Problems when micing a bass cabinet

Henrik

Henrik

Member
I'm currently recording some electric bass, and my problem is that I get a nice fat low end on some notes, while other notes completely disappear down there. And it's not only that the low notes are more bassy than high notes - playing an F on the A string gives a lot more bottom end than a C on the same string.

Here's what I use: A Fender P-bass '76 through a Vox AC-50 '68 and 1x15" speaker.

I have one AKG D-112 placed near the edge of the speaker cone for the low end, about an inch away. THis goes through a Joemeek VC6Q, heavily compressed, some top end rolled off, some bass added.

Then I have a Rode NTK placed about two feet from the speaker. THis goes through a TLAudio 5001 (four channel tube preamp, rebranded in the US as HHB Radius something), and a Drawmer DL241 compressor, just a leetle compression for the snappy attack (playing with a pick).

These signals go through a Delta 1010 to my Mac.

I tried DI'ing through the 5001, but the signal appeared pretty lifeless compared to miced signal.

Does anybody have an idea on what the problem might be? Maybe it's the bass itself (even though I never noticed these big differences when just playing in a band with this setup). Any input is much appreciated!

Cheers
/Henrik
 
It could be a room problem. Do any of the modes of your room correspond to the missing frequencys? You could be getting an out of phase reflection that is in fact cancelling your inital signal.

You could try putting something behind the mic to bloc the reflection and see if that helps.

Cheers
Kevin.
 
Thanks you guys!

Kevin, I think you may be right, even though that type of problem shouldn't be that serious when I'm micing it so closely (or am I wrong?). And I guess the best solution for the time being may be to go direct through the Meek like Gidge says (I just got it, so I haven't tried that yet).

Later on I could build some bass traps for the room and see if that helps.

Thanks again!

/Henrik
 
Comb filter alert!

I only just started reading this forum, sorry I'm late. :)

You said that you get some notes nice and bassy, and some just seem to disappear.

Then you said that you have "one AKG D-112 placed near the edge of the speaker cone... about an inch away ... Then I have a Rode NTK placed about two feet from the speaker."

I was thinking this could easily be explained by comb filtering. By placing one mic 2' behind the other, you've basically created a 2 millisecond delay. The result is a frequency response shaped somwhat like a comb (hence the name).
For more information on comb filters, see:
http://www.tcicomp.com/paul/dsp/chap4/

But then I started doing the math and it doesn't work out! You should be getting some peaks and cancellation, all right, but not at low frequencies. If I've got the right formula here, the nulls of a comb filter can be found by pi / T, 2 * pi / T, 3 * pi / T ... where T is the delay time in seconds. The peak frequencies are exactly half way between nulls, with the first peak being at 0 Hz (sort of like a low shelf EQ). With a 2-ms delay, that means your first null is at 1570 Hz, with the next peak at 2536 Hz.
So you should be getting some weird mid and treble coloration by combining the mics this way; but no serious low end problems except for a nice big bump in the overall low end.

So I thought I was going to give you the correct answer and now I've just convinced myself that I have no idea. :(

But of course, it's possible I've got the math wrong but the principle right. If so, you could find out by turning off one of the mics. If the problem goes away, then that's evidence that you're getting comb filtering.

Wish I had something more helpful to say...
 
Henrik said:
THis goes through a Joemeek VC6Q, heavily compressed, some top end rolled off, some bass added.
Click to expand...

Did you use a shelf or peak type of EQ for the added bass? A Peak EQ could highlight some frequencies, thus letting others disappear. Just my thoughts...

David
 
Thanks for your input guys! Actually I gave up the whole thing with two mics for now. I split the signal, one into the Meek, and one into the amp. I cut the lows on the amp and miced it with a SM57. I backed off some on the compression and EQ on the Meek.

The result was a lot more even (so I think you have a point, Nessbass, the the EQ'ing accentuated only some frequencies), but also it lacked the huge fat low end that I got (on most frequencies) when micing with the D112. So I'm back to "fixing it in the mix". Dammit.

Next time around, I'll try the same settings on the Meek, and put the D112 through that one.

Slinkp,
I thought you'd be free of any phase problems by observing the 3:1 rule? I suppose that was oversimplifying.

Thanks again for your input guys!

/Henrik
 
Henrik,

Anytime I track bass I use a D-112 on the cabinet and then run a DI from the bass into my Presonus VXP. My mixed signal (I *do* keep these on two seperate tracks) is about 60% DI and about 40% cabinet. I have the compression fairly high on the DI and almost non existant on the cabinet (just limiting mainly to keep the levels consistant going to tape).

What I find is that the compressed direct gives me a nice articulate sound that cuts through the mix very well.... then I mix in the cabinet to add some bottom end to the mix. Haven't had any real complaints about the sound.

Hope this helps...
Velvet Elvis
 
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