Variations in Engine Sound Levels Among Different Types

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Author Topic:   Variations in Engine Sound Levels Among Different Types

mikejoyce77 posted 01-23-2008 11:46 PM ET (US)
I have tried to find [information about the sound levels among] different outboard motors but have been unsuccesful. Are [outboard motors using a four-cycle design] quiter than direct-injected two-cycle engines? Or other way around? How come manufacturers don't mention sound [levels] on their specification page?
jimh posted 01-24-2008 12:03 AM ET (US)
There is no agreed-upon method or specification for sound levels for outboard motors to be measured. The usual method is to measure the sound pressure level using an A-weighted filter and at a certain distance from the engine. However, many people who report engine specifications test the sound pressure levels and report them.
Sound levels are completely independent of the combustion cycle configuration. One cannot say that the two categories you framed, all motors used four-cycle design versus all motors using direct-injection two-cycle, have any special claim to loudness or softness. It really depends on the design of the individual motor, and how much attention was paid to noise, vibration, and harshness (NVH). Some manufacturers have intentionally given their engines a louder sound in order to make them more attractive to boaters who want a louder engine.
jimh posted 01-24-2008 12:26 AM ET (US)
A good example of the problem in comparison of sound pressure levels is demonstrated in some recent literature published by one leading outboard manufacturer. This manufacturer's literature presents comparison of sound pressure levels in terms of percentage difference in sound pressure levels. This is a misleading comparison. Human sound perception is much better correlated with logarithmic comparisons of sound level, and the universally used unit of comparison is the decibel. The literature may impress potential outboard motor buyers who have little knowledge about sound pressure level measurement, but in my opinion, it is misleading.
There are disputes about very simple specifications like engine weight. If we cannot get accurate, consistent, and comparable measurements of engine weight between brands, I doubt that we will ever be able to rely on manufacturer published data to compare sound levels.
kwik_wurk posted 01-24-2008 01:25 AM ET (US)
In continuing Jim’s comments the standard measurement human perception for sound is A-weighted dB value. This is a single value given to the overall sound level. (Example: Most home/car stereo’s reveal a dB value when you turn the volume knob, for the overall loudness. But with an equalizer you can adjust the sound levels of many frequencies such as low frequency bass.)
A-weighted levels exist because the human ear perceives certain frequencies of sound differently. These frequencies are attenuated and “appear” louder than they really are when measured with a scientific instrument (which usually measures in Sound Pressure Level - SPL). (While not a true example; think of the fingernails on chalkboard, little sound but very annoying.) A-weighting filters certain octave bands as an attempt to accommodate for these variations in human hearing response.
In most common applications you find a single A-weighted sound level. Sometimes you will find the sound levels presented in octave bands, which gives you more detail about the sound. (Think of these octave bands as the knobs on a high end stereo equalizer, the more knobs you have the more you can fine tune the sound.)
As an end user trying to filter thru manufacture specs, an A-weighted value is the best you likely find. Unfortunately is has deficiencies, but that is all you can run with at times. And yes don’t get caught up in marketing ploys trying to skew decibel numbers.
And keep in mind a few things: Generically speaking four strokes are quieter than two strokes (I won’t go into the details here). And, you can change the muffler on a car and completely change the way it sounds without touching the engine. The same is true for boat motors.
Rob Pirie posted 01-24-2008 01:30 AM ET (US)
I have two boats both with direct-injection two cycle engines.One boat has 200hp Optimax the other 200hp Ho Etec , the Optimax due to it's large compressor mounted on top of the engine is noisy as hell compared to the Etec.
I also fished a tournament last weekend and the Bostun Whaler next to us had a pair of the New Yamaha 350hp V8
4 strokes , we were all blown away by how silent these engines were you simply could'nt hear them until the boat had completly backed up into it's dock.Top marks to Yamaha for sound levels on these.
Rob
zotcha posted 01-25-2008 09:15 AM ET (US)
Probably need to start a new thread but, my 2005 Yamaha F60 (four stroke) was silent first two seasons. Only thing heard at idle was the cooling stream. March 2007 had usual pre-season service done at original dealer, a personal friend. Brought it home and first trip, my non-boating girlfriend said "What is all of that noise?" She'd probably logged 40 or so hours on the boat previously. Jan. 2008, same pre-season service minus water pump, specifically asked tech. to run on hose and listen. He and the shop owner agreed "sound levels were between a 2 Stroke and a 4 Stroke. Dropped the foot, shined a flashlight up and tuner was secure and intact. I really don't have an answer for you." Struggling with this, my brother asked if this were about the same time that I switched to stainless steel Turbo prop. He was correct but everyone I speak to says should not be the cause. I have not yet swapped props to confirm. zot.
boatdryver posted 01-25-2008 10:02 AM ET (US)
mikejoyce77, one reason the manufacturers don't state a noise level in their specs is that there is a huge variation in how much "noise" reaches the operator's ears from boat to boat.
For example, if I'm standing in a center console boat, planing, with air going by my ears at 30 mph I'm going to hear far less engine noise than if I'm sitting in the helm seat of a cabin style boat with canvas around the front and sides, both boats having the same engine going the same rpm.
And how about the poor guests sitting back aft on these transom corner seats with their ears 2 feet from the motor?
There's another aspect to motor noise; It's the quality or mix of frequencies.
For example would you rather listen to a metallic grinding sound at 85 db or your favorite singer humming at 85 db?
JimL
Angel posted 01-31-2008 02:53 PM ET (US)
I've always assumed 4-stroke engines were inherently quieter than 2-strokes and now I don't know why. When I ordered my 2005 15 sport from the dealer I had a choice of 2-stroke or 4-stroke Merc 60's. When asking the dealer for his opinion he said "of course the 4-stroke will be quieter but the 2-stroke will have better hole-shot". Was he mistaken?
mikejoyce77 posted 02-01-2008 01:29 AM ET (US)
angel,
did you go w/ the 60hp 4 stroke outboard with your boat or the 2 stroke?
Angel posted 02-01-2008 12:01 PM ET (US)
I went with the 4 stroke. It is very quiet at idle not so quiet at cruise and WOT-still less noise than I remember my old johnson 9.9 2-stroke making. I believe 4-strokes should be quieter because there is half the 'explosions' per revolution of the crankshaft than a 2-stroke. Power and hole shot are very good. The 15 handles like a sports car.
cooper1958nc posted 02-08-2008 12:37 AM ET (US)
The "number of explosions" is irrelevant. 12 cylinder engines are not noisier than chain saws. Noise comes from mechanical and gas (intake and exhaust) sources. Secondary or sympathetic vibrations are also involved in many cases. Two stroke engines have been noisier than 4 strokes, probably because they represent older technology, often have a lot of vibration at certain harmonic speeds, and have a lot of nonlinear gas dynamics that are harder to silence.
fourdfish posted 02-09-2008 07:02 PM ET (US)
My 200hp E-TEC idles at 450rpms and I troll at 600rpms. At the helm I simply cannot hear it at idle and barely hear it
trolling. When it gets up and runs around 5000rpms it has a very pleasant low growl to it. I love it! The cowling has a special sound cancel incorporated in to it! Forgot the name!

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Author	Topic: Variations in Engine Sound Levels Among Different Types
mikejoyce77	posted 01-23-2008 11:46 PM ET (US) I have tried to find [information about the sound levels among] different outboard motors but have been unsuccesful. Are [outboard motors using a four-cycle design] quiter than direct-injected two-cycle engines? Or other way around? How come manufacturers don't mention sound [levels] on their specification page?
jimh	posted 01-24-2008 12:03 AM ET (US) There is no agreed-upon method or specification for sound levels for outboard motors to be measured. The usual method is to measure the sound pressure level using an A-weighted filter and at a certain distance from the engine. However, many people who report engine specifications test the sound pressure levels and report them. Sound levels are completely independent of the combustion cycle configuration. One cannot say that the two categories you framed, all motors used four-cycle design versus all motors using direct-injection two-cycle, have any special claim to loudness or softness. It really depends on the design of the individual motor, and how much attention was paid to noise, vibration, and harshness (NVH). Some manufacturers have intentionally given their engines a louder sound in order to make them more attractive to boaters who want a louder engine.
jimh	posted 01-24-2008 12:26 AM ET (US) A good example of the problem in comparison of sound pressure levels is demonstrated in some recent literature published by one leading outboard manufacturer. This manufacturer's literature presents comparison of sound pressure levels in terms of percentage difference in sound pressure levels. This is a misleading comparison. Human sound perception is much better correlated with logarithmic comparisons of sound level, and the universally used unit of comparison is the decibel. The literature may impress potential outboard motor buyers who have little knowledge about sound pressure level measurement, but in my opinion, it is misleading. There are disputes about very simple specifications like engine weight. If we cannot get accurate, consistent, and comparable measurements of engine weight between brands, I doubt that we will ever be able to rely on manufacturer published data to compare sound levels.
kwik_wurk	posted 01-24-2008 01:25 AM ET (US) In continuing Jim’s comments the standard measurement human perception for sound is A-weighted dB value. This is a single value given to the overall sound level. (Example: Most home/car stereo’s reveal a dB value when you turn the volume knob, for the overall loudness. But with an equalizer you can adjust the sound levels of many frequencies such as low frequency bass.) A-weighted levels exist because the human ear perceives certain frequencies of sound differently. These frequencies are attenuated and “appear” louder than they really are when measured with a scientific instrument (which usually measures in Sound Pressure Level - SPL). (While not a true example; think of the fingernails on chalkboard, little sound but very annoying.) A-weighting filters certain octave bands as an attempt to accommodate for these variations in human hearing response. In most common applications you find a single A-weighted sound level. Sometimes you will find the sound levels presented in octave bands, which gives you more detail about the sound. (Think of these octave bands as the knobs on a high end stereo equalizer, the more knobs you have the more you can fine tune the sound.) As an end user trying to filter thru manufacture specs, an A-weighted value is the best you likely find. Unfortunately is has deficiencies, but that is all you can run with at times. And yes don’t get caught up in marketing ploys trying to skew decibel numbers. And keep in mind a few things: Generically speaking four strokes are quieter than two strokes (I won’t go into the details here). And, you can change the muffler on a car and completely change the way it sounds without touching the engine. The same is true for boat motors.
Rob Pirie	posted 01-24-2008 01:30 AM ET (US) I have two boats both with direct-injection two cycle engines.One boat has 200hp Optimax the other 200hp Ho Etec , the Optimax due to it's large compressor mounted on top of the engine is noisy as hell compared to the Etec. I also fished a tournament last weekend and the Bostun Whaler next to us had a pair of the New Yamaha 350hp V8 4 strokes , we were all blown away by how silent these engines were you simply could'nt hear them until the boat had completly backed up into it's dock.Top marks to Yamaha for sound levels on these. Rob
zotcha	posted 01-25-2008 09:15 AM ET (US) Probably need to start a new thread but, my 2005 Yamaha F60 (four stroke) was silent first two seasons. Only thing heard at idle was the cooling stream. March 2007 had usual pre-season service done at original dealer, a personal friend. Brought it home and first trip, my non-boating girlfriend said "What is all of that noise?" She'd probably logged 40 or so hours on the boat previously. Jan. 2008, same pre-season service minus water pump, specifically asked tech. to run on hose and listen. He and the shop owner agreed "sound levels were between a 2 Stroke and a 4 Stroke. Dropped the foot, shined a flashlight up and tuner was secure and intact. I really don't have an answer for you." Struggling with this, my brother asked if this were about the same time that I switched to stainless steel Turbo prop. He was correct but everyone I speak to says should not be the cause. I have not yet swapped props to confirm. zot.
boatdryver	posted 01-25-2008 10:02 AM ET (US) mikejoyce77, one reason the manufacturers don't state a noise level in their specs is that there is a huge variation in how much "noise" reaches the operator's ears from boat to boat. For example, if I'm standing in a center console boat, planing, with air going by my ears at 30 mph I'm going to hear far less engine noise than if I'm sitting in the helm seat of a cabin style boat with canvas around the front and sides, both boats having the same engine going the same rpm. And how about the poor guests sitting back aft on these transom corner seats with their ears 2 feet from the motor? There's another aspect to motor noise; It's the quality or mix of frequencies. For example would you rather listen to a metallic grinding sound at 85 db or your favorite singer humming at 85 db? JimL
Angel	posted 01-31-2008 02:53 PM ET (US) I've always assumed 4-stroke engines were inherently quieter than 2-strokes and now I don't know why. When I ordered my 2005 15 sport from the dealer I had a choice of 2-stroke or 4-stroke Merc 60's. When asking the dealer for his opinion he said "of course the 4-stroke will be quieter but the 2-stroke will have better hole-shot". Was he mistaken?
mikejoyce77	posted 02-01-2008 01:29 AM ET (US) angel, did you go w/ the 60hp 4 stroke outboard with your boat or the 2 stroke?
Angel	posted 02-01-2008 12:01 PM ET (US) I went with the 4 stroke. It is very quiet at idle not so quiet at cruise and WOT-still less noise than I remember my old johnson 9.9 2-stroke making. I believe 4-strokes should be quieter because there is half the 'explosions' per revolution of the crankshaft than a 2-stroke. Power and hole shot are very good. The 15 handles like a sports car.
cooper1958nc	posted 02-08-2008 12:37 AM ET (US) The "number of explosions" is irrelevant. 12 cylinder engines are not noisier than chain saws. Noise comes from mechanical and gas (intake and exhaust) sources. Secondary or sympathetic vibrations are also involved in many cases. Two stroke engines have been noisier than 4 strokes, probably because they represent older technology, often have a lot of vibration at certain harmonic speeds, and have a lot of nonlinear gas dynamics that are harder to silence.
fourdfish	posted 02-09-2008 07:02 PM ET (US) My 200hp E-TEC idles at 450rpms and I troll at 600rpms. At the helm I simply cannot hear it at idle and barely hear it trolling. When it gets up and runs around 5000rpms it has a very pleasant low growl to it. I love it! The cowling has a special sound cancel incorporated in to it! Forgot the name!