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Discussion Starter · #1 · (Edited)
There's a few reasons for this initial test.

First is stepping further up the learning curve with REW software - which - in the longer term is part of acoustic experiments related to an ever growing mobile audio system.

Second is 06 is due for new shoes. IME: noticing ride and handling improvements after replacing tires is readily apparent, but road noise is another topic altogether. The psychology of "feel" in road behavior deeply affects the subjective human sense of sound.

I wanted to have something more than my brains influence over my ears to gauge the upcoming change.

Bridgestone "Duelers" as of this morning:

Tire Synthetic rubber Automotive tire Tread Auto part


The measurement system consists of:
- REW software
- Behringer ECM 8000 measurement microphone
- Blue Icicle XLR to USB A/D
- Standard 25mm microphone shock mount
- Vintage Atlas mic stand
- 3" open cell foam pad insolating mic stand base from vehicle floor
- Series of bungee cords limiting mic stand shaft movement while maneuvering vehicle.

In addition to windows software and mic system, 2 additional devices were used during the drive as a confirmation/sanity check:
- Calibrated measurement mic and Android RTA application
- Galaxy handheld SPL

To the degree microphonic induction is minimized in this configuration, vehicle vibrations *should not* be present in the body of the A/D and measurement mic.

Vehicle Motor vehicle Car Automotive exterior Auto part


Sorry for the dust. This Alas stand sits in the home studio most of its life holding up a sweet 60's era Shure SM-55. It didn't occur to me it needed cleaning until the flash made it stand out like a Las Vegas casino sign. SHEESH!

Automotive wheel system Wheel Black-and-white Tire Automotive tire


In the driveway, windows up, engine off. Pure ambient spectrum and pressure as displayed by REW SW and Behringer Mic.

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Android RTA and handheld SPL meter (C weighted) sitting in the driveway, windows up, engine idling.

Two-way radio Electronic device Technology Electronics Measuring instrument


Same conditions above as displayed by REW/Behringer mic.

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Continued....
 

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Discussion Starter · #2 ·
Spectrum and level of road noise @ freeway speed. See notes below.

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In the image above, average is configured "Forever", meaning the curve displayed is the sum of averages across the audible spectrum, gathered over approximately 10 minutes of driving. The software began capturing samples as I left the driveway, drove down the hill from the neighborhood, negotiated about 1 mile of surface streets, then entered the freeway. The point being: averaging in this regard tends to flatten out peaks occurring time. Sort of like taking a snap shot of fuel consumption where MPG appears high but when averaged over the life of a tank, drops significantly.

Anyhow... Next run I'll turn averaging off and take several spectral samples @ freeway speed which should be a more accurate representation of road noise.

When 06 gets new boots, we'll see how much - if any - they make in road noise leaking into the cabin.

The Android app holds 1/3 octave peaks. Here's what that looks like:

Text Colorfulness Technology Font Electronic device
 

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Discussion Starter · #3 ·
According to hand held SPL meter in MAX mode, peak pressure reached 95db C weighted. 74db A weighted. If I recall previous casual glances, they were lower. That would have been approximately 30K miles ago, suggesting the Bridgestones are getting significantly louder as they approach end of service life.
 

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Having owned my RL since June '05, I remember the Stock Michelin Tire LTX, and I thought it was quite good. At the time of needing replacement I was planning a Road Trip to Salt Lake City. I opted to change to the Michelin Latitude, IIRC, at the time the tire was considered an "eco" tire from Michelin, and it would be considered a LRR tire if you search for it Today. Granted my tires had 6 years of desert environment and were starting to show their age. But the change to the Latitudes was as if the road noise was cut in 1/2, Very noticable.

I believe the LRR tires in our environment provide an excellent tire choice. If you'd like to get together and swap them for a test drive PM me and lets discuss.

EDIT: the Latitudes only have about 31k miles in the 5 years since install
 

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2008 Ridgeline RTS in Billet Silver Metallic
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Very interesting test OhSix. I'd also be curious how the Android app Sound Meter compares to your reference system. You are an Android user, right?
 

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Discussion Starter · #6 · (Edited)
Having owned my RL since June '05, I remember the Stock Michelin Tire LTX, and I thought it was quite good. At the time of needing replacement I was planning a Road Trip to Salt Lake City. I opted to change to the Michelin Latitude, IIRC, at the time the tire was considered an "eco" tire from Michelin, and it would be considered a LRR tire if you search for it Today. Granted my tires had 6 years of desert environment and were starting to show their age. But the change to the Latitudes was as if the road noise was cut in 1/2, Very noticable.

I believe the LRR tires in our environment provide an excellent tire choice. If you'd like to get together and swap them for a test drive PM me and lets discuss.

EDIT: the Latitudes only have about 31k miles in the 5 years since install
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Discussion Starter · #7 ·
Very interesting test OhSix. I'd also be curious how the Android app Sound Meter compares to your reference system. You are an Android user, right?
OH HELL YES. Android user here. Not an IOS fan.

Was thinking of a way to overlay the Android spectra graph on top of REW. Gonna grab a few new samples during morning drive tomorrow. ;act028:
 

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Discussion Starter · #8 ·
In retrospect, a more accurate title for this topic might be "Measuring cabin noise". When driving in silence, tuned into the various noises in a moving vehicle, it becomes apparent there are a multitude of vibration induced noises much more diverse than rolling rubber. Can I get a DUH?

Settings such as spectral width, upper/lower scales, octave resolution and a boat load of others options in REW are wildly diverse - and very different from hardware dedicated spectrum analyzers - so the learning curve continues.

One lesson learned, navigating SW settings, capturing logs (vs. screen shots), adjusting band width - dynamically - on the fly is important to acoustic analysis in a moving vehicle. Said another way, driving and using SW simultaneously isn't smart and doesn't produce measurements as detailed as could be if a driver piloted the vehicle while the passenger piloted the SW. Mak has expressed interest in furthering this experiment - and that's great because there's a shortage of geeks 'round here that would have the patience & willingness to participate in this kind of thing. :act006:

This mornings efforts:

Driveway, sitti8ng quietly. Red/yellow arrow points to start of tests. Staircase graph indicates me moving around, keys rattling, insert key in ignition, starter motor turning and engine start/idle.

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Spectrum of the events creating the pressure levels seen above. Note: red line is "peak hold" creating a record of frequency and pressure peaks. The black line is spectrum and pressure of cabin sound at the time the graph was captured. The peak appearing @ approximately 1,700hz is the starter motors signature.

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Leaving setting in the same configuration, the vehicle departs the driveway, climbs a short/steep hill, navigates 2 streets existing my neighborhood, then proceeds downhill reaching a max_speed of 40MPH on an asphalt surface. See time stamps: 10 second intervals between vertical graph lines.

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That kind of data is useful to understand basic cabin acoustics. But in my world, 06 spends most of her time @ freeway speeds, this is where we might find a difference pre/post tire swap. Before reaching any conclusions in the test so far, I'd like to define, save and repeat SW settings to make the test apple/apple when comparing the noise contributions of old to new rubber on the road. For example, the spectrum window is currently set wider than the conversion capabilities of the Blue Icicle A to D. In these first tests, there isn't much ambient noise activity above 10kHz, so why waste graph space in that area? On the low end of the scale, there's no value in leaving the window open to 2Hz - and at the current conversion rate of the A to D, the low end is cut off @ 15Hz. More wasted graph space. So fine tuning settings and saving them for future use should be valuable.

Below is the spectrum of cabin noise @ 60 to 70 MPH on a smooth freeway. The red arrow points to the affects of driving over a textured concrete (a bridge) - interestingly @ approximately 100Hz. The green arrow points to vibration transfer when tires engage raised lane reflectors, centered @ approximately 160Hz.

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This is the SPL histo-graph of the freeway ride this morning:

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The hand held SPL meter - using A weighted scale and MAX (meaning remember highest value measured) confirm, over all cabin noise during the trip.

Electronic device Measuring instrument Technology Two-way radio Tool
 

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Discussion Starter · #9 ·
Notes on Android RTA app with Parts Express calibrated mic:

Screen shot here is quiet interior, engine off. Phone is mounted in its air duct holder - making it susceptible to microphonic influences - which may explain low frequency energy in the graph.

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This shot is the result of this morning ride:

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SPL and frequency content roughly align with REW and Berhinger/Blue. For the cost of a free App and $16 mic, this is a more than reasonable mechanism for understanding sound around you. Fun, portable and cheap. A hard combo to beat.
 

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Does a typical android device mic have the hardware capability to send accurate info to an app? Or are they typically limited above and below certain freqs?
 

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Discussion Starter · #13 ·
Does a typical android device mic have the hardware capability to send accurate info to an app? Or are they typically limited above and below certain freqs?
Basically, Android and base modem SW doesn't filter audio outside of "in-call" TIA band limits - so the only real limitation *should be* frequency characteristics of the mic itself.

Typically, bill-of-material bean counters don't care as much about performance as they do line item supplier cost, so performance takes a back seat to $. Mic's in mobile devices are incredibly small these days - driven into the micro-world by the insatiable desire to pack features into an ever decreasing footprint - which is just a way to say "cheap and small" is the driving concern when sourcing components for mass production.

Having said all that, small and cheap doesn't necessarily mean crummy. Electro-mechanical transducers have come a mighty long way in the last couple years.

You've placed an interesting bug in my ear. Lemme run a test or two to confirm what I think I know. I'll use a calibrated mic with the RTA app, take a snap shot. Unplug the mic, then use the native Moto mic in my X. It'll be cool to actually know the delta (if any). My guess would be the external mic would have superior polar characteristics - but we'll see.
 

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2006 Ridgeline RTS in Steel Blue
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Six,

I love when a "bug" is placed in you ear. It means the "delta" for how much extraneous information we'll all receive is going to grow exponentially.

Everyone, strap on your seat belts, the ROC's Mr Wizard is going to teach us all something.
:grin:
 

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I would expect that since the bandwidth for a phone conversation is limited, the in-phone mic will be optimized (cost-wise!) for that range.

I seem to recall the Bell System was set up for a 4 kHz bandwidth over their copper lines. Not sure what cell technology uses, but it's almost certainly chopped and compressed for transmission to the tower.

Chip H.
 

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Discussion Starter · #16 · (Edited)
CTIA adopted TIA standards at the inception of mobile telephony. Bandwidth being what it is, over the air conservation and voice sample rates at the mobile station modem level still limit "quality" to 1940`s era voice quality band limits of 300 to 3.3kHz. Stinko!

The real tell in mobile mic quality these days is VoLTE. Voice over IP mobile (or high def audio) can be shockingly good. An end to end VOIP call is as amazing as other high def experiences. Burps and farts sound as though they originate in the room you are occupying. Thankfully that's just an analogy. LOL.

So, mics in modern phones have much expanded frequency character when compared to mic's of old.

Tests to follow shortly. :)
 

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Well, I basically meant to ask if the frequency response of the tiny mic in the phone can provide measurably similar results to your reference standard gear. Or that's what I was trying to ask!
 

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Discussion Starter · #19 ·
Well, I basically meant to ask if the frequency response of the tiny mic in the phone can provide measurably similar results to your reference standard gear. Or that's what I was trying to ask!
AH! I misunderstood what you were asking. Thought you were wondering about built in phone mic vs external. There's a few ways to compare App to REW, the easiest being grabbing available graphs and roughly aligning them. Laying one of top of the other comes close - without tweaking REW SW, here's a stab at displaying the differences between their measurement capabilities.

Looks pretty danged close to me. If someone was doing casual signature analysis, the APP would do a fine job capturing both SPL and frequency curves. Close enough for government work....

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Be careful what you ask for... :surprise:
LOL. I know. I make me nuts too. :laugh:
 

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Discussion Starter · #20 ·
Getting to know REW a little better. Recently learning to save files for post event analysis and other fun stuff. In the raw files, time stamps are available, which gave birth to merging data from other devices - so been playing around with a couple things. More to come - but for now, integrating time stamps from Torque App logs provides a way to merge vehicle speed with SPL and spectrum graphs.

So... below is a first pass at associating speed with road noise. This is SPL characteristics of a (portion) of a 31 minute freeway trip to the office. Peak level reached 76db SPL C @ 9:35 + 1/2 second. With Torque logs set to 1 second intervals, the time stamp provides a cool way to isolate what the vehicle was doing at the time of peak interior noise. A whole bunch more data was collected - but parsing it is a bit challenging. As that process improves, we should see some nifty stuff. Nifty being a geek term for geeky. :act002:

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More work to do on this, but for now - it looks to me the 3.5L VTEC acoustic signature hangs right between 38 and 42Hz. Note the short (.22mi) uphill drive mentioned has twin peaks @ 40 & 110Hz. RPM probably hit 3,5K or so but speed never exceeded 30MPH. The remainder of the trip, 40Hz remains prevalent. For now, I suspect the evil effects of resonance are at work. One way to confirm if the 40-ish Hz hump is always related to the engine *might be* to slip her into neutral on a safe stretch, see if that humps flattens out.

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Isolating the freeway graph, we can see most of the action is happening below 2.8kHz or so.

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More fun stuff is coming. Gotta get the base line defined so when new rubber gets attached, the delta can be measured.
 
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