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

[Taustin Powers]

Then, yeah - the 800+ is definitely the way to go in your case, IMO... Nothing against the Quilter, but the D800+ is WAY more versatile - for a "one amp person", it's a no-brainer, IMO...

It sure looks like a great amp. It is also twice the price of the Quilter where I live!

 

[sears]

I bow to @Stumbo mega thread deity. Next: mega thread mega thread

 

[agedhorse]

The variable HPF in the 800+ is a great idea. But, some bass amps already have a " built in ", fixed HPF in their designs, something that I think is never talked about in their manuals, unless you look hard in the spec sheets. For example, the Shuttle line of amp heads have a built in HPF. I for get where exactly it is set, but using an outboard HPF, like the Fdeck, may be counter-intuitive, or not with these heads. Perhaps Agedhorse can comment on this ?

Pretty much every amp I have designed over the last 20 years includes at least a fixed HPF.

Depending on the intended application of the amp, it's typically somewhere in the high 20's Hz to low 30's Hz.

 

[mesaplayer83]

Whew! I was beginning to think I was the only one who was left out in the cold. Never had a problem taming highs or lows via the tone knob. And major props to the NV610 which, IME, makes almost anything sound stellar.

With a sealed cab like the stellar NV610, a HPF most likely would never be needed, since the kind of lows addressed by a HPF are already rolled off... As a player goes up the food chain and starts playing larger venues with big FOH systems and pro sound crews, odds are pretty strong that at least some high pass filtering is being applied to your bass at the board, whether you know it or not...

 

[jnewmark]

Pretty much every amp I have designed over the last 20 years includes at least a fixed HPF.

Depending on the intended application of the amp, it's typically somewhere in the high 20's Hz to low 30's Hz.

Thanks. But what about using an outboard HPF along with the built in HPF? Does one nullify the other ?

 

[baxter_x]

With a sealed cab like the stellar NV610, a HPF most likely would never be needed, since the kind of lows addressed by a HPF are already rolled off...

Then what about those low frequencies? I mean, if it's sent to the cab, the cab is supposed to reproduce it, isn't he? IF not, where do they go?

Thanks. But what about using an outboard HPF along with the built in HPF? Does one nullify the other ?

To me, yes. Unless, you set your outboard HPF higher than the built in one.

 

[Craig4003]

Thanks. But what about using an outboard HPF along with the built in HPF? Does one nullify the other ?

One HPF doesn't "nullify" another, they add together to filter more strongly: two 6 dB/octave HPFs will add together to cut 12 dB/octave. They may not be set to the same cutoff frequency, though, in which case they would add only below the lower of the two cutoffs.

The FDeck HPF has two HPFs: one 12 dB/octave fixed at 35 Hz, and another 12 dB/octave adjustable between 35-140 Hz. I set mine to about 70 Hz, so I'm cutting 12 dB/octave from 35-70 Hz, and 24 dB/octave below 35 Hz. And that's on top of any HPF that might be built into my amplifier or any other part of my signal processing chain.

It's sort of like wearing two pairs of sunglasses at once -- the light is reduced twice as much.

 

[NKBassman]

Then what about those low frequencies? I mean, if it's sent to the cab, the cab is supposed to reproduce it, isn't he? IF not, where do they go?

The cab tries, but can't. It's just excess energy that gets turned into heat. Filtering it out before it gets to the amp takes the load off the speakers and helps them work more efficiently in the audible range.

 

[fermata]

I built a simple passive HPF with a range of somewhere in the high 30s to a bit over 100 Hz, using this calculator/diagram. (Resistor values over 500K Ohms mitigate possible high end tone suck that could come with a lower value resistor.)
Dropping the bass - love at 50Hz
It does a great job of cleaning up boom and tightening my (and by extension, the band's) sound, and I like that it doesn't need batteries/power. It's always part of my signal chain.

 

[mesaplayer83]

Then what about those low frequencies? I mean, if it's sent to the cab, the cab is supposed to reproduce it, isn't he? IF not, where do they go?

I am admittedly no expert on the subject, and am still learning - but it's my understanding that a sealed cab like the NV610, Ampeg SVT810e, etc... aren't designed to "reproduce" everything sent to them - by design, they already roll off some lows - and aren't capable of reproducing some highs, due to the lack of a horn and crossover... Each cab's specs *should* state this info...

As for "where they(the frequencies) go that aren't reproduced - a guess is that they are dissipated at the speaker's voice coils, but that's just a guess...

 

[mesaplayer83]

The cab tries, but can't. It's just excess energy that gets turned into heat. Filtering it out before it gets to the amp takes the load off the speakers and helps them work more efficiently in the audible range.

Thats what I thought...

 

[NKBassman]

In my case, I was using my HPF to cut sub-lows before my compressor on my pedal board. Without the HPF the compressor was over-reacting and clamping down on my signal more than I wanted. My new compressor has a HPF in the sidechain, so the pre-HPF may no longer be necessary. Haven't played with the new setup enough yet to say for sure.

Cutting sub frequencies before the amp also frees up headroom in the power amplifier so it doesn't work as hard trying to amplify content that the speaker cab can't reproduce anyway. Another potential benefit would be reducing distortion in the preamp stages, if you're into that.

 

[leonard]

Here's a link to my DIY HPF stompbox. Based on Fdeck's design. It works fine. I wish it had an even steeper slope.

DIY HPF Stompbox?

 

[BurningSkies]

Another HPF3 user here. Now permanently wired to my board, but I've been using a HPF since 2012. Since I'm using extremely high powered amps, I feel that the HPF has helped me retain my speakers' functionality for the better part of 9 years at high volume. I generally leave mine dialed to 30hz unless there's big problems in the room with wash. Beyond it making me feel a bit more secure about my speakers working safely during my set, or with any transients that might come through at volume given multi-kilowatt amps...I also know that anyone who's opening and using my amp will have less likelihood of wreckin' stuff.

Beyond any of that, even though people never recognize that it's in my chain (players, soundmen audience)...there are some noticeable differences. No destructive infra-wash in the room means even at volume you're playing nicer with the PA (most soundmen are HPF'ing you too). Your end tone sounds cleaner and tighter without it sounding like you've gutted your lows.

How invisible is it? Recently at one out of towner, I mentioned to the sound engineer that I had a 24db per octave HPF at 30hz...and he came back with "I don't know if your filter is working...I'm not hearing it." I swept up the adjustable filter and you could very obviously tell the difference...to which I told him "Yep, there it is...hear my sweep"? I've never ever had any player in dozens if not hundreds who have played my amp ever notice I HPF'ed.

I keep it on my board even when I'm using provided backline...

 

[jj4001]

Are there any mainstream (like MXR) pedal companies making anything like the fDeck? I think tons of musicians would love to have something like this if only it was on their radar.

I love that the fDeck is adjustable. I mostly just set it and forget it, but then I always inevitably encounter a room where the sweet spot is in a different place.

Another thing I love about it is that it helps you beat on a vintage bass rig a little bit less. A backline full of 60s and 70s gear is definitely part of the esthetic of the group I play in and I believe the fDeck helps extend the life of my amp and speakers.

 

[Passinwind]

With all the interest in HPFs and LPFs (basically tailored EQs. that cut off lows and highs), I think it's time to put together all the info TBrs need to make an informed decision about purchasing one or both. If you would be so kind to post your success stories (or not), pics, settings, rigs, amps, cabs, applications, basses, builders, prices, links, etc. it will be very helpful and educational.

OK, I'll start by pimping one of my favorite applications for the variable HPF that I've included in my last several DIY amp and preamp builds. It's not so much about protection for drivers as for use as a tone control enhancement. For example, here's a model of what happens as I sweep the HPF frequency while leaving the bass control boosted at 6/10:

And then with bass boosted to 8/10:

And finally, some measured ("real world") frequency response curves in a slightly different DIY preamp, with various settings for both the bass control and the HPF:

Note that all of this is old hat to users of classic studio EQs like Pultecs, for instance. There are many, many ways to skin felis catus.

Oh: and apologies for
the goofy scaling and image size differences, I just grabbed stuff that was already on my computer.

 

[Wisebass]

All questions, comments, fans, owners, future owners and passerbys are welcome!

Hi Stumbo

I hereby declare: this thread is subbed!!!!

Great read so far, thx everybody!

greetings

Wise

 

[NKBassman]

Guys, I've never felt so validated in all my life.

 

[Taustin Powers]

The variable HPF in the 800+ is a great idea. But, some bass amps already have a " built in ", fixed HPF in their designs, something that I think is never talked about in their manuals, unless you look hard in the spec sheets. For example, the Shuttle line of amp heads have a built in HPF. I for get where exactly it is set, but using an outboard HPF, like the Fdeck, may be counter-intuitive, or not with these heads. Perhaps Agedhorse can comment on this ?

Could it be possible that the D800 also has a built in HPF at a fixed setting? But only the D800+ lets you tweak it?

 

[agedhorse]

Could it be possible that the D800 also has a built in HPF at a fixed setting? But only the D800+ lets you tweak it?

Correct.