Home theater x-overs, bookshelf vs. floorstander

[Xsound]

Still on the great speaker search, just playing around with the set-up on my elite vsx-54, and dreaming about completing my system, when a question occurs to me.

If I am going to set the cross-over in my receiver to the "thx recommended" 80 hz, why should I consider large floorstanding speakers as opposed to bookshelf style? I can select large for my front speaker and still send a full range of frequencies to my L/C/R, but do I really want drivers from my sub and fronts reproducing the same frequencies? It wold seem to me that the drivers would have some differences in the tone or voicing that may not match.

 

[bpape]

Lots of questions.

First of all, even with an 80Hz xover point, depending on the slope, you'll still want something that will do 40-50Hz pretty decently. Most xovers are only 12db per octave so at say 90db for the main signal, at 40Hz, it will still be trying to do 78db.

Second, yes there can be issues with running the fronts full range and duping that into the sub(s). Generally, when you run the fronts full range, only the LFE channel goes to the subs. Also though, your sub is much more flexible in location than the mains. Getting good smooth bass in a room takes some effort - part of which is properly placing the sub. If you get 60-80Hz up off the mains and into the sub you get:

Less strain on the main amp and speakers allowing more 'breathing room'

Better control of bass/room interactions.

Less chance of cancellations between frequencies from the mains and the sub.

It can be done either way - these are just some points to ponder. Personally, I have a bit more freedom in speaker/seating placement than many so I run my xover at 60Hz for HT and 50Hz for music.

 

[annunaki]

80hz is a general guideline. I would not use 80hz as an x-over point in my system unless: 1) a 24 db/oct. slope were used; 2) my speakers were not capable of playing below 80hz +/-3db. My preference is usually around 60hz at 18-24 db/oct. This helps the sub disappear from its location and blend seamlessly with the soundstage. This is why a better speaker is necessary (better = capable of playing lower). If the speaker is doing 100db (pink noise) and crossed over at 24 db/oct., it would do 76 db at 30hz. However, if it were a ported enclosure tuned to say 50hz it will naturally have a 24 db/oct. rolloff below the tuning frequency. So at 30hz we would see an attenuation of about -42 db or output of 58 db. We can see that a capable speaker (in the low frequency range) has its benefits.

Hopefully this helps you some.