Proper Application Of High Pass Filters

[zombywoof5050]

Many people here mention the use of HPF's on power amps, to reduce low end rumble and protect speakers.

I am playing through a pair of Acme Low B-2 speakers, and here are a couple of posts (from another thread) regarding the use of a HPF with Acme speakers:

Originally Posted by alexclaber

I found with my Acme rig that the best performance was with a steep 30Hz highpass, and that the 50Hz highpass caused more speaker excursion (because you're getting less assistance from the low tuned port so you need to make up the lows higher up).

Originally Posted by greenboy

There's also that resonant bump added when using the 50 Hz filter at around 100 Hz that isn't there when using the QSC 30 Hz filter. 30 Hz is really closer to the ideal placement anyway.

So, what I'm gathering here is that since the Acme's port tuning is down at 30hz, it's better to have your HPF set at 30hz (rather than 50hz). This way, you're letting the port assist with those low frequencies in the 30hz region.

(Regarding the above, I'm assuming y'all are talking about use with a 5-String bass, since the low B string is down around 30hz....correct me if I'm wrong in this assumption).

Now, with that said..
What if I'm only playing a four string bass?
Since the frequency of the E-String is 41.2hz, would it be better to run my HPF at around 41hz, or should I still just leave it set at 30hz?

[bongomania]

In your case you don't need to set your filter at 30 hz. If the HPF that you have is very steep, then for your low E you can set the filter as high as 40 Hz. If the filter is less steep, then you may even benefit from going higher, like 50 Hz. Because the specific combination of instrument, amp, and cab is different from one player to the next, the best thing you can do for effective results is experiment, while both watching and listening to your speakers.

[Son of Bovril]

+1 I would try the HPF at 40 hz and try it at 30hz and see which sounds better to you... I like to set a HPF so that it is just below the point where it audibly affects my sound, so usually at 30hz in my case, but it also depends on the cab... my 210 performs better with a HPF at 40hz

Conclusion: experiment with it and see what works best for you...

[tombowlus]

You can pick up one of fdeck's HP-Pre's with the variable HPF and choose the setting that works the best for you.

The sfx Micro Thumpinator is another killer little unit.

[aledeville]

Originally Posted by tombowlus

The sfx Micro Thumpinator is another killer little unit.

Yep it is. Never without it!

[Roadkill]

Originally Posted by tombowlus

You can pick up one of fdeck's HP-Pre's with the variable HPF and choose the setting that works the best for you.
The sfx Micro Thumpinator is another killer little unit.

Just because it was a PITA for me to find those I'll save the next guy the trouble :
http://personalpages.tds.net/~fdeck/bass/hpfpre.htm
http://www.sfxsound.co.uk/mainpage.a...ro_thumpinator

[BassmanPaul]

My main complaint is the sub-sonics that piezo equipped instruments put out. I like how my Acmes sound just as they are so I set the HPF I built at around 17-18 Hz. That leaves my tone unaltered but cuts the sub-sonics completely.

[tombowlus]

Originally Posted by Roadkill

Just because it was a PITA for me to find those I'll save the next guy the trouble :
http://personalpages.tds.net/~fdeck/bass/hpfpre.htm
http://www.sfxsound.co.uk/mainpage.a...ro_thumpinator

Sorry, I was going to look up the links, but it's Monday morning, and I'm multi-tasking, as it is.

[greenboy]

Quite a few bass cabs out there could benefit from steep 40Hz, 50Hz - and even 60 hz - low-cut/high-pass filters. The goal is to leave actual useful content alone while minimizing the chance of damage due to driver unloading below the box's tuning. It also lends additional clarity at performance levels.

When I say steep I'm saying a minimum of 3rd-order (18 dB per octave drop-off) Butterworth. 4th-order (24 dB per octave) is even better. A Butterworth alignment like this is relatively cheap to implement. Also note that a 40 Hz filter of the Butterworth variety is actually already 3 deciBels down at 40 hz, so a box that's competent at 50 Hz may be a candidate for a 40 Hz filter, leaving 50 Hz untouched.

Also the Acmes aren't probably tuned to 30 hz though I hear this repeated a lot around here. What they are is according to Acme supplied spec, -6dB at 30 hz - another thing entirely.

[WCunha]

Originally Posted by greenboy

Quite a few bass cabs out there could benefit from steep 40Hz, 50Hz - and even 60 hz - low-cut/high-pass filters. The goal is to leave actual useful content alone while minimizing the chance of damage due to driver unloading below the box's tuning. It also lends additional clarity at performance levels.

When I say steep I'm saying a minimum of 3rd-order (18 dB per octave drop-off) Butterworth. 4th-order (24 dB per octave) is even better. A Butterworth alignment like this is relatively cheap to implement. Also note that a 40 Hz filter of the Butterworth variety is actually already 3 deciBels down at 40 hz, so a box that's competent at 50 Hz may be a candidate for a 40 Hz filter, leaving 50 Hz untouched.

Also the Acmes aren't probably tuned to 30 hz though I hear this repeated a lot around here. What they are is according to Acme supplied spec, -6dB at 30 hz - another thing entirely.

Do you think the Acmes would benefit from a filter that was higher than 30Hz?

[craig.p]

I run my QSC with its 30 Hz filter enabled. It's extremely effective in doing its job, no matter the cab(s) it's connected to.

I'm not saying another knee point wouldn't give you success, too -- just giving you one more data point from field experience.

FWIW, in the late '70s I used to build these filters into Bud boxes and take them around to live club performances and get the sound men to try them in their mains' effects loops. I'd generally set them at 40 Hz but there were special cases where they had to be set higher. (PA systems at that time were just beginning to evolve from junk, so sometimes you were faced with boxes that had already gone AWOL by 70 or 80 Hz or even higher.) The trick was to pop the grill on one of the bass bins and watch the cone(s) for a set. I still recommend this method for determining where to set a HP filter's knee point.

[jnewmark]

I'm curious about the The Thumpinator. Is it usually connected through the effects loop of a bass amp ? I'm using a GK RB700II into my old school JBL K140 215 cab, and when using the 5/4 switch in " 5 ", the K140's piston like crazy on the low notes. Great sound imho, but I'm worried that I will ruin the speakers. I've also been told that the right amount of compression would alleviate this.

[bongomania]

The Thumpinator can be run either way: in front of the amp, or in the fx loop. The "micro" version is unbalanced only, while the "regular" version can be run either balanced or unbalanced, and can convert between the two as needed. Most people will just need the micro one. The one thing about fx loops is some of them are parallel, and the Thumpinator will not be as effective in a parallel loop.

Whether one will help with the GK's "5" setting will depend on whether the pistoning problem is caused by content above or below 30 Hz.

[zombywoof5050]

Thanks for the replies.

I wasn't sure about the 30hz port tuning frequency on the Acmes, I was just repeating info that I picked up here (though I probably misconstrued it).

My AI Clarus+ has a variable (30-400hz) HPF with -12dB per octave rolloff. Not as steep as some would recommend, but I'm sure it'll suffice.

My ear is probably not near as discerning as a lot of folks here, so I guess I will just listen as best I can and watch the speaker cones to try and determine the optimal HPF settings.

[jnewmark]

Originally Posted by bongomania

The Thumpinator can be run either way: in front of the amp, or in the fx loop. The "micro" version is unbalanced only, while the "regular" version can be run either balanced or unbalanced, and can convert between the two as needed. Most people will just need the micro one. The one thing about fx loops is some of them are parallel, and the Thumpinator will not be as effective in a parallel loop.

Whether one will help with the GK's "5" setting will depend on whether the pistoning problem is caused by content above or below 30 Hz.

Hmmm. Well, I guess the only way I can find out is to get a HPF that can be adjusted to find the correct frequency. Any suggestions ?

[bongomania]

There are some expensive EQ units that can be used as steep adjustable HP filters. The free option is to play your bass (alone in a practice space) with the absolute minimum of dynamics, like a smooth thumb-pluck, but at high volume. That way you are generating the least amount of subharmonic content, so any speaker movement would be caused by the actual fundamentals of your notes, which are all above 30 Hz.

[KJung]

Originally Posted by jnewmark

I'm curious about the The Thumpinator. Is it usually connected through the effects loop of a bass amp ? I'm using a GK RB700II into my old school JBL K140 215 cab, and when using the 5/4 switch in " 5 ", the K140's piston like crazy on the low notes. Great sound imho, but I'm worried that I will ruin the speakers. I've also been told that the right amount of compression would alleviate this.

Um, just don't use that switch in the '5' setting. As you say, it just adds mush IMO anyway. Doesn't make sense to add a ton of deep low end with that switch, and then Hi Pass it out (and adding all that super deep low end just to get a little closer to the fundamental of those one or two lowest notes on your instrument is a kind of strange). The GK heads sound best in the '4 string' mode IMO.

That button, just like some heads that have their padded input called 'active', result in some thinking that if they have a 5 string and/or an active bass, they should use those options. That is far from the truth!

[greenboy]

Originally Posted by zombywoof5050

I wasn't sure about the 30hz port tuning frequency on the Acmes, I was just repeating info that I picked up here (though I probably misconstrued it).

Nah, it seems to get repeated around here often enough by people who should know better by now...

My AI Clarus+ has a variable (30-400hz) HPF with -12dB per octave rolloff. Not as steep as some would recommend, but I'm sure it'll suffice.

Only if it is set a lot higher, and then it's cuting into useful content as well. That should be a EQ decsion rather than a requisite.

Bass players have gotten by a lot of years without high pass/low cut filters just by cutting bass EQ and turning down when hearing the warning sounds. Of course, a lot of people have always blown drivers - but as soon as people start using higher power with drivers that are lax of xmax, then problems are more serious and for a greater number of users. Also, a lot of preamp/head designers put ridiculous boost into their hidden default voicing (they don't go any lower, but they do put some peaky response where it should NOT be).


It's even worse with Acmes because:

1) Acmes have low sensitivity in the midrange which leads aggressive preferring people to throw tons of power at them to compensate

2) Acme drivers have a poor xmax (excursion) to xlim (place where driver damage is imminent) ratio. That xmax/xlim ratio is SHORT - the distance between fartsville and failsville is all too easy to step over with Acme drivers.

Kind of like dropping a bass-boosted mic when the PA is turned on and toasting subwoofers, accidents can happen if there is not more protection. Good HP filtering is much needed here.


30 Hz 3rd or 4th order BW is plenty high for Acmes though. That's likely well above unloading tendencies. If you are still having problems you are driving too hard (see points #1 and #2 above).

[tombowlus]

Originally Posted by jnewmark

I'm curious about the The Thumpinator. Is it usually connected through the effects loop of a bass amp?

I run mine in front of the head.

[KJung]

Originally Posted by greenboy

Nah, it seems to get repeated around here often enough by people who should know better by now...



Only if it is set a lot higher, and then it's cuting into useful content as well. That should be a EQ decsion rather than a requisite.

Bass players have gotten by a lot of years without high pass/low cut filters just by cutting bass EQ and turning down when hearing the warning sounds. Of course, a lot of people have always blown drivers - but as soon as people start using higher power with drivers that are lax of xmax, then problems are more serious and for a greater number of users. Also, a lot of preamp/head designers put ridiculous boost into their hidden default voicing (they don't go any lower, but they do put some peaky response where it should NOT be).


It's even worse with Acmes because:

1) Acmes have low sensitivity in the midrange which leads aggressive preferring people to throw tons of power at them to compensate

2) Acme drivers have a poor xmax (excursion) to xlim (place where driver damage is imminent) ratio. That xmax/xlim ratio is SHORT - the distance between fartsville and failsville is all too easy to step over with Acme drivers.

Kind of like dropping a bass-boosted mic when the PA is turned on and toasting subwoofers, accidents can happen if there is not more protection. Good HP filtering is much needed here.


30 Hz 3rd or 4th order BW is plenty high for Acmes though. That's likely well above unloading tendencies. If you are still having problems you are driving too hard (see points #1 and #2 above).

I'm one who always forgets the 31hz is -6db and not -3db Andy makes such a big deal of his cabs being able to 'reproduce the fundamental of the B string' that it is easy to forget if you haven't looked at the specs for a while.
However, these cabs do sound 'deeper' than almost any other IMO and IME. However, per your point above, that is not necessarily a good thing, and I guess even that 3db at 41hz is much lower than virtually any other production cab, especially, as you point out, that the drivers seem to quickly overwhelm that little mid driver in many gigging contexts, resulting in people applying more power and turning up... and then magic smoke