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Thread: Low cut filter?

  1. #1
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    Default Low cut filter?

    Or high pass, whatever you want to call it. Can anyone suggest an easy way to add a low cut filter set at 80hz to a 2902? I only need it on one channel, reason being that I use the amp for both guitar and bass and then have EVM12L on one side and a 15" bass cab on the other side. Just want to keep everything below 80hz out of the side with the EVMs which aren't designed to go below that. I figure it should go at the input and it should be switchable on/off. Any suggestions would be appreciated.

  2. #2

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    Quote Originally Posted by atomheart411 View Post
    Or high pass, whatever you want to call it. Can anyone suggest an easy way to add a low cut filter set at 80hz to a 2902? I only need it on one channel, reason being that I use the amp for both guitar and bass and then have EVM12L on one side and a 15" bass cab on the other side. Just want to keep everything below 80hz out of the side with the EVMs which aren't designed to go below that. I figure it should go at the input and it should be switchable on/off. Any suggestions would be appreciated.
    If you know the input resistance of one of the power amp channels you could try sticking a capacitor in series with the input. That would lower the input series capacitance thus increasing the corner frequency of the input high-pass. Are you talking about an insert effect out front or modding the amp? Both would be fairly simple.

    FWIW I don't think I would expect that bass guitar frequencies would harm those EVMs, but I've never tried it... Or do you just not like the low end response of them?

  3. #3

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    Quote Originally Posted by atomheart411 View Post
    Or high pass, whatever you want to call it. Can anyone suggest an easy way to add a low cut filter set at 80hz to a 2902? I only need it on one channel, reason being that I use the amp for both guitar and bass and then have EVM12L on one side and a 15" bass cab on the other side. Just want to keep everything below 80hz out of the side with the EVMs which aren't designed to go below that. I figure it should go at the input and it should be switchable on/off. Any suggestions would be appreciated.
    Add a simple eq-pedal ?

    Giga

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    I have s pair of evm12l here...the speaker is not going to reproduce frequencies below 80.... Adding a filter is going to do nothing. There is no reason to add a filter.
    The fact that Stephen appears from nowhere, is sentenced to death in an emotional public trial without anyone interfering at all and is then altogether forgotten as if nothing happened, is already suspicious.

  5. #5

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    Quote Originally Posted by stephen sawall View Post
    I have s pair of evm12l here...the speaker is not going to reproduce frequencies below 80.... Adding a filter is going to do nothing. There is no reason to add a filter.
    Well, in general terms, just because a speaker has a no pressure response at a certain frequency does NOT mean it isn't moving at that frequency. The frequency response of the cone's displacement is generally flat (and also maximal) below the driver's characteristic resonance frequency (55 Hz for the 12L). So just because the driver can't reproduce the frequency doesn't mean it won't damage the speaker.

    Also I might add that just because the 12Ls in your cabinet don't produce frequencies below 80 Hz doesn't mean the the 12Ls in his cabinet won't. The enclosure has a huge effect on pressure response, especially in the bass end.

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    The amp has a natural roll-off starting around 100hz. I don't think you need worry too much about it unless you're playing loud, and then volume is a bigger danger than frequency.
    Dave Phelge
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    support@fryette.com

    "We are what we pretend to be, so we must be careful what we pretend to be". - Kurt Vonnegut

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    Default Think I have a solution

    Ah, I didn't think about the amps possible natural frequency roll off on the low end. I play a short scale six string like a guitar, that is lots of chords. I do get some muddiness in the EVs that I'm trying to see if I can get rid of. Thought about a Boss GEB7 eq pedal which at least goes down to 50hz with the next step set at 120hz. My understanding is that EQs tend to be peak or bell shaped filters and I was never able to figure out if there would be a 'hole' in between those two. Hence my desire to just have a variable shelf filter, ideally, with at least a 12db slope. In looking around I realized that most mic preamps have HPF built in, so called rumble filters. Since I could always use another mic preamp in the studio I have now turned to considering an ART MPA Pro II, two channel mic preamp that has a variable HPF on both channels, 12db slope and goes up to 200hz. I like the fact that it's a tube based pre so I can play with different tubes and it allows for a couple different ways of driving the tubes into breakup. The price is $200 used so pretty easy to acquire.
    I also looked at picking up a couple of passive HPF circuit boards off of Parts Express and just putting them inside the EV boxes. Those cabinets are actually old Rocktron Velocity trapezoidal, ported enclosures and sound really great which is why I'm not letting go of them. Easy one hand pick up too. Don't like the idea of them being 'always on'.
    Depending on venue of course, I can get loud ( like outdoors w/o a mic). Don't want to find myself in a situation where the need for volume destroys much of the more subtle tonal possibilities (contradiction?). Need to keep it clean regardless of volume, that is until I don't want it clean. Hope that clears up some questions somewhat.
    Thanks for the thoughtful responses.

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    A good detailed explanation like yours gives lots of clues. I suspect that it's not the speaker, but the system and that's often the case. The component can only do what it's designed to do if circumstances and application allow.

    What you're thinking now is a band-aid to the problem, not a solution. Tailoring the low end to prevent the speaker from reacting to it will result in moving the concentration of power up the frequency range and will produce more mid focused distortion.

    A ported cab is designed to extend frequency response in a small enclosure. It assumes that power is at a premium otherwise you'd simply throw more power at the problem. If you have a lot of power available, and the information being amplified is heavy on low end content, a ported enclosure is the last thing you want. You need a cab that provides support for the cone to prevent it from excess excursion - which is where the mud comes from. A sealed cab provides a static column of air behind the speaker - kind of like a shock absorber - to control the behavior of the cone and reduce excess excursion, and the distortion that produces.
    Dave Phelge
    Chief Misconception Eradicator
    support@fryette.com

    "We are what we pretend to be, so we must be careful what we pretend to be". - Kurt Vonnegut

  9. #9
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    Default Duh....

    Wow, that is so true, and obvious, that it's embarrassing. It never occurred to me to simply plug up the port. I just spent a couple hours playing with an old Lexicon MPX-1 just so I could try and set up a low shelf filter on the digital Parametric EQ. It definitely helped once I got it dialed in. Kept going back and forth twixt guitar and bass and the A/B-ing both with the bypassed signal to make sure that I was both getting the desired effect on bass and not destroying the guitar tone. Obviously I could just bypass the patch as soon as I pick up the guitar but I wanted to see if I could actually get to that sweet spot that serves both instruments. It always takes a bit of bark off the guitars low end. Not much but still. But the six string bass started to really shine. A low EBE triton rang nice and clear. Having said all that I really would rather not be using a digital parametric.
    Tonight or tomorrow I'll get back in there and try to plug the ports. Just have to find a suitable plug. Cone excursion is definitely one of the things that worries me when pounding away at the bass so this is very much on the right track. Thanks again.
    May I just add what a beautiful animal that amp is. I finally have the head room I've wanted. Hopefully now I can concentrate on finding a preamp I love rather than one I 'think' I need.

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    Default Final installment: "The Attack of the Low Down"

    Okay, speakers are fitted with plugs and it definitely helped tighten things up. But watching the speaker excursion was still a little unsettling and also inspiring. With the speaker covers off I could plainly see the movement. And the attack of the low E string was still pretty brutal on those EVs. A little bit of judicious compression with very quick attack and release and voila. Now the EV symbol on the cones just gets a little fuzzy as compared to full on double vision. More importantly every chord I play on the bass rings nice and clear. And I have to say that the plugs improved the sound of the guitar, at least for my own taste. I love a nice thump like KT88s provide. I can't believe it took me this long to try that simple adjustment. Makes me want to hit the wood shop and build some new boxes.
    Thanks again.

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