What tools do you need to make a notch filter? I looked at the sticky in the General Discussion about notch filters. How do you get resonance frequency, max. driver impedance, etc.? Speakers should be measured in open air? This page? http://www.mhsoft.nl/messen_en.asp I don't even know what a driver is. Is that just the speaker itself?
Basically a notch filter is a simple RCL filter. But I really dont think you need one for car audio. You see, notch filters are used to eliminate driver (speaker) resonence on a crossover network. (we are discussing passive crossovers, not active). As a speaker moves, its voice coil produces an electric current. That current can cause mior annomolies in a passive network. In cars, we all use active (electronic) crossovers. In most cases, even in passive networks, notch filters are unnecessary. Tweeters and midrange speakers are the only speakers that might benefit from a notch filter, but most modern, name brand drivers are already mechanically damped. Most manufactures use ferrofluid to mechanically dampen these drivers. Passive dampening is not necessary or needed.
I'm really going to over simplify this explination. When an electric current is sent to the voice coil. The pole piece then moves up or down. The problem is that as the pole piece move it creates an unwanted induced voltage. Ferrofluid is a material that in the pressence of an magnetic feild, absorbs that induced voltage. Or is the other way around, I can never remember. Anyway its like a shock absorber on a car. The car can still travel through its range of motion, but it does not continue to bounce after it hits a bump. Hope that understandable. Almost forgot, its also a coolant, it also acts as a heatsink for the voice coil
Notch filters are also useful in taming peaks in an mobile ausio sytems. They are simple and effective. Ranger is right, its more for resonant peaks usually, but the situation does arise when the use of them is called for when when a particularly nasty peak is hard to tame due to speaker placement or car acoustics. And passive x-over components are cheap compared to an alectronic eq thats worth anything. Also you can dial in on the particlular frequency very accurately.. Just my 2 cents
