Machine Air compressor muffler

[JustaDB]

There is no scientific proof to support the claim and several studies debunking it. Here are a few references:

First off, when I bought my "Loud Pipes Save Lives" patch & first sewed it on my riding vest, I thought it was a cute, glib saying & not much else. A bit of attitude. Since then it has proven true in real life experience, despite what some paper may claim to the contrary, and I'll explain below.

Second, I've been riding for 42 years myself. All Harleys, all loud pipes. People hear them. I know, because I can see their reactions. I get near, I see them checking their rearview & sideview mirrors.

Now, to the paper's conclusions. The author's note that at a distance of 15 meters cage drivers can't hear motorcycle exhausts. That's 50 feet, close to 3 of todays car lengths. Fine. It's a safe statement that many of the idiots in a cage don't bother mirror checking, shoulder checking or signalling in the first place. If they dive into my lane 50 feet or more in front of me, that's seldom an issue. I have time to react to most of them, unless they slam on their brakes, too. It's the nearer ones that present an issue, the ones that are 10 or 20 feet in front of me, or right beside me. They'll hear my pipes at that distance, guaranteed. Even with the stereo on. As I've noted above, I see them checking their mirrors to see where the noise is coming from.

As far as sound propogating behind the bike is concerned, nice theory, but real life trumps theory every time. If that was true, then why are my ears often ringing after a long ride? The tip of my exhaust is close to 3 feet behind my ears. Is it going to be louder behind the bike? Of course. That doesn't stop the sound from being heard in a forward or lateral direction.

 

[slow-poke]

I think the solution is more rigorous or possibly consistent driver examinations.There are
too many distracted or situationally unaware drivers bombing around.

FWIW I hear them in my quiet car and although somewhat annoying I actually appreciate that the rider is making me aware.

Back on topic......

when I have time I'm going to separate the compressor pump from the tank and place the pump in the garage under my basement stairs, the 8" concrete wall is going to be a better noise insulator than what I was planning to build were the tank will live in the basement. I will report results when and if I ever get to project # 947

 

[Susquatch]

(Slightly tongue in cheek) Admins: do you need to add motorcycle exhausts to religion and politics as banned topics?

With my moderator hat on.

As long as people don't start taking or making things personal or hurtful we should be ok. But it is worth noting that such a risk is real. Please keep it civil guys.

 

[kstrauss]

Getting back to air compressor noise...

I was intrigued by the idea of a wave cancellation muffler so I downloaded a sound spectrum analysis app for my phone. At about 15 feet from my compressor the app claims a sound level of 99.7dB. The spectrum has significant levels (45 to 60dB) across the entire spectrum (30Hz-20kHz) with slight peaks around 100Hz and 300Hz.

How should I size the lengths of PVC pipe?

 

[Susquatch]

I was intrigued by the idea of a wave cancellation muffler so I downloaded a sound spectrum analysis app for my phone.

I'm interested to hear how well the app works.

I would have thought you mostly needed the frequency of operation of the pump and the harmonics of that (1/2, double, etc) but, you never know!

 

[kstrauss]

I'm interested to hear how well the app works.

I would have thought you mostly needed the frequency of operation of the pump and the harmonics of that (1/2, double, etc) but, you never know!

I'm unsure of accuracy of the app although it looks pretty! It is called Sound Spectrum Analyzer by PC Mehanik, available free from the Google PlayStore and with a zillion downloads.

 

[Tecnico]

I think this might be an interesting approach.

5 Types of Mufflers [Working, Design, Explained with Images]

Types of mufflers are Baffle type Wave, cancellation type, Resonance type, Absorber type, Combined resonance and absorber type.

www.theengineerspost.com

Look at this article. The second muffler design is a wave cancellation muffler. A compressor runs at essentially a fixed rpm so the air pulses will be consistent. It is intake air so you could use plastic. It wouldn't be hard to put something together with 2" and 4" PVC pipe. A tiny bit of math would get you in the ballpark for lengths. "the length of the two paths differs by 1/2 wavelength"

Chris

Interesting.


Here's another take on it. I'd want to put a filter on the intake and embed it in the can to make sure the compressor didn't ingest anything. They claim an 8 dB noise reduction.

Vans Airforce Paint Can Muffler

Might learn something useful by looking at what these guys are offering too:

Filter Silencers for Blowers & Compressors

D

 

[Tecnico]

First off, when I bought my "Loud Pipes Save Lives" patch & first sewed it on my riding vest, I thought it was a cute, glib saying & not much else. A bit of attitude. Since then it has proven true in real life experience, despite what some paper may claim to the contrary, and I'll explain below.

Second, I've been riding for 42 years myself. All Harleys, all loud pipes. People hear them. I know, because I can see their reactions. I get near, I see them checking their rearview & sideview mirrors.

Now, to the paper's conclusions. The author's note that at a distance of 15 meters cage drivers can't hear motorcycle exhausts. That's 50 feet, close to 3 of todays car lengths. Fine. It's a safe statement that many of the idiots in a cage don't bother mirror checking, shoulder checking or signalling in the first place. If they dive into my lane 50 feet or more in front of me, that's seldom an issue. I have time to react to most of them, unless they slam on their brakes, too. It's the nearer ones that present an issue, the ones that are 10 or 20 feet in front of me, or right beside me. They'll hear my pipes at that distance, guaranteed. Even with the stereo on. As I've noted above, I see them checking their mirrors to see where the noise is coming from.

As far as sound propogating behind the bike is concerned, nice theory, but real life trumps theory every time. If that was true, then why are my ears often ringing after a long ride? The tip of my exhaust is close to 3 feet behind my ears. Is it going to be louder behind the bike? Of course. That doesn't stop the sound from being heard in a forward or lateral direction.

With apologies for thread drift.....

(Slightly tongue in cheek) Admins: do you need to add motorcycle exhausts to religion and politics as banned topics?

You might be onto something there.

@Susquatch if you want to nuke this whole sub-thread, have at it, my feelings won't be hurt!



@JustaDB

I respect your right to have opinions and to believe in what you consider your experience.

For background I've been a licensed motorcyclist for 48 years having owned bikes from a stock but annoyingly loud 2 stroke dual purpose to a 1000cc sport bike that is so quiet all I hear at speed is wind noise. I also have experience, opinions, plus facts backed up with science.

OK, to the discussion:

Inside the 10 meter zone, or a couple of car lengths, the Romanian study (“some paper”) states that even if the car driver can hear the bike they cannot tell what direction it is coming from because of the frequency of the sound so that is little real help in a dynamic situation. By the time you’re there they will already be making their move.

FWIW, my experience is that until a loud bike is beside me (“idiots in a cage”), passing, it’s unlikely I will hear them in my VW. I will probably already know they are there though because I use the mirrors etc. to look out for other traffic around me so you might still see my eyes.

The biggest problem with relying on loud pipes preventing car/moto accidents is that in between 76% and 83% of accidents there is next to no chance of loud pipes being heard before the accident. According to a Forbes article, quoting the Insurance Institute for Highway Safety. Motorcycles and ATVs https://www.forbes.com/advisor/legal/motorcycle-accident-statistics/, 76% of motorcycle accidents are head on with another vehicle. 7% were rear-ends so loud pipes are unlikely to be useful there too so we’re up to 83%.

As far as sound propagating behind the bike is concerned, science trumps theory (opinion) every time and explains real life. The Romanian study found sound levels behind the bikes were about 5 dB (A) lower than in front. A reduction of 6 dB (A) (logarithmic scale) is a 50% reduction in sound level, so it’s much quieter but not silent. Of course this is because of the directivity of the exhaust pointing to the rear of the vehicle.

In the case of your ears ringing after a ride, a typical textbook graph of sound level around an exhaust pipe illustrates what’s happening.

​

The illustration shows sound level distribution around (fore & aft) of an exhaust pipe. The 69 dB isobel contour is a line on which you measure the same sound level, 69 dB in this case. This chart isn’t an exact replica of the conditions of your bike but it’s close enough to show the science. On your bike, you’re still in a high sound level near the front lobes so that’s why your ears ring after a ride. Note the 4 meter radius dashed reference line.

My opinion, I don’t see the value of loud pipes for me as a motorcyclist and I do find them a nuisance that disrespects the public.

D

 

[Darren]

I'll offer a quick counterpoint. I recently had a car car decide to change lanes beside me and push me into oncoming traffic. She didn't see me. I dropped a gear and brapped it and got in front of her. Im sure if I didn't have my obnoxiously loud exhaust right beside her window, there would have been a collision. My bike is quiet until i open it up. I do believe that it saved me that day.

 

[Susquatch]

I'm unsure of accuracy of the app although it looks pretty! It is called Sound Spectrum Analyzer by PC Mehanik, available free from the Google PlayStore and with a zillion downloads.

I checked it out. Very nice. I have not used it to check exhaust or intake noise but I'm optimistic that it will be helpful.

It would be even better if it could be calibrated, and if there was a standard way of holding a phone to achieve neutral directionality.

Amazing what a cell phone can all do today!

 

[Dabbler]

Amazing what a cell phone can all do today!

It truly has become Star Trek's trichorder.

 

[DPittman]

@Susquatch if you want to nuke this whole sub-thread, have at it, my feelings won't be hurt!

As long as the discussion is civil I would discourage any moderator action on the topic. I've already learned some stuff from reading.

 

[Bandit]

Generly, any noises causing ear ringing, is causing damage to hearing. In my case, tinninitous all the time, with 50% or more hearing loss at a number of different levels. Shooting, noisy cars, motorcycles, operating equipment, working in loud noise places, etc. But each to their own, injury from not "hearing" partner is your problem. LOL, no, louder, can't hear you, LOL, LOL.

 

[Tecnico]

I'm unsure of accuracy of the app although it looks pretty! It is called Sound Spectrum Analyzer by PC Mehanik, available free from the Google PlayStore and with a zillion downloads.

I’m putting that on my Project 42 list. I got to play with an HP acoustic frequency spectrum analyzer back in my sonar days and I’ve often wished I had something similar. Even better that it has a built in sound meter capability.

D

 

[Susquatch]

I’m putting that on my Project 42 list. I got to play with an HP acoustic frequency spectrum analyzer back in my sonar days and I’ve often wished I had something similar. Even better that it has a built in sound meter capability.

D

I have a similar background. The sound analysers I used were Bruel & Kjaer.

I am so interested in this that I have downloaded three different Android frequency analyser apps to try. If they even do half what they promise I will be thrilled. We will see.

 

[Tecnico]

I have a similar background. The sound analysers I used were Bruel & Kjaer.

I am so interested in this that I have downloaded three different Android frequency analyser apps to try. If they even do half what they promise I will be thrilled. We will see.

Oooh, someone doing my homework for me LOL! Do report back & let us know what interesting goodies you find.

D

 

[mbond]

With apologies for thread drift.....



You might be onto something there.

@Susquatch if you want to nuke this whole sub-thread, have at it, my feelings won't be hurt!



@JustaDB

I respect your right to have opinions and to believe in what you consider your experience.

For background I've been a licensed motorcyclist for 48 years having owned bikes from a stock but annoyingly loud 2 stroke dual purpose to a 1000cc sport bike that is so quiet all I hear at speed is wind noise. I also have experience, opinions, plus facts backed up with science.

OK, to the discussion:

Inside the 10 meter zone, or a couple of car lengths, the Romanian study (“some paper”) states that even if the car driver can hear the bike they cannot tell what direction it is coming from because of the frequency of the sound so that is little real help in a dynamic situation. By the time you’re there they will already be making their move.

FWIW, my experience is that until a loud bike is beside me (“idiots in a cage”), passing, it’s unlikely I will hear them in my VW. I will probably already know they are there though because I use the mirrors etc. to look out for other traffic around me so you might still see my eyes.

The biggest problem with relying on loud pipes preventing car/moto accidents is that in between 76% and 83% of accidents there is next to no chance of loud pipes being heard before the accident. According to a Forbes article, quoting the Insurance Institute for Highway Safety. Motorcycles and ATVs https://www.forbes.com/advisor/legal/motorcycle-accident-statistics/, 76% of motorcycle accidents are head on with another vehicle. 7% were rear-ends so loud pipes are unlikely to be useful there too so we’re up to 83%.

As far as sound propagating behind the bike is concerned, science trumps theory (opinion) every time and explains real life. The Romanian study found sound levels behind the bikes were about 5 dB (A) lower than in front. A reduction of 6 dB (A) (logarithmic scale) is a 50% reduction in sound level, so it’s much quieter but not silent. Of course this is because of the directivity of the exhaust pointing to the rear of the vehicle.

In the case of your ears ringing after a ride, a typical textbook graph of sound level around an exhaust pipe illustrates what’s happening.

View attachment 39781​

The illustration shows sound level distribution around (fore & aft) of an exhaust pipe. The 69 dB isobel contour is a line on which you measure the same sound level, 69 dB in this case. This chart isn’t an exact replica of the conditions of your bike but it’s close enough to show the science. On your bike, you’re still in a high sound level near the front lobes so that’s why your ears ring after a ride. Note the 4 meter radius dashed reference line.

My opinion, I don’t see the value of loud pipes for me as a motorcyclist and I do find them a nuisance that disrespects the public.

D

In case anyone wants an unnecessarily complex addition to this answer, the shape of these intensity lines assumes that the air behaves as a Newtonian fluid and is of a constant temperature and density with no wind. The Doplar effect, combined with an assumed (and impossible) point source for the sound indicates a Bessel function describing the sound intensity. And of course the 1st derivative indicating the rate of dissipation. The degree of the Bessel function is given by the forward speed through the medium (air). Real sounds will be produced from a complex interaction from the varying exhaust pressure and the edge effect wave interference pattern.

As the sound source approaches the speed of sound, the degree of the Bessel function approaches infinity and the equation collapses - super-sonic analysis requires complex tensors and there is, of course, no forwards propagation. But at the relatively low speeds of highway driving, sound will certainly propagate ahead of the source. Whether bad drivers can process that information or not is unclear. Good drivers probably don't need to.

I have never driven a motorcycle and know hardly anything about it. I certainly don't doubt anyone's practical experience. I know from my own experience that there are a lot of bad drivers on the road.