Windscreens and Mounts: The Basics

October 8, 2009 at 2:53 pm

windscreenmount

Microphone Suspensions
The purpose of a microphone suspension is to isolate the microphone from noises produced by external mechanical vibrations. These unwanted noises are transmitted to the mic capsule through whatever is holding the mic. If the mic is hand-held one sometimes hears rubbing noises and sometimes thumping noises. These can be effectively controlled by not moving the hand on the mic and by holding it fairly still. Problem solved. Singers and interviewers do it all the time. The human hand can be a reasonably good suspension device. In most film and video production situations hand-held mics are not effective, one arm is too short. We need to mount the mic on a rigid pole. The rigidity of the boom pole is where the problems begin. Boom poles transmit vibrations rather well, some better than others. Many clever people have spent decades trying to build a device, a shock mount, to put on the end of the boom that will do what our hands can do so easily.

The best shock mounts hold the microphone securely while preventing the transmission of vibrations from the support frame. Engineers have tried several techniques over the past hundred years:
coiled metal springs,
spring steel wires and rods,
rubber bands of every size and shape,
molded rubber holders,
neoprene, Sorbothane, and urethane foam blocks,
elastic cords,
silicone or  neoprene O-rings
specially shaped plastic clips and frames

The truth is that none of these completely eliminate handling noise. No matter how much you spend, it still comes down to the hands of the boom operator. Even the best modern suspensions can only attenuate the problem, they can’t eliminate it completely.

A few of the older suspensions still produce excellent results. One of the top 5 suspension mounts is the Electrovoice model 307. It has been around for 50 years. It is still be available in the EV catalogues and still in use by the broadcast industry and some old-school boom ops. It does not fit in a zeppelin, but it can be used outdoors with a slip-on fur windscreen. The EV307 works with almost any mic, long or short. I’ve had one for 30 years and it still works perfectly. Most users, however, find the EV307′s are just too big for many location situations. It’s interesting to realize that some older designs compete successfully with the latest and greatest. A blast from the past – manufacturer specs of the EV 307 (152K PDF)

In modern terms there are several usable suspension designs, depending on the size and weight of the microphone. For short mics (8″ or less) there are compact suspensions from almost every major mic manufacturer plus high-quality models from third party manufacturers. For shotgun mics there are fewer choices but still several good ones worth looking at. There are only a few companies that put much time and effort into suspension research and development. One company has made several significant contributions over a period of 30 years or more, Rycote of England. This company just makes mic support and wind control products and systems.  They have produced several useful innovations over the years. Their suspensions usually become the yardstick against which other products are measured. Other companies have made significant contributions over the years as well, eg, Lightwave, Ktek, and PSC. The best shock mount today is one of the simplest and least expensive. It’s the “Lyre” mount from Rycote.

The suspension mount is only part of the noise problem.  Unwanted handling noise can also get to the mic capsule through the mic cable. Most modern 6-8mm mic cables do, in fact, transmit mechanical vibrations fairly well.  Studio booms originally used cloth covered cables between the mic and the suspension, and some technicians still use this cable. In the ’70′s Electrovoice introduced a thinner, coiled jumper cable on their suspensions.  The original EV cables were not very well shielded and were susceptible to RF interference, but the mechanical isolation was excellent.  Currently, there are superior, lightweight isolation cables available using miniature (4mm) star-quad cable.  This cable offers both improved mechanical isolation and excellent RFI and EMI rejection. The use of this cable will noticeably improve the performance of any suspension mount. Details of Star Quad construction from Canare (67K PDF)

Windscreens
Most microphones are supplied with foam windscreens.  One of the first disappointments felt by beginning sound recordists is how little they do. The most annoying wind noise occurs at lower frequencies. The wind noise sounds like bass drum thumps. These thumps represent the diaphragm of the microphone being deflected beyond its tolerance by changes in wind (air) pressure. When the diaphragm moves too far the output from the mic distorts, and the result is unusable audio. A truly effective windscreen must first diffuse the wind, equalize the air pressure around the capsule, and thus reduce the air turbulence at the diaphragm.  This is achieved with a porous barrier (foam, plastic mesh, fabric, or fur, in various combinations) to create a hollow air chamber, with the microphone capsule suspended in the middle.  The acoustic transparency of the windscreen cover will have a greater or lesser effect on the audio. As the porosity of the cover decreases, as would be the case with heavier, denser fabric, there will be an increasing loss of audio at higher frequencies. There is always a trade-off between the acoustic transparency and the wind-blocking capability of the windscreen cover. Generally speaking, the bigger the dead-air chamber created, the better. This is the classic engineering technique to deal with wind problems.

Many early windscreens were just as effective as the ones we have today.  The advantage of modern designs lies in two areas: ease of use, and light-weight materials. The large boom mics popular in the 40′s and 50′s were usually surrounded by a wire-frame cage, and covered with a semi-porous cloth. They worked well enough but they were the size of basketballs and the whole assembly, with the mic, weighed up to 10 pounds. These mics required a 500 lb Fisher boom or a Mole-Richardson perambulator boom

mole-richardson_perambulato

to hold them up.  In the 1960′s condenser microphones became smaller and lighter, which allowed the use of handheld boom poles.  In the 1970′s, Sennheiser came out with the revolutionary 804/805 condenser shotgun mics.  Not long after that they came out with the first zeppelin windscreen.  You can still find them, and they still work as well as any modern zeppelin.  Sennheiser now makes 2 modern lightweight plastic zeppelins that work very well. They also make a decent 4-point, O-ring type suspension that slides into it.

zepplin_rick

In the 70′s, Lightwave offered their first Zeppelin which used light-weight plastic materials instead of the fiberglass and aluminum used by Sennheiser.  Rycote came along about the same time.  Rycote has continued over the years to create, adapt, and borrow many refinements to the basic zeppelin idea.  Rycote eventually purchased Lightwave. Perhaps the greatest innovation Rycote introduced was the use of synthetic fur wind covers.  The use of faux fur has almost doubled the high-wind performance of windscreens in extreme conditions.  In recent years other manufacturers have introduced versions of the zeppelin and now there are several from which to choose.

Most news crews are familiar with the Foam and Fur type, slip-on windscreens, generically known as Softies (another Rycote innovation). These windscreens are a cost effective solution for working outdoors in light winds up to 20-25 km/h. There is a significant advantage with these windscreens in that they are smaller, lighter, and less conspicuous than the full-on zeppelin models. While they represent a significant improvement over stock foam windscreens they cannot match the high wind performance of a zeppelin design.

fuzzies_rick

Low budget filmmakers should keep in mind it is entirely possible to build home-made suspensions and windscreens that will get the job done. Look closely at the products available commercially. The physics involved is not all that difficult.  A useable suspension can be built with some 3″ ABS drain pipe, a hacksaw, and some fat rubber bands. The windscreen used on some of the early Fellini films was a wire cage, formed with coat hanger wire, covered in cheesecloth.  And that was before duct tape!  Such constructions may not be pretty, but they can be surprisingly effective.

Rain presents special challenges. There is the obvious problem of keeping the mic dry and the secondary problem of the noise that results from raindrops hitting the windscreen. The bigger the drops, the louder the noise. The noise is like someone tapping lightly on the mic. You’ve heard this noise while standing under an umbrella in a heavy rain. It’s very distracting. Foam windscreens do little or nothing to protect the mic and reduce rain noise. Fur and foam wind covers will protect the mic and dissipate the rain noise for a few minutes, until they get soaked through. Then the rain noise will return, the mic will get wet, and fail. Zeppelins with fur covers are the same, the fur protects the mic well but will load-up with water eventually and develop bad acoustics. Once the fur is soaked and matted, the mic will start to sound like it is inside a solid tube.

The old-school solution to rain-on-the-mic was called “hog’s hair”. This was a course, lightweight fiber matting used for packaging large appliances in the days before styrofoam. I think it was actually made out of recycled hogs’ hair. The idea was to bend a piece of hog’s hair matting around the zeppelin so it formed a curved “roof” above the mic. A similar material exists today which is used in industrial air-conditioning applications. It’s no longer derived from hogs. It’s usually blue and about 1″ thick. You occasionally see it at the hardware store in the furnace filter section. It works. Larger pieces of modern hog’s hair can be hard to come by. It has an excellent application for rain noise control on buildings and car roofs.

The most popular solution to rain noise is polyester batting, or Snow Blanket. This is a product used in sewing (quilting) and upholstery fabrication. The material is a light, fluffy polyester fiber mat from 1/2″ to 1″ thick, usually white. It is readily available at sewing supply stores (1/2″) or upholstery supply stores (1″).  If you lay a piece on the ground and step back a few paces, it looks like snow. Special Effects crews carry it on shoots when real snow is unavailable or unreliable. It is light and fluffy so air moves through it easily, making it acoustically transparent. The basic technique is to wrap the zeppelin in one or two layers of batting and hold it in place with a couple of elastic bands. When water drops hit the batting the drops are dispersed on impact, with little or no noise. Polyester batting doesn’t absorb much water, instead, water runs through it, around the zeppelin, and drips off the lowest point of the windscreen. The microphone inside the zeppelin usually stays dry, even in a heavy rain. Booming close-ups in heavy rain can be challenging. As the water drips off the windscreen the drips usually show up right in the middle of the shot. There is a professionally made, snow-blanket style, rain cover for short shotgun mics called “The Rainman”. The Rainman looks quite a bit better than a wrap of ratty looking snow blanket.

A complete zeppelin-type windscreen and suspension system can cost several hundred dollars. That could be more than the cost of the microphone inside the windscreen. That explains the presence of many less expensive wind control products. Just be aware, when you encounter gale conditions (ie, windspeeds above 20 mph or 30km/h), the lower priced products will fail. It was interesting to watch the news coverage of Hurricane Katrina in 2005.  Some crews had lesser windscreens and the reporters’ dialogue was almost unintelligible. Other crews had better windscreens and the audio was terrific.
Rick Patton
Excerpt from “Sound Man” by Rick Patton
C 2009, reprinted with permission.