Recording your amp
There are a few simple ways you can get a pleasing sound clip of your amp. Some of this is really basic, but it always helps to start from the ground up.
There are a few more parts to a speaker but these are the parts you are interested in for recording.
The speaker baffle:
This is the wood front of the guitar cabinet with a hole or holes cut to accept the speaker(s) Usually ½" or ¾"plywood.
The speaker frame:
The stamped steel or cast aluminum metal shell that makes up the support of the speaker.
The speaker frame is bolted to the speaker baffle.
This is the outer rim of the speaker cone that connects the cone to the speaker frame. The surround is glued to the speaker frame at the outer edge. Sometimes companies add speaker "dope" on the surround which changes the tone a bit. This is usually a heavy glue like substance which is somewhat shiny.
The surround is sometimes smooth and sometimes ribbed like an accordion to enable the speaker to flex and push push out in a different way than if it was smooth. This too changes the sound and is a part of the way different speakers differ form one to the other
The main speaker cone:
Some are smooth and some are ribbed. Both sound different. Take a look at Webervst.com and you can compare the differences.
Vintage low wattage speakers used thin paper which compress and distort in a nice way. This is the sound of vintage small amps, and his is why people pay big bucks for the vintage sound. This thin paper has a very distinct sound. Some amp companies have gone to great lengths to get the exact thickness and type of paper used in these vintage speakers.
Most modern speakers made for high wattage use heavy paper to support the high wattage being reproduced. If you play loud rock and really push your speakers then this is what you need . If you are playing through a low wattage amp and don't need the wattage you can afford to use the vontage thin cone material in vintage new and old speakers. Wars have been fought over these topics.
The Dust cap:
In the center of the speaker the cone is glued to a tube that fits over the magnet. Most speakers have a cap glued over this opening called the dust cap. Some speakers have a paper cap and some have a mesh screen cap that is more open and lest air pass. A soft cap gives a smoother sound, a more diffused high end.
When you are close micing a guitar cabinet the closer the mic is to the dust cap/center of the cone, the more treble you pick up. Closer to the surround will give you more or a bassy although slightly distorted sound. Generally, micing the speaker somewhere between the dust cap and the surround is the sweet spot.
If you can have someone play through the amp while you listen you can get your head up close to the speaker and hear the different tones of the surface area of the speaker.
When you are in the audience at a concert and right in front of the band, right in front of a loud guitar cabinet you'll notice that if you move to the left of right of a certain spot that the piercing treble will be less when you are off axis to the cab. This is called beaming, where your ears are right at the speakers treble peak and right in line with the beam of sound from the dust cap area.
The opposite is when when you have your amp on the floor and are standing up above the amp and it sounds more full. What you are hearing is a lot less teble and the piercing sound is pointed towards your knees more than your ears. When you get on your knees or raise the amp up on a chair and have it closer to ear level you can hear the treble a lot more. Sometimes this sounds pretty bad. At any rate it will let you know more closely how your amp really sounds. You want the amp to sound good at ear level because this is how the mic is going to hear it. If the amp sounds bad with your ear about a foot way (at a reasonable, not too loud volume or course) then the mic is going to reproduce that sound.
I have found that micing an amp at about ear level (5-6 feet) with the mic facing the amp at a downward angle can sound good for a more diffused sound. This is the same sound you usually hear while standing and playing through your amp.
Rotating the mic angle will change the sound as well as how close or far the mic is from the dustcap. If the mic is inbetween the dustcap and the surround and pointed at the center of the speaker it wuill be brighter. Rotated towards the surround will be less bright.
A decent mic:
See if you can beg, borrow or steal a Shure SM58 or 57. These are standard dynamic cardiod vocal/instrument mics for most bands and concert venues. Cardiod means that the mic picks up most of the sound from the front of the mic. (Omnidirectional means it picks up from all sides) Most any vocal mic your band uses will work fine to record your guitar.
The main thing you are concerned with it that the mic has the ability to take a lot of volume. The SM58 and similar mics are really almost bullet proof as far as being able to withstand a lot of volume and still producing a decent sound. There are a lot of mics that will work fine for getting a decent guitar sound recorded. Aim for a good dynamic cardiod vocal mic and you will be fine. Omnidirectional works well but most vocal mics pick up in a cardioid patern. An SM57 should be around 50 to $100 new. I usually buy them for $75.
How a guitar speaker sounds:
Guitar speakers don't have much high end or low end. Most of the sound is concentrated at the mid range, this is what makes up the typical sound of a guitar speaker.
Bass build up:
When you raise an amp up on a chair you change the bass response. Not only will the amp be closer to the level of your ears , but you will decouple the bass frequencies from the floor and you will get a little less deep bass.
As with any speaker system, the closer to the floor, wall or a corner, the more the bass increases. If you put your amp in a corner and on the floor you will increase the bass frequencies heard in the room. Each wall will add more low end.
Where you stand in the room makes a difference as well. Low frequency sound waves build up in the corners of a room with right angled walls. The low frequency energy is reflected off the walls and doubled up in corners and in "nodes" a bit away from each wall. (this distance depends on the room size) which causes a build up of low frequencies. These piled up waves are called standing waves. Since the low frequency sound waves are so long, they take a longer distance in which to dissipate. The chart on the right shows the areas bass builds up in a room.
So basically the low sound waves bend around and bounce off the walls of the room until they fold around and causes the room to vibrate and clog up with bass. This can be a good thing or a bad thing. If you have too much bass you can either: lower the bass, make sure your amp is not against a wall or in a corner, raise you amp up on something not solid ( a chair, a piece of thick foam, even amp caster wheels decrease the coupling to the floor. This goes for all speakers ,bass guitar and home stereo as well. Vibrations and coupling from hard wood and plywood floors can be helped this way as well.
If you have never played your guitar acoustically with the headstock pressed against a hollow door or wall and noticed the resonance...you should try this now. Notice how the resonance chages as you touch the wall/door and how it drops of as you break the connection
Unless guitar amps are really loud and cranked up, they wont have too much of this bass build up. It's mainly a problem with guitar and bass amps and home stereo and full frequency speaker systems when cranked (50-100 watts etc) but you can experiment to see how it changes the sound. With low power amps it will be more subtle.
General room acoustics:
Thick soft material absorbs high and mid frequencies. Depending on the density of the material( if it's pretty thick) it may absorb bass as well. Generally bass is absorbed by semi rigid material and transferred through vibration into heat. (thick fiberglass and semi rigid panels etc). Most concert venues are designed to absorb harsh reflections with people in the seats. This is why when you do a sound check at the club, hall, etc. before the audience arrives,the acoustics are pretty bright and have a good amount of live reverb and echo. When the audience files in and the room fills up the sound changes dramatically. Human bodies are good bass absorbers (bass traps) and diffusers (sound bounces off an object and deflects the sound waves producing a softer amount of sound reflection). Some Modular bass traps are shaped like cylinders about the size a human body…
If you have large bookcases and furniture around the room and against the wall your room be won't be too bad off. Desks, blinds, heavy padded furniture, beds and sofas all suck up some of the ambience of the room. The idea behind this article is to make a decent guitar recording not record a chamber orchestra, but still these rules apply if you want to do that.