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Adding a passive Hi-Pass filter to a cabinet

dubhnight

dubhnight

Guest
Jul 26, 2012
70
3
#1
Recently, I built my own 1x15 cabinet, and after getting it to sound as good as I can with stuffing etc, I'm still suffering from some infrasonic mud, with the speaker experiencing a pretty large amount of excursion. I'd like to buy a HPF in the form of a pedal, but I've been looking around for a while and I don't think I can justify spending that amount of money on a pedal at the moment. I'd much rather add a passive HPF filter directly to the cabinet, which will always be there, and I'll never have to worry about loosing an adapter/running out of batteries or loosing the pedal.
Basically I was wondering how I would go about doing this, what I'd need to get etc. The cabinet is tuned to around 45hz, and is ported. I play a standard 4 banger, so I don't think ill ever need anything below 40hz or so.
 
#2
dubhnight said:
Recently, I built my own 1x15 cabinet, and after getting it to sound as good as I can with stuffing etc, I'm still suffering from some infrasonic mud, with the speaker experiencing a pretty large amount of excursion. I'd like to buy a HPF in the form of a pedal, but I've been looking around for a while and I don't think I can justify spending that amount of money on a pedal at the moment. I'd much rather add a passive HPF filter directly to the cabinet, which will always be there, and I'll never have to worry about loosing an adapter/running out of batteries or loosing the pedal.
Basically I was wondering how I would go about doing this, what I'd need to get etc. The cabinet is tuned to around 45hz, and is ported. I play a standard 4 banger, so I don't think ill ever need anything below 40hz or so.
Click to expand...

Active is absolyutely the way to go. The parts count, size and cost for a passive HPF at a low enough frequency to be effective would be prohibitive. Search out the Thumpuinator or FDeck's HPF series 3.
 
#3
What I'm suggesting though is a very simple HPF sort of circuit like the kind included in many speaker designs. I've seen it done before in very many designs that I dismantled in my youth. I really can't afford those stomp boxes at the minute, The thumpinator actually costs more than the amp I'm using at the moment...
 
#6
That's a good point. I've heard that adding a HPF can improve power handling by removing the subsonic frequencies that the amp tends to waste power on, but with a passive one post amplifier those would still be amplified but would be dissipated in the speaker, so it wouldn't help the amplifier at all.
Would anyone be able to link me to some of the cheaper HPFs? I've been trying to find some for a while now but the only ones I can find are those overhyped ones you talk about.
 
#8
dubhnight said:
. . . trying to find some for a while now but the only ones I can find are those overhyped ones you talk about.
Click to expand...

Yeah . . .
The microThumpinator is about $185 US, but I love it 'cause it's portable. Backlines are what they are - hi-passing the signal seems to increase the "tightness" of my lows, plus accents(?) headroom . . .
Of course, YMMV :D
 
#10
I think that Fdeck has DIY plans. A passive filter would have a coil that costs as much as a DIY unit. And would weigh likely about 5#. The biggest problem for me is that I HATE passive filters on the woofers---they really degrade the sound.
 
#11
A small crossover will work like a Rolls SX21
Set the crossover at 50hz, and only take the high out.
Yes, 50hz would be fine for 99% of bass amplifiers.

or F-Mod - these are line level passive.
Invalid Link Removed

or search on
high pass filter calculator
to find out how to build your own line level passive or active filter.
 
#12
Mike Arnopol said:
A passive filter would have a coil that costs as much as a DIY unit. And would weigh likely about 5#. The biggest problem for me is that I HATE passive filters on the woofers---they really degrade the sound.
Click to expand...

Another problem with a passive filter is, it won't behave the way you expect it to due to the massive impedance peak(s) the woofer/box combination will exhibit at and around system resonance. Do it wrong, and you either end up with inadequate protection or you lose too much useful bass energy. Do it right, which requires good measurements to optmize the circuit, and at best it still won't sound very good, as Mike says.
 
#13
dubhnight said:
That's a good point. I've heard that adding a HPF can improve power handling by removing the subsonic frequencies that the amp tends to waste power on, but with a passive one post amplifier those would still be amplified but would be dissipated in the speaker, so it wouldn't help the amplifier at all.
Would anyone be able to link me to some of the cheaper HPFs? I've been trying to find some for a while now but the only ones I can find are those overhyped ones you talk about.
Click to expand...

If you use a passive HP filter, the speaker doesn't receive the low frequencies- they're removed by the HPF.

Active is the way to go- the power amp never sees these frequencies and the problem with passive filters never shows up- insertion loss. Passive filters usually cause at least 3dB of loss, which is the same as cutting the output power by half. Active filters can do their job, then with a bit of an internal boost, you can achieve unity gain- the input and output levels are the same.

If you're using a separate preamp and power amp and have been thinking about using an equalizer, look for one with a crossover and separate outputs for HP and LP.
 

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