naturerecordists
[Top] [All Lists]

Re: [Nature Recordists] Re: Infrasound microphone

To:
Subject: Re: [Nature Recordists] Re: Infrasound microphone
From: Eric Benjamin <>
Date: Wednesday, July 28, 2010, 3:30 PM





=C2=A0









      > James Shatto <> wrote:

> I got the MM-1's to IMPROVE the low end



And I have no doubt that it did that.  My counter-recommendation is based o=
n

incomplete data.  Let me explain.



I know that the MM-1 is spec'd as having flat response +0.1 / -0.5 dB from =
20 Hz

to 20 kHz, and elsewhere it's stated to have 10 Hz to 20 kHz bandwidth.  It=
's

also stated that the input and output are transformer coupled. The unit tha=
t I

had experience with was being used for theatre calibration and that system =
was

returning results that were inconsistent with other measurements.  This was=
 in

conjunction with an array of Countryman B3 lavalier microphones.  I measure=
d the

system of preamp and microphones and it was considerably attenuated at 20 H=
z

relative to the midband.  I measured the microphones and they were flat to =
20

Hz.  My conclusion is that it was the preamp that was at fault.  But that c=
ould

be due to a system level problem and not necessarily to either the preamp o=
r the

microphones individually.  Microphones that are capacitively coupled on the=


output have an impedance that rises towards low frequencies.  Preamps that =
are

transformer coupled have an impedance that falls at low frequencies.  The

combination of the two could result in a rapid roll-off of low frequencies,=


depending on exactly what components are being used.



So my recommendation is basically that, if your intention is to record

infrasound then a transformer coupled preamp is not the way to go.  If you=


really want to know how the recording system performs at low frequencies th=
en

it's probably necessary to test the system as a whole.



Eric




From: James Shatto <>

To: 

Sent: Wed, July 28, 2010 8:24:50 AM

Subject: Re: [Nature Recordists] Re: Infrasound microphone



Heh.  I got the MM-1's to IMPROVE the low end.  And they do just that relat=
ive

to the preamps on my Korg MR-1000.  My Avenson STO-2's are still a little l=
ight

in the low end in general, plus high in the noise floor.  I also got the MM=
-1's

to improve battery life by moving the phantom power burden off the field

recorder.  And they do just that.  2.5 hours on fully and freshly charged N=
iMH

batts for the Korg by itself.  2 hours or less if the batts were charged a =
week

ago and left in the off field recorder.  With the MM-1's, in addition to th=
e

Korg, I've done 4 hours continuous and the field recorder still showed 50% =
on

the meter.  Which takes about 30 minutes to go past with just the field rec=
order

and phantom powered STO-2's.



EQ is your friend.  Not really doable at those frequencies live though.  Ba=
ring

some DIY and other custom electronics.  You also need a monitoring environm=
ent

capable of producing those tones to hear what you recorded.  Otherwise you =
might

need to double the speed or more to bring those frequencies up to the

reproducable range depending on your gear.  Audacity has some tools to anal=
yze

and filter and EQ.



Even if your headphones are spec'd to 5Hz, they probably don't actually pro=
duce

that.  And wind noise and other things can be in that range, so there's not=
 much

proofness in such content.  Although using that range as a location detecto=
r

might be interesting.  Those lower frequencies don't travel as well over

distance in air.  Visions of indians with their ear to the ground come to m=
ind.

I guess I should have done more school.  It's feasible to make a locator wi=
th

three points in contact with the ground.  Strength and timing to each senso=
r

(mic) to determine a direction.  Much like earthquakes and the use of three=


points to determine the epicenter.  I'm not sure how useful it'd be without=
 hard

data to single out the subject from deer, bear, squirrel, wolf, wildcat, mo=
ose,

and whatever other critters.  It's a noisy world out there.  And you'd only=
 be

able to detect when the subject was moving.  And trying to find / catch up =
with

a moving

target might be an exercise in futility.



I've had SM81's that were decent on the low end.  No measurements though.  =
Just

a hankering for some Tuba.  An old AT4033a was pretty sweet on the low side=
.  A

current AT3035 that is okay down low.  Noticeably better than my STO-2's.  =
None

of which I'd want to use outdoors since wind proofing them would be near

impossible.  Plus you need some decent shock mounts or it's all handling no=
ise.

Special cables and other things to further isolate them from the rigging.  =
Good

luck with that as that range is probably the most difficult to do well.  I'=
ve

been longing for some MKH8020's which spec okay down there according to the=


manufacturer anyway.  But not cheap, and not the most favored of the not ch=
eap

mics.



- James



--- On Wed, 7/28/10, Eric Benjamin <> wrote:



From: Eric Benjamin <>

Subject: Re: [Nature Recordists] Re: Infrasound microphone

To: 

Date: Wednesday, July 28, 2010, 1:16 AM



stancourtney  <> wrote:



> ...I am not sure what frequency response I need.



While I'm not at all sure about Sasquatch recording, your recording problem=
 is



similar to many in that you don't know exactly what you need, because you



haven't done it before.  Given that you describe having heard/felt the soun=
ds



that you are interested in recording, I suppose that we would call that nea=
r



infrasound in the terminology of the web pages at:



http://www.esrl.noaa.gov/psd/programs/infrasound/infrasonic.html



I had originally assumed that you want to record sounds for later analysis =
but



not I'm guessing that you also would like to listen to the sound.  That bri=
ngs



up the problem of reproducing the recorded LF sounds, but that's another pr=
oblem



for another forum.



I have had some experiences with the Sound Devices MM-1 in which it had



insufficient bass response.  Unfortunately I no longer have access to any o=
f



that data so I can't say anything specific, other than that other preamps m=
ay



give better performance in this application.



In contrast to another reply, I would say that the choice of microphone sho=
uld



be the first thing to check, and not the recorder; if the low frequency sou=
nds



don't make it through the microphone then it doesn't matter what the record=
er



does.



I do a lot of measurements of recording equipment.  Looking over the few



omnidirectional microphones in my collection, my Audio Technica AT3032 is d=
own



only a few tenths of a dB at 10 Hz, a microflown p-u 'match' probe rolls of=
f



below 100 Hz, a Schoeps Mk2 rolls off at about 23 Hz, Earthworks M30 is dow=
n



just 0.2 dB at 10 Hz, Shure MX183s roll off at about 40 Hz (I'm sure that's=
 the



adapter), a microphone based on the Knowles FG capsule is down 4 dB at 10 H=
z, a



studio projects C4 capsule on a Rode NT5 body was down 0 at 10 Hz (but not=




nearly as good as that on the C4 body).



It seems likely that the Rode NT5 with their new omni capsule would be a go=
od,



low-cost microphone for low-frequency recording.



Your qyery has caued me to expand the range over which I usually test frequ=
ency



response.  I usually go down to 10 Hz but I can extend those measurements d=
own



to 1 Hz or so.  I  have just one portable recorder at present and that's th=
e



Zoom H2, because it records 4 channels.  If you use the microphone inputs i=
t



starts to roll off at 40 Hz and it's about 32 dB down at 1 Hz.  Going in th=
rough



the line inputs it's 3 dB down at 7 Hz and 22 dB  down at 1 Hz.



I want to point out that, just because the recorder or the microphone rolls=
 off



a bit doesn't mean that you can't make a usable recording.  It's quite



reasonable to equalize out the frequency response roll-offs for either the=




purposes of listening or analysis of the files.  If I wanted to make a reco=
rding



that goes down to 10 Hz, I'd just use what I've got.  If I wanted to go dow=
n to



1 Hz I'd have to do some modification of my existing equipment.  Precisely =
what



I would do would depend on whether I could take a laptop into the recording=




situation.



If you would like to see any of these measurements let me know and I'll pub=
lish



some graphs to our web site.



Eric






From: stancourtney <>



To: 



Sent: Tue, July 27, 2010 7:17:56 PM



Subject: [Nature Recordists] Re: Infrasound microphone



Thanks for all the replies.



Although I am interested in all nature recording I do have a special



interest in sasquatch research.  Most serious researchers shy away from



any discussion of the subject. I can understand that view.



Many bigfoot / sasquatch researchers have had experiences in areas of



bigfoot sightings with what they consider to be infrasound. Symptoms



have been various from tingling, paralysis, nausea, fear and dread. Some



of these symptoms may also be associated with pheromones.



I recently had a major experience in the Blue Mountains of Washington



State. I won't discuss it here but you can read my post at:



http://www.stancourtney.com/wordpress/2010/07/26/infra-sound-in-the-blues/=




recording I do have a special interest in sasquatch research. Most



serious researchers shy away from any discussion of the subject. I can



understand that view. Many bigfoot / sasquatch researchers have had



experiences in areas of bigfoot sightings with what they consider to be



infrasound. Symptoms have been various from tingling, paralysis, nausea,



fear and dread. Some of these symptoms may also be associated with



pheromones. I recently had a major experience in the Blue Mountains of



Washington State. I won't discuss it here but you can read my post at:



http://www.stancourtney.com/wordpress/2010/07/26/infra-sound-in-the-blue | =
Reply

to group | Reply via web post | Start a New Topic Messages in this topic (9=
)



Recent Activity:        * New Members 3         * New Files 1

Visit Your Group

"While a picture is worth a thousand words, a

sound is worth a thousand pictures." R. Murray Schafer via Bernie Krause



MARKETPLACE

Stay on top of your group activity without leaving the page you're on - Get=
 the

Yahoo! Toolbar now.






Get great advice about dogs and cats.  Visit the Dog & Cat Answers Center.=







Hobbies & Activities Zone: Find others who share your passions! Explore new=


interests.



Switch to: Text-Only, Daily Digest =E2=80=A2 Unsubscribe =E2=80=A2 Terms of=
 Use

.



































<Prev in Thread] Current Thread [Next in Thread>
Admin

The University of NSW School of Computer and Engineering takes no responsibility for the contents of this archive. It is purely a compilation of material sent by many people to the naturerecordists mailing list. It has not been checked for accuracy nor its content verified in any way. If you wish to get material removed from the archive or have other queries about the archive e-mail Andrew Taylor at this address: andrewt@cse.unsw.EDU.AU