Quote Originally Posted by jhnkvn View Post
If you aren't always there to watch your car, do set a filter. Depending on your amplifier's slope (it's usually a 12dB/octave slope), set it at 60hz or 50hz with 60hz being preferred on a 12dB/octave slope.

Any speaker can handle rolling down to 30hz or something probably. The problem lies with its sound output. If it's playing 30hz but you can't hear it, why bother playing that low -- you'll only stress your speakers. Same goes with whatever frequency it is. What you can't hear is of no use to you. Also, for those doing a low filter on the midbass, it's usually paired with EQ work. Because if you just pass your midbass at 50hz, sure.. you can hear it all the way down to 50hz (since it's still -0dB at that stage), but you won't appreciate the 50hz since your hearing is less efficient at bass levels. That's the reason why people throw like +3dB of EQ and why there's no such thing as a nightclub playing 90 decibels of EDM.
the point in question here is that the speaker can handle 43 Hz, why the heck will you set cut-off frequency to 60Hz?

Regarding the two points,
1. That's not always the case. Amplifier gain is matched to the pre-out voltage of the stock head unit to achieve the "optimal" volume before amplifier clipping. This is the reason why both LnC and SQ peeps love head units with high pre-out voltages like Eclipse CD7200MKs with 8V - it allows them to set their amplifier gains lower for lower system noise.

2. #2 is where the opinion gets terribly wrong.

Optimizing the volume of a system takes consideration of the concept of clipping. Clipping is a state where the hardware is being pushed and it begins sending out erratic signals. If you're without an oscilloscope (as with most of us are), you use your ears to detect distortion. Soft clipping sends out barely-audible distortion but if you hit hard clipping.. man, you'll get horrible distortion and you should be able to detect it easily. Head unit clipping is tolerable but you wouldn't like amplifier clipping since it puts your speakers at risk. It's the #1 reason for damaged speakers after all.

Head units have a clipping volume. And since there's a ton of head units around, nobody really knows what volume does it start. My Hyundai Sonata's stock head unit starts around 28-31 out of 35. A good rule of thumb is 3/4 of the total volume and that's the reason why most installers use this "rule of thumb" to set amplifier gains -- it's just too much time to even bother testing the head unit with an oscilloscope. However, some head units do not reach clipping even if you max it out - a prime example of this is the Alpine CDA 9887.

Amplifier clipping, on the otherhand, is tricky. But the basis of clipping is that it occurs if you push the amplifier to provide "more" than its rated with. So that 75W of power you're throwing at your MMs? It'll probably jump to 150W on a square wave. While this is okay on brief transients, your midbass wouldn't like it if you keep at it since its voice coil can't cool down fast enough. It's usually the tweeter that "blows" once you hit clipping mostly because of power AND additional harmonics in the music signal, but since denber has a passive crossover that does the filtering (like a cap), his tweeter should be able to take the transient clipping.

Most of us won't mind brief clipping on transients (ex. peaks in the music) but you wouldn't really want clipping all-the-time -- it's where it gets dangerous. So tune and set gains properly ;) it's NOT a volume knob.
as i already posted on the previous page, the user manual of p300.2 tells the proper way of setting HU volume and amp GAIN which will give safe result.