Design Direction for new Home theater setup

[JerMu]

Every doubling of amplitude is +3db, to achieve 3db more output you need to double the power or cone area used.
Using the sub/s as an example, say one sub can produce 109db with 500 watts, adding a second increases your potential maximum output by 6db to 115db. 4 times the amplitude of a single sub, +3db for doubling the cone area, +3db for twice the power. For a single sub in this example to produce 115db it would take 2000 watts.

A sub capable of 210db would knock down your house, and the rest of the street

My room is 12' x 11' x8', a single 12" sub with 400w and single 7" woofers in the main speakers with 100w behind them is plenty loud enough.

So should I set up a target db, lets say 115db for example, and then knock 6db's off for every instance of that speaker that will be used more than once. i.e. the tower speakers should add up to be 109db each, so that when they are played together in stereo they add up to be the 115db? If so, how do I properly factor in the center and the surrounds without getting out of whack at certian points? Would the center speaker need to produce the 115 alone and the surrounds add up to the 115 like the tower speakers? Also if I go with 5 identicals would I still treat them like tower, center, surrounds as in the example above or should I knock 30 db's off the 115db so that when the entire system is playing it would add up to the 115db? That would then leave my stereo play lacking.

I've been looking over the websites you linked before, some very nice diy projects there. Do you have any favs?

Are you familar with Ascendant Audio, if so what do you think about their products? What would you recommend for tweeter, mid, woofer? I've read that the vifa xt25 is a little complicated when it comes to tweaking it properly, but when set up right is a very nice tweeter. Is that true?

[FullThrottleRic]

Originally posted by JerMu


So should I set up a target db, lets say 115db for example, and then knock 6db's off for every instance of that speaker that will be used more than once. i.e. the tower speakers should add up to be 109db each, so that when they are played together in stereo they add up to be the 115db? If so, how do I properly factor in the center and the surrounds without getting out of whack at certian points? Would the center speaker need to produce the 115 alone and the surrounds add up to the 115 like the tower speakers? Also if I go with 5 identicals would I still treat them like tower, center, surrounds as in the example above or should I knock 30 db's off the 115db so that when the entire system is playing it would add up to the 115db? That would then leave my stereo play lacking.

I've been looking over the websites you linked before, some very nice diy projects there. Do you have any favs?

Are you familar with Ascendant Audio, if so what do you think about their products? What would you recommend for tweeter, mid, woofer? I've read that the vifa xt25 is a little complicated when it comes to tweaking it properly, but when set up right is a very nice tweeter. Is that true?

You treat each channel separately, to play at reference level each main channel (front left, front right, centre, surround left and surround right) needs to be able to produce 105db at the listening position. The sub has more dynamic range than the main speakers, and needs to be able to produce 115db at the listening position.

Reference level (0db) is very loud, you will rarely use your system at that volume though, a much more realistic target is -10db or -15db. If you use two subs instead of one, each sub can have much lower output than a single sub would be required to have to meet the target level. For example, say a single sub had a 1000w amplifier and a single 15" woofer - by itself it produced 115db over it's full range. If you added a second identical sub both would only need 250w amplifiers to reach the same level as a single sub with 1000w all else being equal. (+3db for twice the cone area means only half the amplifier power is required, hence 2x 250w = 500w).
After modeling the Assasin 12" in WinISD, a single woofer can only produce 111db in a sealed box before it runs out of excursion at 10Hz. So to play at reference level at 1m with some headroom you would need 2, in a 0.7 Qtc box though the system wouldn't go very low. In my experience you are better off aiming for a Q of 0.5 to better match room gain, this would mean around a 6.5cu ft box for each Assasin 12. With the reduced damping of the larger box you would need 3 of them to stop them running out of excursion, each with their own 6.5cu ft box
Have a look at the TC Sounds drivers for subwoofers, two TC-2000 12"s should be plenty for you. Half the box size of the Assasin's, almost 119db output defore running out of excursion with 600 watts total.

For the main speakers a single Ascendant Audio Poly 6.5" per channel would be fine assuming you have an 80Hz high pass filter on it. In a small seled box it gives you around an 80Hz 2nd order rolloff which would match THX spec perfectly. I havn't used these drivers so I no idea of their quality, they are very cheap though so I'd take the quoted Xmax with a pinch of salt and assume that's a maxmum figure, not linear.

Troels and Zaph's designs are highly thought of, pick one that suits your budget and parts availability. I'm in the process of building Troel's Ekta's for fronts, the Scanspeak drivers are very expensive though

I havn't used the XT25 but a lot of people seem to like it, according the Zaph in his tweeter roundup it's pretty much as good as anything so long as you don't cross it too low, so it's better suited to smaller midrange drivers than 6-7" midwoofers.

[JerMu]

How do you properly apply distance to the equation? In WinISD when I put in "x" feet in the signal tab it does not seem to affect anything. How do I know I am getting 105db at the proper distance?

Also is there a good speaker building 101 website/book that is highly recommended? I have learned alot just rumaging through the forumns online, but I would like a guide for just getting my feet wet. something that covers all the basics in a noob friendly manor. Does such a thing exist?

Thanks again for your help thus far.