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Old 14th November 2012, 04:16 AM   #29301
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Quote:
Originally Posted by Wavebourn View Post
Try my record above, the helicopter and rain had been recorded by couple of 22 mm cardioids.

Frogs were recorded by an array of 5 Panasonic omni-capsules.

Where LF is more limited? Sounds like real pressure-gradient mikes recorded LF better than pressure mikes in counter-phase, despite of beliefs.
What were the 22mm cardioids?

Nice recording but they sound typical cardioid with LF roll-off. There's a couple of JHRoy's recordings on ambisonia with frogs. Also some by others with severe LF filtering. I did the digital filters for Roy's mike so I know what the LF response is.

ambisonia just moved to a new server and some stuff has been lost especially the DTS decodes . Many of the files were on torrents cos they were huge.

Try Ambisonic Info | John Leonard for helicopters with correct LF.

If you know of cardioids with better LF response than the true 50Hz of Shure SM81, I'm interested. But please don't just quote the maker's spec. I have a very short list on Yahoo MicBuilders in my Ricardo directory.

Last edited by kgrlee; 14th November 2012 at 04:46 AM.
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Old 14th November 2012, 04:51 AM   #29302
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Quote:
Originally Posted by kgrlee View Post
There's a couple of JHRoy's recordings on ambisonia with frogs. Also some by others with severe LF filtering. I did the digital filters for Roy's mike so I know what the LF response is.
If you download the *.amb files and use VVMic to simulate cardioids, you'll hear what a cardioid flat to 25Hz sounds like. TetraMic is flat to 25Hz too. The Mk4 only to 27Hz.
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Old 14th November 2012, 06:26 AM   #29303
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Quote:
Originally Posted by kgrlee View Post
What were the 22mm cardioids?

Nice recording but they sound typical cardioid with LF roll-off. There's a couple of JHRoy's recordings on ambisonia with frogs. Also some by others with severe LF filtering. I did the digital filters for Roy's mike so I know what the LF response is.
Absolutely not. That helicopter shakes my sofas pretty nice. Capsules were Chinese, from MXL-770 microphones. Electronics was mine, with Tamura transformers oversized for such level, so no rol-off caused by them. I wanted to show you the spectrum picture, but my Audacity under Linux was not compiled with mp3 support, unfortunately. I don't have that original anymore, unfortunately, only compressed file left. And I don't have that prototypes, they live in Boston now. But you can download and check it, I am sure it goes well at least from 10 Hz.

Frogs were recorded by my array with Panasonic capsules. No roll-off as well, just a matrix for figure 8 with flatter rear side. But you hear roll-off there, despite of omni capsules. It was the point I meant.

Quote:
ambisonia just moved to a new server and some stuff has been lost especially the DTS decodes . Many of the files were on torrents cos they were huge.

Try Ambisonic Info | John Leonard for helicopters with correct LF.

If you know of cardioids with better LF response than the true 50Hz of Shure SM81, I'm interested. But please don't just quote the maker's spec. I have a very short list on Yahoo MicBuilders in my Ricardo directory.
What's so special in Shure SM81? It is rated for up to 20 KHz, so capsule is probably 12 mm only, or even smaller. But I suspect it is quite thin, probably 3 microns, while capsules that I used for helicopter were 6 micron thick, but 22 mm in diameter. I don't have precise acoustic measurement equipment, but judging by comparison with Behringer measurement microphone that I used to calibrate my speakers at home, it was flat at least from 20 Hz. Here is the picture I recorded attached, using this microphone back in 2008, you see roll off at highs caused by the microphone, but lows were pretty flat. I don't see any problem to make a mike that goes below 50 Hz.

Click the image to open in full size.
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Old 14th November 2012, 07:28 AM   #29304
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Originally Posted by Wavebourn View Post
Absolutely not. That helicopter shakes my sofas pretty nice. Capsules were Chinese, from MXL-770 microphones.
We don't have recordings recorded simultaneously with both your mikes and mine so all we can do is compare similar recordings. Why don't you try John Leonard's helicopters and tell us which one you think is closest to what you recorded?

Quote:
Frogs were recorded by my array with Panasonic capsules. No roll-off as well, just a matrix for figure 8 with flatter rear side. But you hear roll-off there, despite of omni capsules.
If you are simulating fig-8s with pairs of omnis you will have severe LF roll-off.

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What's so special in Shure SM81? It is rated for up to 20 KHz, so ... but judging by comparison with Behringer measurement microphone that I used to calibrate my speakers at home, it was flat at least from 20 Hz. Here is the picture I recorded attached, using this microphone back in 2008, you see roll off at highs caused by the microphone, but lows were pretty flat.
The SM81 is one of 2 cardioids you can buy today with flat response to 50Hz in free-field conditions. It one of the 2 most extended cardioids you can buy.

If you get to compare your mikes with your SM81, I would really appreciate your comments on the difference in bass response.

What size FFT block are you using with ARTA? Are you windowing? What distance was the source you used to you measure the mikes? What source?

A cardioid -3dB @ 50Hz in free-field will measure flat to 20Hz at 1m from a 'point' source. Most (all?) 'measurements' of cardioids flat to 20Hz are done by the Marketing VP.

There is a discussion of this on the DPA site. A cardioid flat to below 50Hz will show a substantial rise at LF.

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I don't see any problem to make a mike that goes below 50 Hz.
Maybe not for omnis .. but I seem to be the only one to do this for fig-8s & cardioids

On a more serious note, there is an excellent PDF book on the Neumann website which is the only accurate and useful book on mike design I've come across. It explains some of the 'problems'.

Also, from your measurement of SM81, you might want to have your ECM8000 calibrated at HF but be careful who you ask to do this.

Last edited by kgrlee; 14th November 2012 at 07:38 AM.
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Old 14th November 2012, 10:28 AM   #29305
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Default Helicopter Recording Spectrums

Not that it means anything ... different helicopters, different flight patterns etc but here are the spectrums of Wave's & John's helicopters analysed as requested.

23s just before the overload on Wave's
21s around the max. level on John's cos his is 48kHz fs

Vert. scale is 50dB. Horizontal scale 10Hz - 20kHz ie B&K 2307 bogroll
Hanning windowing (smoothing)

I've matched levels @ 1kHz but one could argue I should match between 100Hz & 500Hz as I expect both mikes to be sorta flat in that region and there's a lot of helicopter noise there.

If anyone has made direct comparisons of any cardioid with SM81, I'm interested in those that sound more extended. And even more interested if you've made simultaneous recordings that demonstrate this.
Attached Images
File Type: gif helicopterSpectrums.GIF (19.4 KB, 163 views)
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Old 14th November 2012, 04:30 PM   #29306
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Looks like there were different helicopters, but never the less Chinese copy of Neuman capsule goes well on 30 Hz.
I designed that mic and build couple of prototypes back in January 2006. Last time I tried them with Arta (the picture) was back in May 2008. I don't remember all details, sorry.

Anatoliy
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Old 14th November 2012, 05:28 PM   #29307
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Details of records: when I recorded that helicopter I put microphones about 1 meter (3 feet) from the wall, under the roof edge of my barn. I wanted to record the rain. That curve in the room was recorded on a distance about 5 meters from woofers, about 2.5 meters from the rear wall. Sub is under the left wall (opening in the floor) about 2.5 meters left. I did not test the mic then, I replaced the amp for the sub, and measured relative levels of the sub, woofers, and line arrays in the wall.
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Old 14th November 2012, 06:44 PM   #29308
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Quote:
Originally Posted by kgrlee View Post
If you are simulating fig-8s with pairs of omnis you will have severe LF roll-off.
Yes, if not to equalize properly the difference in response of front and rear capsules.
You can't fool the physics, but you can model a pressure gradient mic from 2 pressure capsules.

Quote:
The SM81 is one of 2 cardioids you can buy today with flat response to 50Hz in free-field conditions. It one of the 2 most extended cardioids you can buy.
Again, I don't see what's so special in them. Judging from datasheet, they were measured on 1 meter. You can measure mine on the same distance, and may get probably even better results.

Quote:
If you get to compare your mikes with your SM81, I would really appreciate your comments on the difference in bass response.
I don't have SM81. But I will probably need to find some lab to measure some mics. I am going to make some array from optical capsules. And to finish a stereo mic prototype with pair of Chinese copies of Numan capsules. If Scott Wurcer is serious about the lab, I may go there.

Quote:
On a more serious note, there is an excellent PDF book on the Neumann website which is the only accurate and useful book on mike design I've come across. It explains some of the 'problems'.
Nicht sprechen.

Quote:
Also, from your measurement of SM81, you might want to have your ECM8000 calibrated at HF but be careful who you ask to do this.
It was not SM81 measurement. If was testing of my speakers using my own mic prototype.

PS: Sorry John for microphone & helicopter off-topic!
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Old 14th November 2012, 08:07 PM   #29309
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Quote:
Originally Posted by kgrlee View Post
23s just before the overload on Wave's
21s around the max. level on John's cos his is 48kHz fs
Got small speakers to reproduce this 'copter LF sound at same/realistic levels?

A music source that all can hear with bass prominant, deep and clear is this album/CD : Hellecasters Jam Tracks by Will Ray.

Last edited by RNMarsh; 14th November 2012 at 08:09 PM.
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Old 14th November 2012, 08:52 PM   #29310
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Got small speakers to reproduce this 'copter LF sound at same/realistic levels?
In my HT it sounds quite real. Sofas are shaking nice.
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