Feedback

gregtarr · Post by **gregtarr** » Sat Jul 03, 2004 9:25 am

I have a question. What actually happens when you get feedback?
Both microphonic, and the regular sort.

ash · Post by **ash** » Sat Jul 03, 2004 11:21 am

Feedback of any sort means that in some way the output signal (sound, vibration, electrical etc...) is feeding back to the input source.

In the case of microphonic feedback of valves and pickups, the sound level produced by the speakers is enough to physically vibrate the unrestrained wires and plates inside the valve/pickup. If the vibration is enough it can influence the operation of the device and induce a signal of its own, which is usually a howling sound.

Guitar (or microphone) feedback works the same way, except that the sound level (vibrations of the air) is assiting the vibration of the strings (or microphone diaphragm), casing their natural amplitude to increase. In this case the frequencies of resonance and feedback signals have to match more closely.

The other one you may not know about is that feedback is the primary control method within your amplifier. Gain across any preamplifier stage is controlled by feeding the output signal back into the input, but reversed so tht it cancels out the input. By controlling the amount of signal fed back you control the gain. Tone controls usually work the same way, by feeding back certain frequency ranges to limit the gain on that specific range...

Post by Bg » Sat Jul 03, 2004 2:54 pm

ash wrote:In the case of microphonic feedback of valves and pickups, the sound level produced by the speakers is enough to physically vibrate the unrestrained wires and plates inside the valve/pickup. If the vibration is enough it can influence the operation of the device and induce a signal of its own, which is usually a howling sound.

Which is why some humbuckers are wax 'potted' within the cover, to fix the coils etc securely in place so that no vibration can be induced - causing the microphonic feedback.

B45-12 · Post by **B45-12** » Wed Jul 07, 2004 12:47 am

Yep and the old Telecaster pups can go that way (microphonic) so much so they can actually squeal!

angry_young_poet · Post by **angry_young_poet** » Wed Jul 07, 2004 3:08 am

in layman's term?

as the bandmates always scream: "point the fackin' mic away from the PA!!!!"

is too much gain also a cause of feedback?

Polar Bear · Post by **Polar Bear** » Wed Jul 07, 2004 7:42 am

ash · Post by **ash** » Wed Jul 07, 2004 7:50 am

Yes, too much gain can cause it. Lower the volume, point the mic away, move it further away or drop the EQ a bit.

My Tele neck pickup is rumoured to be a vintage Fender and it squeals like a hillbilly!

BTW, gain isn't another name for distortion or overdrive. Gain is to the pre-amp what Volume is to the power-amp. Its just how much the signal gets amplified. Even clean channels have gain...

The devious marketing people and dumbass magazine reviwers would like us to think that gain = distortion because they don't really understand themselves.

In reality gain = volume and lots-of-gain = distortion and lots-of-volume = feedback.

Richy11 · Post by **Richy11** » Wed Jul 07, 2004 1:34 pm

angry_young_poet wrote:in layman's term?

as the bandmates always scream: "point the fackin' mic away from the PA!!!!"

is too much gain also a cause of feedback?

I guess people who are on a quest for more and more gain will have trouble then. Mmmmmmmmmmmmmmmmmmmmmmmmm Gain!!!!!!

ash · Post by **ash** » Wed Jul 07, 2004 1:44 pm

angry_young_poet wrote:in layman's term?

The sound level from the amplifier is high enough to vibrate the loose parts inside a pickup or valve so that they act like a guitar string. Their vibration gets sent through the system and amplified too. It sounds like a loud squealing sound.

Guitar feedback is where the amp sound makes the string itself vibrate on its own.

angry_young_poet · Post by **angry_young_poet** » Wed Jul 07, 2004 3:05 pm

wow, it is true.. you do learn new things everyday... i feel smarter today than i did yesterday!

feedback is just one of those things you know how to get the guitar to do, but never really troubled in finding out why the response is so..