Quick question for John K.....

[Caferacer]

Hi. I just read all of your tech pages on you website. Thank you very much. GREAT info! I learned a lot, especially about dipole operation. I have one question. After reading your "Integration of front, and front and rear tweeters to a dipole midrange" article I didn't quite get whether or not the rear firing tweeter should be wired out of phase to the front or if it acted like a dipole either way with the appropriate sized baffle. Thanks again for your insight and great website!

[john k...]

I appreciate you comments.

Assuming that the front and rear tweeters have identical response and the baffle/mounting system has front to rear symmetry then wiring out of phase will assure a null at 90 degrees. However, from a total radiated power perspective the front and rear tweeter are typically separated far enough (unless special design considerations are made) that they otherwise behave as uncorrelated sources and the phase doesn't matter. You may sense some difference when listening but this is probably due to differences in the polar response and effected by interaction with reflective surfaces near by. There is typically little effect on axis by the addition of a rear tweeter.

For ture dipole tweeter action below the dipole peak the separation myst be very small. With a separation of 1" the dipole peak would be at about 7k Hz.

[Caferacer]

"For pure dipole tweeter action below the dipole peak the separation myst be very small. With a separation of 1" the dipole peak would be at about 7k Hz."

So in a practical application, it doesn't really matter. I do take it that the rear tweeter has benefits with a dipole mid regardless right?
Are your NaO tweeters wired in phase then?
Thanks again, time to build my first open back speaker!

[john k...]

The NaO II tweeters are wired out of phase. While this does give the best null at 90 degrees the overriding design consideration in the phase of the rear tweeter was what would yiled the smoothest response when the speaker was measured form the rear. On axis of the rear side if you will. However, switching rear tweeter phase has only a minor audible effect under normal listening. In the final analysis I would set rear tweeter phase to whatever sound best under normal listing. The more significant difference is with or without a rear tweeter.

[Caferacer]

"While this does give the best null at 90 degrees the overriding design consideration in the phase of the rear tweeter was what would yiled the smoothest response when the speaker was measured form the rear. On axis of the rear side if you will."

Of course, you try to match the rear tweeter output with the midrange backwave output. Makes sense. Thanks again!