View Full Version : Questions for the experts

06-23-2010, 03:33 PM
First of all, Resonance Frequency - how do you calculate it and what role does it play in the construction of your box and/or box tuning.

I guess my real question is, when someone brings in a tahoe or suburban or w/e to a car audio shop to have a couple 18" btls thrown in, theres a lot more to it than just that.
Theoretically, mathematically shouldnt there be only one combination of sub (not brand), box(port length, surface area, tuning) that is going to utilize the potential of the vehicle better than other combinations.

Sorry if this doesn't make sense, it's hard to word what im trying to ask in the 2nd part.

06-23-2010, 03:39 PM
EVERYTHING has a resonant frequency. The reason bass is so loud in vehicles is sub bass frequencies are very close to the vehicle's resonant frequency. Finding the resonant frequency can be done a few ways but you have to remember that changing anything in the vehicle changes the resonant frequency. Adding or removing objects or people. Tightening or loosening something.
It can be done by playing tones and clamping the output and calculating impedence rise. The rise will always be highest at the resonant frequency. It can also be done by just using a term lab and measuring the highest output. You will probably have 2 peaks in a normal sealed or ported box. 3 peaks for a band pass. There should be a peak 3-5 hz above the tuning frequency of your enclosure. There should also be a peak at your resonant frequency. Usually a resonant is higher than you'd want to tune a ported box and get good response on the low end so it is not desirable for a daily setup. It is only desirable for a purpose-built spl system.

What did the last 2 sentences mean? It means you get a larger peak if you make your tuning frequency overlap your resonant frequency. Also smaller sub boxes have a larger peak... not desirable for music but highly desirable for spl. They also handle more power but are less efficient. People usually sort of make up for this with a TON of port.

06-23-2010, 05:54 PM
Also smaller sub boxes have a larger peak.

Not true. Larger boxes have larger peaks(given the same tuning), which is why they're more efficient. The benefit of the smaller box is the added mechanical power handling, which in most cases, more than makes up for the lesser peak in the frequency response.