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RE: mufflers - 9/30/2012 7:48 PM   
Bass1



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Status: offline 		Can't say I'm familiar with waterfall tertz band analysis. I mainly trained my ears to identify frequencies by using pink noise generators and old fashioned real time analyzers. After awhile it's rather easy to identify problem frequencies by ear. I once had a hair brained scheme to rig a lavalier mic to a nagging girlfriend with an exteremely irritating whine to her voice when she was feeling hornary . I took a reading with my trusty anaylizer while she was in full form and found that during peak projection she was hitting 2850k very hard. So with an effects unit I had I thought I would run the mic "out of phase" in that frequency range (similialr to the technology used in noise reduction headphones) and running that out of phase signal through my home stereo, thereby removing that gawd aweful frequency from her screeching voice so I could watch football in peace!!

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RE: mufflers - 9/30/2012 9:28 PM   
pe reivers



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Status: offline 		VVBG,

I know our (trained) ear is the most sensitive instrument of all. It's the training part that's difficult.


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RE: mufflers - 10/1/2012 12:53 AM   
Ernie Misner



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Status: offline 		Pe and all, does anyone know if tinnitus (ringing of the ears due to nerve damage) is typically a certain frequency? Hopefully this question isn't too far off topic because if we had mufflers back in the early days of nitro engines my ears would not be so bad today. Anyway I have tinnitus pretty bad and one interesting thing I can do is hum an A (440) note anytime of the night or day, don't even need a tuner for the guitar. Could that possibly be related to the constant pitch of my tinnitus? And that A/440 note seems to blend in well with all noises in nature and industry oddly enough.


Thanks,

Ernie Misner

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RE: mufflers - 10/1/2012 2:23 AM   
Bass1



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Status: offline 		Ernie, I don't know if the relationship of A-440 to tinnitus is common but you could use that A-440 tone you're hearing to identify other notes in the musical spectrum. Just work off the "A" note in the 440 cycles frequency you are constantly hearing to figure out what other note/keys your are presented with and tell all of your musician friends you have "perfect pitch" I've been doing something similar for years by singing my highest non falsetto note (in private of course) which is G and work off that note to indentify other notes/keys. I tell everyone I'm blessed with perfect "relative pitch"

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RE: mufflers - 10/1/2012 5:26 AM   
Ernie Misner



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Status: offline 		Thanks Bass1. Guess you've never noticed how an A440 seems to harmonize with all sounds in nature, industry, hair dryer, etc.?

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RE: mufflers - 10/1/2012 6:47 AM   
Bass1



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Status: offline 		To tell you the truth I do remember a few episodes in my lifetime where 440 cycles seemed to be prevelent all around me. Not sure if it's just easier to identify being a guitarist/bassist myself and A440 is a good familiar, comfortable an extremely playable key for those instruments. I have occasionally noticed some heavy machinery humming along nicely very close to good old A440 as well. Maybe A440 is just the basic frequency of the white noise of our lives??

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RE: mufflers - 10/1/2012 11:08 AM   
pe reivers



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Status: offline 		I do have ear damage due to turbine noise, and only hear frequencies between 4000 and 6000 Hz if louder then 80dB.
The ringing in my ears is more like white noise without any specific frequency.
The joy of music suffers by that lack of all frequencies. However, I can still tune my guitar without tuning fork and be extremely close.
Maybe that 440Hz is indeed a human basic frequency.


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RE: mufflers - 10/1/2012 8:24 PM   
Ernie Misner



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Status: offline 		Ha, got you guys in tune. It's fun to get that A440 sound keyed into your brain, then bring it up when driving or listening to the fan in the shower. It definitely does seem to be a basic frequecy of our lifes. Does anyone have any historical info on how 440 was originaly chosen? I don't. I can tell you that when working or driving that when a song pops into my mind I do usually begin humming it in A or a closely related key. Again, could also be related to my tinnitus which is fixed.

Thanks, Ernie

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RE: mufflers - 10/1/2012 9:57 PM   
Bass1



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Status: offline 		Well we're pretty much way off topic but here is little bit of info on A440 http://en.wikipedia.org/wiki/A440_(pitch_standard) Kind of coincidental but I'm learning a song right now for an up coming wedding gig and the record (MP3) key just happens to be in A-440

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RE: mufflers - 10/5/2012 5:39 PM   
dadragon


 

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Status: offline 		If we have to muffle our engines whats next Smog devices?.

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RE: mufflers - 10/5/2012 6:27 PM   
pe reivers



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Status: offline 		Muffling your engines is for keeping peace with the people around you and saving your hearing ability. Try bribing them with invitations, flowers, or a bottle o' their favorite.
It also shows you are a responsible person who is aware that this planet is not his own but is shared.


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RE: mufflers - 10/9/2012 6:07 PM   
rt3232


 

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To all
Sorry to be so slow in getting back to this Thread, family and med problems. From what I am reading you all have great points and thoughts.
The only reason I mentioned the test cell thingy, was the company did a rebuild and up grade on the exhaust system, (not the building) do to the close proximity of housing, and they did not test any A/B engines. I would like to understand what they did and try to scale it down. From what I was able to look at,, it was a big double walled can and both had a varing size and patterend holes, and it did have a virtical stack

I should have been a bit more specific in my original post as to what engines we are dealing with ie: Gas and size .30 to .111 at present all have some type of can or box shaped muffler with 1 or 2 stacks, Most are fully coweled, with some side mounted mufflers and some wraparound types.

What we are looking for is an easy fix to our existing equipment or a reasonable replacement. we are also aware that most of the engineering/sound studdies etc, have been done so we don't want to reinvent the wheel so to speek.

So in review it looks like our 2 biggest noise areas are exhaust and pro tip.

Again sorry to be so long winded

Cheers Bob T

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RE: mufflers - 10/9/2012 9:34 PM   
pe reivers



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Status: offline 		Add plane resonating surfaces to be part of the top three.
If mufflers are good, prop noise is of prime importance. Prop noise is directly related to prop power, and tip speed ; stay clear of tip speed values in excess of Mach 0.6
Address the issue you hear best. It is bound to be at least 3dB(A) louder than the other two. It's a seesaw process.



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RE: mufflers - 10/10/2012 3:43 AM   
rt3232


 

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Hi Pe,

Yes resonating surfaces are up there, but we have not figured way to get to them to test as yet, about 1/2 of the birds in question are built up hard furfaces ie: balsa sheeting and glass cloth with epoxy or poly bonding and fill, about 1/2 of the rest are plastic film covered, the rest are covered with some type of fabric pre painted or painted.
we have run a couple of the engines with and with out the cowl's with no appreciable differance in sound readings except opposite the carb but only 2 to 5 tents of a db as they are made on the ground at 3 at about 3 meters from the center of the engine, we have also tried to get readings when flying near and over the flight line, and they barely move the scale.
We actualy get higher readings from the trafic (cars trucks and motor cycles) going by on the road behind our field and flight line.

The reason for this exersize is becouse we our club have a neighbor that is giving us fits it is if he can see it and hear it, he complains. We have restricted flying with in about 600 ft from his property, so we are trying to do what ever else we can reasonablie do to keep the piece. Our season is about done for this year, so we have all winter to see what we can come up with and do.

Cheers Bob T
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RE: mufflers - 10/10/2012 5:19 AM   
Ernie Misner



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Status: offline 		Think there's much difference in plane or wing resonating if the engine is mounted vertical or horizontally?

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RE: mufflers - 10/11/2012 12:22 PM   
pe reivers



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Status: offline 		At one field location we have the nearest house at 500 meters, so we just don't fly behind the flight line (nearest house in our back) to keep the inhabitants of that house at peace.

@ Ernie,
In sidewinder configuration the plane has the highest mass resistance mode in regard to the vibration source (the engine). A typical airplane engine generates vibrations in the 10G range, so it pays to think about engine orientation.


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RE: mufflers - 10/11/2012 6:48 PM   
Ernie Misner



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Status: offline 		>>> @ Ernie,
In sidewinder configuration the plane has the highest mass resistance mode in regard to the vibration source (the engine). A typical airplane engine generates vibrations in the 10G range, so it pays to think about engine orientation. >>>

Thanks Pe, so an engine mounted horizontallly actually causes more airframe noise or less? I would think MORE noise from your description.

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RE: mufflers - 10/11/2012 7:51 PM   
pe reivers



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Status: offline 		Should be less noise on most engines, however that is not cast in stone. It probably works for cantilever crankshaft engines which have a problem getting sufficient mass balance. The main imbalance direction depends on how the engine is balanced with the crankshaft counterweight in % of connecting rod and piston weight.


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RE: mufflers - 10/12/2012 4:16 PM   
raptureboy


 

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Status: offline 		"I once had a hair brained scheme to rig a lavalier mic to a nagging girlfriend with an exteremely irritating whine to her voice when she was feeling hornary ."   It's a good thing I wasn't drinking my coffee when I read this.  I assume you meant ornery, then again maybe not


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RE: mufflers - 10/13/2012 12:58 PM   
pe reivers



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Status: offline 		you mean in reply to post #26 ??


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