My usual way of matching levels when comparing mics etc is RMS-Level matching (Steinberg Wavelab has a meta-normalizer plug-in in the batch processing section). Of course you have to manually match levels as closely as possible while recording. Manual matching + automatic RMS-Level matching works pretty well. In fact so well that you begin to question your own ears :roll:
Mic Loading Confusion
- Thread starter chris319
- Start date
Help Support GroupDIY Audio Forum:
pstamler
Well-known member
[quote author="chris319"]
Classic ribbons -- RCA 44, 77, etc., or their clones from AEA. Probably nothing else.
Peace,
Paul
Paul, under what circumstances do you think there would be a need for a 10k load?[/quote]
Classic ribbons -- RCA 44, 77, etc., or their clones from AEA. Probably nothing else.
Peace,
Paul
>> Classic ribbons were designed to work into a high-impedance input: a transformer with the secondary connected to the tube's grid, and no terminating resistor. Use them into a 1.5k load, typical of modern mixers, and you overdamp them, leaving you with muffled highs.
> I am wondering why would be that and what is the theory behind it?
Compare with all other common mikes. A ribbon has a smaller diaphragm area and a weaker magnetic circuit. It does not catch much power, it does not transduce efficiently. Of necessity, it is designed to a target efficiency higher than any other common type, so that despite its losses it can give a usable output.
The diaphragm is "small" all across most of the audio band, but starts to get not-small at the top of the band where diaphragm and baffle size approaches a fraction of a wavelength. Now we have some acoustic loading. This appears in series with the electrical output, somewhat like a hi-compression horn driver reflects acoustic loading as a higher midband input impedance. If the ribbon's electrical load is infinite, that added resistance has no effect. If the ribbon is loaded, the top droops off.
> The reason Beyers work fine with low loads is that they are tiny (about 0.06"x0.910") and work as very rigid pistons--only God knows what is the tuning frequency
I bet they are corrugated at both ends, the rigid part limply suspended, just as cone loudspeakers are. And the bidirectional types "must" be tuned to the bottom of the audio band. The acoustic response rises with frequency, the mechanical response must fall with frequency, so it must be mass controlled over the useful range.
They will not see "real" acoustic loading until half-wavelength approaches 0.233" or 11KHz. The effect may be negligible for another octave or more due to the non-square dimensions (the acoustic impedance gets Real slowly). So the rise of electrical impedance above half-wavelength may have little effect.
> absolutely essential to meticulously compensate for the associated gain loss.
Oh baloney. Decide which product you want to "win". Perhaps the one you like best. Perhaps the one with the best dealer mark-up. Make sure it is louder than the others.
> I am wondering why would be that and what is the theory behind it?
Compare with all other common mikes. A ribbon has a smaller diaphragm area and a weaker magnetic circuit. It does not catch much power, it does not transduce efficiently. Of necessity, it is designed to a target efficiency higher than any other common type, so that despite its losses it can give a usable output.
The diaphragm is "small" all across most of the audio band, but starts to get not-small at the top of the band where diaphragm and baffle size approaches a fraction of a wavelength. Now we have some acoustic loading. This appears in series with the electrical output, somewhat like a hi-compression horn driver reflects acoustic loading as a higher midband input impedance. If the ribbon's electrical load is infinite, that added resistance has no effect. If the ribbon is loaded, the top droops off.
> The reason Beyers work fine with low loads is that they are tiny (about 0.06"x0.910") and work as very rigid pistons--only God knows what is the tuning frequency
I bet they are corrugated at both ends, the rigid part limply suspended, just as cone loudspeakers are. And the bidirectional types "must" be tuned to the bottom of the audio band. The acoustic response rises with frequency, the mechanical response must fall with frequency, so it must be mass controlled over the useful range.
They will not see "real" acoustic loading until half-wavelength approaches 0.233" or 11KHz. The effect may be negligible for another octave or more due to the non-square dimensions (the acoustic impedance gets Real slowly). So the rise of electrical impedance above half-wavelength may have little effect.
> absolutely essential to meticulously compensate for the associated gain loss.
Oh baloney. Decide which product you want to "win". Perhaps the one you like best. Perhaps the one with the best dealer mark-up. Make sure it is louder than the others.
Marik
Well-known member
[quote author="PRR"]>> Classic ribbons were designed to work into a high-impedance input: a transformer with the secondary connected to the tube's grid, and no terminating resistor. Use them into a 1.5k load, typical of modern mixers, and you overdamp them, leaving you with muffled highs.
> I am wondering why would be that and what is the theory behind it?
The diaphragm is "small" all across most of the audio band, but starts to get not-small at the top of the band where diaphragm and baffle size approaches a fraction of a wavelength. Now we have some acoustic loading. This appears in series with the electrical output, somewhat like a hi-compression horn driver reflects acoustic loading as a higher midband input impedance. If the ribbon's electrical load is infinite, that added resistance has no effect. If the ribbon is loaded, the top droops off. [/quote]
A 1" path length around the baffle would be considered as a very small for an efficient ribbon, resulting in a nulling @ 13.5KHz. On the other hand, ribbon width of 0.25" would be considered already as a "very large" and translates into 54KHz. Even half wavelength will be still way out of audio band.
What am I missing?
> I am wondering why would be that and what is the theory behind it?
The diaphragm is "small" all across most of the audio band, but starts to get not-small at the top of the band where diaphragm and baffle size approaches a fraction of a wavelength. Now we have some acoustic loading. This appears in series with the electrical output, somewhat like a hi-compression horn driver reflects acoustic loading as a higher midband input impedance. If the ribbon's electrical load is infinite, that added resistance has no effect. If the ribbon is loaded, the top droops off. [/quote]
A 1" path length around the baffle would be considered as a very small for an efficient ribbon, resulting in a nulling @ 13.5KHz. On the other hand, ribbon width of 0.25" would be considered already as a "very large" and translates into 54KHz. Even half wavelength will be still way out of audio band.
What am I missing?
Here is a manufacturer which specifies a recommended load for its classic ribbon mic clone -- and it's only 1.2k!
http://www.wesdooley.com/pdf/aea_r44_technical_onesheet_2.1_web.pdf
Yet this company's preamp has an input load of 18k.
I like the idea of having a high input load built into my preamp and then being able to bring it down with XLR barrels (or a rotary switch if I want to get fancy). Are we all in agreement that 10k should be the highest impedance supported?
http://www.wesdooley.com/pdf/aea_r44_technical_onesheet_2.1_web.pdf
Yet this company's preamp has an input load of 18k.
I like the idea of having a high input load built into my preamp and then being able to bring it down with XLR barrels (or a rotary switch if I want to get fancy). Are we all in agreement that 10k should be the highest impedance supported?
That's a (common) inaccuracy in nomenclature. What is often called "recommended load impedance" should actually be called "recommended minimum load impedance." Sometimes this is called "rated load impedance" i.e. it is the lowest impedance at which the mic manufacturer guarantees the performance as specified in the data sheet.
A lot of manufacturers don't give you the "or greater" stuff. Which is why a lot of beginners think you have to match the preamp's input impedance with whatever the mic manufacturer recommends. Hence the craze for variable impedance preamps.
In their product literature many of those preamp manufacturers - especially those in the low cost field - recommend low input impedances for use with ribbon microphones. Which tells you they have no idea what they're talking about and have never conducted actual tests.
In their product literature many of those preamp manufacturers - especially those in the low cost field - recommend low input impedances for use with ribbon microphones. Which tells you they have no idea what they're talking about and have never conducted actual tests.
Marik
Well-known member
[quote author="Rossi"]
In their product literature many of those preamp manufacturers - especially those in the low cost field - recommend low input impedances for use with ribbon microphones. Which tells you they have no idea what they're talking about and have never conducted actual tests.[/quote]
Or maybe because they know precisely what they are talking about :wink: .
There is much more into the microphone response and input impedance relationship than one might think.
The microphone loading and acoustical damping both have somewhat similar effect, and both affect frequency response and suppress ribbon's resonant modes. There were good reasons why so called "classic" mics worked best when unloaded where the first and foremost was that their frequency response was taylored by means of acoustical damping, which in turn had also to do a lot with ribbon protection.
On the other hand if we have a cheap ribbon mic which is usually acoustically underdamped (esp. with 5-6um ribbons, which are very common), then ribbons loading can actually improve the response.
Best, M
In their product literature many of those preamp manufacturers - especially those in the low cost field - recommend low input impedances for use with ribbon microphones. Which tells you they have no idea what they're talking about and have never conducted actual tests.[/quote]
Or maybe because they know precisely what they are talking about :wink: .
There is much more into the microphone response and input impedance relationship than one might think.
The microphone loading and acoustical damping both have somewhat similar effect, and both affect frequency response and suppress ribbon's resonant modes. There were good reasons why so called "classic" mics worked best when unloaded where the first and foremost was that their frequency response was taylored by means of acoustical damping, which in turn had also to do a lot with ribbon protection.
On the other hand if we have a cheap ribbon mic which is usually acoustically underdamped (esp. with 5-6um ribbons, which are very common), then ribbons loading can actually improve the response.
Best, M
bcarso
Well-known member
So at the end of the day, maybe we want variable input z preamps?
Marik
Well-known member
[quote author="bcarso"]So at the end of the day, maybe we want variable input z preamps?[/quote]
Prefreakingcisely :thumb: .
Prefreakingcisely :thumb: .
G
Guest
Guest
[quote author="bcarso"]So at the end of the day, maybe we want variable input z preamps?[/quote]
Switchable transformer plugins, "back to the future".
Switchable transformer plugins, "back to the future".
On the issue of nomenclature confusion, it's quite common for people to confuse an input transformer 'designed for x source impedance' to mean the transformer actually loads the source with that impedance, when nothing could be further from the truth. Many think older tube types quoting 150 ohm input have lower input (mic load) impedances than modern gear that may quote 2K ohm, when it's actually higher due to lack of secondary load other than the tube grid itself. Now confuse the difference in modern preamps with variable input impedance with what happens on an antique unit that has 50/250/500 input tap options. A new unit may force the mic load impedance change through more easily predictable resistive loading, while the old unit likely does nothing other than vary the turns ratio, possibly affecting gain more dramatically and giving no obvious clues as to actual reflected impedance seen by the mic.
I know this; my few ribbons all sound far better with my antique 'unloaded transformer secondary direct to tube grid' preamps than they do with any other type. They can sound downright broken with something modern/transformerless like a Sytek. Same goes for mics like the Shure SM7.
Do I ever say anything that makes any sense?
I know this; my few ribbons all sound far better with my antique 'unloaded transformer secondary direct to tube grid' preamps than they do with any other type. They can sound downright broken with something modern/transformerless like a Sytek. Same goes for mics like the Shure SM7.
Do I ever say anything that makes any sense?
bcarso
Well-known member
[quote author="emrr"]
Do I ever say anything that makes any sense?[/quote]
Yes :grin:
Do I ever say anything that makes any sense?[/quote]
Yes :grin:
[quote author="Marik"][quote author="Rossi"]
In their product literature many of those preamp manufacturers - especially those in the low cost field - recommend low input impedances for use with ribbon microphones. Which tells you they have no idea what they're talking about and have never conducted actual tests.[/quote]
Or maybe because they know precisely what they are talking about :wink: .
There is much more into the microphone response and input impedance relationship than one might think.
The microphone loading and acoustical damping both have somewhat similar effect, and both affect frequency response and suppress ribbon's resonant modes. There were good reasons why so called "classic" mics worked best when unloaded where the first and foremost was that their frequency response was taylored by means of acoustical damping, which in turn had also to do a lot with ribbon protection.
On the other hand if we have a cheap ribbon mic which is usually acoustically underdamped (esp. with 5-6um ribbons, which are very common), then ribbons loading can actually improve the response.
Best, M[/quote]
Well, I both listened and measured the effect of low Z loading, and there was no improvement, quite on the contrary. Those modern Chinese ribbons both sound and measure nicer at light loads. Keep in mind that many of those mics use slighly, sometimes heavily overwound transformers.BTW, one of those preamps I'm talking about was a flawed design in various ways (due to lack of very basic knowledge).
In their product literature many of those preamp manufacturers - especially those in the low cost field - recommend low input impedances for use with ribbon microphones. Which tells you they have no idea what they're talking about and have never conducted actual tests.[/quote]
Or maybe because they know precisely what they are talking about :wink: .
There is much more into the microphone response and input impedance relationship than one might think.
The microphone loading and acoustical damping both have somewhat similar effect, and both affect frequency response and suppress ribbon's resonant modes. There were good reasons why so called "classic" mics worked best when unloaded where the first and foremost was that their frequency response was taylored by means of acoustical damping, which in turn had also to do a lot with ribbon protection.
On the other hand if we have a cheap ribbon mic which is usually acoustically underdamped (esp. with 5-6um ribbons, which are very common), then ribbons loading can actually improve the response.
Best, M[/quote]
Well, I both listened and measured the effect of low Z loading, and there was no improvement, quite on the contrary. Those modern Chinese ribbons both sound and measure nicer at light loads. Keep in mind that many of those mics use slighly, sometimes heavily overwound transformers.BTW, one of those preamps I'm talking about was a flawed design in various ways (due to lack of very basic knowledge).
FredForssell
Well-known member
Hi Paul,
I did design the AEA TRP. It does have high input impedance, as do most of my preamps. My FetCode has 5k Zin, and my JMP-6 and SMP-2 preamps have 13k Zin. The TRP has about 19k Zin.
Are you sure that Scott actually tried this? I have and I do not agree that it sounds awful. Of course it probably depends on what you are using your SM57 to mic. I use use the SMP-2 all the time with SM57 and SM58 mics and I think it sounds great. I use the SM57 to mic guitar amps (and have clients in the Metal music world who do the same) and SM58 on stage vocals all the time. Both sound great to me. Of course YMMV.
I have taken this approach to mic preamp Zin for 30+ years and for me it started with designs that used unloaded secondaries directly connected to input grids of vacuum tubes. Back in the 1970s I was using UTC LS series transformers with my preamps and I liked the results a lot. This was a common technique then and it still makes sense now, to me anyway. While I seem to be in the minority with my hatered for the sonic effects of transformers, I do understand how to use them and the concept and effects of critical dampening or under-dampening. I also understand that transformers are the only practical solution to certain problems in audio design such as galvanic isolations (direct boxes and mic splitters), and work well for voltage gain in ribbon mics. I think that they work ok in ribbon mics primarily due to the low source Z presented by most ribbon motors ( < 1 ohm). Still, I'd like to hear a ribbon mic without a step-up transformer, and I'm about to start down the path of designing such a beast. It will NOT be a phantom powered mic, but rather a mic with a dedicated power supply. We'll see how it works, and if it is practical.
But my point in writing this reply is to state that I, for one, do NOT think the SM57 and SM58 mics suck when used with high input impedance preamps. YMMV, so my advice it try it yourself before coming to any conclusions.
pstamler
Well-known member
[quote author="FredForssell"]
Hi Paul,
I did design the AEA TRP. It does have high input impedance, as do most of my preamps. My FetCode has 5k Zin, and my JMP-6 and SMP-2 preamps have 13k Zin. The TRP has about 19k Zin.
Are you sure that Scott actually tried this? [/quote]
Well, he said in his review that he had, and I take him at his word.
Always the best strategy!
Peace,
Paul
Hi Paul,
I did design the AEA TRP. It does have high input impedance, as do most of my preamps. My FetCode has 5k Zin, and my JMP-6 and SMP-2 preamps have 13k Zin. The TRP has about 19k Zin.
Are you sure that Scott actually tried this? [/quote]
Well, he said in his review that he had, and I take him at his word.
Always the best strategy!
Peace,
Paul
G
Guest
Guest
At least, Shoeps' type transformerless output stages will be happy to work on a high impedance load, especially when mic cables are short.
bcarso
Well-known member
[quote author="FredForssell"] Still, I'd like to hear a ribbon mic without a step-up transformer, and I'm about to start down the path of designing such a beast. It will NOT be a phantom powered mic, but rather a mic with a dedicated power supply. We'll see how it works, and if it is practical.[/quote]
I chatted with Wes about this, as I had started to investigate what such a preamp might look like, and he mentioned a few people have proposed to do this from time to time. Yes, phantom power would be way too limiting.
And "practical" is a relative term here :grin: One could go with lots of FETs but I suspect a bunch of low rbb' bipolars are indicated.
I chatted with Wes about this, as I had started to investigate what such a preamp might look like, and he mentioned a few people have proposed to do this from time to time. Yes, phantom power would be way too limiting.
And "practical" is a relative term here :grin: One could go with lots of FETs but I suspect a bunch of low rbb' bipolars are indicated.
Similar threads
