Are subsonic filters important?

Discussion in 'Audio Hardware' started by CBackley, Aug 23, 2019.

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  1. CBackley

    CBackley Chairman of the Bored Thread Starter

    My current phono preamp (MoFi Studiophono) has a subsonic filter button. I’ve always had it activated. I know what the button is supposed to do, but I don’t know if I’ve ever heard problems with rumble or whatnot on my system. Are subsonic filters meant to address problems experienced more often on more advanced systems? I currently have a Pioneer Elite SX-N30 stereo receiver running KEF Q100 speakers, hooked up to a Pro-Ject Debut Carbon DC, so nothing fancy.

    I’m looking at a few new phono preamps, but none of them have a subsonic filter button. Do I need that thing? I live in an apartment building, so I rarely play my music loud without headphones.
  2. Vinny123

    Vinny123 Forum Resident

    I’ve had subsonic filters in the past and never noticed a difference on or off regardless of volume
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  3. Ontheone

    Ontheone Poorly Understood Member

    You use it only if you need it. The only reasons to use a subsonic filter is to correct the woofers from rumbling/pumping or if you're experiencing acoustic feedback. From my experience, proper TT isolation from the low frequency output of the speakers has left me with no need to ever turn on a subsonic filter.
    bluesky and Josquin des Prez like this.
  4. Curiosity

    Curiosity Just A Boy

    United Kingdom
    While there's very little below 20hz recorded on your record, things such as warps can cause issues with subsonic frequencies causing loudspeaker cones to 'flap' and (obviously) tax an amplifier a bit so to avoid this some manufacturers build in a filter to deal with this.
  5. JustGotPaid

    JustGotPaid Forum Resident

    There is plenty of rumble cut into vinyl. Just look closely at your woofer with some volume. It will be dancing without a subsonic filter no matter how well your tt is setup or isolated.
  6. 62caddy

    62caddy Forum Resident

    Vinyl warpage resulting in excessive woofer movement is the primary reason to use the subsonic filter although not necessarily the only reason.

    LF distortion increases dramatically when the woofers oscillate in this way - as high as 50% or higher depending on the severity of warpage.

    The frequency band in some phono sections (as well as some preamplifiers) is intentionally cut off below 20 Hz inhibiting infrasonic "garbage" for this reason. The LF filters on both of my preamplifiers is 50 Hz but does resuls in some sacrifice to bass response. By all means, use the rumble/LF filter if the woofer is making a "rapping" sound which may cause severe damage.
    Last edited: Aug 23, 2019
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  7. Ontheone

    Ontheone Poorly Understood Member

    I think the key is to first remove rumble (if any) that is being caused by your setup before assuming all the rumble is inherent to the vinyl. The most common culprit of rumble is probably an arm/cartridge mass mismatch if you've dialed in your isolation well. I would take all measures to fix your set up first. All things equal I'd rather not be applying a filter to the signal and possibly introduce added noise. A subsonic filter is not transparent because it needs passive or active parts to function and the signal has to pass through it.

    Now with this said, excessive woofer pumping isn't good either and will degrade the sonics - so you do need to decide which to address. I'd fix the system first, to the extent possible, then add a filter if you've done all you can and still have woofer pumping. I highly doubt this is a problem cut onto most vinyl recording so one solution is using the tape loop on your pre-amp (if equipped) and only use it when needed.
    Last edited: Aug 23, 2019
  8. Ontheone

    Ontheone Poorly Understood Member

    I'm surprised so many of you vinyl audio enthusiasts have collections full of warped, poorly cut, and badly centered records ;)
  9. bluenosens

    bluenosens Forum Resident

    malagash centre
    I use my subsonic filter on the Luxman L503S. The Roksan Zerxes Digs out more subsonic guck than some other turntables. It has been suggested it is because of the"gobs" used in its design. UHF Mag noted this when they tested one of the first Zerxes way back when. Once tried a single ended tube pre on an old simaudio 4070. It did magic but the woofers went crazy. Fun, eh?
  10. avanti1960

    avanti1960 Forum Resident

    Chicago metro, USA
    for your system it would not matter to have a subsonic filter.
    they can really come in handy though if you have full range speakers or a subwoofer.
    CBackley likes this.
  11. CBackley

    CBackley Chairman of the Bored Thread Starter

    Thanks! That’s what I suspected. My gear is so basic, I’d almost be proud if my woofers were rumbling and rapping.
    Jimi Floyd and Rick Bartlett like this.
  12. Helom

    Helom Forum member

    Yes, they are necessary, a necessity even. This is because some albums have rumble noise actually cut into the grooves of the vinyl. Woofer pumping is not a phenomenon exclusive to acoustic feedback and warps. From KAB: One of the biggest let downs with phono playback is subsonic rumble. Often part of the recording itself, even the best turntable will reproduce it.

    My experience aligns with this assertion. I have perfectly flat albums that will cause woofer pumping at very low levels, on songs and passages with almost zero bass content. I also have perfectly-flat albums with copious bass (Slightly Stoopid's Chronchitis for example) that cause zero woofer pumping, and at high SPLs.

    Also have albums with warps the size of Everest that didn't cause any rumble/pumping.
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  13. jupiterboy

    jupiterboy Forum Residue

    Buffalo, NY
    Your turntable produces very low frequencies, even if you don't see the woofers moving. If you use a rumble filter, you amp will not work as hard to produce those super low frequencies. Might not be an issue with a beefy SS amp, but with a modest tube amp, you might be doing your amp and your ears a favor if the amp can only work on controlling the drivers in the frequency range where the music is.
    Shiver and Grant like this.
  14. Benzion

    Benzion "Cogito, ergo sum" Forum Resident

    Brooklyn, NY
    It's important to me, and I have mine always one in all my phonos. I had one custom fitted by the proprietor on my Lounge LCR III, a while after purchasing (I got the Silver upgrade at the same time). Incidentally, I also recommend the Lounge, especially with the Silver upgrade, since you're considering another phono. Contact @morinix (the proprietor) about it, he'll be happy to help.
    Gramps Tom, SandAndGlass and CBackley like this.
  15. If your loudspeakers exhibit good mechanical damping then a subsonic filter is superfluous.
    If your mid/bass is wobbling about like jelly (jello) on a plate a subsonic filter is necessary - either that, or you go and get yourself some better designed speakers :D
  16. patient_ot

    patient_ot Senior Member

    It's a nice feature to have and worth using if you have a fair amount of warped records. I've had preamps with them built in before and have used in-line high pass filters to function as a subsonic filter. Currently on my main deck I don't use one. Purists don't like them for philosophical reasons. If you buy a phono pre without one you can always add one as an extra component. The high-pass filter type are usually fairly inexpensive - say, less than $30. The more sophisticated active subsonic/rumble filters like KAB et. al. cost more.
    CBackley likes this.
  17. 62caddy

    62caddy Forum Resident

    Unfortunately it's almost unavoidable. Early LP records were generally better made, thicker & heavier and less susceptible to warpage. Quality began declining in the 1970s and beyond and nearly every LP that I purchased new beginning in the late-70s has some degree of warpage. A good TT clamp can help matters in some cases.

    Not necessarily true. Even the best damped acoustic suspension speakers can still pulsate depending of the state of the LP being played. Whether it rises to the point of being objectionable is another matter.
  18. Helom

    Helom Forum member

    So you run sealed-box speakers exclusively? Have to ask since you didn't fill out your equipment profile. Why does that seem to be a trend with the "perpetually grumpy" members?:shh:
    SirMarc likes this.
  19. Doctor Fine

    Doctor Fine Meat and Potatoes all day long

    I have a KAB subsonic filter on my far field system that can be switched in or out of my tape monitor loop when I need it.
    My system has dual sealed 12" SVS subs.
    And dual 15 inch Velodynes under those for truly deep bass.
    It tests +-3dB down to the low 20s in room using test microphone at listening position.
    My arm resonance is 9hZ.
    Records are normally dead quiet on the quiet passages---zero rumble, hiss and just a tiny bit of groove scrape.
    It is so quiet you think the record is really a CD.
    I'm not bragging on hot air---I am a professional installation guy and retired after 40 years in the trenches.
    Table is sitting on a floating plinth.
    And the table feet are then floated again on their own silicon pads for TOTAL isolation from vibration at ANY volume my main system can put out (measured 105dB on "All Along the Watchtower by Hendrix").

    I can't remember using my subsonic filter at any time during the last year.

    The filter sucks all the separation out off the signal and makes it sound like mono in the bass.
    And it completely alters the tone of the set.
    The bass gets clean as a whistle but everything sounds very closed in when it is in the circuit.

    I would only use it on a truly terrible warp or outrageous rumble that is on the disk.
    But it is nice to know I have it with all that horsepower laying around.
    Otherwise I could conceivably blow out my woofers.

    My two cents.
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  20. Helom

    Helom Forum member

    Strange, I don't have this problem with my KAB even though I expected to.
    389 Tripower likes this.
  21. There's more than driver suspension to consider.
    Cabinet design comes into play, and airflow through ports has to be considered as well.
    It's possible to design and build cabinets that control port airflow to minimise wobbles in the driver.
  22. No, my speakers not sealed box.
    They are ML-TL, and airflow through the port was considered by my good friend who designed them.

    The drive units are dual concentric, and if you dig around the "Best Speaker You've Heard" thread you can see a picture of one of the speakers - follow the link with the picture and you can find out more if you're interested.
  23. There's not just suspension to consider.
    Airflow through ports needs to be controlled, and when it is port/cone resonances become much less of an issue.
  24. Doctor Fine

    Doctor Fine Meat and Potatoes all day long

    The KAB sounds really funky compared to wide open.
    With flat down to low 20s in STEREO I can "feel" the walls in a concert hall running wide open.
    The KAB shifts the bass upward/makes it mono/tightens up the entire presentation killing a LOT of the "life" of the sound.
    It still sounds excellent.
    It just don't sound like my big bad stunning "you are THERE" system any more.

    I am glad I have it standing by for truly bad rumble but I would much prefer a simple linear cut at 25 and below.

    Trouble is every filter and cut I have tried other than the KAB seems to take away a lot of HIGHER frequency information along with the bass cut.
    Filters are not precise enough to just cut from the cutoff point and DOWN.
    They all cut on both sides of the filter frequency so a cut at 25 is a cut at 40 too!

    Darn filters!
    I hate 'em.
    Until I need 'em.
    389 Tripower and Ontheone like this.
  25. Helom

    Helom Forum member

    So you're saying your speaker's drivers are still loaded below their port-tuning frequency?:shh:
    The Pinhead likes this.
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