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Author Topic: Stealth binaural mics, how should I mount them? -AND- Bass roll-off questions...  (Read 5017 times)

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Offline bmr

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Picked up a pair of SP-CMC-6 binaurals the other day. Did some outdoor (festival) taping, and was pleased with the result minus the excessive bass that I had to try and remove in post-transfer to the PC.

I recorded a few different bands, and had the mics clipped onto the sides of the bill of my hat for a couple bands and my sunglasses (right where the arms meet the lenses) for the other bands. I went for a 130-degree angle on them when they were on my hat, and straight forward when on my glasses.

My first of two questions is, is there a "proper" direction to mount stealth binaurals? Should the head be facing toward the sky instead of forward?


It was a two day festival, and after hearing the amount of bass in my recordings on the first day I decided to experiment with my bass roll-off settings on my SP-SPSB-1 batt box w/bass roll-off. The first day I used the 107Hz frequency, as I have in the past when I had a pair of cardioids. For the second day (and because I don't know too much about audio and frequencies), I used the next highest frequency, the 160Hz roll-off.

The bass was much more overpowering and punchier than the first day's recordings, and when editing out the bass I had a considerably tougher time making it sound half-decent.

My second question is, did I do the right thing in attempting to cut down on the bass by going up to the next highest available frequency roll-off on my box? Or is there more to it than that? Also, are there any tips or tricks I can utilize in the future to keep the amount of bass under control that I'm not doing right now?

Thanks for any/all answers you guys and gals can provide!

-Brad
« Last Edit: August 30, 2004, 04:27:03 AM by bmr »

Offline Sean Gallemore

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+ moke

Offline bmr

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Wow, thanks Moke!

From what you said, I think I get where the problem's at. I guess my concern now is the bass; the 107 left everything too bassy overall, but the 160 seemed to merely take away the weight of the bass, leaving the punchiness of it but getting rid of the fullness.

This could also be a limitation on my MD, which will be replaced by a NJB3 here shortly. I'll compare and contrast then.

Thanks again!

Offline Sean Gallemore

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If you want to get rid of any bass problems with those mics, go phantom

Offline bmr

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If you want to get rid of any bass problems with those mics, go phantom

I'm sorry, please treat me like the retard I am and explain the 'go phanom' part if you'd be so kind.

The only 'phantom' I know of is phantom power...which I've been told is not the way to go with these mics, hence the battery box...??

I'm sure I'm off on this one...educate me please.

Offline Sean Gallemore

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nope, you're right on.  These mics are perfect for phantom power.

Offline goose

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Hey Brad, which festival did you record?  Shoot me a PM and I'll help you out with the phantom power questions.

Offline jk labs

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Good posting Moke! And watch out, I can give out +T now!!

One more thing to aware of wrt bass is the effect of nearby boundaries (floor sidewall, rearwall and ceiling) and how
these affects the bass response in omni mics through mirror effects. 

I didn't find a good link pertaining to recording situations but the one included does explain the problem to some degree
http://www.realtraps.com/art_small_rooms.htm

-J

Offline jk labs

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thats quite a threat there Jon ;D
so let me take you out with a +T of my own,.....


one good thing about music, when it hits you feel no pain    bmw


these "mirror effects" would be lessened by baffling the omnis, via a dampening effect of reflected frequencies by isolating it to one mic or the other,... wouldn't it?

You can put the mics in a "shadow", say by the head much as you suggested, but below 500 Hz (wavelenghts 0.66 meter and longer) the head "looks" _very_ small and does just about nothing. Curves for the hrtf vs frequency for sources at -90 degrees shows little effect on the bass that is troublesome for most tapers. (Ok so I stole one graph .... )

The baffles on your Jecklin disk will work likewise, they will be effective down to a frequency scaling with the size of the obstacle. But on playback our ears aren't very good at picking out where the bass is coming from, due to the hrtf, so imaging is fine :-)  Accident or nice planning by nature?

  -J

 
« Last Edit: September 07, 2004, 06:20:32 PM by jk labs »

Offline jk labs

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interesting, many thanks!!

My personal statement / thought about the bass issue was based on my recordings of a 2x sized contrabass in acoustic recordings. I can easily "isolate" him in his position with the baffle. It is not true single channel isolation, but he is always solidly dominant in the right channel of my recordings, and the time delay/ signal intensity difference that does get by the baffle only reinforces the size of the soundstage, (at least from what I hear in my playback).
I compare my recordings with a baffle vs. an a/b pair of earthworks omni's, quite often on the same stand, and you can definitely hear where the baffle adds a stereo panning cohesiveness that the a/b pair lacks.
The a/b pair is much more susceptible to cross channel bleeding that confuses the listener as to the real location of the players. layperson babbling,.........

many thanks again Jon, your posts are always well recevied (at least the ones I can understand ;D )


Thanks ;D

I was thinking mostly about the amplitude in my reply - relating a little back to the original question of too much bass.
But I imagine your baffle adds to the phase shift and contributes to source separation through that mechanism as well.

You have obviosly found a mic placement/mounting solution that works well for you and that is what counts.

I am willing to accept that above some relatively well-defined frequency the effect of the baffle kicks in
(probably at about 6 dB/ octave) but I _speculate_ that this frequency just might be a bit higher
than what one would hope for, and that the harmonics play a significant role in the ability to localize the contrabass.   

An interesting test one could undertake at home is to use one speaker and feed it 1/3 octave wobble tones (to avoid setting up standing waves) and then see how high you have to go in frequency before the microphone array manages to distinguish directions.

Such a test would be challenging to execute indoors due reflections off of boundaries: that bass will reach the mics from several directions simultaneously.



  - J
« Last Edit: September 07, 2004, 08:19:13 PM by jk labs »

Offline bmr

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Re: Stealth binaural mics, how should I mount them? -AND- Bass roll-off question
« Reply #10 on: September 09, 2004, 04:46:49 AM »
I sent a PM to goose, but he hasn't had a chance to get back to me...and as my decision on whether or not to get a NJB3 approaches, I wanted to put my comments and questions I asked here up for public discussion in hopes of understanding what the hell I'm doing a little better than I did when I woke up this morning.

(oh, and goose's comments from a previous message are enclosed in brackets, my comments are not.)

<<<<Schwilly is referring to a modification of the mic cabling/cable termination that will allow the mics you have to acheive their best results - which are much better than the current configuration.  You may or may not want to make the modification.  Search the links for 853 modification or something like that, and there are a couple posts with play by play and pictures of the modification.

The way your mics are currently terminated, the battery box is the only way to go.  If you have bass roll off available, use it.  If it is adjustable - use something higher.  The higher from the ground you keep omnis, the better they will sound - there is more bass closer to the ground.

If you are running line in, then bass roll off settings are nullified and no bass roll off is present - this is due to the difference in mic and line level.  Bass roll off only really works going mic-in.  As an example, Bass roll off set at 88hz going mic in will have the exact same roll of as the 888mz setting going line in.  If 888 is an option, use it for line in.  I would think around 120 if mic in.

Oh yeah, Sound Pros has a new kit for modifying the mics - look at their website.  May be easier to find than searching this site.>>>>

I see the SP mod on their site, but I'm not entirely sure what that will leave me with...XLR connectors? I was always under the impression that "phantom power" meant power from the unit it's connected to (with no additional power supply), as in to the minidisc, but I'm getting the impression that the mod for phantom power implies a 48v battery (pack? box?) would be needed instead.

I'm looking at the thread here - http://www.taperssection.com/yabbse/index.php?topic=18846.0 - in the first photo shown, there's two minijacks...my mics have one, so how would that change things? It seems that, for the mod to work, I'd need to have two minijacks from the get go. I guess my confusion is that I'm missing some basic definitions on what phantom power really is and how I should go about getting the most from my mics.

I'm a bit lost now...is the inefficiency of the battery box I have now with a line-in connection something that's isolated to these mics and similar models? My previous mics seemed to work fine with the bass roll-off on the battery box, but those were cardioids.

If you had my mics, what type of setup (from top to bottom, mics to recorder) would you go with in order to maximize the effectiveness of my mics?

<<<<Cardioids will make a difference, though omnis can sound better, but must be in the right circumstances.  Street Scene is a tough place to tape.  For the type of recording you were doing, the best would probably have been to get as near to one of the speaker stacks (and hold on!) as you could.  I got a jukebox3 recently - I like it.  I have not used it for mic or line in recording, and don't really plan to.>>>>

Do you use the jukebox with the optical in? Coming from something like an Edirol UA5 (that's the first product that I could think of that is one of those 'middle man' items in a rig, but I know there's tons more out there like it)? Also, did you get your jukebox new or used? My girlfriend's looking to buy it for me, and she would rather be able to find it somewhere new instead of going out on ebay or a forum or listserv for a refurb or used one...and is trying to avoid me just having to go out and buy it myself, hehe. I just can't find it anywhere new that has it in stock, but I'd love to hear of a store or a site if you know of one.

Assuming that I get a jukebox...I'd want to run optical in, which I guess would mean I'd have to have something like the UA5...which would mean that with my mics, I'd somehow have to get some sort of XLR adapter put on there, which I don't know how I'd do since there's only one 1/8" minijack coming off my mics instead of the two I'm seeing in other pictures.

<<<<Give me some more information on your setup at the show - where were you, where were the mics, which recorder, relevant recorder settings?>>>>

I was approximately 20' back from the stage, dead center. The mics were clipped to my sunglasses, where the arm of the glasses meets the lenses. I had a hat on, as later in the evening I wanted to record with the mics on my hat to see if there was any sort of noticeable difference (there wasn't). I used my Sharp MD60 minidisc, line in, through the SP-SPSB-1 battery box with roll-off at 160Hz.

======================


So, basically, I'm just curious as to what, if I use these mics, and have an NJB3 or D100 at the end of the line, I should be using to get maximum output from them. From mics to pres to battery boxes (or phantoms, which I'm apparently a bit confused on) to A/Ds to whatever, for a stealther, what should I be going with? And since I'll be doing most of my recordings in small clubs (which I know my mics aren't definitely meant for), is there anything that I can do, which could be explained in relatively simple english, to control the bass of the recordings?

I'm sorry for being such a dunce about all of this, and for asking so many dumb questions...but I figure that if I'm going to do this, I'd like to do it right, and understand it as I'm doing it.
« Last Edit: September 09, 2004, 04:50:24 AM by bmr »

Offline bmr

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Re: Stealth binaural mics, how should I mount them? -AND- Bass roll-off question
« Reply #11 on: September 13, 2004, 09:26:21 PM »
Here's my pity bump for help...seems like I re-killed the thread...

Offline jk labs

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Re: Stealth binaural mics, how should I mount them? -AND- Bass roll-off question
« Reply #12 on: September 13, 2004, 10:54:52 PM »
Here's my pity bump for help...seems like I re-killed the thread...

It was a huge posting!  What were the Qs again?

A) Given omnis you ought to position them close to the desired source in order to get acceptable "signal to audience noise ratio". 

B) Stay away from, or be ON, boundaries ("ON" as in utilizing the pzm principle to increase s/n)

C) Small diameter omnis are close to perfectly omnidirectional ;D. Pointing them here or there might not result in much sonic difference.   

D) Omni mics can easily be made to pick up even the deepest bass well. This feature often results in overpowering bass when recording amplified music over PA systems.  Strong bass might bring the sound pressure level (SPL) above what the mic can handle. A bass cut filter downstream, say in the battery box, will not help on this problem.   

E) The max SPL that the mics can handle, before audible compression effects occur, does depend on the diaphragm, internal electronics and external powering scheme. For the AT line of mics, or rather the particular ones often mentioned in this forum, the method of powering does make a difference. Much could be said but I'll stay out of the "benefits of the 48 volts" issue as I'm working on a solution to this now.

F) As for this or that recorder: Enjoy the music. Harvest experience. Experiment. Trust your ears.

« Last Edit: September 14, 2004, 01:24:03 AM by jk labs »

Offline bmr

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Re: Stealth binaural mics, how should I mount them? -AND- Bass roll-off question
« Reply #13 on: September 14, 2004, 11:15:14 AM »
E) The max SPL that the mics can handle, before audible compression effects occur, does depend on the diaphragm, internal electronics and external powering scheme. For the AT line of mics, or rather the particular ones often mentioned in this forum, the method of powering does make a difference. Much could be said but I'll stay out of the "benefits of the 48 volts" issue as I'm working on a solution to this now.

This is probably what I'm most interested in...I'd like to know what I should have in place of that roll-off box if that isn't going to do the job...

I'm also curious as to why these mics and the battbox/roll-off are "incompatible" with each other. If they don't work well together, that's fine, whatever...I'd just like to know why so I can avoid that sort of thing in the future.

Offline jk labs

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Re: Stealth binaural mics, how should I mount them? -AND- Bass roll-off question
« Reply #14 on: September 14, 2004, 07:12:05 PM »
E) The max SPL that the mics can handle, before audible compression effects occur, does depend on the diaphragm, internal electronics and external powering scheme. For the AT line of mics, or rather the particular ones often mentioned in this forum, the method of powering does make a difference. Much could be said but I'll stay out of the "benefits of the 48 volts" issue as I'm working on a solution to this now.

This is probably what I'm most interested in...I'd like to know what I should have in place of that roll-off box if that isn't going to do the job...

I'm also curious as to why these mics and the battbox/roll-off are "incompatible" with each other. If they don't work well together, that's fine, whatever...I'd just like to know why so I can avoid that sort of thing in the future.

Incompatible is a strong word :-) There are limitations inherent in all the different powering schemes
possible.

It's a fact that for the AT943 f.ex, the P48 method of powering allows a noticeably higher SPL to be recorded before distortion occurs. See the datasheets at www..AT for the exact numbers (123 dB SPL on 9V & 135 dB SPL on P48? - something like that). This may or may not be an issue in your application.

To be able to use the P48 powering method, each AT943 (853 etc) needs to be terminated in
it's own 3 pin Tini-QG (aka miniXLR) into an AT8533, Samson PM-4 or equivalent.
 
S/N ratio is reported to be better on P48 as well. THD will be lower.

The P48 method will not miracoulously turn your ATs into Gefells. But it will change the working conditions for the electronics inside the mic head.   

A taper is going to send me a pair of AT943s to work on. In 6 weeks or so I might release some performance data comparing a few different methods of powering  - if my compact solution is better still that is :-) Before then this is about, well almost, all I know.
« Last Edit: September 15, 2004, 04:34:28 AM by jk labs »

 

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