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Old 27th January 2011, 01:41 PM   #1
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Default Micing a ported guitar/bass cab?

I had a theoretical question about micing a ported guitar cab. My understanding is that at the port's tuning frequency, the port is actually producing the sound and the driver is producing next to nothing. So if I try to mic it using the traditional method - SM57 close miced to the center of the speaker - wouldn't that mean that at the frequency where I want enhanced bass response, I'm actually getting even less through the mic?
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Old 27th January 2011, 03:15 PM   #2
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yes.

but if you look at how the sound is radiated you will find that you will still hear the output from the port rather well... otoh, a bit depends on what you are trying to capture in the recording, and where the port is tuned. IF the port is tuned below the lowest open freq of the instrument (bass guitar?) then the port is not doing anything except on "slaps" where it makes something of a "whoomp" sound or "thump"...

Most "ported" bass guitar cabs (Hartke, for example) are not really "tuned" to anything much, they just are there...

Best to investigate by trying mic placement and listening in your monitors, or off your recording for the best sound and best placement... close up is frequently not the best sound anyhow - it is done that way in LIVE PA/SR situations to keep the S/N and feedthrough minimized (you want the instrument you are mic'ing not the rest of the band).

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Old 27th January 2011, 03:51 PM   #3
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Originally Posted by bear View Post

IF the port is tuned below the lowest open freq of the instrument (bass guitar?) then the port is not doing anything except on "slaps" where it makes something of a "whoomp" sound or "thump"...
with some woofers it could make sense to tune relatively low, to get tighter bass and maintain control, and keeping the woofer within its Xmax limit
depends on woofer
simulation needed
or choose closed box
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Old 28th January 2011, 07:43 PM   #4
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Originally Posted by qingcong View Post

So if I try to mic it using the traditional method - SM57 close miced to the center of the speaker
ahh, you are asking how to measure a ported design, where to place the microphone

I would suggest about 1 meter distance

closer to the driver its mainly the higher frequency

but actually, I know next to nothing about measurements

I dont know really
but maybe it would make sense to measure impedance ressonance peak
and for the lowest frequency I suspect a simple simulation to be more accurate
that is if its based on accurately measured driver specs
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Old 28th January 2011, 11:18 PM   #5
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I guess most bass players have no issue going direct, but guitar players can't go direct unless they're using a modeler. So it seems to me that a ported guitar cabinet is basically useless in live miced situations and a bit complicated to mic in the studio.
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Old 28th January 2011, 11:50 PM   #6
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Why not double mic,one on the cone and one on the port,might need a sock on the port mic.
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Old 29th January 2011, 01:51 AM   #7
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Well see, that's when it starts getting complicated, to me at least. Sure you can double mic it, but how do you place each one for optimal quality? I imagine tweaking it is much more complicated than if you just had one mic. For live situations, forget it. Soundmen in venues don't have the time to mess around with mic placement.
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Old 29th January 2011, 02:37 AM   #8
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For live situations, forget it. Soundmen in venues don't have the time to mess around with mic placement
change your soundman then i'll often move the mics about during soundcheck if they aint giveing me the sound i /the band want.As for placment,if its live maybe an m88 with head just in the hole
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Old 29th January 2011, 12:21 PM   #9
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Originally Posted by bear View Post
Most "ported" bass guitar cabs (Hartke, for example) are not really "tuned" to anything much, they just are there...
bear is right. What cab and speakers are you using?
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Old 30th January 2011, 01:54 AM   #10
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You definitely do NOT want to double mic a bass cabinet or a guitar cabinet or any other cabinet unless you know precisely what you are doing and what you want to get soundwise and are getting soundwise.

The two mics will have "bleed" from each other's source plus everything else on the stage. In an iso booth in a studio, then two mics MIGHT be useful IF you know exactly how to deal with it - or, if you have to ask, don't!

So, if it is a commercial cabinet, likely the best thing to do is to ignore the port. In the case of a guitar cabinet, the port has no meaningful sound to record (unless ur doing something unusual, in which case you know what you are doing already and don't need to ask!!). In the case of a bass cabinet, the port may or may not be doing something useful, best check. But two mics open on the same source are problematic, so you have been warned!

Live sound is a different animal than studio sound...




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