Testing for Time Alignment, time offset, or time delay

**donaldpatten** · January 9th, 2012, 02:27 PM

Comments please

Has anyone tried to measure or verify the offset time on a high frequency horn and a woofer either with a passive or active crossover? To adjust the delay on A7 style speakers, simply slide the horn fore/aft in the cabinet. On 604s it must be done electronically.

To try measuring the timing you need a microphone, mic preamp, and an O’scope

The test signal is FREE and here on the web .

www.donpatten.com

The test signal is after the two schematics and can be played on your PC. Just click on the playback small triangle, in the short box, to start playing the tone. Connect the PC headphones output jack to the amplifier input.
Connect the mic to the preamp and the preamp to the scope input.
Connect the External SYNC / Trigger connection or the second channel input to the amplifier.
Play the test signal with only the woofer connected, and stabilize the scope trace.
Now turn the horn on and off checking for side-to-side jumps in the trace.
Now adjust the horn position or XO time delay to eliminate the side-to-side jumps.

When the trace is stable, check the large pulse, with the horn on; it should get taller and narrower when the timing is correct.

If you have tried this, or any other technique please comment , and share your knowledge.

Don

**Panomaniac** · January 9th, 2012, 03:12 PM

Thanks Don, it looks like a good technique and I have done similar with my own signals and o'scope.
Now that my measurements are computer based, I simply use a free program called HOLMImpulse to do this. It allows you to lock time between measurements and use one as your reference point. Very handy for alignment. It reads phase and (impulse) delay. This was a huge help for me in designing my crossovers.

I don't think it works on MAC OS, tho.

**Alien_Shore** · October 21st, 2012, 10:13 AM

Originally Posted by Panomaniac

Thanks Don, it looks like a good technique and I have done similar with my own signals and o'scope.
Now that my measurements are computer based, I simply use a free program called HOLMImpulse to do this. It allows you to lock time between measurements and use one as your reference point. Very handy for alignment. It reads phase and (impulse) delay. This was a huge help for me in designing my crossovers.

I've looked at the relevant pages in the guide over at DIYAudio, but need some help.
Can someone point me to a guide that tells how to do this in a bit more detail?

**mah** · October 21st, 2012, 09:36 PM

http://www.google.com.au/url?sa=t&rc...szzg_ExbfvObRQ

**Panomaniac** · October 21st, 2012, 10:53 PM

Here is some more detail on how I do it.
And Now For Something REALLY BIG - Page 41 - diyAudio

The idea is that you need to figure out what the actual acoustic curve is, then determine what the phase or impulse would be for that filter. Get as close to it as you can.

**donaldpatten** · October 22nd, 2012, 02:20 AM

Mike
I think that your scope (software) is dual ch', Connect one ch'l to the power amp out and trigger the display on that signal.
Connect the other scope ch'l to the mike pre amp output. Try to synch the pulse to the low freq channel.
Switch the horn off,on,off.'if we can get that working we are close.
Don

**Alien_Shore** · October 22nd, 2012, 11:42 AM

Originally Posted by mah

HolmImpulse User Guide

Thanks mah! Very helpful link.

Originally Posted by Panomaniac

Here is some more detail on how I do it.
And Now For Something REALLY BIG - Page 41 - diyAudio

The idea is that you need to figure out what the actual acoustic curve is, then determine what the phase or impulse would be for that filter. Get as close to it as you can.

OK Pano, thank you for that. I need to register at DIYAudio to be able to see the attachments. I will continue to plug away on this. Still have a lot more reading and experimenting to do.

Originally Posted by donaldpatten

Mike
I think that your scope (software) is dual ch', Connect one ch'l to the power amp out and trigger the display on that signal.
Connect the other scope ch'l to the mike pre amp output. Try to synch the pulse to the low freq channel.
Switch the horn off,on,off.'if we can get that working we are close.
Don

Don, I think that the DATS scope module will allow me to trigger off of the Left or Right channel only (of the same audio device that is selected). I'll take another look tonight to see if I can make it do what you're suggesting. If not, are there any other software scope programs that you have used?

Edit: This one actually looks really good for <$300: PicoScope 2004