Topic: Shotgun mic question

[ts]

Thinking of making shorter shotgun tubes for Nakamichi CM700 mics. My first thoughts were to cut the original tubes, CP703 caps, in half. After making a post in the Team Nak thread another member suggested making new tubes from scratch. Cutting the existing tubes would be alot easier, however it would probably render those caps unsaleable. These caps have a series of tiny holes down one side only. The CP703 caps are 16 inches long not including the body, mic or connecting piece. Total length is close to 26 inches. Cutting them in half or making new 8 inch tubes from scratch would make a more usable product, at least for me. So if I make new tubes should I use aluminum or could plastic/delrin be an option? Would the plastic change the sound? Thanks!

[ScoobieKW]

Changing the shotgun tubes will change the sound. I'd make new tubes so I had an undo available if the experiment wasn't succesful.

[DSatz]

Shotgun microphones are just ordinary directional microphones at low and middle frequencies. The perforated tube in front of the capsule has little or no effect when the wavelengths are long. It's only at upper-mid and high frequencies (the frequencies that determine the intelligibility of speech, by no coincidence whatsoever) that shotguns have narrower pickup patterns than conventional microphones.

The frequency at which the narrower pattern begins to occur depends directly on the length of the tube. If you shorten the tube, you raise the transition frequency, which was rather high to begin with. Also, the narrowness of the pickup pattern at high frequencies will be less. So if you shorten the tubes, you wouldn't be reducing the "shotgun effect" of your microphones by a constant amount across the spectrum; instead you'd be reducing the effect, but also limiting it to frequencies above where most of the acoustic energy of music is. To put it bluntly, this would make the shotgun aspect of the microphones almost completely valueless.

The whole physical principle of the interference tube depends on sound wavelengths; the design can't be miniaturized and still be effective, as long as the medium of sound transmission is air.

--best regards

[John Willett]

Shotgun microphones are just ordinary directional microphones at low and middle frequencies. The perforated tube in front of the capsule has little or no effect when the wavelengths are long. It's only at upper-mid and high frequencies (the frequencies that determine the intelligibility of speech, by no coincidence whatsoever) that shotguns have narrower pickup patterns than conventional microphones.

The frequency at which the narrower pattern begins to occur depends directly on the length of the tube. If you shorten the tube, you raise the transition frequency, which was rather high to begin with. Also, the narrowness of the pickup pattern at high frequencies will be less. So if you shorten the tubes, you wouldn't be reducing the "shotgun effect" of your microphones by a constant amount across the spectrum; instead you'd be reducing the effect, but also limiting it to frequencies above where most of the acoustic energy of music is. To put it bluntly, this would make the shotgun aspect of the microphones almost completely valueless.

The whole physical principle of the interference tube depends on sound wavelengths; the design can't be miniaturized and still be effective, as long as the medium of sound transmission is air.

--best regards

The perfect answer.

I was just about to post something similar, but DSatz beat me to it.

[ts]

I'm not trying to reduce the shotgun effect. I'm just looking for a more manageable length for live PA recording. It's current length is too long for me to use in a concert enviroment. 26 inches total length. The reason I am even attemtping this is because of my previous use of the AKG CK69 caps. Those caps come with two sections. They can be used full length by screwing both pieces together for the long form or using one section for a short 6 inch shotgun tube. I have used the AKG's in both lengths. I have found that shorter shotguns are easier all the way around for what we do and have never noticed a huge difference in sound between the long and short form. What I am doing here is the same thing AKG did with their CK68 and 69 series. I prefer the sound of the shorter tube.

dsatz, as always I appreciate your knowledge. Again, I am not trying to change the characteristics of a shotgun mic. Just looking to have a more manageable length. In this post I am questioning the proper material to use If I decide not to cut the existing tubes. Aluminum or plastic. If I decide to cut the existing tubes I will do it so I can rejoin both halves for full length use.

[Chuck]

ts, there is a lot of engineering that goes into the making of those long tubes. Like the other guys have said... It's not advisable to cut those shotgun tubes up to make them shorter.

[Todd R]

I'm not trying to reduce the shotgun effect. I'm just looking for a more manageable length for live PA recording. It's current length is too long for me to use in a concert environment.

Yes, but unfortunately what DSatz and John are saying is that inherently and by the laws of physics you'll be reducing the shotgun effect merely by the act of shortening the interference tube.

As an example, go to the Neumann site and look at the polar response of the short (~9") KMR 81 and compare it to the long KMR 82, particularly at say 2k Hz and 4k Hz.  The KMR81 is ~5db down at +/- 65 degrees at 2k Hz, whereas the KMR82 is 5db down at about +/- 45 degrees.  At 4k Hz, the KMR is down 5db again at about 65 degrees, whereas the KMR82 is 5db down at about 30 degrees.  The KMR82 simply has a narrower pattern at higher frequencies than the KMR81 and has a much greater shotgun effect.

If you shorten the interference tube, you will pretty significantly lessen the shotgun effect.  At that point, you might be much better off with a good hypercard/supercard mic.

[ts]

I understand what everyone is saying. I know it will change the specs. Changing the specs is not a concern. As I have already said I have owned the AKG CK69 cap. I have used it in both short and long form. The short version got used 99% of the time. I have also owned the Neumann KMR 81i. I selected this one over the 82 not only because of it's length but also because of the specs. I have also owned the AKG CK8 caps and have used the AKG 568. I like shorter shotguns. I now have an opportunity to create a short Nak CP703 shotgun because of easy access to a machine shop and if everything goes well with the conversion I will be able to revert it back to full length with ease. And like Todd R said I will be reducing the shotgun effect but not eliminating it. There must be a reason there are so many 8 inch and shorter guns on the market. Sure I can use hypers instead but I often find myself in situations were a short gun is more pleasing to my ears. Having said that I think it is a worthy project.

[Todd R]

Damn old deadheads and their shotgun mics.    Ok Tony, sounds like you know what you're up against and what the effects might be.  Beyond that, I'm completely beyond my element as I have very little experience with shotguns.

You might want to try on the micbuilders forum on yahoo for ideas on the project:
http://tech.groups.yahoo.com/group/micbuilders/

[DiggerinVA]

Damn old deadheads and their shotgun mics.    O

Hey they worked well behind the board.

http://bt.etree.org/details.php?id=558836
here is a sample. hehe

[ts]

Damn old deadheads and their shotgun mics.    Ok Tony, sounds like you know what you're up against and what the effects might be.  Beyond that, I'm completely beyond my element as I have very little experience with shotguns.

You might want to try on the micbuilders forum on yahoo for ideas on the project:
http://tech.groups.yahoo.com/group/micbuilders/

You got it Todd. Us old farts still like the guns. We don't all have the luxury of living near the finest outdoor venue ever. Thanks for the link. I don't think my type of mod or whatever it is falls into a mic builders group, but it's a link worth checking out.

[John Willett]

I understand what everyone is saying. I know it will change the specs. Changing the specs is not a concern. As I have already said I have owned the AKG CK69 cap. I have used it in both short and long form. The short version got used 99% of the time. I have also owned the Neumann KMR 81i. I selected this one over the 82 not only because of it's length but also because of the specs. I have also owned the AKG CK8 caps and have used the AKG 568. I like shorter shotguns. I now have an opportunity to create a short Nak CP703 shotgun because of easy access to a machine shop and if everything goes well with the conversion I will be able to revert it back to full length with ease. And like Todd R said I will be reducing the shotgun effect but not eliminating it. There must be a reason there are so many 8 inch and shorter guns on the market. Sure I can use hypers instead but I often find myself in situations were a short gun is more pleasing to my ears. Having said that I think it is a worthy project.

The AKG was designed that way and optimised for both.

A normal gun mic is specifically designed for the length of the interference tube it has.

For example you can *NOT* take the innards of a Sennheiser MKH 816 mic. and put it in an MKH 416 housing and expect it to be / sound like a 416 (even thouth it would fit perfectly).

Cut you mic. down if you want - you will have ruined the mic. to make it unsaleable in the future and you will have widened the polar-pattern and upset the frequency response.

It's your mic. and you can do what you want with it - we are just advising correct/best practice.

[runonce]

I would resist cutting.

Those 700 caps are amongst the most rare mics in the Nak line...and collectors items - even outside of our hobby.

Why ruin them?

Why not just look for a different mic?

If you want to stick with Primo/Nak sound - look at the JVC M-510 Shotguns - they fit the Nak 300 bodies, but are about 4 inches shorter than CP4...more of a super cardioid, and sound mighty fine.

[ts]

I understand what everyone is saying. I know it will change the specs. Changing the specs is not a concern. As I have already said I have owned the AKG CK69 cap. I have used it in both short and long form. The short version got used 99% of the time. I have also owned the Neumann KMR 81i. I selected this one over the 82 not only because of it's length but also because of the specs. I have also owned the AKG CK8 caps and have used the AKG 568. I like shorter shotguns. I now have an opportunity to create a short Nak CP703 shotgun because of easy access to a machine shop and if everything goes well with the conversion I will be able to revert it back to full length with ease. And like Todd R said I will be reducing the shotgun effect but not eliminating it. There must be a reason there are so many 8 inch and shorter guns on the market. Sure I can use hypers instead but I often find myself in situations were a short gun is more pleasing to my ears. Having said that I think it is a worthy project.

The AKG was designed that way and optimised for both.

A normal gun mic is specifically designed for the length of the interference tube it has.

For example you can *NOT* take the innards of a Sennheiser MKH 816 mic. and put it in an MKH 416 housing and expect it to be / sound like a 416 (even thouth it would fit perfectly).

Cut you mic. down if you want - you will have ruined the mic. to make it unsaleable in the future and you will have widened the polar-pattern and upset the frequency response.

It's your mic. and you can do what you want with it - we are just advising correct/best practice.

I appreciate your response but you seem to have missed the part stating this mod will allow for joining both halves back together in a very clean way. However, you are correct about making it unsaleable. That is a huge concern. Thanks.

[cashandkerouac]

seems like a tug of war betwen the Nak 700 purists and TS's preference for more flexibility.  i can understand both sides... but if TS knows what he wants and understands there is no going back once he performs the mod then what's the harm?

i suppose the "have your cake and eat it too" solution would be to make new tubes and transfer the electronics.  that way the electronics could be transferred back into the original tubes if desired and it would be like the mod never happened.  am i missing something or would that work?

[John Willett]

I understand what everyone is saying. I know it will change the specs. Changing the specs is not a concern. As I have already said I have owned the AKG CK69 cap. I have used it in both short and long form. The short version got used 99% of the time. I have also owned the Neumann KMR 81i. I selected this one over the 82 not only because of it's length but also because of the specs. I have also owned the AKG CK8 caps and have used the AKG 568. I like shorter shotguns. I now have an opportunity to create a short Nak CP703 shotgun because of easy access to a machine shop and if everything goes well with the conversion I will be able to revert it back to full length with ease. And like Todd R said I will be reducing the shotgun effect but not eliminating it. There must be a reason there are so many 8 inch and shorter guns on the market. Sure I can use hypers instead but I often find myself in situations were a short gun is more pleasing to my ears. Having said that I think it is a worthy project.

The AKG was designed that way and optimised for both.

A normal gun mic is specifically designed for the length of the interference tube it has.

For example you can *NOT* take the innards of a Sennheiser MKH 816 mic. and put it in an MKH 416 housing and expect it to be / sound like a 416 (even thouth it would fit perfectly).

Cut you mic. down if you want - you will have ruined the mic. to make it unsaleable in the future and you will have widened the polar-pattern and upset the frequency response.

It's your mic. and you can do what you want with it - we are just advising correct/best practice.

I appreciate your response but you seem to have missed the part stating this mod will allow for joining both halves back together in a very clean way. However, you are correct about making it unsaleable. That is a huge concern. Thanks.

I had not actually missed the bit about re-joining.

But to do this you will have to make some sort of internal joining ring which will not put it back exactly like it was - and smoothing the cut ends will remove some material and would slightly de-tune the tube as well.

[ts]

I understand what everyone is saying. I know it will change the specs. Changing the specs is not a concern. As I have already said I have owned the AKG CK69 cap. I have used it in both short and long form. The short version got used 99% of the time. I have also owned the Neumann KMR 81i. I selected this one over the 82 not only because of it's length but also because of the specs. I have also owned the AKG CK8 caps and have used the AKG 568. I like shorter shotguns. I now have an opportunity to create a short Nak CP703 shotgun because of easy access to a machine shop and if everything goes well with the conversion I will be able to revert it back to full length with ease. And like Todd R said I will be reducing the shotgun effect but not eliminating it. There must be a reason there are so many 8 inch and shorter guns on the market. Sure I can use hypers instead but I often find myself in situations were a short gun is more pleasing to my ears. Having said that I think it is a worthy project.

The AKG was designed that way and optimised for both.

A normal gun mic is specifically designed for the length of the interference tube it has.

For example you can *NOT* take the innards of a Sennheiser MKH 816 mic. and put it in an MKH 416 housing and expect it to be / sound like a 416 (even thouth it would fit perfectly).

Cut you mic. down if you want - you will have ruined the mic. to make it unsaleable in the future and you will have widened the polar-pattern and upset the frequency response.

It's your mic. and you can do what you want with it - we are just advising correct/best practice.

I appreciate your response but you seem to have missed the part stating this mod will allow for joining both halves back together in a very clean way. However, you are correct about making it unsaleable. That is a huge concern. Thanks.

I had not actually missed the bit about re-joining.

But to do this you will have to make some sort of internal joining ring which will not put it back exactly like it was - and smoothing the cut ends will remove some material and would slightly de-tune the tube as well.

Ok. I call uncle. I've decided not to cut them just because of how rare they are and no other reason. I'll make tubes from scratch at 8 inches in length.

[DSatz]

ts, I'm fairly certain that I'm as old and (sorry to say) as farty as anyone else around here, and I believe that a person will probably make the best recordings with the mikes that he or she is the most familiar with, whose behavior makes the most sense to him or her. I would never try to dissuade you from using shotguns for stereo music recording if they've worked well for you and their behavior fits your expectations.

But I would never advise anyone else to take up that path. All other things being equal, good recordings are far more likely to occur with microphones whose frequency response is as similar as possible across the main angles of sound incidence, or whose directional pattern remains fairly constant across the audio frequency spectrum (which is actually the same thing, viewed from a different perspective). And shotgun microphones are designed from the start to be ... not that. They are designed to reduce the pickup of off-axis sound (which, if they're aimed skilfully, will always be reflected sound) in the frequency range where spoken consonants mainly occur, so as to increase the intelligibility of speech pickup when the miking distance is a little greater than might otherwise be ideal.

That said, you hit the nail right on the head about short shotguns. Most audio professionals who use shotguns will choose a short shotgun over a long one if the directivity of the short shotgun is sufficient; it sounds better, and in applications such as film and video sound, generally lets you get the transducer closer to the sound source. But most audio professionals will also choose a good supercardioid over any kind of shotgun if the directivity of the supercardioid is sufficient, for the same reasons.

The explanation for this is the relative evenness or unevenness of the directional pattern across the frequency spectrum. A good single-diaphragm supercardioid such as a Schoeps, Neumann or Sennheiser can have a uniform directional pattern from the lowest audio frequencies throughout the entire midrange, narrowing only in the top octave-and-a-half or so. A long shotgun, by contrast, will have (usually) a supercardioid pattern at low and low-middle frequencies, narrowing through the midrange/upper midrange while also developing considerable irregularity in its sensitivity to sound arriving at various angles.

This effect becomes more and more severe the higher the frequency in any shotgun microphone, and the longer the tube is. Thus a short shotgun (a) retains a consistent pattern up to a higher frequency than a long shotgun, and (b) has less severe irregularities in its sensitivity at various angles once its pattern does begin to become narrower. This is the main reason why the best-sounding shotgun microphones are invariably short.

--best regards

[John Willett]

DSatz has put this very well - though I would add DPA and Gefell to his list of "Schoeps, Neumann or Sennheiser" as the good mics. 

[DSatz]

John, I certainly know that there are other good microphone manufacturers, but I was referring specifically to small, single-diaphragm supercardioids with polar response that stays essentially constant throughout the frequency range.

I don't follow DPA's product line at all and my knowledge of Microtech Gefell's production isn't as up to date as it should be--do they both offer such microphones? If so, good for them! But I didn't know that they did/do.

--best regards

[John Willett]

John, I certainly know that there are other good microphone manufacturers, but I was referring specifically to small, single-diaphragm supercardioids with polar response that stays essentially constant throughout the frequency range.

I don't follow DPA's product line at all and my knowledge of Microtech Gefell's production isn't as up to date as it should be--do they both offer such microphones? If so, good for them! But I didn't know that they did/do.

--best regards

I would have said that the Gefell M310 and SMS2000 are certainly the equal of Neumann in this respect.

The M300 and M310 have a ceramic capsule that does not expand and contract with temperature changes and remains constant, they also use 80V polarisation voltage (Neumann use 60V I think, at least that is what Stephan Peus told me a few years back) which gives lower noise and better transient response - and they use an optical coupler for the phantom power so any voltage nasties don't get into the audio circuit.

Though, if you really want the perfect polar-pattern, the Sennheiser MKH 50 comes closer than any other super-cardioid on the market that I know of.  As told me by Manfred Hibbing the designer; because they lightly damp the capsule and use the converse of the capsule frequency response in the electronics, the designer can then concentrate much closer on getting a good polar-pattern.

Although I would put DPA with the others in quality, I don't think they do a super-cardioid (other than a gun mic.), so I would agree with you here.

[DSatz]

OK, visiting the Microtech Gefell Web site, I see the capsule M 210 for the SMS 2000 amplifier series. In their German-language materials it is labeled a supercardioid while in English they call it a hypercardioid. The polar diagrams, however, show that it is neither, nor anything in between. The rear lobe in the midrange is about 25 dB below the 0° sensitivity, while the null angle is around 140°. I would call it a slightly narrowed cardioid that has a corresponding, small rear lobe that physics requires of such a construction. But it has more variance in pattern across important areas of the frequency range than I want for high-quality stereo music recording (especially with coincident or closely-spaced microphones), and it isn't much like a supercardioid (at any frequency), which is what I was trying to talk about.

There is also a complete microphone model M 310. The same odd terminology is applied to it (supercardioid if you read German, hypercardioid if you don't), but the Web site seems to carry no specific information on this model apart from a photo that grows and shrinks if you click on it. I have often stopped by the Microtech booth at trade shows and picked up their literature, so I may have some printed material about this model, but will have to look for it this evening. From what I've seen so far, though, I wouldn't choose this particular aspect of their product line to represent the company's best work.

--best regards

[John Willett]

The M310 is the hyper-cardioid/super-cardioid version of the M300 - which is something special.

I have had a go at Gefell for not putting the specs for this on the website, I hope they will soon.

[cashandkerouac]

John, I certainly know that there are other good microphone manufacturers, but I was referring specifically to small, single-diaphragm supercardioids with polar response that stays essentially constant throughout the frequency range.

I don't follow DPA's product line at all and my knowledge of Microtech Gefell's production isn't as up to date as it should be--do they both offer such microphones? If so, good for them! But I didn't know that they did/do.

--best regards

I would have said that the Gefell M310 and SMS2000 are certainly the equal of Neumann in this respect.

The M300 and M310 have a ceramic capsule that does not expand and contract with temperature changes and remains constant, they also use 80V polarisation voltage (Neumann use 60V I think, at least that is what Stephan Peus told me a few years back) which gives lower noise and better transient response - and they use an optical coupler for the phantom power so any voltage nasties don't get into the audio circuit.

Though, if you really want the perfect polar-pattern, the Sennheiser MKH 50 comes closer than any other super-cardioid on the market that I know of.  As told me by Manfred Hibbing the designer; because they lightly damp the capsule and use the converse of the capsule frequency response in the electronics, the designer can then concentrate much closer on getting a good polar-pattern.

Although I would put DPA with the others in quality, I don't think they do a super-cardioid (other than a gun mic.), so I would agree with you here.

John, David:  how does the MKH8050 compare to the MKH50 in terms of the polar pattern?  i assume they are similar.

[John Willett]

John, David:  how does the MKH8050 compare to the MKH50 in terms of the polar pattern?  i assume they are similar.

The MKH 50 is slightly better than the MKH 8050.

Go to the Sennheiser website and download the owners manuals - the polar patterns are there.

Put them side by side and you will see the MKH 50 is a little better.