Active Speaker

[Mark Hennessy]

Hi Mark
I wonder if you could confirm, with the tweeter connected via a single capacitor and no chokes elsewhere in the speaker circuit, should the tweeter be connected in phase with the bass speaker.
Something in the back of my mind tells me the tweeter should be connected in opposite phase, or is that just in a xover with inductors and capacitors.

Sorry - I missed this question earlier.

The shortest answer is to suck it and see.

The slightly longer answer is that we don't know what the large driver is doing up at high frequencies, so we can't predict anything. Because it's not being rolled off by a filter, it's anyone's guess.

When you make a hi-fi speaker, you roll off the drive units when they are still behaving sensibly - they can sound pretty rough outside of their "comfort zone". Hence, the phase response is mostly determined by the filters you design, so you can predict whether you need to flip the phase of the tweeter or not.

In general, if both filter are the same order, then the tweeter usually stays in phase. If different, you probably invert. There are no hard and fast rules, however. Too many variables

Many of the BBC designs are 2nd-order (inductor and cap) on the woofer, and 3rd-order (cap, inductor, cap) on the tweeter - they require a phase flip. I get good results with this topology.

As part of the testing, it's usual to temporarily flip the phase of the tweeter to see how deep the notch is at the crossover frequency - the deeper the notch, the better the phase tracking is when the tweeter polarity is returned to normal.

My crossover breadboard includes a toggle switch to flip the tweeter polarity. It's a centre-off toggle switch so I can measure the woofer on its own. It has a 4 way speakON socket - I mount another on the rear of the test box, and that makes it easy to swap between boxes, etc.