Booming? / Feedback / EQing HELP!!!

[Monz]

A question for you seasoned giggers...

Last night we played a gig in a barn LOL (yes a barn) stop laughing at the back.

Anyway, we set up on a raised concrete area as a sort of stage inside a huge barn and did a few selected parts of various numbers to get the sound check done, however, every time I hit a "C" I got a kind of booming feedback kinda thing coming out of my amp. This happened across all the octaves

I tried altering the EQ but either I was missing the frequency due to lack of knowledge/experience or something else was at fault... Is this something that you get a lot or what?

This was only my 4th live gig and so still on a steep learning curve

My rig was as follows Warwick corvette > Digitech Bass squeeze (level 75%/Xover @ 12 o'clock/lowcomp 40%/highcomp/25%) > Markbass 1x15 (Jeff Berlin) + Ashdown 1x15 cab +> DI to PA

Any help or advice would be appreciated

[mr.sibs]

Sometimes you can get a bass trap that will not necessarily be your equipment, but more likely the angle and positioning of your amp, and where any sound is reflecting from your cabinets. If your bass rig was angled into a corner for instance you might notice something like this. As for the frequency, it is understandable being more prevalent on a C or whichever frequency happens to be being reflected, but I havnt come across it repeating over octaves before?? Im guessing this isnt something that happens in rehearsals too?

[bass_ferret]

When you hit a resonant frequency like that it will also resonate at the octave just like any other harmonic. If its a room resonance then you really need a narrow band parametric or notch filter, but you can tune it out by careful cab placement - see the basschat wiki. If it is stage resonance then decoupling with something like a gramma pad will help.

[LukeFRC]

Warning: may be wrong

think of it like this, your middle C sound comes out of you amp at 264Hz (or whatever it is) that 264 'soundwaves' a second. Now given that the speed of sound is a constant 340m/s (for example- it varies) we can work out that the sound waves you are making have a wave length of 1.2m.
So your bass puts out one 'wave' every 1.29m.
now say that your bass amp is set up on a stage in a big wooden room which is say 25.8m long. now 25.8 is a multiple of our 1.29m wavelength so when the sound reflects off the wall it is going to do so in such a way that it will be in the same phase as the original signal. It will be like the two signals are overlapping and adding to the amplitude of the sound wave. This is what causes it to appear louder.
C notes in other octaves will have wavelengths which would also be multiples of the middle C (i think)
All rooms will have resonant frequencys. Frequencies that will appear louder. If you are really unlucky (or sods law) they will be frequencies on the chromatic scale.
Really you want a parametric EQ to cut out the frequencies that resonate in the room. (Big long I unit rack thing you'll find somewhere near the sound desk with lots and lots of sliders on it, usually at least two of them sat there.) As a bass player though often you will want to use your amp (which doesnt have a big parametric EQ system - though some have a notch filter which does the same thing) so turning the cabs in different directions to try and get reflections off different walls. or something

[Huge Hands]

What was going on with the rest of the band?

Was the drummer mic'd up?

I've had it before with a mic'd kit, the PA is throwing out loads of bass and kick drum. On certain frequencies, the bass drum would act as a resonator and via my amp, the acoustics of the stage room and the PA, the whole stage area would resonate.

The reason in my case was that between soundcheck and gig, I had accidentally knocked the input gain on my amp (the knob is easy to catch and turn). That had turned up both my amp and the feed to the PA (he was using the DI out on my amp).

Turning my amp down would have cured it, unfortunately I didn't realise until we had finished a rather unhappy gig. Shame the sound guy didn't spot it either.

[Monz]

Thanks everyone for your help... looks like I just need to experiment moving the amp round first then

[Kiwi]

[quote name='Huge Hands' post='243571' date='Jul 20 2008, 12:34 AM']I've had it before with a mic'd kit, the PA is throwing out loads of bass and kick drum. On certain frequencies, the bass drum would act as a resonator and via my amp, the acoustics of the stage room and the PA, the whole stage area would resonate.[/quote]

I get this as well in small venues. Sometimes the PA is too loud and I end up having to turn my rig up to compete with it. Then the sound guy turns my channel down and I end up just going from my rig without any FOH support.

FWIW, I've found boom usually happens around 100Hz, so sucking some bass back using the amp eq (if its parametric) is not necessarily a bad thing so long as you can turn the amp up to compensate for any loss in volume (headroom headroom headroom!!)

[bass_ferret]

[quote name='Huge Hands' post='243571' date='Jul 20 2008, 12:34 AM']I've had it before with a mic'd kit, the PA is throwing out loads of bass and kick drum. On certain frequencies, the bass drum would act as a resonator and via my amp, the acoustics of the stage room and the PA, the whole stage area would resonate.[/quote]
Often it is the kick that is too loud but it sounds like the bass booming when it couples. I used to get the same problem with keys but it was always the bass that gets blamed for being too loud.

[thepurpleblob]

It's resonance. Each building/room has a resonant frequency and if it happens to be in your range of notes you have a problem. I used to play a small pub where an A sounded like the building was coming down. You can't really EQ it out that easily (well I couldn't anyway). Doing something to isolate my cab seemed to help, in that case playing on the floor instead of the low stage. Experiment and move things about I suppose.

[Breakfast]

What used to really get on my tits was that the singer in my last band had a guitar that in some venues fed back on A played at 5th fret on the E string, which happened a lot as he liked playing with a capo on second fret. It typically happened worst when he played an A chord and I hit the root note on the bass at the same time. Whenever this happened, particularly during shows it would create a nasty low boom and he would glare at [i]me[/i] for feeding back so badly. Several times I showed him during soundcheck that I could turn the volume to zero on the bass and still the feedback would keep happening, but he simply could not hear facts that he didn't want to hear.