My friend has just told me that he has fitted a bigger resistor across the element to his really hot mic and it has better feedback properties with his amp with out a loss in tone.
I was wondering why are the old mics fitted with a resistor and what is it supposed to do. How does it affect the tone and is there a certain size that works best?
Cheers
Russ ---------- Oxharp
Last Edited by on Feb 24, 2010 5:13 AM
Hello Russ, how's it going. I'm no expert but I believe the resistor rolls off some highs and gives the mic a darker tone. Ronnie Shellist has two videos on youtube where he plays front and center mics. One vid has a mic with the resistor in place and the other vid has no resistor. You can hear the difference. ( I ordered a frontandcenter mic without the resistor yesterday) With resistor
Without resistor
Last Edited by on Feb 24, 2010 6:20 AM
Thanks Luke let me know what its like when it arrives. I may come down and have a go with my new Bassman.
To be precise he has major feed back issues with an epiphone junior with his hot mic so he took a 32K restister out and put in a 470K but said that he was able to get the amp higher before feedback without a noticable loss in tone.
He was also saying that a 2.2uf capciter would do the same job of darkening the tone.
I am not electronic minded but wanted to get some info on this incase I want to do this.
Cheers ---------- Oxharp
Last Edited by on Feb 24, 2010 6:24 AM
The resistors Shure used to put across the terminals were to alter the frequency response characteristics of the mic, for maximum intelligibility of voice in noisy situations. A change in frequency response can mean a change in tone - whether it is in a good way or bad way is up to your own opinion. Most mic builders take it OUT of the circuit.
With all due respect, unless there was a specific frequency that was resonant between the mic and amp, I think your friend's change is more likely to increase feedback, not decrease it. Here's why.
Resistance for the sake of this discussion is the same as impedance. The lower the resistance, the more load is placed on the mic. In electromagnetic generators, this is "felt" by the element as making it harder to move the mic's diaphragm. Just like turning on all the electric stuff in your car makes the engine work a little harder to keep turning the alternator. So lowering the resistance across the mics' terminals is like adding a shock absorber. Not only does the total output drop, but the frequency response changes too.
The formula to figure out the resistance of 2 resistors in parallel is R1R2/R1+R2. The resistance of 2 resistors in parallel is LOWER than the resistance of either one. If your amp's input impedance is 100K ohms (some are less some are more, but the input jack does place a resistor across the input) then the 36K resistor across the element at the terminals lowers the input impedance to 24K - a fairly large load even on a CM element. This WILL reduce its output. If you substitute a 470K ohm resistor, you're only lowering it to 82.5Kohms - not as big a difference, closer to taking the resistor out all together. If you want a MORE dramatic "damping" effect than the resistor that was there, use one with even LESS resistance - a 10K ohm resistor will really damp the element (probably too much.)
Finally, in my opinion looking to a mic to cure a feedback problem is the wrong place to start. Mics make a SMALL difference. Getting that 12AX7 out of the Epi's preamp and subbing in a 12AY7 (as has been suggested in other threads on this forum) will make a much bigger difference.
In the Rod Piazza mod of the JT30, what he's doing is using a correct value volume pot (5meg) that is correct with crystals, but when volume controls are turned down, whast often happens is that the mids often get buried and the lower highs as well, and Rod puts in a low value capacitor so that when the pot gets rolled down, the capacitor boosts the mids and highs so that the response at all volume levels regardless of how far down the pot has been rolled down is the same as it was when the pot was all the way up.
I think this is what you may be thinking about when using a capacitor.
With many amps, one of the first things you need to do is turn the treble WAY down or even off in some amps and turning the treble up is right for guitar but completely wrong for harp unless you like your ears destroyed by feedback. ---------- Sincerely, Barbeque Bob Maglinte Boston, MA http://www.barbequebob.com CD available at http://www.cdbaby.com/cd/bbmaglinte
I have the F&C microphone, with a capacitor across the element to darken it a bit. It sounds sensational, and does indeed resist feedback much better than a typical bullet mic with Shure CM/CR element.
I tested the Front and Center microphones at my blog and recommend them very highly.
Bob, a capacitor cannot boost anything. It is a passive element. It can only cut. What that circuit does is to cut them in the first place, and then return them as the volume is rolled off. A valid aproach - just turn the treble up a bit on your amp - but this is the more accurate description of how it works.
In practice, I've tried connecting/disconnecting that cap while I'm playing - and I can't hear a difference no matter where the volume control is set. (On the other hand, my high frequency hearing ain't what it used to be. Maybe a dog or a young whippersnapper could hear it....)
BBQ Bob, it's time for some tough love here. Your problem is YOUR PLAYING TECHNIQUE and YOUR IGNORANCE ABOUT MICS! It's blatantly obvious that you DON’T KNOW WHAT YOU’RE TALKING ABOUT, and your IGNORANCE will make this situation 100 times WORSE.
Along with that, you're playing very physically uptight, all sphincters tensed, which heavily constricts the air flow to your brain, and thins the tone out and kills your projection.
This is a problem with 96.58% of left-handed harp players, and 51-73% of harp players who wear glasses, and almost none of them know CRAP about microphones until a very experienced pro hits them with the cold, hard, brutal truth.
Blaming the instrument is the easy way out, and nothing short of a flat out cop out. The vast majority of players who WHO DON’T KNOW CRAP ABOUT MICS get quickly winded, have a thin tone, poor agility, can't bend properly, have hotdog finger, a painful rectal itch, and oh yes, blow out harps at a rapid rate, and many of them all blame the MICROPHONE.
What does this come down to? Time to completely reexamine your playing technique and learn to play much better ASAP or it's only gonna get worse, no ifs, ands, or buts, and no excuses, because this is the cold, hard, brutal truth. --------------------------
Ah, just funnin' with ya Bob. As Greg correctly pointed out, you have a fundemental misunderstanding of what a capacitor in a microphone does. It cannot "boost" anything. That takes a gain stage. The cap in a microphone can only attenuate.
I though I had started another harp war or something until I read further.
I am grateful for the tech explanations there were very informative and easy to grasp and understanding.
I was only curious as to why my friend was so obsessed with doing this.
To me he has a really hot mic and it sounded fantastic through a 4x10 amp but I dont think he was getting the tone he was expecting through the epiphone even after we put in the 12ay tube.
Thanks again anyway more research needed I think.
...........More vids up tonight...........
Russ
---------- Oxharp
Last Edited by on Feb 24, 2010 11:03 AM
I always wonder if someone says they are taming feedback with a tube swap or, in this case, reducing the output of a microphone, if they really are doing anything but making the mic less hot, but the total volume you get before feedback is really the same. Nobody actually uses a mic on the speakers amp with a level sensor to test this when they make that statement, right? If something modifies the shape of the frequency output (e.g. a bridging cap, or changes the value of the shunt resistor that feeds the cap) then, I could buy it. More usable sweep on the volume knob is not necessarily equal to more volume before feedback, but it might make the amp easier to use with a specific mic.
There is one instance where feedback can be profoudly affected by mic choice.
A dynamic vocal mic, particularly a unidirectional one, may not feedback at all. My cut-down samson dynamic mic has no feedback issues whatsoever. All my other mics have at least some sort of feedback issue to deal with, whether it's in a small room or on a stage. The samson has none of that. Neither does my beta 57. The amp and speakers i use are the same, so it's a difference in the microphone. I use 12ax7 now in my valve junior because changing to this mic made it possible.
In the world of "harp mics" a mic may make a small difference in feedback, but in the world of vocal mics..well, it's a different world.
Tell your friend to try adding a tone control to his Epi. Alnicomagnet "brownface" works a treat and costs £11.99, less than a good pre-amp tube.
Last Edited by on Feb 24, 2010 5:21 PM
@Walter re: "if they really are doing anything but making the mic less hot, but the total volume you get before feedback is really the same."
I can answer this emphatically - GAIN makes a HUGE difference - it is not a steady state system. Honest, I swear, really, for sure, I've done it, I've experienced it, I ain't lyin', ain't blowin smoke, didn't just come in off a turnip truck, GAIN MAKES A HUGE DIFFERENCE in the feedback equation.
@Congaron - vocal mics are designed to live at the front of the stage and not get feedback even though they're only feet from the monitors. They're very directional and that's why they work. HOWEVER it only works in free air. Once you hand hold a mic, you can throw all its directional characteristics out the window.
@Everyone: I find myself saying this a lot - if you have a feedback problem, the mic is NOT the highest leverage place to look for a change. If you have already re-tubed your amp (the very first, most effective thing you can do), YOU SIMPLY NEED A BIGGER AMP. A Blues Jr sounds ear-splitting-loud in your living room. Yet you get on stage at a jam and wonder why it can't be heard. So you turn it up until it is feeding back and conclude that you have a feedback problem. But you don't.
You have an amp problem!
Even my beloved Sonny Jr Cruncher, which is freakin' loud - isn't loud enough at some of the jams I do. I can get the volume to 9 with no feedback. This honestly isn't much louder than 7, by the way. It just doesn't move enough air, and that's with a 12 and 2 8's. I frequently perform with my own band with the Cruncher because we manage our volume a bit. Plus it lines-out into the house beautifully and then it CAN be heard. But I need to be heard at a jam, I bring out the big guns. 4 Ten's, baby.
A different mic is good for, at best, 1-2 dB more volume before feedback. A different amp is good for 10-15 dB. (AND - the bigger they get, the more important it is to REDUCE their gain to make them manageable.) ---------- /Greg
Thank you, Greg. That is the truth, the whole truth and nothing but the truth. Well put. It took me way too many years to figure that out. But now that I have, I really don't experience feedback problems. For proof, I have about 500 videos on YouTube of me kneeling 3 feet in front of my cranked amps with all kinds of different mics. Rarely do I hear a squeal. 12AU7, 5814A, 12AY7, 12AT7, 5751, etc. Get to know those tube subs. That is the ticket. And having four tens doesn't hurt.
Oxharp ,.. I'm just wondering,.. what type of feedback issue's you have with Louisiana Smoke if any ?? ---------- Simply Unique Kustom Mic's By Rharley
Last Edited by on Feb 24, 2010 6:06 PM
Feed back is the nature of the beast !! The beast being the amp !! Greg an Deluxe 100% correct,.. 12AU7, 5814A, 12AY7, 12AT7, 5751, etc. Get to know those tube subs: Well said Deluxe,..
Resisters will roll off the Hi frequencies on any element,..But do nothing for feedback <> your lookin in the wrong place.
Want to never have feedback problems,. blow through a SM57 Instrument Microphone or any low Z microphone,. Your output won't be there,. but then again you won't deal with feedback. Change Those Tubes !! ---------- Simply Unique Kustom Mic's By Rharley
Greg, yes gain makes all the difference in feedback. That is why simply turning down the volume control on your bullet mic is the FIRST step in feedback control. Players should try this before they start yanking tubes in and out if their amps. Turning down the mic has essentially the same effect on feedback as swapping in a lower gain preamp tube. It also often improves tone.
I prefer smaller amps, and I prefer to line out to the PA. At every jam I go to I am able to run a line to the PA board, so being heard is never a problem, and neither is feedback. There may not be monitors at every jam, however, so a tiny amp like a Kalamazoo or a Champ would make it hard to hear yourself.
If you have a feedback problem, you do NOT necessarily have an amp problem. The mic and amp (and PA and monitors) all work as a system, a loop. If the total gain of the loop exceeds 1 at any frequency you will get feedback, no matter where in the system that gain is generated. It also doesn't matter where in the loop you reduce the gain. As long as the total gain is lower, feedback will be reduced.
You say, "A different mic is good for, at best, 1-2 dB more volume before feedback." That is not right. A 1-2dB relative difference would be barely audible to the human ear. I have tested mics that CLEARY provide a much larger feedback resitance than that.
If you mean among bullet mics with a Shure CM/CR element there is little difference in feedback, I agree. They are all omni-directional feedback magnets, increasing the gain of off-axis signals. That means more feedback potential.
I have to agree with Rick on this, particularly the system approach. To make a blanket statement that the mic isn't the problem and the amp is, defies the principles of feedback reduction in a PA system..or any amplified microphone/speaker combination. Turning anything down will reduce feedback, it's true. Putting lower gain tubes in is simply turning down or turning down certain frequencies, or finding a tube that isn't as microphonic. That's why all tubes sound a little different even within their numbers..minute variations.
That's why I am using a vocal mic, stock 12ax7 tube in the preamp, and a pedal to eq...turn down...the very few frequencies that used to offend. there is no reduction in volume capability this way, just frequency tailoring to reduce feedback on the mics that need it.
As I mentioned, I have two that need nothing. Cupping them correctly does not influence their character regarding feedback, sorry. Once the mic is cupped, tone is up to the player. That is the only true absolute i find. Incorrect cupping is any sound guy's nightmare. I was a sound guy long before I ever learned to play harmonica. I suspect there is always an element of incorrect cupping in a serious feedback issue. That's why i recommended certain vocal mics that tolerate it better. Quest for a certain tone can cause issues if you get stuck on one mic and don't have the skill to use it yet. Look at Adam's videos with a vocal mic cupped in a small room with two amps. He isn't having any feedback issues from changing the characteristics of his vocal/instrument mic.
I tried re-tubing to handle feedback in my living room. Turns out it was unnecessary with a switch to a modified vocal mic. Talking about an 18x14 room here. Besides, live is what matters most to me and the 12ax7 with 2-12 inch jensens and my mic setup gives me the volume and the tone I want on stage, every time. Re-tubing gave unacceptable losses in volume.
I am trying to stay away from making sweeping generalizations here, but for me reduction in pre-amp gain killed my amps growl and volume. Using a vocal mic let's me do anything I want and the amp stays alive.
Last Edited by on Feb 25, 2010 8:48 AM
Very good. I have been a PA guy for years, so a wide variety of vocal mics are here at home and available. It's natural that i gravitated to them and built a number of my own from old radio mics as well. I just wanted to throw out that option for folks who might benefit from trying it. I will freely admit I'd like an old bullet mic of some sort now that I know a little more about how to cup the ones i built.
Rick, re: "Turning down the mic has essentially the same effect on feedback as swapping in a lower gain preamp tube."
NO!!! Sorry, my friend, but you are sorely misinformed. Gain and volume are not the same thing. Let's compare two hypothetical systems. System A has a gain factor 10. System B has a gain factor of 100.
With system A, input of 10 becomes output of 100 and input of 20 becomes output of 200.
With system B, the same difference in input, whether done by playing louder or with a volume control, produces an output between 1000 and 2000.
The same "10" change in input level generated an output volume increase of 100 in the low gain case, but an increase of 1000 in the high gain case. The gainier system will feedback much more readily at the same total volume.
A volume control attenuates input volume. Gain is a function of the amplifier and only the amplifier. Gain determines the difference in output volume based on the change in input volume. In this example, the difference between systems is 10X.
In a perfectly quiet room, with a perfect system, the same output volume (of a pure sine wave) would generate feedback at the same point for these two system. But in the real world, gain makes a huge difference.
I am not saying the mic makes no difference. Your experience correctly suggests otherwise. And maybe I'm being too conservative in saying only 1-2dB - I haven't measured it. But system gain, a function of the amplifier and only the amplifier, is the most important variable for any particular system. ---------- /Greg
I agree that too much gain is the main feedback culprit. However, I own quite a few mics and their feedback sensitivities are quite variable.A hot Cm/Cr element is more feedback prone than a dynamic vocal mic. At least that's what my own personal experience tells me.
"The same change in input level generated an increase of 100x in the low gain case, but an increase of 1000x in the high gain case. The gainier system will feedback much more readily at the same total volume."
You are referring to volume control setting, not volume output I hope. Volume is volume outside at the microphone, regardless of how you get there inside the amp. Gain is internal to the amplifier. Higher gain will accentuate frequencies not accentuated by lower gain, unless high fidelity circuitry is used. Often the frequencies boosted are the very ones a harp mic responds to best. Fortunately, they are not the ones associated with the "chicago sound" and cutting them via EQ reduces feedback and still permits, even accentuates the "chicago" sound when you tighten your cup.
Actual Volume in Decibels at the microphone element determines feedback. Not all frequencies cause a feedback loop in all mics at a given decibel level. There is no guarantee that lowering preamp gain will solve a feedback issue in any given microphone. It may or may not. One of the reasons it works frequently in the old style ham radio and PA mics is the limited frequency response of the elements. In a mic with a broader frequency response or even one that is simply "hotter", chances are you will lower the gain of the preamp, forcing you to increase the volume and the mic will find a feedback loop anyway once you turn it up...unless you have killed the amp down to a reduced volume below what you want. Then you end up micing it into the PA anyway. BTW, small amps mic'd properly are a killer way to play the blues..both for guitar and Harp.
That's why I went with Eq on the front end to tweak the sound coming into my amp before the preamp even touches it. I even experimented with a 31 band eq but it didn't prove to be worth the trouble. The simple eq in my digitech pedal works great. Anti-feedback rack units are common in PA and have been around for years. They use the speed advantage of electronic frequency cutting on a case by case basis to eliminate the need for a sound guy to ride a fader or Eq slider. Lots of amateur sound guys use them to great advantage, but I've found a thorough sound check and 31 bands of eq does the trick for me when running sound.
I am not trying at all to be argumentative here, just hoping to expand the information that might help someone track down issues and eliminate them so they can play without worries.
Every sunday, I Play into one of my churches vocal mics...cupped. i don't even know what kind of mic it is. I have asked the sound guy to keep me out of one of the monitors and that was the solution to a minor feedback issue the first time i did it. There is more than one way to skin the feedback cat. I hope that helps.
I think that might be where Greg and I had a misunderstanding....
Volume only occurs as an input (at the mic), and final output (speaker) wherever that is. Volume knobs (not the same as volume) generally work by attenuating signal as it goes through the amp. Gain multiplies that signal.
Just because there is more gain in a system, it does not mean there is more volume coming out of a system before feedback. My point is, when people make statements about getting more volume before feedback, with different mics, pedal boards, tube swaps etc. they often really mean they can turn the volume knob up (block less of the signal) in the system somewhere more before they get feedback. These statements are rarely backed up by testing a known level of signal input and measuring the absolute volume coming out of the amp.
As congaron says, if the mod (whatever it is) changes the frequency of the signal it might allow for an increase of total volume before feedback. This can be accomplished somewhat by different microphones, different pedals, amp tone controls, and to some degree how tubes are biased and what tubes and speakers are used. You can really fine tune it with an equalizer that notches out the offending frequencies as said before.
I do agree with the amp size problem statement, but not sure why this is true logically. In my experience small amps tend to feed back at lower volumes overall. That might be because they distort at lower total volumes, and distortion is one component that can lead to feedback.
Here's the simplest version. For a given change in INPUT volume, the amp with more gain will produce a greater change in OUTPUT volume. Period. That's what gain is. You guys are trying to explain this in a steady state output volume situation - which is completely unrealistic.
Gainier amps are more prone to feedback, EVEN AT THE SAME OUTPUT VOLUME. Walter, I do NOT mean I can just turn the volume knob higher. I mean more output volume.
I don't need sensitive measuring equipment to hear this. I CAN hear it, and I CAN demonstrate it.
Greg, I believe you, just wanted to make sure the words were not in the way because there are lots of cases of unclear wording on these issues. I wonder if the thing with small amps having feedback is that they try to make up for small size with lots of gain? Are steady state amps more prone to feedback than tube amps? Walter
Hi, Walter - Agree with you there. Words can always be clearer and I am kicking myself that I still can't find the right words to communicate what I'm talking about in a simple enough way that people "get it."
Solid state amps aren't necessarily more prone to feedback because they're solid state. But they ARE, just like tube amps, set up with enough gain to allow guitar players to get on the edge of feedback. That is too much for us microphone users - and with solid state amps it is much harder to reduce the gain unless you're an electronics engineer. Tube swapping on the other hand is so EASY. ---------- /Greg
Greg, you are straining to construct a distinction that has no difference. FACT: A hotter mic provides more feedback potential than other mics. FACT: Turning the hot mic down has precisely the same effect on feedback as swaping in a lower gain tube: It reduces it. To argue otherwise is just silly. Are you seriously suggesting that turning your microphone down does not reduce feedback potential?
Just a quick word to back up Greg's 1-2DB statement. I was a mechanic for a top pro-motocross racer for 12 years. With the recent change from 2 cycle to 4 cycle engines came a decibel limit. It is 99db-anything over that and you are diqualified from racing-why?-because they have determined anything over 99db creates hearing loss. They use a meter to test the level at the exhaust exit-but from years of testing and being involved with the sport,I don't need a meter. I knew if we were within 2db of the limit by ear.
I dunno, tmf... When I listen to blues harp it doesn't sound anything like a motorcycle. That is a pretty tenuous comparison.
Hearing professionals tell us that any sound over 85dB can lead to hearing loss. After spending 12 years around bikes screaming at 99dB perhaps you should get your hearing checked.
"Gainier amps are more prone to feedback, EVEN AT THE SAME OUTPUT VOLUME." This can happen.
This is because of the frequencies accentuated by the higher gain tube give it that "sound" we all associate with high gain. It is a sound full of harmonics that we associate with higher gain. This is not the kind of gain used in high fidelity or Quality PA circuits. It is a design feature of guitar and Harp amps..INTERNAL to the equipment.
That's why We also use the term Gain before feedback or GBF when describing Pa microphones and mixer settings/outboard processing equipment. It's all about increasing the GBF to allow most efficient use of the amps for minimum distortion in the final product.
With a guitar amp or harp amp designed from the ground up to accentuate certain frequencies and cut others to tailor the tone (intentional distortion from a flat curve), GBF relies on the ability to either keep the sound from the speaker out of the mic altogether or make sure the sound geting there is quiet enough or of the optimum frequency distribution to maximize GBF. The frequency response and directional pattern of the mic matters a lot.
This is EXACTLY the same as with a PA system, but harp amps are lower fidelity equipment, which makes it a more common problem for harp. Harp through a PA straight off a mic on a stand doesn't cause these issues, so clearly the mic matters, as does the rest of the amplification ystem. You can sometimes see a difference at the mic on A SPL meter when using a high gain versus a low gain preamp tube on the same amp on the same volume setting. However, In some instances you might not but it will sound louder because your ear also responds to different frequencies and harmonics differently. That's why a screaming guitar or bagpipes sound loud at 85 DB and a cello doesn't.
As for steady state solutions..there are none..inside the amp or outside it. It is all a dynamic situation having so many variables, i just wanted to make sure tube swaps aren't seen as the only way to do things. They are not. Mic swaps can make a huge difference in GBF, as can proper EQ. My own rig is proof of that, even in a 10x14 room i use as my woodshed..even smaller than my living room. I have measured SPLs of 105 db at the mic without feedback and loosely cupped. That is WAY louder than our stage volume playing live. Just saying there's another option for the frustrated harp player battling feedback.
I am only offering the option of EQ as an effective feedback solution that can give you back better use of the volume control on the mic...which was part of the original thread topic....sort of...lol.
Last Edited by on Feb 26, 2010 9:30 AM
I don't want to argue with you. I've learned in the past it is pointless. But I want those who really want the truth to understand there's a difference between input volume and MULTIPLICATION EFFECT of gain.
You are WRONG. Turning down the input volume is absolutely not the same as reducing gain. The former changes your position on a sloped line. The latter changes the slope of the line. Check with an engineer please.
As Mr. Obama said recently, you're entitled to your opinion, but you're not entitled to your own FACTS.
Allow me to illustrate with a picture. God I'm spending WAY too much time on this.
This picture assumes the simple case of a steady state input signal, so feedback (the red line) does indeed appear at the same output volume for both amps. Sliding "max" to the left is equivalent to using a mic with less output, turning down the volume at the mic, or turning down the volume at the amp (which changes input volume, NOT gain.)
But input volume is also a function of our own dynamic range, and what we play isn't steady state at all. The higher gain amp always multiplies a louder note by more than the lower gain amp does. This makes the amp overly sensitive. We have to turn it down even further to stay out of the danger zone, and as a result anything less than our full volume playing is actually not amplified as much as with the lower gain amp, turned up higher.
You MUST compare 2 different input levels (a quieter note and a louder one), not steady state - in order to "get" this.
Conclusion? Gain makes a huge difference in the feedback equation. But I don't ask anyone to buy this on paper. Just try it. ---------- /Greg
that is the point i was making, the line that describes the output level where feedback occurs is at the same volume, regardless of the gain of the amp (the line is flat). The discussion here is mixing two things. What I was arguing is that most people do not measure and prove that the red line on the graph is flat. Some of the statements above imply that the line is not flat, that some mods allow you to get more absolute volume before feedback than others.
Walter youu are absolutely correct but only in principle - as I said in the discussion, it is only true is in a steady state situation. In the real world, feedback is a runaway condition. Think of all of those lines being really thick and fuzzy. The higher the gain, the easier it is to go from something less to something more than the condition required to start it off.
A gainy amp will feedback at a LOWER output volume in the real world. ---------- /Greg
Gain clearly has a big impact, because it clearly has great impact on output volume at the frequencies (fundamental or harmonic)that cause the most trouble, regardless of the overall measured output volume for any given note being played. Frequencies and their harmonics all work together to work with us or against us, depending on the equipment we use and how we use it...especially considering how we harpists want it to sound. The Coolest classic harp sounds are really just a result of what would be classified as inferior equipment today....especially regarding microphones for the sake of microphones and their original intended usage.
There's no denying it is a dynamic process involving ever-changing variables, which makes it such a fly in the ointment in the first place. The original resistor in question was likely part of this very discussion when the manufacturer tailored the frequency response of this mic to respond to the human voice.
There's no denying a tube swap can easily improve many of these issues. There's no denying a mic swap can too. There's no denying EQ is a widely used tool for this sort of thing because it flat out works too, even in other sound applications.
The individual has so much to choose from these days, it is limited only by budget and which approach you want to spend that budget on. I chose to use guitar gear I already had and have done lots of tweaking because my budget is near zero. If I had a big budget, i'd buy a custom harp amp in the 50 watt range for big gigs and use my valve junior for the rest..like I do now. I'd collect mics like Jon does and kingley and so many others. I might even build more like Greg. My own Microphone experiments have worked out extremely well over the years and i have built several very nice-sounding harp mics, including an electret ring mic ala hohner hoodoo...but I don't see the need anymore...like I said..the budget is near zero now. Even my wireless rig is from stuff lying around in boxes from past PA uses and experiments.
I think this discussion has been very cool and probably helped some folks did deep into what makes things tick. Thanks for your inputs Greg, Walter and others. I don't have anything else to add that relates to harp. I'm enjoying the heck out of this though. I hope the OP isn't too irritated with me for my long posts. If so, I apologize.
Greg I agree with your graph with one proviso. There will be a different level for feedback for each frequency. that level will vary by frequency in each room as well as with different equipment so for each set up you need to alter the levels for each frequency. The way I read to do it is to turn the main amp volume up full, then raise an individual mic till feedback occurs and lower the equaliser for the frequency that feedsback. If you then raise the mic level again till the second frequency feedsback you can then set the main volume at a sensible level and know that however much you turn up the volume during the gig feedback won't occur. It always worked for me when running the PA for a big band. I seem to remember that you can get a 'box' to it but I forget the name "two notch bandpass filter" or something like that.
Lumpy, there are products that let you dial in the notch filters you need during sound check and even save a room if you play there alot. There are also digital mixers with this feature. It's very cool.
Rick, I surley have tinitus,but as I stated in my post,the decible level increase came with the advent of the four cycle introduction to pro motcross racing. I always wore hearing protection-my tinitus is not from motorcycles-it is directly due to an Allman Brothers show when i was younger-thought it would be cool to lay my head directly against Dicky Betts PA speaker. I never made any comparison to harp playing-?. I am speaking of the audible difference of +-2db. All of the riders must wear helmets-thats why they set it at 99db-the helmet offers additional hearing protection,but you can still inflict damage after extended periods.
Last Edited by on Feb 26, 2010 11:24 AM
@Lumpy - you are right - there will always be a "next" frequency at which the amp is most sensitive and feedback will occur. I was simply trying to boil this down to the simplest case with the fewest variables to demonstrate the difference between input volume (which a mic can affect) and gain (which it cannot.) That they are not the same thing, and that gainier amps are much harder to manage when it comes to feedback. Also I was referring more to tube amps than PA's - although the same principles apply, we cannot control the PA's gain, only its volume.
Walter, according to the datasheet that came with the 99S556 dual-impedance element (across which the 38K resistor is commonly wired) the change was to BOTH frequency response and output - and the goal was to change the frequency response (that element more than enough output to stand up to the extra load.) I don't have that data sheet handy at the moment so i can't quote it. It's around here somewhere.....
Greg, this is simple: turning down your hot bullet mic has the exact same impact on feedback as swapping in a lower-gain tube: It reduces it. I think you need to take a deep breath here. You've pushed that boulder about as far up the hill as it will go. Nobody is disputing that gain impacts feedback and is fundamentally different that amplitude.
Rather than jamming tubes into an amp, a player who is having feedback issues should first try turning down his mic, perhaps with one of your fine in-line volume controls. It is a FACT that this will reduce his system's feedback potential. Why are you straining so hard to dispute this? It is a bit absurd.
One reason harp players use volume controls on microphones is so they can trim out any stray feedback as it occurs. Are you seriously arguing that this is not true? I'm beginning to think you have an irrational compulsion to argue even when you are helplessly cornered.
Greg, you and I had this same little debate in a different forum. I mentioned in that forum that I had tested the Front and Center microphones and found them to be remarkably feedback resistant, as I did in this thread. You and the others in the forum reacted as if your hair was on fire. I understand your desire to defend the microphones that you make and sell, but the rhetoric got comically absurd. You and others actually claimed that bullet microphones with Shure SC/CR elements do NOT have feedback issues!
Typical bullet microphones with Shure CM/CR elements are very omni-directinal. This combined with their high output voltage (greater than 1 volt on loud passages) make them feedback magnets. It also contributes to their muddy tone. They often overwhelm the input tube, pushing them into square-wave distortion.
Now you keep dragging this red herring of GAIN across your weak argument. We all agree gain is the main culprit in feedback, so give it a rest! The difference is that I view gain as a system wide issue (which it certainly is) while you seem to think it begins and ends in the preamp tube.
You've taken the absurdist position that turning down your mic will NOT reduce feedback, and that bullet mics with CM/CR elements do NOT have feedback issues. Your arguments seem more than a bit desperate. Every time I mention Front and Center Mics it seems to make you appoplectic.
"Rather than jamming tubes into an amp, a player who is having feedback issues should first try turning down his mic. . . . It is a FACT that this will reduce his system's feedback potential."
Admirable restraint, that, suggesting mere half measures in a vain attempt to avoid provoking Greg further. Turn down the mic? Hah! Try turning off the amp: It is a FACT that this will ELIMINATE all feedback, not merely reduce feedback potential, even in high gain amps. For best results, unplug the amp from the AC outlet, like the experts do.
Any resulting impact on dynamics and tone is surely less important than challenging the conventional wisdom.
When you turn down the volume on a mic it makes the input to the amp less. This in turn makes the amp quieter and therefore creates less feedback, but this is not the same as doing a tube swap.
A tube swap alters the character of the gain at the pre-amp stage and that is a completely different beast to simply lowering input volume which is what you do when you turn down a mic volume.
The two do have the same effect in that they reduce feedback but they are simply not the same in the way that they do it.
Rick for you to imply that they do is simply wrong. You are however correct in so far as turning down will affect the feedback level. If however that is the goal then the sensible thing to do would be to turn down the amp and turn up the mic as this would allow for a better overall tone than vice versa.
Rick, with regard to "turning down is the same thing as changing tubes...." I don't know how to say it any more clearly and I won't say it again. You are incorrect. Reducing input volume is about moving along one of those lines on my graph. Changing gain is changing the slope of the line. They are not, nor will they ever be the same thing. GAIN AND VOLUME ARE NOT THE SAME. As someone who professes to be an expert an publishes a blog about amps, you should know this.
As for the second of your posts, go back and look. I NEVER took issue with anything you said about F&C mics. I ONLY took issue with your blanket statement that CMs and CR's are "feedback magnets", which you repeat here. iThis simply isn't true - as several others pointed out to you in that thread. This discussion started out about mics and feedback, and I simply pointed out that the amp is a more important consideration. I stand by that statement.
This is deteriorating into a nasty thread and it sends my blood pressure up. This is my last reply.
I cannot claim much more than a lot of live gigging/mixing experience. I'm not going to dispute any of the info posted about the difference between gain and volume. there are a few things that I'd like to add.
1. Mics have different frequency responses. Bullet mics, due to their original intended purpose in noisy workplace environments have a pronounced midrange peak. Vocal mics designed for live music as opposed to taxi cab dispatching have more musical response characteristics.
2. it is entirely possible to control the gain in the pa: that is effectively what eq is; a gain control for specific freq bands. Furthermore a desk without a gain pot on each channel is IMHO worthless and thankfully pretty rare these days.
3. Re: polar pattern of mics and off-axis rejection. As Greg stated earlier, when you cup a vocal stick mic you will block it's rear and side vents. Without these vents a cardioid / hypercardioid mic becomes omni directional just the same as a bullet. It also becomes subject to the bass freq enhancing proximity effect to a much greater degree. Neither of these is necessarily a bad thing for a harp player tonewise, but comparing the feedback rejection of a stick mic on a mic stand to one tightly cupped is pointless.
4. In my experience an understanding of basic room acoustics and amp placement can be far more productive than anything else in combatting feedback. Too many players (of all instruments) drown their sound in unnecessary reverb and delay that most rooms don't need. Furthermore too many people are obsessed by 'dialling' in their tone that once they find amp settings they like they try to replicate them in every venue without any thought to the acoustics of the room they are in.
