High pass filters

[alexa3020]

I just wanted to check I’m understanding this correctly:

essentially your amp & speakers are trying to reproduce frequencies that cannot be heard and cannot be reproduced accurately. The result of this is inefficiencies in the amp and for the listener ear fatigue.

therefore products such as the thumpinator (specifically) & broughton hpf are available to get around this problem.

Surely hpf should be included into the amp already if the frequencies can’t be reproduced accurately? Obviously some have adjustable hpf dials, but for those that don’t, they should ‘hard wired’ in at fixed parameters.

That said I haven’t been able to find this data for individual amp models I’ve looked at (or is this frequency response )

plus, surely the thumpinator wouldn’t exist if hpf were baked in to the amp.

Any help will be appreciated.

 

Edited May 31, 2022 by alexa3020

[Downunderwonder]

There used to be the odd amp bereft of a 'rumble filter'. Not these days.

 

Past rumble you get into stuff that could be audible if there was massive subwoofer system included. That stuff is what the Thumpinator catches. If bass EQ is boosted those frequencies can do a number on your bass cabinet.

 

Further up it's almost a matter of taste except a whole lot of people agree that wobbly low end detracts from the overall sound. Bonus points for being able to actually use the bass knob and more for at the same time not blowing up your speaker if you want to get loud. HPF ftw.

[alexa3020]

Thanks for the reply.

what’s the purpose of allowing those ‘past rumble’ frequencies through? A bass cab on stage is never gonna reproduce those frequencies is it?

would it be if you di out to a larger PA system that is capable of producing those lows?

[Downunderwonder]

Lack of market direction. GK even briefly went the other way with a '5 string' button that goosed the lows.

 

Many a 810 was blown up by guys expecting the same B string jollies as they got with a low E. The low E they were used to hearing didn't actually have audible 40hz in it. Shoving a whole lot of 30 and 60hz at the situation only killed drivers.

[JPJ]

I’ve been running a micro thumpinator for about five years (maybe more). It’s difficult to describe exactly what it does other than to say the results are ‘cleaner’ and I’ve had a lot of compliments from pro sound guys & girls for using one. Most FOH engineers will engage a high pass filter on your signal anyway, normally around the 50hz mark just to clean and tighten the overall sound. 

[alexa3020]

So if a low E is 40hz and low B is 30hz and you are high passed at 50hz surely you are omitting the frequency of the note.

I think I must be misunderstanding the fundamentals here

[JPJ]

2 minutes ago, alexa3020 said:

So if a low E is 40hz and low B is 30hz and you are high passed at 50hz surely you are omitting the frequency of the note.

I think I must be misunderstanding the fundamentals here

You would think that wouldn’t you. Except, and I’m certainly no expert, what we actually ‘hear’ when we play a low E or B is the 1st harmonic (82hz for E and 62hz for B). So as the human ear can’t discern much below 50hz except with very good headphones, everything below 50hz is waste in a live music situation just eating up amplifier power and loudspeaker cone excursion for no audible gain.

[alexa3020]

Ah right. That’s interesting and sort of making sense - perhaps we feel the fundamental of an e or b but hear the harmonic overtones.

also I’ve played through a couple of cabs where the e feels weak - I guess some cabs are struggling to produce the fundamental.

I guess as you go higher you hear the fundamental + harmonic overtones

[BigRedX]

Almost no bass cabs (despite what the manufacturers figures may claim) will produce fundamentals under 50Hz at any significant volume.

[paulo m]

I have a Tech 21 Q Strip.. 

Four band EQ with adjustable Two Band "Sweepable Mid's.. Boost & Cut' the pedal also has a H.P.F & L.P.F  which atenuate High & Low frequencys at certain set points' 45 Hz for the H.P.F.. not exactly sure for highs on the L.P.F

They certainly clean-up & tighten the bass sound  (More Focused)  & has  been stated remove the freq's your cab or cab's will not reproduce. 

Interestingly I was in rehearsal with a really competent keyboard player who was using a State of the Art Yamaha synth' & really expensive amplification 1'200w of power... The Sub Bass was devistating to the rehearsal for it created what I can only describe as "Velvet Fog"  inarticulate massive  Sub Low's)))) swallowing & clouding everything.. I used my normal rig 400w head & a 1x15 cab on a Auralex Pad.. my sound with those filters engaged produced a far superior tight & focused low end.. SO'  H.P.F's are for myself a very usefull' tool & addition to my Sonic sound. 

Edited May 31, 2022 by paulo m

[alexa3020]

2 hours ago, BigRedX said:

Almost no bass cabs (despite what the manufacturers figures may claim) will produce fundamentals under 50Hz at any significant volume.

So why not high pass at 50hz as a default? Is there no benefit to reproducing those frequencies even if they aren’t accurate or at high volume relative to the overall volume? I certainly hear something if I boost my eq at 40hz

[JPJ]

Law of diminishing returns. It’s a question of how steeply the bottom end rolls off in a cab. You can be 6db down at 40hz compared to 80hz so if I’ve got my maths right the 40 hz will be 1/4 as loud as the 80hz but I’m sure someone cleverer than me will be  along to correct me 😂

[itu]

5 hours ago, JPJ said:

...everything below 50hz is waste in a live music situation just eating up amplifier power and loudspeaker cone excursion for no audible gain.

This is the main point.

 

Let's say your amp is able to produce something like 500 W. Without a decent LPF, your signal (mixed with handling noises) only warms up the coil of the element. You want to be heard? Use the amp power to reproduce string vibrations (from the first harmonic).

 

Bass cab is so small in volume that the first fundamental at 40 Hz is practically impossible (= inaudible) with decent efficiency (1 - 2 %). Yes, you can make it happen in a small Hi-Fi speaker, but the efficiency will be brutally sacrificed: the cabinet size is tiny AND it has a flat frequency response (do not mix this with any of the FRFR PA speaker jokes). It may be in the ballpark of 0.01 %. That is well under 1/100 of a PA/bass speaker.

 

If we combine these two, you can see, that out of the 500 W amp, you are able to produce 5 to 10 watts of sound (remembering efficiency). If you would like to have a (nearly) flat response system, you would have to sacrifice efficiency: the lowest end would be heard as well as the middle, BUT the output would be well under 1 watt of sound power. Think that you would be using a tiny 30 watt clean solid state bass amp beside Marshall stacks. May sound good, but cannot be heard.

 

In short: Cut the lowest end, rely on the first harmonic, and BOOM BOOM BOOM.

[Downunderwonder]

4 hours ago, alexa3020 said:

So why not high pass at 50hz as a default? Is there no benefit to reproducing those frequencies even if they aren’t accurate or at high volume relative to the overall volume? I certainly hear something if I boost my eq at 40hz

Some amps do that and more but then they tell you it's 1000w when it's really 200 and change.

 

You need to have a play sending low volume sines from your phone to your cab. Keep the voltage constant and small or you will hurt things. If you send just enough to get a clearly audible 160hz then change only the frequency to 80 hz it will probably drop off a little in volume. Then it will fall right away at 40hz and vanish at 30hz.

 

I did all that with my Trace cab and got a helluva fright. I turned it up enough to hear what I thought was 30hz. I changed to 60hz and about jumped out of my skin with the racket that sounded curiously the same as the '30hz' I had just 'not heard', it was distortion overtones of 30hz.

 

The power of the sine signal is independent of the frequency but our ears are less sensitive down low. Look up Fletcher Munson curves of equal loudness. Cab response massively worse watt for watt also.

 

To reproduce one cycle the speaker cone must fly further as frequency decreases, or else slower. Hence big power and tough speakers are needed to get really low heard.

 

The tougher you make the speaker the more it costs and the less well it works in the more interesting frequencies.

 

Traditionally we made music with cabs that were ok to very good at 80hz and up with 4 string basses. Then came wide use of 5 strings and whole lot of marketing baloney.

 

The thump you feel in your chest when big systems are pumping you full of bass? Centered at 80hz. Bass guitar commonly highpassed at 50hz or more.

[crazycloud]

The Thumpinator is a 6th order 25Hz filter based upon the data on their website, so it's having very little effect an octave above.

Cut-off frequency: ~25Hz

Slope: 36 dB/oct

 

No 4 string bass guitars tuned E-G that I've ever seen will reproduce a fundamental at the same level as a 2H as the scale length is too short to support it. Move down to B0 and the fundamental is even less significant. Most of the tonality you hear this low is the 2H and up in the lower sections of the instrument.

 

When I ran my PA, one I designed and built, there was a 40Hz hard HPF to limit over excursion in the ported subs, to stop wasting power and to stop spurious rattles on suspended stages. Sometimes I set it higher, but I don't ever recall setting it lower, especially as all my subs were tuned to about 40Hz for max efficiency in the range I wanted to use them in.

 

I'm not buying that cones were destroyed because of B0 being played through them, especially if the cab is sealed. The air spring of the enclosure will prevent this. SVTs and similar sealed 4x10 and 8x10 are sealed and roll off at approx 60Hz - just look at Ampeg's own website: 

 

Frequency Response (-3dB): 58Hz-5kHz

 

Ported enclosures may have been an issue, as all ported enclosures become uncontrolled below tune and excursion rises dramatically.

[Downunderwonder]

16 minutes ago, crazycloud said:

I'm not buying that cones were destroyed because of B0 being played through them, especially if the cab is sealed.

It's all in the archives of talkbass. 810's were being blown up left and right for a few years with creased cones from over excursions. The only way you can do that is with way too much power too low.

[crazycloud]

29 minutes ago, Downunderwonder said:

The only way you can do that is with way too much power too low.

I'm not new to designing speakers and have been doing so since the early 80s when studying EE at Uni. Because people claim something doesn't mean it's true and most musos have no idea of how stuff actually works. So because you say 30Hz damaged your drivers, doesn't mean it's true. I fixed so much MI and PA gear over the decades where it was claimed a certain event caused a fault and it cannot physically have happened. I'd need specifics to believe it as I have a couple of old rigs that have no issues being played very hard with my 5s and 6sl this includes a 2x10 that is basically half of a 4x10 using Ampeg drivers I got from a cab that got partially destroyed in a Qld flood some years back.

 

Also note, I was quite specific about the different issues between sealed and ported cabs.

 

I've also been reading TB a long time and don't recall this being an issue and certainly not lately.

[Downunderwonder]

46 minutes ago, crazycloud said:

I'm not new to designing speakers and have been doing so since the early 80s when studying EE at Uni. Because people claim something doesn't mean it's true and most musos have no idea of how stuff actually works. So because you say 30Hz damaged your drivers, doesn't mean it's true. I fixed so much MI and PA gear over the decades where it was claimed a certain event caused a fault and it cannot physically have happened. I'd need specifics to believe it as I have a couple of old rigs that have no issues being played very hard with my 5s and 6sl this includes a 2x10 that is basically half of a 4x10 using Ampeg drivers I got from a cab that got partially destroyed in a Qld flood some years back.

 

Also note, I was quite specific about the different issues between sealed and ported cabs.

 

I've also been reading TB a long time and don't recall this being an issue and certainly not lately.

How else do you crease drivers in a sealed cab?

[crazycloud]

2 hours ago, Downunderwonder said:

How else do you crease drivers in a sealed cab?

Abuse, maybe stupidity. I have no idea of the specific circumstances of a 3rd hand report of damage. 

How come my cab doesn't have damaged drivers with B0 tuned instruments and no HPF, even when run hard?

[Downunderwonder]

1 hour ago, crazycloud said:

How come my cab doesn't have damaged drivers with B0 tuned instruments and no HPF, even when run hard?

You are going around in circles. I said sealed cabs were blown up by too much low end. You claimed nonsense yet offered no other possibility.

[crazycloud]

No, I said overexcursion causes damaged cones and that is extremely unlikely in a sealed cab due to the air spring in the cab. Overexcursion is a problem in ported cabs with signal below tune, because below tune the cab effectively has no control over the cone.

 

Come back when you actually understand the subject.

[Downunderwonder]

6 minutes ago, crazycloud said:

No, I said overexcursion causes damaged cones and that is extremely unlikely in a sealed cab due to the air spring in the cab. Overexcursion is a problem in ported cabs with signal below tune, because below tune the cab effectively has no control over the cone.

 

Come back when you actually understand the subject.

You're not telling me anything I don't know. I would have said if they were ported. The cabs were subjected to over excursion somehow. Lots of power applied to too low of a range of frequencies, innit?!!!

Edited June 1, 2022 by Downunderwonder

[crazycloud]

10 minutes ago, Downunderwonder said:

The cabs were subjected to over excursion somehow. Lots of power applied to too low of a range of frequencies

As that takes a considerable amount of effort to achieve in normal circumstances, the details of which I'm not aware in the vague examples you mentioned, it comes back to stupidity or abuse. As the fundamental on a B0 is considerably lower than the 2H, doing so will require a lot of EQ and is not the sort of damaged caused by a stock passive 5er going into a flat amp. There is no need whatsoever for a huge amount of LF EQ to be able to discern the B0 because tone is determined by the harmonic structure, not the fundamental.

 

I guarantee I can break any cabinet you give me with sufficient power and EQ if I wish to abuse the cab, not subject it to normal use.

Edited June 1, 2022 by crazycloud

[MGBrown]

What is 'B0' and '2H'? 

[Downunderwonder]

5 minutes ago, MGBrown said:

What is 'B0' and '2H'? 

B for B. 0 for the lowest one.

 

Not sure about the 2H but I believe he's talking about 2nd Harmonic, of something.