Massive volume-build-up at 130 Hz (C3 note) - not a room mode

L

Les Paul Fan

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I connect my FM3 Turbo (Firmware 7) directly to studio monitors. When I fret the note C3 on the guitar (approx. 130 Hz), A-string 3rd fret or E-string 8th fret or power chords with the note C3, and leave the string fretted, the volume increases after a few seconds and continues to build up, deep booming noise that almost bursts your eardrums. This only happens with the C3, other notes (frequencies) do not produce this rapid increase in volume. I have not experienced this phenomenon with other modellers using the same studio monitors in the same location. This is also not a room mode excitation, as a 130 Hz signal and other neighbouring frequencies played through the same studio monitors do not produce a resonance or volume build-up. Note added in proof, I can place the studio monitors wherever I want in the room, this phenomenon does not go away. Has anyone observed anything like this? EQ does not help, Low Cut at 200 Hz and -12 dB reduces the volume build-up somewhat. With heavy gain presets I even need to set low cut to 400 Hz and -18dB, but all these changes affect the tone dramatically and are no solution. With this glitch the FM3 is useless and unplayable. What could be the reason for the volume build-up at C3 (130 Hz)?
 
Have you recorded the FM3 signal directly and is it present in the recording? Is it any preset, multiple presets?

The FM3 does not make only the C note build up for me.

What is the low resonant frequency in the Cab block?

Why set the low cut up to 400 rather than cutting 130 only?
 
I also often struggle with boominess in the 110-150 Hz range. One thing you could try is to choose a speaker impedance curve with a less pronounced low frequency resonance, for example the Brit 800.
 
Joshua_L said:
didi you try to move your monitors? seems just like unwanted resonance feedback
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I thought so too, but I am starting to doubt it or at least I am confused the more I read about it. I moved the monitors to all positions imaginable, vertically and horizontally, build-up boom doesn´t go away.
 
chris said:
Have you recorded the FM3 signal directly and is it present in the recording? Is it any preset, multiple presets?

The FM3 does not make only the C note build up for me.

What is the low resonant frequency in the Cab block?

Why set the low cut up to 400 rather than cutting 130 only?
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1) I have no experience with recording, didn´t need it yet. Might look into it when I have more time
2) and you are not worried?
3) I have to look, currently away from home for a week
4) was a quick shot, 200 cut was not really efficient, don´t expect 130 just by itself to work then
 
Testwise switch of your monitors and hear with a good headphone plugged in the FM3! If there is no resonance than at 130Hz its your Room! So you can reduce this frequency with the global parametric EQ with a high Q so it don't affects the neigbour frequencys.
 
yek said:
It IS room-related resonance. Other equipment may not initiate this, because it involves more than generating just a single frequency.
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what about feeding a 130 Hz signal through my monitors, no resonance observed

what would that "more" be?
 
Have a 130-150 build up in my room even after treatment. If I play quietly (below 75ish, it barely exhibits. If I play 90db, it is very present and 'rattley'. I don't hear it in my Sennheiser HD650s. .02
 
TheTrueZoltan! said:
I also often struggle with boominess in the 110-150 Hz range. One thing you could try is to choose a speaker impedance curve with a less pronounced low frequency resonance, for example the Brit 800.
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And there is control to set the frequency and level in the cab resonance. I have a cab saved for exactly this purpose. So I don't cut lows I don't need to in 'real world' use. You have to go outside the room environment you're in to find out if your corrections are correct, incorrect, not enough, too much, etc.
 
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If you really want to understand what's happening in your room, buy an inexpensive measurement mic and download REW software and do some captures at a fairly loud volume. Check out REW's website. They have a links to purchase compatible measurement mics. I have "miniDSP UMIK-1 calibrated USB measurement microphone" and it works great.

130Hz could be a room mode, or it could be SBIR (Speaker Boundary Interference Response), or a combination of both. I personally had a huge dip at around 120Hz AFTER extensive room treatment, BUT I found that by placing my subwoofer correctly most of that has been corrected. The only way to know for sure what's going on is to measure it.... (and try various fixes if you are inclined)
 
Les Paul Fan said:
what about feeding a 130 Hz signal through my monitors, no resonance observed

what would that "more" be?
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When you feed a 130 Hz test signal into your monitors, there is no feedback loop. When you play a 130 Hz note on your guitar, there is a feedback loop — from your monitor to your guitar.

1) Try using headphones, with your monitors turned off completely. That will break the feedback loop.

2) Try playing at very low volume. That will weaken the feedback loop.

3) Try a different room. That will change the feedback loop.
 
Les Paul Fan said:
what about feeding a 130 Hz signal through my monitors, no resonance observed
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Because in this scenario there is no feedback mechanism. When you’re fretting the note on the guitar, the sound from the monitors is exciting the string which in turn creates a louder sound through the monitors. The resonance will go away if you continue to fret the note but roll down the guitar volume knob.
 
I have that same resonance frequency - A string 3rd fret palm mutes are wayyy boomy. It happened with my real amps, with other modelers, and also with the FM3.

It also occurs at its lower octaves. It's room resonance and can't be fixed without treating the room with acoustic tile and bass traps in the corners.

Playing with only headphones doesn't produce the resonance. So, you could do that. That parametric EQ idea is also good.
 
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Thanks so far for all your input and feedback. I am currently away from home for 1 week or so and will then follow your advice. Thanks too for the amcoustics link, I am pretty curious once I get home and measure my room dimensions. Hope I can figure out the meaning of those diagrams.
 
Amroc is a good tool to understand room modes, though in my experience the theoretical does not always match the real-world. I believe Amroc assumes the walls are 100% reflective at low frequencies. Unless you have concrete or block walls that is not the case. Also, it does not account for SBIR, which can have a significant impact. REW has a similar mode calculator, but it also allows you to place your speakers and the listening position in the virtual room. I have no affiliation with REW btw. It's just a cool, free tool.
 
jakel said:
Amroc is a good tool to understand room modes, though in my experience the theoretical does not always match the real-world. I believe Amroc assumes the walls are 100% reflective at low frequencies. Unless you have concrete or block walls that is not the case. Also, it does not account for SBIR, which can have a significant impact. REW has a similar mode calculator, but it also allows you to place your speakers and the listening position in the virtual room. I have no affiliation with REW btw. It's just a cool, free tool.
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got a link for that REW calculator?
 
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