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Author Topic: Microphones for boxes  (Read 18445 times)

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IanD

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Re: Microphones for boxes
« Reply #60 on: August 30, 2014, 10:34:51 AM »

just to say that there is a course in folk music sound techniques every August in val d' Isère
Maybe festivals ought to insist that their sound guys have been on this before they get to do the sound -- yeah, like that'll happen  :(

Hmm, you know the way that many halls nowadays won't let you play (if you're providing PA) without supplying a PAT certificate? Maybe if all the bands refused to play at any festivals unless they were showed the "Sound guy who knows how to do folk" certificate...  >:E
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baz parkes

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Re: Microphones for boxes
« Reply #61 on: August 30, 2014, 12:10:13 PM »

just to say that there is a course in folk music sound techniques every August in val d' Isère
Maybe festivals ought to insist that their sound guys have been on this before they get to do the sound -- yeah, like that'll happen  :(

Hmm, you know the way that many halls nowadays won't let you play (if you're providing PA) without supplying a PAT certificate? Maybe if all the bands refused to play at any festivals unless they were showed the "Sound guy who knows how to do folk" certificate...  >:E

or the sound gal...thinking of Charlie Roberts...but a great idea.  Last time we did the Anchor gardens we politely asked if that nice Tom Wright could run the desk for us....it made quite a difference
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Owen Woods

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Re: Microphones for boxes
« Reply #62 on: August 30, 2014, 12:25:32 PM »

At Sidmouth the sound at the Ham was almost acceptable at times, the sound at the Bulverton was utterly unacceptable and the sound at the Bedford was really quite nice.
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Chris Brimley

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Re: Microphones for boxes
« Reply #63 on: August 30, 2014, 01:48:55 PM »

Quote
That is, use your ear as a mic, to explore the area around the instrument and see what quality and volume of sound is coming from each place. Get close and put your finger in your other ear to ensure you're hearing the direct sound.

A useful comment in some ways, I thought, and it merits a bit of discussion.  Generally speaking, I quite liked Bob Mills' leaflet, with its straightforward and thoughtful advice.  Unfortunately, he doesn't really cover our issue, and I'm guessing that he's more used to pianos rather than any kind of accordion, as you hint at, Syale!

You can indeed pick up the quality and sound coming from each place, in this way, though you do need to block the other ear well.  So you might be able to gain some understanding about where the strongest sounds are being generated, the extent of the proximity effect (bass 'tip-up'), what difference bellows movement and player movement might make, and possibly how a close mic would perform in picking up sounds generated at different ends of the box.  You'd have to be a bit of a contortionist for that last one, and I don't think you could do it on your own!

However the ear and brain's internal amplification system doesn't suffer from feedback, which is the main issue we are trying to deal with in the first place.  You wouldn't be able to use your ear to judge directly whether a given microphone position is going to give you feedback in this way, you'd have to experiment in other ways.  Another problem is that the directional response of the ear to differently positioned sound sources is not going to be the same as that of the microphone you would be using.

I would suggest that a better way to deal with our issues here (I've tried this) would be to find somewhere with little natural echo, set up a system you are thinking of trying, and put it through a desk and monitor, and position yourself as if you were on stage.  Assuming you've got more than 1 microphone, you will need more than 1 channel, so set them the same.  Without adjusting the equalisation from flat, turn up the monitor and experiment till you're close to feedback.  Noting the level at which that happens, you can then experiment with different microphone layouts and orientations, player positions, etc.  Then, in order to see what the sound is going to be like to the audience, you need to cut out the direct sound from your box, so you need to plug in ear-covering headphones so that you hear mostly the signal from the microphones rather than the box directly.  You will probably find the bass is quite 'tipped-up' - and this will probably happen differently for the RH and LH sides.  What you are aiming for is a compromise - you'll want the maximum volume coming back to you through the monitor, but you'll want it to be even, covering all the buttons reasonably equally, and you'll probably want it to sound reasonably similar to the acoustic sound of your box (though many players seem to like the bass sounds on the LH to be 'tipped-up' artificially, as we discussed earlier.)

If you are using a close-mic system, you may well find that this experiment will immediately show that the proximity effect is significant, and just makes the box sound unnatural.  It sounds as if you've got your ear right up close to it, it's not like it's playing in a space of any sort.  You may have noticed that there was a noticeable difference in my earlier illustration between the sounds produced by a mic 20cm away and one 50 cm away - even with a 'not-so-close' mic, it's a significant effect that we're dealing with.  Next, you may notice with your experiment that there is a noticeable reduction in the volume of buttons in certain locations (the displacement effect), and this also sounds unnatural.

To some extent, you can correct for the proximity effect, using equalisation.  You can cut down the bass of that signal.  But how much, and for which frequencies?  Again, a high spec desk will allow this to be done using a graphic equaliser, and you can probably in theory achieve quite a realistic result.  But hang on, that's going to differ for each microphone position, and what's more the displacement effect will also cause sound sources to exhibit the effect in different ways.  Moreover (and this a severe practical snag), you really can't expect the average sound engineer always to have such sophisticated equipment, to have time to set it up separately for each separate microphone channel, and as we've seen, many of them won't have the experience to do so anyway. 

So, another approach, and one that I might try if I wanted a close mic system, might be to have your own sub-mixer on-stage, specially set up in advance as the best compromise to equalise each of your microphone signals as best you can, and produce a reasonably natural sound.  When I'm playing acoustic guitar, I do something like this by using a box (it's a Zoom A2.1u), which I preset with the settings I've found work best on my own PA system, to give a certain effect with each of my guitars.  This unfortunately brings new problems:  First, it's extra kit to carry around and set up and maintain.  But second, I've noticed it doesn't always work as I expected, with other people's PA equipment.  I now believe the reason for this is that it's sometimes interfering electronically with the sound engineer's own system- one particular example is that if I set up my own reverb, and the sound engineer is doing the same, it can produce truly awful sounds.  Which leads to the third snag - doing something like this yourself is often blurring the line between the player and the sound engineer, and this can be unknown territory for the engineer.  If I'm going to use my guitar box I'll probably explain to the engineer that I'd like just a clean sound with no extra eq or effects.  However, he may have set up the PA for the conditions of the particular venue, and may still want to have certain adjustments made - and I can't know on stage what it sounds like in front, so it's quite right that he/she should still have that overall control.

The approach with a free-standing mic system is somewhat different.  In this situation, you are relying on using directional microphones set up in positions which are some way back from the box (say 20-50cm), and therefore less likely to have as serious proximity or sound-source displacement effects.  Moreover, they will be specially of a kind that has low sensitivity to sound directly from the back (i.e. around 180 degrees from the axis, or direction the mic is pointing in) at all frequencies, and the monitor can therefore be pretty close to them.  Because the mics don't move, feedback is less likely to happen unexpectedly as the player moves about a little.  And another advantage is that it's going to be a pair of fairly clean signals from the mics, and the engineer will know what to do with them.

There's lots of relevant other technical issues here, as I'm sure others will say, but that's the bare bones of the principles as I see them.
« Last Edit: August 30, 2014, 01:59:03 PM by Chris Brimley »
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Chris Brimley

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Re: Microphones for boxes
« Reply #64 on: August 30, 2014, 02:11:45 PM »

Just a comment on the ring system- interesting - it might well compensate for the 'sound source displacement' effect, for the RH.  I would also want to know:  First, do you get noises from moving your fingers about (like you do if you leave a recorder in your pocket)?  Second, how does it perform with regard to the proximity effect?  And third, what happens if you need to put your box down, scratch your nose, turn the music pages, or whatever?
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IanD

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Re: Microphones for boxes
« Reply #65 on: August 30, 2014, 05:44:28 PM »

Just a comment on the ring system- interesting - it might well compensate for the 'sound source displacement' effect, for the RH.  I would also want to know:  First, do you get noises from moving your fingers about (like you do if you leave a recorder in your pocket)?  Second, how does it perform with regard to the proximity effect?  And third, what happens if you need to put your box down, scratch your nose, turn the music pages, or whatever?

The MKE10 is an omnidirectional mic, so -- like your ears -- doesn't suffer from proximity effect ("bass tip-up") -- only mics which respond to pressure gradients (figure-of-eight, cardioid, hypercardioid) do this.
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Chris Brimley

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Re: Microphones for boxes
« Reply #66 on: August 30, 2014, 06:29:57 PM »

Hmm. Does this perhaps mean that other similar mics, such as the Microvox ones, have poor treble response?  I ask because it has struck me in the past that there's a strange and unnatural sound coming from these systems, which maybe could be improved if different mics were used?
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IanD

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Re: Microphones for boxes
« Reply #67 on: August 30, 2014, 06:36:46 PM »

Hmm. Does this perhaps mean that other similar mics, such as the Microvox ones, have poor treble response?  I ask because it has struck me in the past that there's a strange and unnatural sound coming from these systems, which maybe could be improved if different mics were used?
The mics inside Microvox are omni electret condensers which have a good treble response and no proximity effect. However they're very close to the reeds/pallets and pick up unevenly across the notes, with some nasty comb-effect cancellations for the reeds in between the multiple mic capsules, which is probably why they don't sound natural. The ones I've tried also overload when playing right-hand chords on loud boxes (Oakwood, Binci Baffetti...).
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Theo

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Re: Microphones for boxes
« Reply #68 on: August 30, 2014, 06:36:55 PM »

One possible reason for un-natural sounds with the microcox etc is that they use multiple mic elements and in theory this can introduce some filtering effects when the signals are combined.  I have no idea if this is the case in practice.
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IanD

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Re: Microphones for boxes
« Reply #69 on: August 30, 2014, 06:37:55 PM »

One possible reason for un-natural sounds with the microcox etc is that they use multiple mic elements and in theory this can introduce some filtering effects when the signals are combined.  I have no idea if this is the case in practice.
It is, I could hear it easily when I tried one...
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Chris Brimley

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Re: Microphones for boxes
« Reply #70 on: August 30, 2014, 08:31:46 PM »

OK, but I still felt there were some unnatural sounds going on in terms of frequency response of the mics.  Maybe poor pre-amp?
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IanD

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Re: Microphones for boxes
« Reply #71 on: August 30, 2014, 10:36:15 PM »

OK, but I still felt there were some unnatural sounds going on in terms of frequency response of the mics.  Maybe poor pre-amp?
Most pre-amps are pretty flat. Depends what box they were on, they're very close to the pallets and the end of the box so the tonal balance won't be the same as a mic further away, also if there are any resonances in the enclosed space under the grille they'll pick it up more. I don't like the sound of them either...
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Re: Microphones for boxes
« Reply #72 on: August 30, 2014, 11:07:33 PM »

At Sidmouth the sound at the Ham was almost acceptable at times, the sound at the Bulverton was utterly unacceptable and the sound at the Bedford was really quite nice.

I don't know about the other two,but the Bedford sound is run by Doug Bailey of WildGoose Records, who spends much of his time recording folk performers.
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Owen Woods

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Re: Microphones for boxes
« Reply #73 on: August 31, 2014, 03:34:47 AM »

At Sidmouth the sound at the Ham was almost acceptable at times, the sound at the Bulverton was utterly unacceptable and the sound at the Bedford was really quite nice.

I don't know about the other two,but the Bedford sound is run by Doug Bailey of WildGoose Records, who spends much of his time recording folk performers.

I know. I should point out that I am highly biased in that three close friends of mine were on his team ;) But objectively speaking my previous comment stands.
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Chris Brimley

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Re: Microphones for boxes
« Reply #74 on: August 31, 2014, 12:34:49 PM »

I was slightly perplexed by the implications of your earlier comment, Ian, that the microphone proximity effect does not exist for omni-directional microphones or for the ear.  This was because it seemed to me quite clear that if I put my ear close to a cymbal, I hear a totally different character of sound than l do if I move my ear away - there is much more bass if you are right up to it.

Yet I also understand how the microphone proximity effect arises for directional microphones, because of the way they operate, and that this doesn't apply to an omni-directional microphone.

I'm going to suggest that actually the proximity effect we are dealing with is actually comprised of two separate but additive effects. 

The first is the microphone proximity effect we have been discussing, whereby the receiver of the sound (the microphone) can behave differently from the ear, in terms of frequency response.

The second, and possibly sometimes stronger effect, is I suggest to do with the transmitter of the sound - the sound source.  The explanation of the first effect deals with what happens with a perfect and theoretical point source of sound, suspended in mid-air.  Such a point source would transmit sounds of all frequencies evenly, no matter where you are listening to it from. However that's not what we actually have - we have sound coming from various resonating parts of the accordion, and elements of the accordion are also acting as imperfect baffles.  The baffle effect of loudspeaker surrounds is well-known - low frequency sounds 'go round corners' more easily than high frequencies - baffles stop the low frequency sound waves cancelling themselves out by going 'round the back' of the loudspeaker cone (the sound generator).  That's why adding baffles around a loudspeaker brings out the bass.

I suggest this baffle effect is important.  So if you go close to the accordion, not only can you get the microphone proximity effect on the sound receiver, but the character of the sound it produces at different distances away is actually different as well.  This would explain the cymbal effect I referred to, and it could also explain why it is that there's a noticeable difference in the character of my recordings 20 cm and 50cm away, which the Mic prox effect alone shouldn't be able to explain.  What is more, it could also explain why the Microvox 'very close' system seems (to me) to alter the bass frequency response.

If I'm right in this, it could also mean that close mic systems (indeed all mic systems) should really take into account a whole new set of placing issues, to do with the baffle effect in the instrument's construction, and indeed it becomes quite feasible that different accordions could behave differently.
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Anahata

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Re: Microphones for boxes
« Reply #75 on: August 31, 2014, 04:25:00 PM »

Chris is right that the proximity effect applies to sources as well as mics.
As with mics, it also depends on whether the source is primarily a pressure or velocity transmitter.
Obviously (to me!) a cymbal is a dipole transmitter at low frequencies - like a speaker a speaker driver not mounted on any baffle or box,  every movement of the plate creates equal and opposite positive and negative pressure on the two sides, whic cancel out at a distance. I'd think of a melodeon as a pressure transmitter: positive excursion outside is matched by a negative excursion inside the closed box of the bellows which mostly contains it. By that logic a melodeon doesn't have much proximity effect as a source.

But it's a good point, and not one I had thought of before.

Anyway, whatever the theory, an instrument doesn't sound the same if you put a mic very close...

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IanD

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Re: Microphones for boxes
« Reply #76 on: August 31, 2014, 05:12:28 PM »

Chris is right that the sound close to an instrument is different, but this isn't the mic proximity effect we were talking about; as Anahata said it's whether you're in the near field or far field of the sound, which in turn depends on which bits of the instrument radiate sound and how big and far apart they are. If you're in the far field the sound quality doesn't vary with distance, just the volume; in the near field this isn't the case.

For example, stringed instruments like fiddles and guitars radiate not only from the top plate but also the back of the body, especially at low frequencies. From a normal listening distance the low frequencies often cancel out, with a close mic they don't so you get bass boost. The most obvious example is if you close mic a cymbal, you can get some quite loud low-frequency tones coming through (not surprising if you look at the way they wobble when hit) which are inaudible more than a few feet away because they're out-of-phase for the top and bottom sides and so cancel out.

Like I said, there's a rule of thumb for where the near field to far field transition is, and it's equal to the size of the sound radiating part of the instrument, so about a foot for a melodeon treble end, or several feet for a double bass.

Not knowing about how instruments generate sound also means you don't know how to mic them up; for example not all the sound of a sax comes out of the bell, quite a lot comes out of the open tone holes, and what does come out of the bell -- especially the high overtones -- are quite directional, just like a horn speaker. If you use one mic close to and pointing down the bell the sound is harsh (too much treble) and misses all the sound which comes out of the tone holes which accounts for a lot of the richness, so you end up with a thin harsh sound -- it's what the mic is picking up, but it's not what the instrument sounds like to a listener. It's better to use a mic at least a foot -- preferably more -- away pointing towards both bell and instrument body but off the bell axis, so it picks up a more balanced sound -- this is what good studio engineers do, but not so many live sound engineers. However if the musician insists on using a clip-on mic right in the bell you have to live with it, just like a melodeon...

Easiest instrument to mic up? -- no contest, MJ's recorder. Good mic (and player!), same position every time close to the fipple hole, sounds just like the real thing, sound check usually done in under ten seconds :-)
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syale

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Re: Microphones for boxes
« Reply #77 on: August 31, 2014, 06:26:30 PM »

Would it be a good idea to mic up the treble side of a melodeon with X-Y mics in the vertical plane and placed at a at distance so that the angle of the X-Y spans the length of the grill/buttons. I am not saying bring the X-Y in a stereo feed, just two mono's, so that a rounder sound captures all of keys pressed.

Stephen
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Chris Brimley

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Re: Microphones for boxes
« Reply #78 on: August 31, 2014, 07:09:23 PM »

I would have thought that Stephen's idea has some potential merit over using just one microphone that is less directional, in that it effectively increases the width of the even response along the length of the keys, without broadening it across them.  However, a downside might be that you can only have each of the mics at a maximum of 135 degrees away from the line to the monitor (and it's worse because there's two of them), whereas with the single mic you can achieve pretty much 180 degrees.  However, whatever you do, there is still the point that a directional mic for the LH strictly speaking needs X-Ying against the one for the RH side. (I say that, but to be honest, I gave up doing it because it seemed to my ears that the feedback suppression benefits of each being 180 degrees away from the monitor, with the quite wide spacing between the mics, exceeded the disbenefits from the increased fringe interference effects.)
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Chris Brimley

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Re: Microphones for boxes
« Reply #79 on: August 31, 2014, 07:21:58 PM »

Changing subject a bit, I notice that Bob Mills recommended positioning the monitor behind the accordion.  This would seem to be a somewhat drastic step to take, with a number of other consequences, such as for the other band members, and I'm not convinced it's a good idea.  However it is a good point that personal ear level monitors or monitor earphones could have a beneficial effect in reducing feedback, which in turn could allow you to position your microphones further away, and cut down the close-mic problems we've been discussing.  However I seldom recall seeing such devices on folk music stages, so for musicians who play regularly in such situations, I wouldn't have thought that it's worth redesigning your box-miking system accordingly. 
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