Heads with built in high pass filters

[pete.young]

20 hours ago, Al Krow said:

 

I put the question to sfx who make the Thumpinators back in 2019 and received this response which was instructive:  "I do not publish the slope of the micro-Thumpinator filter. The only thing I can tell you is that the micro-Thumpinator cuts at more than 12 dB/oct." All the best, Max [sfx]

 

 

 Interesting thatt, I'm sure when we've talked about this in the past a figure of 24dB/oct has been bandied about. I don't recall whether there was any evidence to back this up. Maybe someone on Talkbass tested it?

[bassace]

Most DB players rely on an adjustable HPF. AI amps have one built in and there are outboards- FDeck  is a good one - to be had. I use a Broughton, it does a lot of useful stuff.

 

Edit, that’s not very clear is it. Knobs from left are HPF, variable impedance, pad, phase reverse.

Edited November 8, 2021 by bassace

[Al Krow]

32 minutes ago, pete.young said:

 Interesting that, I'm sure when we've talked about this in the past a figure of 24dB/oct has been bandied about. I don't recall whether there was any evidence to back this up. Maybe someone on Talkbass tested it?

 

Fyi - my actual question to Max was:

 

"Quick query. I believe the Thumpinator cuts below 28 Hz. Am I correct that it is - 24dB/octave or is it operating at just -12dB/octave?"

 

So it's fair to deduce that his response was implying it was a 24dB/oct cut which would also tie in with the effectiveness at preventing speaker excursion shown in Phil's charts above (although I guess could possibly have been e.g. 18dB/Oct etc. although that would less likely in terms of components?)

Not sure why he was being so coy, though - if it does cut at 24dB/oct that's very welcome given its purpose!

[Phil Starr]

Fair disclosure, my chart was just calculated, not measured, and based upon the oft quoted 24db/octave 30Hz claim. I should probably have said Thumpinator type filter. 

 

I also don't know why he's being coy, it's a bit late to copyright a frequency or a 4th order filter and a matter of minutes to just measure the response. 

[Jack]

6 hours ago, Phil Starr said:

Fair disclosure, my chart was just calculated, not measured, and based upon the oft quoted 24db/octave 30Hz claim. I should probably have said Thumpinator type filter. 

 

I also don't know why he's being coy, it's a bit late to copyright a frequency or a 4th order filter and a matter of minutes to just measure the response. 

He's gone from being the only game in town to having 4-5 strong competitors now. Might make one a tad protective.

[Woodinblack]

13 minutes ago, Jack said:

He's gone from being the only game in town to having 4-5 strong competitors now. Might make one a tad protective.

 

Not surprising, it is an easy device to make with a very small component cost sold for a very non budget price, so you would expect a bit of competition.

[Chienmortbb]

On 07/11/2021 at 08:42, BillyBass said:

All modern amps have them?  Really?  So the class D heads from Gallien-Krueger, MarkBass, Ashdown, Orange, Darkglass, Trace Elliot, TC Electronic etc all have built in high pass filters?  So no need to add a SFX micro-thumpinator to any amp unless its one of a small minority of vintage amps?

I cannot vouch for all those manufacturers but I have measured the frequency response of both Ashdown MiBass 2.0 and the Bugera Veyron1001M and both have baked in HPF. As @Phil Starrsays, there is no need for the ultra low end, it just muddy's the sound, can set off unwanted room resonances as well as stealing the headroom from our amps.

[Al Krow]

1 hour ago, Chienmortbb said:

I cannot vouch for all those manufacturers but I have measured the frequency response of both Ashdown MiBass 2.0 and the Bugera Veyron1001M and both have baked in HPF. As @Phil Starrsays, there is no need for the ultra low end, it just muddy's the sound, can set off unwanted room resonances as well as stealing the headroom from our amps.

 

Thanks for that - did you manage to measure the steepness and cut off frequency of the 1001M internal HPF? If so, I'd be very interested in getting the details off you as a fellow 1001M user.

 

I've managed to slot my Thumpinator underneath my board - prompted by this thread! Turns out I needed to raise the clearance just a touch at one end of the board to accommodate, but a couple of small sticky felt pads did the trick. It will be working in series with my amps' internal HPF to clear out the sub-audio crud and should also benefit when I'm going directly into a PA.

 

Is it the case that most powered PA speakers (aka FRFR) don't have HPF?

 

Edited November 9, 2021 by Al Krow

[Downunderwonder]

6 minutes ago, Al Krow said:

Is it the case that most powered PA speakers (aka FRFR) don't have HPF?

Bet your bottom dollar they do.

[Woodinblack]

30 minutes ago, Al Krow said:

Is it the case that most powered PA speakers (aka FRFR) don't have HPF?

 

 

Absolutely they do, but they might not have it where you want it to be. Very few systems go down to DC as it can be a bit damaging.

 

[Al Krow]

1 minute ago, Woodinblack said:

 

Absolutely they do, but they might not have it where you want it to be. Very few systems go down to DC as it can be a bit damaging.

 

DC = direct current?

[Downunderwonder]

8 minutes ago, Al Krow said:

 

DC = direct current?

As frequency approaches 0, so you approach Direct Current.

[Woodinblack]

20 minutes ago, Al Krow said:

 

DC = direct current?

 

Yes. 0Hz is just direct current, basically if you were at 0Hz it would be the same as sticking a battery across a speaker. It can't do anything with that apart from heat up and eventually melt.

Just because something is marked as Full range, there are limits of human hearing where there is no point (and quite a lot of reason not to) trying to reproduce the frequencies you have coming in, so they will all have LPF and HPF as part of the design.

[fretmeister]

25 minutes ago, Woodinblack said:

 

Yes. 0Hz is just direct current, basically if you were at 0Hz it would be the same as sticking a battery across a speaker. It can't do anything with that apart from heat up and eventually melt.

Just because something is marked as Full range, there are limits of human hearing where there is no point (and quite a lot of reason not to) trying to reproduce the frequencies you have coming in, so they will all have LPF and HPF as part of the design.

 

I never knew that it would get close to DC. Now that it's been mentioned it's so obvious!

 

 

[Phil Starr]

6 hours ago, Al Krow said:

 

 

 

Is it the case that most powered PA speakers (aka FRFR) don't have HPF?

 

Again there is a difference in concept between the 'natural' roll off of an amplifier and the deliberate removal of the lower frequencies to protect the speaker and clean up the sound using a specially designed circuit.

 

If the amp is built in it would make no sense to allow the amp to drive the speaker into a place where it could be damaged, one of the advantages of active systems over passive. Reliability is essential to the manufacturer both in terms o reputation and in repair costs so making active speakers fool proof just makes total sense for sellers and customers

 

Increasingly people are using DSP to protect the speakers in powered PA amps. There are a whole series of parameters that can be monitored to make sure none of the drivers goes outside it's design limits. Even cheap as chips Behringers with DSP offer really high levels of speaker protection. My PA amps have the option of setting HPF frequencies and roll off rates as well as hard and soft limiting and crossover frequencies letting me protect my passive speakers and all of this is pre-set to match the drivers in most active speakers nowadays. It makes a bit of a nonsense of the 1000W PA speaker claim. The amps may well be capable of short term power at this level but the DSP makes sure that inappropriate power never reaches the speaker but hey, we are getting near total reliability and are able to drive the system as hard as it will go with no worries about breaking anything so it's all good.

[Chienmortbb]

On 09/11/2021 at 09:44, Al Krow said:

 

Thanks for that - did you manage to measure the steepness and cut off frequency of the 1001M internal HPF? If so, I'd be very interested in getting the details off you as a fellow 1001M user.

 

I've managed to slot my Thumpinator underneath my board - prompted by this thread! Turns out I needed to raise the clearance just a touch at one end of the board to accommodate, but a couple of small sticky felt pads did the trick. It will be working in series with my amps' internal HPF to clear out the sub-audio crud and should also benefit when I'm going directly into a PA.

 

Is it the case that most powered PA speakers (aka FRFR) don't have HPF?

 

This is the Veyron set with all controls set to 12 o'clock, the -3dB point is approximately 30Hz. I did not notice that the top end went out so far. This is the output of the preamp, from memory at the headphone output. In my opinion 35Hz seems to be the optimum -3dB point for an HPF so  the concatenated filters in the amp and Thumpinator may weel approximate that.

 

[Passinwind]

On 08/11/2021 at 01:25, Al Krow said:

 

Fyi - my actual question to Max was:

 

"Quick query. I believe the Thumpinator cuts below 28 Hz. Am I correct that it is - 24dB/octave or is it operating at just -12dB/octave?"

 

So it's fair to deduce that his response was implying it was a 24dB/oct cut which would also tie in with the effectiveness at preventing speaker excursion shown in Phil's charts above (although I guess could possibly have been e.g. 18dB/Oct etc. although that would less likely in terms of components?)

Not sure why he was being so coy, though - if it does cut at 24dB/oct that's very welcome given its purpose!

As @Phil Starralluded to, actual overall slope will be very amp-dependent and if you use other pedals that will factor in as well. I've been workimg up an open source standalone HPF for a while now and getting the same play feel as the ones in my DIY amps is still a work in progress. But then again, most people probably won't want to duplicate that particular play feel anyway.😉

[Phil Starr]

36 minutes ago, Passinwind said:

. I've been workimg up an open source standalone HPF for a while now and getting the same play feel as the ones in my DIY amps is still a work in progress. But then again, most people probably won't want to duplicate that particular play feel anyway.😉

That sounds like an interesting project

[Al Krow]

2 hours ago, Chienmortbb said:

This is the Veyron set with all controls set to 12 o'clock, the -3dB point is approximately 30Hz. I did not notice that the top end went out so far. This is the output of the preamp, from memory at the headphone output. In my opinion 35Hz seems to be the optimum -3dB point for an HPF so  the concatenated filters in the amp and Thumpinator may weel approximate that.

 

Thanks very much for that - appreciated!

 

I'm reading approx +3dB at 30Hz and down to -12dB at 15Hz: allowing for my error looks like a very respectable 12dB/octave HPF cut.

[Downunderwonder]

40 minutes ago, Al Krow said:

Thanks very much for that - appreciated!

 

I'm reading approx +3dB at 30Hz and down to -12dB at 15Hz: allowing for my error looks like a very respectable 12dB/octave HPF cut.

The zero dB level is plotted a fair bit more than 3dB lower than it should be ie the scale needs a vertical shunt to slice through the flat part at 0dB making the fall off represent the filter.

[Downunderwonder]

Looking at it again you could say the response measured pretty flat to 40hz and call that 0dB. Below 30hz it's on about a 8dB / octave slope and the -3dB point comes in around about 28hz.

[agedhorse]

Except that 8dB/octave is a tough filter to design (successfully).

 

Typically, ~30Hz is about the lowest that a HPF needs to go IMO and IME. The average player seems to settle right around 45-50Hz, but it depends on the bass, the pickup location, the type of strings, playing style, speakers and acoustic environment. Every player is in fact a little different.

[Downunderwonder]

1 hour ago, agedhorse said:

Except that 8dB/octave is a tough filter to design

I did wonder about that having never heard of one but that's what the graph says so caveat emptor.

[agedhorse]

Looks to me to be closer to 18dB/oct.

[Downunderwonder]

13 minutes ago, agedhorse said:

Looks to me to be closer to 18dB/oct.

Yup, I must have got my eyes crossed looking at it on my phone!

 

For the continued mystified:

 

Placing a straight edge on the graph at 0dB& 40hz, parallel to the gist of the intial curve, hits 10hz down at -36dB = 18dB per octave. [10¹ hz to 40hz is 2 octaves]