Why do double bass microphones feed back?

[philw]

Just happened on this thread and while I don't want to be accused of nannying, can I just post a health warning about the dangers of "Heath Robinson" in-ear monitoring? Professional IEM systems incorporate limiters and fail-safe devices that ensure that if something goes wrong in the PA/backline, users aren't rendered immediately and perhaps permanently deaf by a blast of feedback injected directly into their ears. An IEM system created simply by driving a pair of headphones from a monitor mix output has no such safety net and if you use one you're potentially playing Russian roulette with your hearing.

P

[Silvia Bluejay]

Sensible post, Phil, no nannying at all. It was in fact something that crossed my mind when I was reading this thread.

[fatback]

[quote name='philw' timestamp='1344870416' post='1770385']
Just happened on this thread and while I don't want to be accused of nannying, can I just post a health warning about the dangers of "Heath Robinson" in-ear monitoring? Professional IEM systems incorporate limiters and fail-safe devices that ensure that if something goes wrong in the PA/backline, users aren't rendered immediately and perhaps permanently deaf by a blast of feedback injected directly into their ears. An IEM system created simply by driving a pair of headphones from a monitor mix output has no such safety net and if you use one you're potentially playing Russian roulette with your hearing.

P
[/quote]

Ouch! Thanks for the warning. Wouldn't have occurred to me, tbh.

[gcordez]

I've been using pretty much a mic-only for the past couple of years. I've been (for the most part) pretty happy with it.

I was kinda belligerent though in the early stages and decided no matter what happens with feedback etc, I'll make it work. To do this I practise drawing a big and focused sound and get a good pull on the string. I have to use medium-ish action to get my finger under the string Ray Brown style. As a result, I'm getting much better volume acoustically and a better tone from all of this. As I'm using a mic to capture a sounds, rather than a pickup to eq, I'm more aware of the quality of the tone we coax out of our instruments

Most gigs are jazz type stuff, but Ive got used to eq-ing my amp and making sure amp and bass are in good positions.

For me at least, I really wanted to learn how to use a mic and stuck with it through good and bad.
If I wasn't so enthused about the idea I probably would have given up after a coupla gigs.

I have a pickup in the back pocket for those impossible gigs though..

[51m0n]

A mic feedsback when it picks up the output from the speakers loudly enough to cause a loop. That is that the noise from the speakers picked up in the mic makes the speakers reproduce that noise more (louder) so that it is then picked up by the mic more etc etc etc

The closer a mic is to its intended source (the doublebass) the louder the source is compared to background volume (the speakers and everything else), and the lower the gain on the mic, and the less likely you are to get feedback. This is because of the inverse square law, volume = 1 / (distance* distance). If you know your maths you can see that moving a mic away from a source even a little bit produces a very large drop off in volume indeed.

Unfortunately a double bass is an instrument that makes its sound over a very large area (the entire body and sound board). If you close mic a bit of it you dont get the actual sound we hear, you get a part of that sound, that is never ever truly representative of the entire instrument. If you move the mic away from the instrument in order to capture the real complete sound you get more background sound, and more chance of feedback as you have to crank the gain on the mic to compensate.

Its not the bass that causes the feedback, although it can resonate in sympathy to it, its the signal from the speaker(s) being picked up by the bass mic.

Edited August 14, 2012 by 51m0n

[rikodriko]

Hi, not sure if this has been covered already, as i havent read all the posts,

but just to say that the schertler dyn-B contact mic and the PRE AI III matched pre amp is absolutely ACE. Still get feedback, but thats normal - the resonance of the bass body will always cause this at higher volumes. Need to position yourself so that you are not facing your amp.

I had a Realist for AGES, thinking it was the best on the market, but i was never really happy with the sound. Most doubles bassists are after that 'pure' acoustic tone when amplified, and the realist to me was too middy and nasal, and the output from it was far too low.

I investigated the schertler stuff and managed to get the Dyb-B and preamp all in for less than £500 on ebay. Its expensive stuff !!

Im loving the tone of it, and also the portability - it just sticks on the bass with green bluetack so moves between multiple basses with ease. It also has a phase switch to switch out the feedback if you in a cramped rehearsal space for example.

Would defo recommend. but its expensive !!

my 2c...

[thisnameistaken]

So can you get similar volume with the mic to what you got with the realist?

[rikodriko]

loads and loads via the schertler preamp added in... and a more 'real' tone as well... V happy with it...

To be clear i only ever have used the contact mic with the pre amp. so cant say whether there is more if you connect the contact mic directly in to your normal amp...

Sold my realist ages ago and have not looked back since. I dont think its particularly crap - just that my new set up is much better, louder and truer - but i had to pay for it !!

[fatback]

[quote name='rikodriko' timestamp='1346248906' post='1786986']
loads and loads via the schertler preamp added in... and a more 'real' tone as well... V happy with it...

To be clear i only ever have used the contact mic with the pre amp. so cant say whether there is more if you connect the contact mic directly in to your normal amp...

Sold my realist ages ago and have not looked back since. I dont think its particularly crap - just that my new set up is much better, louder and truer - but i had to pay for it !!
[/quote]

You've just sparked the first GAS attack I've had in ages.

[rikodriko]

my pleasure

Your wife and wallet wont forgive you, but who cares..

[fatback]

[quote name='rikodriko' timestamp='1346322906' post='1787805']
my pleasure

Your wife and wallet wont forgive you, but who cares..
[/quote]



Wonder what the mic would sound like directly into my EA Doubler.... hmmm

[jbn4001]

[quote name='bassace' timestamp='1343660901' post='1753271']
Is this question posed in the context of running the mic to backline? If this is the case then feedback will generally follow whatever the quality of the mic and its amplification chain. But if you run the mic to front of house and not have monitors too close it will work very well. Only trouble is the audience will enjoy the great double bass sound but you won't! You will have to run a pickup to backline to hear yourself.
[/quote]

Reviving this old thread --- I'm just researching using mic in a live situation on double bass. I have both a DPA4099 and Headway EDB2.. and also a KK Bassmax pickup and Platinum Pro.

I have a question directly on the above quote: how come putting mic signal through FOH and pickup only through monitor reduces likelihood of feedback? Surely the mic will still "hear" the monitor which is producing the sound from the pickup - which ought to be similar to the sound the mic is picking up ..and thus feedback? A lot of people seem to do this so the approach obviously has merit. I just want to understand why!

Incidentally, my situ is I'll be playing in a jazz duo - hollowbody guitar + double bass in a fairly big restaurant/bar next week. We plan on using our own amps.. taking the output into the house PA which has speakers dotted around the venue.

[Dad3353]

[quote name='jbn4001' timestamp='1394450019' post='2391358']...
putting mic signal through FOH and pickup only through monitor reduces likelihood of feedback? Surely the mic will still "hear" the monitor which is producing the sound from the pickup - which ought to be similar to the sound the mic is picking up ..and thus feedback?
...
the house PA which has speakers dotted around the venue.[/quote]

Good afternoon, jbn...

Almost, but not quite... 'Feedback' is not really dependant upon the level of sound being captured by the mic, but rather the level of [i]its own[/i] sound captured by the mic (ie: how much sound is 'fed back', hence the term 'feedback'...). There are many factors involved, of course. The monitor is likely to issue different frequencies and phase compared to FOH; in some cases could even cancel out some sounds altogether..!
If the resto/bar has dispersed speakers, it is probably to avoid having one single loud sound source, favouring less volume locally to cover a smaller area. This bodes well for your 'feedback' issues, as less 'room' sound will be fed back to your instruments. Good luck with the gig.

[Monckyman]

What hasn't been noted here is that low frequencies aren't directional,which means there's almost as much low end to the sides and rear of your bass as the front, so its difficult to isolate and contain feedback.
On the IEM angle, better buds/molds/seals allow a much lower level of sound to your ear and so reduce the actual decibel count of any "blast of feedback".
You can if you have the inclination, put a compressor/ limiter over either the mix at the mixer output, or the input to your personal mixer, and set it up to act as a brickwall limiter so whatever happens, it will never get louder than you allow.
if you were using a dual mono ( mix in one and bass in the other, you only need limiting on the mix side.)
I would also suggest that any blast of feedback would more than likely be the singer bending down over his monitors,mic in hand to reach his booze/fags/lyrics/sweets so getting him on IEMs should be the bands priority and then the feedback problem is 75% reduced.
This stuff is only fiddly to set up and get used to, but once past that, it'll be quick and easy.

[Jezyorkshire]

what about this, trollmicrophone.com

Edited March 10, 2014 by Jezyorkshire

[thisnameistaken]

I'm so sold on the sound of my Ehrlund pickup/pre that I work really hard to make it work in every situation, and I reckon an IEM system will be the final piece in the puzzle. Currently I either use my own backline or a wedge for monitoring and it's just not practical - if I can hear it loud enough then so can my bass and that's when the trouble starts. It's really only monitoring that creates issues for me.

I do have problems with other peoples backline sometimes though. A guitar cab too close can mean I'm resonating their sound too much, I also have had problems with our DJ recently when he starts cutting in long bass-heavy synth pads, which not only shake my bass but because of the nature of the sound they make me *think* I'm feeding back! I've had to tell him to stop doing that when I'm playing the upright.