Members Telecruiser Posted June 2, 2011 Members Share Posted June 2, 2011 I have seen it on here a few times but I don't remember anyone explaining why this happens. Link to comment Share on other sites More sharing options...
Members dboomer Posted June 2, 2011 Members Share Posted June 2, 2011 I think that is way to broad an assumption. Are you simply misunderstanding the likely output levels? Condenser mics are usually hotter, so if you plug one in, replacing a dynamic and it starts feeding back are you thinking that qualifies as feeding back easier? It's not. In this case it has more output, you're not comparing apples to apples. I think a more correct statement would be that some mics have less gain before feedback than others ... but it's not directly tied to dynamic vs condenser. Link to comment Share on other sites More sharing options...
Members Reson8tor Posted June 2, 2011 Members Share Posted June 2, 2011 Condenser mics are usually hotter, so if you plug one in, replacing a dynamic and it starts feeding back are you thinking that qualifies as feeding back easier? It's not. In this case it has more output, you're not comparing apples to apples. That's been my experience too, and I just ran into it last week at a gig. We were doing an "acoustic" show and I brought my own instrument mics (condensers), using the installed PA at a folk club. The part-timer, non-pro sound guy that usually runs the mixer was freaked by the "hot" mic signals, but it's because he's used to the SM57s and 58s the club usually provides. Once I worked with him to back down the input gain on the channels, it was all fine. There can be other factors too, like some condenser mics might have wider patterns, or pick up more in the "air" frequencies if you're getting feedback up there. But the main misunderstanding I've run into is just not understanding that there's a head amp in the mic, and so duh.... you might be working with a hotter signal to start with. Link to comment Share on other sites More sharing options...
Members Telecruiser Posted June 3, 2011 Author Members Share Posted June 3, 2011 But if a condenser is "hotter" than you would just reduce the gain wouldn't you? It has been said on this forum a few times that I know of that condensers are more prone to feeding back. If you were were replacing a dynamic with a condenser than you would reduce the gain to maintain the same level of volume that you had previously with the dynamic. I mentioned a few weeks ago that I wanted to use an SM81 on my acoustic guitar and was told it would would be more of a feedback problem. I was told that condensers are better choices for the studio and not live sound. Link to comment Share on other sites More sharing options...
Members rodclement Posted June 3, 2011 Members Share Posted June 3, 2011 Handheld condensers usualy have larger capsules and are hotter so you need to think before you plug it in, think where are my monitors? Think were are my speakers? Think, were are the instrument amplifiers...wait...don't you have to do that with ANY microphone? My EV handheld condenser has a huge capsule but also has a very tight pattern, it allows me to get a phenomenal, clean vocal sound by using a lot lower gain than a dynamic so I get every detail of my voice with less feedback since the gain is lower than the dynamic option would be. WOrks for me. Rod Link to comment Share on other sites More sharing options...
Members Reson8tor Posted June 3, 2011 Members Share Posted June 3, 2011 But if a condenser is "hotter" than you would just reduce the gain wouldn't you? It has been said on this forum a few times that I know of that condensers are more prone to feeding back. If you were were replacing a dynamic with a condenser than you would reduce the gain to maintain the same level of volume that you had previously with the dynamic. That would be standard procedure from someone who had wide experience with all the different types of mics out there. At the lower end of the SR food chain, where dynamic mics like SM57s are the norm and always considered "good enough," you'd be surprised how many people have never encountered a condenser mic. And they propagate these myths, because they don't want to move their input gain off their standard setting. And so they get feedback, and start posting myths about condenser mics on their favorite forums. I mentioned a few weeks ago that I wanted to use an SM81 on my acoustic guitar and was told it would would be more of a feedback problem. I was told that condensers are better choices for the studio and not live sound. Yep, sounds like one of those people I just mentioned. Neumann KM184's are considered a studio mic. Guess what... I use 'em for sound reinforcement. They sound terrific on acoustic instruments, through the right PA system. It's an education problem. If you want the better sound reproduction that condensers can offer, especially on things like acoustic guitar, and if the rest of the PA chain is capable of reproducing the difference (not always a given!), then go for it. These myths won't die until enough people start using better mics, and better front-to-back PA signal chains where good condenser mics can do their thing. Link to comment Share on other sites More sharing options...
Members dboomer Posted June 3, 2011 Members Share Posted June 3, 2011 c. I mentioned a few weeks ago that I wanted to use an SM81 on my acoustic guitar and was told it would would be more of a feedback problem. IF that was indeed true (and that's a big unknown if) it would not be because of condenser nature of the element. The pattern and frequency response along with other system factors would be. Link to comment Share on other sites More sharing options...
Members dboomer Posted June 3, 2011 Members Share Posted June 3, 2011 so I get every detail of my voice with less feedback since the gain is lower than the dynamic option would be. WOrks for me.Rod No ... gain is gain and level is level. The important factor here is "gain before feedback". The mic with the best gain before feedback will be able to be louder (level) than one with less GBF. Gain before feedback is not related to mic sensitivity. Link to comment Share on other sites More sharing options...
Members Coaster Posted June 3, 2011 Members Share Posted June 3, 2011 i have actually found it true that sm81's tend to want to feedback more than a lot of other mics on stage, but probably not at all due to the fact that its a condenser. they seem to have a pattern issue around 150ish, like to pick up rumbles from off axis IME. dip the eq around 150 and problem solved, so fail to see the above problem, except i will add i do NOT like 81 on acoustic. i do like 81 on lots of other things, i just tend to like more "body" to my acoustic guitar sounds than what i get from an 81. i dont really want to hear the pick contact every-string-every-time at a rock show, just a general guitar sound will do for me. maybe the OP is looking for the peak voltage in relation to the diaphragm position concept between dynamic and condenser? Link to comment Share on other sites More sharing options...
Members Dogoth Posted June 3, 2011 Members Share Posted June 3, 2011 Why do condenser mics feedback more easily than dynamics? That's a generalization but not a rule. Firstly most condenser mics have a peak in the high end. This makes for more detail and the illusion of more fidelity. It works great at low volume but...... I have a couple of theories which I'd happily see debunked if anyone feels I'm incorrect. Firstly condensers are phase correct (the peak of the acoustic wave is in exact time with the peak of the electrical output (or reverse polarity depending on the bias of the mic & it's wiring) whereas a dynamic is always 90 degrees out of phase (where the peak in voltage is when the digaphram or ribbon is traveling at it's highest velocity - not at the end of it's travel (hence the name velocity mic)). I know this doesn't take into account time differences due to distance from the monitor (which probably blows this theory out of the water but it still may have something to do with the problem). Secondly the way mics get their directionality is (usualy) through plumbing. In other words pressure waves are directed back at the rear of the capsule to cancel out (from the rear) what the front of the mic is hearing. Dynamics have a solid magnetic pole piece (often with vents machined through it) whereas condensers have a relativly solid back plate (with various holes in them as vents). I think the difference is a lot about acoustic plumbing. One exception to this is a dual digaphram condenser which mixes in the back side digaphram output to cause the cancelation electricly (variable pattern mics mix variable amounts to get the different patterns). It's still a quite different "plumbing" arrangment and this may attribute to the posted feedback issue. There are a few condensers that are quite well behaved on stage (as far as GBF goes) so again it's a generalization, not a rule. Go ahead and shoot holes in my theories and let me know what you think. Link to comment Share on other sites More sharing options...
Members Telecruiser Posted June 3, 2011 Author Members Share Posted June 3, 2011 Why do condenser mics feedback more easily than dynamics? That's a generalization but not a rule. Firstly most condenser mics have a peak in the high end. This makes for more detail and the illusion of more fidelity. It works great at low volume but...... I have a couple of theories which I'd happily see debunked if anyone feels I'm incorrect. Firstly condensers are phase correct (the peak of the acoustic wave is in exact time with the peak of the electrical output (or reverse polarity depending on the bias of the mic & it's wiring) whereas a dynamic is always 90 degrees out of phase (where the peak in voltage is when the digaphram or ribbon is traveling at it's highest velocity - not at the end of it's travel (hence the name velocity mic)). I know this doesn't take into account time differences due to distance from the monitor (which probably blows this theory out of the water but it still may have something to do with the problem). Secondly the way mics get their directionality is (usualy) through plumbing. In other words pressure waves are directed back at the rear of the capsule to cancel out (from the rear) what the front of the mic is hearing. Dynamics have a solid magnetic pole piece (often with vents machined through it) whereas condensers have a relativly solid back plate (with various holes in them as vents). I think the difference is a lot about acoustic plumbing. One exception to this is a dual digaphram condenser which mixes in the back side digaphram output to cause the cancelation electricly (variable pattern mics mix variable amounts to get the different patterns). It's still a quite different "plumbing" arrangment and this may attribute to the posted feedback issue. There are a few condensers that are quite well behaved on stage (as far as GBF goes) so again it's a generalization, not a rule. Go ahead and shoot holes in my theories and let me know what you think. OK, now it seems we're getting somewhere. BTW, where is AH on this? Link to comment Share on other sites More sharing options...
Members WynnD Posted June 3, 2011 Members Share Posted June 3, 2011 My sax player's vocal mic is a condensor and the best one on stage at rejecting off axis sound. Don't know what model or manufacturer it is, but I wish all the mics on stage were like that. Our lead singer's Sennheiser picks up everything. (It also sounds very good with his voice.) Link to comment Share on other sites More sharing options...
Members dboomer Posted June 3, 2011 Members Share Posted June 3, 2011 OK, now it seems we're getting somewhere. ) No ... neither of these point support your premiss. They MAY support differences in tonal quality, but that's not what you asked. The class of mic element has no bearing on feedback. Once you adjust everything so that you have a level playing field, feedback is caused by one and only reason ... and this ain't it. What doesn't seem to be sinking in is that adjustment. If you don't make that adjustment, then you could conclude that any higher sensitivity mic will feedback before any lower sensitivity mic. Link to comment Share on other sites More sharing options...
Members lifeloverwg Posted June 3, 2011 Members Share Posted June 3, 2011 Isn't GBF all about the gain? Whether the gain comes from how sensitive the mic capsule is, which may be a function of what type of mic it is, to what pickup pattern it has, to how high the preamp gain is set, to what's happening on the EQ, to whether or not there are matching spikes in the mics and monitors frequency response it's all gain. For some or all of these reasons your condensers feed back before your dynamics because they are louder and have more gain rather than because they are condensers. If you were to measure the voltage produced at the input strip and adjust the two to be the same then they should feed back at the same time assuming they have the same frequency response etc. At least I think so.... Winston Link to comment Share on other sites More sharing options...
Members agedhorse Posted June 3, 2011 Members Share Posted June 3, 2011 Condensers in general have less gain before feedback. It's not an absolute but it is certainly IMO and IME a valid generality. The reasons are many, JR hit on a couple that have merit IMO. Other reasons are that in the quest to achieve extended on axis response, off axis uniformity may not be as smooth and this can be a big factor. Also, to improve high frequency extension, small diaphragms may be used which changes or certainly alters the options for pattern control uniformity. Then there's the intentional manipulation of the on-axis pattern which adds to the off-axis response issues. These factors are generally more significant when the HF response is extended, in part because it's easier to do so with a lighter moving mass. Working with a condenser mic element is a combination of compromises and trade-offs that contribute to the generality that there is less (overall) GBF with a condenser mic. There are some expections, in some situations of course. The EV-BK1 which I assume JR was talking about is one condenser mic that has compromises that lead to pretty good GBF but the HF response is nicely tailored rather than excessive. Link to comment Share on other sites More sharing options...
Members agedhorse Posted June 3, 2011 Members Share Posted June 3, 2011 Isn't GBF all about the gain? Nope, it's about the gain LOOP. That is the abount of gain possible in a closed loop condition. As soon as the loop is opened (as in recording), the GBF term goes to infinity. Link to comment Share on other sites More sharing options...
Members Dogoth Posted June 3, 2011 Members Share Posted June 3, 2011 I see where this thread is going. I guess it's important to define GBF (Gain before feedback). As the term describes, it's the amount of gain (the difference between the acoustic spl at the mic dia to the acoustic spl at the speaker cone) that is achievable before a feedback loop occures. As Agedhorse puts it. In a closed loop there is a point there it becomes unstable and starts feeding back (if this is tightly controled, this is used to an advantage (sometimes a prerequisite) in circuit design but that's another thread entirely). If the mic is more efficient (sensative) at converting acoustic energy to a representative electrical waveform then you have added gain right at the mic (this is the case with most active electronic condensers and some very efficient dynamics). GBF is, again, the total gain, including the mic output, the mic preamp, the power amp, the efficiency of the speakers and all of the various stages of gain used in that particular signal path (I.E. summing amps, makeup gain amps in the board, inserted processors, outboard EQs etc.....), possible before feedback occures. All things being equal except if mic "A" has 6 db more gain at it's output than it's neighbor, mic "B", then the mic pre trim (gain) control for "A" should be turned back down by 6 db to achieve the same amount of system gain as mic "B". If the response and rejection characteristics of both mics "A: and "B" are the same (only a difference in sensativity) then the GBF should be exactly the same. Clear as mud, I'm sure :-) Link to comment Share on other sites More sharing options...
Members Mikeydude1964 Posted August 18, 2019 Members Share Posted August 18, 2019 SOrry I realise this is an old thread...but I had to answer as virtually all of the post are simply not correct. The reason why a condenser has a lower GBF is purely because they tend to have a less tight polar pattern....i.e there sensitivity does not drop off rapidly with distance..this is why they are good for use as overheads as they pick up from a large area.....this means they tend to feedback more in a live situation. Dynamic microphone can be made with much tighter polar patterns allowing them to have better rejection (spill rejection) and so have higher GBF. Link to comment Share on other sites More sharing options...
Members dboomer Posted September 25, 2019 Members Share Posted September 25, 2019 On 8/18/2019 at 7:29 AM, Mikeydude1964 said: SOrry I realise this is an old thread...but I had to answer as virtually all of the post are simply not correct. The reason why a condenser has a lower GBF is purely because they tend to have a less tight polar pattern....i.e there sensitivity does not drop off rapidly with distance..this is why they are good for use as overheads as they pick up from a large area.....this means they tend to feedback more in a live situation. Dynamic microphone can be made with much tighter polar patterns allowing them to have better rejection (spill rejection) and so have higher GBF. With the exception of a very few mics (as in ones you’ve never seen) drop off exactly the same. It’s called inverse square law! Link to comment Share on other sites More sharing options...
Phil O'Keefe Posted September 30, 2019 Share Posted September 30, 2019 On 8/18/2019 at 7:29 AM, Mikeydude1964 said: The reason why a condenser has a lower GBF is purely because they tend to have a less tight polar pattern....i.e there sensitivity does not drop off rapidly with distance. You're talking about two different things here. One is how they "drop off" with distance, and as Don said, that's a function of the inverse square law, and it's going to impact dynamic and condenser mics alike. The other area is polar patterns - the directionality of the microphones in question. And this actually can impact gain before feedback. All other things being equal (such as the microphone's sensitivity and output), a mic with a tighter polar pattern, with the off-axis null aimed at any nearby sources of noise you need to avoid (such as a monitor speaker) will generally perform better / feed back less readily than a mic with a less tight (or omnidirectional) polar pattern. Your theory that condenser mics have "less tight polar patterns" is really not true - it simply depends on the specific mic in question. I currently have a condenser mic in my studio under review from a major manufacturer that has (I kid you not) 270 degrees of off-axis rejection... https://www.lautenaudio.com/ls-308 DBoomer is right - a microphone's gain before feedback is the area that you should be focused on if feedback is a concern. Link to comment Share on other sites More sharing options...
Members happwith12strin Posted October 1, 2019 Members Share Posted October 1, 2019 Imade the switch from dynamic vocal mics to handheld vocal condensers so much better soun d duch much easier on you voice let the condenser mic and the PA do all the work using akg C5 flawless quality mic spectacular sound! soundonsound says the akgC7iseven better Link to comment Share on other sites More sharing options...
Members dboomer Posted October 6, 2019 Members Share Posted October 6, 2019 A lot depends on your playing environment. Pattern is a factor. If you are outdoors in the middle of a football field pattern rejection is a big factor. But if you are playing in a club with a 10’ ceiling and a 20’ wide stage it may make almost no difference. That’s because at that point it is easy to get more reflections off the back wall than sound leakage from outside the pattern Link to comment Share on other sites More sharing options...
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