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Why do frequencies disappear?

Discussion in 'Amps and Cabs [BG]' started by PauFerro, Apr 25, 2018.


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  1. PauFerro

    PauFerro

    Jun 8, 2008
    United States
    I am not sure if this is a bass amp question or an electric bass question. So I will ask it hear as people are likely more knowledgeable in the amp area than in the bass area -- the issue seems to be electronic.

    I have a Cort Curbow -- one of the classic ones from the 90's -- and when I played it through my Peavey Pro Bass 500, certain notes would just disappear from the mix of the band. For example, if I hit a D on the G string, it was like I hadn't played it at all. It was like the amp couldn't pick that frequency up.

    Can anyone explain why this might have happened?
     
  2. It's called a dead spot and frequently is in the area you describe. Some basses are worse than others regarding this issue. It's not all that uncommon and there doesn't seem to be a whole lot you can do to correct it. There are devices such as the Fat Finger that attaches to the headstock and may help. Some people put weights somewhere on or in the peghead to do essentially the same thing. According to some sources, Fender style headstocks with four tuners per side suffer more than two per side headstocks like Gibson or Rickenbacker. Hope this information helps, even though it's not really good news.
     
  3. Flippy

    Flippy

    Jun 9, 2017
    Europe
    It could also be your room and amp placement. Try moving and rotating it a bit.

    If you're unsure, check if the same problem happens when you play on headphones
     
    alesreaper9 and jamro217 like this.
  4. PauFerro

    PauFerro

    Jun 8, 2008
    United States
    I thought it might be a setting on my amp. I didn't have time to mess with it at the gig. but the Pro Bass 500 has a detailed parametric eq section (way too detailed, looking back), and I wondered if perhaps I had de-emphasized a section the frequency spectrum that caused this.
     
  5. beans-on-toast

    beans-on-toast Supporting Member

    Aug 7, 2008
    Sometimes changing strings can help with dead spots on the neck. If the issue is on the entire string, the bridge might have an issue or the pickup might need adjusting.
     
    Arjank likes this.
  6. two fingers

    two fingers Opinionated blowhard. But not mad about it. Gold Supporting Member

    Feb 7, 2005
    Eastern NC USA
    What you are describing sounds exactly like a dead spot. They are most common from the 5th to 7th frets and have more affect on the higher strings. Lots of basses have it. Try hitting the same D on the octave fret of the D string. If the note rings out true, it's not a frequency problem. It's a dead spot.
     
  7. Arjank

    Arjank

    Oct 9, 2007
    Above Amsterdam
  8. Snaxster

    Snaxster

    Nov 29, 2008
    Hello. Though you didn't say, you imply that it's only when you play this bass through this amp that you get the frequency dropouts. Please confirm:

    Do you get the dropouts only with this amp, or also when playing this bass through other amps, etc.?
     
  9. PauFerro

    PauFerro

    Jun 8, 2008
    United States
    I never tried it with a different amplifier. After it let me down on that gig, I put it on the bone pile and plan to put a short scale neck on it But I did a couple gigs where the dead spots didn't seem to exist with a rock band. Either I missed them, or I changed my EQ frequencies. The EQ section is really detailed on the Peavey Pro Bass 500 where you can dial in parametric EQ across the low mids and highs, and cut/boost them too.

    upload_2018-4-26_18-59-51.

    I wonder if I inadvertently cut out a frequency that was in a light dead spot.

    I have lost interest in all this experimentation given all the equipment I have, but if you're suggesting I should do more investigation, I think that's a wise piece of advice. But there seems to be consensus my particular bass might be predisposed to disappearing frequencies in spots.

    The fact that it only happened on one gig makes me wonder if it was a set of EQ settings on the bass, and amp together that did it.
     
  10. Snaxster

    Snaxster

    Nov 29, 2008
    All good. However, what I'm looking for is constants. By changing only one factor in each round of testing, keeping all others constant, there's a good chance that the cause will follow you from test to test either in a given round or across rounds. For example,
    • if
      • when playing bass 1 with its controls set at X, through amp 1 with its controls set at Y, you get the dropouts in rooms A and B and C
    • and
      • when playing bass 1 with its controls set at X, through amp 2 with its controls set at Z, you do not get the dropouts in each of rooms A and B and C
    • then
      • all other factors being constant, the relationship of bass 1 and amp 1 is the cause.

    • but if instead
      • when playing bass 1, through any amp, you get the dropouts in any room
    • then
      • all other factors being constant, bass 1 itself is the cause.
    and so on.
     
  11. dbase

    dbase Gold Supporting Member

    Jan 3, 2008
    South Jersey, USA..
    I get that using a full stack whereas I'm kicking out some bass in the room and I hit a B on the E string and nothing.. dead, flat whatever.. it doesn't resonate. but it will if I hit a B on a different string... each room provides a different sounding board for the bass. Sometimes I just miss striking the string altogether but that's another story.
     
    HolmeBass likes this.
  12. JimmyM

    JimmyM

    Apr 11, 2005
    Apopka, FL
    Endorsing: Ampeg Amps, EMG Pickups
    Sounds to me like boundary cancellation. How far was your cab from the nearest rear wall?
     
    DirtDog, saabfender and Groove Doctor like this.
  13. Yep, boundary cancellation.....
    Walk around and check it at several spots on stage.
    Change speaker position/angle.
    Change EQ.

    I've had the opposite.... a ridiculous boom anytime I played a B, any octave on any string. I was exciting the resonant frequency of that triangular room. Lucky I had my Thunderfunk at that gig, EQ'd the s*** out of it.
     
    JimmyM and PauFerro like this.
  14. PauFerro

    PauFerro

    Jun 8, 2008
    United States
    It was right up against a wall, but to the side of it, maybe angled a bit toward it. What is boundary cancellation?
     
    JimmyM likes this.
  15. saabfender

    saabfender SUSPENDED

    Jan 10, 2018
    Indianapolis
    ”I’m hearing...” ”People are saying” -

    I’ve played a bunch of Fenders over the years and have never encountered one with multiple dead spots. Happily, they are usually 5-6 fret on the G string, so fairly avoidable.
     
  16. BassUrges

    BassUrges

    Mar 14, 2016
    Denver
    Boundary cancellation just means the room itself rings at a particular frequency (like a string) and you are standing in a node. It’s akin to standing on the 12th fret when someone plays the octave harmonic. From where you stand, the string isn’t moving. Same thing but with air.

    But my fretless MIM Jazz has a spot so dead on that D it sound out of tune, even when the tuner says it’s right on. That’s worth checking out.
     
    JimmyM likes this.
  17. JimmyM

    JimmyM

    Apr 11, 2005
    Apopka, FL
    Endorsing: Ampeg Amps, EMG Pickups
    BassUrges has it right, but it can also be caused by your cab being by a nearby wall and the reflections from the wall hitting your ear at a time that cancels out the note, too. But it would have to be slightly less than 2 feet from a wall to cancel out that particular D. Here's a chart for it...the D on the G string is 146.83 hz:

    Boundary Cancellation and Room Modes

    However, I somehow glossed over it being the D on the G, and that's right in the range where you could have a dead spot, as it's typical on certain basses to be in the C-D range. But if it was fine in other settings, I suspect that it might not be a dead spot. It's possible you did de-emphasize a frequency that brings it out.

    Anyway, sorry I missed a very important part of the equation, but honestly, we're all spitballing here. Stuff like that is hard to diagnose for sure over the net. But at least now you have some ideas what it could be, and I'm sure between everything mentioned that you'll figure it out.
     
    saabfender, lowendrv and lowplaces like this.
  18. My J has a wicked dead spot from the C up to the D on the G string. The C is particularly weak, the D a little better, but these notes are weak. Just passing by isn’t too bad, but holding, or with an octaver, they are avoid notes. My octavers won’t track those notes, but work fine on the same notes on the D string. I think it’s pretty common for basses, especially Fender styles, to have dead spots although the severity can vary a lot from bass to bass.
     
  19. chadds

    chadds

    Mar 18, 2000
    At jams playing through provided budget backline some frequencies some notes were nonexistent. This was on a maintained fully functional contemporary 18v bass that has no dead spots and reproduces every note of the fretboard through other gear.
     
  20. DirtDog

    DirtDog

    Jun 7, 2002
    The Deep North
    Was thinking that as well...or phase cancellation...
     
    JimmyM likes this.

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