bouldersoundguy
Well-known member
A humbucking coil generally needs to be close to the coil that it's protecting from interference. I have an Electro-Voice 635a that has a coil around the outside of the capsule (which is unfortunately coming unwound).
E
ecc83
Well-known member
That shows capsule, bucking coil and filter inductor as one unit with 4 wires exiting. I dare say the parts can be split but I wouldn't want to try!
Dave.
CoolCat
Well-known member
what would the physical parts look like?
Is it fine wire wrapped around a wire, like a torrodial coil or magnet? must be a tiny thing to fit inside,
I use chokes on cables, one on the input and one on the output. I suppose its the same in theory.
Is it fine wire wrapped around a wire, like a torrodial coil or magnet? must be a tiny thing to fit inside,
I use chokes on cables, one on the input and one on the output. I suppose its the same in theory.
E
ecc83
Well-known member
A humbucking coil needs some design thought. It has to be of the right inductance so that it picks up close to the level of hum induced in the mic's coil. It need to be oriented correctly and in the correct polarity otherwise it will increase hum instead of bucking it!
Why do you want to know all this?
Dave.
Why do you want to know all this?
Dave.
CoolCat
Well-known member
lol...why? just curious and was surfing through hours of SM7 vs SM7A stuff....it was the "change" that's folklore or real?
It got me wondering what and how is a humbucker in a microphone such a big deal? what is it physically that can create decades of
debating whether it was a good idea or ruined the "tone" man....pffffttt...its all the tone deeewwd...hits the bong...
maybe some hear this Humbucker in the circuit and some don't? it seems pretty 50/50.
do you think adding a humbucker in a circuit would make a tone difference in a capsule? based only off adding this in a circuit in theory?
It got me wondering what and how is a humbucker in a microphone such a big deal? what is it physically that can create decades of
debating whether it was a good idea or ruined the "tone" man....pffffttt...its all the tone deeewwd...hits the bong...
maybe some hear this Humbucker in the circuit and some don't? it seems pretty 50/50.
do you think adding a humbucker in a circuit would make a tone difference in a capsule? based only off adding this in a circuit in theory?
E
ecc83
Well-known member
Now this next is NOT aimed at you CC but it is these sort of debates that hiss me off mightily! As an engineer* I am far more concerned about getting clean signals into a system than any airy-fairy nonsense about "tone"!
AFAIK the SM7b was developed primarily for use in radio TALK studios where there is a lot of 60/50Hz transformer supplies about. The low sensitivity of the 7b is legendary and speech is only at about 75dB SPL (mics are measured at some 20dB higher) so ANY hum pickup is going to be a b'std nuisance.
*I am not a qualified engineer but a technician with a long lifetime's interest in all things audio.
Dave.
CoolCat
Well-known member
You would have done well with Shure as they weren't really in the "tone biz" but instead engineering for applications.
the level of hum and transformers about.... that kind of helps answer why they added this. Interesting and logical reason they added this into the circuit.
googled
A transformer hum is typically at twice the frequency of the power line, meaning it would be 120 Hz in regions with a 60 Hz power supply and 100 Hz in areas with a 50 Hz power supply
So in this application if the "added Humbucker Coil" purpose is filtering out that Hum, aka low freq level 100~120hz.
So I will assume its probably not going to be degrading a Human Voice freq range.
Seems similar to a HPF. I wonder if a HPF is ON, it will drop off the lower FREQS all the time. Does a Humbucker Coil filter all the time or only when it senses the Hum?
the level of hum and transformers about.... that kind of helps answer why they added this. Interesting and logical reason they added this into the circuit.
googled
A transformer hum is typically at twice the frequency of the power line, meaning it would be 120 Hz in regions with a 60 Hz power supply and 100 Hz in areas with a 50 Hz power supply
So in this application if the "added Humbucker Coil" purpose is filtering out that Hum, aka low freq level 100~120hz.
So I will assume its probably not going to be degrading a Human Voice freq range.
Seems similar to a HPF. I wonder if a HPF is ON, it will drop off the lower FREQS all the time. Does a Humbucker Coil filter all the time or only when it senses the Hum?
E
ecc83
Well-known member
I shall take that as a compliment! That quote is BOLLOCKS! The main hum frequency from a power traff is at the mains frequency. Yes, there will be a bit of 2nd harmonic and if the transformer is working very close to its limit a fair bit of 3rd harmonic i.e. 150Hz for Blighty (and most right thinking countries!)
You can confirm this very easily with a passive e guitar and analyser software and if you don't have any dld Right Mark Audio Analyser, free and very easy to use.
"Humbucking" coils are not "filters". They pickup the same hum the mic coil does and 'insert' it, 180dgrs out of phase with the mic signal...voila! No hum. Guitar humbuckers work the same way except they also do the clever thing with the magnets.
Dave.
bouldersoundguy
Well-known member
Since the voice coil is behaving like antenna, you give it a twin nearby (which is not capturing any sound) and wire it in with reverse polarity. It's virtually the same idea as balanced connections.
E
ecc83
Well-known member
Well, a bit but! Balanced operation is a little more subtle in that yes, you have an amplifier with differential inputs but the noise rejection comes about by the "balance" of the feed and receive impedance.
Dave.
CoolCat
Well-known member
thanks... that's kind of what my brain was looking for "how it works" so its 180deg out reverse polarity...using wire instead of a chip.
I was reading surfing around but most posts seem to be about guitar pickups and not microphone, SM7A in particular.
ok , thanks again, its all making more sense when and why and how they did this humbucker-change.
I was reading surfing around but most posts seem to be about guitar pickups and not microphone, SM7A in particular.
ok , thanks again, its all making more sense when and why and how they did this humbucker-change.
rob aylestone
Moderator
You are all overcomplicating this a bit. The key features of humbucking coils have been mentioned but sort of hidden?
A dynamic mic has a magnet. It has a diaphragm with a fine copper coil wound around the edge which waggles in the magnetic field as you make noises into it - the movement is in effect, a generator of electricity. if you add a second coil NOT connected to anything that moves, it generates nothing at all. Now the clever bit is to take the generating coil and put it in parallel with the non generating one, but wired backwards - reverse polarity. Make a noise and sound is converted to voltage and out comes your audio. If you happen to be next to interference producing devices like transformers or other generators of hums and buzzes, the interference enters both coils and cancels out. With just one coil, being next to that big transformer puts a big hum component onto the audio.
A dynamic mic has a magnet. It has a diaphragm with a fine copper coil wound around the edge which waggles in the magnetic field as you make noises into it - the movement is in effect, a generator of electricity. if you add a second coil NOT connected to anything that moves, it generates nothing at all. Now the clever bit is to take the generating coil and put it in parallel with the non generating one, but wired backwards - reverse polarity. Make a noise and sound is converted to voltage and out comes your audio. If you happen to be next to interference producing devices like transformers or other generators of hums and buzzes, the interference enters both coils and cancels out. With just one coil, being next to that big transformer puts a big hum component onto the audio.
E
ecc83
Well-known member
Yes Rob, in PRINCIPLE very simple but making the null effective takes work. The coil (which from that schematic appears to be in series* with the VC) needs to have the right inductance, governed by number of turns and magnetic properties of any materials in or around it. This needs some design finessing since the buck coil cannot be in the same physical place as the coil it is "bucking".
*Humbucker G pups are mostly put in series and it is the doubling of inductance that gives them their 'darker' sound as HF is reduced. Some guitars give the option of parallel connection. That brightens things up but reduces sensitivity...yer pays yer money...
Dave.
CoolCat
Well-known member
So Im getting a picture of this capsule "humbucking coil" that needs the interference to do anything.
Without interference it does nothing, cancels nothing. Is this right?
If Im following this right, if there's no interference around, then the SM7 would be the same as the SM7A. right?
Without interference it does nothing, cancels nothing. Is this right?
If Im following this right, if there's no interference around, then the SM7 would be the same as the SM7A. right?
bouldersoundguy
Well-known member
Well, at least in the case of guitar pickups, they alter the tone a bit just by being part of the circuit.
E
ecc83
Well-known member
There is a subtle difference between the way that mic defeats hum and the way balanced operation does it.
For the mic (and h'bucker pups) hum is picked up on both the "wanted" coil and the buck coil (which collects no sound) The buck coil's signal is then inserted in opposite polarity to the hum from the speech coil..voila! Hum is bucked.
The pickup is a bit different in that both coils 'collect' string signal (and hum) the coils are in series OOP which would of course normally result in a very low, emasculated sound. The pups get over that by reversing the magnet polarity on one coil.
A balanced feed from say a mic is designed to reject hum induced IN THE CABLE. The mic and the input amplifier form part of a "Wheatstone Bridge" and a differential amplifier (or transformer) sits at the null point.
(I did type all this before but it never seemed to arrive!)
Dave.
For the mic (and h'bucker pups) hum is picked up on both the "wanted" coil and the buck coil (which collects no sound) The buck coil's signal is then inserted in opposite polarity to the hum from the speech coil..voila! Hum is bucked.
The pickup is a bit different in that both coils 'collect' string signal (and hum) the coils are in series OOP which would of course normally result in a very low, emasculated sound. The pups get over that by reversing the magnet polarity on one coil.
A balanced feed from say a mic is designed to reject hum induced IN THE CABLE. The mic and the input amplifier form part of a "Wheatstone Bridge" and a differential amplifier (or transformer) sits at the null point.
(I did type all this before but it never seemed to arrive!)
Dave.
E
ecc83
Well-known member
I am reminded now of "humbuckers" that were used with early loudspeakers. These speakers did not use a permanent magnet but were "energized" by a coil of 1000s of turns of fine wire. "WTF!"? you say. Well PMs were expensive and not very good but also the coil was usually used as a smoothing choke in the HT supply. "Why?" again! Because capacitors above about 100nF were bulky, expensive and not very reliable so you generally only got 1/2 doz 4mfd caps in a radio. The choke helped reduce hum. But! there was a ripple current in the energizing coil and that made the speaker hum! So they fitted a second voice coil in the speaker and fed that with valve heater current to cancel the choke hum.
I.e. Bucked it!
Dave.
I.e. Bucked it!
Dave.
CoolCat
Well-known member
I went and blew some money on a SM7 -non Humbucker and compared to the SM7b and couldn't hear much if any difference and actually impressed in such little difference heard or saw on the meters.
Of course, I don't have any Transformer hum-and Tube gear running as a radio station would.
Interface only - was a very very nice Antelope Audio interface with great preamps 75db and all the best newer specs, etc.etc.to be transparent and low noise.
Both mics set at 60db.of the 75db max, and both mics showed my room noise floor with exact same noise floor around -72db idle noise. (PC fan noise)
The Non-Humbucker SM7 is a very above average condition/shape and appears little usage visually.
I'm not tearing it apart to see if the capsule is original which could be questionable on any "vintage" mic.
But considering the excellent condition of the body, decal, paint, grill, I skeptically lean its an original capsule. Preponderance of the circumstantial evidence!
1984 to 1999 model.
Anyway, this mic capsule thing is how ECC describes it, I agree, its nothing like a difference between a Guitar Humbucker pickup and a Guitar single coil guitar pickup as where its pretty obvious difference in tone., which I had wondered about these mics. My only experience was guitar pickups Humbucker vs single coil guitar pickups...even some noiseless guitar pickups were noticeable.
So "would the pre1999 or the 1999-current sound noticeably different?" was the question.
This brief simple test showed there wasn't any difference heard or seen, at least when there is NO Nearby Hum Creating Machines nearby..lol
appreciate the tech info from everyone! Id never understood the whole Humbucker coil difference in design thing, or upgrade talked about.
Of course, I don't have any Transformer hum-and Tube gear running as a radio station would.
Interface only - was a very very nice Antelope Audio interface with great preamps 75db and all the best newer specs, etc.etc.to be transparent and low noise.
Both mics set at 60db.of the 75db max, and both mics showed my room noise floor with exact same noise floor around -72db idle noise. (PC fan noise)
The Non-Humbucker SM7 is a very above average condition/shape and appears little usage visually.
I'm not tearing it apart to see if the capsule is original which could be questionable on any "vintage" mic.
But considering the excellent condition of the body, decal, paint, grill, I skeptically lean its an original capsule. Preponderance of the circumstantial evidence!
1984 to 1999 model.
Anyway, this mic capsule thing is how ECC describes it, I agree, its nothing like a difference between a Guitar Humbucker pickup and a Guitar single coil guitar pickup as where its pretty obvious difference in tone., which I had wondered about these mics. My only experience was guitar pickups Humbucker vs single coil guitar pickups...even some noiseless guitar pickups were noticeable.
So "would the pre1999 or the 1999-current sound noticeably different?" was the question.
This brief simple test showed there wasn't any difference heard or seen, at least when there is NO Nearby Hum Creating Machines nearby..lol
appreciate the tech info from everyone! Id never understood the whole Humbucker coil difference in design thing, or upgrade talked about.
CoolCat
Well-known member
Just adding some pictures of a SM7. Early 1970's version I just picked up.
I returned the "assembled in Mexico" SM7 non-humbucking coil version used in previous posts here, because I convinced myself it might be a fake , as it was in too good of condition and others online line looked really identical, Im probably wrong but anyway...an early 1970s one popped up seeming more "original" so I grabbed it instead.
Both had the same noise floor in my closet studio. So humbucking coil or not , I didn't see a difference in the idle noise graph, but I don't have a CRT humming away either.
I tore the mic apart being as careful as I could, and thought I might as well take some pictures, an thought I might as well post some here for any gearhead taking apart a SM7.
From searching around there is little data on replacement screws for this mic. The miniscule tiny screws for the back plate are M25, its 0.086 inch diameter! so tiny and the part number Shure doesn't have listed as stock to buy. Super tiny screws to take the backplate off and adjust the EQ settings. Length is 0.110 inch. Philips head/ cross. I think I found some on Amazon. The three screws holding the basket and yoke, allowing to pull the capsule and body out are a strange cross/Phillips screw but like a socket head 0.65 dia, .585 length. Also noticed the yoke pipe with XLR attached is smaller the old one 0.65 in and the SM7b is 0.90 in dia.
Seems the first version had the weird paint job, term used is Partina, I call it speckled, it was a lighter gray color, then it seems ithe SM7 soon went to a smooth black to todays smooth black. The inside of the SM7 is fully painted, which the "assembled in Mexico" was also fully painted inside the body cavity (I thought that was a sign it was fake which I was wrong).
Anyway, I took it apart. The back plates and took pictures. Then I took the body apart and last I took the thumb wheels off that was a bit difficult due to the brass slip-washer has to "wiggle" in. This old one is missing a wavy-washer and so its a bit loose as it hangs. Someone had flipped it around putting the XLR in front, like the new SM7B, but the XLR can be turned to the back as the original if its preferred but the thumb knobs and body has to be disassembled to flip the XLR to front or back.
To clean the capsule up I only used the soft brush and it cleaned up easily. I didn't use any liquids and didn't need the cotton ball.
I didn't take the capsule out but noted some differences to the new capsule mainly only tape noted and the clamp ring looks brass not pot steel as the new capsules (humming coil wires etc must be inside? I couldn't see anything.
I returned the "assembled in Mexico" SM7 non-humbucking coil version used in previous posts here, because I convinced myself it might be a fake , as it was in too good of condition and others online line looked really identical, Im probably wrong but anyway...an early 1970s one popped up seeming more "original" so I grabbed it instead.
Both had the same noise floor in my closet studio. So humbucking coil or not , I didn't see a difference in the idle noise graph, but I don't have a CRT humming away either.
I tore the mic apart being as careful as I could, and thought I might as well take some pictures, an thought I might as well post some here for any gearhead taking apart a SM7.
From searching around there is little data on replacement screws for this mic. The miniscule tiny screws for the back plate are M25, its 0.086 inch diameter! so tiny and the part number Shure doesn't have listed as stock to buy. Super tiny screws to take the backplate off and adjust the EQ settings. Length is 0.110 inch. Philips head/ cross. I think I found some on Amazon. The three screws holding the basket and yoke, allowing to pull the capsule and body out are a strange cross/Phillips screw but like a socket head 0.65 dia, .585 length. Also noticed the yoke pipe with XLR attached is smaller the old one 0.65 in and the SM7b is 0.90 in dia.
Seems the first version had the weird paint job, term used is Partina, I call it speckled, it was a lighter gray color, then it seems ithe SM7 soon went to a smooth black to todays smooth black. The inside of the SM7 is fully painted, which the "assembled in Mexico" was also fully painted inside the body cavity (I thought that was a sign it was fake which I was wrong).
Anyway, I took it apart. The back plates and took pictures. Then I took the body apart and last I took the thumb wheels off that was a bit difficult due to the brass slip-washer has to "wiggle" in. This old one is missing a wavy-washer and so its a bit loose as it hangs. Someone had flipped it around putting the XLR in front, like the new SM7B, but the XLR can be turned to the back as the original if its preferred but the thumb knobs and body has to be disassembled to flip the XLR to front or back.
To clean the capsule up I only used the soft brush and it cleaned up easily. I didn't use any liquids and didn't need the cotton ball.
I didn't take the capsule out but noted some differences to the new capsule mainly only tape noted and the clamp ring looks brass not pot steel as the new capsules (humming coil wires etc must be inside? I couldn't see anything.
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