Question on drivers for a project

Hi all, this is my first post.
I'm new to this forum but have been messing around with speakers since a couple years now.

I have some questions :

- I would like to build a speaker system for a home thearter, that would be also very good to listen music. I have an idea consisting of one or two subs (NHT1259), and all speakers would be an MTM with 2 Vifa P13. My problem is the tweeter, which do you think would be better between the Vifa XT25 and a BG NEO3PDRFP ? I'm open to anything else.
I think the P13 will be ported in a 10L enclosure tuned around 75Hz (thin column baffle). My other concern is the notch created by the distance between the two vifas.... with the dimensions of the drivers, the minimal distance between centers would be 24cm, that would be a notch around 1400Hz right ? i wanted to drive the P13 up to 2.5-3KHz... is there a way i can avoid that thing ?
I would like to Bi-Amp these columns with the little S5electronics tube kit and an active XO (so no passive XO at all). What do you think of that project ?

-Another point :
Right now I have 2 JMLabs Symbol II (mains) and 3 Boston Acoustics CR-8 (center and surrounds), wich are not really sound matched :(
Does anybody have the references of the drivers used in these speakers ?

Well, i think that is it for now..... sorry for all the questions... :)

Thanks in advance
Pierre.
 

CHRIS8

Disabled Account
2001-12-12 8:47 am
VA, USA
"which do you think would be better between the Vifa XT25 and a BG NEO3PDRFP"

This is a tough call.

-The neo3 has better spectral decay characteristics, and better off axis rolloff characteristics, considering interphase(right term?) distortion, due to non linear diahpragm flexure, that is much more significant with the dome tweeter

-The XT25 can be crossed much lower

Considering the 3rd factor, the vifa midwoof. It has rather poor spectral decay, but is 'smooth' sounding up to 4khz, for sure. Using the neo, while providing higher fidelity HF response, will actually degrade your lower midrange slightly by having to operate the vifa that high. Using the xt25, you can cross lower, preserving more upper mid range content. This, at the expense of slightly worse spectral decay of the vifa xt and increased cost of the driver, but you will improve spectral decay in teh lower end of the tweeter/upper range of woofer by crossing lower. But, on the otherhand you can move the crossover out of the sensitive band, and up to 3.5-4khz. This is of course automaticly, you should use the neo3 then IMO. But, what do YOU want? I would actually purchase the neo and the xt, and try both of them....and return the one i did not want. No problem if you don't make a mark on it, PE will take it back.

The driver spacing issue you bring up, their is not one. Spacing is relevant between INTEGRATING drivers mainly, the woofers are integrating with the tweeter in this case. Also, your problem will be vertical error/lobing the higher distance you space the drivers, but this is counteracted partially, by using steeper sloped rolloffs.

-Chris
 

CHRIS8

Disabled Account
2001-12-12 8:47 am
VA, USA
Most subwoofers are not meant to be used above 100hz approx. However, this is simply the norm, not the rule. Since this is an active crossover, it will easy to try 150-250 hz. But you will have a compromise either way you go, if the NHT you specified behaves as most subwoofers the lower mids will sound flat, possibly. This is a subjective judgement on my part, I have not performed testing on this specific phenomen. No situation has yet caused me to have to use a subwoofer significanlty beyond 100hz, but in subejctive evaluation I have judged this to be the case. Why not just cross at around 150hz with a 4th order active crossover? If your vifa p13s(i presume are using the H model, since this is a vented box) tuned to 75 Hz, you will sufficient power handling to do this with a 4th order electrical slope. But, in any event if you have the subwoofer more than a foot or so from the midrange, it will begin to become directional at that relatively high frequency, even 150hz.

-Chris