Hi all,
I'm a little confused on the whole "sub-woofer crossing with low end on speakers". After reading a bit about it it looks like those 2 are not suppose to cross, or cross just a bit. so for example if I get a Sub that goes 20-100 Hz and my speakers do (lets take KEF for argument sake):
Q500 = 41Hz - 40 KHz then 40Hz to 100Hz will overlap and I will need to choose if I want to run it through sub or speakers
or if i take
T301 = 80Hz - 30KHz overlap only goes from 80 to 100 so i set crossing to 90 Hz and still cover a full range
So I guess the question is whats the point of having speakers with low frequencies if your sub will do a better job anyways. Would it mean that bookshelfs or even something like KEF T301 set will sound as good as tower set given a good sub-woofer?
Am I missing somthing here?
The problem with the KEF T301 sounding as good as a more full range speaker is partly explained by sholling's remark about a crossover not being an absolute brick wall, but creates a slope in the frequency response such that frequencies below the crossover point are still going to the upper speaker, but at an increasingly reduced rate. And frequencies above the crossover point are still going to the lower speaker, but at an increasingly reduced rate. See the diagram at:
http://www.bcae1.com/xovrslop.htm
where the different colored lines represent different crossover slopes; not all crossovers reduce the frequencies at the same rate.
Because of this, you want the upper speaker to be able to deal with frequencies below the crossover point, to some extent.
Additionally, as sholling indicated, but did not state overly well, as the frequency goes up in the bass, human ability to locate the frequency by sound alone increases. The THX standard is to set the crossover frequency at 80Hz which will make it difficult or impossible to locate the subwoofer by sound alone (excepting cases where the subwoofer is distorting, which will often produce harmonics of a higher frequency than what is fed to it). Going higher than that increases your chances of localizing the sound, which is not good, because those sounds are supposed to be coming from one of the main speakers, not from the direction of wherever the subwoofer is placed.
If you were to use test tones to try to find out when you could localize the sound and when you could not, you would find that the transition is not sudden from absolutely can't tell to it being perfectly obvious what direction it is coming from; it would go from not being able to tell, to thinking that maybe it is coming from that direction but aren't sure, to being pretty sure, to being reasonably certain.
In practice, how easy it is to locate the direction of the sound is going to depend on other sounds that are occurring at that same time; it would be easier to locate a single tone than to locate that tone combined with a bunch of other tones, so there isn't a simple answer to precisely what frequency you can get away with using, though you should be okay with 80 Hz or lower, and with
most speakers, 80Hz will likely be the best choice.
In fact, it is due to the human inability to locate the direction of a sound of a low frequency by the sound alone that enables the use of subwoofers at all; otherwise, all speakers would need to be full range in order to have the proper directional effect of surround sound.
As to your question about what will sound best with a bookshelf and subwoofer versus a more full range speaker and subwoofer, it is going to depend upon the specifics involved. Let us assume that we are going to compare two systems that cost the same, that use the same subwoofer. If you select tower speakers that are more full range, you will not be buying in the same lineup as a bookshelf speaker that costs the same as that tower speaker. So you might actually get better sound for your money if you go with a bookshelf speaker instead of a tower speaker.
Most people compare such things improperly, as they typically think of one line of speaker and then compare the bookshelf in that line with a tower in that line. But that is comparing a more expensive speaker with a cheaper one, and is not comparing speakers at the same price point.
Now, often, a tower speaker is going to be able to play louder than the bookshelf speaker, but for that same amount of money, you could get a better quality bookshelf speaker, and so it is very questionable which is going to be better in practice. It might turn out that one will play louder without distortion, but that at lower volumes the other one sounds better. Really, though, we would have to look at specific examples to know what will be better, and even then, we will have subjective preferences regarding what is better.
In my case, I use high quality bookshelf speakers for all channels (except subwoofers, of course), and I am very happy with the setup. My bookshelf speakers have a -3dB of 50Hz, and I use an 80Hz crossover for my subwoofers. With my system using identical speakers all around, I get perfect voice matching of my speakers. My system is also capable of playing louder than I ever want to hear it in my room, without noticeable strain on my bookshelf speakers.
But, I am not trying to recreate the volume of the loudest rock concert ever, and so it might be the case that someone who wanted to do that would be dissatisfied (or not; I do not know how loud my system will play). But playing things at such high volumes does permanent damage to one's hearing, so I would advise against it anyway, particularly if you want to be able to enjoy your system when you are old, and do not want to end up needing a hearing aid.
