Feedback and the Harmonica
What to do about it.
What is feedback?
Feedback is the shrill noise that an audio system makes when the input device (your mic) can pick up a signal from the output device (the amp speaker). A noise can be cycled around and around in the audio system from mic to speaker, back to mic until it blocks out all other sounds and takes on the natural feedback frequency for the audio system. The mic, the size of the room, the settings on the amp, and the placement of the components all contribute to feedback. Feedback is different for each configuration. Since feedback is so 'organic' there is no simple way to block it. Simple feedback blockers just don't work and the expensive ones work most of the time, but cost way too much.
Guitar amps are designed to allow feedback. It contributes to the ringing quality of the guitar. Harp players can get the Paul Butterfield honking sound by utilizing the effects of playing through an overdriven amp, but the price you pay is that it easy to set the system into feedback mode.
How do I stop feedback?
Turn down. When you hear feedback, dive for the amp and turn it down. Feedback is very destructive. A nice Jenson 12 can be destroyed in a second by feedback, costing you upwards to $100 to get it fixed. The simplest solution is to turn you amp up to the point where you start feeding back and then turn down a bit.
No one can hear me when I turn down. What do I do?
Tell the band to turn down. Amateur musicians and garage band SRV's want to play loud. Professionals want to balance the sound. They don't need to break the audience's ear drums to sound good.
The band only gets louder when I ask them to turn down. What do I do?
Get another gig.
Things to do to help stop feedback.
1. Point your amp away from you. Don't walk near the amp. Hold the mic behind you when you adjust the volume. If your amp has an open back, don't walk behind it.
2. Get a volume control for the mic. It helps control the feedback, combine this with a long cord and you have more than half solved the problem.
3. Turn the Bass up full and the treble all the way down. Common mythology has it that is the way Little Walter set his amp. (In actuality, nobody knows how Little Walter set up his amp. Little Walter used a great variety of amps and microphones and I believe that for the most part studio engineers set the volume on the equipment that he recorded on. I don't believe Little Walter was as anal as modern day harp players and tried for the best sound from what was available. Nobody wants to hear it, but I'll say it again - the sound comes from the harp player and not the gear.) The feedback comes mostly from the treble. It helps to keep the treble down on the more powerful amps. In low power amps, the tone controls also cut back on the volume. You need as much volume as you can get so turn up everything and then turn the volume back until it stops squealing.
(Scott Dirks tells me: When I play, I set my amps pretty much the opposite of the way you recommend: If it's an amp with seperate bass and treble controls, I set the bass at about 3 or 4, and the treble at about 6 or 7. If it's an old Gibson amp or something with just a single "tone" control, I always turn it all the way up to the treble side. I have a rather bassy sound no matter how the amp is set, and if I don't CUT the bass it gets really muddy and the sound gets completely lost and doesn't cut through the band at all.)
4. Get a good seal with your hand on the mic and the harp. If you can feel your breath pulling on the flesh of your hand you have a good seal. Make sure the only sounds the mic hear come from your harp. You hand muffles the sound coming from the amp. This makes the sound of the harp louder so the amplifier is more efficient and you can be heard.
5. If you are singing into a mic, don't cup or touch the mic in any way. Sometimes the PA mic will start to scream if you bring you hand near it. In this case your hand acts like a megaphone.
6. Play in a well padded room or outside. It's the echoes that get the sound back to the mic from the amp and start feedback. Out doors you can turn the amp up all the way and as long as you don't walk in front or behind the amp you can wail as loud as you want.
7. Wireless mic rigs are said to help fight feedback. Effects such as octaves, delays and tube screamers can change feedback and make it manageable. Borrow some toys from the guitar guys and see what helps.
8. Play through the PA. PA amps are designed to limit feedback. If you have a nice modern one, they are very stable and don't feed back easily. You won't get the dirty amp sound, but you will be heard. Also you can impress everyone by making all kinds of hand motions that may or may not contribute to the sound. James Cotton rarely uses anything but the PA mic.
9. Mic the AMP. Take a PA mic and drape it over the front of your amp so that the ball of the mic is directly over the speaker. Turn your amp up to a point where it sounds good. The PA makes the natural sound of the amp louder, but since the PA doesn't feed back as easily, everyone can hear you. This is best for low power amps such as the Fender Champ or the 50's Gibsons that sound great, but can never be heard above the Super Reverbs.
By the way, PA's are often more readily available at pawn shops and used music stores than vintage amps and may be much cheaper. You don't need more than a couple of channels. If you are going to gig or jam where they don't have a PA, I would consider it as part of my rig. You become very much in demand if you can bring the right equipment to a gig. Frank Sinatra got his start by buying some expensive sound equipment for his group. They couldn't fire him because if he left, he'd take the equipment with him.
10. Put in a "pickle plug". Wire a socket from the speaker of your tube amp that directly plugs into the PA or another amp. This is a good way to pop an amp, but some people swear by it.
11. Slave two amps. If you have an amp with two inputs, you can run another cable from the input of the first amp to the input of another amp. You can have several amps daisy chained. Some amps have a 'Hot' side which goes through an extra pre-amp stage. Plug your mic in this hole and then run a cable from the 'normal' socket to another amp. You'll get the benefit of an extra pre-amp stage before the second amp. This configuration really kicks ass. The logic here is that two amps on 5 is equal to one amp on 10. (Actually, it's probably a log curve, 5+5=7)
Scott Dirks comments:
I've also had lots of harp players ask me how to be heard over a band without feeding back. I always tell 'em to go out and buy two '50s Gibson 1-12" tube amps....and then give them to the guitar players :)
Sounds like good advice!