Mic'ing the Guitar Amp

Now that we have the best mic position set and the mic stand and cable is anchored down and the amp baffled if needed, before we EQ the guitar signal, you may ask the guitarist to change amp tone control settings. Of course, if you Before we get the mic's out, a word about amplifier speaker cabinet grill cloth, grill cane, or metal grill covers. These things are passive frequency filters, meaning they hurt frequency response and can actually ring if made of metal. If your's are made of cane, you may hear a buzzing sound that sounds like a blown speaker. This is rare but I discovered this myself on a 1956 Fender 4/10 Bassman amp.

The obvious purpose of the grill cloth is to protect the speaker, especially when transporting the amp. Yes, the trade off is obvious - the speaker will sound better with the grill removed, BUT you risk the chance of damaging the speaker. If the grill cover is removed. If you decide to remove your amp's grill cloth (if you can - and don't do it if it will ruin the look of your amp) it is most important to not let a mic hit the speaker. Be very careful! Sand bag down the mic stand and if using a boom, after positioning, screw it down tight! More on this as things unfold.


Positioning The Mic

We will be miking the speaker from the front. If you have an open back cabinet, you could mic from the rear, but we'll get to that later.


Front view of the speaker. The circle in the center is the speaker cone (or dust cover over the cone). The small circle to the left of the center cone is the mic. The mic distance is about one inch from the left edge of the cone (or dust cover)  Note that the mic (small circle) needs to be pointed at a 20 degree angle towards the cone center while remaining about an inch from the cone (or dust cover).

We will use a guitar amp speaker cabinet with one speaker to start. If the speaker bottom has grill cloth and you can't see the center of the speaker clearly, use a flashlight. Look at the speaker and notice the dust cover in the center. Point the mic at the exact center and then move the mic left without changing the height of the plane until you are about an inch left from the edge of the center dust cover. Now place the mic about once inch back from the grill cloth. If you have no grill cloth, imagine where the grill cloth would be in front of the speaker. Now position the mic capsule at a 20-degree angle pointing towards the center of the speaker.

We used the positioning to the left side but you could use the right side, or below or above the center point using the same positioning logic. For some reason, the left position seems to work best in most cases.

If the amp is a combo amp, the amp electronics may create an electronic field the mic may hear. This will be obvious when monitoring the mic over the studio monitors as you will hear a strange hum. In this case, you might need to mic on the low side of the speaker - closer to the floor - instead of to the left, right or above the center of the speaker.

There are a few good reasons to mic in such close proximity to the speaker. The main reason is this gives a "punchy" sound, since the speaker air is not diffused by distance, and the air movement is blasted into the mic diaphragm. There are other reasons that will be covered when we get into recording details.

The key to this mic positioning is to get a blend between the speaker cone (under the dust cover, if a dust cover exists), which produces the upper mid and treble frequencies, and the rest of the speaker, which produces the low mids and low frequencies. The farther the mic is placed away from the center cone in any direction, the more the sound will thicken up with lower frequencies. You will lose the upper-mids and treble information. You want to get the mic placement to sound as good as possible before adding EQ or anything else to the signal path. I'll give you more on this when we get into monitoring the guitar over the studio monitor speakers.


Multiple Speaker Cabinets

If you're using a speaker cabinet with more than one speaker, one of the speakers will sound better than the other(s). When we get to the point of monitoring the guitar amp mic over the control room speakers, it will be best to test all the speakers to find the best sounding speaker. 

You'll especially want to run this test If you're using a 4x12 speaker cab, such as a Marshall type cabinet. After years of experience, I have noticed that the slant cabs do not sound as good as straight cabs.


Setting Up The Guitar Mic Chain Within The Mixer And Recorder Signal Path

At this point, we assume the guitarist has set the amp sound to his or her taste for the part that will be played (clean, dirty, crunchy, etc.). These settings may be changed later.

Before we test other amp speakers (if you have more than one) and adjust the mic for the best "sweet spot," we need to get the guitar mic signal up on the mixer and through the recorder path for monitoring.

Whether you are using a stand-alone mixer (analog or digital) that routes to a recorder, or a computer based hard-disk recorder, it is all the same in the long run, since the path is technically the same.

Before we plug the guitar mic into the mixer (or computer-based analog to digital converter), it is very important that the mixer module to be used for the guitar mic is set all the way down, meaning minimum gain/volume setting. Also make sure the master mixer volume control is set all the way down as well.

If you forget to turn these levels down, and plug in a mic while the source module fader is active in the monitor chain, and the control room monitor volume is up, you will hear a loud low-end thump that may blow up the monitor speakers! Further, whenever starting a recording session, it is a good idea to "zero out the mixer" meaning all faders and "auxiliary sends" are down (volume controls off) and set all EQ volume positions to "flat." Any switches should be set to your standard starting positions.

We need a fictitious set up so let's use a mixer with 16 inputs and an 8-track recorder. If you're using a hard-disk recorder with a built in mixer, lets use the same lay out to make things simple. Simply adapt as all should be obvious.

Let's say that we are using mixer module 9 for the guitar mic input and we are recording the guitar on track 7 on the recorder. If you're using a digital recorder with a built in mixer, simply adapt with the same layout.

1. Plug the guitar mic into mixer module #9's mic input.
2. Assign mixer module #9 to bus #7 (the recorder track we are using for the guitar). Make sure that module #9 is not sent through the monitor chain and is only routed to record track #7.
3. Set recorder track #7 into "input mode" so we can monitor through the recorder.
4. Bring up module #7 (recorder track volume fader) to about half way.
5. Bring up the studio control room monitor level up to a normal listening level.
6. On module #9, set the mic pre-amp trim to -20 dB. (If you only have one input trim knob, that is the same as a mic-pre amp control. If you're using a computer hard disk recorder with outboard analog to digital inputs, use the same setting on the input level control).
7. Ask the guitarist to play the part for the song. While the guitarist is playing, slowly bring up the fader on module #9 (guitar mic fader source) to zero (unity gain). This level setting is typically around 3/4ths up on the fader throw.
8. If using an analog recorder (yes, hardly used these days, but some artists and producers swear by them) adjust the mic pre-amp trim level to average zero dB on the recorder track meter for now.
9. If you're using a digital recorder format, adjust the trim level to -6 dB on the recorder track meter for now. Always remember that going "into the red" (zero) on a digital machine peak meter will definitely "clip" the A to D converter (analog to digital converter) which is not advisable.

Regarding #7 above, if you are the guitarist and engineer, if the amp is in a separate room (or closet or some kind of seriously baffled enclosure), you will be monitoring over the control room speakers. If you have no guitar amp isolation, meaning the amp is in the same room (and only partially baffled), you will be using headphones to monitor. In any case, if you're playing chords for the guitar part, play all the open strings when adjusting the level. If you're playing single notes for the part, simply play one string for now, preferably the "D" or "G" string.

OK, you should be hearing the guitar signal. If you have no sound or metering, pull down all the volume controls in the path - as well as the master volume control - and check your routing path. In haste, I still sometimes make stupid mistakes when doing the routing. Take your time and slowly think through the path. It is always best to start at the beginning (the amp).


If the path is correct and still you have no signal, the mic or mic cable may be bad. Replace the mic. If still no signal, replace the cable. If still no signal, plug the mic cable output into another module and re-route. Eventually you will find the problem. If the problem is a mic, mic cable, or module, get some red marking tape and place a piece of this red tape on the faulty component. Red tape means it needs to be fixed and will remind you to not use the item until repaired. If you do not label bad components, this may cause time-wasting and frustration every time you try to record, because you don't remember or know which piece is broken (broken mics and cables rarely look broken).


So, when hearing the guitar signal through the path, it is now time to tweak the mic position before we get into EQ'ing and other stuff. Remember we want to get the mic path to sound as good as possible by positioning the mic.

In the above section "Positioning The Mic," we have set the mic up for the standard sweet spot. If you're using a speaker bottom with only one speaker, the odds are good the sound will be very good. Even so, moving the mic by a 16th of an inch will change the sound. You get the drift.

If you are not the guitarist (just the recording engineer) and have a 2nd engineer, have the 2nd engineer put on a set of headphones and go into the recording room to adjust the microphones, but do not have the guitar monitored in the headphones. The reason for the 2nd engineer to use headphones is twofold: If the guitar amp is set loud, the 2nd will not get blasted!!! Also, you'll be able to communicate with the 2nd as the following happens:

To find the best sonic mic position, while the guitarist is playing, the 2nd engineer slowly moves the mic while you listen in the control room. As the mic is being moved, you can communicate with the 2nd engineer via the studio talk back system that is fed into the headphones. While the mic is being moved, when the best spot is found, announce this information and ask the 2nd engineer to stop moving and note the position. If only using one speaker, skip the next paragraph.

If you're using a speaker bottom with multiple speakers, all speakers should be checked using the starting mic position. Have the 2nd engineer set the position and listen to like 10 seconds and then go to the next speaker. It will be obvious which is the best speaker, so after finding it, use the above technique in the above paragraph to really dial it in.

If you are the guitarist and engineer, this is major work since you will need to record about four bars of music for each mic position noting the mic position using a ruler for each recorded pass. Since you might be recording over and over again, it's most important to keep notes and relate them to the recorder time. So record four bars and stop. Now change the mic position ever so slightly and record the next four bars after the first four bars, again noting the recorder time or counter, and making appropriate notes about the mic position during those four bars. Continue the process while listening for the best sonic spot.


Anchoring Down The Mic Stand And Mic Cable

OK, you have the mic placed to your taste so now it's time to so some safety work. Now that the mic is positioned, cable tie the mic cable to the mic stand and duct tape down the mic cable. Here is how to do this:

After positioning the mic, you have tightened up the mic stand hand screw points. If using a mic boom stand, you have tightened those hand screws as well. 

Without moving the mic position, wrap the mic cable around the mic stand or  "boom stand piping" a few times and leave a little slack at the back of the mic to keep the cord from moving the mic on its swivel mount. If the mic does not have a swivel mount (moveable angle mount), still, you do not want any tension from the cable. To keep the mic cable from moving, we need to "cable tie" down the cord using removable "cable ties." If you're using a boom mic stand, put a few cable ties on the boom and a few on the main mic stand all the way down to the base of the stand. If you're using a standard mic stand, simply put a few cable wraps on the stand and cable tie.

Removable cable ties should be available in most electronic supply stores. DO NOT USE PERMANENT CABLE TIES. Make sure the type you buy are removable or you will have to cut the cable tie and throw it away when putting away the mic and stand. Velcro cable wraps are easy to deal with quickly. Another great product for cable management are the Planet Waves Cable Clamps, which allow you to clamp cables to almost anything, and are reusable. Most recording supply companies will have these.

Now that the cable is secure on the mic stand, we need to anchor the mic stand with sand bags or any stable heavy object that will not slip or rattle. I use fairly heavy sand bags (I guess around 20 pounds) that rest on all sides of the base of the mic stand. Typically, I use three sandbags in a triangular position. The best type of sandbag has a handle in the middle as to carry. Again, a pro recording supply company should have these.

You may be wondering why the paranoia regarding the stability of the mic stand. The following is most important:

If a mic stand falls over with the mic on it, you will get a sinking feeling in your stomach that will be awful! Microphones are sensitive pieces of equipment and not meant to take the abuse of slamming against the floor. Many microphones are expensive, and even if they are inexpensive, a busted mic will cost you time and money one way or another. Also, the microphone and stand can damage amps, instruments, or anything else they hit when they fall. Take precautions against this and you won't have to experience any regrets about unintentional damage to your or the studio's gear.

Most mic stand bases can easily tip. The bigger the mic stand base, the better. Even though we have secured the mic stand and cable, it is very possible for the mic and stand to be knocked over by someone tripping over the mic cable. To avoid this possibility, perform the following:

If you're on a wood floor, duct tape the cable to the floor from the base of the mic stand to the mic input panel or recording console mic input. The best way is to cover all the cable with tape. Start taping down the mic cord from the base of the mic stand and duct tape all the way to the mic patch bay or mixer. There should be a very little amount of mic cable slack at the mic stand base. Since there will typically be cable slack at the other end, "cable tie" the slack in a circle after plugging into the mic patch bay or mixer and tape this down if someone could possibly trip over the mic cable slack.

If you are low on duct tape, cross the cable in one foot strips about every two or three feet. If you have very little duct tape, spread out the strips further. "Artist tape" or any thin easily ripped tape will not do the job. Keep the cable taped down tight, meaning no slack between the spaced out tape strips. In the "cabled areas" where foot traffic will be heavy, do your best to cover the cable totally with duct tape.

If you're on carpet, pass on the duct tape (this leaves glue residue) and put something over the cable, such as throw rugs. Bathroom rugs seem to work in a pinch. Get some carpet remnants and cut them up to suit your needs. If you use carpet on a wood floor, make sure that it won't move if someone walks across it. A rubber type bottom on the carpet is necessary in this situation.

Next we'll get into miking the amp using two mics, as well as dealing with open back speaker cabinets. And in upcoming columns we'll explore dialing in the guitar sound for a variety of clean, distorted, and crunchy applications.

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