| Author | Message | ||
| Thomas Griffin Rating: N/A |
Hi guys. I want to get the bus noise down as much as I can. Has anybody ever used these, and can anybody with half a brain install them. Here is a link so you can see what I'm talking about.. http://www.pacificmarine.net/criticallevel.htm Does anybody have a great experience with it? | ||
| Jon W. Rating: |
It is not clear if you want to be quieter inside the coach or outside. FWIW bus converters do several things to keep the genset quiet. Most important is to put it in a box within a bay and the box has multiple sound deadeners including acoustic foam and lead foil. The radiator is remotely located and a squirrel cage blower is used for cooling the radiator. The exhaust on my coach runs through a glass pack and then a conventional muffler. The Cruise Air air conditioners make as much if not more noise than the genset. I have had two Prevost coaches and my 1987 was loud in the bedroom, but the bed was located over the engine / transmission. The current 1997 has a rear closet over the engine / transmission and the sound transmitted inside the coach is minimal. Both had a removeable cover with a sound deadener of foil and fiberglass. Like any diesel the Series 60 is loud outside, but inside from the driver's seat it is almost undetectible. | ||
| Brian (Bigbusguy)
Rating: N/A |
The more you silence the noise on the exhaust the more back PSI you will have and your MPG and HP will go down and the heat in your motor and turbo will go up. On my 8v71 in my 4905 I have more noise comming from the intake then the exhaust. Brian 4905 Oregon | ||
| Tim Strommen (Tim_strommen)
Rating: N/A |
Mr. Griffin, I'm using the level 400 Nelson (the brand of silencer you are looking at on that page) for both my prime mover (after its muffler) and my DC plant. I'd recommend looking at the Nelson Web page, they have a guide for sizing your silencer, and calculations for reducing the effects of backpressure (be warned, my 6V92TA needed a 96" long 24" dia. silencer...) I do agree with Brian that special attention must be paid to the intake noise, especially if you have a turbo... Cheers! Tim | ||
| Thomas Griffin Rating: N/A |
Thanks for the information. I'll look at the page and come back with questions I'm sure..... LOL Thank!! | ||
| Thomas Griffin Rating: N/A |
OK.. Tell me about the intake noise. How do you reduce that? | ||
| Tim Strommen (Tim_strommen)
Rating: N/A |
Hi Thomas, Glad you're finding the info usefull. Effectively controlling your sound levels is a space-consuming (can also be expensive) endevor. The soulutions are as plentifull as the people who are on this board. Without getting into a full two hour lecture on noise, sound control, etc. (my forte), I'll give you some basic sound concepts which will hopefully guide you on the path to your best solution. I'll start from where sound is made, and end at your ears: Noise in an engine intake can come from several places. Starting with the engine, the valves that allow air into the engine make a "vibration" metal-against-metal which is a clicking sound (this is only true if you have a 4-cycle. A two cycle will catch the end of the combustion cycle and allow that shockwave into the intake plenum - another way of saying a "box"). The bigger effect that the valves have, is that they obviously meter the air that enters the engine. This causes several thousand low and high pressure waves in the intake system (very noisy), and makes up a majority of the noise that you hear from the intake on a car. I'm assuming that you have a diesel not gas, so the next device the sound sees is the "roots-blower". This is what crams the air into the intake manifold. It affects the sound coming throught the intake system, as it behaves like a one way valve for air. However, in order to compress the air into your engine the vanes of this compressor must be aligned very well and the effect of these spinning at engine speeds is on par with a kid at school with a paper cutter - cutting ~1700 times a minute (very, very noisy). If you have a turbo, that's next. A turbo is yet another compressor, but this one takes air from the intake, and using centrifical force, "throws" it from the center of the turbine to the outlet (and into the blower). As it does not seal, it allows "shockwaves" (noise) from the blower to pass back into the intake ducting. the worse effect is that it ic cutting through the ait with its leading edges which make that sweet turbo "whine" (REALLY noisy). Everything up to here, there isn't a whole lot you can do about, but most of the sound 'till now is "contained" inside the engine. what happens now is your sound gets into your ducting. Ducting, will have turbulent air in it. Air shockwaves will bounce around inside this duct, and the effect is similar to taking a tin can and rattling a pencil in the open end. A way you can counter this noise is by putting a "loaded-limp-mass" on the exterior of the duct (Rhino Liner, Line-X, Noise-Killer, Dynamat, etc.) to combat the higher frequencies, and a blanket insulation over the top of that to reduce lower frequency emissions. Of course, one could line the inside of the duct (like many HVAC systems do), but I NEVER advocate inserting anything inside a duct after an air filter (it would really "suck" to have a chunk of something break off and get ingested by the turbo...). The next device the sound will most likely run into is the air-filter/filter-plenum. I'm going to take a quick pause before I get into air filters to mention that air velocity directly contributes to the sound generated (and in some cases amplified) by turbulence. Depending on which expert you ask, some say 16db increase of sound for every doubling of velocity, others say 20db. To get your bearings, 3db basically is a doubling of percived sound level (you can measure this with a cheap Radio Shack SPL (Sound Pressure Level) Meter. When you get to an air filter, you can (depending on your space/money) use a larger filter than is required on your engine, which will reduce the speed of the air moving through it (which will also reduce more sound from being generated by turbulence through the filter - think of it like sucking through a bunch of straws), or increase the size if the plenum (box) the filter is attached to (remeber every time you halve the air speed from the turbo, you reduce the turbulence sound level by ~16-20db). Again, coating the EXTERIOR of the air filter plenum with a loaded-limp-mass, and wrap (mineral fiber sheets work well here) will cut down on resonated sound. What you'll have left, is the sound that passes through the air filter out into the world. Here, before the air filter, it'l be okay to put an internal attenuation media (mineral fiber again works here, but you may have to change your filter a little more - unless you increased the size of the filter, which would reduce the air speed). The best way to reduce sound here is with a silencer type baffeling setup on a larger volume duct. The more curves air must go around the better, but BE CARFULL!!! If you make it HARD for the air to get around, you'll end up making your problems worse. The air will make noise at the filter intake (which would be right where you want it to be mostly gone) and you'll starve the engine for air (which will make your engine put out black smoke, and no power, sputtering, etc...). There are two ways to increase air voulme; 1) Increase the speed through the same size pipe, 2) Increase the size of the pipe and keep the same speed. For this, I recommend constantly increasing the size of the pipe as you go around bends (start at the filter size when you do this to avoid caving in the filter...) Recently, some people over here in California have been making some breakthroughs with sound (they are known as Meyer Sound Labs), in where they have proven that sound is more direcional than was previously thought. Therefore, if you can direct the final path of the sound (intake) away from any listening ears, you'll be better off (this goes for your exhaust too!). All that just covers air-borne noise. Transmitted mechanical noise is what you'll mostly hear inside the bus. The best way to fix that is a loaded-limp-mass coating on the fire-wall (inside and out) and a mineral fiber with aluminum foil insulation. Several people on this board are doing it this way. You'll also want to check out the condition of your motor mounts. If you have solid metal mounts (I've seen them on a few busses, to my horror) you can replace them with newer vibration isolators. I think GumpyDog did something similar to that when he pulled his engine. I know it's a scattered mess of information, but I'm on my way to Ohio tomorrow, so I didn't want to miss posting for you. Good luck with your project, I recommend going to Rad-Shack an' getting an SPL Meter to test how well you actually do on sound reduction. And if you can't get it down to where people don't complain about the noise, a bunch of these "Passive Noise Reducers" in the bus will help. Cheers! Tim |
