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Author Topic: DPA 4090 + 20 mm APE  (Read 831 times)

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Offline Organfreak

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DPA 4090 + 20 mm APE
« on: February 14, 2022, 09:40:29 AM »
In an attempt to use my DPA 4090 for more distance recording of pipe organs in churches, I have made a 20 mm wooden-ball shaped APE to fit on top. It works to enhance the clarity, but I wonder how the flat frequency response will be changed by this attachment. I use it with the mics in vertical upward direction.
I guess - as a 40 mm APE has a shallow bump centered at about 5 kHz, this 20 mm one will have a flat hill, centered at 10 kHz, with a maximum rise of about 2 dB?
Mics: Rode NT55, DPA 4090, Beyerdynamic M101
Pres: Lake People C360, M-Audio DMP3
Recorders: Marantz PMD661 OADE super mod & plus mod, Denon DN-F450R, Zoom F6

Offline Gutbucket

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Re: DPA 4090 + 20 mm APE
« Reply #1 on: February 14, 2022, 02:22:08 PM »
Nice looking machining.

You can see the relative response effect of various sized APE ball attachments here: https://www.dpamicrophones.com/mic-university/acoustic-modification-accessories

Your 20mm ball is 10mm smaller in diameter than the smallest of the three shown on that page, but the general trend is apparent.  Expect the on-axis response bump to be centered around 5-7kHz, with a bit less emphasis than what is shown for the 30mm APE. 

When viewing those, remember that the polar response diagrams are normalized to a flat on-axis response, so the effect of the response bump is sort of buried in the polars by the normalization. One take away of that is the true polar response is actually wider than indicated in the region where the on-axis response is bumped up.  In other words, you don't see the "bump" directly in the polars, and the off-axis polar angle responses are affected just like the on-axis normalization so if trying to determine the response at say 90-degrees by looking at the polar graph, you sort of need to look at the plot lines and shift them outward by a few dB within the range of the "bump".   So if you point the microphone upward with ball attachment installed, the clarity enhancement effect of the response bump will be applied to the pickup of sound arriving from the ceiling direction.  At 90 degrees off-axis, the response bump and off-axis roll-off more or less cancel each other out, leaving just the higher frequency roll-off where the "presence range" bump response tapers back down again. Beyond 90-degrees pickup will be somewhat less present and less bright.
 
With the attachment in place, the change in response will be tied to the direction in which you orient the microphone.  The increased clarity effect will be apparent on-axis, while moving off-axis the response will transition the opposite way.  Averaged across all directions, overall sensitivity remains about the same with and without the ball attachment in place.  In essence use of the attachment shifts the balance of high frequency sensitivity toward on-axis by simultaneously reducing sensitivity in that range from off-axis directions. With the ball attachment, sounds arriving on-axis will "see" the response bump, whereas sounds arriving from off-axis will see a corresponding roll-off that increases with off-axis angle, generally.

Most of the time when APE spheres are used the microphones are pointed toward the source, causing on-axis pickup of the source to become somewhat brighter and clearer, due to the bump in the "clarity presence" range on-axis.  However, you can "tune" how much of that high-frequency emphasis is imparted to the source by pointing the microphone more toward or away from the source.  The ball attachment amplifies that effect.  With an omni as small as the 4090 is without the ball attachment installed on it that angular response tuning effect may not be apparent.  With the ball attachment in place it should be. 

The farther away the omni is from the source, the more likely it will be that pointing the microphone at the source with the ball attachment installed is appropriate.

The ball attachments can be used simply as an on-axis response modifier (in combination with microphone angle as mentioned), but the most productive use of ball attachments in my way of thinking is in combination with EQ across the same frequency range that the attachment modifies.  In that way you can un-link the frequency response modification aspect of the attachment from its polar modification aspect.  Point the microphone with the polar-response modification aspect in mind, then alter the frequency-response aspect of the direct sound pickup form the source as needed.  In that way you gain some degree of control over both both frequency response and directionality in the high frequency range.
« Last Edit: February 14, 2022, 05:02:57 PM by Gutbucket »
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Offline Gutbucket

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Re: DPA 4090 + 20 mm APE
« Reply #2 on: February 14, 2022, 05:05:47 PM »
Just a heads up for anyone who may have read my post immediately above before I made a few edits.  It's hopefully somewhat more clear and flushed out now.
musical volition > vibrations > voltages > numeric values > voltages > vibrations> virtual teleportation time-machine experience
Better recording made easy - >>Improved PAS table<< | Made excellent- >>click here to download the Oddball Microphone Technique illustrated PDF booklet<< (note: This is a 1st draft, now several years old and in need of revision!  Stay tuned)

Offline fireonshakedwnstreet

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Re: DPA 4090 + 20 mm APE
« Reply #3 on: February 14, 2022, 05:54:21 PM »
Looks awesome! I use homemade ones using gb's Nerf ball design and they do help with the presence from further back.
Mics: AT 3031; AT 853Rx (C,O); CA-14(c); Studio Projects C4 (C,O,H); Nak 300; JVC M510
Recorders: Tascam DR-680 MkII; Tascam DR-70D; Tascam DR-5; Tascam DR-2D
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Offline Organfreak

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Re: DPA 4090 + 20 mm APE
« Reply #4 on: February 15, 2022, 03:35:53 AM »
Looks awesome! I use homemade ones using gb's Nerf ball design and they do help with the presence from further back.

I used simply wooden beads, 20 mm diameter, predrilled with a 4 mm hole. The tip diameter of the DPA 4090 is 6.7 mm. I first drilled the bead completely through, using a 6.5 mm drill, that makes a nice press fit at the tip of about -0.2 mm. After that I opened the inner side of the 20 mm bead further, using subsequent drills of 8 mm and 10 mm.
Mics: Rode NT55, DPA 4090, Beyerdynamic M101
Pres: Lake People C360, M-Audio DMP3
Recorders: Marantz PMD661 OADE super mod & plus mod, Denon DN-F450R, Zoom F6

Offline Organfreak

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Re: DPA 4090 + 20 mm APE
« Reply #5 on: February 15, 2022, 05:52:10 AM »
Just a heads up for anyone who may have read my post immediately above before I made a few edits.  It's hopefully somewhat more clear and flushed out now.

Thanks Gutbucket for your clear explanation!

I do however not completely understand theory - practice with regard to the location and amount of the on-axis response bump.
See attachment.
The figure for spheres suggests a rising on-axis response starting where D/ʎ=0.15, and coming/remaining at a maximum of +5 to 6 dB where D/ʎ=1.0 and higher.
D=20mm.
D/ʎ=0.15 corresponds with a wave length ʎ of 133 mm = 2,6 kHz
D/ʎ=1.0 corresponds with a wave length ʎ of 20 mm = 17 kHz
So the starting point of the bump corresponds with the DPA published info for spheres, but not its further development?
« Last Edit: February 15, 2022, 07:19:10 AM by Organfreak »
Mics: Rode NT55, DPA 4090, Beyerdynamic M101
Pres: Lake People C360, M-Audio DMP3
Recorders: Marantz PMD661 OADE super mod & plus mod, Denon DN-F450R, Zoom F6

Offline Gutbucket

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Re: DPA 4090 + 20 mm APE
« Reply #6 on: February 15, 2022, 12:07:27 PM »
I'm not sure why the DPA APE response plots show a roll back down at higher frequencies on-axis rather than maintaining a shelf response.  Some of that may be the inherent higher frequency roll off of the microphone without the ball installed, yet it would seem to occur at a lower frequency than the native response shown in the plots for the 4006.  This is complicated by not knowing what grid was used on the microphone in the APE plots.

To empirically find out what is really going on with your arrangement, you could make a couple simple comparative recordings of a pink/white noise source with and without the ball attachment (without moving the microphone or source between recordings) plot the response and compare the difference between them.  Without a calibrated source or compensation either of the two curves on their own won't be meaningful, but the difference between them will show exactly what that particular ball attachment on that particular microphone is doing.
« Last Edit: February 15, 2022, 12:11:32 PM by Gutbucket »
musical volition > vibrations > voltages > numeric values > voltages > vibrations> virtual teleportation time-machine experience
Better recording made easy - >>Improved PAS table<< | Made excellent- >>click here to download the Oddball Microphone Technique illustrated PDF booklet<< (note: This is a 1st draft, now several years old and in need of revision!  Stay tuned)

Offline Organfreak

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Re: DPA 4090 + 20 mm APE
« Reply #7 on: February 16, 2022, 03:04:37 AM »
I'm not sure why the DPA APE response plots show a roll back down at higher frequencies on-axis rather than maintaining a shelf response.  Some of that may be the inherent higher frequency roll off of the microphone without the ball installed, yet it would seem to occur at a lower frequency than the native response shown in the plots for the 4006.  This is complicated by not knowing what grid was used on the microphone in the APE plots.

To empirically find out what is really going on with your arrangement, you could make a couple simple comparative recordings of a pink/white noise source with and without the ball attachment (without moving the microphone or source between recordings) plot the response and compare the difference between them.  Without a calibrated source or compensation either of the two curves on their own won't be meaningful, but the difference between them will show exactly what that particular ball attachment on that particular microphone is doing.

I have a test CD including a track with pink noise. I can play this track and put a microphone with and without the attachment in front of one of my speakers (~1 meter distance?) and record 2 tracks. But how can I plot and compare the respond curves?
The only program I use to handle and sometimes to apply some small eq. on my recordings is Audacity.
Mics: Rode NT55, DPA 4090, Beyerdynamic M101
Pres: Lake People C360, M-Audio DMP3
Recorders: Marantz PMD661 OADE super mod & plus mod, Denon DN-F450R, Zoom F6

Offline Gutbucket

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Re: DPA 4090 + 20 mm APE
« Reply #8 on: February 16, 2022, 11:09:24 AM »
Looks like Audacity has a spectrum plotting function built into it (Analyze menu>Plot Spectrum)
https://manual.audacityteam.org/man/plot_spectrum.html
musical volition > vibrations > voltages > numeric values > voltages > vibrations> virtual teleportation time-machine experience
Better recording made easy - >>Improved PAS table<< | Made excellent- >>click here to download the Oddball Microphone Technique illustrated PDF booklet<< (note: This is a 1st draft, now several years old and in need of revision!  Stay tuned)

 

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