Shotgun Microphone Assembly

[MAGUS2500X]

Looking at building a shotgun mic for a project i'm working on but although I understand the basics on most of the project I am at a slight loss on one part. I'm not sure if I can simply Drill holes in the housing or if I HAVE to have slots along the side. Some sources I'm finding on builds state either or but without any specification as to the difference or if there is one. I am having trouble getting slots to come out properly (tools I am using are the main culprit) and I am wondering if I can simply drill holes instead. I'm also having trouble finding any information on what configuration I would need the slots in to help with phase cancellation with certain frequencies, assuming you can with a standard mic enclosure (most of the information I've seen on this part is for a multi-tube design that is large and impractical for my use.) Any information would be greatly appreciated as I am a novice when it comes to DIY of these.

 

[Steenamaroo]

I don't have the knowledge to help with this but I can tell you one thing.
People will need to know what mic you're modifying, or what components you're starting with if it's a complete new-build.

I imagine this thing is going to be an exact science but I'll be interested to hear what experienced guys say.
Good luck.

 

[MAGUS2500X]

I don't have the knowledge to help with this but I can tell you one thing.
People will need to know what mic you're modifying, or what components you're starting with if it's a complete new-build.

I imagine this thing is going to be an exact science but I'll be interested to hear what experienced guys say.
Good luck.

Thanks for the input XD.

I'm actually starting with various parts from scratch, making a couple of these with different starting components, I know what I need to do with everything but the enclosure which is what makes the "shotgun" portion of the mic, so I really don't need help on the rest of the build to be honest. For now I'm just using a generic made microphone using a couple of old audio headsets (turning the speaker into a microphone) and using those in the enclosure to test and make sure i'm making that part right before I actually build the entire thing from scratch since that is likely to be the hardest part of the build. I just basically need to know can I substitute holes instead of slots and if there is a specific formation needed with them or if randomly placed holes around the casing will suffice. I do understand how it works for the most part, using phase cancellation to remove sound that approaches the mic from the sides leaving only the sound coming from directly in front of the mic with an exception on low frequencies though i'm not sure the specific range it includes. I know the longer the "tube" the more cancellation, I just don't know if spacing and placement makes a difference. Hoping someone can help fill the holes in my knowledge so I can get one of these prototypes together and tested soon. Thanks in advance.

 

[MAGUS2500X]

I did find part of the answer to what i've been researching, though only in how it works and not in anyway close to knowing the specific calculations needed. The design of a shotgun microphone is based off a different concept design of multiple tubes of various lengths bundled together to a singular source where the microphone is positioned at the base. These tubes have one direct source which is considered on axis and all noise produced from the sides enters the tube at an angle instead of straight in, causing it to, for lack of a better description, bounce around the tube throwing the timing off by the time it reaches the end. One offset tube causes a small amount of frequencies to be off time, thus the multitude of tubes used. The longer the tube the lower the frequency it effects. This is the bases of the standard shotgun mic, the slots in the side of the tube act similar to the multiple tubes causing the same offset timing of frequencies. The length also effects the pitch of frequency in the same manner. To me this means that although slots vs. holes may have a small difference between the two, in theory they would both have similar if not the same effect so long as there are many and spread out over a length of the tubing.
I am not sure about the legality of posting links to other sites on this forum so in lue of the source i am linking a descriptive picture of how the multiple tubes absorb sound to help offset that.
When the frequencies being offset from the slots/holes in the tube reach the bottom phase cancellation occurs and the "stronger" "on-axis" signal remains.

I would still love to hear input from people more knowledgeable than myself on this though as there may be more information about specifics out there.

 

[southpark]

I looked into this very briefly a couple of weeks ago and did some test. I cut symmetrical slots in the side of a card board tube leaving just a small strip on both sides to keep it held together(just look at any shotty on sweetwater and you'll catch my drift) and than placed the mic capsule even with the last slot. It rejected sound to the sides and increased the range directly in front. If you wanted to spend lots of time cutting different sized slots in something like pvc, you could possibly come up with something useable. I think if you use a hyper-cardioid capsule you could get a little better result.

How that helped