For a basic explanation of delay, well: soundwaves travel at a certain speed, your system is all horn loaded so the sound takes a certain amount of time to travel down the horn and out to the listener's ears, your horns are different lengths so the times involved are different, you use delay on the shorter horns so that their soundwaves line up with the longer horns. You on the bus? :)

Thanks

I have been tinkering about with a couple of mine lately, two racks on two stacks is a very nice way to do direct comparisons, even the shortes or smallest change in delay times can be noticed.

Suck it and see would be my best answer, this is how I worked it out. (took three bloody days though)

Its not too difficult to measure for correct delay alignment with an spl meter and some test tones if you've got a big room to do it in, and want to get scientific :)

thanks

Now invert the phase of one cab EG the HD15. - this means reverse its polarity (Yes these terms have meanings outside of Star Trek episodes!). There may be a button marked Phase, Polarity or Φ on the crossover or you may have to swap the red and black wires on the amplifier. Now play the test tone again thru both cabs at the same time, it may have got quieter or louder, don't worry.

Now you adjust the delay. Starting at zero mS, advance the delay on the HD15. The SPL reading should decrease and decrease to a point and then start to increase again as you add more delay. What you want is the delay value at the point of minimum SPL. This means that at that delay value the waves from the "in-phase" W bin and "out-of-phase" HD15 are cancelling each other as perfectly as possible. You should be able to hear this as well as the difference should be about 10dB SPL.

Now put the connections/phase setting on the HD15's back to normal (button out/red to red and black to black.) Now the waves from each bin will be nearly perfectly in phase at the crossover frequency and reinforce instead of cancelling. This is what you are trying to achieve.

(you can also do this without the phase reversal steps, but then you are looking for a peak in SPL which is harder to hear though still readable with the meter.)

Now repeat for the other frequency bands using appropriate test tones.

As you get up to the tweeter bands things become more difficult as the difference between the "right" and "wrong" delay value gets exceedingly small and SPL measurements are affected by reflections from the room boundaries. But this does not mean you should delay your tweets differently for indoor and outdoor gigs even if your meter says so! Try moving it 5cm left and watch the reading change 6dB...aargh....

You can also measure the length of your horns and use that to get approximate delay values, not taking into account group delay (look it up). IE if your W bins have around 1m horn and the HDs have about a 50cm horn, you'll want to delay the HD's by about (50cm/100cm)/344ms-1 = 0.00145 seconds = 1.45 mS. 

SO thats (short horn/m÷long horn/m)÷speed of sound (344m/s)x1000=delay in mS.

For a ported design like your W's though group delay is quite important so you want to take it into account, and try and use the measurement method.

Ding ding, tickets please....

thanks greatly