Windshield sound test comparisons

[EddyQ]

If you plan on riding an ’07 RT with OEM windshield for long periods at highway speeds, you will definitely benefit by replacing the OEM shield. This post targets only noise level improvements. But other features such as rain deflection, visibility over the shield, cooling air needed for hot weather and other characteristics should be considered when picking a new shield. A really well done writeup comparing windshields was done by a really great person on this board.

LINKY

DiggerJim has contributed a lot to this board with many great posts and suggestion as this. But that was not the end of Jim’s kindly giving and support. In the past month, Jim let me borrow his favorite Ztechnik Vstream shield for a few weeks and also meet me for another shield swap so I can test his California Scientific shield. What a great opportunity to measure the noise of these shields and get first hand experiences with other characteristics of the two shields.

I determined a long time ago that the high helmet noise at highway speeds was caused by a stream of air squarely hitting the forehead area of the helmet. The only real fix is a new windshield. To test, all you need to do is block the stream by placing your hand over your forehead and the ripping noise goes away. This ripping loud noise is so loud I wondered if my ear plugs with 25-30dB attenuation would be enough to lower the level where hearing damage would not occur. So I devised a method of measuring the sound level (comparatively) in my helmet, next to my ear.

I purchased a Zoom H2 sound recorder which has the capability of downloading sound files (wav format) to my PC where I could edit them, process them and compare with other sounds. The H2 also allows for an external mic which is necessary for placing in the helmet next to one ear and is small enough to fit in my jacket pocket while riding. I found an old PC microphone that fit well in my helmet and had no issues with wire length and produced a repeatable response. I’m certain it does not have a nice flat frequency response, but it does repeat a measurement and is linear enough to make very accurate noise level comparisons.

Since noise is not a constant level, one method of measuring it is to record long durations and average many levels across the duration. I found I needed to do my own math on the recorded wav file in order to average the sound levels. My math first takes the first 4096 sound samples and converts to a frequency spectrum (FFT). Then it does this again for the next 4096 samples. Then again and again until it reaches the end of the wav file. The levels of all the calculated spectrums are averaged producing a smooth consistent level across frequency. Since the sample rate is 44.1KHz (44,100 samples per second), I was able to average 100’s of spectrums with as little as 10-20 seconds of recording. That time interval is long enough to produce a reasonably accurate sound measurement and not suffer from riding environment changes such as a passing truck. Once I obtain the average spectrum, I can “A weight” and integrate to determine the overall sound level. I used a calibrated noise level meter to calibrate white noise (played through PC speakers to both the meter and mic) to get a reasonable estimate of the actual sound pressure level dBA.

While riding, I’m continuously recording. I never stop the recorder. During the ride, I talk which records the specifics of the test. For instance, “windshield up, 80mph” . . . lower shield “windshield down, 80mph”. . . Later, I edit the large wav file making many small wave files for each scenario.

Test Results. My bike is an ’07 RT. I am 5’10, 170lbs, 32in inseam and wear an Arai Profile full face helmet. Unfortunately, I had to make some measurements on the highway near where I live and others out in CT on secondary roads. Surrounding noises at high speeds become less significant, but still have some contribution. Since I did not have a lot of time and a had a lot of scenarios, many sound samples were less than 10 seconds (some as small as 3 seconds). So, my results have errors. But I think you will see clear quantitative differences with each.

The plot above is the A weighted spectrum for many of the measured scenarios. The y axis is an un-calibrated level. But the plot clearly shows how smooth the measurements become and how high the peak spectrum is with OEM shield relative to the other tests. The peaks with the OEM are roughly 10dB above the Vstream and CalSci under very similar conditions.

The plot above is unweighted spectrum for some of the scenarios with the three shields and Cal noise. It is interesting to note that there is a lot of noise at lower frequencies that would get attenuated by the A weighting function. Take it what it is worth . . .

The above plot shows the calibrated SPL for all the senarios. The left blue area is with the shield down (loudest), middle area is shield midway up and right red area is shield fully up (quietest). The CalSci was the quietest with all three positions, but also provided the least air when fully down. It could be that the CalSci data being taken secondary roads was quieter for that reason. Regardless, the Vstream shows much better noise levels than the OEM and quite comparable levels to the Cal Sci. Also note that with OEM shield, the levels do exceed 85dB which according to OSHA will cause hearing damage. Even with Vstream and CalSci shields, the levels are still quite loud requiring ear plugs IMO.

As I said earlier and Jim identified nicely in his post, there are other factors for selecting the right shield other than noise. What I witnessed while riding closely correlates with Jim’s findings. But I was amazed that the much wider Vstream shield provided very nice cooling air when down and you could tune in the right balance by bumping the shield up. The way it should be IMO. This sold me the Vstream over the CalSci, which was not my path going into these tests. The CalSci is also a very nice shield.

Since I did these tests, I purchased a Vstream, installed and rode it 1,500 miles of highway and backroads. I heard from some posts that it is pulls the bike with cross winds, but I’m quite certain mine is no worse than the OEM. It was tested in some rain while on the highway and I am happy to report that my seat was drier that it would have been with OEM. Overall, I am quite pleased with the purchase. Thanks a million DiggerJim !!

[DiggerJim]

Thanks a million DiggerJim !!

No problem I liked your recording setup so I found a Zoom H2 (actually a pair of them) on Ebay to use when I'm doing motoref duties for USAC races - the alternative is trying to write notes on a dive slate and then later trying to decipher them for the race report. Using the Zoom lets me hit a PTT switch, record the note and keep on riding without distraction. Great little tool.

[EddyQ]

Gee, I'll have to look into the PTT feature. I could have used it for the testing I did. I simply recorded many minutes and edited later. Zoom now has a H3. But H2 is more than good enough for me. 24 bit converters have a huge dynamic range.

 

I wish it had a DC coupled input so I could record voltages from accelerometers. That way, I could really find out how bad my suspension really is.

 

Not many replies to my post. Probably too geeky. It was fun.

 

 

[Mike]

Thanks for sharing this. It belongs in the BMWST Pantheon . . . the sort of uber-geeky, really helpful info that has been such a big part of why we're still around after all these years.

 

Really, this is great!

[Guest Kakugo]

Thanks a lot Eddy.

 

I had a Calsci screen on my Kawasaki and it was the only one which made wind noise bearable. Plus it was so thick it looked like you could shoot at it and it would stop the bullet! (Not that I encourage this practice)

I haven't any issues with the BMW OE screen but it's nice to know should I choose so there are quietere option available.

 

Job well done!

[walton66]

I'm not sure about what I'm seeing here so what conclusions did you come to regarding your ear plugs?

[EddyQ]

I'm not sure about what I'm seeing here so what conclusions did you come to regarding your ear plugs?

 

I think the OSHA exposure limit for 8hrs is 85dBSPL with A weighing. The plot I show says I am below this level with Vstream and CalSci up to 80mph marginally with shield down and have margin with it mid or up possitions. With OEM, the noise exceeds this limit at 70-80mph even with the shield half up. But with half decent ear plugs, I should be fine with OEM.

 

But I am not sure I would want my ears exposed to much above 75dBSPL for any length of time without ear plugs. There is a lot of low frequency noise, which I am not convinced is safe with long exposures. At a minimum, it is not comfortable. Plus, cross winds tend to add a lot of noise which isn't accounted for here. So even with the aftermarket shields, I am wearing ear protection when above 50mph.

[walton66]

I always ear protection just because I don't like loud noise ... anymore. My ears are dinged enough from loud rock in my youth. Alright, I still like loud music occassionally but don't like the wind noise. I have a cal-sci shield but during the hot months, I have come to like my C-B sport shield for the extra air. Probably couldn't use it without earplugs.

 

thanks for the science

[Selden]

I always ear protection just because I don't like loud noise ... anymore. My ears are dinged enough from loud rock in my youth. Alright, I still like loud music occasionally but don't like the wind noise....

I'll bet this applies to a lot of people here. From age 10 or so, I can list: lawnmowers, power tools (especially saws) firecrackers, guns (the first handgun I can remember shooting was a Civil War Navy Colt), loud music, and motorcycles. I finally started using earplugs about 15 years ago. Tinnitus 24x7, and I can't hear anything over 8 kHz. These are my favorite disposable earplugs, soft, and very comfortable. $4 for 20 pairs on Amazon, with free shipping. I ordered 40 pairs a few days ago. If you aren't using ear protection, start now!