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Sound Reinforcement - Forums for Live Sound Professionals - Your Displayed Name Must Be Your Real Full Name To Post In The Live Sound Forums => LAB: The Classic Live Audio Board => Topic started by: Joe Brugnoni on May 19, 2013, 04:25:01 PM
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I love live sound but also enjoy my redneck side of dirt car racing,,, There is a local track that is in trouble with a local noise ordinance. long story short it is a unattainable 65 db,, from where they measure I have no idea,,, ANYWAY Some time ago some engineer told them to place some Semi Trailers around the track to block the sound??They did that and a few other things..The semi trailer are in place on the side of the track closest to town,, They are also in the process of erecting new stands.. They are metal but solid with no Holes in them..
So this is my question as the rumble of motors with mufflers is low pitched,,,is there a way if can measure the primary freq the motors operate at to turn these large boxes (semi Trailers) into some kind of low freq traps?? They could be placed two high if needed,,, They problem is reduced after the trees have all their leaves and it is hot enough to keep the air on,, Also with the new stands could they be treat to "absorb" sound if they are not full of people? I think they are being placed with the idea to divert sound and not that they would be full..
Any ideas,,, thanks,, And if it is a truly dumb question,, sorry in advance!! Also Thanks for any advice in advance
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I think it depends on what is harder to change, the laws of physics or the local ordinances. If the law is poorly written or unenforceable then perhaps a lawyer would do better than an engineer. In any case try to work WITH the local board and enforcement agency. Some sort of compromise on time or where the levels are measured. Get there input and try to show the economic advantages of the racetrack. Try to form an constructive relationship, not an adversarial one. You cant fight city hall, well you can try but it gets expensive.
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ford experimented with a out of phase speaker instead of a muffler and it worked. only problem was the muffler was much much cheaper. record the engines while they are racing. play back at 180deg opposite and see if it works. i am a hot rodder and have a 65 roadrace mustang and go to willowsprings racetrack at times. when i lived in missippi i use to go to 2 of the dirt tracks so i am very familiar with race car exhaust sound and keeping my soda cup covered when the cars pass the stands. the one thing that might make what i suggested not work is the(i forgot the word) and that is as sound is coming toward you , is in front of you and is moving away from you it changes. like a horn on a moving car. its hard to say if barriers will work. at willowsprings when the mustangs,camaros, etc are on the back straight you can barely hear them. when they are on the front straight they are fairly loud. is this race track new ? if the race track has ben in that location for years and the town moved next to them they should be able to get a "go pound sand noise exemption". i live about 1 mile from the airport and love it. the airport was built when all this area was bare land. developers built houses next to the airport and people moved in and for over 50 have ben trying to shut the airport down. the politicians told the people to go pound sand !
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ford experimented with a out of phase speaker instead of a muffler and it worked. only problem was the muffler was much much cheaper. record the engines while they are racing. play back at 180deg opposite and see if it works. i am a hot rodder and have a 65 roadrace mustang and go to willowsprings racetrack at times. when i lived in missippi i use to go to 2 of the dirt tracks so i am very familiar with race car exhaust sound and keeping my soda cup covered when the cars pass the stands. the one thing that might make what i suggested not work is the(i forgot the word) and that is as sound is coming toward you , is in front of you and is moving away from you it changes. like a horn on a moving car. its hard to say if barriers will work. at willowsprings when the mustangs,camaros, etc are on the back straight you can barely hear them. when they are on the front straight they are fairly loud. is this race track new ? if the race track has ben in that location for years and the town moved next to them they should be able to get a "go pound sand noise exemption". i live about 1 mile from the airport and love it. the airport was built when all this area was bare land. developers built houses next to the airport and people moved in and for over 50 have ben trying to shut the airport down. the politicians told the people to go pound sand !
The Town was there first,, but the track was built before the the town grew by about 150% according to the mayor,,, Lawyers,,, Yes they are looking into the sound issue and the levels that have been set,,, the track is not far from I70 interstate and i would think if I stood in the front yard of a house that the DB levels from the Highway would not change much if any when the track runs,,, I know that the more "stuff" you have around the more sound will get absorbed,,, so if they could put 6000 fans in there every weekend the bodies would absorb a lot of it... Economics They track will not generate as much income as property taxes will or will not offset the loss of taxes if property values go down,,, All of this being said,,, I really was interested if something like this could be done,, most of the other issues talked about have and are being explored
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The Town was there first,, but the track was built before the the town grew by about 150% according to the mayor,,, Lawyers,,, Yes they are looking into the sound issue and the levels that have been set,,, the track is not far from I70 interstate and i would think if I stood in the front yard of a house that the DB levels from the Highway would not change much if any when the track runs,,, I know that the more "stuff" you have around the more sound will get absorbed,,, so if they could put 6000 fans in there every weekend the bodies would absorb a lot of it... Economics They track will not generate as much income as property taxes will or will not offset the loss of taxes if property values go down,,, All of this being said,,, I really was interested if something like this could be done,, most of the other issues talked about have and are being explored
Maybe its as simple as better mufflers on the cars,,, But I would sure like to know if one of these trailers could be turned into a huge bass trap,,
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they make race mufflers but they are still loud. as you quiet the exhaust you loose horsepower.
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I have heard the technique of playing the noise at 180 degrees to cancel it out but would guess it needs to be exact with virtually no delay. Guessing being this is low frequency it may be pretty expensive to get enough live microphones playing back to subwoofers around the perimeter. But boy that is an experiment I would love to see.
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I have heard the technique of playing the noise at 180 degrees to cancel it out but would guess it needs to be exact with virtually no delay. Guessing being this is low frequency it may be pretty expensive to get enough live microphones playing back to subwoofers around the perimeter. But boy that is an experiment I would love to see.
the doppler effect is what i was refering to. yes i would probably cost a ton of money and getting it right and dealing with the doppler effect
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they make race mufflers but they are still loud. as you quiet the exhaust you loose horsepower.
Jeff, you're right on both points.
That said, the track could mandate a spec muffler, same for everyone. Everyone would lose approx same hp. Teams could tune around the muffler.
Like it or not, we're losing tracks to noise ordinances. Racing will eventually have to come to grips with reducing noise. I'm surprised NASCAR, SCCA, and other sanctioning organizations have not seen the writing on the wall, and taken some steps in noise abatement. Like the HD folks wanting to hold on to their straight pipes, or Rice Rockets with the race cans.
No, it won't be the same; no feeling the pressure in your chest as a car or bike goes by at full song. It will better than not racing, however.
Sent from my iPad using Tapatalk HD
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There aren't easy/cheap/portable solutions. What is needed are "soundwalls", like what you see lining interstates, backed with high-mass earthen berms. Trees are not enough. Sound energy from VLF to VHF reflects up & away (mostly).
Sears Point/Sonoma Raceway enacted this technique first in US years ago with great success. Laguna Seca's location allows this to pretty much occur naturally. Money-tight oval short tracks have a survival issue here. Ditto drag racing.
Then, after you take care of unwanted noise exposure offsite, there are the OSHA regs for onsite support personnel.
BTW- I love racing. I am a huge F1 & Indycar fan since (yikes!) the 1970s. Visceral noise is definitely part of the attraction...But do I want my kids exposed? Not so much.
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I believe they require mufflers on drag race tracks in Oz. I suspect the noise is part of the attraction.
A physical sound barrier that reflects the noise back toward the race track and slightly down, rather than up should help. You don't mind the noise at the track.
Adding turbo chargers would reduce the exhaust SPL.
JR
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record the engines while they are racing. play back at 180deg opposite and see if it works.
Recording them wouldn't work, you'd have to have a live mic going to the speaker. The waveforms have to be exactly correlated which is pretty much impossible given the distances and directions involved. If the source of the noise weren't so large and the area in which you wanted to reduce the levels was all in one direction it just might be possible.
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Noise canceling mufflers "could" mitigate the noise at the individual sources without the horsepower robbing back pressure, but this is a lot of high technology expense that would not likely be embraced by the competitors.
JR
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I Grew up in Slinger Wi. If you google Slinger Super Speedway you will find that they are 1/4 mile track on the edge of the town and the town is growing around it.
There is a ski hill next door followed by a city park.
Distance is a good thing with a ski hill to block some.
The track actually sits down in a bowl of hills allowing them to have banked straights and steep turns for the fast 9 second 1/4 mile track.
Adding the trailers is not as good as the concrete highway barriers because these go from ground up and side walls are joined leaving no air gaps except above.
What would the city and the track share the cost of the highway sound barriers.
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The semi trailer are in place on the side of the track closest to town,, They are also in the process of erecting new stands.. They are metal but solid with no Holes in them..
So this is my question as the rumble of motors with mufflers is low pitched,,,is there a way if can measure the primary freq the motors operate at to turn these large boxes (semi Trailers) into some kind of low freq traps?? They could be placed two high if needed,,, They problem is reduced after the trees have all their leaves and it is hot enough to keep the air on,, Also with the new stands could they be treat to "absorb" sound if they are not full of people? I think they are being placed with the idea to divert sound and not that they would be full..
Joe,
A 40 Hz wave is 28 feet long, to divert it requires height.
Double stacking the trailers would help, as would skirting the trailers or removing the wheels and placing them directly on the ground.
The trailers could be turned in to bass traps by cutting port holes in the sides facing the track.
Helmholtz bass traps work over a relatively narrow band, the trailers individually could be tuned to a variety of frequencies.
There are a number of port calculators on line, just plug in the volume of the particular trailer and the frequency you want it tuned to (Fb), the calculator will tell you the size hole required to ruin the resale value of the trailer :).
The bass traps would only be absorbing a small portion of the radiated low frequency energy, making sure the sound wall is basically air tight would be the primary concern.
Art
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Art makes some good points. I especially like his idea of a wall of double stacked trailers, only a subwoofer maven would have come up with that one! Unfortunately, that would only approach 1 wavelength in height for 40 Hz, kind of a puny sound shield for low frequencies.
Regarding the OP's question about using trailers as bass traps, bass traps are typically used indoors to reduce the resonant modes in the bass frequencies that occur when parallel walls reflect the sound waves back and forth and create standing waves. Outdoors, the observed sound is either direct or reflected, but there are generally no standing waves set up. So as bass traps the trailers would not have much impact.
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One observation, we don't need to disappear the noise, just direct it away from neighbors. Physical barrier large enough and solid enough to steer it in a benign direction. Of course this is not trivial.
Back in the day when we had empty ocean freight containers coming out of ears, they could be repurposed, but these days not really a cheap option. Just think dirt, lots of dirt.
JR
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The effectiveness of a barrier depends on a number of factors including the transmission loss of the barrier, the frequencies in question, the barrier height relative to the sources and listeners and the distance the barrier is located from the sources and listeners. The effects of a 20' high barrier with a noise source 10' to one side and a listener 10' on the other side is much different than the same barrier but with the source and listener both 100' away or with the listener almost at the top of the barrier.
For environmental noise you also get into the effects of topography, thermal conditions, wind and so on. Basically, it can get rather complicated, especially when looking at not only multiple listener locations but also multiple moving sources with constantly varying locations, levels and frequency content.
I know that Road Atlanta used to limit the activities based on the time of day. And while the low frequency noise of big blocks can be problematic, I watched one of the AMS Winston Cup races from the pits and was amazed at how loud they were, probably the most annoyingly loud cars I've heard are unmuffled or lightly muffled rotaries, see http://www.torquenews.com/1084/forza-4-records-loudest-racecar-planet-video (http://www.torquenews.com/1084/forza-4-records-loudest-racecar-planet-video) and http://www.topspeed.com/cars/car-news/video-the-mazda-787b-is-the-loudest-car-in-forza-4-ar127395.html (http://www.topspeed.com/cars/car-news/video-the-mazda-787b-is-the-loudest-car-in-forza-4-ar127395.html). I was at Road Atlanta for one track day where you could easily hear the scream of one 2nd gen RX-7 over any of the Porsches, Corvettes, BMWs, Mustangs, etc.
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I have heard the technique of playing the noise at 180 degrees to cancel it out but would guess it needs to be exact with virtually no delay. Guessing being this is low frequency it may be pretty expensive to get enough live microphones playing back to subwoofers around the perimeter. But boy that is an experiment I would love to see.
"180 degrees" at what frequency?
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"180 degrees" at what frequency?
It would have to be a live microphone. If you can duplicate the sound exactly 180 degrees out of phase, it would cancel out. (Theoretically but probably not possible)
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Active noise cancellation is not going to work in this situation. To reduce noise levels at the sensitive properties, you woudl need to reduce noise at source or provide effective barriers. By "effective" I would suggest a large earth bund. Here's an example that was used to protect a nearby town from jet engine test noise:
http://maps.google.co.uk/maps?q=hucknall&hl=en&ll=53.017681,-1.221886&spn=0.004434,0.011362&sll=52.8382,-2.327815&sspn=9.123282,23.269043&hnear=Hucknall,+Nottinghamshire,+United+Kingdom&t=h&z=17
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It would have to be a live microphone. If you can duplicate the sound exactly 180 degrees out of phase, it would cancel out. (Theoretically but probably not possible)
shhhhush..
Actually they have made vehicle mufflers that work using active noise canceling, but in that case they have good information about and good control over the specific waveforms they wish to cancel.
In 3d space, with multiple moving noise sources not remotely practical. Too expensive to apply to each vehicle... think dirt, lots of dirt.
JR
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Quote from: Doug Fowler at 02:55:33 pm
"180 degrees" at what frequency?
It would have to be a live microphone. If you can duplicate the sound exactly 180 degrees out of phase, it would cancel out. (Theoretically but probably not possible)
The cancellation would occur at only one place in space.
In other areas, the additional "noise cancelling" sound would create areas of additional SPL.
To use "noise cancelling" sound would require a loudspeaker/mic/amp at the location of every person that complains about the noise, totally impractical.
A sealed wall of trucks, a sound wall as used along hiways, a dirt burm, or mufflers on the cars all would work without huge expense.
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Quote from: Doug Fowler at 02:55:33 pm
"180 degrees" at what frequency?The cancellation would occur at only one place in space.
In other areas, the additional "noise cancelling" sound would create areas of additional SPL.
To use "noise cancelling" sound would require a loudspeaker/mic/amp at the location of every person that complains about the noise, totally impractical.
A sealed wall of trucks, a sound wall as used along hiways, a dirt burm, or mufflers on the cars all would work without huge expense.
For noise canceling to work, you'd either need headphones on each individual, or have the noise canceling happen as near as possible to the source. The inverse square law from point of origin would mean that if you placed the canceling sound at a significant distance from the source, the levels would offset only at one single point. So, sound canceling on each vehicle at the exhaust point could be possible, at least enough to be partially effective. Cost and implementation likely quite prohibitive, as your sound canceling device would need to be able to create the SPLs that the engine does at the exhaust point. Good luck with that.
Solid dirt walls will work the best. Semi trailers are a partial solution, but won't block all frequencies. They'll help, but may not do as much as needed.
Knowing the exact rules is key to this game. Realizing the exact rules don't exist means you have to play politics more than anything else. 65dB is all you mentioned for the max volume, but not knowing WHERE that measurement is makes it much more difficult to achieve. 6000 people in the stands will create more noise than that, by far. Now, if you get them to pinpoint a location that it has to be 65dB, you can set up your sound barriers so that you fit within the rule. However, if the sound is still annoying to residents, then the rules WILL change, and your efforts are lost. For some people, just being able to discern the sound of the racetrack will be too much. You won't be able to measure any increase in volume with a dB meter over ambient noises, but it's still going to irk someone. If you find a way to make them happy, that's cheaper than eliminating the sound completely.
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Knowing the exact rules is key to this game. Realizing the exact rules don't exist means you have to play politics more than anything else. 65dB is all you mentioned for the max volume, but not knowing WHERE that measurement is makes it much more difficult to achieve. 6000 people in the stands will create more noise than that, by far.
You also need to know the weighting (A, C) and time range (peak, fast, slow, continuous equivalent) that's specified.
Now, if you get them to pinpoint a location that it has to be 65dB, you can set up your sound barriers so that you fit within the rule. However, if the sound is still annoying to residents, then the rules WILL change, and your efforts are lost. For some people, just being able to discern the sound of the racetrack will be too much. You won't be able to measure any increase in volume with a dB meter over ambient noises, but it's still going to irk someone. If you find a way to make them happy, that's cheaper than eliminating the sound completely.
Ultimately it will come down to psychology. The street outside their door may be objectively louder than your noise at their location, but if they just don't like hearing race cars then any audible level will be considered objectionable. If they don't like the music it's too loud no matter what. If they like the music it's never loud enough.
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You also need to know the weighting (A, C) and time range (peak, fast, slow, continuous equivalent) that's specified.
Ultimately it will come down to psychology. The street outside their door may be objectively louder than your noise at their location, but if they just don't like hearing race cars then any audible level will be considered objectionable. If they don't like the music it's too loud no matter what. If they like the music it's never loud enough.
Thanks so much for all the replies!!
Yes,, it seems that the best solution is better mufflers and the owner shot himself if the foot a couple years back when he opened the rules to get more cars quickly, And you know we racers NEVER Cheat!! LOL So while I do not think that there is one solution,, it seems that combining a few things might effect some changes,, reflecting the noise is possible..
Big earth berms,, not so much,,, if the track did not sit on top of an old marsh,, maybe they could have just move it deeper into the ground this winter,,,,
The trailers do set on their wheels at this time and are not tightly stacked or pushed together
Basically the track sits in an east west alignment with the city to the west of the track,,, had it been possible to build the track in a north south way and place all the stands and scoring towers on the west side it may have helped..
They have a Sprint Car show tonight,,5/22,, I am going and for fun taking my DB meter,,, gonna play with that a bit both a and C weighted and see what happens.. Thanks again for all the replies,,,
I think that a call to some of the suppliers of headers and mufflers for these cars is in order,,, I will bet there is a way to make them sound like a street car and still keep a lot of the power.
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Earth burms may eventually sink in. but if you build the skirts onto the trailers to create a solid wall then add some earth burms inside the trailers. Keep the earth burms inside the trailer as 1 foot wide floor to ceiling and filled. This will allow the trailer to act like a ship and float and distribute the weight to keep it from sinking. Providing a double chamber internal to allow some tuning if needed. Place the one on the bottom on the roof upside down and the wheels in opposites Giving one hole between the trailers to cover and one area to fill a burm in the middle.
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As Patrick noted, you need to see exactly what the law states as far as which scale this is measured with. You might be able to beat them at their own game.
If they are using A-weighting, the low frequencies fall off rather quickly on that scale, and you MIGHT be able to affect the measurements with the treatment you described, since you would be cutting into the middle frequencies.
If they are using C-weighting (or especially Z-weighting) then you are pretty much SOL.
Of course, this all goes out the window if there is a temperature inversion at the wrong time and all the noise goes over the barricades.
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Earth burms may eventually sink in. but if you build the skirts onto the trailers to create a solid wall then add some earth burms inside the trailers. Keep the earth burms inside the trailer as 1 foot wide floor to ceiling and filled. This will allow the trailer to act like a ship and float and distribute the weight to keep it from sinking. Providing a double chamber internal to allow some tuning if needed. Place the one on the bottom on the roof upside down and the wheels in opposites Giving one hole between the trailers to cover and one area to fill a burm in the middle.
Giant earth deflectos are the only real solution to a problem like this. After implementing those neighbors will likely continue to be annoyed by the unwelcome noise pollution regardless of the levels and you may need even bigger piles. Once the berms are established... you may consider localized inverted signal cancellations. But this would need to be implemented with measurement mics and delayed output to coincide with the arrival time at each speaker. Anything short of (I would think at least at every 30 degrees of horizontal noise spread on the far side of the berm perimeter) this will likely be fruitless efforts.
If it were my design I might also consider some extraneous noise output to decrease the ratio of 'car engine' to 'other sound' also originating outside the berm perimeter. Home owners are much more tolerant of bird song, or "white noise wind" for instance. And if this were 30db louder than the race track, that might be a good step in the right direction.
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For your metering pleasure... Many city ordinances specify the DB limit levels to be at property lines (pick the shortest line to a neighbor).
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How far away are the residences and how do they compare in elevation? A common misconception is to assume that the noise reduction noted a few feet from a berm or barrier will also apply at geater distances away but that is not true with any significant change in distance or elevation for either the source or receiver. When I worked at an amphitheater the complaints came not from adjacent properties but from those some distance away where the berms and barriers had limited effect while thermal, wind and other factors diffracted the sound back down.
So trucks, berms or whatever may help where the cars and listeners are both at ground level and physically close to the barrier but they may not be as effective where the distances to the cars or listeners are larger and where the listeners may be at a higher elevation.
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For today's outside the box suggestion we need an anti-horn on the end of each tailpipe. Instead of the typical megaphone-like flare at the end of the header/tailpipe, we need a reverse taper or an inverted cone a few inches from the pipe outlet so the sound goes into the cone and bounces around to interfere with itself, rather than couple to the outside world.
The speed of sound is faster(?) than the speed of the exhaust gas traveling in the headers so it seems the two can be somewhat treated separately. If a larger cone is located a few inches from the pipe outlet it shouldn't introduce that much back pressure.
How many dB attenuation is needed to keep the neighbors happy?
JR
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For today's outside the box suggestion we need an anti-horn on the end of each tailpipe. Instead of the typical megaphone-like flare at the end of the header/tailpipe, we need a reverse taper or an inverted cone a few inches from the pipe outlet so the sound goes into the cone and bounces around to interfere with itself, rather than couple to the outside world.
The speed of sound is faster(?) than the speed of the exhaust gas traveling in the headers so it seems the two can be somewhat treated separately. If a larger cone is located a few inches from the pipe outlet it shouldn't introduce that much back pressure.
How many dB attenuation is needed to keep the neighbors happy?
JR
If you look at 2-stroke motors you'll see something just like that, but it's designed to produce precisely timed reflections of the exhaust pulse that return to the exhaust port just in time to assist with compression.
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If you look at 2-stroke motors you'll see something just like that, but it's designed to produce precisely timed reflections of the exhaust pulse that return to the exhaust port just in time to assist with compression.
I think you're talking about expansion chambers(?) and they are only tuned for a specific rpm range. I always thought they were returning a negative pressure wave to scavage gas out of the cylinder and pull more charge through it. That may be a 4 stoke thing, but it seems any motor would want more suck than blow at the exhaust port. A reflected pressure wave at the exhaust port seems like it would reduce charge flowing in a 2 stroke motor, and reduce BHP.
JR
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If you look at 2-stroke motors you'll see something just like that, but it's designed to produce precisely timed reflections of the exhaust pulse that return to the exhaust port just in time to assist with compression.
I'm guessing that you're talking about something like the muffler below from a Stihl FS 45/46/55 trimmer? They have an inverse cone on the exhaust exit. I'm not sure that they improve the engine performance(they seem to run just as good w/out the plug). They do significantly reduce the volume of the exhaust as well as change the pitch to a less offensive one. The plug on the Stihl does have a spark arrestor screen behind it that frequently gets stopped up(I worked for around a year in a Stihl dealer's shop), but that's a topic for a different forum. ;D When those things get stopped up they do get real quiet(and weak) though assuming they run at all.
Edit: added picture.
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I think you're talking about expansion chambers(?) and they are only tuned for a specific rpm range. I always thought they were returning a negative pressure wave to scavage gas out of the cylinder and pull more charge through it. That may be a 4 stoke thing, but it seems any motor would want more suck than blow at the exhaust port. A reflected pressure wave at the exhaust port seems like it would reduce charge flowing in a 2 stroke motor, and reduce BHP.
JR
Yes, expansion chambers. In addition to helping draw the fuel-air mixture with negative pressure they also improve compression with positive pressure. They work over a wide RPM range since they're acoustically tuned and the speed of sound is pretty consistent.
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Perhaps also an analysis of what frequencies in the noise, carries the furthest and is the source of annoyance. Tuning exhaust to reduce noise could be pretty different depending on the frequency range of that noise being addressed.
JR
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Might be cheaper to hire a 100 or so "gangsters" with competition-level sound systems to cruise thru the neighborhoods playing recordings that mimic the cars when there is an event......