Follow-up question on sound deadening material for Borla drone ....

drf · 06-21-2006, 11:20 AM

One of the solutions to counteract the Borla S-Type droan at 2K RPM or so was to use professional sound deadening material.

By some accounts, this approach was questionable.

My question is: Is there a test that using sound deadening material will help before going to the expense of buying the actual stuff?

How about a pile of old news papers strategically placed to some other test material???

I don't mean to use the cheap stuff as a final solution, just to see if it reduces the sound a little to see if this approach is on track.

Sounds off-the-wall, but what the heck!!!

Furinox · 06-21-2006, 12:10 PM

I'd be interrested in some opinions as well. I think putting something in the doors would help. I know when my windows are down the drone is not near as severe. I think the sound echoes inside the doors making the drone 2x as bad.

CrazyAl · 06-21-2006, 01:15 PM

This is an enormously complicated subject, so I'll see if I can make this as concise as possible.

There are various forms of "noise" in your car.

1) Rattling or resonating sheet metal, vibration transferred though the sheet metal (road noise)

2) Noise that comes from outside the car.

3) Noise that, once in the car, reverberates inside the car.

Sound deadening material is only TRULY effective against #1, and is somewhat effective against #2.

In order to truly "block" noise from outside the car you need a lot of mass, especially as the frequnecy drops. This is why a brick wall does a good job at blocking noise, but a sheetrock wall isn't nearly as good. For a good discussion on all of this this, see the "Bible" of acoustics: The Master Handbook of Acoustics by F. A. Everest.

If the drone problem has to do with #3 you have little hope of fixing it with deadening material. Any fixed volume of air will resonate at a particular frequnecy. This is how wind instruments (and speaker boxes) work, and the behavior is called a "mode" or "node" in acoustics. If your exhaust drone happens to be exciting a particular node inside the car, then there are only two ways of dealing with it:

A) change the volume of the inside of your car significantly (very difficult, and all this will do is change where the node is, not get rid of it)

B) eliminate whatever is exciting the node, in other words stop whatever is making noise at that particular frequnecy, thereby stopping it from starting the droning altogether. (This is what a more effective muffler or added resonator will do).

...the problem with #3 (drone) is that the resonance is what kills you. Even if the source of the sound is diminished a lot (if this were possible with deadening material), it doesn't matter becasue the interior airspace in your car will still vibrate. It's the same principle that allows a brass musician to blast out a really loud note, even though the actual sound he's making with his lips is quiet--it is exciting the node of the trumpet. Same principle...

As I said before, my advice is to deal with the drone AT ITS SOURCE. Install resonators in your exhaust. This is cheaper than sound deadening material, it doesn't cost you any HP, and it will be much more effective at getting rid of the drone.

As for the sound deadening material, there are basically two kinds. One is a mat or spray that dampens vibration and adds mass to the panels in your car. This stuff only works if it is FIRMLY BONDED to the body of the car, so there isn't really any way to simulate it aside from doing it.

The second kind of material is a foam (or simliar) mat, which soaks up sound. This doesn't have to be bonded to anything in order to work, so you could always just put some on the floor in your car and see if hit helped. However, I am willing to bet big money that this won't help appreciably. The reason is that foams, even those designed specifically for sound deadening, work well for high frequnecies, but they are very poor at low frequnecy absorbtion. Exhaust drone is much too low of a frequnecy for foams to be affective against. Foam carpet padding is cheap and you can get it any home center. This is useful for TESTING. However, this stuff is NOT safe to use in a car for an actual permanent install. It is not safe to use for the kind of temperatures that it could experience in your car--and then it becomes a major fire hazard. For your actual install, get special AUTOMOTIVE carpet padding or purpose-made sound blocking foam. (Over Kill or Luxury Liner from SecondSkin is a good choice.)

Take it from me: I have Borlas and headers. My exhaust was LOUD. Deadening didn't help appreciably (and I did a FULL job that cost $300 in materials alone; if you had a shop do this it would be $1000+ easily). Adding resonators eliminated the problem.

Now don't get me wrong--the deadening is great. It's worth it's cost four or five times over in the sound quality improvement for your stereo. But it doesn't help drone much.

drf · 06-21-2006, 01:27 PM

Quote:

ORIGINAL: CrazyAl

Adding resonators eliminated the problem.

What kind of resonators did you use and where did you place them?

Thanks in advance.

CrazyAl · 06-21-2006, 01:37 PM

I bought two Borla XR-1 "bullet" style race mufflers.

There is really only one spot where you can put resonators, which is the long straight section of pipe after the H (or X) pipe, but before the bend that goes over the rear axle. The install is very easy. Cut out a section of the overaxle tube, insert resonator, weld into place. Even the crappiest of muffler shops should get this right.

If I had to do this again, I wouldn't buy the XR-1's. The are nice, but they were too expensive IMHO. I'd just buy a set of stainless resonators (or small mufflers--there isn't any significant difference) from somewhere else. Verocious Motorsports is a forum sponsor, they sell resonators (stainless as well). Or you can use any small, "open" or "glasspack" type of muffler. These are common. Some examples: Dynomax Ultra-Flo, Dynatech Split-Flow, Magnaflow round, Borla XR-1, and so on.

scubadog · 06-21-2006, 03:56 PM

ear plugs............

What,.... couldn't hear you..............

I have the Borlas and it seems tolerable, but I have lost some hearing flying airplanes over the years, so I'm not the best to give any advice.

Crazy Al seems to have it nailed....

Good Luck,

SD

tedjac06GT · 06-21-2006, 05:41 PM

Is the Borla exhaust in question the same as FRPP axle-back exhaust? This is an axle-back version, not a full cat-back. Does anyone have any experience with the FRPP model (or the Borla exact equivalent)? I just bought the FRPP axle-backs and I'm hoping I don't regret it because of the "dreaded drone."

CrazyAl · 06-21-2006, 05:56 PM

Quote:

ORIGINAL: tedjac06GT

Is the Borla exhaust in question the same as FRPP axle-back exhaust? This is an axle-back version, not a full cat-back. Does anyone have any experience with the FRPP model (or the Borla exact equivalent)? I just bought the FRPP axle-backs and I'm hoping I don't regret it because of the "dreaded drone."

Yes, it's the same. For what it's worth the "cat back" is really no different than the axle backs. They sound the same.

However, the "drone" problem isn't really the Borla exhaust by itself. It's what happens when you combine straight-through mufflers (such as the Borlas, but other brands too) with either an off-road X pipe or high-flow cats.

If you don't have any other exhaust mods then I doubt you'll have a problem.

drf · 06-21-2006, 06:50 PM

Quote:

ORIGINAL: CrazyAl

Quote:

ORIGINAL: tedjac06GT

Is the Borla exhaust in question the same as FRPP axle-back exhaust? This is an axle-back version, not a full cat-back. Does anyone have any experience with the FRPP model (or the Borla exact equivalent)? I just bought the FRPP axle-backs and I'm hoping I don't regret it because of the "dreaded drone."

Yes, it's the same. For what it's worth the "cat back" is really no different than the axle backs. They sound the same.

However, the "drone" problem isn't really the Borla exhaust by itself. It's what happens when you combine straight-through mufflers (such as the Borlas, but other brands too) with either an off-road X pipe or high-flow cats.

If you don't have any other exhaust mods then I doubt you'll have a problem.

My Borla axle-backs are my only exhaust mod and I have the drone.

tedjac06GT · 06-21-2006, 07:05 PM

Quote:

ORIGINAL: drf

Quote:

ORIGINAL: CrazyAl

Quote:

ORIGINAL: tedjac06GT

Is the Borla exhaust in question the same as FRPP axle-back exhaust? This is an axle-back version, not a full cat-back. Does anyone have any experience with the FRPP model (or the Borla exact equivalent)? I just bought the FRPP axle-backs and I'm hoping I don't regret it because of the "dreaded drone."

Yes, it's the same. For what it's worth the "cat back" is really no different than the axle backs. They sound the same.

However, the "drone" problem isn't really the Borla exhaust by itself. It's what happens when you combine straight-through mufflers (such as the Borlas, but other brands too) with either an off-road X pipe or high-flow cats.

If you don't have any other exhaust mods then I doubt you'll have a problem.

My Borla axle-backs are my only exhaust mod and I have the drone.

So... is it really annoying or what? I can imagine a drone that would be very annoying... but I can also imagine just louder exhaust. If it rattles your brain and numbs your hearing... that would annoy me... or if it makes having a converstaion in the car difficult... that would annoy me. Can you describe as best you can???
Thanks.