This may be a little (ok very) long winded, but maybe it can help with some of our more recent discussions:
Speaker, Crossover and HT Setup Basics:
As we all know, speakers exist to reproduce an audio signal, for AVR and musical purposes, this signal can cover a frequency range of 20Hz to 20,000Hz (20KHz) in the main channels and 120Hz to 3Hz in the LFE channel, but most speakers will not be able to cleanly reproduce all of this range, most of the time they are simply not designed to do so.
This is where crossovers (and filters) come into play.
Crossover (and filter) basics:
Crossovers (and filters) are simply a way to attenuate an audio signal so that only a certain range of that signal is then distributed to the speaker (or individual driver of a speaker, when referring to a speakers internal crossovers).
While crossovers and filters perform the same basic function, their rate of attenuation makes them different.
We've all heard the saying "Crossovers aren't brick walls", filters basically are.
Crossovers will have different rates of attenuation, this is known as a slope or curve because of how it looks in a visual representation, and this will quite often be referred to as the "roll off". Depending on the type of crossover, these slopes/curves will either be fixed or adjustable.
So..., let's say someone mentions a crossover having a 6db per octave roll off... What does that mean?
What they are saying is, that from the crossover frequency point, the signal will attenuate down (lessen in volume/power) 6db for every octave below the set point.
An 80Hz Crossover with a 6db per octave roll off is saying that at 80Hz you will still be hearing all of the signal, at 40Hz (one octave below 80Hz) that frequency will sound 6db quieter, it will still be playing, just 6db quieter, at 20Hz (another octave down) it will be another 6db quieter, 10Hz another 6db and so on. This is why the degree of roll off matters when fine tuning a speaker.
Filters simply have an extremely sharp/steep roll off. (More of a brick wall)
For the most part you'll only run across LPF (LowPassFilter) for the LFE channel or Sub itself, this basically means Low CAN pass, meaning you will only hear the signal from the set point down.
You may also encounter a High Pass Filter on some Subs, the translation is the same high CAN pass, and is only on Subs with built in crossovers so that you can use the Sub itself to cross your full range signal instead of your AVR. (Usually only found on older Subs)
Crossovers and Speakers:
Most speakers will have some type of crossover built in, either passive (made up of resistors and capacitors) or electronic (DSP), because most speakers are comprised of at least 2 different types/sizes of drivers, and each of these individual drivers play certain frequencies optimally, then figuring in driver, crossover and cabinet design, each complete speaker will play in a certain frequency range, and will often have what is known as natural roll off, where a speaker does its own low frequency attenuation without the help of an external crossover. (This is most often to protect the speaker from damage caused by trying to get it to play a frequency it just can't)
Crossovers and your AVR/Processor:
The crossover in your AVR is an adjustable electronic crossover, it not only attenuates the signal, it can mix/direct the attenuated portion of the signal into a different channel (LFE), where you should have speakers(Sub) more capable of reproducing those frequencies accurately.
In most cases you'll find two types of crossover options in an AVR, a Global crossover, meaning that there is only one crossover setting for ALL the non-LFE channels, and individual crossovers, allowing you to set separate crossovers for each individual channel/position.
Speaker, AVR & HT setup:
One thing to realise is that all of this falls in the category of Bass Management, which is no more than a shortened way of saying, what speakers do I want to play the bass.
And because of the nature of Bass sound waves, Bass Management is not only speaker dependant, but extremely room dependant, which in turn makes it very individual for each different space/room. This is why room correcting can be a good thing, it measures the speakers actual response in the room, it doesn't just guess according to a speakers spec.
In the AVR, setting a speaker to Large, simply means that it is sent the entire Full Range signal without a crossover applied, setting a speaker too small, means the selected crossover will be applied to that speaker and the portion of the signal that has been attenuated out will be mixed into the LFE output.
First an understanding of why we use Bass Management and how it came about.
Surround Sound came about as an extension of stereo sound, which as some will remember, was supposed to mean two big full range towers for L/R in your room somewhere. In the earliest incarnation of Surround Sound, this still worked just fine, there was no LFE channel and the Surround and Center channels were nothing more than matrixed portions of the Full Range stereo signal being sent to the L/R.
But then came discrete channels capable of the full 20Hz to 20KHz signal and the separate LFE channel, capable of a 120-3Hz signal, but it still wasn't that bad because mixers hadn't yet started to place dynamic full range sounds into the Center and Surrounds, but once they did, the realization came about that the only way to truly recreate the theatre experience was to have Full Range speakers in all the positions, and most people were unable or unwilling to do this.
This is where Dr. Floyd Toole and the Harmon Group came into play. They started researching people's reaction to sound using study groups and trained listeners, within this research they realised that some of the people started to be unable to localize a sound (determine its exact origin in the room) once it started to dip below 120Hz, and almost everyone lost this localization by 80Hz. Therefore it was determined that a good compromise to using Full Range speakers was to Bass Manage those signals and mix the lower frequency portion of a sound into the LFE channel output where it could be properly reproduced by a purpose built Subwoofer, with minimal or no loss to the experience, since most people couldn't determine where that portion of the sound was coming from anyway, In turn opening up a better experience and more options for speakers, for the general public and enthusiast.
Ok, back to setup... Because Bass Management is so speaker and room dependant the general rule of thumb is set the crossovers to 80Hz (where most people can't tell the difference) and you're done. But this is not an actual rule, and is normally recommended because it's simple and applies to most systems. (The only time you shouldn't do this is if your speakers won't actually play clean down to 80Hz, then it should be set to they're capability)
But there is absolutely no reason you can't determine the actual response characteristics of your individual speakers, in your room, (either by ear or measurement) and simply set the crossover(s) accordingly. Which includes setting them to Large and playing the Full Range signal.
Finally, speaking of Large and playing a speaker Full Range, there are two basic scenarios where this would be appropriate and completely acceptable if "you" choose to do so.
1. The speaker in that position can truly reproduce the entire 20Hz to 20KHz range
2. The speaker in that position has a clean enough natural roll off at the bottom, that you don't really mind completely losing that portion of the sound.
(Example: even in today's best recordings, you still only get minimal examples of sound below 30Hz in any of the channels besides LFE, so if your speakers play clean down around 35-40Hz, and they have a smooth natural roll off below that, there's no reason you can't set them as Large if you think it sounds better.)
That's basically it, sorry this was so long, hope it helps to explain some of the recent dialogue and recommendations, and gives those who need it a better understanding of what, when, and why.
And as always, it still boils down to how much time and effort "you".want to put into your setup, and what sounds and works best for "you", in "your" space.
Last edited by ALtlOff; Today at 02:35 AM.