New Tweeters: In or Out of Phase?

I've replaced tweeters on several occasions and find that in some cases using a series resistor will increase the impedance and shift the crossover point slightly -more noticeably with higher order networks (such as the 3rd & 4th order filters most often used by KEF, or low impedance tweeters(4ohms).

I would recommend using an "L-Pad", which is two resistors (one in series, one in parallel) to maintain the correct tweeter impedance. here is a link to a page where there is a calculator for the correct values.

http://www.lalena.com/audio/calculator/lpad/

Try it both ways and see which you prefer.

FWIW, another consideration is that KEF may have used a Zobel/conjugate network to tame the fundamental impedance peak of the KEF tweeter. Unless the Vifa has the same Fs resonant frequency/impedance peak,there may be a mismatch(Just my 2 cents)

Good luck and good listening.

-chas

My suspicion is that the Vifa tweeter has lower impedence than the KEF T27.Even if they are rated at the same nominal impedence their actual impedence could be quite different.

Impedence affects crossover points so there are other factors to consider other than just sensitivity.

The KEF T27s do sound a bit dull.I have been told this is due to fatigue-so a new tweeter probably should sound a bit brighter.

Thanks for all the replies, here's the latest: The Vifa's do have a very small + - stamped on the inside of the plastic face frame, but I had to remove it to install the tweeters (I tested then with a 9V battery to determine correct polarity). I let them burn in for a week so they don't sound as bright, or is it that I've grown used to it. My girlfriend said she likes the mellow sound of the Shahinian/Theta living room system but she says that the 7:1 KEF hometheater with an 8 foot screen is overload. Please, no suggestions on getting a new girlfriend.
Thanks