Our New 2012 PRHT SS Project....

Miata Parts, Intakes, Superchargers, Headers, Exhausts, Shocks, Springs, Sway Bars, Brake Kits, Autocross and track mods.
skeeler
Posts: 282
Joined: Mon Mar 31, 2008 7:31 pm
Location: Ann Arbor, Michigan
Contact:

Re: Our New 2012 PRHT SS Project....

Post by skeeler »

OK, rear spoiler makes sense. I'm curious to see what your splitter design looks like, since you don't have one for the NC2 yet.
2009, STR & DD. 1995, HPDE. 2004 MSM, sold. 2010 Mazda3, hers.
eluviis
Posts: 65
Joined: Sat Mar 24, 2012 8:16 pm
Location: San Diego

Re: Our New 2012 PRHT SS Project....

Post by eluviis »

Hi Brian, I have an idea for a rear spoiler and it's something that hasn't been done yet for the NC. It's a ducktail spoiler that's integrated with the tunklid, with no seam.

Of course, it means you'll need a new trunklid, carbon or fiberglass... or you'll need to attach a separate spoiler unto the factory trunklid and blend it it and then paint. Of course, this is quite expensive and involved, but it's a big plan that I have for my car. My idea is I want to buy a separate trunk lid to work on the project without having to disable my car. That way I can take my time. Once ready, and fitting is done, I'll have it painted to match.

This is what I have in mind:

Image
Image
My car: The 1995 RallyWays Miata
Ruiner
Posts: 19
Joined: Sun Oct 14, 2007 8:28 am

Re: Our New 2012 PRHT SS Project....

Post by Ruiner »

Re: sound deadening

I did the floor, tunnel, doors, trunk, trunk lid and rear deck with Damplfier Pro and Overkill. It helped subjective NVH quite a bit, but added more than a few pounds. I'd guess adding some to the roof lid would work wonders, but have never found out how to remove the plastic 'headliner' to do so.
2007 PRHT
eluviis
Posts: 65
Joined: Sat Mar 24, 2012 8:16 pm
Location: San Diego

Re: Our New 2012 PRHT SS Project....

Post by eluviis »

Re: Sound dampening - The problem with trying to lower the car's boominess is that fact that in order to do that, the material needs to be dense - which adds weight.

Why dense? Well, specially with PRHT, the problematic frequencies are the lower frequencies (below 500Hz). When you add material that is not dense enough, you continue to cut the upper and mid frequencies of the sound spectrum. These are easily lowered because the sound waves re small and short. However, the sound waves of the lower frequencies are VERY big. Some frequency's waves are as big as 5 feet across - The only way to cut low frequencies is with dense materials. And unfortunately, they all add weight.

The reason the PRHT feels more boomy than the soft top is because the soft top does not cut the mids and highs like the PRHT. While the soft top might be louder, the sound is more balanced. The PRHT is "quieter" but the low frequencies still get through. Thus, making it sound boomier.

Look at the attached graphic. Imagine is a PRHT Miata. The red line is close to the 500 Hz mark. The light blue shading to the right of that is the PRHT pushing down the mid and high frequencies. The squiggle line throughout is the sound. Everything to the left of the red line is the low frequencies (the boomy sound)... By effectively reducing the mid and high frequencies you end up with much more lows - which, while the overall decibels are less - the sound, since it's unbalanced is actually more annoying than if it were louder but equalized. DISCLAIMER: This graphic is NOT of a recording of an actual PRHT car running - It's just a representation of what's happening

I've learned to be fine with mine. It doesn't bother me. But the above is a simple explanation of what's going on.

Yes, I have lots of experience with sound.
frequency_graphic.jpg
frequency_graphic.jpg (60.97 KiB) Viewed 9126 times
My car: The 1995 RallyWays Miata
jboemler
Posts: 304
Joined: Fri Oct 10, 2008 6:15 pm
Location: Mukilteo WA

Re: Our New 2012 PRHT SS Project....

Post by jboemler »

That's the best dissertation on the boominess subject I've seen, Danny -- thanks! Do you have the equipment to be able to generate the actual plots for the car?

Are these peaks purely a function of resonances within the cabin, or the character of the original sounds created by the car? Specifically, how much could the booming be reduced by tunning it out of the exhaust? Many have experimented with this, but few have the audio background to attack it scientifically -- if you do, it would be a great contribution to the NC community.
eluviis
Posts: 65
Joined: Sat Mar 24, 2012 8:16 pm
Location: San Diego

Re: Our New 2012 PRHT SS Project....

Post by eluviis »

^ Thanks. I guess I could plot the soundtrack of the car inside. It's just a matter of putting a mic in the car plugged into an audio interface along with a laptop running recording software. Then run an EQ analyzer like the one above and see what it brings up. There are other factors at play that will muddy up the data, (like the mics dynamic range) but it still should yield some useful info. Plus, comparing the PRHT with the soft top would be interesting.

I wouldn't be able to do it right this second because I'm running my audio software on a desktop Mac. It's in my new future plans to buy a MacBook Pro... But having some savings, plus some coilovers for my MX5 are getting in the way of that. Haha.

Also, I'm sure some resonance within the inside of the car is at play - but I don't think it's the root of the problem. Midrange and high range frequencies within the car are simply diffused with all the stuff in the car (driver, seats, dash, carpet, etc.). The low range frequencies don't really bounce around inside. Those go through the cabin like x-rays pretty pretty much. (The reason why when you listen to someone else stereo from a car beside you with the windows up, you typically only hear the bass). If you add a liner to the inside of the PRHT for example, you cut more mids and highs - The lows still get through. A thicker steel roof (as in heavier sedans) with some air gap between the liner and the very top is much more effective at that. (Denser and some air space).

As far as the exhaust goes, of course there are frequencies that will be worse than others. There's also something called "sympathetic vibrations" where if a frequency coming from a sound source is the same an a standalone object, both will vibrate together making even more racket! (scientific definition there ;)
My car: The 1995 RallyWays Miata
jboemler
Posts: 304
Joined: Fri Oct 10, 2008 6:15 pm
Location: Mukilteo WA

Re: Our New 2012 PRHT SS Project....

Post by jboemler »

Well, if we could quantify just where those resonances were, perhaps different exhausts could also be measured to see which ones most excite those frequencies?
oldjag
Posts: 3
Joined: Sun Apr 22, 2012 4:40 pm

Re: Our New 2012 PRHT SS Project....

Post by oldjag »

I don't understand the aversion to adding a little weight. I installed 10 square feet of 80 mil Fat Mat in trunk of my PRHT and only weighed <4 lbs. I would gladly loose 4 lbs. for the improvement in NVH and drone reduction.Well worth it.
eluviis
Posts: 65
Joined: Sat Mar 24, 2012 8:16 pm
Location: San Diego

Re: Our New 2012 PRHT SS Project....

Post by eluviis »

Well that's fine I'm sure. It's more or less what Brian said he wanted to do with this car. Shed a little weight here to add a little weight there.
My car: The 1995 RallyWays Miata
Brian
Site Admin
Posts: 11308
Joined: Tue Feb 15, 2005 11:44 am
Location: San Diego CA
Contact:

Re: Our New 2012 PRHT SS Project....

Post by Brian »

Yep...we do plan to add some sound killing material, knowing it will add a few pounds. Given the spirit and purpose of this project that's okay....this is not a race car and improvement of the entire 'real world' driving experience is the goal. Thus, we want it faster, better handling, and more comfortable. Overall I expect the project will end up less weight than stock...though perhaps not much less. Our exhaust mods have shed about 10 pounds already and more will be saved with the wheels when they get here. Will also swap out some of the heavy steel braces for aluminum versions, etc. Then I won't feel too guilty about adding some weight back to further 'tune' the driving experience.

Would love to hear more stories from those who have added sound killing materials, particularly interested in what areas of application were most effective. Hopefully some PRHT owner did it in stages and can tell us the trunk paid off the most, and the doors were a waste of time, etc.
Brian Goodwin
Good-Win Racing
www.good-win-racing.com
Post Reply