The "speed" of ("deeper") bass frequencies in car interiors

[AJM1981]

A few months ago I listened to an interesting conversation about an audio engineer in which the topic of car audio came across. He told that systems that he designed sounded really well and that everything is fine as long as there is no subwoofer, and when that came into play it was a challenge to get them lined up.

I kind of sense what he could mean; as it always seems that bass of the woofer / subwoofer in car systems comes a minor fraction later and seems to 'float' a little apart from the mids and trebles. Perhaps the amount of noise that is generated by the engine and / or wheels on the road overlapping parts of the bass and mids while driving generates the illusions of difference.

Since car interiors are not (really) versatile in options to arrange the loudspeakers and needs workarounds; I wonder if there can be some solution in DSP in order to break the frequencies apart and shift the recording of mids and treble a bit in time to audibly match the problematic bass frequencies.

 

[Looneybomber]

I’ve never had an issue with bass in a car. 80hz has a wavelength ~14ft! Midbass cancellation, however, that’s tricky to combat.

 

[staticV3]

I wonder if an implementation similar to DBA/Dirac ART/Trinnov WaveForming would be feasible in a car.

Meaning you'd employ twice the amount of woofers, half of them to produce the wave front, the other half to absorb it, to greatly reduce the bass lingering as standing waves.

 

[Keith_W]

DSP in cars has been a thing for many years. Back when it was possible to install your own sound system, I had a fairly rudimentary DSP system in my car. All it allowed me to do was make a crossover and put in a few PEQ's. There was rudimentary time alignment. The DSP did not come with any software or any capability to program it, instead you needed to know your settings and put them in via the rotary knob. It was extremely painful.

I can imagine that engineer's pain trying to time align a subwoofer in a car. It is already painful to time align subwoofers in rooms. I never attempted to measure the time delay between sub and my mains. Instead, I estimated the delay by calculating the delay using a tape measure for the distance and the speed of sound. For a professional that kind of time alignment probably won't fly.

However, cars do have one advantage - because the volume of the interior or so small, and the longest dimension is short compared to a listening room, most of the lower frequency band is in the pressure zone. So bass behaves in pressure mode rather than forming standing waves. This also greatly increases the efficiency of car subwoofers. The standing waves that do occur are much higher in the FR. The Schroder frequency is much higher, both because the volume of the interior is so small, and the T30 is quite low.

 

[DVDdoug]

I don't know what causes the perception but it's not really "speed" or delay. You can't hear a distinct echo with a delay of less than 40 or 50 milliseconds. At the speed of sound that's 40 or 50 feet. And with low frequencies, I think you need a longer delay before you hear it.