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Dyno - Noise Complaints

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revvedmoto

Mechanical
Dec 17, 2023
4
Hopefully, this is the right place to answer my questions. I recently picked up a motorcycle dyno that is placed in a metal shipping container where one side and back doors open while in use. Long story short I've gotten a few complaints about it and want to try and understand what my neighbors are hearing and coming up with a plan of attack to remedy the issue.
For all intents and purposes, we are talking about a Harley Davidson producing 115db at around the 50Hz mark and up.
I'm about 45ft from my closest property line and the other is 140ft (this is the neighbor that has been complaining). I dont expect my results to be silent but to slide a little more under the radar. We are by a busy street that creates 85-90db (measured at the road) pretty consistently and even has big trucks going by with their jack brakes on.

I've been playing with this little app here to help me understand what db they are hearing.
[1.5,50,115]&receiver=[2,45]&barrier=[0]&display=2

My first question is how is the reverb off the container hurting me? I would imagine that as the sound is ricocheting around the container it may sound like a herd of 115db bikes instead of a single bike.

The second question is about motor mechanical noise vs exhaust note. Most of the bikes ill see will have an altered exhaust and will be much louder than stock but I would be curious how much of my issue is intake and mechanical engine noise? If I were to feed my exhaust into a silencer such as one of these I may be able to chop the exhaust down by 15+ db.

If I keep the dyno in this container I plan to pad the walls and ceiling. A friend has some experience with soundproofing on trains and has some sort of foam that he speaks highly of. It's expensive stuff so I don't plan to wrap the whole thing top to bottom with it. I've seen some wall treatments that studio guys will make out of fiberglass insulation that I would finish off the room with. I'm curious if that will even accomplish much?

The last resort is to build room for the dyno. This would be a room inside a room thing and in the end might be the route I have to go. I would hate to lose precious shop space and more importantly the cost of building it out.

I would be curious about your thoughts and if there is something I'm not considering.
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Wow, yeah that's going to be loud. Might as well put the motorcycle inside a snare drum. Perhaps filling with a layer of adhesive acoustic insulation will help. Or build an inner wall and fill the space between with sand.

I wonder if it would be more practical to build a stack of concrete walls with an open top to send the sound 'up' like highway noise walls and berms around rifle ranges? But with the house being two stories and so close I don't know if that will do it.

Last but not least, if you're a Harley mechanic you may already have hearing damage, but I'm sure you're beating the piss out of your eardrums. Earplugs and headphones may not be enough. Tinnitus is debilitating.
 
Screenshot_20231219_082003_Google_Earth_kzjuss.jpg


Thanks for the response. Yeah it's not ideal for sure. Above is a picture of my lot and location of the container. The neighbor that is complaining is to my left in the image. My house sits between me and them as well as a row trees at the property line.

I'm curious what the sound would be like if it wasn't in the container.

The muffler I attached in my first post would site out side the dyno and direct the sound up as well as hopefully reduce it by 15-20db. Then I would be left with more or less the mechanical noise of the motor and dyno.

Yeah its pretty loud in there. I run in ear ear plugs as well as over the ear protection.
 
I might even try and make my own muffler here are a few designs I've been considering

The first one is a 55-gallon barrel with tires in it. I considering stacking 3 barrels up and Putting a 6in pipe/whole between each one to define 3 different chambers.
silencer_qmspn0.jpg


Here is a little demonstration with just tires.


Heres another option but I do not know how it performed in comparison.
 
That design would not be especially effective at low frequencies. You really need an expansion chamber like a truck muffler or the one you linked to. Now, assuming these bikes are running fairly minimal exhausts you also have a high frequency problem so the rifle silencer would help. Unfortunately without knowing which frequencies are upsetting your neighbor it is a bit hard to be specific.

Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376
 
You can get a whole bunch of good practice ideas from these sources:

Acoustic theory, not too heavy reading:
Room Acoustics, Heinrich Kuttruff
Master Handbook of Acoustics, F. Alton Everest & Ken C. Pohlmann

Practical aspects:
BBC Engineering, Guide to Acoustic Practice, Keith A. Rose
- Includes a section on practical room construction, with drawings (e.g. figure 20, box within a box)
Unified Facilities Criteria (UFC), Noise and Vibration Control, Department of Defense, Donald l. Basham, Dr. James W. Wright, Kathleen I. Ferguson, Dr. Get W. Moy
- Includes a section on Sound Propagation Outdoors

These are all available in PDF form.

DG
 
Recommend looking at mineral wool batts or acoustic panels rather than acoustic foam. Mineral wool does not burn. Sound damping increases as the material gets denser and thicker.
Websearch for rockwool acoustic panels (TM).
For this application an abrasion resistant cover is needed, which can be either expanded metal, or punched sheet with say 50% or more open area.

Some application information

You will generally get better results from a commercial off the shelf muffler than a home built one. Mufflers are generally cataloged after the OEM matches the muffler to the engine, you may need to make a technical inquiry to determine the best selection for your application. Muffler performance will impact dyno measurements just like exhaust tuning.

Somthing on exhaust tuning
 
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