Multi-miking speaker cabinets, EQ & phase

[Paul W]

A lot of the advice I've seen lately about miking speaker cabinets calls for using two close mics with different frequency response (often a dynamic like an SM57 or 421 plus a ribbon like the Royer 121), and fading between them to control tone.

Sometimes this is very explicitly about not EQing the mics, even if they've just given the advice to EQ the amp so that the sound in the room from the cab is good. Often it seems implicit that EQ is Bad, and you should prefer use mic choice & position to achieve any EQ effects you may need.

It is sometimes claimed that by avoiding EQing the mic signals you can fade between them with no phasing issues. (Usually they've said to put both mics the same distance from the driver to keep the signals hitting the mics in phase.)

If I've correctly understood what Ricardo and others have said around here, that doesn't actually make sense, because mics behave pretty much like conventional minimum phase EQ filters anyhow, with phase shifts that correspond to the shape of the FR in a deterministic way, so for example choosing a mic with more bass or treble rolloff incurs the same phase shifts as using a mic with more bass or treble extension and then rolling it off with EQ.

And besides, moderate EQ (low Q, not steep) minimum-phase EQ filters don't incur enough phase shift to be problematic anyway; it doesn't create nulls and the phase effects are generally inaudible in this kind of context. (?)

Am I right to think it makes sense to use mic position for other reasons (like choosing between the center of the cone, which moves almost pistonically, and near the edge, which may not due to cone breakup / flexing), but trying to get all your EQ effects from mic choice and position is just making things too hard and doing it wrong.

People often say that EQ isn't a substitute for using the right mic in the right position, but I'm increasingly thinking that those aren't a substitute for EQ, either. You shouldn't need different mics just to shave off a few dB here or there, and you should be using mic choice and positioning to accomplish other things that you can't do with EQ.

For example, it seems like using a $1,500 ribbon to get a dark tone with lots of bass due to figure 8 proximity effect (only to then fade much of that away) is a back-assward way of doing things. That isn't what a figure 8 mic is for, much less an expensive ribbon. (Especially if you just EQ'd the amp so that it sounds good in the room.)

Any thoughts?

 

[kingkorg]

Using cardioid dynamic, and F8 ribbon (different patterns) an inch away from the source which is more or less flat surface (cone), which reflects sound bounced back from the diaphragm (comb filtering), which is screwed into a crude box with it's own resonances and internal reflections to basically record white noise (distorted guitar - harmonically rich content) at high SPL, and talking about using an EQ which is somehow going to degrade the sound is just ludacris. Phase shift, after phase shift, after phase shift...

You are recording a semi-controlled chaos of all the things that should sound bad, yet they don't. If we go by theory, every step down the chain of electric guitar is just horrific form of signal degradation. This is such a complex setup that you can't go by anything else but your ears. If it sounds good, it's good.

Response of a mic in front of a cab is nothing like an EQ. Just look at any IR visual representation. All nulls and sharp spikes + time domain. EQ can bring some balance, high pass, low pass... Apples and oranges, they shouldn't be compared, and or used interchangeably.



Once a mic is placed so close to the source, it's published frequency response goes out the window. Nothing wrong with using EQ to brighten up sound you are satisfied with. Using different, brighter mic, will substantially alter other stuff.

 

[Tubetec]

I just read a paragraph or two ,
I think both mic selection and positioning is key to good sound and its so often missed nowadays with post processing
blending two mics of different charachter , its like paint on the artists brush without an touching EQ ,

Suffice to say , miking a snare top/bottom or a speaker cab front back you need to flip the phase on one of the mics assuming its pin 2 hot,
Front mic can get the close up sound of the driver , rear mic distance can be adjusted to get cab/room resonance as required ,

Im not saying I dont use EQ , but preferedly as sparingly as possible ,
In the case of guitar or bass where you usually have EQ on the amp ,and blending a DI and a couple of mics and you should be very close to job done .

 

[Khron]

Just to drop a slight Finnish Eurovision song hint - "No Rules" If it sounds good, it is good. And/or, if it's stupid and it works, it ain't stupid...

 

[Tubetec]

I was on a few sessions where the producer had me set up a bunch of mics for the guitar overdubs ,
typically one will stand out ,

I like the old BBC addage , dont touch a control unless you have to ,

Khron ,
this is definately brewery fodder ,
the Eurovision has no place in this discussion ,

 

[Paul W]

To add to the list of weirdnesses about electric guitars, at the very front end there is a comb filter that results from where you pluck the strings, because different modes will be stimulated less or more depending on where your picking position is in relation to their nodes of vibration. (Near a node will not stimulate that vibratory mode, right in the middle between two nodes will maximize it.) Then there is a different comb filter per string per pickup, depending on pickup position, because the pickup will pick up different modes depending on whether it's near or between the nodes for that mode, and those modes' pitches are relative to the fundamental of the string.

Then at the cabinet, you often have a twin speaker or 2 x 2, spaced horizontally, so you have comb filters from the different sound delay times from the different speakers, somewhat different for each ear. That's part of the sound in the room, but typical mic positioning is designed to minimize it by miking one speaker or same distance from different speakers.

I hadn't thought about comb filtering from sound reflecting off the mic, off the speaker, and back into the mic.

I have wondered about what happens to proximity effect with such close miking of something big like a guitar speaker. Do you reach a point of diminishing returns because the speaker isn't a point source, and it's putting out something resembling a plane wave close up?

 

[abbey road d enfer]

One thing that has apparently not been touched is that, with two (or more) the different acoustic distances result in cancellations.
E.G. two mics with 5" difference in acoustic path will cancel 2.5kHz.

 

[abbey road d enfer]

To add to the list of weirdnesses about electric guitars, at the very front end there is a comb filter that results from where you pluck the strings, because different modes will be stimulated less or more depending on where your picking position is in relation to their nodes of vibration. (Near a node will not stimulate that vibratory mode, right in the middle between two nodes will maximize it.) Then there is a different comb filter per string per pickup, depending on pickup position, because the pickup will pick up different modes depending on whether it's near or between the nodes for that mode, and those modes' pitches are relative to the fundamental of the string.

Then at the cabinet, you often have a twin speaker or 2 x 2, spaced horizontally, so you have comb filters from the different sound delay times from the different speakers, somewhat different for each ear. That's part of the sound in the room, but typical mic positioning is designed to minimize it by miking one speaker or same distance from different speakers.

I hadn't thought about comb filtering from sound reflecting off the mic, off the speaker, and back into the mic.

You are asking a lot of good questions, and most answers are included in the questions.
It just shows that the audition has enormous capabilities at extracting the fundamental aspects of sound from an apparent chaos.

I have wondered about what happens to proximity effect with such close miking of something big like a guitar speaker. Do you reach a point of diminishing returns because the speaker isn't a point source, and it's putting out something resembling a plane wave close up?

Certainly. However I have never seen a proper study of this. It should be done, since close micing is a dominant method today.

 

[Tubetec]

5:1 rule

 

[john12ax7]

Mic choice, position and eq all have their place. But the time domain and frequency response of mic and position is more variable and complex than a 4 band parametric eq will give you. In practical terms, you will get a better result having mic and position get you 90% there and the eq the last 10%, than doing the reverse.

 

[abbey road d enfer]

5:1 rule

Rules are made to be infringed.
Many kids just stack microphones hapazardly because someone told them it offers more possibilities.
I do that only when the artist/producer asks specifically for it.
I think it's a waste of time compared to carefully positioning a single mic.
I know a producer who spends hours fiddling with 4(!) mics on a single cab, quite often to use just one in the mix.
He should have learnt a lesson.

 

[abbey road d enfer]

I have wondered about what happens to proximity effect with such close miking of something big like a guitar speaker. Do you reach a point of diminishing returns because the speaker isn't a point source, and it's putting out something resembling a plane wave close up?

Actually, there's a link here https://www.dpamicrophones.com/mic-university/source-dependent-proximity-effect-in-microphones that provides a good overview of it.

 

[Paul W]

You are asking a lot of good questions, and most answers are included in the questions.
It just shows that the audition has enormous capabilities at extracting the fundamental aspects of sound from an apparent chaos.

Certainly. However I have never seen a proper study of this. It should be done, since close micing is a dominant method today.

It's often not clear to me what are the fundamental things that audition is good at detecting.

For example, when I'm playing an electric guitar (clean) and cross from the b to the top e string, I can tell that the tone changes. I have no idea whether the difference I'm hearing is just a change in the overall FR curve, because of a thinner string and so on, or the comb filter due to pickup placement suddenly shifting all its notches up a perfect fourth.

I'm aware that static comb filters are often not obvious, but if you continuously vary the delay you get striking and qualitatively very different effects, like flanging (if the delay is short) or chorus (if it's a bit longer). But if you change the comb filter in a big jump from one fixed setting to another while also changing the note being played, I just don't know what the differences are that I am actually hearing.

 

[kingkorg]

To add to the list of weirdnesses about electric guitars, at the very front end there is a comb filter that results from where you pluck the strings, because different modes will be stimulated less or more depending on where your picking position is in relation to their nodes of vibration. (Near a node will not stimulate that vibratory mode, right in the middle between two nodes will maximize it.) Then there is a different comb filter per string per pickup, depending on pickup position, because the pickup will pick up different modes depending on whether it's near or between the nodes for that mode, and those modes' pitches are relative to the fundamental of the string.

Then at the cabinet, you often have a twin speaker or 2 x 2, spaced horizontally, so you have comb filters from the different sound delay times from the different speakers, somewhat different for each ear. That's part of the sound in the room, but typical mic positioning is designed to minimize it by miking one speaker or same distance from different speakers.

I hadn't thought about comb filtering from sound reflecting off the mic, off the speaker, and back into the mic.

I have wondered about what happens to proximity effect with such close miking of something big like a guitar speaker. Do you reach a point of diminishing returns because the speaker isn't a point source, and it's putting out something resembling a plane wave close up?

Also when you add F8 signal to the cardioid at equal levels, you are getting a hypercardioid sum. So when you move those faders and adjust the levels between the mics, you're not just changing the frequency but the pattern as well. The effect of the whole room on the sound changes as you move the faders.

 

[Khron]

Khron ,
this is definately brewery fodder ,
the Eurovision has no place in this discussion ,

Rules are made to be infringed.

That was my entire point, only referencing that song's title (and where it might be known from), that's all

 

[Rob Flinn]

Then at the cabinet, you often have a twin speaker or 2 x 2, spaced horizontally, so you have comb filters from the different sound delay times from the different speakers, somewhat different for each ear.

All the cabinets I have for recording bass & guitar only have one speaker for that reason. Maybe I'm missing out though .....

 

[mhelin]

Maybe it's better just to record the amp output (using attenuator, L-PAD, step down transformer or something) and then use a cabinet simulator (Mikko - https://ml-sound-lab.com/collections/plugins - is my first name) with IR's in mixing... There are though plugins which claim to be able to auto-align multiple microphone recordings (https://www.soundradix.com/products/auto-align/ for an example - "That's amazing - I cannot believe that"), guess they are far from perfect phase-align ability (as it's an impossible task) but might help a little anyway.