I have been sitting here waiting for my RC-F and thinking about the lack of spec on sound levels
of stock and after market exhaust systems. I wish there was a standard aftermarket spec of exhaust sound level db vs RPM that one could compare against. Today I saw the Novel video post and earlier this week I saw an listened to JoeZ's RC-F prototype exhaust system for the RC-F It got me thinking about how to compare vs stock sound when you can not hear them in person and these of course the recording are done at different distances from the car.

If folks used something like the free iPhone app (decibel 10) on their phone or tablets, we could the post samples taken at the same distance or a known distance or in the drivers seat and show the app reading as an overlay or just post the reading values. Given measurements one would have a better way to compare. Since the free db apps dont seem to support video, one could take stills of the tach to show db level per RPM from the driver's seat. Yes, not as impressive as a video of the tail pipes but maybe more useful.
Even better would be for the after market manufactures to do this as a standard measurement spec.

I will update this post when I get my RC-F and measure it. Until then, here is a db reading of my IS-F with after market dual catback with Magnaflows, 2 resonators and 2 mufflers but it sounds great. Also, I decided on road trips with windows up I wanted some sound dampening in the cabin so I added some B-Quiet to the trunk and behind the back seat.
At 4000 RPM the sound level near the bumper was up 6-8db from stock sound and was just under the 94db limit at my local track.

But right now with all 4 windows open and in the drivers seat, with iphone at the steering wheel, car at idle just after starting, i get 68db.
Same iphone location but after a 9min warm up 63db.
Same iphone location At 4000 RPM after 10min 79db.
Move to the trunk area, iphone at 3ft away looking at left exhaust tips 74db (idle)


Maybe someone can do this with a stock RC-F and with after market exhaust.

 

Finally took time to measure the db levels from the RC-F stock exhaust. This could be a way to compare after market exhaust system sound levels.

I placed an iPhone 20ft behind the tail pipes and about 3ft high on a tripod. The goal was to find an approximate distance away from the car that had about the same sound level as in the car with the windows up. I recorded a image of the meter reading at idle and I took data at increasing revs and then plotted the dB levels. I also did the measurement with a iPhone near the steering wheel so one could see the dB level and the rpm in the images. One can look at the overall sound level but even better is to look at the sound level for each frequency at increasing RPM point. I took dB reading at both behind the wheel since I could see the RPM there but also at my ear location which had smaller dB values. Plot attached as a jpg.

The FFT plots in the PDF are from the behind the wheel location and also show 2 RPM points each so you can see
the increase in sound level as I do each increase by 1000 rpm.
I will repeat this when I get my JoeZ PTS exhaust installed.

I will attach Db vs frequency (FFT) for different RPM if anyone is interested.

The iPhone app ($4) I used is SPLnFFT. I 1st tried out the app Decibel 10th but it filtered out low frequencies and no FFT plotting.
Line to SPLnFFT
https://itunes.apple.com/us/app/spln...355396114?mt=8

 

Best way to test the ASC system is like so.

- Windows Closed -

Hold a steady gear like 3rd in a decent speed in Sport S

Then do the same and flip into Sport S+.

You can do this test flipping back & fourth from Sport S & Sport S+

You will clearly be able to distinguish the added sound from ASC speaker box, which is located behind the glovebox inside the dashboard

Once you have familiarized yourself with the sound, you will know what your trying to record interior wise..

Also after adding in a FULL Catback exhaust... The OEM Intake Flap & ASC pretty much become none existent l, sound wise when spirited driving..

They still can be heard in normal driving

Joe Z

 

Thanks for the tip. Not much volume (db) change, clearly just added lower frequency components at 50mph. Will try to measure db at other speeds in 3rd gear or maybe create a frequency spectrum plot of the 2 settings.

 

There is a lot of similarity between the levels inside and outside the F. Let us know what you get when testing sport+.

Thanks for doing the test.

 

I did the Sport+ ASC test at 3,3.5k,4k, and 5k rpm in 3rd gear, manual shift, holding rpm steady. 3.5k rpm showed the largest volume increase. After the switch I saw about 2.5db increase going to sport+. At 4k only 1.5db difference and at 5k I did not see a difference on the meter but could still hear a bit of the lower frequencies that ACS system supplies.

The hwy was pretty rough so these readings were in the range of 79 to 82.5 db, windows up. I wish I would have shifted to N and coasted for a reading of the road noise.

Again I did a video recording of the iPhone5s app Decibel 10's display.
The numbers will be a little high due to the placement of the camera and meter down near the drive mode switch instead of up by the drivers ear area.

Info on db measurement if your interested:
http://www.sengpielaudio.com/calculator-levelchange.htm
3db is only heard as about a 25% change in loudness. (1.25x)

Aftermarket exhaust systems can make a much larger change of course.
10db is 2x louder to the ear and as JoeZ says would make the ACS change unnoticeable. My old 08 IS-F with a magniflow dual cat back sound was 15db higher at 3k rpm vs my new RC-F stock.

 

I see that you have a Lifeproof case on your phone, was this done with it on or off? Thanks!

 

Thanks to the people who have the taken the time to get this data.

What would be really nice is if exhaust manufacturers did stuff like this themselves so you could actually know ahead of time what kind of db increase their exhaust would make! As a potential consumer, it would be really useful info.

 

I agree. When I got my IS-F exhaust there was no spec. After the install, it would not pass the track's less than 94db rule (over by 5db). Had to put some resonators in each pipe and even then it was a bit much at 3k rpm. It would be so simple for manufactures to publish db per rpm at some known distance from the rear of the car. At least one would have one set of measurements to compare brands against. One would still be missing the frequency component levels. "How does it really sound?" And you need to have the before and after sound track and/or a frequency spectrum plot vs rpm and maybe a quick rev. Some problems: different microphone response, microphone placement vertically and horizontally, so you really need some reference test tones of a known volume and frequency to do some test equipment calibration before doing the product measurement.

 

Yeah, different "experiment" setups could give wildly different results. But I figure that if you bring a car in for an aftermarket exhaust - there's your before! Can't they just run a couple tests with the car in the shop before they put the new exhaust on, then the same tests afterwards? Put the car/mic/whatever in the same place and you'll extract the differences. The *absolute* db values may not equate across perfectly across the board, but at least the "gains" should -- pretty much the same thing for any dyno tests. Seems like not that much work for companies to do, but really helpful for buyers. Honestly part of the reason why I don't want to spend $1k+ on an exhaust is that I have no idea how loud the car's going to be when I get it back, and afterwards it doesn't even meet track (and/or street?) requirements like you said and I'd have to buy more parts?... I'd feel kinda jipped.

 

One could put something like Spectrum View on your iphone or ipad. Or some other spectrum analyzer app if you use android.
The idea would be to capture and compare exhaust sound signatures.

I like this app.

https://itunes.apple.com/us/app/spec...472662922?mt=8

http://www.oxfordwaveresearch.com/j2...s/spectrumview

This app allows you to see the spectrum live in 2 forms and you can record and replay the sound tracks. With the live mike or the playback you can look at display using a Specctrogram (frequency vs time plot) or the Spectrum analyzer view (amplitude vs frequency) as the recording is played back.
You can save the recording or email it.

I see a camera icon to capture the screen but does not function FREE version so you would have to upgrade or use another camera to photograph the screen.

Attached is a rough example attached. It my RC-F stock recorded with the app and the 2 display images. (signature of the sound) I think if one really liked doing this a better external microphone would be helpful. And then buy the full app to allow expansion of the Y axis and zoom as needed.

 

RCF500
I just saw your question to me about the Lifeproof case on the phone.
Sorry about the late answer. Yes I did have it
on the phone. I know the protection film over the mike can cause volume reduction problems if its not in in the correct position after attachment of the case and one can blow on it to get it down away from the case fins and a workaround.

BUT I have had no problem with people hearing conversations. Best case would be to remove the case for people doing this test to eliminate any such error.

Link to Lifeproof workaround text
http://www.lifeproof.com/en/support/...e/solution/13/

 

Today I did the JoeZ dB sound level to OEM sound level measurement.



I started doing the measurement of the outdoor background sounds and measured about 52dB.


RC-F engine start up with the microphone (iPhone5s) placed about 1 meter behind the license place resulted in sound level peaks around 104.6db but then idles is about 84.5dB.

RC-F start up sound level - YouTube

I also took measurements inside the car at with increasing RPM and plotted the dB values vs the OEM values taken when I first got the RC-F. See attached plot. These measurement were made while in park and I did videos of the iPhone5s display as the RPM was increased with the windows up and down. The plot shows the OEM values as dashed lines and the JoeZ is the solid lines. You can see the windows down increased the sound level by about 5db at the peak of 3000 RPM. More important is the difference between the JoeZ and OEM max differences. The plot shows a max of 24dB at 1 meter from the rear and about 15db in the driver seat both in the 2500-3000 RPM range.

.
For reference: a difference of 10dB is about twice as loud and 20dB is four times as loud.

In the video link below I spent too much time trying to hold at exactly 1500rpm, after that I paused every 500rpm up to 5k.

 

Man you got your system super fast...!!!

Thanks for posting your test results..

Levels may change a small bit after approx. 1,000 miles of burn in...

~ Joe Z

 

JoeZ
I will retest in 1000 for you.
The sound is great! Nice work.

After getting package install I see small spider web scratches (see pic) on the tips and some rub marks. Any suggestions on how to polish them out. I have some Meguires Ultimate compound but it did not do anything noticeable. I did a web search and it looks like its easy to create fine scratches the chrome with some products. I waxed them but still see them.