Need help minimizing outside sound

D

David W. Richardson

Chapelgrove Films
I'm preparing to shoot a series of training videos. The shoot location is provided by the client. It's a former school band room, so it has some sound absorbing tiles on the walls, which is fine. However, the building sits mere feet from a fairly busy road, and traffic noise is a problem.

I think a good deal of the traffic noise comes into the room via a set of glass doors, which lead straight from the room to the sidewalk outside. I'm looking for something I can use to block those doors to help reduce the amount of sound coming through them.

My budget is extremely limited -- I'm making very little on these videos, just trying to help a buddy out.

When we shot 'Tangled Web', we leaned mattresses against room walls to help cut down on the reverb. Most materials I can think of that are for sound absorption seem to work best with keeping sound from reflecting, and don't seem geared towards preventing sound from passing through them.

My mic is a Rode NTG-2. I know -- not the best choice for indoor dialogue work, but it's what I have available.

Anybody got a CHEAP, outside-the-box idea for cutting down on this unwanted sound?

Thanks in advance!
 
Sound absorption requires mass. If you've got no dough, the only things I can recommend (in order of effectiveness):
1) move to a better location that doesn't have the problem
2) get the microphone incredibly close. A lavaliere sticking in his beard and an inch away from his mouth would be ideal and would overcome most all exterior noise. Proximity is vital; the background sound will double in volume as the mic distance doubles, so 2" away would mean twice the background noise, 4" away means 4x, 8" away means 8x as much background noise.
3) park a big ol' semi truck or moving van in front of the window, to block some of the noise. I don't actually think that'd work, but hey, it probably wouldn't hurt...
 
Padded moving blankets are cheap and can be very effective. They are very commonly used in recording studios for various kinds of sound absorption and isolation. Barry's right that mass is the key (real "soundproofing" uses, among other things, layers and layers of sheetrock sandwiched with absorptive material), but absent that, moving blankets are among the cheapest, most efficient, and adaptable of solutions. You can layer them as many times over a door or whatever as you need (and you may need several, so bring plenty), and they can still be easily lifted for access to it. They are also very effective at cutting excess room ambience (ever notice how dead the ambience is inside of a blanket-lined elevator?).

One thing to remember is that they are heavy, and will generally not stay put when attached to a wall by something like gaffer tape. They'll stick for a while, then fall off at just the wrong moment, which will drive you nuts, I promise. They need to be draped over something (easy) or hung by some kind of hardware (not so easy in many cases). In the case of doors like you describe you might be able to devise some kind of coathanger-wire S-hooks that would slip over the top of the closed door and hook into holes in the blankets. Try placing the holes well below the blanket's top edges so there's an overlapping flap above the door, which will be light enough that it can be successfully taped up. Blankets that are specifically designed for elevators have grommet holes in them (which can be good), but are generally much smaller than non-grommeted ones (not so good).

I should also note that solutions of this kind are much better at reducing higher frequencies than lower ones. Big truck engines, fire trucks, big motorcycles, etc. will still get through them to a lesser extent, but general traffic noise/outside ambience will be greatly reduced.

A google search for "padded moving blanket" will quickly turn up some vendors.

Hope this helps
 
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As Mr. Green and Mr. Spencer have observed, sound is primarily absorbed by either mass or distance. Moving blankets are effective at reducing reflection, but NOT reducing sound transmission, particularly low-frequency traffic rumble. It seems quieter in the freight elevator with the moving pads on the walls, but we automatically filter out the rumbling sounds of the elevator itself. The microphone doesn't do that automatic filtering (alas!)

If I had to shoot there I would:
1. Use your idea of mattresses leaned up against the big glass door (and windows also).
2. Use a very close mic. Even go to Radio Shack and get a 33-3012 Headset Microphone (~$25). If you can't reduce the ambient noise then make the desired signal much higher to increase the signal-to-noise ratio (SNR). If this is a training video, then having the headset mic on-camera should not be an issue.

A $25 mic at the right distance will outperform a $10000 mic that is too far away (or used improperly as using a shotgun mic indoors, etc.)

Oh, and tell them that next time YOU get veto on location selection!
 
Richard Crowley said:
Moving blankets are effective at reducing reflection, but NOT reducing sound transmission, particularly low-frequency traffic rumble.
Click to expand...

I beg to differ, to an extent...

As I said above by way of agreement, they will not be nearly as effective where low frequencies are concerned. But they do reduce sound transmission in the midrange and especially upper frequencies to a highly useful extent - certainly enough to warrant their use given their low cost, ease of transportability (they can even be used to protect other gear you're schlepping), and flexibility in use.

In recording studio sessions, which I have done thousands of, moving blankets are ubiquitous for additional isolation on grand pianos, bass drums (within a drum kit), hung over gobos (audio-ese for movable baffles), and any other darn thing you can stick them on. Believe me, they absolutely DO reduce sound transmission (called "leakage" when it's between instruments in the same room in a recording session), even at low frequencies. Several layers of blankets over the open side of a grand piano can reduce overall leakage by a very significant amount, and likewise on a bass drum, will keep other drums and cymbals substantially out of its mic (which is normally inside it) while containing the bass drum's own sound transmission outward a fair bit as well.

At the risk of sounding arrogant here, I'll state unequivocally that this is the case, and will engage in no arguments on the matter, since I've proven it to myself thousands of times over in my very long career in music recording. To assert flatly that moving blankets, particularly multiple layers of them, will not reduce sound transmission is simply incorrect.

Harrumph! : )

Oh, and tell them that next time YOU get veto on location selection!
Click to expand...

Yeah. That is so key, and so many projects are all but ruined sonically by a bad choice there. All the more regrettable when much better alternatives are usually quite easy to find.
 
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Ted Spencer said:
I beg to differ, to an extent... As I said above by way of agreement, they will not be nearly as effective where low frequencies are concerned. But they do reduce sound transmission in the midrange and especially upper frequencies to a highly useful extent - .
Click to expand...

So we appear to be in "violent agreement" :grin:

Yes, certainly I have used sound/moving blankets (and their equivalents) as "gobos" to achieve some separation, both in a studio and on location. As often as not, I will use the grand piano cover to control its sound projection, etc.

But you will need a whole grip truck full of sound blankets to achieve any significant mitigation of traffic noise. And as Mr. Green suggested, parking the truck itself in a strategic spot to intercept the noise may be of more benefit than unpacking the moving pads out of the truck and hanging them about.
 
Well like I said, I'm helping a buddy. He teaches martial arts to low income folks, so he uses the location he can get. It's good for his purposes, not ideal for ours.

And because the videos involve him instructing in martial arts, there's a lot of movement and sparring and falling and rolling and kicking and stuff, which played havoc with the wireless lav we tried to use before. So a lav is not really going to work for us.

If we had a hyercardioid, that would at least help cut some of the sound from behind the mic, which is where the road outside will be. But it wouldn't be a huge change.

Been talking with my brother, who is an engineer. We're considering a multi-layered approach. First, an eggshell foam mattress cover placed over the doors, with the bumpy side facing the street outside. The bumps (pyramids) will help break up the smooth sound waves and turn them into smaller wave fragments.

Behind that, several inches of dense foam rubber. This will absorb some of the noise, especially the higher frequencies. Then behind that, a layer of styrofoam, whose properties will help to absorb a different spectrum of the noise.

All of this designed to fit TIGHTLY into the cavity in which the doors are set.

It won't be ideal. And it won't cut much, if any, of the lower frequency sound. But unless anybody can add something that will help, it's all I've got to go on right now. (Still thinking about laying a mattress on it too.)

Because of the nature of what the subject is doing, he'll be moving around a fair bit. So distance to the mic will vary, but we'll try to keep it as close and clean as we can.

Thanks guys! Any other thoughts? (Someone suggested blowing up the road.) :)
 
It's also been suggested that piling something like heavy bags of rice or beans or something similar against the doors themselves would help to keep the glass from resonating like the diaphragm of a speaker, and keep it from transmitting the sound as efficiently. That's another interesting thought.
 
Anyway of him demonstrating his martial arts in that room, and recording a V/O separately...? or have him stop what he is doing, cut to a new shot ( a CU perhaps) and have him speak with a lav on??
If changing the room and mic wont work, you might have to consider changing the format of your shoot in someway... even if i just means recording the V.O in the hallway outside....?

Just some suggestions on top of what has been said, hope it gives you some ideas.

Tom.
 
The mattress foam will do almost nothing due to its almost complete lack of density (it's about 95% air). An equivalent thickness of moving blankets would have far greater absorption.
 
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Once you get the "Woobie" vs. Mattress thing figured out another consideration for sound from a road way is time of day. There is usually more traffic noise in the morning and afternoon rush hours then at other times of the day. The best time to deal with a roadway is early Sunday morning, if that is not possible, then latter in the evening, after rush hour may be better. The most quite time may vary with each road, so maybe research that for your situation. If you can't veto the location, maybe try to get your choice of time to shoot it.

This is also a consideration for future use, when you are scouting a location make sure that scout it at the time of day (and day of week) very close to when you think that you will be shooting there. Trust me on this one. I have made the mistake of doing location scouting early on weekend mornings, and found nice quite surroundings, just to get back to the location to shot on a week day and had to endure loud traffic that almost ruined the audio. Live and learn.

I do keep a lot of blankets and comforters around to use as sound blankets and have just collected them over the years. I get old used ones from family basements and garages pick them up from tossed out rubbish and gotten a stack or two from yard sales. I like the big foam filled comforters, but they are a pain to keep taped up and to deal with. Good luck.
 
chapelgrovefilms said:
It won't be ideal. And it won't cut much, if any, of the lower frequency sound. But unless anybody can add something that will help, it's all I've got to go on right now. (Still thinking about laying a mattress on it too.)
Click to expand...

So if it is martial arts, he can simply yell everything! (In the finest tradition of Monty Python) :grin:

I have heard reports that piling up a wall of hay-bales (the traditional rectangular ones) produces a very substantial sound block. Of course you need to make it big enough (at least as big as the entire wall that faces the road) or the pesky low frequencies will simply go around it.

I have no idea whether this might be the slightest bit practical in your situation, but others have quite amazed at the sound absorption and blocking (two different functions) of hay bales.
 
Lots of good suggestions here. Shoot at 3 a.m. and you might have dramatically lower traffic noise. Hay bales are very dense, I bet a wall of 'em would indeed work to cut some noise. Lots and lots of heavy sound blankets can effectively cut high-frequency and, if you have lots of 'em, middle-frequency sound transmission. But don't get it wrong -- what you want is MASS. Don't think that a little u-haul 10-oz blanket is going to do anything for you. The moving blankets I use are nine pounds each. Put a gross of those up, and you'll now have some serious mass, and can maybe make some progress there.

Do not underestimate the value of close mic'ing. If you can't get that mic right in on him, *nothing* else you do is going to matter. Just try it -- see what an astonishing difference an extremely-close mic can do for you.

Finally, if you get it to the point where you're actually blocking some of the high and mid frequencies, and your soundtrack is now only being polluted by a low rumble, you can always try a high-pass filter in your NLE to eliminate all those lower frequencies. Don't go too far or you'll take the meat out of the host's voice, but you can clean up a lot of rumble if you're willing to sacrifice part of your audio spectrum.
 
Barry_Green said:
Do not underestimate the value of close mic'ing. If you can't get that mic right in on him, *nothing* else you do is going to matter. Just try it -- see what an astonishing difference an extremely-close mic can do for you.
Click to expand...

At least know what is the cost of renting a decent wireless rig with a headset mic for the project. It may end up being the least expensive way of getting decent audio in a difficult situation. Lots of exercise and martial arts people use headset mics even during vigorous movement, so that should not be a deal-breaker.

And, of course, Mr. Green is correct that after all is said and done, rolling off the LF will certainly go a long ways toward reducing the noise below the fundamental of the instructor's voice. You would be better off if he were a tenor and not a bass. :)
 
A big aspect of sound isolation, especially bass isoation, is getting an air tight seal on any treatment you're doing. One of the simplest bass isolation strategies most people use is adding weather stripping around doors.
Which is also to say make sure that any sound treatment strategies you try block 100% of the glass and edges.

A safety warning, before you start blocking any doors, make sure you're not breaking any fire codes and that there's another exit close by.

chapelgrovefilms said:
Been talking with my brother, who is an engineer. We're considering a multi-layered approach. First, an eggshell foam mattress cover placed over the doors, with the bumpy side facing the street outside. The bumps (pyramids) will help break up the smooth sound waves and turn them into smaller wave fragments.

Behind that, several inches of dense foam rubber. This will absorb some of the noise, especially the higher frequencies. Then behind that, a layer of styrofoam, whose properties will help to absorb a different spectrum of the noise.

All of this designed to fit TIGHTLY into the cavity in which the doors are set.
Click to expand...

I'm an acoustical engineer, and egg crates used in that fashion are going to be nearly worthless. I agree it seems like it'd work, but not really the case. The only way to "break up" sound is through diffusion, and that's designed to reflect sound rather than break it up as it passes through it.

Dense foam rubber is going to be most effective against bass. An acoustical product example would be Auralex's SheetBlok which is fairly transparent to HF sounds, but blocks out a high % of bass. (Expensive and not very portable for this project, but just the principle involved)

I'd say the best overall bet would be heavy layers of blankets covering 100% of the glass, then rubber, and finally mattresses.

Don't forget to check if sound could leak around your isolation through ceiling tiles (commonly thin and with air behind them, in which case you'd want to stuff insulation throughout), the walls, or the floor.

Biggest factors are likely going to be getting the mic close, and rolling off the bass though when all's said and done.
 
Richard Crowley said:
At least know what is the cost of renting a decent wireless rig with a headset mic for the project. It may end up being the least expensive way of getting decent audio in a difficult situation. Lots of exercise and martial arts people use headset mics even during vigorous movement, so that should not be a deal-breaker.

And, of course, Mr. Green is correct that after all is said and done, rolling off the LF will certainly go a long ways toward reducing the noise below the fundamental of the instructor's voice. You would be better off if he were a tenor and not a bass. :)
Click to expand...

There were several problems with the wireless mic. Lots of noise on movements. It kept dropping out. And the biggest problem was he often has his assistant pulled tight against him when demonstrating a hold or position -- effectively covering the mic with the guy's body.

Additionally, the wireless mics we have are omnis, which means even more likelihood of picking up the street noise.

We did scout the location at the same time of day, and same day of the week, as the time we'll be shooting. That's how we know what the noise situation will be. We'll be shooting on a Sunday afternoon. Other than the dead of night, it's not likely to get much quieter than that.

The hay bales might be worth trying. I know a farmer. :)

Any other thoughts???
 
That's why a headworn Wireless mic (as suggested earlier) would be the best choice as it will eliminate the clothing noise problems and the other person blocking the mic problems.
 
Also record some roomsound with the rode mice. And also some sounds of fighting, hitting, falling on ground...

You might not need it... but precausing is better then healing (don't know if this is said also in english ?)
 
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