How common are rumble filters?

riker1384 · #1 05-10-2009, 02:21 PM

People here talk about speaker designs and their power handling at bass frequencies, but they rarely talk about subsonic transients, especially from slapping. I've always wondered, how common is it for a head or combo to have a subsonic filter? Is it something that's standard, or is it rare?

Also, has anyone measured how much a typical bass (with various playing techniques) puts out in the subsonic range, or at least below the lowest fundamental?

JimiLL · #2 05-10-2009, 02:27 PM

Thats a good question, I had one on my amp back when I was really into car stereo's, and It definitely helped to tighten up the sound. For sure.

I always had mine set at 20hz

ashtray · #3 05-10-2009, 02:34 PM

My QSC power amp has a low filter - I set it to 50hz, just to protect my cabs. I don't do the "thunderous bass" thing, and even with this set, the low B string sounds just fine to my ears.

alexclaber · #4 05-10-2009, 03:29 PM

Quite a lot of heads and combos either have a significant roll-off in the lower lows or some kind of steeper highpass filter built in.

Alex

**Marcus Willett** · #5 05-10-2009, 03:30 PM

At one of my shows I use a Fishman Platinum Pro DI with a HPF. I usually set it around 50Hz or so and there's no lack of low end at all. In addition it really helps to tighten up the low end, as JimiLL suggested.

bongomania · #6 05-10-2009, 03:51 PM

The only issue I see commonly is that the low end rolloff built into most amps is not indicated or controllable. IOW there "may or may not be" subsonic filtering built into the design, and if there is, there "may or may not be" any indication of that fact in the manual, and there is often no switch to dis/engage it, and even more often no choice of frequencies.

I use a para EQ, so I have no problem myself. But the question of "how common are rumble filters" is a hard one to answer--even if we agree they are common by design in many MI amps, it is woeful that we users are not given much in the way of information or controls to work with.

steveksux · #7 05-10-2009, 06:32 PM

I found some for audiophiles, put one in line btw my power amp and preamp.

Subsonics from string handling are all wasted power and risk overexcursion for speakers.

I used to see my cones dancing a lot, thought it was bass. Put in the subsonic filter (< 20Hz), and suddenly most of the visible cone movement was gone. That surprised me...

Randy

riker1384 · #8 05-10-2009, 06:38 PM

Quote:

Originally Posted by steveksux

I found some for audiophiles, put one in line btw my power amp and preamp.

Subsonics from string handling are all wasted power and risk overexcursion for speakers.

I used to see my cones dancing a lot, thought it was bass. Put in the subsonic filter (< 20Hz), and suddenly most of the visible cone movement was gone. That surprised me...

Randy

What did you use; would it work in the effects loop of an amp, and with readily available connectors/adapters? I remember Parts Express having some cheap passive line-level filters for subwoofers and such, but I can't seem to locate them now.

Edited to add: The ones I was thinking of are "FMOD"s. They're 12db/octave filters with RCA jacks and are apparently available with F3 of 20, 30, or 50 Hz as well as other frequencies that aren't applicable. Would these work if they were inserted into an amp's effects loop?

dhomer · #9 05-10-2009, 09:32 PM

Edited to add: The ones I was thinking of are "FMOD"s. They're 12db/octave filters with RCA jacks and are apparently available with F3 of 20, 30, or 50 Hz as well as other frequencies that aren't applicable. Would these work if they were inserted into an amp's effects loop?[/quote]

Absolutely it will work. I have an FMOD-Sub in my Bmax's effects loop, set at 35.

anonymous02282011 · #10 05-12-2009, 12:47 PM

Check out TBer Fdecks HPF.

http://personalpages.tds.net/~fdeck/bass/hpfpre.htm

It's a pass-filter and a polarity switch preamp. 10mega ohm input, 3dB of gain. Runs on a 9volt and it's 50 bucks. I've been using one for a while now and it's great.

**butchblack** · #11 05-12-2009, 08:38 PM

BassmanPaul · #12 05-13-2009, 03:36 PM

For the more technically minded take a look at this site: http://sound.westhost.com/project99.htm

It's a simple but effective filter for those power wasting subsonics.

Paul

BBEgo · #13 07-05-2011, 11:29 AM

I just bought a 30Hz FMOD Sub-Filter to put in the FX loop of my BBE BMax-T preamp, like dhomer.
Sounds like a really good idea. Can't wait to try it.

Petebass · #14 07-05-2011, 09:19 PM

What's the filter slope on those Fmods? My guess is they're only 6dB per octave. If so you may have to choose a frequency which sounds too high when you first say it or it won't do anything.

I engage the HPF on my Acoustic Image head all the time. From memory it's 12dB per octave. It's often set to 60Hz, yes my bass still sounds like a bass, and yes the speakers move visibly less.

Codger · #15 07-05-2011, 10:08 PM

Quote:

Originally Posted by Petebass

What's the filter slope on those Fmods? My guess is they're only 6dB per octave.

It's a two pole high-pass, so 12 dB/octave. It is adjustable and all transistor (no op-amp). Very Cool.

bongomania · #16 07-05-2011, 11:58 PM

Quote:

Originally Posted by Codger

It's a two pole high-pass, so 12 dB/octave. It is adjustable and all transistor (no op-amp). Very Cool.

There are no transistors in it-- whereas there ARE transistors in an opamp.

It's a passive device, only has passive components like resistors and caps.

Some of their models are 12 db/oct, and others are 18 db/oct. I found they drop the signal level significantly, as you'd expect from a passive filter with no resonant hump--so they worked well with very high-output preamps, but not well with low-output ones where the voltage drop had a noticeable impact on how a given preamp drives a given power amp.

Munjibunga · #17 07-06-2011, 12:07 AM

Quote:

Originally Posted by ashtray

My QSC power amp has a low filter - I set it to 50hz, just to protect my cabs. I don't do the "thunderous bass" thing, and even with this set, the low B string sounds just fine to my ears.

I've always set mine at 30hz when there's bass going through it since low E is about 40 hz and low B is about 30.

Codger · #18 07-06-2011, 06:37 AM

Quote:

Originally Posted by bongomania

There are no transistors in it-- whereas there ARE transistors in an opamp.

It's a passive device, only has passive components like resistors and caps.

Total late night screw up on my part - I was talking about the Fdeck part, not FMOD. I got the "F" part right anyway.

FuzzBoxVoodoo · #19 07-06-2011, 08:57 AM

I just put a FMOD 30hz in the Effects circuit of my Trace Elliot V-Type Preamp and it helps alot but the 12db slope isnt steep enough to completly eliminate the sub freq.
Im probobaly going to do the Subsonic / Rumble Filter for Phono preamps and Sub-Woofers
The Effects loop seems like a really good place because both the DI post EQ and output are filtered.
I soldered leads in on the board on the 5001 and then covered the FMOD with heatshrink so I can still use the external jacks on the effects loop.

billfitzmaurice · #20 07-06-2011, 09:48 AM

Quote:

Originally Posted by riker1384

how common is it for a head or combo to have a subsonic filter? Is it something that's standard, or is it rare?

More common than you'd think. Most well designed amps have high-pass filtering around 30Hz or so incorporated into the pre-amp, though few of them make note of it.
As for FMods, they're very imprecise in their corner frequency, as that's dependent on the impedance that they work into, which will vary a lot from amp to amp.