Miking guitar amps

[mezcalhead]

My first couple of goes at recording a guitar actually plugged into an amp have led me to wonder how you guys are placing microphones in this situation.

I started off using an amp with 2x10" speakers but couldn't get a sound I liked out of it .. switched to an amp with 1x10" and found a decent sound pretty quickly with the mic placed a couple of inches from the grille, lined up with the outer edge of the speaker and pointing roughly into the centre of the speaker.

This may not be helped by the cheap condenser mic I'm using but I'm pretty sure my placement wasn't the best either. What do you guys do?

[sookwinder]

Jon, let me first say although I am not "sound engineer", I am an "applied acoustician", so the way I mic up amps is based on my technical background as well as experience in just recording various scenarios.

I very rarely ever place a mic close to the speaker  ... (in my experience) to capture the low frequencies you need to be 1m - 2m away from the amp/box.  The wave length of 125Hz  (1 C below middled C) is approx 3m, ..... one quarter of a wavelength is approx 0.75m, (that is the node to the antinode), so closer than 0.75 - 1.5  metres the low frequencies haven't even gone/produced a full "half wavelength" of sound.  When I have the mic at about 2 metres, I get a fuller sound.

Also do not put the mic parallel with the centre of the speaker (or any one speaker)   stick it somewhere inbetween
If you are too close to the speaker the actual physical movement of air may cause the microsphone to not perform to it's optimum.  (sort of like recording in a strong wind)

Certainly close mic'd amp is a "sound" that is used in music, but I would say they use mics that have a high tolerance to dB and air movement.

The other thing ... mic'ing close you are effectively only recording the near field  ... this means that the reverb field  (the noise of the sound "in the room" )  is more than 15 dB below the near field sound (the sound of just purely the amp)  In this case all you record is the near field  (the dry sound of the amp).

If the mic is moved away from the amp, the near field drop relative to the reverb field   (ie  the combination of the near and reverb sounds like it has more reverb in it from the room).  So you can create some great natural reverb  sounds by just moving the mic back and having a few hard surfaces in the room ..... which is why people often use the bathroom  (yes I mean the bathroom and not the toilet) as a location for the amp.

many famous guitar sounds recorded over the past 50 years were just an amp placed in a large room in a studio with a mic 10 feet away...

[mezcalhead]

Thanks sook .. gives me somewhere to start. I had the mic close to the speaker partly because we live near a busy road so I was trying to reduce any outside noise as much as possible.

to capture the low frequencies you need to be 1m - 2m away from the amp/box.

Oddly enough I found that the sounds I was getting were too bassy if anything, even with the Princeton which is quite a trebly amp when clean.

I guess I need to get a handful of mics and experiment.

[sookwinder]

Jon, I implied it with my first answer (well almost), but I'll explicitly say it.  All amplifiersare designed for "far field" , that is you stand 5 , 10, 20 metres back and listen.  They are not designed for near field listening, as studio editing minotors would be (ie  sitting infront on of on a mixing desk).  So the designer of the amp/speaker assumed that you (or thye mic) would be a little bit away from the amp and the further you are away the better chance you have of capturing the entire sound of the amp/speaker.

Oddly enough I found that the sounds I was getting were too bassy 

you may well have been too close and was picking up the bass, and/or inline with the centre of the speaker (the cone).

And yes obviously different mics affect the colour of the sound recorded. 

The other thing to consider is that it is the sound that YOUR RECORD that you are interested in, not the sound actually coming out of the amp.  If you get a great sound on your computer after you add a little EQ (even thouigh the sound out of the amp is so so, as maybe the raw recorded sound)m  that is just as valid a recording method.  That's what those EQ thingys are for.....

[FireAarro]

Interesting, most sources state the closer the mic is to the amp, the more bass will be recorded.

Proximity Effect

When recording with cardioid type microphones, be aware of proximity effect. Proximity effect causes an increase in the bass response as the microphone gets closer to the sound source. This often results in a boomy recording and care should be taken to avoid this by not placing the microphone too close the sound source. Proximity effect usually occurs when the microphone is within one foot of the of the source. Onmi-directional microphones do not exhibit proximity effect.

Proximity Effect

Anyone using microphones must understand proximity effect. When you get close to a microphone there is a rise in the low frequencies called the proximity effect. This low end boost can be 20+db boost at 50Hz!! A vocal mike like the Shure SM58 has a built in roll off to compensate for this because live performers like to sing close to the mike, but if you stand back from the mike it will start to sound thin, in other words if you want the SM58 to sound flat you must be close to it. Most mikes will have proximity effect so a low cut filter option is often supplied to compensate for it.

Have you searched the internet for some help? There's a ton of tutorials and such on the subject. Might be a good place to start, if you haven't seen them already.

[mezcalhead]

Good idea .. I'll look for some and add them to my list of reading material.

[sookwinder]

Interesting, most sources state the closer the mic is to the amp, the more bass will be recorded.

This often results in a boomy recording and care should be taken to avoid this by not placing the microphone too close the sound source.

this is what I was trying to say in my most inarticulate manner 

too close and you get a bass response that is (as they say) boomy, unclear , not defined, muddy.  reason ... there is no focus in the lower frequencies.

This happens less with higher frequncies when close mic'd because their wave length are so much shorter and by the time they hit the mic diaphram there wave length/pattern  is already well structured

[1946dodge]

This post was completely wrong and I dumped it.
Hey I'm getting old and stupid.

Read what I wrote below instead.
I think it is right.

[RumorsOFsurF]

Check out this article on Musician's Friend...
http://www.musiciansfriend.com/document ... c=3SOSWXXA

Pretty interesting, really.

[1946dodge]

Actually I was all wet in my above post. I thought about it and this is what I came up with:

For bass frequencies, the speaker aperture is very omnidirectional, while for treble frequencies it is directional. This is because the lower frequency for the bass end means longer wavelength which means the speaker aperture is not many wavelengths in size, which means it is more like a "point" radiator which will radiate equally in all directions forward.

The higher frequencies mean shorter wavelengths which means the aperture is many wavelengths in size and that will radiate a directional field pattern that is maximum at the beam peak (right in front of the speaker) and has minima at all other off boresight directions.

So you get bass in all directions and highs accentuated in the direction the speaker is pointing to.

This is, however only valid in the FAR ZONE FIELD.

The far zone field, however depends on the wavelength - the longer the wavelength the closer it is to the speaker.

The far zone is calculated appoximately as  pi*D*D/lwavelength where pi = 3.14159 and D is the aperture width.

So the longer the wavelength, (the more bassy the sound) the shorter the far field is and the closer it is to thespeaker. So the omnidirectional property of the bass is  pretty much most of the surrounding concert hall. In order to get more of a balance it is probably necessary to place the mike in the center of the speaker but in the far field of the highest or most treble frequency you want.

This also doesnt consider the fact that the sound will reflect off walls and stuff. The above considerations are only strictly valid for an infinite sized room and no reflections.
Consideration of reflections indicates that since the bass is radiated omnidirectionally, it will reflect from all surfaces, while the treble being directional will only reflect from objects in its beam, more or less. Reflections will mix with the main radiated sound and either cancel or reinforce depending on whether the crest of the directly radiated sound arrives at a point in space where a crest of the reflection does (reinforcement) or where a trough of the reflection does (giving destructive interference).

I guess...

[mynameisjonas]

when i record guitars, i usually have an sm57/58 pointed pretty much in the middle between the center and the edge of the speaker, about 1-2 decimeters from the grille. i also have a condenser mic placed 2-3 meters away, just pointed in the general direction of the amp. and then when mixing i pan the sm57/58 off to the side, and keep the condenser in the middle. this way you get a feeling of actually being in the room with the amp.

[Amber]

^I do this too.

I also have an amp about a metre away from a wall, mic it close with a 57/58 and then have a condensor pointing AT the wall to catch slap back and depth. I usually have to turn this track up louder to hear it but it works well.

If you don't have an acoustically treated room there's lot of cool things you can do that a lot of proper recording studio people would freak at.

[greenlander]

Another trick you can use if you don't have two mics available is to re-amp. Record a track of guitar with a close mic on your amp, then play back your track through your monitors and set up a room mic and just record your previously recorded track as it plays back. Then you can blend the two, gives it a lot more depth.

[DB]

... i usually have an sm57/58 pointed pretty much in the middle between the center and the edge of the speaker, about 1-2 decimeters from the grille. i also have a condenser mic placed 2-3 meters away..

I agree with Jonas.

This comment is about recording bass, not guitar, but I think much of it applies. The best bass tone I ever got personally was about 1980 with an SM-57 pointed at my ampeg 4x10 (1/2 of my split 8x10) and an Ampeg SVT, and an unknown condenser mic to pick up the ambient sound.  It was kind of a punk/alternative thing I was briefly involved with.  I played a Jazz Bass with a pick, and the tone was to die for (too bad the song isn't worth remembering!).  It sounded very "live", not like it was done in a studio.  If only you could reproduce some of these sounds live (real live situations with too much room ambience can really mess up a bass tone).

Bottom line: 2 mics, one close, one far.  Hard to go wrong with an SM-57 for the close mic.  And it's pretty cheap!

DB

[mynameisjonas]

the best bass sound i ever recorded was when using two different cabs, 4 mics and a direct signal

i played through a 100W marshall JMP MkII master volume guitar head hooked up to a JCM900 4x12 and a fender 2x15 bass cab. the cabs were placed next to eachother ("shoulder to shoulder") in a slight V shape, facing away from eachother. the 4 mics were placed like in my guitar micing scheme mentioned above. the direct signal from the bass had all the treble cut out, and was pretty heavily compressed.
the sound was huuuuuge, without ever getting blurry or unclear.