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Junior Varsity
Test what you think you know: Part 2
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<blockquote data-quote="Jay Barracato" data-source="post: 121491" data-attributes="member: 24"><p>Re: Test what you think you know: Part 2</p><p></p><p></p><p></p><p>We can keep your photos as an example of how to do this is you have to...</p><p></p><p>But,</p><p>Your setup doesn't tell us anything about the effect of the foam and if the foam is causing any differences from the normal mic response. But I am not sure that even matters because my original testable question was not What is the effect of wrapping the mic in foam? it was What is the effect of blocking the rear ports of a directional mic? Given my question, your test doesn't tell me much because I don't see the foam blocking the ports in any way. A better test to tell if the type of foam is a critical variable would be to move your wrap forward until the ports are covered.</p><p></p><p>In addition, I think you are quibbling over the type of foam. Open cell foam comes in many different densities. The foam used in the picture I posted is open cell (air escapes when it is compressed) but of a much higher density than what you pictured.</p><p></p><p>Given that the length of the mic ball/diaphragm corresponds to a wavelength of about 4000 hz. I would not expect any type of foam as you have placed it to make a major difference. Actually at that wavelength I would expect the mic body itself to be a larger source of scattering.</p><p></p><p></p><p></p><p>We are going to have to agree to disagree on this. I can still see no way that this affects the situation. You keep saying boundary without explaining why you think that boundary is important. My point, once again, is that the boundary serves to make the time of arrival of the direct sound and the reflected sound as close as possible. If the soundboard is the source of the sound, it can't be a boundary as well because the sound is not reflected off of it. I can think of no other significant source of sound around the bridge area that might possible be reflected. The strings themselves make an insignificant amount of sound when compared to the soundboard (try playing an electric upright like a NS designs unplugged).</p><p></p><p></p><p></p><p>Once again I think you missed a basic premise of my experimental design. (This is also reflected in the lack of a control in what you posted) I am looking at the difference in the response that can be isolated as being caused by the single change made. If you change more than one variable, you can't attribute changes to anything. No one denies that proximity effect changes the absolute response, but I am comfortable that the trend in the change observed at 1 ft and 3 ft can be extrapolated to closer differences. I would like to test it, but it is a physical impossibility to place the rear of the diaphragm in a 8 inch long mic closer to the source than that. In order to compare response it is critical that the measurement at 0 degrees and 180 degrees take place at the same distance from the source. </p><p></p><p></p><p></p><p>Actually with my nd487 technique the physical coupling is part of the magic. I don't want the mic decoupled from the instrument. With the other techniques there is almost no coupling. When the pro35 is used in the boom, the element is just supported by the windshield, when it is attached to my little modeler's clamps, I attach it by a loop in the cord so the element hangs free.</p><p></p><p></p><p></p><p></p><p>I have never noticed that really low proximity effect in the pro37 but I usually use the LF rolloff on it. Once again, I think your test shows a comparison of different mics in a particular situation, but it doesn't tell me if the foam has any effect, or what the effects of blocking the ports would be.</p><p></p><p>I think I have to stand by my original conclusions:</p><p></p><p>I said in the original Facebook conversation that blocking the rear ports of a directional mic changes the pattern to omni.</p><p></p><p>While the context was about stuffing the tailpiece of an acoustic bass, the sound profile of the instrument, the proximity effect of different mics, or even the type of foam have nothing to do with the question I posed.</p><p></p><p>My test shows a pretty positive result. </p><p></p><p>So to extend this to the bass question, if you block the ports you will change the response of the mic. If you have some sort of acoustic transparent foam, fine; or if you can wrap the mic so the ports are not blocked, fine; but, if you block the ports the response will change.</p><p></p><p>I will not be doing any experimentation during any live shows. A pro35 is about $129. If you are working with acoustic basses a lot, I recommend you just get one. It is a lot smaller package then carrying around a bunch of foam.</p></blockquote><p></p>
[QUOTE="Jay Barracato, post: 121491, member: 24"] Re: Test what you think you know: Part 2 We can keep your photos as an example of how to do this is you have to... But, Your setup doesn't tell us anything about the effect of the foam and if the foam is causing any differences from the normal mic response. But I am not sure that even matters because my original testable question was not What is the effect of wrapping the mic in foam? it was What is the effect of blocking the rear ports of a directional mic? Given my question, your test doesn't tell me much because I don't see the foam blocking the ports in any way. A better test to tell if the type of foam is a critical variable would be to move your wrap forward until the ports are covered. In addition, I think you are quibbling over the type of foam. Open cell foam comes in many different densities. The foam used in the picture I posted is open cell (air escapes when it is compressed) but of a much higher density than what you pictured. Given that the length of the mic ball/diaphragm corresponds to a wavelength of about 4000 hz. I would not expect any type of foam as you have placed it to make a major difference. Actually at that wavelength I would expect the mic body itself to be a larger source of scattering. We are going to have to agree to disagree on this. I can still see no way that this affects the situation. You keep saying boundary without explaining why you think that boundary is important. My point, once again, is that the boundary serves to make the time of arrival of the direct sound and the reflected sound as close as possible. If the soundboard is the source of the sound, it can't be a boundary as well because the sound is not reflected off of it. I can think of no other significant source of sound around the bridge area that might possible be reflected. The strings themselves make an insignificant amount of sound when compared to the soundboard (try playing an electric upright like a NS designs unplugged). Once again I think you missed a basic premise of my experimental design. (This is also reflected in the lack of a control in what you posted) I am looking at the difference in the response that can be isolated as being caused by the single change made. If you change more than one variable, you can't attribute changes to anything. No one denies that proximity effect changes the absolute response, but I am comfortable that the trend in the change observed at 1 ft and 3 ft can be extrapolated to closer differences. I would like to test it, but it is a physical impossibility to place the rear of the diaphragm in a 8 inch long mic closer to the source than that. In order to compare response it is critical that the measurement at 0 degrees and 180 degrees take place at the same distance from the source. Actually with my nd487 technique the physical coupling is part of the magic. I don't want the mic decoupled from the instrument. With the other techniques there is almost no coupling. When the pro35 is used in the boom, the element is just supported by the windshield, when it is attached to my little modeler's clamps, I attach it by a loop in the cord so the element hangs free. I have never noticed that really low proximity effect in the pro37 but I usually use the LF rolloff on it. Once again, I think your test shows a comparison of different mics in a particular situation, but it doesn't tell me if the foam has any effect, or what the effects of blocking the ports would be. I think I have to stand by my original conclusions: I said in the original Facebook conversation that blocking the rear ports of a directional mic changes the pattern to omni. While the context was about stuffing the tailpiece of an acoustic bass, the sound profile of the instrument, the proximity effect of different mics, or even the type of foam have nothing to do with the question I posed. My test shows a pretty positive result. So to extend this to the bass question, if you block the ports you will change the response of the mic. If you have some sort of acoustic transparent foam, fine; or if you can wrap the mic so the ports are not blocked, fine; but, if you block the ports the response will change. I will not be doing any experimentation during any live shows. A pro35 is about $129. If you are working with acoustic basses a lot, I recommend you just get one. It is a lot smaller package then carrying around a bunch of foam. [/QUOTE]
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Test what you think you know: Part 2
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