rew 5.1 help

Status
This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.
You can use the impulse response plot to see gross time misalignment of the tweeter (usually leading phase) to correct for large misalignment issues. This impulse plot will show the duration of the time smear between the midrange and tweeter.

Once you get the time alignment well within 180 degrees of phase of the center frequency, then you can use the "SPL + phase" plot to do the fine tuning of phase alignment and match the phase slopes in the crossover passband.

Just do an upsweep starting at least an octave below the crossover center frequency and finish at least an octave above the center frequency.
 
Last edited:
hello,
thank you for your help.
below is the impulse responses of the tweeter and the midrange (each driver measured separately using sweep 20-20k).
the time delay i must apply to the tweeter is the difference between the two peaks in ms? (295us)
those graph delay is at what frequency? i must find the delay at cross frequency am i right?
thank you
 

Attachments

  • mid imp.jpg
    mid imp.jpg
    73 KB · Views: 77
  • tweeter imp.jpg
    tweeter imp.jpg
    72.7 KB · Views: 78
I'd use about 60-75 us, then play both together in a sweep to verify the combined impulse response.

This time delay is equivalent to about 1 inch (2.54 cm) physical delay - does this sound correct? You're trying to get within 1/4 wavelength or less time offset at the center crossover frequency, then the time alignment will just fall into place.

Getting the above to within 180 degrees of time alignment will allow you to fine tune by ear using sine waves at the center crossover frequency, by either:

1) playing a sine wave at the center crossover frequency, then varying the time delay and listening carefully for a pure sine wave sound, or

2) inverting the phase on one driver, then playing a sine wave at the center crossover frequency, and varying the delay to get maximum attenuation.

Both of these techniques assume that you have a digital crossover that allows you to dial in the time delay. They are both good to within a few 10s of microseconds at midrange-tweeter frequencies of being exactly aligned.

If you are dealing with non-adjustable discrete crossover components (a discrete all-pass, for instance), you might be able to release the tweeter within the baffle, place it on top of the cabinet, and move it back and forth to achieve the same effect: the alignment should coalesce at the time-aligned position--within 1/10 wavelength.

Chris
 
Last edited:
hi
yes this distance about 2.5cm sounds correct, but how do you calculate this time 60-75us? I thought that the two peaks must be at the same time (they are at 295us difference)
How the combined impulse response must like after the alignment?
 
Last edited:
Look only at the initial rise (or dip--as the polarity case might be).

The combined response should have a steep and regular rise (or dip), followed by lower level rebound response that has characteristics of both drivers' non-perfect impulse response.
 
Status
This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.