miserable droning between 70 and 80mph... Adding a side branch resonator.

[muddysub]

after re-gearing to 4.88, my Suburban drones unbearably between 70 and 80mph. it's downright peaceful at 65 or 85mph but all the speed limits in the southwest are 75 or 80mph, where it's actually 65, nobody does 65... i still need to add more sound deadening to the rear floor but this is more than it'll take care of. i'm not sure if i need better sound insulation, some kind of shield between the floor and exhaust or a new muffler altogether. on the way home i was contemplating a quieter muffler, rubber motor/trans mounts and more sound deadening. i'd rather not do all of that...

 

[wetoolowdingbangow]

after re-gearing to 4.88, my Suburban drones unbearably between 70 and 80mph. it's downright peaceful at 65 or 85mph but all the speed limits in the southwest are 75 or 80mph, where it's actually 65, nobody does 65... i still need to add more sound deadening to the rear floor but this is more than it'll take care of. i'm not sure if i need better sound insulation, some kind of shield between the floor and exhaust or a new muffler altogether. on the way home i was contemplating a quieter muffler, rubber motor/trans mounts and more sound deadening. i'd rather not do all of that...

Its gotta be your fuel pump.


Haha im sorry...my last chevy had a fuel pump go bad, 3 times, once on a steep road and I had to roll back down at night.

In all seriousness a drone noise under throttle would indicate gear mesh to be too close. However I dont think its that since you took your time to set it up right and the drone would worsen quickly. Im thinking its the fact that you regeared and now your rpm level is a little higher than it was, causing that sweet spot drone in the exhaust.

If its easy to do it might be worth while to pull the muffler, get it up to 70 to 80 and see if it makes a difference. May just need a different muffler.

 

[Greg72]

Throw a bunch of heavy moving blankets in the back of the truck before your next long trip as an experiment. If the drone goes away, you will probably be successful with a dynamat /dynaliner solution back there.


-G

 

[454Sub]

One box of Dynomatt works better than you could ever imagine. I ended up using 10 boxes in my Burb, did parts of the floors, doors, roof and sides, as completely covering the floor with it is heavy, expensive, and really not needed. You will be impressed when your done with it. The last time I actually wheeled mine, I could run with the radio on low, all 4 windows down, and the open headers were not awful at all, carried on almost normal vehicle conversation in it as far as sound deadening went. Mine has zero rattles, doors sound like they are full of lead, I ended up adjusting all of them afterwards because the had the only rattles left due to wornish door pins and latches, plus worn out seals after I finished, and it bothered me.

 

[muddysub]

The biggest problem with sound insulation is that it blocks higher frequency sounds better than low frequency.
I've been doing some reading about helmholtz or "side branch" resonators. They're basically a length of exhaust tube tee'd into your existing pipe with the other end capped off. The length of the tube needs to be 1/4 of the wavelength of the drone you're trying to eliminate.

the length of the pipe depends on your application. I found this on another forum that explains it pretty well.

The speed of sound in feet per second (say, 1072feet/second)
divided by
The frequency you wish to eliminate (say, 128cycles/second)
equals
8.375feet/cycle (numbers divide/seconds cancel out)
This is the length of a full wave form; much too big to work with under a vehicle.
To get a quarter-wave length, divide 8.373feet/cycle by 4 to get 2.09373feet/quarter-wave length.
Multiply 2.09373feet/quarter-wave by 12inches/foot to get the chamber length of 25.125".

Before that, you need to figure out the frequency you're trying to block out.
A V8 fires 4 times per revolution. 2500rpm/4 =625. 625/4 = 156.25. So the frequency I'm trying to cancel out is 156.25hz.

Now divide the speed of sound at 100*f, roughly 1159fps by 156.25 and I get a wave length of 7.41'. Divide that by 4 to get a quarter wave length and I get 1.85'. Multiply that by 12 to break it down into inches and I end up with a 22.25" side branch pipe.

This SHOULD cancel out the pulsating drone I'm getting from my exhaust. I've read a lot of threads from forums ranging from performance trucks to nissans to audis, it applies to anything with an engine.

Here's some examples.

 

[blazinzuk]

Did it have the sleeping platform?

That might be setting up some sort of resonance chamber thing.

The hemholtz resonate is interesting. I want you to try this just cause

 

[454Sub]

Very interesting.

 

[sweetk30]

some aftermarket gears hum more than oem .

and what muffler do you have now ?

were is the tail pipe exiting ?

 

[muddysub]

miserable droning between 70 and 80mph... suggestions?

some aftermarket gears hum more than oem .

and what muffler do you have now ?

were is the tail pipe exiting ?

True. But would that sound go away over 85mph?

Borla proXS

Straight out the back.

I've got over 6000 comfortable miles on it so far. But with the RPMs being higher what used to be noisy at 85 is now noisy at 75. It wasn't an issue before because I had no need to go that fast. A gear whine doesn't come on all at once and go away all at once.

 

[kdo1958]

i had mine regeared from 3:08 to 4:10 complained to the place that did the work about the droning noise. Oh thats normal they said,less than a year later the rearend blew up.

 

[y5mgisi]

I have read about those resonator J pipes. Always wanted to try them.

 

[blazinzuk]

Gear drone or whine doesn't come and go. It's fairly constant. At some points certainly louder than others. But if if was the gears it would be a fairly consistent noise

 

[JoshHefnerX]

I'm on the grrr8.net forum and people have been making hemholz pipes to work out drones w/ some success.

Dynamat does tend to block higher frequencies. If you want to block lower frequencies you would want to use different type of sound deadening.

Lay down some closed cell foam and then some mlv over the top of that. It blocks sound by using mass and making a floating floor type effect.

Josh

 

[Deuling]

Make your seat angle back more and cruise slow


JK. Mine does this too, im sick of being deaf when i get home from dunes. Nice old man exhaust is in my future.

 

[runamok151]

Slow down and do the speed limit?

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[FAB454]

Make your seat angle back more and cruise slow


JK. Mine does this too, im sick of being deaf when i get home from dunes. Nice old man exhaust is in my future.

Is yours a specific rpm drone or just an all around "Too loud"?

I'd love to make a set up and try them but, I don't know if my " all hell is breaking loose" tone would really change/benefit.

 

[blazinzuk]

Slow down and do the speed limit?

That is the speed limit 75 in Nevada 80 in Utah

 

[82355]

They are probably not use to that out East.....

Martin

 

[FAB454]

Muddy, is that assuming the added pipe is the same size?
I see one of the examples has a shorter but larger pipe.

 

[muddysub]

miserable droning between 70 and 80mph... suggestions?

Slow down and do the speed limit?

You ain't from around here are ha?

Muddy, is that assuming the added pipe is the same size?

I see one of the examples has a shorter but larger pipe.

I'm using 2.5" for the added piece, it's what I've got laying around and I've read several times that pipe diameter has little effect. So I'm going to give it a try.

I'm on the grrr8.net forum and people have been making hemholz pipes to work out drones w/ some success.

Dynamat does tend to block higher frequencies. If you want to block lower frequencies you would want to use different type of sound deadening.

Lay down some closed cell foam and then some mlv over the top of that. It blocks sound by using mass and making a floating floor type effect.

Josh

Mlv huh? Never heard of that one. I'll look it up.