PA+ Delay Question

The hows and whys of running sound.
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chrisj360
Posts: 112
Joined: Fri Sep 20, 2013 1:37 pm
Location: Bellingham, WA

PA+ Delay Question

#1 Post by chrisj360 » Wed Oct 17, 2018 10:36 pm

I don't have my PA+ in front of me and only going off the manual. Will jump in front of it tomorrow after work. Can't seem to get a definitive answer from the manual if the delay can be set only for the tops (to compensate for the travel path of the horn) or if it delays everything together. The description for delay settings doesn't specifically say it's separate between the highs and lows, but the schematic for the signal path shows separation between high, mids (not used), and lows.

Can anyone share some insight? I was remembering an old conversation that I can't seem to find about delaying the tops to compensate for the distance the bass travels inside the horn path.
2 x 21" T30's with Lab12's
2 x 28" T30's with Lab12's
2 x OTop12 with Deltalite 2512

CoronaOperator
Posts: 1484
Joined: Wed Mar 25, 2009 7:07 pm
Location: Medicine Hat, Alberta, Canada

Re: PA+ Delay Question

#2 Post by CoronaOperator » Wed Oct 17, 2018 11:45 pm

The block diagram shows separate delay for highs/mids/and lows so I'd go off of that. It wouldn't be of much use outside of live sound if it didn't.

Unfortunately that unit (pa+) only has 10ms of delay which equates to about 11 feet of flight for sound. Depending on your setup that might not be enough unless your subs are much closer to the audience than your tops. There is more going on than just the time of flight for the sound to travel through the horn path. The sound of the subwoofer is also delayed electrically due to the inductance of the large(r) voice coil of the driver. Inductors oppose changes in the flow of electricity and since AC is always changing, the current always lags the voltage. The crossover filter you use also effects the phase (time) of the signal for both the tops and subs. All that along with placement of the tops and subs all adds (or subtracts) up to affect the acoustic delay needed to bring the system into alignment. Also, unless your tops and subs share the same physical space, you can only align your system for 1 place in the room, it will be off everywhere else. Some places more than others.

So what does a sound guy do? Doesn't worry about it. Indoors, with reflections off the ceilings and walls and floors all bouncing around, your ears are going to hear multiple arrivals of the bass no matter what you do so don't get too hung up on trying to get the timing just right. Although our ears can noticed 0.5 ms of time difference at 1kz, down low (and up really high) we don't hear small time differences. What is important is that you get the tops and subs phase aligned around the crossover frequency so you don't get a deep cancellation where they overlap and share the workload.

Quick and dirty way to do it: play a sine wave tone at your crossover freq. Probably around 100hz for otops. Play the tops and subs at the same volume. Have someone stand out front and flip the polarity of the subs in the driverack. Whichever way is loudest wins. If you don't hear any difference then flip a coin for which way you want the polarity. Also, If you forgot your tone at home, try it with music.

Better way to do it: do the same as above with the tone but flip the polarity of the subs first. Then use the delay you have (always put the delay on the tops) to try and get the LOWEST volume out front. Once you find that point with your delay, flip the polarity back to where it was (loudest) and you are done.

Sometimes an even better way to do it is with measurement software: This way you can also look to see if the tops and subs line up from about an octave below the crossover freq to an octave above the crossover freq instead of just the 1 tone used in the examples above. Sometimes you can get the phase lined up at the crossover using the above method but below or above that frequency things get haywire and you can get a cancellation. Beware that getting any kind of useful measurement indoors at the lower frequencies is like nailing jello to a tree. You can try but don't automatically believe what the screen tells you because it isn't accurate.
Built:
17" width 10" driver Autotuba
2 x 29" width dual Lab12 Tuba60
6 x DR250 2510/asd1001
In progress:
2 x DR250 2510/asd1001
For best results, point the loud end of the array towards the audience

chrisj360
Posts: 112
Joined: Fri Sep 20, 2013 1:37 pm
Location: Bellingham, WA

Re: PA+ Delay Question

#3 Post by chrisj360 » Thu Oct 18, 2018 6:41 am

Thank you CoronaOperator!
2 x 21" T30's with Lab12's
2 x 28" T30's with Lab12's
2 x OTop12 with Deltalite 2512

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