Baffling and Isolating Your Amp
I know you're eager to jump right to the recording process, but before you can hit that red record button, you've got to set up your gear. Baffles are an important part of that set up, both because they help eliminate leakage and because they just might keep the neighbors from calling the police on you. They'll also help save your ears for hour upon hour of recording session wailing.
Baffling the Guitar Speaker Cabinet
Before we get to recording, there are a few things we should cover about baffles. Baffles keep your guitar sound from bleeding into other microphones when your guitar is not the only instrument in the room being recorded, such as when a full band is recording a take live in the studio.
When overdubbing a guitar part, baffling the guitar amp is not needed; if you have isolation booths, baffling is not needed. The following relates to recording more than just one miked electric guitar amp in the same room with other miked instruments at the same time.
If the guitar amp is in the same room as the drums or any other miked instrument or vocal, you should baffle the amp unless you want the guitar amp to bleed into the drum mics, or other instrument or vocal mics in the same room. Other instruments will leak into the guitar mic as well.
Remember, if this is the case, if there is noticeable (and undesired) leakage into other instrument mics, or if you need to fix a guitar performance after the basic track has been recorded (replacing in part or in full), this will be a major problem since the guitar amp leakage will be heard through other mics recorded. After you fix your part, the bad part will still be heard on the recording faintly on the tracks of the other instruments (drums, etc.) If this happens, and the leakage is too severe, everyone will have to record their part over, from scratch. This could get very expensive in a pro studio situation.
So let's assume that you need to baffle the guitar amp. There are many options, so here we go:
If you have studio baffles and packing blankets, great. Typically studio baffles have a soft surface on at least one of the two sides, stuffed with a cotton type substance and with soft cloth nailed on to hold in the cotton. This construction helps eliminate bouncing around of waveforms that would cause comb-filtering problems. (More on comb filtering in future articles).
If you do not have or wish to construct such baffles (see sidebar How To Build Your Own Baffles) many items around the house and studio will work. You'll need stuff like an ironing board, thick blankets, mic stands, milk crates, or tall boxes, etc.
Baffles may need to function differently depending on the type of speaker and amp combinations so I will list and deal with each individually:
Separate Closed Back Speaker Cabinet (ie. Marshall 4x12)
In most studio situations, whenever possible, you'll separate the amp head from the speaker cabinet. In a pro studio with a separate control room, you'll often run a long speaker cable from the cabinet to the amp head, which you'll have with you in the studio control room (where you arent bombarded by the volume of a cranked up speaker cab). This is particularly common when overdubbing lead guitar parts. Even if you're just recording the basic rhythm tracks, and you're standing in the studio room with the rest of your bandmates, recording live, youll still want to remove your amp head from your cabinet.
We do not want the amp head sitting on top of the speaker cabinet for one main reason: We are going to box in the speaker cabinet with baffles and since amp heads get very hot, we do not want to chance a fire! Further, its always best to have the amp head off the speakers to avoid vibration abuse (and rattles) caused by the speaker bottom. If you're using a tube amp, this logic will extend your tube life as well as avoiding components from shaking loose that could cause a number of problems, including the degradation of your amps tone.
I put the amp head on a chair to have easy access to the tone and volume controls. It is most important to make sure the amp electronics have breathing room (ventilation). If you place the head on a chair with a closed back, make sure to position the amp at least a few inches from the back of the chair.
By the way, always use a speaker cable from the amp head to the speaker cabinet. Never use a guitar cable since the design is totally different and will affect the sound in a bad way.
In this set up, only the front of the speaker cabinet needs to be baffled. If you're using studio baffles, its best to use two (if theyre wide enough) and create a V shape in front of the amp. Position the baffles as close to the sides of the speaker cabinet as possible (without touching the cabinet), and leave room for a mic stand at the closed end of the V.
If you have more baffles you could box the speaker in using three baffles to allow for more speaker breathing room. Create any shape you like, and consider non-parallel positions, BUT make sure that the baffles on the sides of the speaker bottom are as close as possible without actually touching the speaker cabinet.
How To Build Your Own Baffles
So you want to build your own baffles. It's really not all the difficult but you will need some basic tools and materials.
You now have the front of the speakers boxed in. If you need to get more isolation, the top of the speaker cabinet needs to be closed off. This requires a packing blanket or a thick blanket. Duct tape the blanket on the top of the speaker cabinet and drape over the front of the baffles. If the baffles are not as high as the speaker bottom, the draping may interfere with the mic stand.
In this case, you have a few options. You'll want to make a tent, so place two mic stands (left and right) a few feet forward from the speaker cabinet. Set the mic stands position and height to allow the blanket to drape down in front of the baffles. The mic stands may tip over so, to avoid that happening, use sand bags on the base of the mic stands (more on sand bags in the next article).
You may want to duct tape the blanket down to the baffles completely to close off all openings in your tent.
Another concept is to use an ironing board instead of a mic stand. Elevate the ironing board to taste, put the ironing board directly in front of the baffles and drape the blanket over it. Again, you may want to use duct tape to close off all openings in your tent.
Another option is to use milk crates instead of baffles and stack up using one or more blankets to make a tent.
OK, here is another option. If you do not have baffles but your studio has soft surface non-reflective walls, position the speaker cabinet against a wall in a corner, on an angle facing straight into the corner. This gives you the same V shape I mentioned before. This will require a little more work regarding setting the mic position, so leave about a foot on one side between the speaker bottom and wall so youll be able to reach in. If you need to isolate the speaker further, use a blanket. Simply duct tape the blanket on top of the speaker cabinet and to the wall (be careful not to ruin your speaker or wall with duct tape!). You may also want to drape the blanket down on the open side you used for setting the mic. All areas are now covered.
Separate, Open Backed Speaker Cabinet
All of the above applies. The only addition is, if you need total isolation, duct tape another small blanket on the back of the speaker cabinet to cover the open back. It's best to let the speakers have some breathing room so use milk crates or boxes to make the tent fan out behind the speaker cabinet.
All of the above applies, but its most important to make sure the amp electronics are not covered in the back of the amp with a blanket! The amp needs open space to ventilate or it will get too hot, which could toast the amp electronics and possibly cause a fire!
If the combo amp is open back, or if you need further isolation on the back of the amp, duct tape another small blanket starting from below the amp electronics, letting the blanket hang to the floor. You might want to slightly tent the blanket if the sound is too dead. Start as low as possible beneath the amp electronics while still covering the speaker(s).