Sound deadening (Dynamat) worth it?

[~SlideWays~]

Does anyone have experience with Dynamat or copies of it?

I'm thinking about installing some in the boot of my Chaser for when my wife uses it with soon to be baby in the back. The reason being that I built an exhaust for it a while ago, it sounds nice and is fine for daily use. But at certain loads it is a bit droney, so I'm wondering if the boot is acting like an amplifier of the sound.

So maybe covering the boot floor and behind the back seat rest would help?

Does this stuff make much difference or does the sound just travel through the chassis anyway?
Does it have to cover everything or will patches of it in hard to reach places still improve sound absorption?

[thegreatestben]

How far beyond the rear of the car does the exhaust tip end?

This can make a big difference to drone in my experience.

[~SlideWays~]

How far beyond the rear of the car does the exhaust tip end?

This can make a big difference to drone in my experience.

Its just inside the outer edge of the bumper, hadn't thought about it being a factor to be honest. I could test it with with scrap tube maybe.

[DeeCee]

Damping/Mass loading - adding weight to the panel to reduce panel resonance (commonly mastic or bitumen based material)
Absorption/insulation - introducing a barrier to absorb magnitude of sound waves and reduce overall sound
Barrier/Reflection - introduction of another layer for sound waves to get through (commonly foil)

Dynamat does all things from the above list but primarily Damping and Barrier, but due to the thickness and need to in panel gaps between door and door trim (in most common application of door speakers) the effectiveness is not as great as one would think. Ideally you would use two layers of dynamat or a similar product to increase the damping and barrier properties to reduce resonance of panels and overall noise output.

For Absorption, you would ideally use a closed cell foam based product (I have used wetsuit material in the past) to reduce noise transmission. This is a technique they use in middle to high level cars like BMW where the noise transmission is lowered due to a 1" thick layer of foam on the floor of the car.

To effectively reduce noise into the cabin, you would need to damp/absorb and barrier the floor and boot of the car (boot includes sides of the boot and underside of parcel tray as well) with a double layer of dynamat or with a layer of dynamat and a layer of foam. This is a time consuming job as you have to isolate the cabin as effectively as possible by covering up utility holes, spreading the coverage of sound deadening products to the edges without gaps etc. Will also get expensive.
You would reduce noise transmission through the chassis and body of the car through Damping and create an isolated environment with Absorption and Barrier.

To answer the question directly, a dynamat bulk pack could be used for two layers on the boot floor, sides, back of rear seat and under parcel tray to reduce the overall noise into the cabin, but it will not completely isolate it from the cabin.

If the drone is of particular concern, change the tip to something smaller or change the resonator to a muffler at the rear.

My personal opinion is that I would do as much as possible to save the kid's ears at such a young age, be it changing the exhaust system to suit or isolating the cabin as much as possible. I hate to think about the problems that some kids will have that I have seen, with their parents playing their stereo and subwoofer's at 90% in the car.

Any other q's, feel free to ask

[~SlideWays~]

Damping/Mass loading - adding weight to the panel to reduce panel resonance (commonly mastic or bitumen based material)
Absorption/insulation - introducing a barrier to absorb magnitude of sound waves and reduce overall sound
Barrier/Reflection - introduction of another layer for sound waves to get through (commonly foil)

Dynamat does all things from the above list but primarily Damping and Barrier, but due to the thickness and need to in panel gaps between door and door trim (in most common application of door speakers) the effectiveness is not as great as one would think. Ideally you would use two layers of dynamat or a similar product to increase the damping and barrier properties to reduce resonance of panels and overall noise output.

For Absorption, you would ideally use a closed cell foam based product (I have used wetsuit material in the past) to reduce noise transmission. This is a technique they use in middle to high level cars like BMW where the noise transmission is lowered due to a 1" thick layer of foam on the floor of the car.

To effectively reduce noise into the cabin, you would need to damp/absorb and barrier the floor and boot of the car (boot includes sides of the boot and underside of parcel tray as well) with a double layer of dynamat or with a layer of dynamat and a layer of foam. This is a time consuming job as you have to isolate the cabin as effectively as possible by covering up utility holes, spreading the coverage of sound deadening products to the edges without gaps etc. Will also get expensive.
You would reduce noise transmission through the chassis and body of the car through Damping and create an isolated environment with Absorption and Barrier.

To answer the question directly, a dynamat bulk pack could be used for two layers on the boot floor, sides, back of rear seat and under parcel tray to reduce the overall noise into the cabin, but it will not completely isolate it from the cabin.

If the drone is of particular concern, change the tip to something smaller or change the resonator to a muffler at the rear.

My personal opinion is that I would do as much as possible to save the kid's ears at such a young age, be it changing the exhaust system to suit or isolating the cabin as much as possible. I hate to think about the problems that some kids will have that I have seen, with their parents playing their stereo and subwoofer's at 90% in the car.

Any other q's, feel free to ask

Awesome reply Deecee, that's particularly interesting that gaps will make a noticeable difference with dynamat type products. I think I'll buy a bulk pack and see what difference it makes then look at adding a foam layer.

I removed the rear seats and parcel shelf trim to have a look at fitting extra baby seat restraints and was surprised how much insulation the parcel shelf has, but the boot and rear seat rest has bugger all really.

The exhaust is fine most of the time, it's just low revs cruising up Ngauranga Gorge at 80kph sort of thing that its a bit droney. It's 3" straight through but I fitted 2 resonators and 2 mufflers, the rear is an Adrenalin R muffler which made a good difference. I could possible change the rear exit though.

[DeeCee]

Somewhat. Filling the gaps between the body shell and the internal shell, eg body shell on rear quarter and wheel arch, would isolate the cabin more. Common trick to use in SPL and SQ days was to fill the gaps with expanding foam to fill the void. I tended to use those soft foam blocks you could buy at payless plastics and cram them in to fill the void and isolate the cabin (helped that they were also removable after, unlike expanding foam)

If laying down a sheet of dynamat, it is more common to just stick on a whole sheet and trim the edges to suit a curve or line of the body or panel you are applying to. You don't have to cover all of the metal if you don't want to, as a lot of panels have ridges or supporting ribs embossed into the metal for strength. The strength and/or thickness of the metal will reduce the resonance transmitting through the panel.

Example: a flat sheet of metal or a sheet of metal with some support ribs embossed in it. Wave it around or tap it with a hammer, you will hear more sound ripple through the flat sheet vs an embossed sheet.

Cars have a lot of panels with reinforcement embossed into it, so with the dynamat, the damping helps, but the isolation helps more.

Depends on the car, but the old cars had diffuser type material such as the strand blanket or maybe some bitumen like sound deadening panels for damping. On the firewall of the celica, I found a vinyl sheet with light foam on the back = diffuse + barrier.

If you need a hand, I am local.

Cheers
Dave

[~SlideWays~]

Fountain of sound deadening info

It's a '98 JZX100 Chaser sound deadening in the back is very minimal so I think there is much room for improvement.

PM'd