Shkreet Car Interior Deshibul Levelsh
 

Fighting a problem in my street car build.

It's OBSCENELY loud inside at the normal BP "node" RPM points. ~1500 and again in the 3000-4500rpm range. We're talking 115-120db.

Exhaust is RB front to back. Header, midpipe, Power Pulse muffler. Vteckiller measured decibels on a phone app, so take the actual numbers with a grain of salt. The frequencies that are strongest are at nodes that we would have expected the HUGE resonator in the RB midpipe to cancel. Rubber hangers.

We initially chalked most of it up to the header and oil pan contacting the subframe due to motor mount issues. I swapped mounts since then and have miles of clearance, but the interior volume level is still completely out of control. Car has no soft top, hard top is bolted on with brackets, not latches.

Anyone else running this same exhaust setup that could ballpark decibel level for me? Any similar experiences fighting noise? Car is pretty subtle outside, the interior drone is just horrid. I had a similar issue with a full FM exhaust on our original MSM. Whisper quiet outside, horrendous headache-inducing drone inside, though wasn't quite as bad as this car.

turbo owners don't have these dumb problems :p

Oh?

when you build major h8ter vibr8er, you must embrace the vibr8ions

Decibels, not vibrations. Why is this so haaaaarrrrrrdddd?

This is an exhaust drone issue i/we am/are reasonably sure. I can put stock engine mounts in it, but i've swapped engine mounts enough times in the last month or so that i'd rather shut my nether regions in a door than do it twice more.

I've driven many rs/rb/fm cars and none were anything like you're describing. Biggest ugly noise inducing thing was no cat. Made the ugliest sound ever

Ok well... if anyone is reading this and currently has any similar setups, would they mind taking an unscientific measurement with their phone? I find it somewhat unlikely that i've "won" this lottery twice and nobody else has.

hmm. On my naturally aspired 1.8NA, I've got jr header --> stock cat --> non-resonated rb sport midpipe --> single power pulse muffler. Mazda comp motor mounts if it matters. It's quiet. I've also had a resonated test pipe instead of the stock cat and the car was still quiet..like stock car quiet.

Would you mind downloading some sort of app and measuring interior cruise db for me at some point? I would greatly appreciate it. :)

"Stock car quiet" is pretty much what i was expecting with this setup.

are you catless?

Yes. It's an RB setup front to back. RB does not make a catted system for NBs. So.... if you've been in/driven an NB with an RB setup front to back, you've been in/driven a catless RB-equipped NB.

yup
catless = crap
catted = much better

Now you're backtracking and being confusing. You said you've driven many RB cars and didn't experience this. The car is super quiet outside and sounds great.

I'm after hard data measured unscientifically with phone apps, as well as anecdotes with similar systems. You have the anecdotes and say it was quiet and good. Got it, will put in spreadsheet. <3

I'M POSTING COLD HARD FACTS!!!

want me to bust out technology and post datalogs with sharpies and masking tape?


better check yoself

Mmmmmmm the logging kit!

last rb header car + catted rs3 exhaust I drove sounded real nice, bot in and out
then we swapped out the catted midpipe for catless
it sounded like you in the bathroom after you ate a bucket of cheese curds

dunno how you had this problem with the msm. I had both the fm old school and fm new school exhausts on my msm, sounded great with both

catless egay downpipe too

I think we're still confused. I don't have a single issue with exterior volume. It's QUIET (easily as quiet as the MSM was outside). I don't have a single issue with the KIND of noise it makes, it sounds GREAT. Zero fart and gross shit you normally associate with a catless car.

My ONLY issue is with interior drone/decibel level. The noise i hear inside is a good noise, there's just WAAYYYYYYY too much of it. Got me, sugar?

just route exhaust into interior. it will muffle and baffle

Yooooooj resonator!

Car sounds great. Like really great.

I measured using my android device and two new apps. Got different numbers. It's still super uncomfortable in cabin.


Outside at idle, <10' away: 58-62db
Inside at idle: ~65db
Inside at 3500rpm free-revving: 75-78db

i could try to get some db readings later but my app sensitivity is questionable. I sat in my stock accord during my lunch break and it was reading 75db at idle..

I used both "Sound Analyzer App" and "Sound Meter" this last go around. Both spit out identical numbers.

kk i was using Decibel X. I just downloaded soundmeter. I'll post my results once i get home

My Datalogging Group Buy is still open, as it happens. Unfortunately, what you're describing is all-too-common among the "ricer" crowd, and is undoubtedly just another unfortunate side effect of your excessive rear brake bias. This may not make sense to you, but if you'd competed in F Prod for as many years as I have, you'd understand.

Are all the exhaust gaskets good? U personally checked they are not leaking air?

I had rb header, stock midpipe, rb dual tip exhaust and it was almost stock quiet. Just a tad more aggressive sounding.

on my current car while while waiting for EFR turbo I put on stock nb2 header, into 3" catless exhaust with a big magnaflow muffler, it was louder, but still perfectly ok on the hwy.

now I drove my new EFR turbo setup to a shop with Just an open downpipe to the muffler shop to get it welded to my exhaust, and I seriously almost went deaf. Even with full ear, ear muffs it was rediculously loud.

Every exhaust gasket is brand new. I installed them. No leaks. I even installed brand new gaskets again when i swapped the diff despite the old ones only having been on the car for 200 miles. No leaks.

On the same phone? If so, then that's because they're both using the same uncalibrated microphone hardware.

Sound meters on phones are toys. Proper sound meters not only need to be calibrated, they also need to be frequency weighted because the same sound pressure is perceived as different volume at different frequencies. The phone sound meter apps I've seen are all flat.

--Ian

You already know the frequency of droning, as you know the RPM. Is there space beneath the car to add a tuned Helmholz resonator suppressing these frequencies?

Also, have you done the bare minimum interior soundproofing, like stuffing foam or other similar shit in the body tunnels and whatnot? Get a couple sleeping bags and unroll them and stuff them in the trunk so they fill the space; see if that changes the sound at all.

Right. This is why i've used the term "unscientific" a few times in this thread when pertaining to measuring decibels with a phone.

I can pay more dollars to swap out my muffler that i paid dollars and hassle to get for one that has a Helmholz resonator. It's something i'm considering, just trying/wanting to gather more data points. I'm mostly trying to determine if what i'm experiencing is "normal" for this setup or similar, though i'm sure that request got lost in the initial many posts of irrelevant bantering.

No i haven't. I can mess with that, but no amount of soundproofing is going to make what is currently happening acceptable. Looking for data points/experiences with similar/anecdotes, not solutions at the moment.

My father(in his 60s) has a VVT swapped NA6. Full poly suspension/diff bushings with mazdacomp engine mounts, RB header and unresonated power pulse muffler w/poly hangers. Magnaflow hi-flow cat.

I find it slightly quiet unless youre flooring it. My father doesnt mind it and the wind noise bothers her more than the exhaust(top down for that). Ill try to get some DB readings.

(also last year I can the same set up on my car but MSM swap(w/o turbo) and AWR engine mounts + FM 2.5" turbo exhaust. That was louder but not really drone-y or unbearable)

My car is like concealer's. NA6 with VVT and 6758. Full 3" exhaust with resonator, cat and end can. The drone is driving me nuts. I have pool noodles underneath the parcel shelf and around the fuel pump/tank cover void. Full carpet. Even with the opt full of luggage it will drone like hell. From the outside my exhaust sounds sporty but not overly obtrusive. The intake noise and spool is certainly louder.

I'll try the big ass MT Magnaflow muffler next.

install the big ass magnaflow muffler and enjoy life.

I have full 3" catless, no resonator, only the muffler and its VERY quiet. Almost stock quiet. Just deeper sounding

Helmholz. He's your huckleberry.

I believe you can tee off the existing exhaust system and solve this problem. Takes some reading to nail down, I imagine.

big magnaflow (MT flavor) for eunos
helmLOLZ for revealer

lose the 1hp and toss a cat back on it. problem solved.

Don't have one, never had one, don't think there's enough real estate to get one sized worth a damn in the existing midpipe because the majority of the midpipe is hugenormous resonator.

About to just shelf the car anyways. Update in my "DD Sybian" thread.

yep, you hit the nail on the head.

Have you guys put the 3 inch vibrant ultra quiet resonator to a 3 inch exhaust in an NB? I saw folks mention they were using it on 2.5 exhausts ages ago and it was tight. I was going to order that or the 'regular' vibrant one, but would prefer to go with the ultra quiet if it fits somewhere in the midpipe area....
Going to go to an exhaust shop and have a resonator and big maggie dropped in because my car sounds insane...

Oh and Vlad, my old setup with FM ish and their 2.5 exhaust with cat was pretty droney...but tolerable. There was just one spot in the rev range between 3-3.5k where it was awful inside.

Here's a link:
Ultra quiet: Regular 1: Regular 2:
Regular 3:



What do you think you're going to do Ben... once you un-give-up on the car.

Haven't had a chance to do anything much with it.

But just thought this data point was interesting.

Rattle-trap 20 year old, 180k mile hugely lifted Montero with the rear two rows of seats removed, crappy window seals, tons of exhaust leaks, and 35" mud tires at 75mph on the highway. (Under lots of load because it requires 60-70% load to maintain speed at cruise.)

Somehow this thing is quieter at speed than the Miata is at IDLE. Awesome. Ignore the 77db, that was either me messing with stereo or hitting a huge bump. Roads are awful here.

https://farm2.staticflickr.com/1809/...409611c7_c.jpg
2018-07-07_02-34-52 by concealer404, on Flickr

I believe you have a local friend that can do some exhaust wizardry.

I bought the 17950 or whatnot res. Let's see what that does. I'll download an app to check mine tomorrow, but it is awful lol.

Download the spectrum analyzer app to see what the frequency is that's being produced. For science. I don't actually know what good it will do.

It would be good for figuring out one of those j tube sound canceling things in the exhaust that vtechkiller taught me about yesterday! Basically manipulates the wave to phase cancel the noise.

That's precisely how a Helmholz resonator works.

Aka exhaust wizardry!

Will have to get new trans in the car to post screenshot at this point, but i did previously do that. Our phones (vteckiller and myself) showed a bit of a hump in the 120-140hz area. Precisely where Goodwin targets.

My buddy and I are welding in a heimholtz on my car this weekend. My car was around 120hz or so ( 3500-4500rpm ) where the drone is pretty bad. On his FD with LS7 the heimholtz totally cured his drone issues.

Mkay post results in here. I'm putting a new trans in the car tomorrow night and then will stuff the tunnels with Walmart pillows on Thursday.

yessir will do

Ok i have measurements at 70mph cruise for both of my miatas. Windows up (mostly, will explain below), stereo off, hvac off. As quiet as possible.

Subject A: 1999 w/ original motor (+5A cam), 6spd/4.30 combo, RB header, RB midpipe, RB Power Pulse muffler. (Oem hangers) K&N Typhoon intake. OEM hardtop, 56k miles, actual nice car. Full interior, everything seals nicely.
Subject B: 2000 w/ original motor (+5A cam), 6spd/4.30 combo, RB header, 949 Racing Laguna midpipe/muffler. (Poly hangers. Loud. Stupid loud. Irresponsibly loud.) K&N Typhoon intake, Junk2 throttle body. POS Treasure Coast hardtop that doesn't come close to sealing, front quarter window vents open (because i couldn't reach while driving), and the two huge "portholes" in my rear window open. Car has a.... not full interior. 106k miles, pile of junk.

Cheggit.

https://farm2.staticflickr.com/1805/...20f117c8_c.jpg
2018-07-14_01-31-53 by concealer404, on Flickr

https://farm2.staticflickr.com/1829/...c81d8872_c.jpg
2018-07-21_10-29-21 by concealer404, on Flickr

Good, right?

https://cimg2.ibsrv.net/gimg/www.mia...3e0adb44bf.jpg
https://cimg9.ibsrv.net/gimg/www.mia...26d27f5576.jpg

i had measured db levels at 84 max. But it wasn't so much the decibel level that we are concerned with. It's the frequency in hz that causes drone. My Miata was in the 110-120hz range. I did some math calculations and figured on 29" for my heimholtz . My buddy welded it for me and now the car is completely transformed. Literally where it would drone to no end 3k-4500rpm range it's completely gone . The car sounds totally different now, much more mellow hollow sound. Before it was super deep bass sounding.

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that is pretty good, does it still drone though?

I think the db numbers across different phones doesn't really mean anything, it's just relative at this point.

My concern is that the car is loud pretty much at every RPM. It's fairly bass-y everywhere.

No, it's not good. db levels are going to depend on phone mic calibration. This is bad, because the street car/dd is just as loud as the loud, and i mean OBSCENELY, IRRESPONSIBLY, STUPID AF FAM, LOUD car.

Measure the hz frequency. Weld in heimholtz, profit

Yeah i mean maybe. But realistically this needs to be 15db quieter everywhere. At least. I don't really have room for a heimholtz either, because my muffler is huge. 2-3x the volume of yours. Unfortunately if i start messing with that sort of thing, the entire exhaust needs to be changed.

I haven't measured db since we welded it in but it's significantly less. On the highway you can barely hear the exhaust. You don't have room under the car where the midpipe is for one?