resistances in for the testing, plus a couple of terminals for croc clips , so I'll have to try quite hard to get an earth short, but the point is well made, thanks.

 

[Stumbo]

...If I do need a HPF I would much rather build a passive circuit into the speaker cabinet.
I appreciate its the wrong way to do it, in that the subsonics would consume power in the amp that is just lost in heat, but I have more volume than I need, and the convenience of no extra external gear is rather compelling in my circumstances.

There were a few posts on the topic of internal speaker cab HPFs in another thread:

...Since the two 10" speakers are both 8ohms, 16ohms in series. And the 15" is 8ohms. The 15" is getting 2/3rds of the amount of power..
I should have placed an HPF on the 15" to make sure everything under 42Hz is going back to the amp for the use of a synth.

Contact [sfx]: high performance audio and have them modify their [sfx]:micro-thumpinator HPF to what you need.
It's external so it works with whatever is plugged into it that goes to your amp.
For more info, check out my HPF mega thread with the link below.

Thanks but I really want it to be internal!

You are wanting to put an HPF inside the cab to protect the speaker?
It's much better to follow @Stumbo 's advice and remove the sub-audio harmonics before amplification. That conserves the precious wattage in the amplifier sections of your system.

A passive HPF inside a cabinet isn't going to work as you hope. Not even close.

 

[agedhorse]

I would not recommend a passive speaker level high pass filter on the low end, with the size of capacitor plus the speaker inductance, there exists a very real possibility of an unintentional tuned circuit (resonant tank with very little damping) that could upset the stability of some amplifiers... to the point of spectacular failure.

 

[JimChjones]

... a very real possibility of an unintentional tuned circuit

So much for that idea then!

 

[-Asdfgh-]

... to the point of spectacular failure.

Challenge accepted!

 

[-Asdfgh-]

I just got a dual EQ/feedback suppressor rack mount to go with my PA. This also has a cross over with a fairly steep filter, so I am hoping that for the PA, this will allow me to use it as a reasonable HPF, and leave the EQ (or feedback suppression untouched). It's stereo, which to me means one lot of EQ or suppression for FOH or monitors, or potentially chaining EQ and feedback suppression together as one mono unit, with EQ to tune the sound for a pleasant listening experience, whilst squelching feedback. Hopefully that doesn't result in spectacular failure.

I'll have to book a hall to test the parameters, rather than do it at the sound check for a gig.