Originally Posted by OllieS
The crossovers inside speakers are used to direct the appropriate frequencies to the drivers in the speakers.
Read it again.
If you have a 2 way speaker, the crossover blends between the woofer and the tweeter so the tweeter isn't dying from trying to play bass and the woofer isn't resonating and beaming from trying to play high treble.
Crossover to a tweeter is typically around 2000 Hz. 2000 Hz. two thousand hertz.
If the speaker is three way, it might have a crossover from woofer to midwoofer in the 500 Hz range.
There is no crossover inside any typical speaker that is intended to blend between the drivers in the speaker and some other drivers elsewhere. So there's not a crossover sitting there so you can connect a supertweeter and reproduce sound up to 40,000 Hz even though you could not hear it.
There's also not a crossover in a normal speaker that would blend between the speaker's biggest woofer and a sub.
When you apply a crossover in a receiver, the crossover is intended to blend between the main speakers, as a whole, however many woofers it has plus its tweeter, and the sub. From speaker to sub. Typically, folks suggest keeping that crossover to 80 Hz but many receivers allow settings up to 200 Hz.
Okay, let's say you set the receiver's crossover at 200 Hz. That means the receiver starts turning down (rolling off) the signal going to the speaker somewhere above 200 Hz and the input to (and output from) that speaker (the main speaker not the sub) is decreased by either 3 or 6 dB at 200 Hz. It's doing the same basic thing to the signal from the sub, turning it down from some frequency below 200 Hz so that it is at -3 or -6 dB at the 200 Hz crossover point. Ten the sub and main speaker add up the way the crossover topology is intended to work. They add correctly according to the topology not only at the 200 Hz crossover point but also below (as the sub gets louder and the speaker gets quieter) and above (as the spekaker gets louder and the sub gets quieter).
Sooooo, if your lowest crossover in the speaker is 500 Hz, and the receiver's crossover keeps out (essentially) 200 Hz and BELOW from going to the speaker, do you see how not having any 200 Hz material to roll off is irrelevant to the crossover that's already down 3 or 6 dB more than an octave higher at 500 Hz?
Can you see how a rolloff for a 200 Hz crossover is not relevant to what a crossover centered at 2000 Hz is doing? That's over three octaves above the sub's crossover. So the sub's output is rolled off (assuming typical 24 dB per octave slope) by well over 70 dB at frthe tweeter crossover's center frequency. that's less than one ten-millionth of the power present in the signal getting into the subwoofer at 2000 Hz. Depending on the topology inside the speaker, the tweeter may be electrically reduced by anywhere from 30 dB 1/1000 of power present in the signal) to over 72 dB (less than one ten-millionth of the power present in the signal) They aren't cascading because their significant effects are in different places. LIke vacuuming the bedroom doesn't change what you have to do to vacuum the living room.
Now one reason you don't want to have speaker-frequency crossovers inside receivers (although there are real potential benefits from active biamping) is because the speaker already has a crossover. If I have a receiver crossover set for 2000 Hz and the speaker's crossover is 2000 Hz, I've potentially doubled the effective slope of the crossover. Instead of being reduced by 3 or six dB at the crossover point, both the tweeter and the woofer may down by 6 or 12 dB. That means that at the crossover point (where hearing is pretty darn sensitive) there's going to be too little sound, and things will sound dull and unexciting.
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