Hello folks… today’s post comes courtesy of Shure Microphone’s newsletter… this article appeared in issue #27. some of this stuff is wicked technical… so for those techno-buffs… this is a treat… for those who arent… some of it is actually legible!
Debunking Common Audio Myths
When we decided to devote this issue to dispelling common audio myths and legends, we had no trouble impaneling a group of experts. Culled mostly from Shure’s Applications Engineering Group, these individuals devote their days, and sometimes their nights, to setting the record straight. Chief among this talented group is Tim Vear, who served as our primary mythbuster and spokesperson.
Some microphones are more sensitive than others but microphone sensitivity is not inherently related to quality. Condenser microphones are more sensitive than dynamic microphones, but in most musical applications when a mic is placed very close to the sound source, the sensitivity of a microphone is not important. There’s more than enough signal even from a less-sensitive microphone to give an adequate signal into a PA system.
If the microphone is overly sensitive, it just means you have to dial in more attenuation on the mixer channel so you don’t overload the mixer. If you’ve got a mic on a snare drum that’s 10 dB more sensitive than another mic on the snare, you’ll have to turn down the one that’s more sensitive.
Extra sensitivity is not related to the sound quality.
In many cases, “hotter” is equated with louder. In the days when neodymium magnet microphones were introduced, it was a common demonstration technique to line up several microphones, connect them to a mixer and set each channel level the same. Each microphone was tested and when it came to the neodymium magnet microphone, it was noticeably louder because the structure was more efficient than the alnico types.
Psycho-acoustically, listeners tend to equate louder with better and that’s been a common sales technique used in selling stereo speakers. If one pair in a store demo is turned up a little louder than the others, customers tend to think they sound better. Or are better. It’s the same with microphones. It’s a loudness difference, not a quality difference.
An in-store demo of a microphone or any other acoustic product is greatly affected by the acoustic environment of a store. (That’s why there are listening rooms.) If the store is noisy or quiet, if you’re listening to the microphone through loudspeakers or headphones, all of those factors change the perceived sound of the microphone.
A clever salesperson can set up a demo to favor a particular microphone or a loudspeaker. If you’re evaluating products in the store yourself and can control what you’re doing, you can normalize the levels and the EQ so that each microphone is getting into the system flat. Then, the only differences you’ll hear are the tonal differences of each microphone.
In-store demos are not really indicative of how the microphone will perform in real life. Ideally, you want to take a mic to a gig and use it in the environment you normally work in. Evaluate it that way.
“To hear what the microphone really sounds like, you need to record your voice speaking or singing a phrase and then listen to it in playback.”
Most people test the mic in the store wearing headphones (or listening through loudspeakers) and saying “Test, one two … test, one two” into the microphone. Because the sound of your voice reaches your ears directly through bone conduction, what you’re hearing is not just the sound of your voice through the headphones or loudspeakers, but the sound that is conducted internally.
To hear what the microphone really sounds like, you need to record your voice speaking or singing a phrase and then listen to it in playback. You can compare several mics that way and listen to the recording right in the store, wearing your own sound-isolating earphones or headphones. That will give you the best idea of what the mic really sounds like.
When the SM58 was introduced in 1967, it was aimed at broadcast applications for which it was not ultimately embraced. But it was discovered by the fledgling live sound industry where it quickly gained a reputation as a reliable, good-sounding and affordable mic for a huge range of applications. It maintains that reputation – undiminished – 40 years later.
The basic technology is the same – the diaphragm voice coil magnet assembly, the shape and size are pretty much the same as when it was first engineered.
Dynamic microphone technology hasn’t changed. Take the internal combustion gasoline engine. A 327 small-block Chevy engine is old technology. It was designed in the early 1960s and is highly regarded and widely used today because it is a proven design that offers great performance.
One of the things that makes this technology perfectly appropriate is that it is extremely stable over long periods of time. It’s going to sound and perform as well a year from now, five years from now, ten years from now and twenty years from now. And that goes right to the heart of why sound pros love these microphones. They’re extremely predictable. There’s a lot of value in knowing that this microphone is going to work.
The second part of this myth is false.
There have numerous improvements in reliability and manufacturability. There was a secondary tap on the transformer that was eliminated about 15 or 20 years ago related to a 50 ohm output impedance condition that was no longer a factor. The voice coil wire was changed to a copper clad aluminum to improve the solderability of the voice coil leads into the cartridge structure. The grounding mechanism for the output connector was changed. The paint formulations have been improved. The grille plating has been improved – the things that relate to long-term reliability have been changed incrementally throughout its history.
The sound quality of an SM58 is not a high-fidelity sound. It’s shaped in certain ways: the extreme low frequencies and the extreme high frequencies are rolled off. Those frequencies are outside the range of the human voice. If it were designed to pick up those frequencies in live sound applications, it would pick up a lot of undesired noise.
But within the vocal range, it has a characteristic rising response in the 2-10kHz range. It’s referred to as the presence rise or the presence peak – that sound characteristic, while not flat or high fidelity, is extremely useful in live sound applications because it boosts and improves the intelligibility of the human voice in the midst of other amplified sounds. That range is where the real color and identifying characteristics of a human voice exist and that is extremely useful in a vocal microphone.
The level and sound quality of the human voice varies considerably with microphone distance from very close to very far away and all points in between. It is not conducive to a consistent sound quality in a sound system. Most sound engineers will try to get performers to stay pretty much the same distance from the microphone, whether that’s two or eight inches away.
The “trombone effect” of pulling the microphone away two or three feet back when a vocalist is singing a really loud note isn’t necessary or desirable. If the system is set up and equalized for a singer who is holding the microphone an inch away and suddenly he’s holding it eight inches away, the sound will be very thin.
Every time the distance between your mouth and the microphone doubles, you lose 6 dB of sound level at the mic. That’s the Inverse Square Law. If it’s two inches away (double the distance), you get 6 dB less. If it’s four inches away (double the distance again), you get another 6 dB less. At eight inches away (double the distance yet again), the level is another 6 dB less. This is a total of 18 dB less than the level at one inch away! This means that in order to get a consistent sound level, the engineer has to push the fader up 18 dB when the mic moves from one inch away to eight inches away. This is nearly impossible without causing feedback .
On the other hand, a mic held too close will boost the low frequencies. It’s called Proximity Effect.
It’s not usually possible to overload the microphone itself. Let the sound engineer control the dynamics if necessary and you’ll get a better sound.
In the days when this myth came into existence, the average condenser microphones were very expensive, studio-grade models. The microphone they were compared to might have been a dynamic like the SM58. If I take the ultra expensive, circa 1930s vacuum tube Telefunken microphone and I dunk it into a glass of beer or drop it on the stage ten times – or even one time – it will probably stop working. It’ll become a paperweight while the SM58 will survive all that.
Today, all our condenser microphones are engineered to hold up to exactly the same abuse as an SM58 – they go through the same exact environmental testing. Drop testing. Temperature testing. Humidity testing. Salt spray testing. Vibration testing. Electromagnetic testing. They have to pass the same battery of tests – and they do.
The SM81 was introduced around 1978 as a studio condenser microphone. But because it is made from a machined steel handle and has the same sort of milspec environmental capability as the rest of our microphones, it was quickly embraced by the touring sound industry. There are SM81s out there on tour today that are probably fifteen or twenty years old. You can drive over them with a truck. Drop them on the floor. Hit them with a drumstick. And the same is true of all our condenser vocal mics.
So, in the modern era, the fragility of Shure condenser microphones is just not true.
For a sound source that has a very wide frequency range, you want a microphone that can reproduce it in a high fidelity manner. That’s what a flat response should do. The assumption is that whatever the destination of that sound, either a playback system or a live sound system, the mic will reproduce the range that you’ve gone to so much trouble to get.
The average rock and roll sound system is not a wide range flat response thing itself. So putting wide range flat response mics on the front end doesn’t get you much. You can’t hear the performance difference.
But with a very high quality sound system or a recording environment, yes.
Some sound sources like close-up pop vocals, electric guitar amps and snare drums have fairly narrow frequency ranges. There’s no reason to have a microphone that goes down to 50 Hz picking up an electric guitar amp or a voice. So a shaped response mic may be more desirable. Close-up vocals, instrument amplifiers and certain percussion instruments really can benefit from not flat, not super wide range response.
It’s completely dependent on the sound source and the environment.
We’re probably talking about vocal mics that take on a certain amount of bodily fluids during their normal lifespans.
The foam windscreen inside the grille absorbs most of the effluent that spews on microphones. If you want to clean that, you just remove the grille, wash it in warm soapy water, rinse it thoroughly in fresh water and let it air dry. That can be done many, many times before the foam disintegrates. But when that happens, you can just replace the grille. (Available at a nominal cost wherever Shure mics are sold.) We don’t recommend spraying anything (like a disinfectant) on the grille.
The cartridge is never really exposed to the kinds of things that might concern someone. Cleaning or replacing the grille pretty much restores the microphone to its original condition.
There’s no risk of damaging a microphone in either of these ways. But those kinds of noises are sometimes a problem for the sound system if it’s turned way up because those impulses can damage the loudspeakers. And either irritate or potentially damage the hearing of anyone in the room.
A more appropriate way to test the mic is to talk into it or sing into it at whatever level you’re using and let the sound engineer set the representative level.
In absolute terms, condenser mics have some characteristics that dynamic microphones don’t have. For instance, very wide frequency response, very flat frequency response and very high sensitivity. For an application that requires these things, a condenser microphone would be a better choice. But in that case, it might sound better because it captures a wider range of the original sound source in a more high fidelity fashion.
There are many sources that don’t benefit from the flatness or the frequency range of a condenser microphone. A good example is miking close up vocals for pop music. Its hardly necessary to use a microphone that has a frequency response from 20 hertz to 20 kilohertz to pick up the a sound that only has a frequency range of maybe 100 Hz to 14 or 15 kHz. The sound system that is reproducing it might not even have that wide a range.
Particularly with pop music, a flat frequency response is not going to give you the presence or the ability to cut through a mix of other amplified instruments like guitar, drums and so forth. For example, an electric guitar plugged straight into a sound system has a very dull, bassy sound. But when it’s plugged into a guitar amp that has a shaped response designed for that instrument, you get all of the brights and textures and exaggerated midrange response you want to hear in an electric guitar. A microphone with a shaped response works the same way and is often going to give you a better sound quality for that application.
Same for a kick drum — it doesn’t benefit from a flat response mic in contemporary or pop music applications. You want something with a little bit of shape to give it the oomph or the snap you need to define that drum. You’re not trying to get a high fidelity sound. You’re trying to get a particular sound.
There are numerous examples where a dynamic microphone has a more appealing or preferred sound. Snare drums. Electric guitar amplifiers. Kick drums. Close up rock & roll vocals. Certain percussion instruments. They all benefit from a dynamic microphone’s shaped response.
Reach is not a specification of a microphone. Mic users have a concept of reach as the ability of a microphone to reach out and grab the desired sound in the midst of some ambient undesired noise conditions. They believe that some microphones can pick up from farther away than other microphones.
The reality is that microphones do not reach out and grab the sound from a distance. They merely measure pressure variations right at the diaphragm itself. The microphone doesn’t “know” anything about what is happening at any distance from itself. For this reason, if you try to characterize a microphone’s “reach”, it’s almost completely dependent on the ambient acoustic conditions around the microphone.
Here’s an example: Take a microphone to the Superbowl on a Tuesday morning at 2AM in the middle of July. There’s nobody there. They’ve turned off the air conditioning and it’s a huge quiet box. You put your microphone at one side of the stadium and drop a nail on the concrete on the other side of the stadium. Yes, the microphone will pick up the sound of that nail a couple hundred yards away because there’s no ambient noise. Go back on Superbowl Sunday in the middle of the fourth quarter when the opposing quarterback is lining up to call the play. Put your microphone down on one side of the stadium, clear out the beer vendors and drop the same ten-penny nail on the concrete. Can you hear the nail? What changed? Same mic, same nail, same concrete, same building. But the ambient noise level is now 100 decibels higher.
The reach of the microphone, if you can even call it that, is mostly dependent on the ability of the microphone to pick up sound in the middle of all that noise. No microphone has a “reach” that is defined independent of ambient noise.
The one specification of a microphone that loosely corresponds to the concept of reach is directionality or the microphone’s polar pattern. The directional characteristic of a microphone describes how much sound it picks up from ambient sources compared to how much it picks up on-axis.
The numbers are there, but they’re not huge. The difference between how much ambient noise an omni-directional and a hypercardioid microphone will pick up in the same conditions is only about 6 dB. (The hypercardioid mic picks up 6 dB less ambient noise than an omni.) Because of the Inverse Square Law of Sound, if I double the distance between the sound source and the microphone, the level of the sound source drops by six decibels at this greater distance. The ambient noise stays the same. If an omnidirectional microphone picks up a certain ratio of ambient noise to on-axis sound at one foot away from a sound source, then a hypercardioid microphone can be used at two feet from the sound source and still pick up that same ratio. This is NOT because the hypercardioid is more sensitive to the on-axis sound but because it is 6dB less sensitive to the ambient noise.
In that sense, the hypercardioid has more “reach”. But neither one will work at great distances in the presence of any significant background noise. They just measure little pressure variations right at the diaphragm.
DTV: February 17, 2009 is the completion date for transition from analog television broadcast to digital television broadcast (DTV). All broadcast television stations will be required to operate in what are now channels 2-51. Only DTV stations will remain on the air. The analog stations will be gone. The former TV channels 52-69 are going to be reallocated for other purposes; one of them is Public Safety, which will be using Channels 63, 64, 68 and 69. The rest of that spectrum will be primarily used by communications services in devices that resemble cell phones.
Wireless microphone or personal monitor system products that operate in these former television bands may begin to suffer more interference from these services. That doesn’t mean that the systems won’t work any longer. But users will probably have to change frequencies to avoid these new services.
There’s still likely to be a fair amount of open spectrum in different places around the country on some of the frequency ranges. In some places though, it may be difficult to operate as many systems as previously because there may not be enough spectrum for all of it. If users have frequency-agile systems, they’ll be likely to continue using that system with very few problems in the foreseeable future.
Shure will not sell equipment that operates on channels 52-69 after February 2009 and we haven’t sold equipment in that range for some time now.
DTV is completely separate from the White Spaces issue. The only common denominator is the date – February 17, 2009.
White Spaces: Even when all the remaining TV stations are in the range of channels 2-51, there will be plenty of open channels in most places. There won’t be 51 channels on the air in every city. But there may be 15 to 33 open TV channels scattered around the country in different cities. These are the licensed channels that wireless microphones and personal monitors currently occupy.
There is a White Spaces Coalition that includes Microsoft, Intel, Google, Hewlett-Packard and several other companies proposing that a class of consumer electronic devices operate in the unused portion or the open television channels. These devices would be unlicensed, that is, anyone could operate such a device without obtaining an FCC license. Cell phones, cordless phones, and wireless laptop computers are examples of unlicensed devices. Historically, the nature of consumer electronic devices has been to heavily populate the unlicensed bands in which they have been allowed to operate. This includes the 49 MHz band, the 900mHz band, the 2.4 GHz band and several others. The concern is that new devices could disrupt professional audio users because their operation would be unpredictable.
The FCC’s issue is deployment of rural broadband Internet access, using unused TV channels to provide service. Cable is expensive to run to these areas and satellite is a downlink only, so rural high-speed broadband access via wireless transmission offers a good solution.
Shure, as part of a group of concerned audio users and manufacturers, has organized a very strong campaign within Congress and the FCC to make sure that the interests of wireless microphone users are protected. There are various technical schemes that are being proposed for these unlicensed devices to be able to detect the operation of current users of the spectrum in order to avoid interference. Pending the outcome of FCC testing, the initial target date proposed for introducing these devices is February 18. 2009 and that’s the only nexus with the DTV issue.
The task of the FCC is to weigh the needs of the current users of the spectrum (broadcasters and audio professionals) versus potential new users (consumers)–and make sure that the incumbents are not disrupted. We believe that wireless microphones will get appropriate consideration from the FCC.
The best advice for wireless audio users is to purchase frequency-agile systems.
Note: Shure posts updates on White Spaces on the company’s website, a good way to stay up-to-date on the most recent developments.