Exhaust too loud? I might have a solution.

[VinceLA]

It doesn't involve selling the exhaust and it won't cost too much.

Two words: Acoustical Insulation.

If you have a chance to remove the engine compartment cover, feel the inner walls of the engine bay. You will notice that smart has a rather thin layer of insulation. More like a carpeting barrier with a 1/8" thick fabric-like insulation. The objective is obvious to insulate the engine bay thermally and acoustically. Not to mention the insulation that lined the compartment cover is, well, really skimpy too.

Now, there are several types of acoustical insulation and the technical terms can get scary. Common measures are the Noise Reduction Coefficient (NRC) and Sound Transmission Loss (STL). Just standards the determine how good a material of a certain thickness reduce sound or transmit sound respectively.

Polyurethane foam seems to be a popular choice. But keep in mind, some foam are not heat, oil, chemical resistant. Polyurethane foams also have vinyl barriers, foil faced etc. The purpose is to enhance sound absorption. The foil faced foam also acts as a thermal insulation (or reflector). And then there's more commonly seen coned or egg-crate shaped foams.









So after doing some research, I ordered different foams and installed them. The available space in the engine bay is seriously constrained. Still I managed a few different designs and ideas.

The verdict? The exhaust note is quieter from inside the cabin. I will post pictures very soon after trying out a few more ideas. How much quieter in dB? Well, a digital sound meter should be on the way but I do plan to get it sorted out hopefully this weekend.

[WilyB]

Do you have a good fire extinguisher?

[brian r]

Great approach, Vince. VW has used the same technique placing dense foam under the plastic engine cover of the new TDI-and it really works.

I have gutted my interior and applied sound deadening. Stay tuned for pictures...

[VinceLA]

Ok, what's this top secret project you working on now?

Originally Posted by brian r

Great approach, Vince. VW has used the same technique placing dense foam under the plastic engine cover of the new TDI-and it really works.

I have gutted my interior and applied sound deadening. Stay tuned for pictures...

[John_H]

Good discussions on sound absorption usually point out that foam does next to nothing. For sound waves, you need mass between source and listener. As far as cutting down vibration of surfaces, you have a little help with sheets of foil opposite rubber that change the vibration characteristics of sheet metal; this can help cut sound transmission via the metal bodywork but mostly on the flat surfaces where vibrations occur (bends, corners, and welds tend not to vibrate much).

If you want to go all out, I'd recommend vibration dampening on the wall between the seats and the engine compartment and thermal insulation material more for comfort than for noise level. I never have a problem bringing ice cream home from the grocery; things stay very pleasant with the thermal insulator I use.

Durable damping pads for cars
and
Thermo-Acoustic Blanket
are the products I used.

[sharonlee]

I have noticed engine noise but I guess I am willing to put up with it.

A possible dumb question from someone who knows NOTHING about this. Using these methods and materials, how about engine overheating?

[John_H]

Originally Posted by sharonlee

Using these methods and materials, how about engine overheating?

The engine is not cooled by conduction to or airflow within the cabin. The engine is cooled mostly by the radiator in the front of the car. Air still gets in and around the engine within the engine compartment. The *interior* side of the cabin is where sound deadening and thermal insulation material should be used.

There are no fire dangers and any puppy kept in the back would be much more comfortable.

[lowndex]

I added Dynamat Xtreme Bulk Pack to both door panels using Tapp Plastics adhesive (meant for platsic). This ensured the Dynamat does not come off from heat during the summer. I took out both seats and and the carpet down to the metal pan/liner. I added Extremeliner to the entire floor surface, including the engine bay (from the inside).

And I still sold my DTH single-tip for my new 4smartcar DTH dual-tip exhaust!

[ZZAAA]

this review of various car sound deadeners might be of interest:

Sound Deadener Showdown

[Cruising n Coasting]

Originally Posted by lowndex

I added Dynamat Xtreme Bulk Pack to both door panels using Tapp Plastics adhesive (meant for platsic). This ensured the Dynamat does not come off from heat during the summer. I took out both seats and and the carpet down to the metal pan/liner. I added Extremeliner to the entire floor surface, including the engine bay (from the inside).

And I still sold my DTH single-tip for my new 4smartcar DTH dual-tip exhaust!

I just got my dual tip but haven't had time to install. How does it sound?