WarrenM
02-06-2011, 07:59 AM
THE BEST SPEAKERS AMPS DSP AND CABLES - BUT ALL I HEAR IS ROAD NOISE!
At 110 KM/H, the wind around you is whipping up a storm and your motor has opened up nicely to a reassuring roar. The ribbed road under your tyres sounds like a cattle-train.
So much for hi-fi!
It's time to learn about noise deadening.
There are three aims to noise deadening:
Stop panels from vibrating in response to motor, wind, road/tyre noise etc.
Block the transmission of external noises such as wind, motor, exhaust and road/tyre noise
Stop reflected and refracted speaker-initiated sounds from muddying the music
Each of these has its own optimal means of suppression.
Panels vibrate at their natural resonant frequency. Hit a panel with a rubber lump hammer and you will hear it "ring". If you can attach a non-resonant weight to the centre of that panel, you will stop it ringing, by lowering the resonant frequency and at the same time damping the size of the resonance. This type of attachment is called a constrained layer dampener. The best compromise material for this purpose is aluminium-backed butyl rubber. The heavier the aluminium, the greater the effect but the harder it is to cut and press the material into place. This material is quite expensive, especially the most well known brand - Dynamat Extreme.
What most suppliers don't tell you is that constrained layer dampeners are best used for this specific purpose, i.e. as a vibration damper, and as such, only need to cover about 25% of the panel for full effect. They want you to use this material to cover the entire panel, using it as both a vibration damper and a noise insulator. Because they make more money that way.
The best value noise insulator is Mass Loaded Vinyl (MLV) in combination with foam rubber. MLV is very heavy vinyl sheeting, impregnated with heavy metal dust. The MLV reflects or absorbs low frequency noise. The foam rubber reflects or absorbs high frequency noise. Together they suppress a remarkable 15dB or more, from 80Hz to 4KHz. Keep in mind that, if your amp is driving your speakers at 40 watts per channel, increasing the volume by 15 dB would require the amp to pump out over 1200 watts per channel! - I dare say somewhat more than your 4-channel amplifier can deliver. In other words, using MLV to suppress noise all over your car is equivalent to replacing your 40 W RMS per channel amp (costing say $400) by a 1200 W RMS per channel amp (costing say $5000).
You can use constrained layer dampening material as a noise insulator, but it typically is about half as effective as MLV (at a much higher price). You should actually use both types of product in concert: damp vibrations by gluing constrained layer dampening in the centre 25% of each panel; glue MLV/foam rubber (the foam rubber side) to the entire panel.
Another material which works about as well as MLV is sound deadening paint. This paint has bitumen components in it and smells like tar until it is fully dried. As such it is not the best material to be sound-deadening inside the car. However it is excellent for sound-deadening the wheel arches, which are the main conduits for tyre/road noise into the car. There are different thicknesses for brushing, air-gun spraying and aerosol spraying. The aerosol is obviously easiest to use but doesn't go very far. Assume about one aerosol can per wheel arch. At $15 per can plus $15 for the pre-spray cleaner, that's $75 and elbow grease to eliminate 90% of your tyre noise. Jack up the car. Take off a wheel. Clean off any grease or dirt from the wheel arch, using wax remover or thinners. Pat dry (it is OK if it is sticky). Then spray several thin coats of sound deadener, waiting five to ten minutes between coats. Put back the wheel and repeat with the other 3 wheels in turn. The volume of noise from your tyres should be instantly and substantially lessened.
Where else should sound deadening go?
Door panels
Floor
Inside Firewall
Boot floor
Boot lid
Bonnet lid
Roof
What if I can't afford to do all that? Everything helps!
Doors are probably the biggest single improvement against wind.
Firewall and Bonnet lid against engine noise
Wheel arches against tyre/road noise
Boot against exhaust noise
Floor against wind and general noise under the car
Roof against wind in big cars and in vans
Vibration damping the boot is also a big help against sympathetic vibration from a boot-mounted or rear-shelf-mounted sub-woofer.
The last type of noise to deal with is reflected sound behind the speakers. When noise is projected forward, noise is projected backward (for every action there is an equal and opposite reaction). That noise bounces off the panel behind the speaker at any number of angles, finding its way out of the speaker via the speaker cone. Any sound which reflects directly back the way it came is fine, as the delay is so small that it does not affect the clarity of the sound. But any sound which reflects off at an angle is going to bounce around the inside of say the door, for a while before finding its way out through the speaker cone, perhaps milliseconds delayed. This somewhat diminished and delayed sound will muddy the sound which reaches your ear. So mats are available to absorb back reflections. Frankly I do not know how they differ from MLV.
NEXT:
A STEP BY STEP INSTALLATION APPROACH TO GET THE MOST NOISE REDUCTION FOR THE LEAST COST
Regards
Warren
At 110 KM/H, the wind around you is whipping up a storm and your motor has opened up nicely to a reassuring roar. The ribbed road under your tyres sounds like a cattle-train.
So much for hi-fi!
It's time to learn about noise deadening.
There are three aims to noise deadening:
Stop panels from vibrating in response to motor, wind, road/tyre noise etc.
Block the transmission of external noises such as wind, motor, exhaust and road/tyre noise
Stop reflected and refracted speaker-initiated sounds from muddying the music
Each of these has its own optimal means of suppression.
Panels vibrate at their natural resonant frequency. Hit a panel with a rubber lump hammer and you will hear it "ring". If you can attach a non-resonant weight to the centre of that panel, you will stop it ringing, by lowering the resonant frequency and at the same time damping the size of the resonance. This type of attachment is called a constrained layer dampener. The best compromise material for this purpose is aluminium-backed butyl rubber. The heavier the aluminium, the greater the effect but the harder it is to cut and press the material into place. This material is quite expensive, especially the most well known brand - Dynamat Extreme.
What most suppliers don't tell you is that constrained layer dampeners are best used for this specific purpose, i.e. as a vibration damper, and as such, only need to cover about 25% of the panel for full effect. They want you to use this material to cover the entire panel, using it as both a vibration damper and a noise insulator. Because they make more money that way.
The best value noise insulator is Mass Loaded Vinyl (MLV) in combination with foam rubber. MLV is very heavy vinyl sheeting, impregnated with heavy metal dust. The MLV reflects or absorbs low frequency noise. The foam rubber reflects or absorbs high frequency noise. Together they suppress a remarkable 15dB or more, from 80Hz to 4KHz. Keep in mind that, if your amp is driving your speakers at 40 watts per channel, increasing the volume by 15 dB would require the amp to pump out over 1200 watts per channel! - I dare say somewhat more than your 4-channel amplifier can deliver. In other words, using MLV to suppress noise all over your car is equivalent to replacing your 40 W RMS per channel amp (costing say $400) by a 1200 W RMS per channel amp (costing say $5000).
You can use constrained layer dampening material as a noise insulator, but it typically is about half as effective as MLV (at a much higher price). You should actually use both types of product in concert: damp vibrations by gluing constrained layer dampening in the centre 25% of each panel; glue MLV/foam rubber (the foam rubber side) to the entire panel.
Another material which works about as well as MLV is sound deadening paint. This paint has bitumen components in it and smells like tar until it is fully dried. As such it is not the best material to be sound-deadening inside the car. However it is excellent for sound-deadening the wheel arches, which are the main conduits for tyre/road noise into the car. There are different thicknesses for brushing, air-gun spraying and aerosol spraying. The aerosol is obviously easiest to use but doesn't go very far. Assume about one aerosol can per wheel arch. At $15 per can plus $15 for the pre-spray cleaner, that's $75 and elbow grease to eliminate 90% of your tyre noise. Jack up the car. Take off a wheel. Clean off any grease or dirt from the wheel arch, using wax remover or thinners. Pat dry (it is OK if it is sticky). Then spray several thin coats of sound deadener, waiting five to ten minutes between coats. Put back the wheel and repeat with the other 3 wheels in turn. The volume of noise from your tyres should be instantly and substantially lessened.
Where else should sound deadening go?
Door panels
Floor
Inside Firewall
Boot floor
Boot lid
Bonnet lid
Roof
What if I can't afford to do all that? Everything helps!
Doors are probably the biggest single improvement against wind.
Firewall and Bonnet lid against engine noise
Wheel arches against tyre/road noise
Boot against exhaust noise
Floor against wind and general noise under the car
Roof against wind in big cars and in vans
Vibration damping the boot is also a big help against sympathetic vibration from a boot-mounted or rear-shelf-mounted sub-woofer.
The last type of noise to deal with is reflected sound behind the speakers. When noise is projected forward, noise is projected backward (for every action there is an equal and opposite reaction). That noise bounces off the panel behind the speaker at any number of angles, finding its way out of the speaker via the speaker cone. Any sound which reflects directly back the way it came is fine, as the delay is so small that it does not affect the clarity of the sound. But any sound which reflects off at an angle is going to bounce around the inside of say the door, for a while before finding its way out through the speaker cone, perhaps milliseconds delayed. This somewhat diminished and delayed sound will muddy the sound which reaches your ear. So mats are available to absorb back reflections. Frankly I do not know how they differ from MLV.
NEXT:
A STEP BY STEP INSTALLATION APPROACH TO GET THE MOST NOISE REDUCTION FOR THE LEAST COST
Regards
Warren