BJM

iTrader: (1)

I took some measurements of my convertible's sound environment. I was trying to figure out what I could change to recover some of the sound quality that seemed to disappear while on the road top down. These are really noisy cars in general but there is a spectral change with the roof down, not all frequencies are affected equally. Also, vehicle noise while moving has a definite shape, treble is not affected much at all, but bass and mid range are slowly drowned out as you drive faster.

First graph below shows all the measurements together.



Similar graph with some lines removed for clarity. You can see the gap between the roof up and roof down lines in the mid range regions.




This graph has the idle sound line subtracted off of the other lines. This graph just shows the increase in sound levels due to driving. So if you have your stereo sounding good idling, the levels rise as shown, unevenly. From 20-2000 Hz you have wind, road rumble, vehicle conducted sound, etc. As you go up to 20000 Hz there is an ever decreasing effect from the car. You can really see the difference the roof makes when its up, it really cuts down a lot of noise. On a hard top car this would be even more noticeable.




Finally, for convertibles, the difference between roof up and roof down looks like this last graph. On my Pioneer I have my normal equalizer setting that I like while I am driving set to my tastes (roof up). I have a second custom setting I switch to (roof down) that has increased levels compared to my normal settings, roughly in the shape of this graph. Overall it does seem to sound better.