Crossovers

[gadget]

I was wondering if someone could explain to me crossovers since I am just starting to get interested in Home Theatre and getting familar with the terms.

[P-Dub]

Welcome gadget.

Crossovers in the hometheater sense is typically defined as to what frequency the receiver will direct the lower bass region signals to the powered subwoofer.

The basic frequency range that a human can hear is between 20 Hz to 20,000 Hz. To replicate that sound range, in the hometheater sense, you will ideally have 5 speakers and a subwoofer. Now the 5 speakers will all have some kind of frequency response per their specifications. You'll typically see something like 50Hz - 20KHz +/-3dB. All this means is that this particular speaker can reproduce a signals from 50Hz to 20,000 Hz and it should only vary in sound levels by 3 dB. (dB is the measurement used to describe how load something sounds)

Now just by looking at the specs, you should be asking, what about the 20Hz to 50Hz? Well that's where the subwoofer comes in. This unit will produce these lower frequecies. In the Dolby Digital 5.1 specification, the .1 track, or the LFE track, is a seperate signal that is used to feed the subwoofer. It's a .1 because the signal only goes from 20Hz to 120Hz, so it's not a full range signal.

So this is where the crossovers come into play. Since the signal being sent to your speakers is capable of a full 20 Hz to 20 KHz frequecy range, and since most speakers cannot reproduce the lower frequencies, you need a receiver that will send the lower frequency range from your main speakers to your sub. Receiver manufacturers have different crossover settings, you can check out this thread that lists several popular brands and their crossover points. So let's take for example a 80Hz crossover point. This just means that when any signal below 80Hz is sent to the main, center, or surround speakers, it will be redirected to the subwoofer.

Did that make any sense at all?




Paul

There are three kinds of people in this world; those that can count, and those that can't.

[John Holmes]

Welcome to the Guide Gadget!

Paul gave a good explanation of x-overs. Hope it helps out.




"I came here, to chew bubble gum and kickass. And I'm all out of bubble gum!!!" My DVD's

[Andrew Pratt]

I did a really quick and dirty plot in excel to give you some idea of what happens at the cross over point that paul did such a good job explaining.



As you can see from the plot above the red line represents the signal from the main speakers and the green is the sub. So with this plot the cross over point seems to be at 80 Hz meaning that below this point all the signal will be reproduced by the subwoofer and above it the main speakers will play it.

Now where it gets confusing is that on a 5.1 sound track you have 5 main channels for the fronts, centre and sides as well as the .1 track which is the bass channel or LFE (Low Frequency Effect). Now the LFE channel can contain bass from 0 to 120 Hz and will always be sent to the sub. As well the other 5 channels can also contain bass from 0 to 20 KHz so for those channels anything below the cross over point will be sent to the sub as well just like the image above providing you set them up as small speakers in the setup of your receiver. If you have large front speakers you could set the as large in which case the bass below the cross over point would not get rerouted to the LFE channel but remain in the large speakers. In reality though there are very few speakers capable of playing low bass thats found in todays movie soundtracks so more often then not you're best to set them as small.

Now if you don't own a subwoofer you have no choice but to call all your speakers large even though they may or may not be able to play the low bass so you will likely miss out on the low bass depending on how low your speakers can play down to.

PS Welcome to the forum :W

[gadget]

Thank you for the explanation and the graph. Both were really helpful. Now it makes sense.

Thanks!!