By Chris Haak
Do you drive a convertible or know someone who drives one regularly? If so, there may be a lot of “what did you says” and “I didn’t catch that” uttered during the course of most conversations, according to a study published in the Journal of Laryngology & Otology on the noise exposure levels in several different convertible models. (Download a PDF of the full five-page article here.)
The authors of the study tested five different convertibles at speeds of 55, 65, and 75 miles per hour with the convertible tops both open and closed, and measured the noise levels from the passenger seat between 8 and 10 times from the driver’s left ear position. When the tops were open, all windows were also opened, and when the tops were closed, all windows were closed.
The convertibles tested were a mixed bag of current and slightly older cars, none more than ten years old. They included a 2009 Saturn Sky 2.0T, 2004 Nissan 350Z, 2001 Porsche 911 Carrera 4, 2005 Saab 9-3 Aero, and a 2005 Mustang GT. Overall, none of the five cars exceeded recommended NIOSH (National Institute of Occupational Safety and Health) time-weighted average permissable noise exposure limits with the tops sealed and the windows closed, with a mean noise exposure of 72.9 dB at 55 MPH, 73.7 dB at 65 MPH, and 75.8 dB at 75 MPH.
However, once the sunshine was allowed into the cars and the tops were opened, recommended noise-exposure limits were exceeded in each of the five convertibles at every speed of 55 MPH and above. Top-open noise levels were 85.3 dB at 55 MPH, 88.4 dB at 65 MPH, and 89.9 dB at 75 MPH. NIOSH recommends limiting exposure to noise intensities of 85 dB to no more than eight hours.
Among the cars evaluated, the 2009 Saturn Sky was by far the loudest with its top down, with a 91.1 dB reading at 55 MPH, 95.9 dB at 65 MPH, and a staggering 98.7 dB at 75 MPH. NIOSH recommends limiting exposure to 97 dB noise levels to no more than 30 minutes, and to exposure of 100 dB to no more than 15 minutes, so the Sky falls somewhere between those two.
Having spent a bit of seat time in the Sky’s cousin, the Pontiac Solstice GXP, around a racetrack, aside from the semi-incomplete development of these comely but parts bin-constructed convertibles, there is an enormous amount of air whipping around the passenger cabin at higher speeds. Specifically, I remember that a lanyard around my neck lifted off my chest and went airborne at some speed north of 100 MPH. The Solstice and Sky also had very short windshield headers, which enhanced the cars’ looks, but also put the tops of tall drivers’ heads right in the path of unblocked wind. That was likely another factor in the car’s dismal showing in this test.
With the top down, the Mustang GT Convertible (2005 vintage, but a similar car from a hard-points perspective to the current 2011 model) was the quietest at 55 and 65, and nearly the quietest at 75. Having spent a week testing a new 2011 Mustang GT 5.0 Convertible, I didn’t notice any particularly obnoxious noise or wind levels, so this is in line with my personal experience as well.
The Saab 9-3 Aero Convertible was the quietest with the top closed, and although this “win” may be relative against a fixed-roof car (since in our review of the 2009 version of this car, we noted that noise levels were somewhat high above 65 MPH). The Porsche 911 Carrera 4, though one of the quietest with the roof open, was actually the loudest with the roof closed. Perhaps its engineers were more concerned about weight saving than top insulation. It’s also worth noting that the Porsche was the oldest car tested, a 2001 model, so it’s possible that age may have played a role.
The bottom line is that driving a convertible regularly will likely cause permanent damage to your hearing. The noise levels recorded in these cars are high enough, but they also were done without any ambient conversation, air conditioning, radio playing, or – perhaps most importantly – passing cars. My own hearing is already beginning to fail at age 35, and I haven’t driven that many convertibles in my life, but thinking back to a highway trip to visit a friend about an hour away in a Mazda Miata PRHT, I literally winced when I was next to a tractor trailer – not because I was in a tiny car, but because there was an unbearable amount of noise. I still remember the sense of tranquility I experienced when I finally pulled into his driveway and turned off the car; my hearing had “adjusted” to the point that normal outdoor sounds were almost inaudible for a period of time.
Convertibles are a lot of fun on nice days, especially around town and at lower speeds. But the next time you think about buying one or going on an extended trip in one, you may want to consider using some sort of hearing protection, or better yet, closing the roof. Your ears will thank you, and you will also have more trunk space available as an added benefit.